MDOT Density Testing Manual: Max Density & Optimum Moisture for Soils & Aggregates, Study Guides, Projects, Research of Construction

Download MDOT Density Testing Manual: Max Density & Optimum Moisture for Soils & Aggregates and more Study Guides, Projects, Research Construction in PDF only on Docsity! CONSTRUCTION FIELD SERVICES DIVISION DENSITY TESTING AND INSPECTION MANUAL 2003 EDITION Revised December 2020 FOREWORD This manual provides guidance to administrative, engineering, and technical staff. Engineering practice requires that professionals use a combination of technical skills and judgment in decision making. Engineering judgment is necessary to allow decisions to account for unique site-specific conditions and considerations to provide high quality products, within budget, and to protect the public health, safety, and welfare. This manual provides the general operational guidelines; however, it is understood that adaptation, adjustments, and deviations are sometimes necessary. Innovation is a key foundational element to advance the state of engineering practice and develop more effective and efficient engineering solutions and materials. As such, it is essential that our engineering manuals provide a vehicle to promote, pilot, or implement technologies or practices that provide efficiencies and quality products, while maintaining the safety, health, and welfare of the public. It is expected when making significant or impactful deviations from the technical information from these guidance materials, that reasonable consultations with experts, technical committees, and/or policy setting bodies occur prior to actions within the timeframes allowed. It is also expected that these consultations will eliminate any potential conflicts of interest, perceived or otherwise. MDOT Leadership is committed to a culture of innovation to optimize engineering solutions. The National Society of Professional Engineers Code of Ethics for Engineering is founded on six fundamental canons. Those canons are provided below. Engineers, in the fulfillment of their professional duties, shall: 1. Hold paramount the safety, health, and welfare of the public. 2. Perform Services only in areas of their competence. 3. Issue public statement only in an objective and truthful manner. 4. Act for each employer or client as faithful agents or trustees. 5. Avoid deceptive acts. 6. Conduct themselves honorably, reasonably, ethically and lawfully so as to enhance the honor, reputation, and usefulness of the profession. This manual has been prepared to document procedures used by the Michigan Department of Transportation (MDOT) to assure quality in density testing and inspection in the field. It reflects current Michigan Department of Transportation practice, as based on past experience and on recognized national standards in testing procedures. This manual is written to serve as a procedures manual and training aid for technicians performing density testing on MDOT projects. Technician qualification requirements are documented in accordance with 23 CFR 637. Furthermore, this manual is part of MDOT’s Materials Quality Assurance Program. Inquiries concerning the information presented in this manual may be directed to: MDOT Density Technology Unit P.O. Box 30049 Lansing, MI 48909 (517) 636-4970 Copies of the Density Testing and Inspection Manual can be obtained from: MDOT Engineering Prints Office 7575 Crowner Drive Dimondale, MI 48821 (517) 636-0650 MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 iv 8. REPORTS AND RECORDS a. General ................................................................................................................. 68 b. Precautions for Records and Reports .................................................................. 74 C. DENSITY TESTING METHODS 1. THE CONTROLLED DENSITY METHOD a. Description ............................................................................................................ 74 b. Moisture Content ................................................................................................... 75 c. Placement and Compaction of Material ............................................................... 76 2. THE TWELVE-INCH LAYER METHOD a. Description ............................................................................................................ 77 b. Obtaining, Preparing, Compacting and Weighing the Sample ............................ 77 c. Determining Moisture Content .............................................................................. 77 d. Determining Maximum Density ............................................................................. 77 e. Precautions in Performing the Twelve-Inch Layer Method .................................. 78 II. TECHNICIAN QUALIFICATION PROGRAM FOR FIELD DENSITY TESTING A. Technician Qualifications .................................................................................................. 79 B. Maintaining Records ......................................................................................................... 79 C. Disqualification of Technicians ......................................................................................... 80 III. APPENDIX A. DEFINITIONS ................................................................................................................... 81 B. CHECKLIST FOR THE ONE-POINT T-99 TEST ............................................................ 85 C. CHECKLIST FOR THE AASHTO T-99 TEST .................................................................. 86 D. CHECKLIST FOR THE ONE-POINT MICHIGAN CONE TEST ...................................... 87 E. CHECKLIST FOR THE MICHIGAN CONE TEST ........................................................... 88 F. CHECKLIST FOR THE MICHIGAN MODIFIED T-180 TEST .......................................... 89 G. CHECKLIST FOR THE TWELVE-INCH LAYER METHOD ............................................. 90 H. CHECKLIST FOR USE OF THE NUCLEAR GAUGE ..................................................... 91 I. SPECIAL NOTES ON WEIGHING PROCEDURES ........................................................ 92 J. CHECKLIST FOR THE CALCIUM CARBIDE GAS PRESSURE METER ...................... 93 K. POLICY ON MINIMUM FREQUENCY OF TESTING ...................................................... 94 L. EQUIPMENT FURNISHED IN DENSITY KITS.......................................................... 95gau MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 v MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 1 I. DENSITY TESTS AND METHODS A. Introduction 1. SOILS Soil is a natural body occupying the portion of the earth mainly composed of mineral and organic materials and, unless otherwise specified, may include any unconsolidated deposit down to hard rock. Soils, as found in the field, are mixtures of soil particles, air and water. The soil particles are classified as clay, silt and sand and these are called soil separates. Clay is the finest grain size, silt is the next finer and sand is the most coarse. Texture classes are also called clay, silt and sand. They are so classified because they carry the predominant characteristics of the soil separate name they are identified with. A clay soil is very sticky when wet and lumpy when dry. It has strong cohesion (attraction between particles) and is commonly called a cohesive soil. Clay soils have relatively high natural moisture contents. Silt is floury in appearance, has a talcum powder “feel” and a great affinity for retaining water. Sand is a non-cohesive soil which is not sticky when wet and very loose and fluffy when dry. The natural moisture content of sand is relatively low as compared with clay. Soil mixtures may also contain some amounts of gravel, which is a granular material. By AASHTO definition gravel will pass the 3 inch sieve and be retained on the No. 10 sieve. Cobbles and boulders are larger rocks which may also be present in soils. For the purpose of this manual, the term “soil” refers to mixtures of soil, air and water. The terms clay, silt and sand refer to their textural class. 2. HOT MIX ASPHALT (HMA) MIXTURES HMA mixtures are hot plant-manufactured materials. The mixtures consist of predetermined amounts of sand, stone, fines and bitumen. The mixtures could also consist of various amounts of recycled materials. Delivered to the job site, the HMA mixtures are placed in layers and are normally used as bases, binders, leveling and top courses. 3. STABILIZED MIXTURES Stabilized mixtures consist of any existing material which is retextured or mixed with a stabilizing agent. The most common method of stabilization consists of mixing hot bitumen with an existing mixture of ground-up HMA surface and aggregate base. The layer of stabilized material is then used as a base course for a new HMA surface. Stabilization increases the bearing capacity and stability of the existing material and reduces reflective crack patterns normally associated with resurfacing projects. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 4 10. EQUIPMENT Figure 1. One-Point T-99 Test and AASHTO T-99 Test Figure 1 shows the equipment used for the One-Point T-99 and the AASHTO T-99 Tests. It consists of a cylindrical mold (Proctor mold) 4 inches in diameter with a detachable collar and base plate, a 5.5 pound rammer (or hammer device) with a 12 inch drop, a strike-off bar, a solid wood pounding block, a ¼ inch mesh screen mounted on a wood frame and a water bottle. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 5 Figure 2. One-Point Michigan Cone Test and Michigan Cone Test The equipment used for the One-Point Michigan Cone Test and Michigan Cone Test is shown in Figure 2 and consists of an inverted funnel mold commonly referred to as a “cone” having a solid bottom at the larger end, a hardwood pounding block and a water bottle. The Twelve-Inch Layer Method uses equipment of either the T-99 Test or the Michigan Cone Test depending upon the percent loss-by-washing of the soil being tested. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 6 Figure 3. Michigan Modified T-180 Test The equipment used for the Michigan Modified T-180 Test is shown in Figure 3 and consists of the following: a wood pounding block, a cylindrical mold (Proctor mold) 4 inches in diameter, 10 pound rammer with an 18 inch drop and strike-off bar. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 9 Figure 6a. Troxler nuclear gauge secured in the MDOT Type A box in a cab of a pickup truck. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 10 Figure 6b. Troxler nuclear gauge secured in the manufacturer’s carrying case housed in the NUX Safety Containment Box. 11. PERSONAL PROTECTIVE EQUIPMENT (PPE) When conducting density inspection and testing always abide by MDOT’s policy for personal protective equipment. For complete details as to the requirements contained in this policy refer to MDOT Guidance Document # 10118. As a minimum, the following PPE must be worn at all times when conducting density testing: ● hard hat ● safety glasses ● safety vest ● safety toe footwear Additional PPE may be necessary depending on the specific test performed and may include: ● hearing protection ● hand protection MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 11 B. DENSITY TESTS 1. THE ONE-POINT T-99 TEST a. DESCRIPTION A Michigan adaptation of the AASHTO T-99 (Method C, Modified) Test is the “One-Point T-99 Test.” The modification to the AASHTO test procedure is described in the Michigan Test Method (MTM) 404. The equipment used and the procedures for compacting the mold are the same as in the full AASHTO T-99 Test plus a One-Point T-99 Chart. The test name is derived from the fact that only one mold needs to be completed. In Michigan, it is the primary test used to determine the Maximum Density of soils having a loss-by-washing greater than 15 percent. Figure 1 shows the equipment used for the One-Point T-99 Test. It consists of a cylindrical mold (Proctor mold) approximately 4 inches in diameter with a detachable collar and base plate; a 5.5 pound rammer or hammer device with a 12 inch drop; a sharp-edge strike-off bar; a solid wood pounding block; a ¼ inch mesh screen mounted on a wood frame; and a water bottle. b. PREPARING AND COMPACTING THE SAMPLE A representative sample, approximately 3500 grams, is taken from the In-Place Density test site. This sample should be thoroughly broken up by running it through the screen as shown in Figure 7. The coarse material retained on the screen is then visually inspected. Stones estimated to be larger than 1 inch are removed and replaced with an equivalent weight of smaller stone. The replacement stone must be less than 1 inch but still large enough to be retained on the screen. This process must be completed as quickly as possible to avoid loss of moisture through evaporation. The coarse material retained on the screen is now added back to the sample. Figure 7.Typical sample of approximately 3500 grams of soil after screening The test should be started with the soil moisture content within a range from optimum to 4 percent below optimum. The closer to optimum the moisture content, the more MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 14 Figure 11. Entries and computations for the One-Point T-99 Test c. WEIGHING THE SAMPLE Next, the base plate is removed and the mold and sample are weighed to the nearest gram (Figure 12). This weight is recorded in Column D (Wet Soil + Mold) on Form 0582B as shown in Figure 11. The volume of the mold and the weight of the mold when empty are painted on its side. The weight is recorded in Column E and the volume in Column C. The correct method of weighing is very important. If using a digital scale, be sure the scale is clean and level on a hard flat surface. Careless weighing procedures can cause significant differences in test results. Figure 12. Weighing proctor mold and material on the scale provided in the density box MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 15 d. MOISTURE DETERMINATION If the moisture content of the sample was determined by the hand cast method to be within the appropriate range, from optimum to 4 percent below optimum, then the Moisture % from the In-Place Density Test is recorded in Column B on Form 0582B (Figure 11). If the moisture content of the sample was adjusted before the mold was compacted, then the moisture content must be determined using the “Speedy” moisture tester. Refer to page 58 for instructions on the use of the “Speedy.” Record the Moisture % in Column B. Place a circled “S” in the box to indicate that the Moisture % was determined by the “Speedy” moisture tester. Complete the computations through Column H (Compacted Soil Wet) as shown in Figure 11. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). e. DETERMINING MAXIMUM DENSITY AND OPTIMUM MOISTURE Maximum Density and Optimum Moisture are found by applying the Moisture % (Column B) and the Compacted Soil Wet (Column H) to the One-Point T-99 chart, shown in Figure 16. As an example, assume that the results from a One-Point Test are as follows: Compacted Soil Wet (Column H) or “Wet Density” is 119.0 pounds per cubic foot and the moisture content is 17.3 percent. Referring to figure 15, locate this moisture content on the horizontal leg (abscissa) and the Wet Density on the vertical leg (ordinate), and then project lines on the chart as indicated by dashed lines 1 and 2 to an intersection A. Next, project point A upwards and to the right, as indicated by dashed line 3 to an intersection B with the solid outside boundary line. This point of intersection B is the Maximum Dry Density, in this case 103.4 pounds per cubic foot. To obtain Optimum Moisture, proceed downward vertically from point B as indicated by solid line 4 to intersect the horizontal leg (abscissa) at point C. The percentage shown at point C is the Optimum Moisture, in this case 19.6 percent. Record the Maximum Density (Column I) and Optimum Moisture % (Column J) on Form 0582B as shown in Figure 11. If point A falls to the right of the Maximum Density curve, the soil is too wet. The moisture content should be reduced by drying the sample and the test repeated. