Analyses of Laboratory and Accelerated Pavement Testing Data for Warm-Mix Asphalt Using California Mechanistic-Empirical Design Method

As part of the study to evaluate warm-mix asphalt performance for use in California, an extensive testing program has been conducted at University of California Pavement Research Center (UCPRC) on various warm-mix asphalt technologies along with their control mix. The program includes laboratory, field and accelerated pavement testing. The data generated provide all the necessary inputs for running the California Mechanistic-Empirical Design, which has been implemented in a software called CalME. This paper presents analysis of all related data and CalME simulations of various accelerated pavement testing sections on several warm-mix asphalt technologies and their control. CalME was found to provide simulation results that almost perfectly match the shape of the rut accumulation curves during accelerated pavement tests. CalME also predicted no fatigue cracking which matches the observation as well. CalME was then used to evaluate the effect of unbound layer stiffness on rutting performance and it was concluded that the effect was minor and did not affect general conclusion drawn from the accelerated pavement testing results. Introduction The research presented in this paper is part of Partnered Pavement Research Center Strategic Plan Element 4.18 (PPRC SPE 4.18), titled “Warm-Mix Asphalt Study,” undertaken for the California Department of Transportation (Caltrans) by the University of California Pavement Research Center (UCPRC). The objective of this project is to determine whether and how warm-mix asphalt technologies influence mix production processes, construction procedures, and the short-, medium-, and/or long-term performance of hot-mix asphalt. Specifically, this research is focused on various warmmix technologies available in 2007 that use additives intended to reduce the production and construction temperatures of asphalt concrete. UCPRC developed a detailed work plan for Heavy Vehicle Simulator (HVS) and laboratory testing in September 2007. Following the work plan, a test track was constructed at the Graniterock A.R. Wilson quarry near Aromas, California with four test cells: 1. Control Cell: conventional dense graded hot mix asphalt (HMA). 2. Advera Cell: HMA mix with Advera WMA additive. 3. Evotherm Cell: HMA mix with Evotherm DAT additive. 4. Sasobit Cell: HMA mix with Sasobit additive. In Phase 1 of the study, HVS tests were conducted in each of the four cells to evaluate early rutting potential at elevated temperatures for WMAs. Laboratory tests were carried out on specimens taken from the test track. The results of the research can be found in the project report [1]. In a separate study, UCPRC is developing a mechanistic-empirical (M-E) simulation program called CalME for Caltrans. CalME is a generic program for predicting rutting and cracking performance of new flexible pavements and asphalt overlays. It takes into account the effect of different material, structure, environment and traffic. The models have been calibrated using HVS and WesTrack test results. For more information on CalME, see for example [2-3]. This paper presents analysis of laboratory and HVS test data under the CalME framework. Specifically, laboratory test data were used to develop model parameters for used in CalME. Then CalME is run to predict pavement rutting and fatigue cracking performance which is then compared with HVS test results. The objective of this paper is to validate CalME with data that was not used as part of the calibration. Data Collection A number of tests were conducted to collect necessary data during the project such as beam bending frequency sweep tests to determine flexural stiffness master curve, bean bending fatigue tests to determine laboratory fatigue performance, and repeated simple shear test at constant height (RSST-CH) to determine permanent deformation. Some of the data were used to develop inputs for running CalME. Laboratory Testing Laboratory testing was conducted on specimens taken from the test track. These are referred to as field-mixed field-compacted (FMFC) specimens. Samples were taken in the form of slabs 500 mm by 500 mm (20 in.) sawn from an area 20 m by 0.5 m (66 ft by 1.6 ft) along the edge of each cell in the test track as shown in Figure 1. Slabs were sawn to the bottom of the asphalt concrete layers, extracted, stored on pallets, and then transported to the UCPRC Richmond Field Station laboratory. A standard set (see Table 1) of laboratory tests were conducted for each of the four mixes.