The environmental concerns of global warming and energy consumption are among the most severe issues and challenges facing human beings worldwide. Due to the relatively higher predicted temperatures (150–180 °C), the latest research on pavement energy consumption and carbon dioxide (CO₂) emission assessment mentioned contributing to higher environmental burdens such as air pollution and global warming. However, warm-mix asphalt (WMA) was introduced by pavement researchers and the road construction industry instead of hot-mix asphalt (HMA) to reduce these environmental problems. This study aims to provide a comparative overview of WMA and HMA from environmental and economic perspectives in order to highlight the challenges, motivations, and research gaps in using WMA technology compared to HMA. It was discovered that the lower production temperature of WMA could significantly reduce the emissions of gases and fumes and thus reduce global warming. The lower production temperature also provides a healthy work environment and reduces exposure to fumes. Replacing HMA with WMA can reduce production costs because of the 20–75% lower energy consumption in WMA production. It was also released that the reduction in energy consumption is dependent on the fuel type, energy source, material heat capacity, moisture content, and production temperature. Other benefits of using WMA are enhanced asphalt mixture workability and compaction because the additives in WMA reduce asphalt binder viscosity. It also allows for the incorporation of more waste materials, such as reclaimed asphalt pavement (RAP). However, future studies are recommended on the possibility of using renewable, environmentally friendly, and cost-effective materials such as biomaterials as an alternative to conventional WMA-additives for more sustainable and green asphalt pavements.

One effective method to minimize the increasing cost in the construction industry is by using coal bottom ash waste as a substitute material. The high volume of coal bottom ash waste generated each year and the improper disposal methods have raised a grave pollution concern because of the harmful impact of the waste on the environment and human health. Recycling coal bottom ash is an effective way to reduce the problems associated with its disposal. This paper reviews the current physical and chemical and utilization of coal bottom ash as a substitute material in the construction industry. The main objective of this review is to highlight the potential of recycling bottom ash in the field of civil construction. This review encourages and promotes effective recycling of coal bottom ash and identifies the vast range of coal bottom ash applications in the construction industry.

The use of geopolymer in pavement constructions is strongly encouraged. Many studies have demonstrated the vast potential of using industrial-by-products-based geopolymers. This paper discusses the modification of asphalt binders with geopolymers, namely geopolymer-modified asphalt (GMA) and geopolymer-modified asphalt mixture (GMAM). In addition, curing geopolymer materials, engineering properties, production techniques, and prospective utilisation in the pavement construction, such as durability and sustainability, are also discussed. The literature review showed that many industrial by-products, including red mud, blast furnace slag, fly ash, and mine waste, are used to produce geopolymers because of the metal components such as silicon and aluminium in these materials. The geopolymers from these materials influence the rheological and physical properties of asphalt binders. Geopolymers can enhance asphalt mixture performance, such as stability, fatigue, rutting, and low-temperature cracking. The use of geopolymers in asphalt pavement has beneficial impacts on sustainability and economic and environmental benefits.

Polymer modification is extensively used in the Kingdom of Saudi Arabia (KSA) because the available asphalt cement does not satisfy the high-temperature requirements. It was widely used in KSA for more than two decades, and there is little information regarding the differences in the performance of different polymers approved for binder modification. Pavement engineers require performance comparisons among various polymers to select the best polymer for modification rather than make their selection based on satisfying binder specifications. Furthermore, the mechanical properties can help select polymer type, producing mixes of better resistance to specific pavement distresses. The study objective was to compare the mechanical properties of the various polymer-modified asphalt (PMA) mixtures that are widely used in the Riyadh region. Control mix and five other mixes with different polymers (Lucolast 7010, Anglomak 2144, Pavflex140, SBS KTR 401, and EE-2) were prepared. PMA mixtures were evaluated through different mechanical tests, including dynamic modulus, flow number, Hamburg wheel tracking, and indirect tensile strength. The results show an improvement in mechanical properties for all PMA mixtures relative to the control mixture. Based on the overall comparison, the asphalt mixture with polymer Anglomk2144 was ranked the best performing mixture, followed by Paveflex140 and EE-2.

The utilisation of reclaimed asphalt pavement (RAP) as a suitable substitute for natural aggregate and binder offers an energy-saving and cost-effective approach to enhance the performance of asphalt mix. Realising the potential use of RAP as a promising recycling technique, many countries are seeking to recycle RAP as part of the global effort to address the rising challenge of climate change and contribute to a sustainable environment. This study aimed to develop an integrated approach to determine the amount of RAP to be used in an asphaltic concrete wearing course with 14 mm nominal maximum aggregate size (ACW14). The RAP was incorporated with two waste materials comprising waste engine oil (WEO) as a rejuvenator and Crumb Rubber (CRM) as a binder modifier. A total of five different mixes, which include R0 (control mix), R30, R50, R70, and R100 (replacement of 30%, 50%, 70%, and 100% of RAP aggregates in the mix, respectively) were evaluated. The Marshall parameters, resilient modulus (M_R), indirect tensile fatigue, moisture susceptibility, and mass loss (ML) tests were conducted to investigate the performance of each mix. Finally, an arbitrary scale was developed to optimise the RAP content. The results showed that the Marshall parameters, moisture susceptibility, and ML values of the RAP mixes met the criteria outlined in the standard. According to the M_R performance, the R50, R70, and R100 mixes were more resilient than the R0. In terms of fatigue resistance, the R30, R50, and R70 mixes showed better performance than the R0. Overall, the collective performance of all RAP mixes was above the R0 and it increased with the increment of RAP content. Therefore, it was possible to design ACW14 mixes with up to 100% RAP in combination with WEO and CRM.