Adsorption phenomena and surface interactions between superplasticisers and ground blast furnace slag and metakaolin particles in alkali solutions: Implications for low-carbon cements

The performance of superplasticisers in alkali-activated materials (AAMs) remains poorly understood, limiting the wider adoption of low-carbon cement technologies. This study examines the behaviour of lignosulfonate- (LS), naphthalene- (NP), and polycarboxylate ether (PCE)-based superplasticisers in NaOH/Na₂SiO₃-activated systems with ground granulated blast furnace slag (GGBFS) and metakaolin (MK). The adsorption phenomena and polymer conformation were investigated by combining mini-slump tests (flow behaviour), ATR-FTIR (chemical interactions), DLS (polymer size), TEM-EDX (polymer conformation), zeta potential measurements (surface charge), and total organic carbon analysis (polymer uptake). Results show that in both GGBFS and MK systems, high alkalinity alters polymer ionisation, suppresses electrostatic interactions, reduces superplasticiser solubility, and drives polymer agglomeration. In GGBFS systems, Ca2+ enhances superplasticiser adsorption to solid particles. LS-based superplasticisers demonstrated superior alkaline resistance, slump retention, and adsorption capacity relative to NP and PCE. These findings provide new mechanistic insights to guide the design of high-performance superplasticisers tailored for low-carbon AAM systems.