Study of the Performance of Warm-Mix Asphalt Containing Recycled Concrete as a Coarse Aggregate in Egypt and the Middle East

Abstract

This paper aims to evaluate the possibility of using recycled concrete aggregate (RCA) as an alternative to coarse natural aggregates (NAs) in warm-mix asphalt (WMA). The index engineering characteristics of the RCA used for the asphalt mixtures were determined. The physical and rheological characteristics of virgin and modified asphalt binders were specified using conventional and performance grade (PG) tests. The WMA was manufactured by two approaches. The first approach involved modifying the asphalt binder properties by incorporating Sasobit as an organic additive into the heated asphalt binder (wet process). The second approach incorporated Asphamin as a synthetic zeolite foaming additive into the aggregate during the mixing process (dry process). Nanosilica fume (NSF) was used as an economical alternative to nanomaterials to improve the investigated WMA’s performance compared with a control hot-mix asphalt (HMA) containing 100% coarse RCA/100% fine NA. The performance of the asphalt mixtures in terms of Marshall, indirect tensile strength (ITS), dynamic modulus (E*), and flow number (FN) was also estimated. The Marshall test results of WMA mixtures with the two types of additives were relatively identical with the control HMA mixture with a slight difference in the optimum asphalt content (OAC). However, the NSF incorporation as a replacement to the mineral filler within the WMA mixtures led to an increase in stability values by up to 35%, especially at 40% NSF with low OAC. The tensile strength ratio (TSR) values for WMA mixes were lower than 80%, but the use of NSF showed a slight enhancement in their values to meet the minimum requirement set by Egyptian specifications. Also, the results revealed a decrease in E* and FN values for the WMA mixtures compared with those for the HMA control, whereas the addition of NSF enhanced the results significantly to outperform the HMA. This research highlights the use of recycled concrete aggregate as a replacement for coarse natural aggregates for manufacturing warm-mix asphalt with two different technologies and compares their performance with hot-mix asphalt. In addition, the effect of using by-product materials such as nanosilica fume as an economical alternative to nanomaterials for raising the efficiency of warm-mix asphalt mixtures was sought. The results provide a better understanding of the performance of warm-mix asphalt mixtures, which contribute effectively to achieving environmental sustainability in the pavement industry.