Non-adsorbing polymers and yield stress of cement paste: Effect of depletion forces

In this work, we study the effect of non-adsorbing polymers with molar masses varying over several decades in both dilute and semi-dilute regimes on the yield stress of cement and calcite pastes. In both suspensions, we measure an increase of yield stress, the magnitude of which mainly depends on the polymer concentration regimes. From interparticle force calculations, we show that non-adsorbing polymers are at the origin of interparticle attractive depletion forces. In the absence of superplasticizers, Van der Waals attractive forces are the dominant flocculating mechanism in the system and depletion forces resulting from non-adsorbing polymers arenegligible. The repulsive forces that result from superplasticizers' steric contribution increase the average interparticle distance and therefore decrease the magnitude of the attractive van der Waals forces. In this latter system, attractive depletion forces induced by non-adsorbing polymers become important and greatly contribute to the flocculation mechanism

Understanding silicate hydration from quantitative analyses of hydrating tricalcium silicates

Silicate hydration is prevalent in natural and technological processes, such as, mineral weathering, glass alteration, zeolite syntheses and cement hydration. Tricalcium silicate (Ca3SiO5), the main constituent of Portland cement, is amongst the most reactive silicates in water. Despite its widespread industrial use, the reaction of Ca3SiO5 with water to form calcium-silicate-hydrates (C-S-H) still hosts many open questions. Here, we show that solid-state nuclear magnetic resonance measurements of 29Si-enriched triclinic Ca3SiO5 enable the quantitative monitoring of the hydration process in terms of transient local molecular composition, extent of silicate hydration and polymerization. This provides insights on the relative influence of surface hydroxylation and hydrate precipitation on the hydration rate. When the rate drops, the amount of hydroxylated Ca3SiO5 decreases, thus demonstrating the partial passivation of the surface during the deceleration stage. Moreover, the relative quantities of monomers, dimers, pentamers and octamers in the C-S-H structure are measured.ISSN:2041-172