Multi-scale synchrotron X-ray scattering studies on thermo-induced changes in structural and mechanical properties of CSH/PCE composites

The influence of thermal deformation in lattice structure and inter-atomic distance on the residual mechanical properties of calcium silicate hydrate (CSH)/polycarboxylate superplasticizer (PCE) composites at varying Ca/Si ratios remains ambiguous. Here, correlations between the multiscale structural transformation and mechanical properties of CSH/PCE composites with Ca/Si ratios ranging of 0.6–1.0 are investigated using ex situ small-angle X-ray scattering (q = 0.005–2.7 Å⁻¹) and in situ loading wide-angle X-ray scattering (q = 1–18.5 Å⁻¹). The temperature-driven CSH/PCE composite transformation stages were divided into dehydration (105–200 °C) and decomposition (300–500 °C) stages. Increased pore pressure, attributed to the well-packed particles in composites with low Ca/Si ratios and high PCE contents, induced significant thermal deterioration of residual elastic modulus. Swollen CSH building blocks with adsorbed PCE molecules at low Ca/Si ratios exhibited notable shrinkage after exposure to high temperatures, whereas the particle-to-particle distance decreased with constant radii of CSH blocks at high Ca/Si ratios.