The Impact of Retarder on the Properties of Gypsum Foamed Materials

This paper studied the impact of borax, citric acid, carboxymethyl cellulose and gelatin on retarded time and mechanical properties of gypsum foamed materials. Scanning electron microscopy (SEM) was conducted to investigate microstructure of gypsum and phase composition of substances on plaster surface as well as the retardation mechanisms. The result showed that when the content of citric acid reached 0.2%-0.3%, the setting time of sample significantly prolonged, but the strength of samples significantly reduced and had defoaming effect. When the content of borax was more than 0.5%, retarding effect was obvious, but flexural strength of samples reduced to 1.22 MPa, it could not meet the requirement of the national standards on the properties of building gypsum. When the content of carboxymethy cellulose was 0.3%, the retarding effect was obvious, but the strength loss was serious, and the consistency of gypsum slurry significantly increased. When the content of gelatin was 0.2%, the comprehensive retarding effect was good, the strength reduction was smaller, so choose gelatin as a retarder in this paper.