Low-Energy Consumption Preparation of Fine Waterproof Cementitious Material with High-Volume Phosphogypsum

Abstract

Phosphogypsum (PG) is an industrial solid waste which is difficult to dispose of and can cause environmental pollution. This paper investigated a low-energy-consumption preparation from PG of an environmentally friendly building material. PG was converted to α hemihydrate gypsum (α-HH) using the nonautoclaved method. Then the α-HH from PG (PGHH) was mixed with different dosages of fly ash and/or cement to obtain PGHH–fly ash–cement (PFC) cementitious materials, enhancing the water resistance of the corresponding hardened material. Results showed that the optimal mix proportion (by weight) of PGHH:fly ash:cement was 70∶24∶6 when the water resistance and mechanical strength properties of the corresponding hardened materials were comprehensively compared. With this proportion, the 3-, 28-, and 90-day softening coefficients were more than 25%, 50%, and 70% higher than those of the control group (PGHH alone). It was demonstrated that the Ca(OH)2 from hydration of cement can activate the pozzolanic reaction of fly ash, thus forming ettringite and C─ S─ H gel and making the hardened materials denser and more waterproof. The prepared PFC cementitious material has application as a building material which can provide a low-energy-consumption and environmentally friendly method for utilizing PG.