Effect of very high limestone content and quality on the sulfate resistance of blended cements

Sulfate attack was investigated on blended ordinary Portland cement (OPC) based mortars with limestone replacements up to 65 wt-% in 30 g·L−1 Na2SO4 solutions at 20 °C and 8 °C for 200 days. Although CEM I 52.5R with ∼12 wt-% C3A was used, some blended mortars with a water/powder ratio of 0.35 and ≤50 wt-% limestone replacement passed the test requirements (Δ-expansion ≤0.5 mm/m after 91 days) and exhibited a better performance than pure OPC reference mixes with water/powder ratios of 0.5 and 0.6. Under accelerated test conditions, the deterioration level of blended mortars arising from sulfate attack can be approximated by the reaction of portlandite with aqueous sulfate to secondary expansive gypsum, ettringite and thaumasite. The pore structure and the reactivity of carbonates and cement hydrates originally present in blended cements should be considered for predicting the long-term stability of concrete in sulfate-loaded environments.