New insight into structural build-up modification by PCE superplasticizers during early C3A hydration

The much-complicated physical and chemical modification effects induced by PCE pose significant challenges in elucidating the role of C₃A hydration in structural build-up. The research reveals a two-stage structural build-up in C₃A-gypsum-CaCO₃ pastes, wherein varying dosages of PCE significantly influence the dynamics. The dominant driving force of structural build-up is the enhancement of colloidal interparticle bonds among bare surfaces. PCE weakens these bonds strength through steric hindrance and reduces the increment of number of these bonds due to its preferential adsorption on surfaces of ettringite formed in the solution. We identify two distinct structural build-up rates: a logarithmic growth rate (G_AFt) associated with the number of bonds between bare surfaces, and a linear growth rate (G_thix) linked to bond strength. As PCE preferentially adsorbs onto C₃A particles, the reduction in G_AFt occurs more rapidly than that of G_thix with increasing surface coverage, which causes the dominant driving force during the first stage to shift from bond number to bond strength. Consequently, the strengthening of these bonds remains the predominant factor throughout the structural development with escalating PCE dosages, explaining why, at higher PCE levels, a coherent developmental pattern is observable across both stages.