Influence of ligands as chemical admixtures in the early hydration of sodium carbonate-activated blast furnace slag
Rajeswari Ramaswamy, Mirja Illikainen, Juho Yliniemi
Abstract
Insufficient strength performance at early age impedes the use of sodium carbonate (SC) activator to produce sustainable blast furnace slag-based binders. To solve this issue, this study aimed to accelerate the early hydration kinetics of SC-activated slag system using ligand admixtures: triethanolamine (TEA), triisopropanolamine (TIPA), trisodium nitrilotriacetate (NTA), tetra potassium pyrophosphate (TKPP), and 2,3-dihydroxynapthalene (DHNP). Effect of ligands were investigated by isothermal calorimetry, compressive strength determinations, workability tests, XRD analysis, TGA, and batch dissolution tests. Results showed that the effect of the ligand on the reaction mechanism and strength development depends on the ligand functional group, concentration, and dissolution and metal complexing properties. Between the investigated ligands, 25 mM of DHNP accelerated the hydration kinetics by 28 h and produced 2-day strength of 41 MPa compared to the reference of only 2 MPa. Mechanism behind this acceleration is by affecting the ion activity product (IAP) of layered double hydroxides (LDHs) or C-(A)-S-H phases and not hindering the underlying carbonate salts (gaylussite, calcite) precipitation kinetics. These findings show the potential of ligands as admixtures in binder forming reactions and holds the key to potentially develop and fine tune sustainable low-CO2 binders.