Physical, mechanical, and durability properties of gypsum–Portland cement–natural pozzolan blends

Abstract

This paper deals with the effect of gypsum–Portland cement and gypsum–Portland cement–natural pozzolan ratios on the physical, mechanical, and durability properties of gypsum–Portland cement–natural pozzolan blends. The results indicate that the setting time of these paste decreases with the increase of gypsum content in the mixture, ranging from 8 to 11 min. The addition of superplasticizer increases the setting time from approximately 11 to 35 min. This increase is greatly dependent on the plasticizer admixture dosage. These blends show a kinetic of capillary water absorption very similar to that of the Portland cement binder. Sorptivity is strongly influenced by the type of binder, binder composition and water–binder ratio. Porosity of blended gypsum binders ranges from 12% to 37%. Their water absorption is high, reaching 27% in the blends with a greater proportion of gypsum. The gypsum–Portland cement blends themselves possess good water resistance, which is further enhanced by the addition of natural pozzolan and superplasticizer. The water-cured blends with the composition of 41:41:18 (gypsum : Portland cement : natural pozzolan) and 41:41:18S1 (gypsum : Portland cement : natural pozzolan : 1% superplasticizer) offer a compressive strength of approximately 20 MPa at room temperature. These blends give excellent properties retention after aging in water at 20°C for 95 days. Their good resistance to water decreases as the gypsum content in the mixture is raised. However, the strength loss for the gypsum–Portland cement–natural pozzolan blends is generally less than that observed for the gypsum binder.Key words: gypsum, Portland cement, natural pozzolan, physical, mechanical, durability.