Enhancing the mechanical and durability properties of subzero-cured one-part alkali-activated blast furnace slag mortar by using submicron metallurgical residue as an additive

Cold weather (<0 degrees C) is known for its detrimental impacts on concrete, and thus expensive and energy-consuming heating and insulation systems are used in cold-weather concreting to prevent frost damage. Supplementary cementitious materials are not recommended for use in cold-weather concreting because they slow down the setting time of concrete. In this study, one-part alkali-activated slag (AAS) was presented as an alternative environment-friendly binder for winter construction. The impacts of iron-containing submicron metallurgical residue on the reactivity, hardened properties, and durability of subzero-cured one-part AAS pastes and mortars were comprehensively studied. The incorporation of submicron particles (SMPs) enhanced the reactivity of AAS pastes by increasing the amount of precipitated hydrate phases and developing supplemental hydration products like calcium ferrosilicate hydrate. The positive effects of SMPs were highlighted via the denser microstructure, higher ultrasonic pulse velocity, increased compressive strength, and better durability properties of the AAS mortars. These improvements were attributed to the nucleation and filling behaviors of the added SMPs. On the contrary, decreased subzero curing temperature hindered the reaction progress, which adversely affected the hardened and durability properties of the mortars and limited the SMPs efficiency. With additional above-zero curing, higher compressive strength and lower water absorption and permeable porosity were measured in the AAS mortar cured initially at 5 degrees C compared to that cured at +20 degrees C.

Automated summary

In this study, the addition of submicron particles enhanced the reactivity and durability of one-part alkali-activated slag (AAS) for winter construction. A denser microstructure, higher compressive strength, and better durability properties were observed in AAS mortars with submicron particles, showing the positive effects of these additives on cold-weather concreting.