Comparing polycarboxylate and -phosphate ethers as stabilizers for C-S-H based cement accelerators

Polymer-stabilized calcium silicate hydrate (C S H) nanoseed suspensions accelerate cement hydration and support the early strength of low-clinker binders. Their performance is governed by two largely independent parameters: the chemical nature of the comb polymer’s anionic anchor, and the concentration of free, non-adsorbed polymer remaining in suspension. By evaluating carboxylate- and phosphate-based copolymers, we demonstrate that phosphate anchors produce smaller, more stable primary C S H particles and adsorb more completely. Within the carboxylate family, longer polymer side chains reinforce these effects through stronger steric stabilization. Crucially, we show that high free-polymer concentrations retard the silicate reaction and perturb early aluminate hydration by enhancing ettringite formation. The independence of this free-polymer parameter is confirmed by a controlled dosage reduction, which converts a strong retarder into an accelerator without altering the seed chemistry. By separating anchor chemistry and free-polymer concentration as independent design parameters, this study reframes the rational design of polymer-stabilized C S H nanoseed suspensions for acceleration performance and dosage efficiency.