Mechanical strength, water resistance and drying shrinkage of lightweight hemihydrate phosphogypsum-cement composite with ground granulated blast furnace slag and recycled waste glass

Phosphogypsum (PG) is an industrial waste from fertilizer production which causes environmental problems. Hemihydrate phosphogypsum (HPG) can be derived from dehydration of PG by low temperature calcination (about 180 °C). The low mechanical strength and poor water resistance of HPG restrict its application as building material. In view of this, various amount of ground granulated blast furnace slag (GGBS) (5–25%) and Portland cement (15%) were mixed with the HPG and compared with the corresponding mixtures with commercial hemihydrate building gypsum (HBG). Compared to HBG-based composite (HBGC), the HPG-based composite (HPGC) had higher compressive strength. Besides that, the inclusion of GGBS is beneficial and up to 25% can significantly improve the softening coefficient (by up to 89%) and compressive strength (by up to 205%) of the HPG-cement composite. Different types of fine aggregate, namely silica sand and recycled waste glass (RWG) were also added in the HPGC with the latter recording improved performances in mechanical strength, water resistance and drying shrinkage. In overall, HPGC containing RWG with lightweight bulk density (1849 kg/m3), low drying shrinkage (378 µε at 28 d), adequate strengths (42.6 MPa compressive strength and 7.67 MPa flexural strength) and good water resistance (softening coefficient of 0.98) were developed.