Poly(ethylene oxide)-grafted lignosulfonate superplasticisers: improving performance by increasing steric interactions

Abstract

Lignosulfonates are a leading water reducer for cement and concrete, but their mechanism of controlling aggregation is primarily electrostatic. In contrast, polycarboxylate ether superplasticisers function via steric interactions and impart high degrees of fluidity at low concentrations. In this study, it is demonstrated that grafting lignosulfonate with mono-functional, low molecular weight poly(ethylene oxide) significantly enhances performance in type I/II Portland cement pastes as well as in models of mortar. Polymer grafting did not affect the zeta potential but altered the adsorption profile onto Portland cement, with poly(ethylene oxide)-grafted lignosulfonate reaching saturation rather than forming a multi-layer structure as observed with lignosulfonates. The grafted lignosulfonates increased slump values by up to 30% compared with non-grafted lignosulfonate while allowing for significant reductions in water content. Poly(ethylene oxide)-grafted lignosulfonate represents a hybrid superplasticiser that offers the advantages of both lignosulfonates and polycarboxylate ethers.