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 16 Figure 15. Steps 1, 2, 3 and 4 MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 19 2. THE AASHTO T-99 TEST a. DESCRIPTION The department uses the AASHTO T-99 (Method C, Modified) test as a referee or supplemental test to the One-Point T-99 test to determine the Maximum Density of soils having a loss-by-washing greater than 15 percent. It is usually used by the inspector at the direction of the Area Density Specialist. The equipment used is the same as that used for the One-Point T-99 Test (Figure 1) except for the One-Point Chart. b. PREPARING AND COMPACTING THE SAMPLE A representative sample, approximately 5000 grams, is taken from the soil to be tested. This sample should be thoroughly broken up by running it through the screen as shown in Figure 7. The coarse material retained on the screen is then visually inspected. Stones estimated to be larger than 1 inch are removed and replaced with an equivalent weight of smaller stone. The replacement stone must be less than 1 inch but still large enough to be retained on the screen. This process must be completed as quickly as possible to avoid loss of moisture through evaporation. The coarse material retained on the screen is now added back to the sample. The test should be started with the soil having a moisture content approximately 4 percent below optimum, which is determined by the hand cast. Figure 17 (left) shows a cast of soil having approximately this moisture content. At 4 percent below optimum, the cast will barely hold together, is readily friable, and will break easily with minimal hand pressure as shown in Figure 17 (right). It may be necessary to either add water or to dry the sample to obtain the desired moisture content. When water is added, the sample should be thoroughly mixed and run through the screen a second time. If the sample is too wet, it should be dried by running it through the screen and spreading it out on top of the density box. Figure 17. Appearance of soil cast approximately 4 percent below Optimum Moisture (left), and easily broken under minimal pressure (right) MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 20 The Proctor mold is then assembled and placed on a hardwood block, supported on firm ground or existing pavement, but not on the tailgate of a pickup truck. A layer of soil is placed in the mold in a quantity sufficient to fill one-third of its volume after compaction. The soil is then compacted in the mold by 25 blows of a 5.5 pound rammer, dropping 12 inches as shown in Figure 9. While compacting the soil, the rammer should be moved about the soil surface in the mold to obtain uniform compaction of each layer. It is important that the rod be held straight and the rammer weight dropped freely since it is a standard compactive effort. Any increase or decrease in the effort may materially affect the accuracy of the test. A second layer of soil is added, filling another one-third of the volume of the mold after compaction. This too is compacted by 25 evenly distributed blows. The third and final layer is added, including enough soil to extend slightly above the top of the mold, after compaction. The third layer is compacted by 25 evenly distributed rammer blows. After the collar has been removed, the compacted soil should extend ¼ to ½ inch above the top of the mold as shown in Figure 10 (top). If the soil does not extend above the mold or if it extends more than ½ inch above the mold, the test should be repeated. The material is struck-off even with the top of the mold using the strike-off bar, as shown in Figure 10 (bottom). If pebbles encountered at this level are disturbed, they may either be pushed down or replaced by soil pressed down firmly with the strike-off bar. c. WEIGHING THE SAMPLE Next, the base plate is removed and the mold is weighed to the nearest gram (Figure 12). This weight is recorded in Column D (Wet Soil + Mold) on the density form (Form 0582B). The volume of the mold and its weight when empty are painted on its side. This weight is recorded in Column E (Mold) and this volume in Column C (Volume Mold). d. COMPLETING THE TEST PROCEDURE The sample is removed from the mold by loosening the handle on the mold and pushing out the soil. The moisture content of the soil is determined by the “Speedy” moisture tester. Refer to page 58 for instructions on the use of the “Speedy.” The Moisture % is entered in Column B of Form 0582B. Complete the computations through Column H (Compacted Soil Wet) as shown in Figure 11. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). e. COMPLETING THE FULL TEST CURVE The soil remaining in the mold is again broken up by running it through the screen and mixed with the remainder of the original sample. Water is added to raise the moisture content approximately 2 percent. An experienced inspector can judge moisture content by the feel and appearance of the soil. A novice inspector should weigh the total sample and compute 2 percent of that weight to determine the amount of the water MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 21 needed. The water is added and the sample is thoroughly mixed by working the soil through the screen until the water is uniformly distributed throughout. After the sample has been broken up and mixed, the same procedure (compacting three layers in the mold, obtaining the moisture content, and determining the Compacted Soil Wet) is followed. This procedure is repeated until there is a decrease in the Compacted Soil Wet (Column H). Ordinarily this will require 4 or 5 molds of varying moisture contents to determine moisture-density results for the complete curve. f. DETERMINING MAXIMUM DENSITY AND OPTIMUM MOISTURE A graph is then prepared with a horizontal leg (abscissa) showing Moisture % and the vertical leg (ordinate) showing the Compacted Soil Wet values in pounds per cubic foot. The Compacted Soil Wet and moisture content from each test are plotted on the graph. A smooth parabolic curve is then drawn through these points. The apex or high point of the parabolic curve gives the Maximum Density and Optimum Moisture of the particular soil. The Maximum Density is recorded in Column I and Optimum Moisture % in Column J. It can be seen after plotting a curve why it is necessary to have at least four points to establish a definite peak. Two points are needed on each side of optimum to establish the slopes of the parabolic curve, which are nearly straight lines. g. PRECAUTIONS IN PERFORMING THE AASHTO T-99 TEST This test establishes a moisture-density relationship; thus, it is important that the compactive effort is standard and uniform throughout the entire series of molds to ensure accuracy of the results. Experience has shown that the following items are important to keep in mind when performing this test: 1) Establish a new Maximum Density any time the material changes (minimum of one per day) or the percent compaction exceeds 100. 2) Have the sample thoroughly broken up by running it through the screen before pounding. 3) Make sure the clamp on the collar and mold is tight. 4) Make sure the mold is seated squarely on the base and the wing nuts are secured with equal tension. 5) Place the mold on a solid block that is supported on firm soil or pavement. 6) Hold the rammer vertically so that it will fall freely. 7) Drop the 5.5 pound rammer weight freely for each 12 inch blow. 8) Use exactly 25 blows on each layer. 9) Reposition large stones away from the sides of the mold and away from other stones to prevent voids. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 24 Figure 18. One-Point Michigan Cone Test Chart MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 25 Figure 19. Striking cone on block Figure 20. Cross-section of properly compacted cone mold MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 26 Figure 21. Entries and computations for the One-Point Michigan Cone Test After the cone is fully compacted, the material is leveled off the top using a straight-edge or the stopper. The cone is then weighed to the nearest gram. The weight is recorded in the “remarks” section of Form 0582B, Moisture and Density Determination. In order to verify that the maximum consolidation has been obtained, the following procedure must be followed. This procedure is commonly referred to as the 20/10 Rule, and is intended to determine the correct end point for the One-Point Michigan Cone Test. A small handful of material is added to the top of the cone and the cone is pounded an additional 20 times. The material is again struck level and the cone is re-weighed to the nearest gram. The weight obtained is then compared to the previously recorded weight. If the increase in weight is 10 grams or less, maximum consolidation has been obtained and the test is complete. Record the final weight, the highest weight obtained, in column D (Wet Soil + Mold) as indicated in Figure 21. If the increase in weight, the highest weight is greater than 10 grams, maximum consolidation has not been obtained, and the process is repeated as needed until the incremental change in weight is less than or equal to 10 grams. The volume and the weight of the cone are painted on the bottom of the cone. The volume of the mold is recorded in Column C (Volume Mold) and the weight is recorded in Column E (Mold). After the cone has been weighed, obtain a moisture sample from the center of the cone if the moisture was manipulated by either drying or adding water. Empty the cone by striking the open end (not the sides of the cone) on the wood block. Note: The cone should be checked periodically for accuracy by the Area Density Specialist. The weight and the volume of the cone should never be changed in the field. These values can only be changed when the cone is recalibrated. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 29 e. PRECAUTIONS IN PERFORMING THE ONE-POINT MICHIGAN CONE TEST Experience has shown that the following items are important to keep in mind when performing the One-Point Michigan Cone Test: 1) Establish a new Maximum Density any time the material changes (minimum of one per day) or the percent compaction exceeds 100. 2) Sample must have a moisture content between 5 percent and optimum moisture. If necessary, add water to the collected sample and not to the grade at the test location. 3) Use a hardwood pounding block placed on firm ground, not on the pickup tailgate. 4) Strike the cone squarely on the end grain of the block. 5) Pound the cone until no more consolidation occurs. 6) Check for maximum consolidation by the 20/10 Rule. 7) Empty the cone by inverting it and lightly striking the open end on the face of the block. Do not empty by striking the cone on its side, as this can cause dents which may change the volume. 8) Take the moisture sample from material at the center of the cone. 9) If the point on the chart obtained by plotting the Compacted Soil Wet (Column H) and Moisture % (Column B) falls to the right of the Maximum Density curve, the sample is too wet. The sample should be dried and the test repeated. 10) Determine the Maximum Density and Optimum Moisture % to the nearest tenth. 11) Record the Maximum Density (Column I) and Optimum Moisture % (Column J) on Form 0582B. 12) Clean out the cone after each test. Soil residue remaining in the cone may cause errors in weight and volume in the next test. Cleaning is easily done by shaking a few stones in it. 13) Check the empty cone weight periodically. If any change is observed, contact the Area Density Specialist. The cone should be recalibrated by qualified personnel only. 14) Maximum Density cannot be determined using a cone if the sample is saturated. 15) Additional precautions for weighing and moisture sampling for this test and others are provided in the appendix. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 30 4. THE MICHIGAN CONE TEST a. DESCRIPTION The Michigan Cone Test is a series of cone tests used to determine Maximum Density of granular soils having a loss-by-washing of 15 percent or less. It is usually used as a referee or supplemental test to the One-Point Michigan Cone Test, by the inspector at the direction of the Area Density Specialist. The equipment used is the same as that used for the One-Point Michigan Cone Test (Figure 2) except for the One-Point Michigan Cone Test Chart. b. PREPARING, COMPACTING AND WEIGHING THE SAMPLE (SAND OR GRAVEL) The weight of the representative sample of sand or gravel used in this test is approximately 3500 grams. A 10 inch by 10 inch pan (furnished in all density kits) filled level to the top usually contains enough material. For all granular materials, the moisture content must be at least 5 percent. This may require the addition of water for most granular soils and aggregates. Mix the water thoroughly with the material. Enough soil is placed in the cone to fill it about one-third its height after compaction. It is then pounded 25 times or more by raising the cone above the wood pounding block and striking it sharply, flat on the end grain of the block (Figure 19). A second layer, filling the cone about two-thirds its height after compaction, is added and pounded 25 times or more. The third layer, which fills the cone to the top, is added and pounded another 25 times or more. After the third layer has compacted, the cone is again filled to the top and then 10 blows or more are continued, holding a hand or stopper over the opening. Material is added at intervals to keep the mold full and then 10 blows or more are continued until no further consolidation occurs (Figure 20). A common error in this test is to discontinue the blows before it is certain that no more material can be compacted into the cone. If free water appears at the top of the cone, the material is saturated. The moisture content of the sample should be reduced and the test repeated. After the mold is fully compacted, the material is leveled off the top, using a straight- edge or the stopper. The cone is then weighed to the nearest gram. This weight is recorded in Column D (Wet Soil + Mold) as shown in Figure 21. The volume and weight of the cone when empty are painted on the bottom. This volume should be recorded in Column C (Volume Mold) and the weight in Column E (Mold). The weight of the cone should be checked periodically for any change. The cone should occasionally be checked for volume accuracy by the Area Density Specialist, since the repeated poundings may bulge the bottom of the cone and change its volume. If any change is observed, the cone should be recalibrated for weight and volume by qualified personnel only. After the cone has been weighed, obtain a moisture sample from the center of the cone sample. Empty the cone by striking the open end (not the sides of the cone) on the wood block. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 31 c. DETERMINING MOISTURE CONTENT (SAND OR GRAVEL) The moisture content is determined using the “Speedy” Moisture Tester. Refer to page 58 for instructions on the use of the “Speedy.” The Moisture % is entered in Column B of Form 0582B. d. DETERMINING MAXIMUM DENSITY OF GRANULAR SOIL OTHER THAN PROCESSED AGGREGATES Complete the computations through Column H (Compacted Soil Wet) as shown in Figure 21. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). If the result of Column H (Compacted Soil Wet) is less than 120 pounds per cubic foot and the moisture content is between 5 percent and optimum, the Maximum Density is the result of one cone test. Enter this result in Column I (Maximum Density). If the result of Column H (Compacted Soil Wet) is more than 120 pounds per cubic foot, a series of two or three cone tests should be repeated at varying moisture contents between 5 percent and a point short of saturation. Suggested moisture contents for the cone series are 7, 9 and 11 percent. The highest test result of this series of cones is the Maximum Density or Maximum Unit Weight and is entered in Column I. e. DETERMINING MAXIMUM DENSITY OF AGGREGATE BASE COURSE AND SURFACE AGGREGATES Research has shown that moisture content does have an appreciable effect on Maximum Unit Weight of gravel. This weight is greatest within 5 to 8 percent moisture content. Thus the Maximum Density of aggregates is determined at a moisture content ranging from 5 to 8 percent, as follows: 1) Run a series of cone tests with moisture content of the aggregate at different points within the 5 to 8 percent range. Two or three points within this range generally should be sufficient to determine the highest unit weight. For example, one test could be run at approximately 5 percent moisture, a second at approximately 6 percent moisture and a third at approximately 7 percent moisture. a) If the cone is saturated (free water appears at the top of the cone), reduce the moisture content but not below 5 percent. If the cone test is run on saturated aggregate, the results may be inaccurate. b) If the aggregate in the cone exhibits the “swell” effect (rises slightly above the top of the cone), reduce the moisture content but not below 5 percent. 2) The highest test result of the series of cones within the 5 to 8 percent moisture range is the Maximum Unit Weight or Maximum Density. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 34 Figure 25. Recycled material being compacted in the mold Figure 26. Mold with collar removed and recycled material ¼ to ½ inch above the top of mold MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 35 Figure 27. Mold with the material struck-off even with the top of the mold c. WEIGHING THE SAMPLE Next, the base plate is removed and the mold and sample are weighed to the nearest gram (Figure 28). This weight is recorded in Column D (Wet Soil + Mold) on Form 0582B as shown in Figure 29. The volume and weight of the mold when empty are painted on the side. The volume is recorded in Column C (Volume Mold) and the weight in Column E (Mold). Figure 28. Weighing the mold and recycled material to the nearest gram MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 36 d. DETERMINING WET MAXIMUM DENSITY The Wet Maximum Density can now be determined by completing the computations through Column H (Compacted Soil Wet) as shown in Figure 29. