Innovative valorization of basic oxygen furnace slag in gypsum-based sustainable building blocks

Abstract

Incorporating supplementary cementitious materials (SCMs) like ground granulated blast furnace slag (GGBS) into gypsum-based blocks enhances their compressive strength. However, over-reliance on GGBS is a concern due to its extensive use in the construction industry. To address this, basic oxygen furnace slag (BOFS) was introduced as a substitute for GGBS in producing gypsum-based blocks. Three mixture proportions of gypsum-based blocks were prepared with varying hemihydrate building gypsum contents and combined with 5 % ordinary Portland cement as an alkaline activator. The remaining SCM content, initially GGBS, was progressively replaced with BOFS. The results indicated that the low reactivity of BOFS, lower Al³⁺ content (5.50 %), and the presence of C₁₂A₇ led to decreased early compressive strength with increasing BOFS replacement. Nevertheless, the compressive strength development improved due to the formation of secondary hydration products. Microscopic analysis revealed that increased BOFS content enhanced the alkalinity and water content of the reaction system, thus promoting hydration reactions. In addition, the increase in BOFS content changed the morphology of C-S-H from an amorphous form to a fibrous-like structure with superior mechanical properties. In summary, gypsum-based blocks with 20 % BOFS used solely as the SCM attained a satisfactory 28-day compressive strength, which was 24 % higher than the counterpart specimens using GGBS as the SCM. These findings demonstrate the potential of BOFS as a novel SCM in gypsum-based materials.