Effects of curing temperature on sulfate-induced expansion of cement mortars

This study aims to understand the effects of the curing temperature on the phase assemblage and the distribution of aluminum-bearing hydrates (AFm and AFt), and how these affect external sulfate attack. Mortars were prepared with Portland cement (PC) and slag-Portland cement at a water-to-cement (w/c) ratio of 0.5. Specimens were cured at 20°C, 40°C and 60°C for 28 days prior to full immersion in sodium sulfate solutions at 50 g/L. The results showed that curing at higher temperatures shortened the latent period before expansion in both PC and slag systems. High-temperature curing altered both the pore structure and the phases embedded in the C-(A-)S-H matrix, leading to more expansion and degradation. Expansion occurred much later and to a lesser extent in slag-Portland mortars due to lower contents of fine monosulfoaluminate (X-ray amorphous) in the C-(A-)S-H, compared to Portland cement mortars.