Fluidity, mechanical properties, shrinkage of alkali-activated slag/stainless steel slag mortars with composite activators

Abstract

In order to efficiently utilize steel slag and reduce carbon emissions, the performance of alkali-activated slag/stainless steel slag mortar (ASM) prepared with a composite activator is investigated. In this work, CaO, Na2CO3 and water glass (WG) are used as composite activators, where the alkali equivalents of CaO and Na2CO3 are maintained at 4% and the alkali equivalents of WG (i.e. WG content) as variables were 0, 0.5%, 1.0%, 1.5% and 2.0% respectively. The properties of ASM, including mechanical properties, autogenous and drying shrinkage, are investigated. Results show that the mechanical properties of ASM decrease and then increase as the WG content increases, with the worst mechanical properties of ASM occurring when the WG content is 0.5%. The autogenous shrinkage of ASM decreases as the WG content increases from 0 to 0.5% followed by an increase as the WG content increases further to 2.0%. Autogenous shrinkage depends on chemical shrinkage, small pore (<50 nm) volume, MCL and capillary pressure. When the WG content is increased from 0 to 0.5%, the hydration reaction is inhibited by the reaction of the WG and CaO which reduces the pH of activator solution and gel amount, leading to a reduction in chemical shrinkage, small pore volume, MCL and capillary pressure. However, the high WG content accelerates the hydration reaction when the WG content is greater than 0.5%, which increases the autogenous shrinkage. The drying shrinkage of ASM decreases and subsequently increases as the WG content increases. The higher drying shrinkage is associated with weight loss due to the excellent connectivity of the pores.The pore structure also affects the drying shrinkage, which can be justified on the basis of capillary pressure.