Sulphate-expansion tests were performed on mortar bars manufactured with two types of subbituminous fly ash and two types of cement. One fly ash was from Alberta, Canada while the second, a high-calcium ash, was from the United States. Ordinary and sulphate-resistant cements were used in the examination.

Bars were exposed to attack when they reached a given strength level. Some bars were soaked in a mixed solution of sodium and magnesium sulphate under controlled conditions; the pH of each solution was maintained at either 7 or 9.5 by regular additions of sulphuric acid. For other bars the pH of the solution was not controlled. Behaviour of bars in water baths where pH was maintained approximately constant was also examined. Bars were soaked in individual three-bar groups so that possible correlation between amount of acid added and linear bar expansion with time could be observed. Post-expansion examinations included strength degradation, qualitative X-ray analysis and thermal analysis.

Results show some interesting correlations, or lack therof, between acid addition and sulphate attack. Mortars made with the Alberta ash performed better than the corresponding control mortars; however, in a mixed magnesium/sodium solution expansions were much greater than in previous tests where only sodium sulphate was used. Bars made with the high-calcium subbituminous ash performed very poorly under all conditions.