Compressive strength and gel structure improvement in the high-volume calcium carbide residue activated-blast furnace slag system combined with sodium carbonate and silica fume

Abstract

Calcium carbide residue (CCR) with high alkalinity favorably corresponds to the alkaline activator in the alkali-activated materials (AAMs) production. Its utilization could reduce the carbon footprint and facilitate cast-in-situ applications compared to traditional liquid alkaline activators. A high-volumed CCR from 10 % to 25 % as alkaline activators in an alkali activated-blast furnace slag system was investigated, in which sodium carbonate (Na2CO3) and silica fume were used to improve the mechanical properties of CCR-activated blast furnace slag (CCR activated-BFS) pastes. Isothermal Calorimetry, X-ray diffraction (XRD), 29Si nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) were used to characterize the reaction process, phase transformation, and gel structure. The results show that the highest compressive strength of CCR activated-BFS pastes was obtained when the CCR proportion was 20 %. Na2CO3 addition significantly improved the compressive strength, especially at the CCR to Na2CO3 mass ratio at 1:1.5. However, the compressive strength deterioration appeared at 28 d because of the gel structure decomposition in CCR activated-BFS pastes. The silica fume addition inhibited the structure decomposition, improved the connectivity of gel structure, favored the formation of gel, and thus suppressed the compressive strength deterioration. The study established a sustainable waste recycling from acetylene gas production by using CCR as feedstock to mitigate carbon emissions from AAMs production.