Discussion of the implementation of water compensation methods for recycled aggregate concrete: A critical review

High water absorption is a typical characteristic of most types of recycled aggregate (RA). In the production of recycled aggregate concrete (RAC), it is common practice to either wet the RA prior to mixing or increase the amount of water during mixing. Those two procedures, often referred to as water compensation methods, can bring the effective water-cement ratio of RAC to the target value. Nevertheless, there is some uncertainty among researchers and manufacturers regarding the exact amount of water that needs to be compensated for when implementing water compensation methods, which leads to errors in the effective water-cement ratio of RAC. This review article identifies part of the uncertainty that can noticeably affect the performance of RAC. The root of that problem lies in the current knowledge gaps in the dynamic migration laws of water for different water compensation methods and their effects on the new interfacial transition zone and new cement paste. It is anticipated that this review will encourage efforts to improve accuracy in the use of water compensation methods, thereby contributing to the quality control and scaling up of RAC.