This paper investigates the influence of fuel-resistant polymer on the consistency and performance properties of asphalt binder and hot mix asphalt (HMA) mixtures. The study uses wearing course gradation (nominal maximum size of 19 mm), penetration grade 60/70 bitumen, and Elvaloy reactive elastomeric terpolymers (RET) 4170 as a fuel-resistant polymer. Laboratory tests conducted on unmodified and modified (1–4% Elvaloy) mixtures include an indirect tensile (IDT) strength test and a resilient modulus ($M_R$ ) test for evaluating cracking potential and stiffness parameters, respectively; a Hamburg wheel tracker (HWT) test for quantifying the rut propensity; and a solubility test to determine the fuel-resistance capacity. The two-level factorial design of the experiment is conducted on the rheological properties of the binder including elastic recovery/complex modulus and creep stiffness values, which suggest that 1% polymer-modified binder (PMB) is least susceptible to high-temperature and low-temperature variations. Performance evaluation reveals that 1% PMB is an optimal proportion of Elvaloy in asphalt concrete mixtures, yielding maximum $M_R$ values (both before and after conditioning in fuel), the lowest rut susceptibility, and high fuel resistance. This research is useful for public aviation/highway agencies and private contractors to minimize the deterioration caused by fuel slippage and to control foreign object debris damage to aircraft.

The use of waste, recycled, and modified materials is increasingly popular in roadway construction for sustainability and pavement longevity. This research examines the combination of steel slag (SS) and low-density polyethylene (LDPE), commonly used in plastic bags and steel manufacturing by-products, to mitigate environmental pollution. LDPE was tested as a binder modifier in two bitumen grades, 60–70 and 80–100, at concentrations of 3%, 5%, and 7% by weight. SS was used as a replacement for coarse aggregate. The physical properties of both modified and unmodified bitumen grades and SS were analyzed before creating and testing hot-mix asphalt (HMA) samples. The dynamic modulus of these samples was measured at temperatures of 4.4 °C, 21.1 °C, 37.8 °C, and 54.4 °C with frequencies of 0.1 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, and 25 Hz. Master curves were developed, and the dynamic modulus data underwent design of experiment (DOE) and computational intelligence (CI) analyses. Using KENPAVE, a mechanistic–empirical tool, the analysis assessed the design life and enhancements in damage ratio for each modifier and grade. The results showed that adding LDPE increases the softening point and penetration grade but decreases ductility due to increased bitumen stiffness, leading to premature fatigue failure at higher LDPE levels. Both 3% LDPE and 3% SS-modified LDPE improved Marshall Stability and dynamic modulus across all temperature and frequency ranges. Specifically, 3% LDPE enhanced stability by 13–16% and 3% SS-LDPE by 30–32%. The KENPAVE results for 3% LDPE showed a design life improvement of 19–25% and a damage ratio reduction of 15–18%. In comparison, 3% SS-LDPE demonstrated a design life improvement of 50–60% and a damage ratio reduction of 25–35%. Overall, this study concludes that 3% LDPE- and 3% SS-LDPE-modified HMA in both bitumen grades 60–70 and 80–100 provide optimal results for improving pavement performance.

The performance of a pavement mainly depends on the quality of the subgrade layer. Expansive soils (ES) are extensively found worldwide including Pakistan. The inadequate strength and swelling behaviour of these soils are the main problems in any road construction project. Several researchers in the last decades have attempted to improve expansive soil utilizing various materials such as lime, brick kiln dust and fly ash. The purpose of this research was to evaluate the effect of lime on the engineering properties of the ES of a highway subgrade in the Sialkot region of Pakistan. The influence of different lime dosages (0%, 2%, 4% and 6%) at curing ages (1, 7, 14 and 28 days) has been examined by pH tests, plasticity tests, compaction tests, unconfined compressive strength (UCS), free swell index, and California Bearing Ratios (CBR). A field CBR and plate load test (PLT) on the natural soil and optimum lime-treated soil with various curing periods have been carried out for applicability as subgrade material. The test findings demonstrated that higher lime dosages increased the strength and ultimate bearing capacity (𝑞𝑢𝑙𝑡) of improved ES and at the same time decreased the free swelling index (FSI), optimum moisture content (OMC), maximum dry density (MDD) and permanent deformation of the subgrade soil. The UCS values of soil treated with 2%, 4% and 6% lime increased almost by 324%, 523%, and 249% for unsoaked samples and 285%, 351% and 231% for soaked samples respectively as compared to the plain soil at 28 days curing period. The laboratory CBR values significantly increased 2.35-8.50 times and field CBR improved 5.6 times as compared to the plain soil. The 𝑞𝑢𝑙𝑡 of lime-treated soil increased by 162% as compared to the plain soil and permanent deformation reduced from 33 mm to 2 mm after 28 days. Furthermore, equations were developed to estimate the best fit for the prediction of various geotechnical parameters and coefficient of determination (R2 ) values for all equations were found higher than 0.90. From the results, it has been concluded that adding the optimum lime content of 4% by weight satisfies the requirement for the subgrade construction of highways and the developed expressions can provide a scientific basis for estimating the geotechnical parameters.

This study examined the synergistic effects of Styrene–Butadiene–Styrene (SBS) polymer and nanoclay on asphalt concrete mixture performance through a systematic experimental program using 4.5% SBS with varying nanoclay concentrations (0–8%). Performance evaluation included Indirect Tensile Strength (ITS), Indirect Tensile Resilient Modulus (E_RI), and Hamburg Wheel Tracking Tests (HWTT), along with novel quantitative analysis of visco-plastic and moisture resistance indices. Results demonstrated that 4.5% SBS with 6% nanoclay (4.5S6N) yielded optimal performance, achieving 38% increase in dry ITS, 68% improvement in wet ITS, and enhanced moisture resistance with Tensile strength Ratio (TSR) improving from 79.53% to 97.14%. The E_RI value increased by 39%, while rutting resistance improved by 39.3%. At this optimal concentration, nanoclay’s uniform dispersion and layered silicate structure created an effective reinforcement network, enhancing stress distribution and interfacial bonding with the SBS polymer network and asphalt components. However, exceeding 6% nanoclay content led to performance deterioration due to particle agglomeration. These findings demonstrate that optimized SBS–nanoclay modification effectively addresses both mechanical and moisture-related performance requirements for modern pavement applications.