Recycled concrete aggregates (RCAs) have low quality when compared with natural or conventional aggregates as the paste adhering to it is the key aspect that affects its functionality. Since the adhering cementitious paste weakens the adhesion between the aggregate and the binder, it becomes a decisive factor in the mechanical behavior of the asphalt mixture. It turns out that enhancing the surface of the aggregate or eliminating the paste attached to the NA (natural aggregate) is crucial for improving interfacial bonding. Therefore, the treatment and evaluation of the RCAs by laboratory testing method were studied in this research to assess their reuse in the asphalt pavement surface coarse layer. With the various techniques for removing paste from the RCA, a combination of three enhancement processes were developed for the effective removal of the cement paste, which are mechanical, chemical, and 400 °C conditioning thermal treatment. The RCAs were first charged in a Los Angeles machine for the mechanical treatment to remove parts of the attached cement. Then they were soaked in two types of acids, namely hydrochloric and sulfuric, with different concentrations to determine the most effective or optimum molarity for about a 48 h soaking duration. Then a 2 h thermal treatment was conducted on the RCA samples. After all the treatments were done, the RCA aggregates were subjected to different types of tests to examine their properties in order to ensure their full potential in terms of their physical, chemical, mineralogical, and surface microstructure characteristics. Based on the experiment design, the study intends to examine the quality of the treated recycled aggregates generated by the combination approach as well as to investigate the optimal acid concentration and type. The results show that the proposed mechanochemical and thermal treatment reinforced the quality of the RCAs when compared to the non-treated samples. Meanwhile, HCl proved to be the optimum compared to H₂SO₄ in most examinations of the properties. In the end, better chemical qualities were validated, and the RCA qualities were improved.

Micro-surfacing (MS), made of emulsified asphalt, is the most commonly used preventive maintenance technology in asphalt pavement. However, the studies on profile features of MS based on aggregate morphology are few. This study evaluated the profile features of MS and its effect on skid resistance. The aggregate morphologies were first characterized and modified emulsified asphalt was prepared. The three-dimensional profile features of four kinds of MS samples were captured by laser texture scanner. Results illustrate that steel slag aggregate can be used to enhance the skid resistance of pavement surface and bring about larger profile indexes than basalt and limestone due to its angularity index and flatness values. Further aging of steel slag to eliminate free calcium oxide (f-CaO) is recommended before being used in pavement surface layer.

An enormous surge in the pavement sector requires the evaluation of interface bonding in asphalt composite, since the assessment of bonding brings considerable cost savings. Microscopic and mechanical analyses were performed to study the status of the interface transition zone of four groups of asphalt mixtures, using thin-slice preparation to obtain asphalt mixture slices with a flat surface for microscopic analysis. The interface transition zones were characterized using good knowledge of blending or diffusion phenomena by conducting tests both at the micro and macro levels to determine mixture quality. Asphalt mixture components were observed using fluorescence microscopy imaging and evaluated by the gray value change law. Asphalt mixture groups, (virgin, recycled of 30% aged and 70% unaged, 6%, and 4% rejuvenator dosage mixtures) under the same process parameters, which are a mixing time of 270 s and a mixing temperature of 150 °C, been considered optimum for component fusion in a hot asphalt mixture were used. This study relied on the influence of morphology law, assessed through rutting tests for high temperature performance, semi-circular bending tests for low temperature performance, and pull-off tests for interface bonding strength. The relationship between interface transition zones and macro performance was studied. The self-developed pull-off method was a research innovation which can be used as an alternative to study interface transition zones in asphalt mixtures, and provides the necessary data needed with 3D surface failure mode calculations. The device measured the bonding strength of a single aggregate in distinct positions using the bitumen penetration test method. The main goals were to determine a correction factor, identify the appropriate alteration, and compute the actual fracture surface area. Using scanning electron microscopy for interface characterization and micro-morphologies of mortar transition zone, our analysis provides adequate knowledge about interface position and the components present. The applied approaches to characterize asphalt mixture interfaces proved workable and reliable, as all methods have similar trends with useful information to determine asphalt pavement quality.

The reuse of industrial silicate solid wastes, including fly ash, slag, and waste rubber, is one of the most significant environmental and economic concerns worldwide