Pavements in tropical regions are affected by high temperatures and ageing, and are susceptible to rutting, which reduces their resilience and durability. Hence, this study investigates the modification of bitumen with Styrene–Butadiene Rubber (SBR) at 0%, 3%, 6%, and 9% by weight. Conventional tests showed that SBR modification improved high-temperature properties up to 6%, followed by a sudden reduction at 9% modification, as evidenced by increased softening point and reduced penetration. At 6% modification, the SBR-modified bitumen would remain uniform and stable during storage. It would not affect performance upon use after storage, demonstrating its suitability as a performance-enhancing polymer for hot-climate applications. Multiple Stress Creep Recovery (MSCR) testing shows reductions in non-recoverable creep compliance and enhanced elastic recovery, making the modified bitumen. The 6% SBR modified binder showed a significantly higher Jnr diff value with a Jnr diff value of 53.42%. Similarly, the SBR-modified binders showed improved recovery, with %R 0.1 values of 14.89% to 18.45% at 64 °C and %R 3.2 values of 0.32% to 1.71%. Linear Amplitude Sweep (LAS) results showed that a 9% modification yielded the highest N_f value, but beyond 6%, the improvement was negligible. Considering cost and optimal performance, 6% SBR content modification should be considered. Glover–Rowe parameters showed that SBR-modified binders retained their elasticity and reduced the brittleness of bitumen, unlike unmodified binders, which shifted towards brittle behaviour. Pearson correlation analysis shows a strong positive cluster among fatigue life, % recovery, Fail Temperature (Unaged and Aged), G*/sin δ, softening point, elastic recovery, and rutting parameters, with correlation values exceeding 0.90 in most cases. Grey Relational Analysis (GRA) shows that a 6% SBR with a Grey Relational Grade (GRG) of 0.843 was ranked highest among all modifications. Principal Component Analysis (PCA) shows that a 6% SBR modification of the bitumen is optimal, providing a balance among rutting resistance, fatigue performance, and ageing durability. These findings highlight the potential of SBR-modified bitumen to enhance pavement performance and service life in tropical climates.

Crumb rubber-modified asphalt concrete (CMAC) has gained increasing attention as a sustainable pavement material capable of improving mechanical performance while utilizing waste tire resources. This study investigates the rutting resistance and fatigue behavior of CMAC using a combined experimental and mechanistic–empirical modeling approach. Asphalt mixtures containing 0–25% crumb rubber by binder weight were prepared and evaluated through Marshall stability and indirect tensile fatigue tests, whereas Fourier-transform infrared spectroscopy (FTIR) was used to examine binder–rubber interactions. The results indicate that crumb rubber significantly influences both the volumetric and mechanical properties of asphalt mixtures. Mixtures containing 10–15% crumb rubber exhibited optimal performances, achieving up to 36% higher Marshall stability and improved fatigue life compared with conventional asphalt mixtures. FTIR analysis revealed that rubber particle swelling and limited chemical interactions enhanced binder elasticity and improved binder–aggregate compatibility. However, excessive rubber content (≥20%) resulted in reduced stability owing to increased binder absorption and decreased effective binder film thickness. A mechanistic–empirical model incorporating viscoelastic, viscoplastic, and fatigue damage parameters successfully reproduced the experimental trends and identified the same optimal rubber content range. The findings demonstrate that CMAC with a moderate rubber content can enhance pavement durability and structural performance while promoting environmentally sustainable road construction through the reuse of waste tires.

The ever-growing need to build roads to meet the necessary transportation demands is challenging, especially for developing countries. Low-volume roads (LVRs) are usually the backbone of catalyzing economic growth in these countries. With impediments surrounding Petroleum bitumen (price fluctuations) and environmental concerns, scientists are putting their effort into finding an alternative. The presented research is an attempt to check if Natural asphalt can be used as a full or partial replacement of the Petroleum bitumen. To the best of the authors' knowledge, only limited studies have focused on characterizing and understanding the engineering properties of Natural asphalt. The available techniques do not provide reliable information to the road authorities and hence they are discouraged from using it in practice. Particularly for countries, where the Natural asphalt source is available, the overall dependence on importing the Bitumen could be substantially reduced. Empirical and experience-based design criteria may not be sufficient as the standards were never developed for such materials, hence, a scientific approach is required before bringing it into practice. In this research, Natural asphalt sourced from different locations in Nigeria was assessed. Before performing the mixture level tests using Marshall and Cantabro design methods, the rheological and fatigue properties of the extracted Natural bitumen were examined in the laboratory. In the design of the experiment, various percentages of Natural asphalt were added between 0 % and 20 % by total mix weight; implying that the remaining required fraction of binder was fulfilled by the addition of petroleum bitumen. By using a ranking system (supported by statistics), an optimal design of mixture was obtained which was used in the field (exposed to normal traffic) at 30 different sections.

The demand for alternative bitumen which could fully/partially replace Petroleum sourced bitumen for pavement construction is globally increasing. The increase in demand can be associated with several factors: depletion in crude oil resources, advances in crude oil refining processes, increased demand for highway infrastructure, and regional transportation-environmental policies. Since the production of Petroleum bitumen consumes energy and generates emissions, there is an effort to decrease harmful emissions which has inspired researchers to look for so-called "green alternatives". Natural bitumen could be considered a green alternative as it is a mixture of bitumen and mineral matter present naturally on earth, mainly if the Natural bitumen can be transported easily to the construction site. This paper reviews the state-of-the-art information on pavement construction using Natural bitumen from laboratory and field perspectives. The Physico-chemical properties, rheological properties and field behaviour of asphalts pavements containing Natural bitumen were assessed. Many road authorities would hesitate to utilise Natural bitumen for pavement applications due to a lack of available data, knowledge and a systematic research study. To the best of the authors’ knowledge, there is no comprehensive literature review article on Natural bitumen. Thus, the presented article aims to comprehensively review Natural bitumen resources and their types, Physico-chemical properties, application in pavement constructions, and reported field performances. At the end of the paper, future research challenges, future recommendations and a methodological framework is proposed.