This research study aimed to assess the influence of different particle sizes of crumb rubber modifier on phase separation when mixed with virgin asphalt binder (PG 64-22). Both Superpave and multiple stress creep recovery (MSCR) tests were conducted to determine the optimal particle size. Three sizes of crumb-rubber particles (≤0.5 mm, ≤1 mm, and 1–2 mm) were individually incorporated into the binder at a weight proportion of 10%. The findings revealed that an increase in particle size resulted in higher viscosity, which reduced workability. However, the use of particles with a size of ≤0.5 mm effectively decreased viscosity. Furthermore, larger particle sizes enhanced resistance to rutting and improved the lifespan of the pavement. Multiple shear creep recovery (MSCR) tests confirmed that larger crumb-rubber particles exhibited a higher load-bearing capacity. Additionally, phase separation studies demonstrated that larger particle sizes were associated with increased phase separation. Notably, particles with a size of ≤0.5 mm performed exceptionally well in reducing phase separation across all combinations. In conclusion, crumb-rubber particles with a size of ≤0.5 mm were identified as the most effective in minimizing phase separation when blended with virgin asphalt binder. These findings provide solid scientific evidence related to the effects of crumb-rubber particles on the storage stability of rubberized asphalt binder and have significant implications for future research in this field.

The study presents an experimental evaluation to improve the resistivity of binders with “Styrene-Butadiene-Styrene” (SBS) and “Processed oil” by studying the physical properties, rheology, and cracking. For this experiment, PG 64-22 was mixed with SBS at different percentages of 5%, 10%, and 15% by weight of the original binder with two processed oil contents of 6% and 12% by weight of the binder. Laboratory tests have been conducted at various high, medium, and low temperature ranges to evaluate their properties. The processed oil polymer modified asphalt (PMA) binder is artificially aged in both the short and long-term using a Rolling Thin Film Oven (RTFO) and a Pressure Aging Vessel (PAV). The Superpave testing method was performed on modified binders using a Rotational Viscometer (RV), Dynamic Shear Rheometer (DSR), and Bending Beam Rheometer (BBR). The results of this study illustrate (1) The addition of SBS leads to higher viscosity, but the co-modification of asphalt binder with the processed oil shows a significant modulation of the viscosity value. (2) In addition, processed oil reduced the resistance to rutting, but the addition of SBS significantly improved the rutting resistance of the asphalt binder. (3) The addition of SBS and processed oil improved the value of G sin δ, notably. (4) According to BBR, it has been shown that the addition of SBS in addition to the processed oil improves the stiffness values of modified asphalt binders.

Crumb rubber modifier (CRM) binders easily suffer from instability at high temperatures, with many suggestions being developed to evaluate their storage stability. However, much uncertainty around CRM binders still exists regarding the relationship between mixing methods and experiments in order to calculate the separation index. In this study, a laboratory investigation into how CRM binders behave regarding storage stability using different mixing methods and experiments was conducted. The CRM asphalt binder in this study was prepared through a wet mixing process with the addition of 5% and 10% crumb rubber modifier (by weight) at 200 °C. The three main modification methods were method A: high-shear mixing (8000 rpm) for 2 h, method B: low mixing (300 rpm) for 8 h, and method C: high-shear mixing (8000 rpm) for 2 h + low mixing (300 rpm) for 6 h. In addition, the effect of separation index (SI) on storage stability was assessed, measuring viscosity, G*/sin δ, and percentage recovery. In general, the results of this study revealed that method C appeared to have the most prominent effect on decreasing the difference between the values of the top and bottom parts; the results for 5% CRM using method C showed that there were no differences among the values for the top, middle, and bottom parts; from the MSCR test, method C was effective in decreasing the difference between the values of the top and bottom parts. It was observed that method C improved storage stability. However, the results for percentage recovery were relatively higher than the separation index when using rotational viscosity and G*/sin δ.

The aim of this study is to analyze the phase separation that occurs between treated and untreated rubber crumb particles produced by wet processes in the laboratory. The percentage of replacement used for both the treated and untreated crumb rubber-modified asphalt (CRMA) was 5%, 10%, 15%, and 20%. Tests to evaluate binder properties were performed using a rotational viscometer and a DSR, and the following properties were determined—viscosity, G*/sinδ, % recovery, and J_nr. The phase separation study was analyzed using the viscosity and G*/sinδ results. In general, the results of the study show the following. (1) The treated CRMA binders had higher viscosity values than untreated CRMA binders, although some values could not be measured due to the high viscosity values. (2) The G*/sinδ, % recovery and J_nr results also had a similar trend with viscosity results. (3) The viscosity and G*/sinδ phase separation values demonstrate that treated CRMA binders perform better than untreated CRMA binders. (4) Different experimental methods have shown variations in the calculated SI value; hence, a more improved approach should be explored to accurately assess the storage stability of asphalt binders containing various additives.

Modified asphalt binders are still considered important in asphalt pavement. However, the comprehensive use of various modifiers is limited due to storage stability issues. Moreover, there is a scarcity of detailed analyses regarding the degree of separation for asphalt binders among each method despite the utilization of various methods to assess the storage stability of binders. Therefore, a comprehensive analysis was conducted to assess the storage stability of asphalt binder modified with a crumb rubber modifier (CRM) and styrene–isoprene–styrene (SIS), utilizing five evaluation factors following the ASTM D7173 guidelines based on four mixing methods (A: high-shear mixing method, B: low-speed agitating method, C: high-shear mixing method + low mixing method, D: low-speed agitating method + low mixing method). To produce the modified asphalt binder, the proportions of the CRM were 5% and 10% for each binder, and 10% SIS was added to all binders. The results in this study convey that (1) the addition of the modifier led to an increase in G*/sin δ with different mixing methods, but using mixing methods (C and D) for a relatively long time resulted in a lower G*/sin δ, indicating suboptimal performance; (2) through the multiple stress creep recovery (MSCR), rheological properties of J_nr and % rec exhibited trends similar to G*/sin δ evaluation, highlighting an improved elastic recovery with a higher modifier content; (3) storage stability assessment revealed consistent trends in high-shear mixing groups (A and C), while low-speed mixing groups (B and D) exhibited an elevated separation index (SI), suggesting a sensitivity to modification conditions; (4) evaluation using the MSCR method indicated that % rec with a 3.2 kPa load is effective for the sensitive assessment of binder storage stability and J_nr showed a limited sensitivity across varying loads, advocating for % rec for precise evaluation; and (5) despite permitting various tests, achieving consistent results remains challenging. Future research should explore diverse modifiers and optimal evaluation methods to enhance knowledge of binder behavior and separation dynamics.

This study delves into the transformative effects of Trinidad Lake Asphalt (TLA) on asphalt binders, revealing significant improvements in various performance metrics. Our findings indicate that TLA substantially increases binder viscosity and enhances rutting resistance, as evidenced by elevated G*/sin δ values in both original and RTFO-aged states. TLA-modified binders demonstrate superior rheological properties, including improved Jnr and percentage recovery, indicating enhanced resistance to permanent deformation and reduced fatigue cracking. However, an increase in TLA content correlates with higher G*·sin δ values, suggesting a trade-off with fatigue resistance and a higher susceptibility to cracking. Additionally, while TLA initially improves binder flexibility at low temperatures, excessive content can increase stiffness, adversely affecting stress relaxation properties. Notably, TLA enhances storage stability, ensuring minimal phase separation and excellent homogeneity. These insights underscore the need for the precise control of TLA content to optimize pavement durability. Future research should focus on fine-tuning TLA incorporation with additives like crumb rubber to maximize the structural integrity and longevity of asphalt pavements.