Hydration and microstructural development of calcined clay cement paste in the presence of calcium-silicate-hydrate (C–S–H) seed

Abstract

The microstructure of Portland and calcined clay cement paste incorporating calcium-silicate-hydrate (C–S–H) seed was investigated to understand the role of nucleation seed in cement hydration, and to study the potential synergy between C–S–H seed and calcined clay. The development of compressive strength of samples with and without seed was monitored until 28 days of hydration. Microstructural analysis techniques including thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and quantitative X-ray diffraction (QXRD) were used to study the phase assemblage and composition of the cement paste specimens. Image analysis (IA) of backscattered electron (BSE) micrographs was used to determine the hydration degree of cement at the age of 1 day and 28 days. The results showed that the introduction of C–S–H seed clearly accelerated the hydration of cement and enhanced the hydration degree of cement even at the later age. The presence of seed also modified the composition of the inner products (IP) formed around the anhydrous cement grains. The combination of calcined clay and C–S–H seed enabled high replacement levels (up to 40 wt%) of cement without compromising its mechanical properties.