Recycling of the end-of-life lightweight aggregate concrete (LWAC) with a novel approach

Abstract This work proposed an environmental-friendly approach for high-grade recycling of the end-of-life LWAC. The mechanical performance of mortar with recycled powder (RP), mortar with recycled fine aggregate (RFA) and recycled lightweight aggregate concrete (RLWAC) were investigated. Microstructure of mortar and RLWAC was detected to identify the properties of interfacial transition zone (ITZ). RP can prolong the setting of reference cement and the 10 % dosage is better than 2 % in not only retarding effect but also strength development. An appropriate content of RFA is beneficial for compressive strength. Replacing standard sand with 10 % RFA increases the compressive strength of mortar by approximately 10 %. However, a high replacement content (40 %) of RFA brings about a reduction of compressive strength. The amount of RFA below 20% will not increase the dry shrinkage of mortar. The compressive strength of RLWAC is reduced by 10 % RLWA but it has a significant increase when the replacement content reaches 30 %. In mortar with RFA, cracks initiate from the ITZ of new sand and new paste and few cracks generate from old paste and old sand. Four types of ITZ that have distinct features are observed between cement paste and LWA in RLWAC.