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). The Compacted Soil Wet (Column H) is also the Wet Maximum Density and should be recorded in Column I (Maximum Density). A new Maximum Density should be determined any time the material changes, or the moisture changes ± 1.5 percent. As stated previously, for the Michigan Modified T-180 test, the Maximum Density is determined at the existing moisture content and multiple Maximum Density values may be necessary as the moisture content of the material changes. For example, after taking an In-Place density test and determining a Wet Maximum Density, the In-Place density test did not meet requirements. The contractor, before applying more compactive effort, elects to add water to the area of the failing test. After the failing area is further compacted, the area is retested with another In- Place test. If the same Maximum Density was used for the retest, the test would probably pass, not because of the additional effort so much as from the addition of water. It is possible to obtain passing retests just by adding water if the previous Maximum Density obtained at a lower moisture content is still used. Whenever water is added to a failing area, a new Wet Maximum Density must be established when the In-Place retest is taken. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 39 When not in use, the source rod must be fully retracted in the SAFE position. When the Troxler gauge is lifted by the handle, the source rod automatically returns to the SAFE position. b. LOCATION AND FREQUENCY OF TEST The Density In-Place Test should be taken in those areas of fill (embankment) or backfill that appear to be the least compacted. The test area is selected by watching the movement of the contractor’s compaction equipment. If the tests are run in the visibly poorer areas and they meet specification requirements, it may be assumed that the remainder of the test section also meets specifications. The controlled density specifications require each layer to be compacted to a minimum of 90, 95, 98, or 100 percent of Maximum Density, depending on the item of work. Details on frequency of testing are provided in the appendix of this manual. The gauge offers the option to test by Direct Transmission or Backscatter. Always use Direct Transmission tests on soil and recycled materials. The Backscatter test is used only on Hot Mix Asphalt mixtures. c. TROXLER MODEL 3440 In this manual and in the density certification class the Troxler Model 3440 gauge is used. The Troxler Model 3440, as shown in Figures 30 and 31, is a direct transmission gauge. Mechanically, this gauge is the same as the older Model 3411B. The 3440 gauge also contains a microprocessor which is programmed to perform a wider range of functions and has larger memory capacity for ease of operation. The 3440 gauge is more user friendly than the 3411B which prompts the user during testing and shows more information in the display window. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 40 Figure 30. Troxler Model 3440 nuclear gauge Figure 31. Troxler Model 3440 controls MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 41 1) Keys Description Below is a functional description of the keys found on the Model 3440 control panel: KEYS DESCRIPTION YES EXIT Answers display prompt. Permits exit from the calculator mode. NO/CE C/CE Answers display prompt/Clear last entry. Clears calculator entry. STATUS 7 (SHIFT function) Display status of gauge functions. Number key. MODE 8 (SHIFT function) Asphalt or Soils selection. Number key. SPECIAL 9 (SHIFT function) Provides access to special functions. Number key. STORE MS To store data in gauge memory. Memory store function for the calculator mode. OFFSET MR Select measurement offsets. Memory recall function for the calculator mode. PROJECT 4 (SHIFT function) To enter, view or erase a project Number key. PRINT 5 (SHIFT function) Download data Number key. ERASE 6 (SHIFT function) Erase data Number key. PROCTOR/MARSHALL + Proctor or Marshall value selection. Addition sign for calculator functions. TIME - Selects time interval for testing and measurement. Subtraction sign for calculator functions. COUNTS 1 (SHIFT function) Displays last moisture and density counts. Number key. DEPTH 2 (SHIFT function) Automatic or manual depth operation. Number key. CALC. 3 (SHIFT function) To access the calculator mode. Number key. SHIFT x Activates all SHIFT function modes. Multiplication sign for calculator functions. STANDARD / Provides access to standard count mode. Division sign for calculator functions. RECALL 0 (SHIFT function) To recall data for viewing Number key. . Decimal point key START/ENTER = See manual text and index. Equals sign for calculator functions 2) 3440 Keypad Layout The Troxler Model 3440 control panel consists of 22 keys (Figure 31): the 20 key control section and the ON/OFF keys. Keystrokes result in an immediate “beep” MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 44 To begin taking a standard count, press STANDARD for the display: - Standard Count - DS = _____ MS = _____ Take new count? Press YES for the display: Is gauge on Std. Block & Source rod in SAFE pos? Make sure the gauge is placed on the reference block correctly. Place the source rod in the SAFE position and press YES to begin taking the 4 minute standard count: Taking Standard Count 240 seconds remaining After count completion, the display is: MS=____ _._ %P DS=____ _._ %P Do you want to use the new STD? The standard count (operating standard) should not deviate from the chart standards obtained from the Gauge Book by more than 1 percent for density or 2 percent for moisture. If the standard counts are within acceptable limits, press YES to accept. Record the standard counts in the lower right corner of Form 0582B, (Figure 29) under Operating Standards. If either value is out of range, press NO and take another standard count. Before repeating the standard count, make sure the gauge base and reference block are clean and the gauge is positioned correctly on the reference block. If either standard is still out of tolerance, call the Area Density Specialist or Lansing Density Technology staff immediately to make arrangements to have the gauge serviced or replaced. The gauge should be serviced or replaced within 24 hours. To determine if the gauge can continue to be used until serviced or replaced, do the following: Repeat the standard count procedure 5 times, saving each result when prompted. On completion of the fifth standard count, check the display to determine status. If MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 45 the standards for the fifth count are within tolerance, ± 1 percent for density and ± 2 percent for moisture, a P will show next to the percentages in the display. If passing results are indicated, you may continue to use the gauge for 24 hours. If either standard fails, an F will show on the display and the gauge should be taken out of service immediately. 6) Viewing the Last Four Standard Counts To “view” the last 4 standard counts, press STANDARD for the display: -Standard Count- DS = ____ MS = ____ Take new count? Press NO for the display: - Standard Count - Want to view last four Standard Counts? Press YES for the display: Density Std Cts 1:____ 2:____ 3:____ 4:____ (YES for Moist) To view the “Moisture Standard Counts” press YES. The display will be: Moist. Std Cts 1:____ 2:____ 3:____ 4:____ (Press any key) The “View Standard Count” function may be exited by pressing any key. 7) Setting Measurement Units Prior to taking measurements, the user should determine the “Unit of Measurement” that is required for screen displays and/or printouts. The available selection is either “PCF” or “Metric”. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 46 To execute the “SET UNITS” function, press SHIFT and SPECIAL for: SPECIAL FUNCTION YES- Next menu 1- STAT TEST 2- DRIFT TEST Press YES 3 times for the display: YES - Next menu 9- SET UNITS 10- BAUD RATE 11-COMM PROTOCOL Press 9 for the display: UNITS in PCF Press: 1-PCF 2-METRIC ENTER- No change or the display will be: UNITS in METRIC Press: 1-PCF 2-METRIC ENTER- No change Press either 1 or 2 for the required units. 8) Count Time Selection The 3440 gauge provides 3 different count times to be used for taking readings. When running In-Place Moisture/Density Tests always use the 1 minute time cycle. Never use the 15 second time cycle. Press TIME for the display: Time: ____ min 1 - 15 sec 2 - 1 min 3 - 4 min MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 49 To start the measurement, press START/ENTER for the display: Depth: __ inches PR:_____ PCF Time: ___ sec. After the gauge completes its count time, the display will be: %PR=_____% DD=_____ PCF WD=_____ PCF M=___ %M=___ Record DD, WD, M and %M in the correct columns on Form 0582B. Note: Do not record %PR until the correct Maximum Density has been enabled. To obtain the density and moisture test counts press SHIFT and COUNTS for the display: Dens ct.=_____ Moist ct.=____ SHIFT/RECALL to see Readings. Record the counts in columns 3 and 6 on Form 0582B. b) Asphalt Mode Enable the ASPHALT mode prior to taking a test on HMA materials. Check units of measurement, count time and Maximum Density. Select the test site and make sure the site is flat before setting the gauge down. Place the source rod in the BACKSCATTER position. Start a measurement by pressing START/ENTER. The display will be: Depth: __ inches MA:_____ PCF Time: ___ sec. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 50 After the gauge completes its count time, the display will be: %MA=_____ % WD=______ PCF M=___ %M=___ Record WD, M and %M in the correct columns on Form 0582B. Note: Do not record %MA until the correct Maximum Density has been enabled. To obtain the density and moisture test counts press SHIFT and COUNTS. Record the counts in columns 3 and 6 on Form 0582B. 11) Proctor (Cone)/Marshall/Voidless Function The 3440 gauge provides for up to four different Proctor (Cone) values and four different Marshall values to be stored for later use. To select or change a Proctor (Cone) or Marshall Density value press the PROCTOR /MARSHALL key for the display: MA=_____ PCF PR=_____ VD=_____ Want to change? If a value is to be enabled or a new value added or changed, press YES. The display is: Select: 1 - MA 2 - PR 3 - Voidless Marshall and Proctor (Cone) functions are identical as far as operation is concerned. Therefore, only Proctor (Cone) will be illustrated. To change a Proctor (Cone) value, press 2 for: Select source of Proctor value: 1- Stored value 2- New value MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 51 a) Recall a Stored Proctor (Cone) / Marshall Value To enable a previously stored value, press 1. The display is: Select desired Proctor: 1:____ 2: ____ 3:____ 4: ____ Select the desired Proctor (Cone) value by pressing 1, 2, 3 or 4 for the display: Proctor: _____ PCF ENABLED! b) Enter a New Proctor (Cone)/Marshall Value From this display press 2. The display will be: Enter the new value and press ENTER for the display: PR=______ PCF Do you want to save this value for later use? Press YES to save the new Proctor (Cone) value in a memory cell, for later use. The display will be: Select Proctor Memory cell: 1:____ 2: ____ 3:____ 4: ____ Select source of Proctor value: 1- Stored value 2- New value Proctor: ______ PCF Press ENTER when completed MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 54 d. PRECAUTIONS IN PERFORMING THE DENSITY IN-PLACE (NUCLEAR) TEST 1) Keep the gauge clean. 2) Do not use the gauge when it is raining. Moisture can damage the gauge resulting in loss of use and costly repairs. 3) Contact the Area Density Specialist when the gauge needs servicing. 4) Transport the gauge according to US DOT regulations. 5) Do not scratch or gouge the surface of the Standard Block. 6) Protect the gauge at all times and handle carefully. 7) Fill holes or voids in the test surface with sand or fine material from the area near the test site. 8) Do not recharge batteries unless the battery indicator signals a low battery. 9) Be aware of safety standards when the gauge is stored or when charging the batteries. 10) If the gauge is involved in an accident, refer to the nuclear gauge transport book. 11) Do not run comparison tests. 12) Return the gauge to its Type A Box in the pickup truck on the front passenger floor board, behind the passenger seat or in the NUX Safety Containment Box when not in use. e. CARE OF NUCLEAR GAUGE AND EQUIPMENT After the test is completed, the gauge should be returned to the transport case in the cab of the pickup truck. Always secure the gauge in the Type A box prior to transporting the device. Do not transport the gauge on the tailgate or in the bed of the pickup truck as this is in violation of the department’s license issued by the Nuclear Regulatory Commission. If the gauge malfunctions, the Area Density Specialist should be notified immediately. Due to the radioactive materials located within a nuclear density gauge, there are regulations governing the storage, transportation and use of the gauge. The Nuclear Regulatory Commission, United States Department of Transportation and the Michigan Department of Transportation have established safety requirements that must be complied with. These safety requirements include, but are not limited to, the usage, storage, security, transportation of nuclear density gauges, and occupational doses and doses to members of the public. These regulations are located within 10 CFR (Energy) and 49 CFR (Transportation). The safety features built into the Troxler density gauge provide shielding of the radioactive material, which allows an operator to use the gauge while minimizing the exposure to radiation. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 55 1) The following steps must be taken when the gauge is damaged within a construction project: a) Immediately stop all construction-vehicle movement (in the immediate proximity). b) Detain witnesses until they are interviewed. c) Establish a fifteen (15) foot perimeter (minimum). d) Isolate the gauge from all people. e) Contact the Area Density Specialist. f) Contact the Statewide Density Specialist g) Contact MDOT’s Radiation Safety Officer. h) Complete an incident report form. i) All of the above steps are to be conducted in the order indicated. 2) The following steps must be taken when the gauge is damaged outside the limits of a construction project: a) Detain witnesses until they are interviewed. b) Establish a fifteen (15) foot perimeter (minimum). c) Isolate the gauge from all people. d) Contact the nearest Michigan State Police Post. e) Contact the Area Density Specialist. f) Contact the Statewide Density Specialist. g) Contact MDOT’s Radiation Safety Officer. h) Complete an incident report form. i) All of the above steps are to be conducted in the order indicated. 3) The following steps must be taken when a gauge is lost or stolen: a) Contact the Area Density Specialist. b) Contact the Statewide Density Specialist. c) Contact MDOT’s Radiation Safety Officer. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 56 d) Contact MDOT’s Emergency Management Coordinator. e) Complete an incident report form. f) All of the above steps are to be conducted in the order indicated. Refer to the gauge book for the incident report form, telephone numbers and radio numbers. 7. CALCIUM CARBIDE GAS PRESSURE METER (“SPEEDY” MOISTURE TESTER) a. DESCRIPTION The Michigan Department of Transportation uses a calcium carbide gas pressure meter for determining moisture content. This test is used when the moisture content of the test sample has been manipulated. The current model in use is the “Speedy” Moisture Tester, which was developed in England and in the soils laboratory of the Federal Highway Administration. Test apparatus must meet the requirements of AASHTO T 217. Only use pressure meters sized for specimens having a mass of at least 20 grams. The pressure meter (Figure 32) replaces the two-burner gas stove for the purpose of determining the moisture content of soils. With the pressure meter, the moisture can be determined in five minutes or less which permits obtaining density results much faster than with the stove drying method. The principle on which the pressure meter is based is a chemical reaction which begins when the soil in the cap and calcium carbide in the body are mixed together. The moisture in the soil combines with the calcium carbide to produce acetylene gas. The gas pressure is registered on the gauge as moisture content, percent of wet weight. When testing very wet soils, an initially high reading and heat are caused by the reaction generated by the higher moisture content. Be sure that the heat has dissipated and the needle has stopped moving before the final reading. b. CARE OF THE PRESSURE METER The density kit contains a place designated to store and work with the equipment. It is important that the pressure meter be carried in this compartment (Figure 5). Within the pressure meter box is a place for each piece of equipment to be stored to prevent damage to the gauge, the tester, the balance beam and also to prevent the loss of small parts such as the half sample weight (Figure 32). The care of the pressure meter is important and is the responsibility of the density inspector. The cap in which the soil is placed should be cleaned after each test. The body of the pressure meter should be cleaned before and after each test. If at any time something is wrong with the equipment, contact the Area Density Specialist. The cap should be cleaned after each test (Figure 33). A special cloth is provided with each kit for this purpose. This cloth should only be used to clean the cap, the scale pan MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 59 a replacement. DO NOT use a nylon brush in the meter body which could generate a static charge capable of igniting any residual acetylene gas. Figure 34. Proper technique for cleaning the body of the meter This is a precision instrument. While it is considered rugged for its intended use, it will not withstand abuse due to careless handling. The accuracy of test and the useful life of the pressure meter will depend on the skill and technique of the inspector and the general care taken to keep the equipment in good condition. c. USE OF THE PRESSURE METER The gauge reading is applied to the conversion chart supplied with each “Speedy” moisture tester (Figure 35). Note: The gauge reading is based on the wet weight of the sample. The chart converts this to dry weight. In cold weather, run a sample through the meter to warm up the body. Disregard this reading. The test procedure is different when testing cohesive soils than when testing granular soils. