Use of slurry fluorogypsum (FG) with controlled pH-adjustment in FG-based blends

Abstract

This study investigates the mechanical and durability properties of blends made of fluorogypsum (FG) with the pH adjusted by using controlled amounts of circulating fluidized bed combustion ash (CFBCA) and denoted as C-FG, class C fly ash (FA), and type II Portland cement (PC). A series of pH tests was conducted on samples of C-FG to develop an analytical relationship between acidity and CFBCA content, which can be used to determine the optimal amount of CFBCA needed to obtain a specified pH value. Two compositions of C-FG-based blends were investigated in detail to identify the effects of CFBCA content on compressive strength, modulus of elasticity, Poisson’s ratio, relative volumetric expansion, unit weight, and setting times. The obtained properties were compared with those of FG-based blends having the same composition and made using FG with the pH adjusted by using uncontrolled amounts of CFBCA (U-FG). Results suggest that the amount of CFBCA can have significant effects on the properties of C-FG-based blends, depending on the composition. In addition, C-FG-based blends generally achieve a higher compressive strength and initial stiffness than the corresponding U-FG-based blends.