Influence of Silica Fume and Fly Ash on Settlement Cracking Intensity of Plastic Concrete

Using mineral admixtures as cement replacement substance in concrete tends to increase in the future to provide greater sustainability in the construction industry. This paper aimed to study the influence of adding silica fume and fly ash as a weight of cement replacement on settlement cracking intensity of plastic concrete. Fifty-six mixtures were cast to evaluate the purpose of this study. Two types of cement (Portland cement and sulfate resistance cement) and two types of aggregates (dolomite and gravel) were considered. The cement was partially replaced by different ratios of silica fume (3%, 6%, 8%, and 10%) and different ratios of fly ash (10%, 15%, 20%, and 25%) of cement weight. In all concrete mixtures, a water-to-cementitious content ratio (w/cm) was 0.42. The results exhibited that the cracking intensity of settlement decreased as the slump decreased. Adding silica fume to the concrete significantly reduced the rate of appearance of settlement cracks. The ideal ratio for adding silica fume to the concrete mix was 8% from cement weight. Adding fly ash to mixtures did not significantly affect settlement cracking intensity, but enhanced the workability of fresh concrete.