W. H. HARRISON and M. E. GAZE
Building Research Establishment, Garston
Small specimens of mortar made by normal brick-laying techniques were subjected to wet/dry, freeze/thaw cycles to simulate severe exposure. Variables included two different types of mortar, two types of cement, seven sands and three levels of cement content. All 84 mixes had similar consistences and a similar air content in each plasticized mix. The compressive strength and drying shrinkage of the hardened mortars were determined on moulded specimens. Specimens of mortar beds laid between pairs of dry porous bricks had higher strength, lower carbonation rates and better durability than specimens laid between saturated or low absorption bricks which exerted no suction.
Durability was assessed by the amount of degradation after exposure to 25 cycles of frost, sulphate or the combination of sulphate and frost. Resistance to frost was increased by the presence of entrained air. Only the air-entrained mortars made with sulphate-resisting Portland cement and a cement: sand ratio of at least 1:6 were resistant to the combination of frost + sulphate.