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 60 Figure 35. Calcium carbide gas pressure meter (“Speedy”) conversion chart MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 61 d. TEST PROCEDURE FOR SAND AND GRAVEL (LOSS-BY-WASHING OF 15 PERCENT OR LESS) Place 3 scoops of calcium carbide in the body of the “Speedy” (Figure 36). Figure 36. Place calcium carbide in body of the “Speedy” Clean the cap in preparation for the sample (Figure 33). Weigh the sample as quickly and as accurately as possible (Figure 37). The sample will be either 20 or 26 grams, depending on the size of the “Speedy.” Only material passing the ¼ inch screen will be used. Figure 37. Weigh moisture sample Place the sample in the cap (Figure 38). MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 64 Figure 42. Read dial with “Speedy” held horizontally Refer the dial reading to the wet-dry conversion chart, which determines the moisture content based on dry weight. Interpolate to the nearest tenth of a percent (Figure 35). Record the moisture percent (dry weight basis) in Column B, with a circled “S” at the bottom of Form 0582B. While holding the “Speedy” downwind and away from your body, release the pressure slowly and empty contents (Figure 43). Figure 43. Hold “Speedy” downwind and away from body. Slowly release pressure and empty the “Speedy.” Clean the cap and pressure meter body in preparation for the next test. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 65 When using the pressure meter to determine the moisture content of gravels (processed aggregates), the gravel sample must be screened. Using the screen from the density kit, rub the gravel sample through the screen until all of the fines and small stones are through and just the large stones are left. Obtain the moisture sample from the material that has passed through the ¼ inch screen. e. TEST PROCEDURE FOR COHESIVE SOIL (HALF SAMPLE (13 GRAM or 10 GRAM), PROPORTIONAL METHOD and LOSS-BY-WASHING GREATER THAN 15 PERCENT) Place 3 scoops of calcium carbide in the body of the “Speedy” (Figure 36). Hold the body of the “Speedy” horizontally. Roll in the two 1-inch steel balls into the body of the “Speedy” (Figure 44). DO NOT drop the steel balls directly into the body of the “Speedy” when it is sitting upright to avoid damaging the orifice of the pressure gauge. Figure 44. Place steel balls in body of “Speedy” with 3 scoops of calcium carbide MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 66 Clean cap with cloth provided in kit (Figure 45). Figure 45. Cleaning the cap of the meter Using the ¼ inch screen from the density kit, rub the soil sample through the screen (Figure 46). Figure 46. Using the ¼ inch screen from the density kit, always screen cohesive soil before obtaining the moisture sample MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 69 A test can fail by either moisture or density or both requirements. If a test fails to meet the density requirement, the percent of compaction (column 11) should be circled. If a test fails moisture requirements, the Moisture % (column 8) should be circled. If the inspector encounters an in-place density test over 100 % compaction, the test does not fail. However, the inspector must establish a new maximum density within three (3) feet of that test. This is to ensure that the results at that location are verified and documented or if there has been a change in material that is not visually apparent. The location of each In-Place Density Test should be recorded by stationing, distance right or left of centerline and depth below plan grade. Identify the item of work (Column 16) using the abbreviations on the back of the form. Entries on Form 0582B, Determination of In-Place Density, (Columns 5, 7-11) are recorded to the nearest tenth (0.1). Entries for Determination of Maximum Density are recorded as follows: Columns D-F nearest gram Columns B, H-J nearest tenth (0.1) Column C nearest ten-thousandth (0.0001) Column G nearest one-hundredth (0.01) When conducting a recheck, if the Maximum Density is imported from a previous report, recopy the complete Maximum Density line from the original report. Record the date of the original test in the margin to the left of the test number. See examples of Form 0582B in Figures 48 to 51. The distribution for Form 0582B is as follows: ORIGINAL to the project file and COPIES to the Area Density Specialist and Lansing Density Technology Unit. Form 0582B must be submitted by the tester to the office daily. Distribution of Form 0582B to the Area Density Specialist and the Lansing Density Technology Unit must be made weekly at a minimum. Electronic submittal of scanned test reports can be sent to the Lansing Density Technology Unit at the following address: MDOT-NuclearDensityTestReports@Michigan.gov MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 70 Figure 48. Form 0582B: Density Determination of Soils MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 71 Figure 49. Form 0582B: Density Determination of HMA Aggregate Base (BAB) Mixtures CONSTRUCTION FIELD SERVICES DIVISION DENSITY TESTING AND INSPECTION MANUAL 2003 EDITION Revised December 2020 FOREWORD This manual provides guidance to administrative, engineering, and technical staff. Engineering practice requires that professionals use a combination of technical skills and judgment in decision making. Engineering judgment is necessary to allow decisions to account for unique site-specific conditions and considerations to provide high quality products, within budget, and to protect the public health, safety, and welfare. This manual provides the general operational guidelines; however, it is understood that adaptation, adjustments, and deviations are sometimes necessary. Innovation is a key foundational element to advance the state of engineering practice and develop more effective and efficient engineering solutions and materials. As such, it is essential that our engineering manuals provide a vehicle to promote, pilot, or implement technologies or practices that provide efficiencies and quality products, while maintaining the safety, health, and welfare of the public. It is expected when making significant or impactful deviations from the technical information from these guidance materials, that reasonable consultations with experts, technical committees, and/or policy setting bodies occur prior to actions within the timeframes allowed. It is also expected that these consultations will eliminate any potential conflicts of interest, perceived or otherwise. MDOT Leadership is committed to a culture of innovation to optimize engineering solutions. The National Society of Professional Engineers Code of Ethics for Engineering is founded on six fundamental canons. Those canons are provided below. Engineers, in the fulfillment of their professional duties, shall: 1. Hold paramount the safety, health, and welfare of the public. 2. Perform Services only in areas of their competence. 3. Issue public statement only in an objective and truthful manner. 4. Act for each employer or client as faithful agents or trustees. 5. Avoid deceptive acts. 6. Conduct themselves honorably, reasonably, ethically and lawfully so as to enhance the honor, reputation, and usefulness of the profession. This manual has been prepared to document procedures used by the Michigan Department of Transportation (MDOT) to assure quality in density testing and inspection in the field. It reflects current Michigan Department of Transportation practice, as based on past experience and on recognized national standards in testing procedures. This manual is written to serve as a procedures manual and training aid for technicians performing density testing on MDOT projects. Technician qualification requirements are documented in accordance with 23 CFR 637. Furthermore, this manual is part of MDOT’s Materials Quality Assurance Program. Inquiries concerning the information presented in this manual may be directed to: MDOT Density Technology Unit P.O. Box 30049 Lansing, MI 48909 (517) 636-4970 Copies of the Density Testing and Inspection Manual can be obtained from: MDOT Engineering Prints Office 7575 Crowner Drive Dimondale, MI 48821 (517) 636-0650 MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 iv 8. REPORTS AND RECORDS a. General ................................................................................................................. 68 b. Precautions for Records and Reports .................................................................. 74 C. DENSITY TESTING METHODS 1. THE CONTROLLED DENSITY METHOD a. Description ............................................................................................................ 74 b. Moisture Content ................................................................................................... 75 c. Placement and Compaction of Material ............................................................... 76 2. THE TWELVE-INCH LAYER METHOD a. Description ............................................................................................................ 77 b. Obtaining, Preparing, Compacting and Weighing the Sample ............................ 77 c. Determining Moisture Content .............................................................................. 77 d. Determining Maximum Density ............................................................................. 77 e. Precautions in Performing the Twelve-Inch Layer Method .................................. 78 II. TECHNICIAN QUALIFICATION PROGRAM FOR FIELD DENSITY TESTING A. Technician Qualifications .................................................................................................. 79 B. Maintaining Records ......................................................................................................... 79 C. Disqualification of Technicians ......................................................................................... 80 III. APPENDIX A. DEFINITIONS ................................................................................................................... 81 B. CHECKLIST FOR THE ONE-POINT T-99 TEST ............................................................ 85 C. CHECKLIST FOR THE AASHTO T-99 TEST .................................................................. 86 D. CHECKLIST FOR THE ONE-POINT MICHIGAN CONE TEST ...................................... 87 E. CHECKLIST FOR THE MICHIGAN CONE TEST ........................................................... 88 F. CHECKLIST FOR THE MICHIGAN MODIFIED T-180 TEST .......................................... 89 G. CHECKLIST FOR THE TWELVE-INCH LAYER METHOD ............................................. 90 H. CHECKLIST FOR USE OF THE NUCLEAR GAUGE ..................................................... 91 I. SPECIAL NOTES ON WEIGHING PROCEDURES ........................................................ 92 J. CHECKLIST FOR THE CALCIUM CARBIDE GAS PRESSURE METER ...................... 93 K. POLICY ON MINIMUM FREQUENCY OF TESTING ...................................................... 94 L. EQUIPMENT FURNISHED IN DENSITY KITS.......................................................... 95gau MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 v MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 1 I. DENSITY TESTS AND METHODS A. Introduction 1. SOILS Soil is a natural body occupying the portion of the earth mainly composed of mineral and organic materials and, unless otherwise specified, may include any unconsolidated deposit down to hard rock. Soils, as found in the field, are mixtures of soil particles, air and water. The soil particles are classified as clay, silt and sand and these are called soil separates. Clay is the finest grain size, silt is the next finer and sand is the most coarse. Texture classes are also called clay, silt and sand. They are so classified because they carry the predominant characteristics of the soil separate name they are identified with. A clay soil is very sticky when wet and lumpy when dry. It has strong cohesion (attraction between particles) and is commonly called a cohesive soil. Clay soils have relatively high natural moisture contents. Silt is floury in appearance, has a talcum powder “feel” and a great affinity for retaining water. Sand is a non-cohesive soil which is not sticky when wet and very loose and fluffy when dry. The natural moisture content of sand is relatively low as compared with clay. Soil mixtures may also contain some amounts of gravel, which is a granular material. By AASHTO definition gravel will pass the 3 inch sieve and be retained on the No. 10 sieve. Cobbles and boulders are larger rocks which may also be present in soils. For the purpose of this manual, the term “soil” refers to mixtures of soil, air and water. The terms clay, silt and sand refer to their textural class. 2. HOT MIX ASPHALT (HMA) MIXTURES HMA mixtures are hot plant-manufactured materials. The mixtures consist of predetermined amounts of sand, stone, fines and bitumen. The mixtures could also consist of various amounts of recycled materials. Delivered to the job site, the HMA mixtures are placed in layers and are normally used as bases, binders, leveling and top courses. 3. STABILIZED MIXTURES Stabilized mixtures consist of any existing material which is retextured or mixed with a stabilizing agent. The most common method of stabilization consists of mixing hot bitumen with an existing mixture of ground-up HMA surface and aggregate base. The layer of stabilized material is then used as a base course for a new HMA surface. Stabilization increases the bearing capacity and stability of the existing material and reduces reflective crack patterns normally associated with resurfacing projects. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 4 10. EQUIPMENT Figure 1. One-Point T-99 Test and AASHTO T-99 Test Figure 1 shows the equipment used for the One-Point T-99 and the AASHTO T-99 Tests. It consists of a cylindrical mold (Proctor mold) 4 inches in diameter with a detachable collar and base plate, a 5.5 pound rammer (or hammer device) with a 12 inch drop, a strike-off bar, a solid wood pounding block, a ¼ inch mesh screen mounted on a wood frame and a water bottle. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 5 Figure 2. One-Point Michigan Cone Test and Michigan Cone Test The equipment used for the One-Point Michigan Cone Test and Michigan Cone Test is shown in Figure 2 and consists of an inverted funnel mold commonly referred to as a “cone” having a solid bottom at the larger end, a hardwood pounding block and a water bottle. The Twelve-Inch Layer Method uses equipment of either the T-99 Test or the Michigan Cone Test depending upon the percent loss-by-washing of the soil being tested. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 6 Figure 3. Michigan Modified T-180 Test The equipment used for the Michigan Modified T-180 Test is shown in Figure 3 and consists of the following: a wood pounding block, a cylindrical mold (Proctor mold) 4 inches in diameter, 10 pound rammer with an 18 inch drop and strike-off bar. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 9 Figure 6a. Troxler nuclear gauge secured in the MDOT Type A box in a cab of a pickup truck. