Effect of environment conditions on volume deformation of blended cement mortars containing blast furnace slag and steel slag powder

As the use of cement -based materials in complex environments continues to grow, understanding their volume deformation behavior across these various conditions becomes crucial to ensuring project quality. In this study, the impacts of mineral admixtures and various curing environments on volume deformation of mortar were investigated. The potential effects from factors such as the hydration process, hydration products, and microstructure were also taken into comprehensive consideration. The results show that mineral admixtures influenced the volume deformation of mortar by affecting its hydration heat, types, and content of hydration products. Blast furnace slag (BFS) increased the content of ettringite (AFt) and calcium silicate hydrate (C-S-H) gel in the mortar, thereby improving its resistance to total shrinkage in natural coastal environment. The formation of Ca(OH)2 and Mg(OH)2 from free calcium oxide (f-CaO) and free magnesium oxide (fMgO) present in steel slag (SS) also contributed to shrinkage resistance. Volume expansion dominated the volume deformation of mortar under both standard curing conditions and seawater immersion environments, with the expansion being more pronounced under seawater immersion. In the standard curing conditions, there was a positive correlation between volume expansion of the mortars and its BFS content; whereas in a seawater immersion environment, volume expansion was positively correlated with both SS content and porosity of the mortars. The volume deformation of mortars used in combination with BFS and SS in different environments did not show significant specificity.