Impact of C–S–H seeds on cementitious hydration kinetics: New insights on porosity and microstructure

In the past decade, several studies have demonstrated C-S-H seeds to be a new series of concrete admixtures which can accelerate hydration kinetics and improve strength. However, data on microstructural changes in the presence of these seeds is limited. In this study, we systematically investigate the impact of a range of C-S-H seed dosages (0–3.5%). Broadly, on one hand, we find that increasing C-S-H seed dosage decreased the setting time and porosity. On the other hand, the addition of seeds increased the compressive strength via the precipitation of additional hydration products. Specifically, in 3-day-old mixtures, at the highest seed dosages (3.0–3.5%): a) porosity decreased from 15.5% to 10.9%, and b) compressive strength increased from 20.7 MPa (3004 psi) to 31.3 MPa (4532 psi). Finally, and most importantly, our laser profilometry experiments indicate that two key surface roughness parameters S_pc (peak curvature) and S_pd (peak density) strongly correlate to the mixes' open porosity, providing evidence for microstructural refinement.