C–S–H–PCE nanocomposites as hydration accelerator in calcined clay-limestone-blended low carbon cement

Abstract Recently, providing admixtures to improve the performance of the novel low-carbon-blended cement is needed to meet the requirement for environmentally friendly cements. In this study, calcium-silicate-hydrate (C–S–H) nanocomposites which are known as hydration accelerator for Portland cement were employed in such low-carbon cements. The investigation focused on the effect of polycarboxylate ether (PCE) possessing different side-chain lengths on the morphology of C–S–H nanocomposites synthesized from sodium silicate and calcium nitrate via chemical co-precipitation and on their performance (especially early strength enhancement) when applied in a calcined clay-blended cement (OPC substitution rate of 46 wt%). As observed by TEM, addition of PCE effectively controls the size of the C–S–H nanoparticles and delays the transition from C–S–H globules to foils. PCEs with short side-chain (23 EO units) exhibited the highest inhibition effect on the growth of the C–S–H nuclei, which was confirmed by particle size measurements. Additionally, incorporating such C–S–H–PCE nanocomposites into the calcined clay-blended cement (dosage 2.0 % by weight of cement) significantly improved fluidity of the cement pastes. Regarding compressive strength, pristine C–S–H produced only a minor improvement, whereas C–S–H–PCE nanocomposites yielded substantial enhancement, especially after 16 h and 1 day of curing. Remarkably, C–S–H–23PCE pronounced the strongest seeding and strength enhancing effect, owed to its particularly small particle size ( d = 21.8 ± 0.3 nm). It also significantly accelerated the hydration of the silicate phases (C 3 S and C 2 S) in this blended cement, as was evidenced by isothermal heat flow calorimetry and XRD measurements.