Improving the carbonation resistance of self-compacting concrete containing recycled concrete aggregates using blended cements

The current investigation assess the relative efficacy of Silica Fume (SF) and Metakaolin (MK) blended with Portland Cement (PC) and Fly Ash (FA) in compensating the loss of carbonation resistance due to inclusion of Coarse Recycled Concrete Aggregates (RCA) in Self-Compacting Concrete (SCC). To evaluate the carbonation resistance, different SCC mixes at curing age of 28-120 days were tested for accelerated carbonation for 4-16 weeks. The influence of SF and MK has been observed for both low and high volume FA based SCC mixes containing various levels of RCA. As anticipated, the maximum loss of carbonation resistance of RCA based SCC was observed for those mixes in which full replacement of Coarse Natural Aggregates (CNA) with RCA was done. The observed loss was offset to varying degrees by the use of SF and MK. It has been observed from this investigation that inclusion of SF/MK compensates the loss of carbonation resistance of SCC up to 50% replacement of CNA with RCA. Based on the experimental results, it can be seen that the performance of SF blended mixes was better than that of MK blended SCC mixes which lends support to wider use of SF. © 2019 Associated Cement Companies Ltd.. All rights reserved.