Effects of Carbonation and Saturation on the Leaching Characteristics of Recycled Concrete Aggregates

Abstract

Abstract This study assessed the efficacy of water leach tests (WLTs) and pH-static leach tests in evaluating the leaching behavior of distinctly carbonated recycled concrete aggregates (RCA). The leaching of barium (Ba), calcium (Ca), chromium (Cr), magnesium (Mg), and sulfate (SO4) from seven RCA samples were studied. WLTs at several liquid-to-solid ratios (L/S) and pH-static leach tests were conducted to examine the effects of carbonation on the release of elements. In addition, a novel experimental approach was introduced to gauge the impact of moisture saturation on the leaching attributes of RCA. The saturation effect on the leaching potential was explored by inducing eight different matric suctions in laboratory-compacted RCA cores. Moreover, geochemical modeling was performed to evaluate the leaching mechanisms of the elements. Results showed that a carbonation-based leaching assessment of RCA could be premised on laboratory WLTs and pH-static leach tests. Ba and Ca leaching decreased while Cr and SO4 leaching increased with the RCA degree of carbonation. The L/S ratio could be used as a substitute for RCA carbonation. At a higher L/S ratio, fresher and aged RCA samples had similar leaching fingerprints. The pH-dependent leaching of the elements was regulated by the RCA degree of carbonation, especially in the alkaline pH range. Irrespective of carbonation level, geochemical modeling suggested solubility-controlled leaching mechanisms. The leaching of metals from RCA was a dynamic process, and the changes in matric suction and consequently saturation could diversely influence the leaching characteristics of RCA.