Effect of varying water content and extreme weather conditions on the mechanical performance of sludge bricks solidified/stabilized by hemihydrate phosphogypsum, slag, and cement

•Hemihydrate phosphogypsum and slag were mainly used to solidify/stabilize the waste river sludge.•Mechanical properties and durability of samples are highly dependent on the PC/GGBFS ratio.•Compressive strength, water resistance, and absorption could meet the requirement of Chinese standard.•The decrease in water/powder ratio increased the compressive strength due to the tougher and denser microstructure. The accumulation of sludge in harbor and water channels causes serious environmental pollutions. The recycling of sludge into building materials compensates for the shortage of raw materials in the construction industry and mitigates the environmental impacts of sludge simulation. Therefore, in the current study, the waste river sludge (WRS) was solidified/stabilized by the combination of hemihydrate phosphogypsum (HPG), ground granulated blast furnace slag (GGBFS), and Portland cement (PC). The effect of different mixing proportions and WRS’s moisture content on the mechanical properties of specimens were investigated. Besides, the performance of prepared samples under extreme weather conditions, including acid/alkaline erosion, freeze–thaw cycling, and Na2SO4 immersion was systematically evaluated and discussed. The results show that the mechanical properties of solidified bricks increased with the incremental dosage of GGBFS and decreased with the rise of WRS’s moisture content. The acid/alkaline corrosion resistance and freezing-thawing resistance ability increased with the decrease of PC/GGBFS ratio due to the denser and tougher microstructure and the additional hydration and pozzolanic reactions of GGBFS. However, the inclusion of GGBFS accelerated the deterioration of specimens under Na2SO4 immersion.