The price of asphalt binder has increased dramatically due to the increase in oil prices and the increase in traffic volumes occurring worldwide. This situation has prompted calls for greater viscosity, lower‐cost asphalt for pavement construction, and the development of alternative materials that have a good rheological effect, are less expensive, and have a reduced negative impact on human health and the environment. The application of fibers in asphalt mixes has been studied over the past few decades to improve pavement performance around the world. This study was conducted on three types of asphalt binders that were modified with two types of fibers: brown recycled wool fiber (BRWF), available locally in Iraq, and China polyester fiber (CPF), which is considered as waste, to produce fiber‐modified asphalt binders. The samples were conducted using traditional physical testing (penetration, softening point, and rotational viscosity tests) as well as the Dynamic Shear Rheometer (DSR) test. In comparison to the original asphalt binders, the fiber‐enhanced asphalt binders had greater softening point, viscosity, and complex modulus but decreased penetration. The tests revealed that using both kinds of fibers as modifiers for asphalt binders improves their high‐temperature performance by increasing the grade of the control binders (PG). This increase in asphalt binder stiffness is anticipated to enhance pavement rutting resistance. Consequently, these fibers can be used as additives for asphalt binders and asphalt mixtures to enhance their performance.

Enhancing the performance of asphalt binders is essential for ensuring the long-term durability and serviceability of asphalt mixtures, as it can help reduce the frequency of maintenance and repair work, ultimately leading to the development of more sustainable transportation infrastructure. To achieve this goal, this study investigates the effects of incorporating recycled polymer materials, including reclaimed polyvinyl chloride (PVC) and polystyrene (PS) derived from household waste, into hot mix asphalt. The experimental work involved subjecting the polymer-modified asphalt binders to a range of physical tests, such as softening point, penetration, ductility, indirect tensile strength, Marshall stability, and moisture susceptibility, and the results showed that the addition of recycled polymers, with an optimal content of 4%, led to lower penetration values and higher softening point temperatures, indicating improved resistance to temperature changes. Further analysis of the asphalt mixture performance revealed several beneficial outcomes, including a decrease in flow, a boost in the asphalt mixture's resistance to moisture-induced damage, and an improvement in Marshall stability and indirect tensile strength, with the inclusion of 4% recycled polymers yielding increases in Marshall stability of 43.7% and 37.4% for PVC and PS-modified mixes, respectively, and increments in indirect tensile strength of 32.2% and 29.7% for the same mixes. The study concludes that the use of recycled polymers can effectively enhance the performance and durability of asphalt mixtures, contributing to the development of more sustainable asphalt pavement construction practices by utilizing locally available or reused materials, which could lead to the increased knowledge and application of stronger and more weather-resistant asphalt mixes, ultimately promoting the advancement of sustainable transportation infrastructure.

The usage of polymer-modified asphalt binders has increased as a result of the significant increase in the number of conventional cars operating on Iraqi roads in recent years. This has resulted in increased strains being placed on pavement structures and materials. Global exploration has focused on the development of stabilizing Stone Mastic Asphalt mixtures for improved pavement behavior. Numerous effective efforts were made to stabilize stone mastic asphalt mixes with polymers and fibers. Iraq produces a considerable amount of waste polymer materials each year. Usually, they are sent to landfills for disposal. These wastes are dumped, occupying a sizable portion of landfill space and creating various serious environmental issues. The study focuses on how waste polymer additions, such as recycled plastic bottles, shopping boxes, and tire crumb rubber, affect the mechanical performance and durability of stone mastic asphalt mixtures. The mechanical performance attributes were assessed. It is evident from the findings that the drain-down amounts were within the permissible requirement range. The findings also showed that the indirect tensile strength, Marshall Stability, moisture damage resistance, and resistance for permanent deformation of stone mastic asphalt mixtures have all increased as a result of the use of waste polymer components. The recycled polymer-modified mixes are the combinations that are most resistant to rutting, according to the results of the repeated load axial creep tests. Iraq may have new options to employ the significant volumes of recycled polymers that are becoming accessible as a result of recycling waste polymers.

For a long time, bitumen has been utilized as the essential material for asphalt pavement construction. The factors of increasing axle loads, increasing traffic movement, critical climate conditions and many forms failures in construction have steered many researchers to seek some methods to enhance the asphalt binder properties. Even though various types of modifiers have been utilized in strengthening asphalt concrete, fibers have attracted the most attention due to their high and desirable characteristics. It is realized that the good distribution of the modifier in asphalt binder can generate a strong network in the interior structure of the blend, causing bitumen mastic to be more coherent. In this study, a laboratory investigation of the rheological and physical properties of various grades of bitumen modified by two types of fibers was conducted. Three grades of asphalt were used in this study (60-70 penetration grade, 80-100 penetration grade and PG-76 grade) with two types of fibers with different percentages- Cellulose oil palm fiber (COPF) (0.15, 0.3, 0.45, 0.6, and 0.75%) by weight of asphalt and carbon fiber (0.75, 1.25, 1.75, 2.25, and 2.75%) by weight of asphalt. The results showed enhancement in physical performance of the modified bitumen in terms of the decrease in penetration values, as well as a rise in the softening point and viscosity values. The fibers’ modified asphalt binders showed improved rheological properties and can raise the grade of asphalt depending on the base asphalt type.

For stone mastic asphalt (SMA) mixtures, the aggregate gradation is the significant requirement to achieve the best structural design. In this research, an attempt to evaluate the effect of nominal maximum aggregate size (NMAS) and gradation on SMA volumetric and mechanical properties. Samples for each mixture were designed and fabricated according to NAPA specifications. A total of 9 SMA mixtures with three NMASs, each with three different aggregate gradations, one asphalt binder (styrene butadiene styrene SBS) modified binder were studied. Volumetric analysis of specimens revealed that the voids in the mineral aggregate (VMA), and voids filled with asphalt (VFA) rise with a reduction in NMAS. SMA samples with higher NMAS have lower optimum asphalt than those of lower NMAS. From the laboratory study, SMA mixes fabricated utilizing the upper limit of gradation showed the highest mechanical properties in terms of Marshall Stability and indirect tensile strength. It was recorded also that the SMA mixtures with larger NMAS had higher ITS and Marshall stability contrasted to the others. This improvement could be because of the larger portion of coarse aggregate in the SMA mixture.