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 10 Figure 6b. Troxler nuclear gauge secured in the manufacturer’s carrying case housed in the NUX Safety Containment Box. 11. PERSONAL PROTECTIVE EQUIPMENT (PPE) When conducting density inspection and testing always abide by MDOT’s policy for personal protective equipment. For complete details as to the requirements contained in this policy refer to MDOT Guidance Document # 10118. As a minimum, the following PPE must be worn at all times when conducting density testing: ● hard hat ● safety glasses ● safety vest ● safety toe footwear Additional PPE may be necessary depending on the specific test performed and may include: ● hearing protection ● hand protection MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 11 B. DENSITY TESTS 1. THE ONE-POINT T-99 TEST a. DESCRIPTION A Michigan adaptation of the AASHTO T-99 (Method C, Modified) Test is the “One-Point T-99 Test.” The modification to the AASHTO test procedure is described in the Michigan Test Method (MTM) 404. The equipment used and the procedures for compacting the mold are the same as in the full AASHTO T-99 Test plus a One-Point T-99 Chart. The test name is derived from the fact that only one mold needs to be completed. In Michigan, it is the primary test used to determine the Maximum Density of soils having a loss-by-washing greater than 15 percent. Figure 1 shows the equipment used for the One-Point T-99 Test. It consists of a cylindrical mold (Proctor mold) approximately 4 inches in diameter with a detachable collar and base plate; a 5.5 pound rammer or hammer device with a 12 inch drop; a sharp-edge strike-off bar; a solid wood pounding block; a ¼ inch mesh screen mounted on a wood frame; and a water bottle. b. PREPARING AND COMPACTING THE SAMPLE A representative sample, approximately 3500 grams, is taken from the In-Place Density test site. This sample should be thoroughly broken up by running it through the screen as shown in Figure 7. The coarse material retained on the screen is then visually inspected. Stones estimated to be larger than 1 inch are removed and replaced with an equivalent weight of smaller stone. The replacement stone must be less than 1 inch but still large enough to be retained on the screen. This process must be completed as quickly as possible to avoid loss of moisture through evaporation. The coarse material retained on the screen is now added back to the sample. Figure 7.Typical sample of approximately 3500 grams of soil after screening The test should be started with the soil moisture content within a range from optimum to 4 percent below optimum. The closer to optimum the moisture content, the more MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 14 Figure 11. Entries and computations for the One-Point T-99 Test c. WEIGHING THE SAMPLE Next, the base plate is removed and the mold and sample are weighed to the nearest gram (Figure 12). This weight is recorded in Column D (Wet Soil + Mold) on Form 0582B as shown in Figure 11. The volume of the mold and the weight of the mold when empty are painted on its side. The weight is recorded in Column E and the volume in Column C. The correct method of weighing is very important. If using a digital scale, be sure the scale is clean and level on a hard flat surface. Careless weighing procedures can cause significant differences in test results. Figure 12. Weighing proctor mold and material on the scale provided in the density box MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 15 d. MOISTURE DETERMINATION If the moisture content of the sample was determined by the hand cast method to be within the appropriate range, from optimum to 4 percent below optimum, then the Moisture % from the In-Place Density Test is recorded in Column B on Form 0582B (Figure 11). If the moisture content of the sample was adjusted before the mold was compacted, then the moisture content must be determined using the “Speedy” moisture tester. Refer to page 58 for instructions on the use of the “Speedy.” Record the Moisture % in Column B. Place a circled “S” in the box to indicate that the Moisture % was determined by the “Speedy” moisture tester. Complete the computations through Column H (Compacted Soil Wet) as shown in Figure 11. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). e. DETERMINING MAXIMUM DENSITY AND OPTIMUM MOISTURE Maximum Density and Optimum Moisture are found by applying the Moisture % (Column B) and the Compacted Soil Wet (Column H) to the One-Point T-99 chart, shown in Figure 16. As an example, assume that the results from a One-Point Test are as follows: Compacted Soil Wet (Column H) or “Wet Density” is 119.0 pounds per cubic foot and the moisture content is 17.3 percent. Referring to figure 15, locate this moisture content on the horizontal leg (abscissa) and the Wet Density on the vertical leg (ordinate), and then project lines on the chart as indicated by dashed lines 1 and 2 to an intersection A. Next, project point A upwards and to the right, as indicated by dashed line 3 to an intersection B with the solid outside boundary line. This point of intersection B is the Maximum Dry Density, in this case 103.4 pounds per cubic foot. To obtain Optimum Moisture, proceed downward vertically from point B as indicated by solid line 4 to intersect the horizontal leg (abscissa) at point C. The percentage shown at point C is the Optimum Moisture, in this case 19.6 percent. Record the Maximum Density (Column I) and Optimum Moisture % (Column J) on Form 0582B as shown in Figure 11. If point A falls to the right of the Maximum Density curve, the soil is too wet. The moisture content should be reduced by drying the sample and the test repeated. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 16 Figure 15. Steps 1, 2, 3 and 4 MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 19 2. THE AASHTO T-99 TEST a. DESCRIPTION The department uses the AASHTO T-99 (Method C, Modified) test as a referee or supplemental test to the One-Point T-99 test to determine the Maximum Density of soils having a loss-by-washing greater than 15 percent. It is usually used by the inspector at the direction of the Area Density Specialist. The equipment used is the same as that used for the One-Point T-99 Test (Figure 1) except for the One-Point Chart. b. PREPARING AND COMPACTING THE SAMPLE A representative sample, approximately 5000 grams, is taken from the soil to be tested. This sample should be thoroughly broken up by running it through the screen as shown in Figure 7. The coarse material retained on the screen is then visually inspected. Stones estimated to be larger than 1 inch are removed and replaced with an equivalent weight of smaller stone. The replacement stone must be less than 1 inch but still large enough to be retained on the screen. This process must be completed as quickly as possible to avoid loss of moisture through evaporation. The coarse material retained on the screen is now added back to the sample. The test should be started with the soil having a moisture content approximately 4 percent below optimum, which is determined by the hand cast. Figure 17 (left) shows a cast of soil having approximately this moisture content. At 4 percent below optimum, the cast will barely hold together, is readily friable, and will break easily with minimal hand pressure as shown in Figure 17 (right). It may be necessary to either add water or to dry the sample to obtain the desired moisture content. When water is added, the sample should be thoroughly mixed and run through the screen a second time. If the sample is too wet, it should be dried by running it through the screen and spreading it out on top of the density box. Figure 17. Appearance of soil cast approximately 4 percent below Optimum Moisture (left), and easily broken under minimal pressure (right) MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 20 The Proctor mold is then assembled and placed on a hardwood block, supported on firm ground or existing pavement, but not on the tailgate of a pickup truck. A layer of soil is placed in the mold in a quantity sufficient to fill one-third of its volume after compaction. The soil is then compacted in the mold by 25 blows of a 5.5 pound rammer, dropping 12 inches as shown in Figure 9. While compacting the soil, the rammer should be moved about the soil surface in the mold to obtain uniform compaction of each layer. It is important that the rod be held straight and the rammer weight dropped freely since it is a standard compactive effort. Any increase or decrease in the effort may materially affect the accuracy of the test. A second layer of soil is added, filling another one-third of the volume of the mold after compaction. This too is compacted by 25 evenly distributed blows. The third and final layer is added, including enough soil to extend slightly above the top of the mold, after compaction. The third layer is compacted by 25 evenly distributed rammer blows. After the collar has been removed, the compacted soil should extend ¼ to ½ inch above the top of the mold as shown in Figure 10 (top). If the soil does not extend above the mold or if it extends more than ½ inch above the mold, the test should be repeated. The material is struck-off even with the top of the mold using the strike-off bar, as shown in Figure 10 (bottom). If pebbles encountered at this level are disturbed, they may either be pushed down or replaced by soil pressed down firmly with the strike-off bar. c. WEIGHING THE SAMPLE Next, the base plate is removed and the mold is weighed to the nearest gram (Figure 12). This weight is recorded in Column D (Wet Soil + Mold) on the density form (Form 0582B). The volume of the mold and its weight when empty are painted on its side. This weight is recorded in Column E (Mold) and this volume in Column C (Volume Mold). d. COMPLETING THE TEST PROCEDURE The sample is removed from the mold by loosening the handle on the mold and pushing out the soil. The moisture content of the soil is determined by the “Speedy” moisture tester. Refer to page 58 for instructions on the use of the “Speedy.” The Moisture % is entered in Column B of Form 0582B. Complete the computations through Column H (Compacted Soil Wet) as shown in Figure 11. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). e. COMPLETING THE FULL TEST CURVE The soil remaining in the mold is again broken up by running it through the screen and mixed with the remainder of the original sample. Water is added to raise the moisture content approximately 2 percent. An experienced inspector can judge moisture content by the feel and appearance of the soil. A novice inspector should weigh the total sample and compute 2 percent of that weight to determine the amount of the water MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 21 needed. The water is added and the sample is thoroughly mixed by working the soil through the screen until the water is uniformly distributed throughout. After the sample has been broken up and mixed, the same procedure (compacting three layers in the mold, obtaining the moisture content, and determining the Compacted Soil Wet) is followed. This procedure is repeated until there is a decrease in the Compacted Soil Wet (Column H). Ordinarily this will require 4 or 5 molds of varying moisture contents to determine moisture-density results for the complete curve. f. DETERMINING MAXIMUM DENSITY AND OPTIMUM MOISTURE A graph is then prepared with a horizontal leg (abscissa) showing Moisture % and the vertical leg (ordinate) showing the Compacted Soil Wet values in pounds per cubic foot. The Compacted Soil Wet and moisture content from each test are plotted on the graph. A smooth parabolic curve is then drawn through these points. The apex or high point of the parabolic curve gives the Maximum Density and Optimum Moisture of the particular soil. The Maximum Density is recorded in Column I and Optimum Moisture % in Column J. It can be seen after plotting a curve why it is necessary to have at least four points to establish a definite peak. Two points are needed on each side of optimum to establish the slopes of the parabolic curve, which are nearly straight lines. g. PRECAUTIONS IN PERFORMING THE AASHTO T-99 TEST This test establishes a moisture-density relationship; thus, it is important that the compactive effort is standard and uniform throughout the entire series of molds to ensure accuracy of the results. Experience has shown that the following items are important to keep in mind when performing this test: 1) Establish a new Maximum Density any time the material changes (minimum of one per day) or the percent compaction exceeds 100. 2) Have the sample thoroughly broken up by running it through the screen before pounding. 3) Make sure the clamp on the collar and mold is tight. 4) Make sure the mold is seated squarely on the base and the wing nuts are secured with equal tension. 5) Place the mold on a solid block that is supported on firm soil or pavement. 6) Hold the rammer vertically so that it will fall freely. 7) Drop the 5.5 pound rammer weight freely for each 12 inch blow. 8) Use exactly 25 blows on each layer. 9) Reposition large stones away from the sides of the mold and away from other stones to prevent voids. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 24 Figure 18. One-Point Michigan Cone Test Chart MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 25 Figure 19. Striking cone on block Figure 20. Cross-section of properly compacted cone mold MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 26 Figure 21. Entries and computations for the One-Point Michigan Cone Test After the cone is fully compacted, the material is leveled off the top using a straight-edge or the stopper. The cone is then weighed to the nearest gram. The weight is recorded in the “remarks” section of Form 0582B, Moisture and Density Determination. In order to verify that the maximum consolidation has been obtained, the following procedure must be followed. This procedure is commonly referred to as the 20/10 Rule, and is intended to determine the correct end point for the One-Point Michigan Cone Test. A small handful of material is added to the top of the cone and the cone is pounded an additional 20 times. The material is again struck level and the cone is re-weighed to the nearest gram. The weight obtained is then compared to the previously recorded weight. If the increase in weight is 10 grams or less, maximum consolidation has been obtained and the test is complete. Record the final weight, the highest weight obtained, in column D (Wet Soil + Mold) as indicated in Figure 21. If the increase in weight, the highest weight is greater than 10 grams, maximum consolidation has not been obtained, and the process is repeated as needed until the incremental change in weight is less than or equal to 10 grams. The volume and the weight of the cone are painted on the bottom of the cone. The volume of the mold is recorded in Column C (Volume Mold) and the weight is recorded in Column E (Mold). After the cone has been weighed, obtain a moisture sample from the center of the cone if the moisture was manipulated by either drying or adding water. Empty the cone by striking the open end (not the sides of the cone) on the wood block. Note: The cone should be checked periodically for accuracy by the Area Density Specialist. The weight and the volume of the cone should never be changed in the field. These values can only be changed when the cone is recalibrated. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 29 e. PRECAUTIONS IN PERFORMING THE ONE-POINT MICHIGAN CONE TEST Experience has shown that the following items are important to keep in mind when performing the One-Point Michigan Cone Test: 1) Establish a new Maximum Density any time the material changes (minimum of one per day) or the percent compaction exceeds 100. 2) Sample must have a moisture content between 5 percent and optimum moisture. If necessary, add water to the collected sample and not to the grade at the test location. 3) Use a hardwood pounding block placed on firm ground, not on the pickup tailgate. 4) Strike the cone squarely on the end grain of the block. 5) Pound the cone until no more consolidation occurs. 6) Check for maximum consolidation by the 20/10 Rule. 7) Empty the cone by inverting it and lightly striking the open end on the face of the block. Do not empty by striking the cone on its side, as this can cause dents which may change the volume. 8) Take the moisture sample from material at the center of the cone. 9) If the point on the chart obtained by plotting the Compacted Soil Wet (Column H) and Moisture % (Column B) falls to the right of the Maximum Density curve, the sample is too wet. The sample should be dried and the test repeated. 10) Determine the Maximum Density and Optimum Moisture % to the nearest tenth. 11) Record the Maximum Density (Column I) and Optimum Moisture % (Column J) on Form 0582B. 12) Clean out the cone after each test. Soil residue remaining in the cone may cause errors in weight and volume in the next test. Cleaning is easily done by shaking a few stones in it. 13) Check the empty cone weight periodically. If any change is observed, contact the Area Density Specialist. The cone should be recalibrated by qualified personnel only. 14) Maximum Density cannot be determined using a cone if the sample is saturated. 15) Additional precautions for weighing and moisture sampling for this test and others are provided in the appendix. