Despite the environmental and compaction benefits of warm mix asphalt (WMA), several researchers have expressed concerns over laboratory and field performances of WMA mixes. In this study, a wide range of laboratory tests, namely, dynamic modulus, creep compliance, fatigue, moisture damage, and rutting, was conducted to evaluate the performance of different types of WMA mixes. For this purpose, three WMA mixes, consisting of one mix produced using a zeolite-based WMA additive (containing water), one surface course mix, and one base course mix, the latter two produced with a chemical-based WMA additive with surfactant technology, were collected from different field projects in Texas. In addition, three hot mix asphalt (HMA) mixes with aggregate gradations similar to those of the collected WMA mixes were produced in the laboratory to compare the performance of WMA and HMA mixes. Overall, the WMA mixes yielded lower stiffness, reduced potential of low-temperature cracking, lower fatigue resistance, and a higher rutting potential compared with their HMA counterparts. However, a mixed trend of moisture-induced damage potential was observed for WMA and HMA mixes, when evaluated using retained tensile strength ratio (TSR) and stripping inflection point (SIP) obtained from the Hamburg wheel tracking (HWT) test. In other words, no correlation was found between TSR and SIP values, indicating that passing a TSR test does not guarantee better performance of a mix when tested using an HWT. The results from this study reveal that performance of a WMA mix widely depends on the technology and the type of other additives (e.g. anti-stripping agent) used. The findings of this study are expected to be useful to pavement professionals to better understand the performance of WMA mixes and to develop a database of input parameters for the Mechanistic-Empirical Pavement Design Guide

Lack of mechanistic foundation and poor correlations with field performance of conventional laboratory-based tests has accelerated the search for a mechanistic-based approach for screening of asphalt mixes for moisture-induced damages. According to recent studies, surface free energy (SFE) method can be used to mechanistically quantify bond strength and debonding of binder-aggregate system in presence of water. This study was undertaken to evaluate the effects of different additives, namely warm mix asphalt (WMA) additive (amine-derived), amine-based anti-stripping agent (ASA), polyphosphoric acid (PPA) and reclaimed asphalt pavement (RAP) on the moisture-induced damage performance of asphalt mixes through the use of laboratory-based performance tests and SFE method. For this purpose, different energy parameters were determined from SFE components of binder blends and aggregate. Asphalt mixes with different additives were produced to evaluate moisture-induced damage using indirect tensile strength (ITS) and Illinois semi-circular bend (IL-SCB) tests. A new parameter, known as fracture energy ratio (G_f ratio) obtained from IL-SCB test, was used to correlate fracture energy with moisture-induced damage potential of mixes. Also, the effect of short-term and long-term aging on the moisture-induced performance of asphalt mixes were evaluated. Furthermore, correlations between moisture-induced damage parameters from laboratory-based performance tests and SFE method were investigated.

The current study was undertaken to evaluate the effect of Polyphosphoic Acid (PPA) on rheological properties of different grades of asphalt binders containing a chemical Warm-Mix Asphalt (WMA) additive in presence and absence of a liquid Anti-Stripping Agent (ASA). Also, the effect of chemical WMA additive, PPA and ASA on rutting and moisture-induced damage potential of asphalt mixes was evaluated. Polymer-modified and non-modified asphalt binders were blended with different amounts of PPA, WMA additive, and ASA and tested in a Dynamic Shear Rheometer and a Bending Beam Rheometer. The results indicated that blending WMA additive and PPA with all tested binders increased their rutting and fatigue resistance. However, blending PPA with asphalt binders in presence of the WMA additive and ASA was found to reduce their resistance to fatigue cracking. Also, the use of WMA additive, ASA and PPA was found to reduce the effectiveness of the PPA in bumping the high-temperature Performance Grade (PG) of asphalt binder with an insignificant effect on low-temperature PG. Furthermore, conducting Hamburg wheel tracking and indirect tensile strength ratio tests on asphalt mixes containing WMA additive, PPA and ASA showed a low susceptibility to rutting with no significant indication of moisture-induced damage.