Modeling the Drying Shrinkage of Cement Paste Prepared with Wastewater

Abstract

In the majority of the world, tap water is not available for construction and water containing various salts is the only choice. However, the effect of such water has not been scrutinized systematically. In this work, the mechanism of the drying shrinkage of ordinary Portland cement paste prepared with various salts was investigated systematically. The paste was prepared with wastewater containing three types of salts, i.e., sodium hydroxide (NaOH), sodium sulfate (Na2SO4), and calcium sulfate (CaSO4), and cured at two different relative humidity (RH) conditions. Various fresh and hardened properties of the mixtures were examined. Tests results showed that the workability decreased with the addition of various salts, among which NaOH produced rapid setting, whereas Na2SO4 was more effective than NaOH and CaSO4 at improving the strength of cement paste. Moreover, the addition of various salts produced a larger magnitude of drying shrinkage, and the drying shrinkage of cement paste was less at higher RH. A robust mathematical model for drying shrinkage of cement paste was established considering physical and chemical meanings. The mechanism is discussed using a conceptual model.