Quantitative hydration analysis and mechanical-microstructural properties of cement with hollow glass microspheres

Hollow glass microspheres (HGMs) have been used as cement substitutes to produce lightweight cementitous materials, but the effect on cement hydration is still unclear. This study aimed to study the effect on the hydration and mechanical-microstructural properties of HGMs partially replacing cement (5 wt%, 10 wt% and 15 wt%), combined with experimental and thermodynamic modelling. Life cycle assessment (LCA) was also included in the study. X-ray diffraction (XRD), thermogravimetric (TG) and nuclear magnetic resonance (NMR) were used to quantify the hydration kinetics of cement. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were utilized to evaluate the microstructure. The results showed that the hydration of the cement increased from 79.44 % (H0) to 89.20 % (H15), and the mean chain length of C-S-H increased from 5.32 to 6.32. Thermodynamic modelling showed that the mass of C-S-H dominated the compressive strength of the samples, with a linear relationship (R² = 0.95). The deficiency of C-S-H led to increased harmful pore volume and reduced paste thickness (from 75.3 μm to 18.46 μm) surrounding the HGMs. The LCA results showed that in the “cradle-to-gate” stage, using HGMs did not reduce energy consumption but showed better environmental friendliness in the other categories.