The effect of substituting silica gel for a portion of the Portland cement in standard and graded-sand mortars on the expansion and loss in strength of the mortars in sulphate solutions was determined. Portland cement silica gel sand mortars were cured in steam at 100 °C. and the effect on their sulphate resistance measured; the behavior of lime-silica gel sand mortar in solutions of sodium and magnesium sulphate was also studied. It was found that the addition of silica gel to the mortar, very effective in preventing expansion and maintaining the tensile strength of the mortar in solutions of sodium, and calcium sulphate, was not so effective in solutions of magnesium sulphate. Steam-cured mortars containing silica gel to the extent of 20% of the cement present showed a slightly greater resistance to the action of solutions of sodium and calcium sulphates, but less resistance in solutions of magnesium sulphate, than similar steam-cured mortars containing no silica gel. Lime-silica gel sand mortars behaved very similarly in sulphate solutions as Portland cement mortars containing silica gel. The possible causes of the effects produced by the addition of silica gel to Portland cement mortars are considered, and several explanations discussed.
