Dissolution-precipitation reactions of blast furnace slag and sodium carbonate with 2,3-dihydroxynaphthalene

Chemical admixtures are needed to enhance the reactivity of the industrial waste by-products to expand their utilization in the cement and concrete industry to create low CO2 sustainable binders. One such chemical admixture which is a complexing ligand (2,3-dihydroxynaphthalene) has been shown to accelerate the hydration kinetics and enhance the mechanical strength (from 2 MPa to 40 MPa) of sodium carbonate-activated blast furnace slag binder. This study aims to understand the working mechanism of 2,3-dihydroxy naphthalene as an accelerator and the formation of the micro- and nano-surface precipitates for sodium carbonate-activated slag through batch dissolution experiments. Both solution (pH evolution, element concentration, organic and inorganic carbon content) and solid (identification and chemical composition of the phases) chemistry were investigated using various analytic and microscopic techniques. The results showed that the ligand significantly increased the extent of the slag dissolution, which affected the solution chemistry, consequently accelerating the precipitation kinetics. Further, the ligand affected the amount of precipitation (calcite and gaylussite) and the modification of Mg-Al-Si-Na-Ti-rich nano- and micro-sized precipitate morphology in the ligand system compared to the reference system. This work provides important information on ligand-carbonate-slag reactions, which pave the way for developing new chemical admixtures for a sustainable future.