When exposed to sun radiation and heat, asphalt binders age, resulting in reduced flexibility, cracking, and pavement failure. Given the increasing demands of traffic, environmental concerns, and resource scarcity, highway agencies and researchers are actively seeking solutions that meet performance requirements and demonstrate awareness of using non-renewable resources. Epoxy asphalt (EA) promotes sustainability concepts due to its production at significantly lower mixing and compaction temperatures, enhanced durability, improved serviceability, reduced maintenance needs, and successful recycling and reuse in hot asphalt mixtures. Crumb rubber, a widely recognized recycled waste tire material, is considered a viable option for promoting sustainability and enhancing asphalt binder properties. This study aims to enhance the durability and long-term performance of asphalt binders by utilizing sustainable materials. Six types of asphalt binders were employed: PG 67-22 base asphalt binder; styrene–butadiene–styrene (SBS)-modified PG 76-22 and PG 88-22H (3.5% and 7.0% dosage rates, respectively); a hybrid PG 76-22CS-modified asphalt binder prepared with SBS and crumb rubber modifiers; and 25EAB and 50EAB epoxy-modified asphalt binders prepared at 25 and 50% dosage rates, respectively. Results indicate that the sustainable asphalt binders PG 76-22CS, 25EAB, and 50EAB demonstrated comparable or superior performance compared to SBS-modified asphalt binders, as measured by rutting and fatigue factors. Additionally, epoxy asphalt binders had better anti-aging and cracking resistance, as shown by the outcomes of Fourier-transform infrared spectroscopy and linear amplitude sweep tests, respectively. This study contributes valuable insights into the potential of sustainable materials to enhance the overall performance and resilience of asphalt binders.

Moisture damage is a common distress in asphalt pavements caused by infiltrated moisture, which degrades mixture strength and affects pavement durability. Loaded wheel tracking (LWT) and modified Lottman (ML) tests are the two commonly used mechanical tests for assessing the moisture susceptibility of asphalt mixtures, but they have been reported to show limitations in consistently ascertaining the moisture sensitivity of different asphalt mixtures under field conditions. This study evaluated the effectiveness of different laboratory mechanical tests (LWT, ML, and semi-circular bend [SCB]) in ascertaining moisture sensitivity of asphalt mixtures. LWT, ML, and SCB tests were conducted on asphalt mixtures prepared with two asphalt binders (an unmodified PG 67-22 and a styrene-butadiene-styrene polymer-modified PG 70-22) and three aggregate types (limestone, crushed gravel, and semi-crushed gravel). Before testing, asphalt binder and mixture samples were exposed to five moisture conditioning levels: (1) unconditioned (dry), (2) single freeze-thaw cycle, (3) triple freeze-thaw cycle, (4) moisture induced stress tester (MiST) 3,500 cycles, and (5) MiST 7,000 cycles. A multiple stress creep recovery test was conducted on asphalt binders subjected to the five moisture conditioning levels. Results showed that the stress sensitivity of asphalt binders decreased after freeze-thaw and MiST conditioning. LWT rut depth and a new parameter which was developed as part of the study, SCB J _d ratio, were found to capture the progressive moisture damage in asphalt mixtures associated with different moisture conditioning levels. Mixtures containing PG 70-22 asphalt binder exhibited better moisture damage resistance compared with mixtures containing PG 67-22 asphalt binder.

The coefficient of thermal contraction or expansion (CTE) of asphalt mixtures is a property that describes how asphalt mixtures respond to thermal loading during cooling or heating. The CTE is an important mixture property used as an input parameter in the thermal cracking model of the AASHTO Mechanistic Empirical Pavement Design Guide software. CTE measurement has proven quite a challenging task; however, many researchers have developed various methods for measurement using linear variable differential transducers (LDVTs), which have proven robust and suitable for routine tests. In this paper, a laboratory test method was devised using LVDTs to measure the CTE and determine the asphalt mixture properties affecting the CTE. The mixture properties investigated in this study included binder grade, binder content, the presence of recycled asphalt pavement (RAP) and recycled asphalt shingles (RASs), compaction effort, aggregate CTE, and size and aging. Mixture properties such as binder grade, binder content, aging, and the inclusion of recycled materials (RAP and RAS) resulted in a significant change in the CTE and the glass transition temperature ($T_g$ ) of mixtures.