THE SULFATE RESISTANCE OF CEMENT AND ITS TESTING

Portland cement with a low C(3)A content is sulphate resistant because its hydration products react either not at all or only to small exten t with sulphate ions. Blastfurnace cement with a high content of blast furnace slag is sulphate resistant because on hydration it produces a hardened cement paste into which the sulphate ions are virtually unabl e to penetrate. Rapid tests are capable, with certain limitations, of ranking cements in the correct order of sulphate resistance. However t he scatter of the measured values in tests carried out in different te sting laboratories is so large with all known methods that standardiza tion is not a possibility. The experience gained when testing highly s ulphate-resistant cements indicates that, with certain preconditions, the addition of fly ash to concrete increases the sulphate resistance and that a definitive assessment is only possible when the effect of t he very slow progress of hydration of the fly ash, especially in the f irst 28 days, has been clarified.