Study on dynamic and static structural build-up of fresh cement paste with limestone powder based on structural kinetics model

Abstract

The structural build-up of fresh cement-based materials is of great significance to the early forming and later performance. A structural kinetics model (SKM) used to indicate the structural build-up was developed by combining a kinetic equation described by structural parameter (λ) and a relationship between yield stress (τy) and λ in the paper. SKM transforms the structuration rate (Athix) in linear Roussel model and the characteristic time (tc) in non-linear Perrot model into more specific indicators such as initial solid volume fraction (ϕ0), rate of hydration during induction period (α̇ind), and shear rate (γ.). The yield stress (τy) obtained by RHEOLAB QC rotary viscometer was explored the dynamic and static structural build-up of fresh cement paste. The yield stress of fresh cement paste (W/C = 0.4) exhibits a quasilinear pattern with rate of 0.42 Pa/s for 210 min of mixing, with rate of 0.88 Pa/s for 100 min of resting after 4 min of mixing. The static yield stress of fresh cement paste evolves from linear to non-linear patterns within 100 min of resting after beyond 30 min of mixing. The fitting results show that SKM can well fit the evolution of yield stress including linear and nonlinear phases. Comparing with the dynamic structural build-up, the effect of limestone powder on the static structural build-up of cement paste is more obvious. When the mixing process is longer than 60 min, the content of limestone powder less than 20 wt% is beneficial to the structural build-up of fresh paste. Additionally, a declined rate of cement hydration in the induction period with increasing mixing time indicates that the rising yield stress, in this case, cannot be attributed entirely to the contribution of hydration to structural build-up.