Freeze-thaw, chloride penetration and carbonation resistance of natural and recycled aggregate concrete containing rice husk ash as replacement of cement

This study investigated the effect of using rice husk ash (RHA) as replacement of cement (i.e., replacement ratios of 0%, 10%, 20% and 30%) on the durability of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). We examined the freeze-thaw resistance, chloride penetration resistance, and carbonation resistance of NAC and RAC (with 50% recycled coarse aggregate replacement ratio). It was found that during the freeze-thaw process, both NAC and RAC showed an overall weight increase, which was further enhanced by the addition of RHA. Meanwhile, the compressive strength of NAC was reduced more obviously than that of RAC after 100 freeze-thaw cycles. A replacement of 10% cement with RHA resulted in larger reduction in strength loss for NAC (by 36%) compared to RAC (by 4%). As the RHA replacement ratio increased, the chloride penetration resistance of RACs was improved more rapidly than that of NACs, and the difference in the total charge passed between NACs and RACs also decreased considerably. In addition, an increase in the RHA replacement ratio led to an increase in the carbonation coefficient of NAC. Conversely, in the case of RAC, the carbonation coefficient displayed an initial decrease at a 10% RHA replacement ratio, followed by a subsequent upward trend, indicating a positive impact of RHA on preventing carbonation for RAC.