Acid treatment technique for determining the mortar content of recycled concrete aggregates

Abstract

The presence of old cementitious mortar in recycled concrete aggregates (RCA) has been reported to be one of the main factors contributing to a lowering of the performance of concrete made with RCA relative to those made with natural aggregates (NA). This difference in performance has been attributed to the proportion of mortar present in the RCA vis-à-vis the NA used to cast the original parent concrete. Therefore, determining the mortar content might provide an effective means of assessing the overall quality of RCA. Also, as reported in the available literature, it is essential to take into account the amount of mortar present in RCA as part of the total mortar present when designing concrete mixes cast with RCA. However, an easy-to-use standard method for accurately determining the cementitious mortar content of RCA is not available at present. In this study, an acid treatment testing method is proposed to determine the mortar content of RCA. The method is able to remove most, if not all, of the cementitious mortar and takes approximately 24 h to carry out. In addition, the effects of mortar content on properties of RCA including 24-hour water absorption, bulk density, and Los Angeles abrasion resistance were investigated. The effects of the original parent concrete strength on the relationships between mortar content and RCA properties were also investigated. The study was confined to only granitic coarse aggregates. Copyright© 2013 by ASTM International.