The effect of SCMs and curing time on resistance of mortars subjected to organic acids

Agricultural effluents such as liquid manure and ensilage effluents contain organic acids that constitute a severe chemical threat toward the concrete of agricultural structures. In contact with an acidic solution, the chemical equilibrium of the hydrates in cement paste is destabilized, causing negative effects on porosity, reinforcement corrosion, mechanical strength, and, in the long term, may result in the collapse of the structure. More durable concrete in this environment is needed. The purpose of this study is to examine the effect of the nature of the supplementary cementing materials (SCMs) as well as the curing time on the chemical and the physical modifications of cement pastes and on the compressive strength, mass loss, altered depth and microstructure of mortars immersed in acetic acid at a pH of 4. This study concentrated on three types of hardened cement pastes or mortars made with ordinary Portland cement (OPC), slag and metakaolin cements, cured for period varying from 28 days to 1 year. The results show the beneficial effect of the curing time before the acid immersion, the better durability of metakaolin cement and the good chemical resistance of the slag cement against acid attack. The latter develops low compressive strength and is more sensitive to the curing time but the drop of its resistance due to the acid immersion is minimal due to its strong chemical resistance.