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 30 4. THE MICHIGAN CONE TEST a. DESCRIPTION The Michigan Cone Test is a series of cone tests used to determine Maximum Density of granular soils having a loss-by-washing of 15 percent or less. It is usually used as a referee or supplemental test to the One-Point Michigan Cone Test, by the inspector at the direction of the Area Density Specialist. The equipment used is the same as that used for the One-Point Michigan Cone Test (Figure 2) except for the One-Point Michigan Cone Test Chart. b. PREPARING, COMPACTING AND WEIGHING THE SAMPLE (SAND OR GRAVEL) The weight of the representative sample of sand or gravel used in this test is approximately 3500 grams. A 10 inch by 10 inch pan (furnished in all density kits) filled level to the top usually contains enough material. For all granular materials, the moisture content must be at least 5 percent. This may require the addition of water for most granular soils and aggregates. Mix the water thoroughly with the material. Enough soil is placed in the cone to fill it about one-third its height after compaction. It is then pounded 25 times or more by raising the cone above the wood pounding block and striking it sharply, flat on the end grain of the block (Figure 19). A second layer, filling the cone about two-thirds its height after compaction, is added and pounded 25 times or more. The third layer, which fills the cone to the top, is added and pounded another 25 times or more. After the third layer has compacted, the cone is again filled to the top and then 10 blows or more are continued, holding a hand or stopper over the opening. Material is added at intervals to keep the mold full and then 10 blows or more are continued until no further consolidation occurs (Figure 20). A common error in this test is to discontinue the blows before it is certain that no more material can be compacted into the cone. If free water appears at the top of the cone, the material is saturated. The moisture content of the sample should be reduced and the test repeated. After the mold is fully compacted, the material is leveled off the top, using a straight- edge or the stopper. The cone is then weighed to the nearest gram. This weight is recorded in Column D (Wet Soil + Mold) as shown in Figure 21. The volume and weight of the cone when empty are painted on the bottom. This volume should be recorded in Column C (Volume Mold) and the weight in Column E (Mold). The weight of the cone should be checked periodically for any change. The cone should occasionally be checked for volume accuracy by the Area Density Specialist, since the repeated poundings may bulge the bottom of the cone and change its volume. If any change is observed, the cone should be recalibrated for weight and volume by qualified personnel only. After the cone has been weighed, obtain a moisture sample from the center of the cone sample. Empty the cone by striking the open end (not the sides of the cone) on the wood block. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 31 c. DETERMINING MOISTURE CONTENT (SAND OR GRAVEL) The moisture content is determined using the “Speedy” Moisture Tester. Refer to page 58 for instructions on the use of the “Speedy.” The Moisture % is entered in Column B of Form 0582B. d. DETERMINING MAXIMUM DENSITY OF GRANULAR SOIL OTHER THAN PROCESSED AGGREGATES Complete the computations through Column H (Compacted Soil Wet) as shown in Figure 21. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). If the result of Column H (Compacted Soil Wet) is less than 120 pounds per cubic foot and the moisture content is between 5 percent and optimum, the Maximum Density is the result of one cone test. Enter this result in Column I (Maximum Density). If the result of Column H (Compacted Soil Wet) is more than 120 pounds per cubic foot, a series of two or three cone tests should be repeated at varying moisture contents between 5 percent and a point short of saturation. Suggested moisture contents for the cone series are 7, 9 and 11 percent. The highest test result of this series of cones is the Maximum Density or Maximum Unit Weight and is entered in Column I. e. DETERMINING MAXIMUM DENSITY OF AGGREGATE BASE COURSE AND SURFACE AGGREGATES Research has shown that moisture content does have an appreciable effect on Maximum Unit Weight of gravel. This weight is greatest within 5 to 8 percent moisture content. Thus the Maximum Density of aggregates is determined at a moisture content ranging from 5 to 8 percent, as follows: 1) Run a series of cone tests with moisture content of the aggregate at different points within the 5 to 8 percent range. Two or three points within this range generally should be sufficient to determine the highest unit weight. For example, one test could be run at approximately 5 percent moisture, a second at approximately 6 percent moisture and a third at approximately 7 percent moisture. a) If the cone is saturated (free water appears at the top of the cone), reduce the moisture content but not below 5 percent. If the cone test is run on saturated aggregate, the results may be inaccurate. b) If the aggregate in the cone exhibits the “swell” effect (rises slightly above the top of the cone), reduce the moisture content but not below 5 percent. 2) The highest test result of the series of cones within the 5 to 8 percent moisture range is the Maximum Unit Weight or Maximum Density. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 34 Figure 25. Recycled material being compacted in the mold Figure 26. Mold with collar removed and recycled material ¼ to ½ inch above the top of mold MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 35 Figure 27. Mold with the material struck-off even with the top of the mold c. WEIGHING THE SAMPLE Next, the base plate is removed and the mold and sample are weighed to the nearest gram (Figure 28). This weight is recorded in Column D (Wet Soil + Mold) on Form 0582B as shown in Figure 29. The volume and weight of the mold when empty are painted on the side. The volume is recorded in Column C (Volume Mold) and the weight in Column E (Mold). Figure 28. Weighing the mold and recycled material to the nearest gram MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 36 d. DETERMINING WET MAXIMUM DENSITY The Wet Maximum Density can now be determined by completing the computations through Column H (Compacted Soil Wet) as shown in Figure 29. This is accomplished by subtracting the weight of the mold (Column E) from the weight of the material and mold (Column D). The result is recorded in Column F (Wet Soil). Convert the weight in grams (Column F) to pounds by dividing by 453.59 and record in Column G (Wet Soil, lbs.). The Compacted Soil Wet (Column H) is determined by dividing the Wet Soil (Column G) by the volume of the mold (Column C). The Compacted Soil Wet (Column H) is also the Wet Maximum Density and should be recorded in Column I (Maximum Density). A new Maximum Density should be determined any time the material changes, or the moisture changes ± 1.5 percent. As stated previously, for the Michigan Modified T-180 test, the Maximum Density is determined at the existing moisture content and multiple Maximum Density values may be necessary as the moisture content of the material changes. For example, after taking an In-Place density test and determining a Wet Maximum Density, the In-Place density test did not meet requirements. The contractor, before applying more compactive effort, elects to add water to the area of the failing test. After the failing area is further compacted, the area is retested with another In- Place test. If the same Maximum Density was used for the retest, the test would probably pass, not because of the additional effort so much as from the addition of water. It is possible to obtain passing retests just by adding water if the previous Maximum Density obtained at a lower moisture content is still used. Whenever water is added to a failing area, a new Wet Maximum Density must be established when the In-Place retest is taken. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 39 When not in use, the source rod must be fully retracted in the SAFE position. When the Troxler gauge is lifted by the handle, the source rod automatically returns to the SAFE position. b. LOCATION AND FREQUENCY OF TEST The Density In-Place Test should be taken in those areas of fill (embankment) or backfill that appear to be the least compacted. The test area is selected by watching the movement of the contractor’s compaction equipment. If the tests are run in the visibly poorer areas and they meet specification requirements, it may be assumed that the remainder of the test section also meets specifications. The controlled density specifications require each layer to be compacted to a minimum of 90, 95, 98, or 100 percent of Maximum Density, depending on the item of work. Details on frequency of testing are provided in the appendix of this manual. The gauge offers the option to test by Direct Transmission or Backscatter. Always use Direct Transmission tests on soil and recycled materials. The Backscatter test is used only on Hot Mix Asphalt mixtures. c. TROXLER MODEL 3440 In this manual and in the density certification class the Troxler Model 3440 gauge is used. The Troxler Model 3440, as shown in Figures 30 and 31, is a direct transmission gauge. Mechanically, this gauge is the same as the older Model 3411B. The 3440 gauge also contains a microprocessor which is programmed to perform a wider range of functions and has larger memory capacity for ease of operation. The 3440 gauge is more user friendly than the 3411B which prompts the user during testing and shows more information in the display window. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 40 Figure 30. Troxler Model 3440 nuclear gauge Figure 31. Troxler Model 3440 controls MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 41 1) Keys Description Below is a functional description of the keys found on the Model 3440 control panel: KEYS DESCRIPTION YES EXIT Answers display prompt. Permits exit from the calculator mode. NO/CE C/CE Answers display prompt/Clear last entry. Clears calculator entry. STATUS 7 (SHIFT function) Display status of gauge functions. Number key. MODE 8 (SHIFT function) Asphalt or Soils selection. Number key. SPECIAL 9 (SHIFT function) Provides access to special functions. Number key. STORE MS To store data in gauge memory. Memory store function for the calculator mode. OFFSET MR Select measurement offsets. Memory recall function for the calculator mode. PROJECT 4 (SHIFT function) To enter, view or erase a project Number key. PRINT 5 (SHIFT function) Download data Number key. ERASE 6 (SHIFT function) Erase data Number key. PROCTOR/MARSHALL + Proctor or Marshall value selection. Addition sign for calculator functions. TIME - Selects time interval for testing and measurement. Subtraction sign for calculator functions. COUNTS 1 (SHIFT function) Displays last moisture and density counts. Number key. DEPTH 2 (SHIFT function) Automatic or manual depth operation. Number key. CALC. 3 (SHIFT function) To access the calculator mode. Number key. SHIFT x Activates all SHIFT function modes. Multiplication sign for calculator functions. STANDARD / Provides access to standard count mode. Division sign for calculator functions. RECALL 0 (SHIFT function) To recall data for viewing Number key. . Decimal point key START/ENTER = See manual text and index. Equals sign for calculator functions 2) 3440 Keypad Layout The Troxler Model 3440 control panel consists of 22 keys (Figure 31): the 20 key control section and the ON/OFF keys. Keystrokes result in an immediate “beep” MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 44 To begin taking a standard count, press STANDARD for the display: - Standard Count - DS = _____ MS = _____ Take new count? Press YES for the display: Is gauge on Std. Block & Source rod in SAFE pos? Make sure the gauge is placed on the reference block correctly. Place the source rod in the SAFE position and press YES to begin taking the 4 minute standard count: Taking Standard Count 240 seconds remaining After count completion, the display is: MS=____ _._ %P DS=____ _._ %P Do you want to use the new STD? The standard count (operating standard) should not deviate from the chart standards obtained from the Gauge Book by more than 1 percent for density or 2 percent for moisture. If the standard counts are within acceptable limits, press YES to accept. Record the standard counts in the lower right corner of Form 0582B, (Figure 29) under Operating Standards. If either value is out of range, press NO and take another standard count. Before repeating the standard count, make sure the gauge base and reference block are clean and the gauge is positioned correctly on the reference block. If either standard is still out of tolerance, call the Area Density Specialist or Lansing Density Technology staff immediately to make arrangements to have the gauge serviced or replaced. The gauge should be serviced or replaced within 24 hours. To determine if the gauge can continue to be used until serviced or replaced, do the following: Repeat the standard count procedure 5 times, saving each result when prompted. On completion of the fifth standard count, check the display to determine status. If MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 45 the standards for the fifth count are within tolerance, ± 1 percent for density and ± 2 percent for moisture, a P will show next to the percentages in the display. If passing results are indicated, you may continue to use the gauge for 24 hours. If either standard fails, an F will show on the display and the gauge should be taken out of service immediately. 6) Viewing the Last Four Standard Counts To “view” the last 4 standard counts, press STANDARD for the display: -Standard Count- DS = ____ MS = ____ Take new count? Press NO for the display: - Standard Count - Want to view last four Standard Counts? Press YES for the display: Density Std Cts 1:____ 2:____ 3:____ 4:____ (YES for Moist) To view the “Moisture Standard Counts” press YES. The display will be: Moist. Std Cts 1:____ 2:____ 3:____ 4:____ (Press any key) The “View Standard Count” function may be exited by pressing any key. 7) Setting Measurement Units Prior to taking measurements, the user should determine the “Unit of Measurement” that is required for screen displays and/or printouts. The available selection is either “PCF” or “Metric”. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 46 To execute the “SET UNITS” function, press SHIFT and SPECIAL for: SPECIAL FUNCTION YES- Next menu 1- STAT TEST 2- DRIFT TEST Press YES 3 times for the display: YES - Next menu 9- SET UNITS 10- BAUD RATE 11-COMM PROTOCOL Press 9 for the display: UNITS in PCF Press: 1-PCF 2-METRIC ENTER- No change or the display will be: UNITS in METRIC Press: 1-PCF 2-METRIC ENTER- No change Press either 1 or 2 for the required units. 8) Count Time Selection The 3440 gauge provides 3 different count times to be used for taking readings. When running In-Place Moisture/Density Tests always use the 1 minute time cycle. Never use the 15 second time cycle. Press TIME for the display: Time: ____ min 1 - 15 sec 2 - 1 min 3 - 4 min MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 49 To start the measurement, press START/ENTER for the display: Depth: __ inches PR:_____ PCF Time: ___ sec. After the gauge completes its count time, the display will be: %PR=_____% DD=_____ PCF WD=_____ PCF M=___ %M=___ Record DD, WD, M and %M in the correct columns on Form 0582B. Note: Do not record %PR until the correct Maximum Density has been enabled. To obtain the density and moisture test counts press SHIFT and COUNTS for the display: Dens ct.=_____ Moist ct.=____ SHIFT/RECALL to see Readings. Record the counts in columns 3 and 6 on Form 0582B. b) Asphalt Mode Enable the ASPHALT mode prior to taking a test on HMA materials. Check units of measurement, count time and Maximum Density. Select the test site and make sure the site is flat before setting the gauge down. Place the source rod in the BACKSCATTER position. Start a measurement by pressing START/ENTER. The display will be: Depth: __ inches MA:_____ PCF Time: ___ sec. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 50 After the gauge completes its count time, the display will be: %MA=_____ % WD=______ PCF M=___ %M=___ Record WD, M and %M in the correct columns on Form 0582B. Note: Do not record %MA until the correct Maximum Density has been enabled. To obtain the density and moisture test counts press SHIFT and COUNTS. Record the counts in columns 3 and 6 on Form 0582B. 11) Proctor (Cone)/Marshall/Voidless Function The 3440 gauge provides for up to four different Proctor (Cone) values and four different Marshall values to be stored for later use. To select or change a Proctor (Cone) or Marshall Density value press the PROCTOR /MARSHALL key for the display: MA=_____ PCF PR=_____ VD=_____ Want to change? If a value is to be enabled or a new value added or changed, press YES. The display is: Select: 1 - MA 2 - PR 3 - Voidless Marshall and Proctor (Cone) functions are identical as far as operation is concerned. Therefore, only Proctor (Cone) will be illustrated. To change a Proctor (Cone) value, press 2 for: Select source of Proctor value: 1- Stored value 2- New value MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 51 a) Recall a Stored Proctor (Cone) / Marshall Value To enable a previously stored value, press 1. The display is: Select desired Proctor: 1:____ 2: ____ 3:____ 4: ____ Select the desired Proctor (Cone) value by pressing 1, 2, 3 or 4 for the display: Proctor: _____ PCF ENABLED! b) Enter a New Proctor (Cone)/Marshall Value From this display press 2. The display will be: Enter the new value and press ENTER for the display: PR=______ PCF Do you want to save this value for later use? Press YES to save the new Proctor (Cone) value in a memory cell, for later use. The display will be: Select Proctor Memory cell: 1:____ 2: ____ 3:____ 4: ____ Select source of Proctor value: 1- Stored value 2- New value Proctor: ______ PCF Press ENTER when completed MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 54 d. PRECAUTIONS IN PERFORMING THE DENSITY IN-PLACE (NUCLEAR) TEST 1) Keep the gauge clean. 2) Do not use the gauge when it is raining. Moisture can damage the gauge resulting in loss of use and costly repairs. 3) Contact the Area Density Specialist when the gauge needs servicing. 4) Transport the gauge according to US DOT regulations. 5) Do not scratch or gouge the surface of the Standard Block. 6) Protect the gauge at all times and handle carefully. 7) Fill holes or voids in the test surface with sand or fine material from the area near the test site. 8) Do not recharge batteries unless the battery indicator signals a low battery. 9) Be aware of safety standards when the gauge is stored or when charging the batteries. 