Carbonation of blended Portland cements with residual rice husk ash and limestone

The carbonation of Portland cements with different percentages of residual rice husk ashes (RRHA1 and RRHA2) and limestone filler (LF) as cement substitutions were studied according to UNE EN 13295 in binary mixtures with one of the mineral admixtures and ternary mixtures with 0–30% RRHA and 5% LF. For 5% cement substitution, the binary mixtures with LF or RRHA presented similar results. For higher cement substitutions in binary mixtures with LF, the carbonation depth and coefficient increased very quickly compared with those of the other mixtures with the same substitution percentage. The lowest carbonation coefficients and depths were obtained for the binary mixtures with RRHA, with the values similar for the two types of RRHA used. In the ternary mixtures, the carbonation coefficients and depths were higher than those in the binary mixtures with RRHA, and were higher with RRHA2 than with RRHA1. Carbonation of the ternary mixtures differed due to the synergy of the ashes with the cement, the LF and the substitution percentages used. The results obtained provide a theoretical–experimental foundation for the development of Portland cements blended with RRHA, with or without a small amount of LF, obtaining better benefits than limestone cements.