Water resistance of composite binders containing phosphogpysum with different pretreatment processes

The influence of pretreated phosphogypsum on water resistance of composite binders containing phosphogypsum (CBPG) was investigated. Six pretreatment processes in total were conducted on phosphogypsum using autoclaving and calcination. Three parameters of the CBPG mortars were comparatively studied to evaluate their water resistance: the ratio of the compressive strength in the wet-saturated state to that in the dry state (W/D); weight loss after static water attack (WLSW); and weight loss after flowing water attack (WLFW). The crystalline phases could be transformed and the impurities could be effectively purified for original phosphogypsum by the pretreatment process. Therefore, water resistance of the CBPG mortars from pretreated phosphogypsum was improved significantly when compared to that of the mortars from original phosphogypsum. Regarding the weight loss and strength after static or flowing water attacks, WLSW and WLFW could effectively evaluate the water resistance of CBPG mortars, when compared with traditional evaluation by W/D.