Effect of Low-Calcium Fly Ash Content on Drying Shrinkage of Cement Paste under Different Relative Humidities

Abstract

This study aims to investigate the effect of the replacement level of low-calcium fly ash on the drying shrinkage of cement paste under different relative humidity conditions. The materials used in this study include Portland cement type I and low-calcium fly ash, with a water-to-binder ratio (w/b) of 0.55 and fly ash replacement level of 0%, 20%, 35% and 50% by weight of the binder. Cement paste specimens with dimension 3×13×300 mm were cast and cured under sealed conditions at a temperature of 20 ± 1 °C for 252 days. Subsequently, the specimens were cut to a length of 100 mm and subjected to drying at relative humidity levels of 11%, 23%, 40%, 55%, 79%, and 95% for 56 days. The results indicate that replacing Portland cement with fly ash can reduce the drying shrinkage of cement pastes, with a decreasing tendency for the fly ash content to increase under relative humidity below 40%, while the replacement of fly ash did not significantly affect the drying shrinkage under relative humidity above 79%. In addition, increasing the amount of fly ash in cement pastes resulted in a decrease in the drying shrinkage but an increase in the weight loss.