Ayman Ali

This study evaluated the storage stability and performance of composite plastic modified binders at 1-3% dosages using polyethylene grafted maleic anhydride (PE-g-MA) and reactive elastomeric terpolymer (RET) stabilizers. Thermal characterization using differential scanning calorimetry (DSC) showed melting points of 130-155°C, suitable for wet blending. Storage stability was evaluated using complex shear modulus separation index (SI) and fluorescence microscopy (FM). Both stabilizers improved stability up to 2%, but RET achieved more uniform and homogeneous plastic dispersion in asphalt binder matrix. Rheological properties were evaluated through Superpave performance grading (PG), multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS). Composite plastic alone raised the high PG by up to one grade, and RET added a further two grades, producing three grades for HDPE + PP (HP) and two for LDPE + HDPE + PP (LHP), while PE-g-MA had minimal effect on high PG. Both stabilizers maintained base-binder low PG, with RET providing greater improvement. RET significantly improved rutting by enhancing recovery and lowering Jnr, outperforming PE-g-MA. Plastic degraded fatigue performance, but stabilizers mitigated this; RET and PE-g-MA improved fatigue life by approximately 1,500% and 270%, respectively. The RET 2% binder without plastic showed the highest recovery, lowest Jnr, and longest fatigue life among modified binders, indicating RET is the principal performance determinant, while composite plastic provides recycled supplementary high-temperature stiffening within the RET-stabilized matrix. Overall, RET was more effective than PE-g-MA. Thus, composite plastic modified binders with up to 2% dosage with stabilizers can offer better storage stability and performance for sustainable pavement applications.

Pavement insulation is commonly evaluated using temperature extrema, frost depth, or freeze–thaw response; however, these metrics do not directly describe how thermal signals propagate through insulated pavement systems. This study presents a frequency-resolved field evaluation of five adjacent full-scale pavement sections: an uninsulated Control, 2-in. Extruded Polystyrene (XPS2), 4-in. XPS (XPS4), Foamed-Glass Aggregate (FGA), and Tire-Chip (TC) insulation. One year of 15-min pavement-temperature and meteorological measurements was analyzed using multiharmonic decomposition to separate seasonal and diurnal responses. Harmonic amplitude, phase lag, depth-dependent attenuation, and across-insulation transmission were quantified, while residual analysis characterized aperiodic weather-driven behavior. Moving-block bootstrap analysis was used to estimate uncertainty.,The annual harmonic remained measurable throughout the pavement depth, whereas the 24-h and 12-h components attenuated rapidly within the upper pavement. Seasonal attenuation across the evaluated insulation zone was 6.7% for the Control and increased to 40.6, 51.4, 33.2, and 36.2% for XPS2, XPS4, FGA, and TC, respectively. Corresponding seasonal delays ranged from 19.7 to 41.1 days in the insulated sections. Insulation reduced seasonal variability below the insulation while maintaining or increasing thermal variability above it, indicating thermal decoupling of the upper pavement and subgrade. The results demonstrate that amplitude attenuation and phase delay provide complementary field metrics for evaluating insulated pavement thermal performance.

This study investigates the rheological behavior and aging characteristics of plastic-modified asphalt binders incorporating two Reactive Elastomeric Terpolymer (RET) stabilizers with different melt flow indices (MFI). A comprehensive experimental program was conducted with performance-grade asphalt (PG) 58-28 as the control binder to assess the effect of RETs on the performance of plastic-modified binders. Separation index and fluorescence microscopy were used to evaluate storage stability, while rheological behavior was analyzed using black space diagrams and performance grading. Aging effects were examined using low-temperature grade, stress dissipation capacity (ΔT _c ), and Linear Amplitude Sweep testing. In addition, rutting resistance was assessed under higher stress levels by conducting the Multiple Stress Creep Recovery test. The results showed that RET stabilizers improved the storage stability of plastic-modified binders, with the higher MFI stabilizer being more effective. Black space analysis revealed the formation of elastomeric networks and morphological complexity because of RETs, with RET B (lower MFI) exhibiting higher stiffness and lower phase angles, indicating improved rutting resistance. RETs also enhanced high-temperature PG by four grades and restored low-temperature PG, mitigating the reduction caused by plastics. Although ΔT _c values degraded with plastic addition, stabilizers improved ΔT _c , indicating enhanced resistance to low-temperature cracking. Moreover, RET stabilizers enhanced fatigue life by 660%–1,200% compared with plastic-modified binders. Under extended aging, RET-modified binders showed slightly greater ΔT _c and fatigue life reductions but still outperformed other binders. The combination of 2% plastic + RET B provided superior rutting resistance, reducing nonrecoverable creep compliance by 70% and increasing recovery by 3,000%. The results emphasize the potential of RETs in developing high-performance binders.

