Influence of Na2SO4 solutions on the capillary absorption and shrinkage of mortars made with cement containing silica fume

Abstract

Mortars containing cement with silica fume (sf) replacements of 0, 10, 20 and 30% were produced. Following 28 days of curing in water at 20 degrees C +/- 2 degrees C, the mortars were kept in water, Na,SO, solution of pH = 6 and in laboratory atmosphere at 20 +/- 2 degrees C and 65 +/- 5% R.H. The specimens kept in water and sulfate solution were tested for absorption and unit mass, and those stored in air were tested for shrinkage. The coefficient of capillary absorption of 0%, sf mortar exposed to sulfate increased up to 3.07 times that of the mortar cured in water while the value for the 30% sf mortar was 0.48; indicating a reduction when exposed to sulfate. The water absorption decreased by 12% at sf replacement of 30%. Shrinkages of the 20% and 30% sf were close to each other and were about 1.5 times that of the 0% and 10% sf, starting with the age of 7 days. (C) 1997 Elsevier Science Ltd.