Abstract
This study focused on the quick initial setting time and the expansion strain that occurs during the early aging of α-calcium sulfate hemihydrate (αHH) and examined the setting, compressive strength, and shrinkage strain of αHH-replaced cement mortar. The results show that the initial setting time significantly decreased with an increase in the αHH replacement ratio. Drastic occurrence of ettringite was observed early in the aging of cement mortar when αHH was substituted into the cement; however, the ettringite was not converted to monosulfate with increasing age and thus was not favorable for the development of the compressive strength. When αHH was substituted into cement, using Portland blast-furnace slag cement (PSC) was more advantageous than using ordinary Portland cement (OPC) for the development of the compressive strength. Meanwhile, the expansion of early age αHH can decrease the shrinkage strain of cement mortar. The generation of ettringite is more effective when αHH is substituted into PSC than into OPC and is thus more effective in suppressing the shrinkage strain.
Highlights
Gypsum is a material in which the amount of water of crystallization varies with its surrounding conditions, such as temperature or humidity, and can be classified into three groups, namely, calcium sulfate anhydrite (CaSO4 ), calcium sulfate hemihydrate (CaSO4 ·1/2H2 O), and calcium sulfate dihydrate (CaSO4 ·2H2 O) [1]
Guan et al [13] and Ye et al [14] evaluated the effects of particle size on the compressive strength of α-calcium sulfate hemihydrate (αHH). αHH significantly hardens at an early age, and after reaching maximum strength, the strength shows minimal change or a decreasing trend; this has been verified in previous studies [15,16]
This study evaluated the effects of αHH, which is characterized by a quick initial setting time and
Summary
Gypsum is a material in which the amount of water of crystallization varies with its surrounding conditions, such as temperature or humidity, and can be classified into three groups, namely, calcium sulfate anhydrite (CaSO4 ), calcium sulfate hemihydrate (CaSO4 ·1/2H2 O), and calcium sulfate dihydrate (CaSO4 ·2H2 O) [1]. Previous studies have focused on the production of calcium sulfate hemihydrate from calcium sulfate anhydrite and calcium sulfate dihydrate [2,3,4,5,6]. Β-calcium sulfate hemihydrate are soluble gypsums that are hydrated via the surrounding moisture, and they characteristically hydrate and set into calcium sulfate dihydrate in the presence of water. Tang et al [12] investigated the effects of different crystal sizes and shapes of αHH on its strength and microstructure. Lewry and Williamson 2[17]
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