In cold regions, the flexibility of asphalt mixtures is often insufficient to prevent low-temperature cracking caused by thermal contraction. To mitigate the resulting tensile stresses, several highway agencies considered cutting and sealing control joints at the surface layer of asphalt pavements. This process involves cutting a fixed-width joint through the top layer of pavement, then filling the joint with a sealant to prevent intrusion of moisture or incompressible materials. Although field implementations have shown promising results, issues such as premature sealant adhesion failure have been observed. This study introduces a new test, the “low temperature asphalt sealant tensile test,” which addresses the limitations of ASTM D5329 by incorporating asphalt substrates, extremely low temperatures, and a failure mechanism tailored toward thermal contraction events. A modified version of the overlay test was adopted, incorporating an asphalt substrate and joint filled with flexible sealants. This test frame was selected based on the similarities in the failure mechanism between cracking owing to thermal contractions and reflective cracking. The test temperature was reduced to as low as −40°C. Loading was applied at a fixed displacement of 0.5, 1, or 2 mm/min to evaluate the impact of loading rate. Specimens with varied joint widths and sealant types were evaluated using a servo-hydraulic testing machine. This enhanced procedure provides a more representative assessment of joint and sealant performance under thermal stress and offers insights for improving the durability of asphalt pavements in cold climates, such as reducing thermal stress accumulated at the joint by 50%.

Asphalt pavements undergo several distresses such as rutting and fatigue cracking under the influence of coupled effects of traffic and environmental loads. Use of reclaimed asphalt pavemen...

Extreme thermal expansion–contraction cycles in cold regions can cause significant thermal stresses in asphalt mixtures and result in thermal cracking. The current study focuses on evaluating the in-situ thermal cracking resistance of pavement test sections made using highly elastic asphalt binders (HEBs) under extreme cold conditions. Four pavement test sections prepared with one control binder (PG 52-28) and three HEBs were constructed in Fairbanks, Alaska. The HEB mixtures were prepared using binders modified with 7.5% styrene-butadiene-styrene polymer and two softening agents, namely hydrolene oil (7%) and corn oil (7%, and 14%), respectively. Asphalt strain gauges (ASGs) and thermocouples were installed in the hot mix asphalt (HMA) layers to monitor field-induced thermal strains from August 2024 to July 2025. Daily and seasonal temperatures and respective HMA strain variations were recorded to understand the criticality of strain amplitudes under field conditions. Results showed that HMA mix temperatures were warmer throughout the monitoring period and exhibited a nonlinear relationship with ambient air temperatures. HMA mixtures exhibited positive tensile strains and negative compressive strains during the day–night thermal expansion–contraction cycles. HEBs showed higher strain recovery capacity during both summer and winter seasons because of their enhanced flexibility by softening agents. Interestingly, HEB mixtures showed higher and lower cyclic strain variations during winter and summer seasons, respectively. HEB mixtures exhibited higher coefficient of thermal expansion and contraction (CTE and CTC) values during winter, but lower CTE and CTC values during the summer season, respectively.

This study investigates the fatigue and healing performance of asphalt mixtures incorporating nanoparticle-modified binders, using nanoclay and nanosilica. Two binders (PG 58-28 and PG 76-22) were selected to assess their effect on healing behavior. Asphalt mixtures were prepared using granite aggregates and UFGS Gradation 3, then subjected to mechanical and simulation-based evaluations. Cyclic fatigue testing was conducted using the asphalt mixture performance tester at 25°C, with a strain amplitude of 800 microstrains and a loading frequency of 10 Hz. To simulate in-service conditions, 10- and 20-minute rest periods were introduced after 25% of the specimen’s estimated fatigue life, representing early stage fatigue damage accumulation. Healing was quantified by comparing the number of cycles to failure (N _f ) before and after rest period. Dynamic modulus testing and FlexPAVE™ simulations were also performed to assess viscoelastic behavior and long-term pavement performance. Results showed that both nanoclay and nanosilica modified mixtures exhibited notable improvements in fatigue life relative to the control, with nanoclay modified mixtures achieving the highest fatigue life improvement, while nanosilica modified mixtures demonstrated consistent intermediate gains across both binder types. FlexPAVE™ simulations indicated a 37% reduction in total fatigue damage over 20 years for nanoclay-modified mixtures with rest periods. Rutting and cracking resistance also improved significantly, as observed from indirect tensile asphalt cracking test and asphalt pavement analyzer tests. The findings confirm that nanomodification, especially with nanoclay, enhances the intrinsic healing capacity, fatigue resistance, and durability of asphalt mixtures. Incorporating rest periods in design further optimizes long-term performance, offering a sustainable strategy for modern pavement systems.