Carbonation resistance of recycled sand concrete and its splitting tensile strength after carbonation

Carbonation is unavoidable during the service of concrete, especially for recycled sand concrete (RSC). This paper presents a systematic experimental study of the various factors affecting the carbonation resistance of RSC. The carbonation test was conducted to investigate the effects of recycled sand (RS) replacement ratio (0 %, 30 %, 50 %, 70 %, 100 %), recycled fine powder (RP) content (3 %, 7 %, 10 %) in RS, degree of pre-wetting (0 %, 50 %, 100 %) of RS, water/binder (W/ B) ratio (0.37, 0.45, 0.58), and various mineral admixtures on the carbonation resistance of RSC. Moreover, the variation of splitting tensile strength of RSC after carbonation was determined, and the microstructural change of RSC after carbonation was also analyzed using mercury intrusion porosimeter (MIP) and scanning electron microscope (SEM). Results indicate that the carbonation resistance of RSC can be improved by reducing the water/binder ratio, increasing the pre-wetting degree of RS, and adding composite mineral admixtures. The carbonation depth of RSC decreased by 59.8 % when the W/B was reduced from 0.58 to 0.37, and by 16.2 % when the pre-wetting degree of RS was increased from 0 % to 100 %. Ternary composite mineral admixture (15 % fly ash + 15 % ground granulated blast furnace slag powder + 8 % silica fume) reduces carbonation depth by 49 %. The increase in splitting tensile strength of RSC after carbonation is positively correlated with the depth of carbonation. This is due to the carbonation products filling some of the pores and improving the pore structure of RSC.