Relationship between Resilient and Dynamic Modulus in Pavement Engineering, Schemes and Mind Maps of Design

Download Relationship between Resilient and Dynamic Modulus in Pavement Engineering and more Schemes and Mind Maps Design in PDF only on Docsity! 1 Resilient Modulus to Dynamic Modulus Relationship and Pavement Analysis with the Mechanistic- Empirical Pavement Design Guide Prepared by Jeff Stempihar Assistant Research Professor Reviwed by Shane Underwood Assistant Professor Kamil Kaloush Associate Professor Submitted to FORTA Corporation 100 Forta Drive Grove City, PA 16127-9990 April 2015 2 Resilient Modulus to Dynamic Modulus Relationship and Pavement Analysis with the Mechanistic-Empirical Pavement Design Guide Summary Research work over the past decade has investigated the relationship between dynamic modulus and resilient modulus of AC pavements. A result of this work is an approximate relationship between dynamic modulus values at 5 Hz and resilient modulus values at the same test temperature. Such a relationship means that analysis and conclusions based on changes in dynamic modulus values can be extended to similar changes in resilient modulus values. Several MEPDG design simulations were performed on a FORTA fiber reinforced pavement and a conventional pavement to determine relationships between AC layer thickness and percent improvement in total rutting and fatigue cracking resistance due to the addition of the FORTA fibers. These design simulations used laboratory data, specifically dynamic modulus and fatigue test data for both AC mixtures. Based on these MEPDG design simulations, the maximum AC layer thickness reduction of the FORTA fiber reinforced pavement to provide equivalent predicted pavement performance of conventional pavements for both total rutting and fatigue cracking is 32%. Given the relationship between dynamic modulus and resilient modulus, it is expected that similar thickness reductions may be achievable for AC pavements designed using resilient modulus data. Resilient Modulus in Pavement Analysis Despite the widespread measurement and use of the resilient modulus, the most advanced pavement analysis tools rely on the dynamic modulus. Both of these material properties relate the magnitude of a strain response to some applied stress. In the case of the resilient modulus the loading pattern involves a haversine load pulse followed by a rest period (0.1 seconds of loading and 0.9 seconds of rest). It is often measured at three different temperatures (approximately 40, 70, and 100°F) although the test at the middle temperature (70°F) is most often used in analysis. The dynamic modulus represents the stress-strain response under continuous cyclic loading. Two protocols exist, but the one most often used in practice also covers the range from 40 to 100°F but includes multiple frequencies of loading between 10 and 0.1 Hz. The relationship between these two quantities has been an issue of interest to researchers and practitioners, with the majority of work being produced in the years between 2003 and 2010 (1- 4). Essentially this work proves that the two moduli values are related. It also shows that if one knows the dynamic modulus at the aforementioned frequencies and temperatures that they can readily calculate the resilient modulus through mathematical manipulation of linear viscoelastic stress-strain relationships. The same calculations also show that if one knows the resilient modulus they cannot directly calculate the dynamic modulus. This inability stems from the fact that dynamic modulus is a quantity with a stronger mathematical foundation, e.g., it is more fundamental. Although it is not possible to mathematically convert resilient modulus to dynamic modulus, the citations above do propose conversion methods. 5 reduction in AC thickness was determined such that an AC pavement modified with FORTA fibers has equivalent predicted performance as the same AC mixture without FORTA fibers. The following observations are made in relation to Figures 2 and 3: 1. The maximum reduction in the AC layer thickness of the FORTA fiber reinforced pavement to provide the same predicted pavement performance of conventional pavements against total rutting and fatigue cracking are 38% and 32%, respectively. 2. The maximum reduction in the AC layer thickness of the FORTA fiber reinforced pavement to provide the same predicted pavement performance of conventional pavements for both total rutting and fatigue cracking is 32%. Figure 2 Effect of thickness reduction of fiber reinforced pavement on total rutting enhancement percent. Figure 3 Effect of thickness reduction of fiber reinforced pavement on fatigue cracking enhancement percent. y = -0.0082x2 - 0.6223x + 35.634 R² = 1 -5 0 5 10 15 20 25 30 35 40 0 10 20 30 40 50 T o ta l R u tt in g E n h an ce m en t (% ) Thickness Reduction (%) y = 0.0016x3 - 0.0943x2 - 0.4369x + 59.043 R² = 1 -20 -10 0 10 20 30 40 50 60 70 0 10 20 30 40 50 F at ig u e E n h an ce m en t (% ) Thickness Reduction (%) 6 Conclusion Work by several researchers (1-4) has investigated the relationship between dynamic modulus and resilient modulus of AC pavements. Based on this work, a useful rule of thumb is that the resilient modulus is equivalent to the dynamic modulus at the same temperature and at a 5 Hz continuous loading frequency. Such a relationship means that observations regarding improvements in dynamic modulus in mixtures containing FORTA fibers are equally applicable to expected improvements in resilient modulus. Based on MEPDG design simulations which used laboratory dynamic modulus and fatigue cracking data, the maximum AC layer thickness reduction of the FORTA fiber reinforced pavement to provide the same predicted pavement performance of conventional pavements for both total rutting and fatigue cracking is 32%. Given the relationship between dynamic modulus and resilient modulus, it is expected that similar thickness reductions may be achievable for AC pavements designed using resilient modulus data. References 1. Clyne, T. R., Li, X., Marasteanu, M. O., and Skok, E. L. Dynamic and resilient modulus of Mn/DOT asphalt mixtures. (No. MN/RC-2003-09,), 2003. 2. Lacroix, A., Khandan, A.M., and Kim, Y. "Predicting the resilient modulus of asphalt concrete from the dynamic modulus." Transportation Research Record: Journal of the Transportation Research Board, 2007, pp. 132-140. 3. Lacroix, A., Kim, Y.R. and Ranjithan, S. R. "Backcalculation of dynamic modulus from resilient modulus of asphalt concrete with an artificial neural network." Transportation Research Record: Journal of the Transportation Research Board, 2008, pp. 107-113. 4. Xiao, Y. "Evaluation of engineering properties of hot mix asphalt concrete for the mechanistic-empirical pavement design." Ph.D. Dissertation, Florida State University, 2009. 5. Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures. Final Report. NCHRP, National Research Council, Washington, D. C., March 2004. 6. Kaloush, K.E., K.P. Biligiri, W.A. Zeiada, M. Rodezno, and J. Reed. “Evaluation of Fiber- Reinforced Asphalt Mixtures Using Advanced Material Characterization Tests,” Journal of Testing and Evaluation, ASTM International, Volume 38, Number 4, 2010, pp. 400-411. 7. Kaloush, K.E., K.P. Biligiri, W.A. Zeiada, C. Cary, S. Dwivedi, J. Reed, and M. Rodezno. “Evaluation of FORTA Fiber-Reinforced Asphalt Mixtures Using Advanced Material Characterization Tests – Evergreen Drive, Tempe, Arizona,” Final Report Submitted to FORTA Corporation, Grove City, PA, April 2008.