Early age cohesion of building materials via SAOS

Abstract

The worldwide use of concrete is linked to its excellent solid properties, developed during the hardening process and triggered by the precipitation of calcium silicate hydrate C-S-H. The cohesion developed during the early hydration defines the fresh properties of the cement paste and is extremely important for the final solid ones. Despite the many studies on cement cohesion, direct measurements during early age hydration are scarce (Lesko et al. 2001), and C-S-H precipitation and morphology are studied at longer timescales (Van Damme et al. 2013). Small oscillatory rheology (SAOS) has proved a promising method to measure the nature of interactions between particles of inorganic materials (Liberto et al. 2019). In order to further understand the early cohesion development in cementitious pastes, the fresh and cohesive properties of a model paste of tricalcium silicate (C3S) and a pure C-S-H gel are measured by SAOS. These measurements show that the C-S-H gel and the C3S paste, despite the common viscoelastic behavior, have an intrinsic different nature in terms of elasticity (i.e., G'(γ)) and reactivity (i.e., G'(t)). In particular, the temporal evolution of the elastic modulus (G') shows the reactive nature of the C3S paste (due to C-S-H nanoparticle formation in a strong ionic environment), in contrast with the non-reactive one of the C-S-H gel. We strongly believe that these results are related to the different ionic composition of the interstitial solution in the two samples, leading to a different material structure. In this context, the X-ray total scattering data presented here provides structural information at the atomic- and nanoscale to further this analysis.