Crumb rubber modifier (CRM) is considered one of the most commonly used modifiers that enhances the rheological properties of asphalt binders. Optimizing the interaction process between CRM and asphalt binder to enhance the asphalt binder’s elasticity without additional additives is the main purpose of the article. Rheological properties were measured in this article for neat asphalt and crumb rubber modified asphalt (CRMA) binders. Two sets of interactions were selected. In the first interaction set, one interaction temperature (190°C), one interaction speed (3,000 rpm), and different interaction times (0.5, 1, 2, 4, and 8 h) were used. The used CRM percentage was 10 % by weight of the neat asphalt binder. Two sources of asphalt binder, one source and different percentages of CRM, one interaction temperature (190°C), one interaction speed (3,000 rpm), and different interaction times were selected for the second interaction set. This set was designated to confirm the rheological properties obtained for the first set. Thermogravimetric analysis (TGA) was performed on CRM particles before and after their interaction with asphalt binder after different interaction times. The CRMA binders that interacted for the entire 8-h interaction times had significantly enhanced properties, especially the elasticity, as compared to the neat asphalt binder. The 8-h interaction time showed the highest CRM dissolution percentage by dissolution and TGA testing. At this interaction time, more CRM components were released into the asphalt binder liquid phase, which was detected by observing Fourier-transform infrared peaks at 966 cm−1 for polypropylene and 699 cm−1 for polystyrene.

This study seeks to find the influence of replacing a portion of the asphalt–rubber binder with the bio-based material “guayule resin.” This replacement could be beneficial in terms of sustainability, economics, and environmental concerns related to the asphalt industry. Nine asphalt–rubber–guayule binders were investigated to find their rheological properties. Consecutively, the study proceeded with five selected binders being compared to the original asphalt (PG64-22). Investigations underwent whole matrices (crumb rubber modifier (CRM) residue included) and liquid phases (CRM residue extracted). Additionally, these properties were partially sought for their corresponding asphalt–rubber binders to compare and judge the contribution of the guayule resin. Likewise, a thermo-gravimetric analysis was done for the guayule resin to recognize its moisture and composition complexity. Such an analysis was also done for the as-received CRM and some extracted CRMs to determine the release and residue of rubber components. Outcomes showed that the guayule resin has the potential to compensate the performance required against the original asphalt at elevated temperatures while greatly decreasing the asphalt cement proportion. For instance, a blend of 62.5% asphalt, 12.5% CRM, and 25% guayule resin provided better performance than that of the original asphalt.

Open-graded friction course (OGFC) is a thin asphalt mixture surface layer designed primarily to improve the functionality of a roadway. It is designed with a special aggregate structure with high air voids and stone-on-stone contact that accelerates rainwater drainage. It has many advantages, such as reducing hydroplaning, splashing, and spray, and enhancing roadway visibility and skid resistance under wet weather conditions. However, these mixtures exhibit premature failures and moisture damage that limit their usage in pavement construction. Further, the current specifications might inaccurately reflect field conditions. Therefore, this study was aimed at evaluating and comparing the effect of various asphalt binder types on the performance of OGFC mixtures under different aging and moisture conditions. Three types of asphalt binder were utilized: conventional styrene-butadiene-styrene asphalt binder performance grading (PG) 76-22M and diluted epoxy asphalt (EA) binder with two different dosages. A suite of physical and mechanical tests was conducted to evaluate OGFC mixtures, namely, draindown, permeability, Hamburg wheel tracking (HWT) test for rutting and moisture susceptibility, Cantabro abrasion loss test for durability, semi-circular beam (SCB) for fracture resistance, and indirect tensile strength (ITS) test for tensile strength and moisture susceptibility. Results indicated that EA mixtures exhibited improved draindown results, compared with 76M mixture. Further, the developed cross-linked network associated with EA binder might explain the improved rutting and abrasion loss resistance. EA mixtures showed significantly better moisture resistance, as measured by HWT, ITS, and SCB tests. Cost-effectiveness ratio results showed higher effectiveness for EA mixtures than conventional 76M mixture.

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of $0.65–0.69\mathrm{kJ}/{\mathrm{m}}^2$ compared to $0.46\mathrm{kJ}/{\mathrm{m}}^2$ for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, $400\mathrm{J}/{\mathrm{m}}^2$ ). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered $591\mathrm{J}/{\mathrm{m}}^2$ at its performance grade low temperature ($-16°\mathrm{C}$ ) and $409\mathrm{J}/{\mathrm{m}}^2$ at $-22°\mathrm{C}$ compared to $429\mathrm{J}/{\mathrm{m}}^2$ for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.