Sulphate resistance of metakaolin mortar

The partial substitution of cement (both high C(3)A and intermediate C(3)A) with metakaolin (MK) is investigated in terms of resistance of MK mortar to sodium sulphate (Na2SO4) solution. Results on strength, porosity, pore size distribution, and calcium hydroxide (CH) contents are also reported. The sulphate expansion results demonstrate that the sulphate resistance is increased as the replacement level of cement with MK increases, up to at least 25% replacement. Refinement in pore structure and reduction in CH content increase with increase in MK content (for moist-cured mortar), and these two factors are considered to be the principal factors affecting improvement in sulphate resistance. Also, although after prolonged periods of exposure to Na2SO4 solution, there is (relative to water-cured specimens) significant strength loss of PC mortars and mortars with low levels of MK (5 and 10%); for mortars with high levels of MK (15, 20 and 25%), there is consistent strength gain. (C) 1998 Elsevier Science Ltd.