Influence of sustained compressive load on the carbonation of concrete containing blast furnace slag.

• Carbonation rate of concrete under uniaxial compressive load was tested. • Carbonation resistance of BFS concrete is improved by compressive service load. • Microcrack healing and pore densification caused the slower carbonation under load. • Crack propagation caused the faster carbonation above the threshold load level. Carbonation of concrete, in which 0%, 50% and 70% of cement was replaced by blast furnace slag (BFS), under different levels of sustained compressive load (0, 0.25, 0.5 and 0.75 times the breaking load) was investigated. The results show that the carbonation rate first decreases with load level and then above a threshold value (approximately 0.25–0.5 times the breaking load) increases with load level. The carbonation rate of BFS concrete becomes closer to that of Portland cement concrete under sustained compressive load. An investigation of the load-induced microstructure changes showed that the densification effect dominates in the carbonated zone in terms of lower porosity, denser interfacial transition zone, lower crack width and autogenous healing of fine cracks. The cracking effect plays a more significant role in the non-carbonated zone and leads to a notable increase in the carbonation rate at a high load level. The average major principle strain obtained by digital image correlation can be used to evaluate the combined effect of densification and cracking. [ABSTRACT FROM AUTHOR]