10) If the gauge is involved in an accident, refer to the nuclear gauge transport book. 11) Do not run comparison tests. 12) Return the gauge to its Type A Box in the pickup truck on the front passenger floor board, behind the passenger seat or in the NUX Safety Containment Box when not in use. e. CARE OF NUCLEAR GAUGE AND EQUIPMENT After the test is completed, the gauge should be returned to the transport case in the cab of the pickup truck. Always secure the gauge in the Type A box prior to transporting the device. Do not transport the gauge on the tailgate or in the bed of the pickup truck as this is in violation of the department’s license issued by the Nuclear Regulatory Commission. If the gauge malfunctions, the Area Density Specialist should be notified immediately. Due to the radioactive materials located within a nuclear density gauge, there are regulations governing the storage, transportation and use of the gauge. The Nuclear Regulatory Commission, United States Department of Transportation and the Michigan Department of Transportation have established safety requirements that must be complied with. These safety requirements include, but are not limited to, the usage, storage, security, transportation of nuclear density gauges, and occupational doses and doses to members of the public. These regulations are located within 10 CFR (Energy) and 49 CFR (Transportation). The safety features built into the Troxler density gauge provide shielding of the radioactive material, which allows an operator to use the gauge while minimizing the exposure to radiation. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 55 1) The following steps must be taken when the gauge is damaged within a construction project: a) Immediately stop all construction-vehicle movement (in the immediate proximity). b) Detain witnesses until they are interviewed. c) Establish a fifteen (15) foot perimeter (minimum). d) Isolate the gauge from all people. e) Contact the Area Density Specialist. f) Contact the Statewide Density Specialist g) Contact MDOT’s Radiation Safety Officer. h) Complete an incident report form. i) All of the above steps are to be conducted in the order indicated. 2) The following steps must be taken when the gauge is damaged outside the limits of a construction project: a) Detain witnesses until they are interviewed. b) Establish a fifteen (15) foot perimeter (minimum). c) Isolate the gauge from all people. d) Contact the nearest Michigan State Police Post. e) Contact the Area Density Specialist. f) Contact the Statewide Density Specialist. g) Contact MDOT’s Radiation Safety Officer. h) Complete an incident report form. i) All of the above steps are to be conducted in the order indicated. 3) The following steps must be taken when a gauge is lost or stolen: a) Contact the Area Density Specialist. b) Contact the Statewide Density Specialist. c) Contact MDOT’s Radiation Safety Officer. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 56 d) Contact MDOT’s Emergency Management Coordinator. e) Complete an incident report form. f) All of the above steps are to be conducted in the order indicated. Refer to the gauge book for the incident report form, telephone numbers and radio numbers. 7. CALCIUM CARBIDE GAS PRESSURE METER (“SPEEDY” MOISTURE TESTER) a. DESCRIPTION The Michigan Department of Transportation uses a calcium carbide gas pressure meter for determining moisture content. This test is used when the moisture content of the test sample has been manipulated. The current model in use is the “Speedy” Moisture Tester, which was developed in England and in the soils laboratory of the Federal Highway Administration. Test apparatus must meet the requirements of AASHTO T 217. Only use pressure meters sized for specimens having a mass of at least 20 grams. The pressure meter (Figure 32) replaces the two-burner gas stove for the purpose of determining the moisture content of soils. With the pressure meter, the moisture can be determined in five minutes or less which permits obtaining density results much faster than with the stove drying method. The principle on which the pressure meter is based is a chemical reaction which begins when the soil in the cap and calcium carbide in the body are mixed together. The moisture in the soil combines with the calcium carbide to produce acetylene gas. The gas pressure is registered on the gauge as moisture content, percent of wet weight. When testing very wet soils, an initially high reading and heat are caused by the reaction generated by the higher moisture content. Be sure that the heat has dissipated and the needle has stopped moving before the final reading. b. CARE OF THE PRESSURE METER The density kit contains a place designated to store and work with the equipment. It is important that the pressure meter be carried in this compartment (Figure 5). Within the pressure meter box is a place for each piece of equipment to be stored to prevent damage to the gauge, the tester, the balance beam and also to prevent the loss of small parts such as the half sample weight (Figure 32). The care of the pressure meter is important and is the responsibility of the density inspector. The cap in which the soil is placed should be cleaned after each test. The body of the pressure meter should be cleaned before and after each test. If at any time something is wrong with the equipment, contact the Area Density Specialist. The cap should be cleaned after each test (Figure 33). A special cloth is provided with each kit for this purpose. This cloth should only be used to clean the cap, the scale pan MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 59 a replacement. DO NOT use a nylon brush in the meter body which could generate a static charge capable of igniting any residual acetylene gas. Figure 34. Proper technique for cleaning the body of the meter This is a precision instrument. While it is considered rugged for its intended use, it will not withstand abuse due to careless handling. The accuracy of test and the useful life of the pressure meter will depend on the skill and technique of the inspector and the general care taken to keep the equipment in good condition. c. USE OF THE PRESSURE METER The gauge reading is applied to the conversion chart supplied with each “Speedy” moisture tester (Figure 35). Note: The gauge reading is based on the wet weight of the sample. The chart converts this to dry weight. In cold weather, run a sample through the meter to warm up the body. Disregard this reading. The test procedure is different when testing cohesive soils than when testing granular soils. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 60 Figure 35. Calcium carbide gas pressure meter (“Speedy”) conversion chart MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 61 d. TEST PROCEDURE FOR SAND AND GRAVEL (LOSS-BY-WASHING OF 15 PERCENT OR LESS) Place 3 scoops of calcium carbide in the body of the “Speedy” (Figure 36). Figure 36. Place calcium carbide in body of the “Speedy” Clean the cap in preparation for the sample (Figure 33). Weigh the sample as quickly and as accurately as possible (Figure 37). The sample will be either 20 or 26 grams, depending on the size of the “Speedy.” Only material passing the ¼ inch screen will be used. Figure 37. Weigh moisture sample Place the sample in the cap (Figure 38). MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 64 Figure 42. Read dial with “Speedy” held horizontally Refer the dial reading to the wet-dry conversion chart, which determines the moisture content based on dry weight. Interpolate to the nearest tenth of a percent (Figure 35). Record the moisture percent (dry weight basis) in Column B, with a circled “S” at the bottom of Form 0582B. While holding the “Speedy” downwind and away from your body, release the pressure slowly and empty contents (Figure 43). Figure 43. Hold “Speedy” downwind and away from body. Slowly release pressure and empty the “Speedy.” Clean the cap and pressure meter body in preparation for the next test. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 65 When using the pressure meter to determine the moisture content of gravels (processed aggregates), the gravel sample must be screened. Using the screen from the density kit, rub the gravel sample through the screen until all of the fines and small stones are through and just the large stones are left. Obtain the moisture sample from the material that has passed through the ¼ inch screen. e. TEST PROCEDURE FOR COHESIVE SOIL (HALF SAMPLE (13 GRAM or 10 GRAM), PROPORTIONAL METHOD and LOSS-BY-WASHING GREATER THAN 15 PERCENT) Place 3 scoops of calcium carbide in the body of the “Speedy” (Figure 36). Hold the body of the “Speedy” horizontally. Roll in the two 1-inch steel balls into the body of the “Speedy” (Figure 44). DO NOT drop the steel balls directly into the body of the “Speedy” when it is sitting upright to avoid damaging the orifice of the pressure gauge. Figure 44. Place steel balls in body of “Speedy” with 3 scoops of calcium carbide MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 66 Clean cap with cloth provided in kit (Figure 45). Figure 45. Cleaning the cap of the meter Using the ¼ inch screen from the density kit, rub the soil sample through the screen (Figure 46). Figure 46. Using the ¼ inch screen from the density kit, always screen cohesive soil before obtaining the moisture sample MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 69 A test can fail by either moisture or density or both requirements. If a test fails to meet the density requirement, the percent of compaction (column 11) should be circled. If a test fails moisture requirements, the Moisture % (column 8) should be circled. If the inspector encounters an in-place density test over 100 % compaction, the test does not fail. However, the inspector must establish a new maximum density within three (3) feet of that test. This is to ensure that the results at that location are verified and documented or if there has been a change in material that is not visually apparent. The location of each In-Place Density Test should be recorded by stationing, distance right or left of centerline and depth below plan grade. Identify the item of work (Column 16) using the abbreviations on the back of the form. Entries on Form 0582B, Determination of In-Place Density, (Columns 5, 7-11) are recorded to the nearest tenth (0.1). Entries for Determination of Maximum Density are recorded as follows: Columns D-F nearest gram Columns B, H-J nearest tenth (0.1) Column C nearest ten-thousandth (0.0001) Column G nearest one-hundredth (0.01) When conducting a recheck, if the Maximum Density is imported from a previous report, recopy the complete Maximum Density line from the original report. Record the date of the original test in the margin to the left of the test number. See examples of Form 0582B in Figures 48 to 51. The distribution for Form 0582B is as follows: ORIGINAL to the project file and COPIES to the Area Density Specialist and Lansing Density Technology Unit. Form 0582B must be submitted by the tester to the office daily. Distribution of Form 0582B to the Area Density Specialist and the Lansing Density Technology Unit must be made weekly at a minimum. Electronic submittal of scanned test reports can be sent to the Lansing Density Technology Unit at the following address: MDOT-NuclearDensityTestReports@Michigan.gov MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 70 Figure 48. Form 0582B: Density Determination of Soils MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 71 Figure 49. Form 0582B: Density Determination of HMA Aggregate Base (BAB) Mixtures MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 74 b. PRECAUTIONS FOR RECORDS AND REPORTS Experience has shown the following items are important to keep in mind when recording test results: 1) Report all tests, failing or passing, on Form 0582B. 2) Check all calculations. 3) Circle percent of compaction and/or moisture for all failing tests. 4) All failing tests require a passing retest. 5) Use original test number and date to identify retests. 6) Use the “Remarks” space at the bottom of Form 0582B to document failing tests and when corrections and retests were not completed on the same date. 7) Submit original test reports to the office daily. Retyped or recopied versions are not acceptable. 8) Distribution of Form 0582B to the Area Density Specialist and the Lansing Density Technology Unit must be made weekly at a minimum. 9) Electronic submittal of test reports can be sent to the Lansing Density Technology Unit at the following address: MDOT-NuclearDensityTestReports@Michigan.gov C. DENSITY TESTING METHODS 1. THE CONTROL DENSITY METHOD a. DESCRIPTION The Controlled Density Method is the standard procedure used by the Michigan Department of Transportation to control the placement and compaction of embankment and backfill material. This method must be used unless otherwise shown on the plans or in the proposal. Material is placed in horizontal layers not exceeding a thickness of 9 inches for clay/cohesive soil or 15 inches for granular soil. The loose soil layer must be compacted by mechanical means to the minimum specified density. Each layer is tested and accepted before the succeeding layer is started. The equipment used to spread the material and the type of equipment used to compact the material is determined by the contractor. The primary requirement is that the material be placed in discreet horizontal layers and uniformly compacted to the specified density throughout the fill area. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 75 Where tests indicate inadequate density, it is generally due to one of two reasons: 1) Improper moisture content 2) Insufficient compactive effort b. MOISTURE CONTENT Improper moisture content is the greatest single cause of difficulty in attaining the specified density requirement, especially for cohesive soil. MDOT specifications require that cohesive soils have moisture content not greater than 3 percent above optimum at the time of compaction, except for the top 3 feet of embankment which must not exceed optimum. If the material contains excessive moisture, it must be aerated and dried by disking or other effective methods before being compacted. The succeeding layer must not be placed until the specification requirement is met. Sometimes, where large areas of embankment are to be constructed, a layer of wet material may be left to dry while placing or compacting operations are alternately being performed at another embankment area. Because the natural moisture content of clay soil is often near optimum or above optimum, the addition of water is generally not required. However, if the material is dryer than optimum, water may need to be added to facilitate compaction. The closer the moisture content is to optimum, the easier it is for the contractor to attain density. At times, where the cut material is composed of both wet and dry material, grading operations may require some mixing after the material is deposited on the grade and before compacting. Although it is generally not economically practical for the contractor, he may elect to waste the wet material and replace it with an equal volume of drier material. When atmospheric conditions permit little or no evaporation, wet material cannot be manipulated, aerated and dried. During such periods, which generally include later fall, winter and early spring, the contractor often chooses to wait for more favorable construction weather. The compaction characteristics of sand soils are much less sensitive to moisture variation and can be satisfactorily compacted over a wide range of moisture content. In as much as the natural moisture of sand soils is often in a bulking range of 3 to 5 percent, compaction is often attained more quickly and with less effort by adding water. Excessive moisture is generally not a problem with sand, except for saturated fine sand which has been excavated from below the water table. In this case, the usual solution is to allow the material time to dry until the moisture content is less than optimum before placement and compaction are attempted. The succeeding layer must not be placed until the specification requirement is met. The compaction of granular material can generally be conducted in wet weather and sometimes even in freezing weather. At times, the soil of the original ground contains enough moisture to become spongy when trying to place the first layer of an embankment, making compaction almost impossible. If this spongy condition is not corrected, the embankment will usually continue to be spongy with each succeeding layer. Sometimes it is possible to remedy this problem by disking and aerating the original ground. If the original ground contains an excess of moisture so that manipulation is not practical, it may be necessary to construct the first layer of Granular Material Class III to the minimum elevation at which the equipment can be operated. