Soundness of Cement

Soundness is the ability of set cement to retain its volume without significant delayed expansion. Unsoundness is caused by excess free (uncombined) lime or magnesia which hydrate very slowly after setting, expanding and cracking/disintegrating hardened concrete months or years later. It is tested by the Le Chatelier method (expansion of a split mould measuring free-lime unsoundness) and the autoclave test (sensitive to magnesia), per IS 4031 Part 3.

IS 269 limits Le Chatelier expansion to ≤10 mm and autoclave expansion to ≤0.8% for OPC. Unsound cement is a serious latent defect — there is no field remedy once placed — so it is a mandatory acceptance test for every cement lot, particularly important for cement stored long or from secondary plants.