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

10 The performance of superplasticisers in alkali-activated materials (AAMs) remains poorly 11 understood, limiting the wider adoption of low-carbon cement technologies. This study 12 examines the behaviour of lignosulfonate- (LS), naphthalene- (NP), and polycarboxylate ether 13 (PCE)-based superplasticisers in NaOH/Na₂SiO₃ -activated systems with ground granulated 14 blast furnace slag (GGBFS) and metakaolin (MK). The adsorption phenomena and polymer 15 conformation were investigated by combining mini-slump tests (flow behaviour), ATR-FTIR 16 (chemical interactions), DLS (polymer size), TEM-EDX (polymer conformation), zeta 17 potential measurements (surface charge), and total organic carbon analysis (polymer uptake). 18 Results show that in both GGBFS and MK systems, high alkalinity alters polymer ionisation, 19 suppresses electrostatic interactions, reduces superplasticiser solubility, and drives polymer 20 agglomeration. In GGBFS systems, Ca²⁺ enhances superplasticiser adsorption to solid particles. 21 LS-based superplasticisers demonstrated superior alkaline resistance, slump retention, and 22 adsorption capacity relative to NP and PCE. These findings provide new mechanistic insights 23 to guide the design of high-performance superplasticisers tailored for low-carbon AAM 24 systems. 25