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 76 When the moisture of the embankment material is at or near optimum, the contractor should have little difficulty in obtaining satisfactory density if adequate compactive effort is applied. When heavy earthmoving equipment places the material in thin layers over a large area, and if the units break track for maximum compactive coverage, they can usually attain satisfactory compaction alone. A common problem occurs when many units are hauling a short distance to a small embankment area. To obtain uniform compaction, supplemental compaction equipment must be added. c. PLACEMENT AND COMPACTION OF MATERIAL Whenever density tests indicate that the contractor has not obtained the specified density, he must be directed that the succeeding layer must not be placed until the specification requirement is met. The decision as to how the corrective work is to be done is left up to the contractor. From the test results and from observation, however, the inspector should recognize the reason for the low density and could suggest appropriate action such as disking the wet soil to dry it, adding water to a dry soil, or simply doing more rolling if moisture is not the problem. While specifications permit the placement of clay in layers up to 9 inches thick and sand in layers up to 15 inches, better results are obtained if the material is spread and compacted in thin layers. Layers 3 to 5 inches thick require less compactive effort and promote better hauling conditions. Heavy earthmoving equipment generally causes some “kneading” or movement of a compacted clay fill under passing wheel loads even though the soil is at Optimum Moisture. In all but dry cohesive soils a moderate amount of such movement is to be expected and is not detrimental. In general, the surface should rebound after the wheel passes and should not leave a rut more than 1 to 3 inches deep. Occasionally, some sensitive clays are observed to rut deeply even though the density and moisture requirements are within specification. When such actions are observed, density test computations, procedures and equipment should be reviewed to confirm that specification requirements are being met. The Area Density Specialist should participate in this review. If the condition continues up to subgrade elevation, it is suggested that the Delivery Engineer consult with the Region Soils Engineer to determine whether disking and drying should be performed to ensure a more firm subgrade. Although the type of compaction equipment used is left entirely to the option of the contractor, experience has shown that certain equipment is more efficient for compacting one type of soil than another. A sheepsfoot roller, for example, is generally more effective in compacting clay than sand. Vibratory equipment is effective on granular soils and relatively inefficient for compacting clay. Heavy, multi-wheel, pneumatic rollers are effective for all types of soils. Small plate vibrators are generally more efficient than tampers for compacting granular trench backfill. For many types of soil, the very top 2 inches or so of the layer being compacted remains loose until it has been confined by placement of the succeeding layer. For that reason, it is important that the loose surface be scraped away before the density test is taken. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 79 II. TECHNICIAN QUALIFICATION PROGRAM FOR FIELD DENSITY TESTING A. TECHNICIAN QUALIFICATIONS Technicians performing field density testing must be certified and evaluated as necessary by Independent Assurance Test (IAT) in accordance with the following criteria: 1. Certification. Technicians performing Quality Assurance testing on departmental projects must become certified and maintain certification through a program conducted or approved by the MDOT Construction Field Operations Section, Density Technology Unit. 2. Independent Assurance Tests (IAT). a. NHS routes. Technicians who perform density testing on federal aid projects on the National Highway System (NHS) must be evaluated by an IAT. IAT procedures outlined in the MDOT Quality Assurance Procedures Manual will be used for this evaluation. b. Non NHS routes. Evaluation by IAT is not required; however, MDOT reserves the right to evaluate technician proficiency using IAT procedures outlined in the MDOT Quality Assurance Procedures Manual. B. MAINTAINING RECORDS Construction Field Services (CFS) Construction Field Operations Section maintains a data base which includes the following information for Field Density Testing Technicians: 1. Radiation safety training data 2. Density certification training dates 3. Certification number 4. Expiration date 5. Technician name and address* * The technician is responsible for informing the department of address change. The database is updated periodically as training sessions are conducted. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 80 C. DISQUALIFICATION OF TECHNICIANS 1. Falsifying Data. Technicians found falsifying data will be disqualified from acceptance testing on MDOT and federal aid projects. The term of disqualification may be permanent and will be determined by the Engineer of CFS. 2. Failure to obtain Recertification Technicians who allow their certification to lapse are not qualified to perform density testing on MDOT or federal aid projects. Reinstatement will be considered only after successful completion of a training program conducted or approved by the MDOT Construction Field Operations Section, Density Technology Unit. The specific coursework necessary for reinstatement will be determined by the Engineer of CFS. 3. Failure to meet the requirements of the IAT program. a. NHS routes. Technicians who fail to meet the requirements of the IAT program as outlined in the MDOT Quality Assurance Procedures Manual will be disqualified from acceptance testing on NHS routes. b. Non NHS routes. MDOT reserves the right to evaluate and disqualify technicians from density testing using IAT procedures outlined in the MDOT Quality Assurance Procedures Manual. If evaluation is deemed necessary, technicians failing to meet these requirements may be disqualified from density testing. 4. Other actions deemed detrimental to the MDOT Quality Assurance Program. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 81 III. APPENDIX A. DEFINITIONS AASHTO - American Association of State Highway and Transportation Officials. AGGREGATE - in highway density work this refers to gravel used as base course or shoulder material. AGGREGATE BASE COURSE FOR HMA SURFACES - the layer or layers of select material of designed thickness placed on a subbase or subgrade to support a HMA surface. AGGREGATE BASE FOR CONCRETE SURFACES - the layer or layers of select material of designed thickness placed on a subbase or subgrade to support a concrete surface. AMERICIUM 241: BERYLLIUM - the fixed neutron source in the Troxler nuclear moisture- density gauge used to determine the in-place moisture content of the material being tested. BACKFILL - material which replaces previously excavated material from trenches or sewers, culverts, etc.; also, fill placed in contact with retaining walls, bridge abutments, etc. BACKSCATTER TEST - a test ran with the radiation source and detectors in the same horizontal plane. HMA AGGREGATE BASE - pulverized pavement mixtures consisting of existing Hot Mix Asphalt (HMA surfaces, pulverized and mixed with some portion of the underlying aggregate base. The resulting mixture of pulverized HMA and aggregate base material is then compacted and used as a base course for new or recycled pavement surfaces. CERTIFY - to award a certificate to (a person) attesting to the completion of a course of study or the passing of a qualifying examination. CESIUM 137 - the gamma source in the Troxler nuclear moisture-density gauge used to determine the in-place density of the material being tested. COHESIVE SOILS - fine textured soils bound together (or obtaining strength) by an internal attraction or bond between individual grains, generally clay or clayey soils with loss-by-washing greater than 15 percent. COMPACTION - densification of a soil or HMA mixture by means of mechanical manipulation. CONCRETE AGGREGATE BASE - pulverized pavement mixtures consisting of existing concrete surfaces, pulverized and mixed with some portion of the underlying aggregate base. The resulting mixture of pulverized concrete and aggregate base material is then compacted and used as a base course for new or recycled pavement surfaces. CONSOLIDATION - rearrangement of soil particles to form a more dense material, resulting from either natural or mechanical action. COUNTS/MINUTE - the amount of radiation picked up by a detector tubes and registered on digital modules or digital indicators for a one-minute period. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 84 SOURCE - the radioactive material sealed in the gauge. STABILIZATION - a recycling method used to improve the stability and bearing capacity of HMA material by admixing hot bitumen in-place and compacting. STANDARD BLOCK - a polyethylene block which is used daily to field calibrate (standardize) the nuclear gauge. STANDARD COUNT - the Counts/Minute ran and recorded daily on the Standard Block. The Standard Count is sometimes referred to as the Operating Standard. SUBBASE - the layer of granular material placed on the subgrade as a part of the pavement structure. SUBGRADE - the portion of the earth grade upon which the pavement structure is constructed. TEMPLATE (SCRAPER PLATE) - a metal plate used to prepare the test site. It is used to guide the drill rod in preparing a hole for the source rod for direct transmission measurements. TEST COUNTS - the amount of radiation detected by the gauge for a moisture or density test. UNITED STATES DEPARTMENT OF TRANSPORTATION (U.S. DOT) – federal agency that regulates the transportation of nuclear density gauges. VOIDS - spaces between individual soil particles occupied by air and/or water. WET DENSITY - the total weight of a unit volume of material. This includes the weight of solids plus the weight of water. WET MAXIMUM DENSITY - Wet Density (unit weight) of a material obtained by a specified amount of compaction at the existing or modified moisture content. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 85 B. CHECKLIST FOR THE ONE-POINT T-99 TEST Checklist for the One-Point T-99 Test 1. Obtain sample (approximately 3500 grams). 2. Break up the sample by working it through the ¼ inch screen. 3. Check moisture content, which should be within a range from optimum to 4 percent below optimum at the start of the test. 4. Assemble the Proctor mold. 5. Place the mold on the pounding block. 6. Place a layer of soil in the mold (enough to fill the mold one-third full after compaction). 7. Compact this first layer by 25 evenly distributed rammer blows. 8. Place a second layer of soil in the mold (enough to fill it two-thirds full after compaction). 9. Compact the second layer by 25 evenly distributed rammer blows. 10. Place a third layer of soil in the mold (enough so that after compaction, it will extend from ¼ to ½ inch above the top of the mold. 11. Compact this third layer by 25 evenly distributed rammer blows. 12. Remove the collar. 13. Use the strike-off bar to trim the sample even with the top of the mold. 14. Remove the base plate. 15. Weigh the mold and sample. 16. Remove the soil from the mold. 17. Obtain a moisture sample from the center of the soil sample. (Required when the moisture content has been manipulated). 18. Determine Moisture % and Compacted Soil Wet, pcf. 19. Use the One-Point T-99 Chart to determine Maximum Density and Optimum Moisture. 20. Record the test results on Form 0582B. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 86 C. CHECKLIST FOR THE AASHTO T-99 TEST Checklist for the AASHTO T-99 Test 1. Obtain sample (approximately 5000 grams). 2. Break up the sample by working it through the ¼ inch screen. 3. Check moisture content, which should be approximately 4 percent below optimum at the start of the test. 4. Assemble the Proctor mold. 5. Place the mold on the pounding block. 6. Place a layer of soil in the mold (enough to fill the mold one-third full after compaction). 7. Compact this first layer by 25 evenly distributed rammer blows. 8. Place a second layer of soil in the mold (enough to fill it two-thirds full after compaction). 9. Compact this second layer by 25 evenly distributed rammer blows. 10. Place a third layer of soil in the mold (enough so that after compaction it will extend from ¼ to ½ inch above the top of the mold. 11. Compact this third layer by 25 evenly distributed rammer blows. 12. Remove the collar. 13. Use the strike-off bar to trim the sample even with the top of the mold. 14. Remove the base plate. 15. Weigh the mold and sample. 16. Remove the soil from the mold. 17. Obtain a moisture sample from the center of the soil sample. 18. Determine the Moisture %. 19. Compute compacted soil wet, pcf (Maximum Density, pcf, Form 0582B) 20. Thoroughly break-up the remaining portion of the molded specimen by working it through the screen. 21. Recombine with the original sample and mix thoroughly. 22. Add approximately 2 percent moisture and mix thoroughly. 23. Reassemble the mold and repeat steps 5 through 22. This process will need to be repeated at least three times. 24. Plot moisture content versus dry density for each data set. 25. Connect the graph points for all tests with a smooth parabolic curve. 26. Determine the Maximum Density, pcf and Optimum Moisture content. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 89 F. CHECKLIST FOR THE MICHIGAN MODIFIED T-180 TEST Checklist for the Michigan Modified T-180 Test 1. Perform the In-Place tests in the “Asphalt Mode.” 2. Obtain the Maximum Density sample from the In-Place test location. 3. The mold is pounded at existing in-place moisture. 4. Make sure the Proctor mold is assembled correctly. 5. The pounding block should be placed on firm ground or pavement. 6. Place a layer of material in the mold (enough to fill the mold one-fifth after compaction). 7. Compact the layer with 25 evenly distributed blows using the 10 pound rammer. 8. Place the second, third and fourth layers in the mold, each layer filling one-fifth of the volume of the mold, and compact each layer with 25 evenly distributed blows. 9. Place the fifth layer in the mold. Enough material is used so that after compaction, the material will extend from ¼ to ½ inch above the top of the mold. 10. Compact the fifth layer with 25 evenly distributed blows. 11. Remove the collar. 12. Use the strike-off bar to trim the excess material even with the top of the mold. 13. Remove the bottom plate from the mold. 14. Weigh the sample and mold to the nearest gram. 15. Complete the computations through Column H (Compacted Soil Wet, PCF) on Form 0582B. 16. The resultant value from Column H is the Maximum Density (wet) and should also be recorded in Column I (Maximum Density, PCF). 17. This test is normally used on In-Place recycling jobs. The material changes frequently for this type of work, and therefore, the Maximum Density will have to be re-established more often and also when the moisture changes more than 1.5 percent. MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 90 G. CHECKLIST FOR THE TWELVE-INCH LAYER METHOD Checklist for the Twelve-Inch Layer Method 1. Obtain the Maximum Density from the In-Place test location. 2. The Loss-By-Washing determines the test method used to establish Maximum Density. 3. The mold or cone is pounded at existing field moisture. 4. Do not use the One-Point Chart to establish Maximum Density. 5. If the Loss-By-Washing is greater than 15 percent, work the sample through the ¼ inch screen before pounding the mold. Pound the mold in three equal layers using 25 blows per layer. 6. If the Loss-By-Washing is 15 percent or less, use the cone to establish the Maximum Density. 7. Weigh the completed mold or cone to the nearest gram. 8. Using the moisture content obtained from the In-Place test, compute the Maximum Density. Maximum Density, dry weight basis, is obtained using this formula: Compacted Soil Wet x 100 (Moisture % + 100) MDOT Density Testing and Inspection Manual 2003 Ed., Rev. Dec. 2020 91 H. CHECKLIST FOR USE OF THE NUCLEAR GAUGE Checklist for Use of the Nuclear Gauge Troxler Model 3440 1. Check the ID number on the gauge book and the standard block and be sure they match the ID number on the gauge. Gauge books and standard blocks are not interchangeable. 2. Turn the gauge on and allow a 20 minute warm-up before running standards. 3. Record Chart Standards for Density and Moisture. 4. Run Operating Density and Moisture Standards daily and record. 5. Select the test location and prepare the test site. 6. Run the Density and Moisture tests and record the test readings. 7. Record the Wet Density, PCF and Moisture, PCF. 8. Record the Dry Density, PCF and Moisture, %. 9. Record the Density and Moisture Counts. 10. Record and program the gauge with the correct Maximum Density, PCF. 11. Record the Percent of Compaction. 12. When finished running a test, lock and return the gauge to the transport case in the pickup truck cab. 13. Rechargeable batteries have a memory and repeated needless charging will shorten the battery life. Do not recharge batteries unless <Batteries Low!> is visible on the display. For a full charge, re-charge the gauge for 16 hours. A full charge should last from four to six weeks. 14. Report malfunctions promptly to the Area Density Specialist. 15. Gauge users are not authorized to make field repairs or perform gauge maintenance. Only Statewide and Area Density Specialists are permitted to maintain or repair gauges. 16. Follow all safety rules and regulations. 17. Transport the gauge according to US DOT regulations. 18. When the gauge is left unattended in a vehicle, both the vehicle and the gauge must be locked.