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.

Despite significant economic and environmental benefits, performance of warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP) remains a matter of concern. Among the current WMA technologies, the plant foaming technique (called “foamed WMA” in this study) has gained the most attention, since it eliminates the need for chemical additives. In the present study, the laboratory performance, namely rutting and moisture-induced damage potential of foamed WMA containing RAP were evaluated and compared with those of similar hot mix asphalt (HMA) containing identical amount of RAP. Dynamic modulus, Hamburg wheel tracking (HWT) and flow number tests were performed to assess the rutting resistance of the mixes. Also, stripping inflection point from HWT tests and tensile strength ratio after AASHTO T 283 and moisture induced sensitivity test (MIST) conditioning were used to evaluate the moisture-induced damage of asphalt mixes. It was found that MIST conditioning effectively simulates the moisture-induced damage and can capture the propensity of asphalt mixes to moisture damage more distinctly compared to AASHTO T 283 method due to application of cyclic loadings. The foamed WMA was found to exhibit higher rutting and moisture-induced damage potential due to lower mixing and compaction temperatures compared to HMA. However, the increase in RAP content was found to reduce rutting and moisture-induced damage potential for WMA. Therefore, the lower stiffness of foamed WMA may be compensated with the addition of stiffer binder from RAP.

In this study, the mix design volumetrics and cracking potential of foamed Warm Mix Asphalt (WMA) containing various amounts of Reclaimed Asphalt Pavement (RAP) were evaluated. It was found that the increased coating ability of the foamed WMA binder counteracted the lowering of mixing and compaction temperatures for WMA. Therefore, both control HMA and foamed WMA exhibited similar mix design volumetrics up to certain lower temperatures. However, further reductions in the mixing and compaction temperatures for foamed WMA were found to exhibit improper mixing between aggregates and foamed binder. Despite foamed WMA exhibiting similar volumetric properties as HMA up to certain lower temperature, their fatigue cracking performance was found to be significantly different. The foamed WMA was found to exhibit higher cracking resistance compared to HMA in Louisiana Semi-Circular Bending (SCB) and Illinois Flexibility Index Test (I-FIT) tests. A similar trend in the cracking resistance was observed for coarser mixes in the Abrasion Loss Test (commonly known as Cantabro test). However, the Cantabro test could not screen finer mixes for their cracking resistance as it lacks a mechanistic basis. Finally, the foamed WMA technology was found to increase the cracking resistance of asphalt mixes. The higher RAP content in the foamed WMA, on the contrary was found to lower the cracking resistance of asphalt mixes due to incorporation of aged and stiffer binder from RAP.

In recent years, use of postconsumer recycled (PCR) plastics in asphalt mixes has been gaining popularity owing to increased environmental awareness, and the need to promote sustainability and conserve natural resources. When using the dry process, incorporation of PCR plastic in asphalt mixes poses several challenges, including mixing, sample preparation, and testing. Use of balanced mix design (BMD) for asphalt mixes containing PCR plastic poses additional challenges that have not been adequately covered in previous studies. To this end, changes in the volumetric properties and performance of PCR plastic-modified asphalt mixes were investigated in this study. For this purpose, an asphalt mix having a nominal maximum aggregate size (NMAS) of 9.5 mm and PG 64-22 binder was designed using the BMD approach. Three different percentages (0.25%, 0.5%, and 1% by weight of aggregate) and two different PCR plastics, namely low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) were incorporated in the mix using the dry process. Volumetric properties, namely maximum theoretical specific gravity, bulk specific gravity, voids in mineral aggregate, voids filled with asphalt, air void contents, and densities were determined for both control- (0% plastic) and modified mixes. Also, indirect tensile strength, indirect tensile asphalt cracking test, and Hamburg Wheel Tracking tests were performed to assess the performance of these mixes. A comparison of performance for both plastic type and amount and issues related to the incorporation of PCR plastic using the dry process are discussed in this paper.