New insights into dynamic evolution of colloidal network structure during early-age hardening of cementitious materials

The evolution of microstructure in cementitious materials during their transition from fluid to solid state plays a critical role in determining their ultimate mechanical strength and overall performance. This hydration stage primarily involves a dynamic densification process occurring within the colloidal network. However, the field of cement-based materials currently lacks a comprehensive theoretical framework and associated parameters capable of effectively characterizing the specific structural regions within this network. In this study, we propose an Improved Particle Linkage (IPL) theory for describing the strength, types, and quantities of particle linkages within colloidal network. The IPL theory classifies the internal network structure into three distinct regions, namely the α_weak, β_strong and γ_inherent. The γ_inherent and β_strong region predominantly influence the strength of the colloidal network at the initial and later hydration stages, respectively, whereas the α_weak region contributes steadily to the network strength across all hydration stages. Furthermore, the progressive intensification of the β_strong region during hydration is identified as the principal driving factor for microstructural evolution, leading to a critical transition point in fresh properties. Additionally, a novel parameter, termed the network hydration index (ξ), to quantitatively characterize the overall degree of hydration within the colloidal network is establishment.