Moisture susceptibility and fracture resistance of hot mix asphalt containing treated recycled concrete aggregate

The construction industry produces substantial amounts of waste materials, which contribute to negative environmental impacts when disposed of in landfills. Recycling Construction and Demolition Waste (CDW) as secondary materials is an effective approach to reducing these negative effects. Recycled Concrete Aggregates (RCA) derived from distressed pavements, buildings, and concrete structures have potential for a variety of applications, including in asphalt mixes. This paper reports experimental research on the use of treated and untreated RCAs in preparing Hot Mix Asphalt (HMA). RCA materials were added in both treated and untreated form to HMA mixes. To improve the quality of recycled mixes, RCAs were treated with lime solutions. In order to improve quality of recycled mixes, RCAs were treated with lime solutions before that the recycled mixes were subjected to various tests. The treatment was applied to coarse RCA materials. The coarse RCAs were washed thoroughly, so that all noticeable impurities, including wood chips and other similar materials, were removed. These were then dried at ambient temperature for 24 h before that the treatment was applied. In order to reduce stripping susceptibility of the recycled asphalt mixtures, hydrated lime was added as a treatment additive. The addition of hydrated lime solution was beneficial due to, its abundance the convenience of application in HMA mixes. RCAs were impregnated in a 6% solution of hydrated lime for 24h at ambient temperature. Then these were dried at ambient temperature before being used in asphalt mixes. The physical and mechanical characteristics of the treated/untreated RCAs were determined. Asphalt mixtures were prepared that contained 25% and 50% RCAs of the size ranging from 4.75 to 12.5 mm. Various asphalt mixtures containing different amounts of RCAs were prepared. Moisture susceptibility of HMA mixes were evaluated using indirect tensile strength test (ITS). Fracture properties of mixes applying Semi-Circular Bending (SCB) were determined. SCB testing was performed according to ASTM D 8044 Standard testing method. Samples were prepared containing three different notches of 25, 32, and 38 mm. SCB samples were tested using a UTM machine. The loading mode as in monotonic compression at the speed of 0.5 mm/min. J-integral suggests as a criterion for resistance of materials to cracking. Testing was performed on HMA mixes treated and untreated samples. The results indicated that although treating RCAs might require more effort in production processing, significant benefits result in reducing moisture susceptibility and increasing fracture toughness of samples. It was also found that replacing virgin aggregates with RCA, improved fracture properties of HMA mixtures. The results indicated that with using RCA instead of conventional aggregates in asphalt mixes, has positive benefits for the environment and enhanced mechanical properties of HMA mixtures. A limited percentage of RCAs can be used in asphalt mixtures without significantly affecting performance of asphalt mixtures. The treatment resulted in reduced water absorption and increased fracture energy of mixes. Asphalt mixes containing 50% untreated RCA materials showed some moisture susceptibility while asphalt mixes containing 50% treated RCA showed improved moisture resistance. In conclusion, the study demonstrated that treating RCAs with hydrated lime solution improved the moisture susceptibility and fracture resistance of recycled HMA mixtures. Furthermore, utilizing recycled construction materials as secondary materials in asphalt mixes has significant environmental benefits. Future research can explore the potential use of various waste materials, including RCAs, in asphalt mixes.