Dispersant mechanisms in clays stabilized with MgO-based cement
Raphael Kuhn, Pietro Lura, Daniel Rentsch, Guillaume Habert, Ellina Bernard
Abstract
Clay-based, low-CO₂ cement-stabilized materials offer a sustainable alternative to conventional building materials. This study examines the impact of various admixtures (Na-hexametaphosphate, Na‑carbonate, Na-silicate, Na-citrate, and Na-oxalate) on the rheological behavior of poured systems containing a MgO-metakaolin cement as stabilizer. The yield stress reduction follows the order Na-hexametaphosphate > Na-silicate > Na-citrate > Na-oxalate ≥ Na‑carbonate > no admixture. The zeta potential data with the solution analysis of the suspensions show that the adsorption of admixtures and/or a change in pH leads to a more negative surface, enhancing dispersion through electrostatic repulsion. Silicate and phosphate are not found in the suspension, 29 Si ssNMR indicates that silicate precipitates and polymerizes most likely as M-S-H. The phosphates are most likely adsorbed onto particles with opening of the phosphate rings observed by 31 P NMR. The anionic charge density of adsorbed polyphosphates was calculated and linked to the decreased colloid sizes observed with increasing Na-hexametaphosphate concentration. • Stabilization induced colloidal agglomerates. • Admixtures improve the rheology of stabilized kaolinite with MgO- and CaO-based cement. • NaHMP, Na 2 CO 3 and Na-silicate disperse MgO-based cement stabilized kaolinite. • Polyphosphates hydrolyze and adsorb onto particle surfaces, inducing repulsion. • Agglomerates are avoided through NaHMP addition.