Influence of C-S-H seed and sodium sulfate on the hydration and strength of limestone calcined clay cement

Reducing the cement content in blended cements is one of the most promising ways to achieve low carbon di-oxide emission and sustainable development of cement industry. However, as the substitution level of cement increases, the early age strength of blended cements decreases significantly, limiting their application in situa-tions where sufficient early age strength is required. In the paper, the influence of 0.5% C-S-H seeds and 2% sodium sulfate (CS) on the hydration and strength of limestone calcined clay blended cement (LC3) with three different cement content were systematically studied, trying to understand the potential of this technique in improving the mechanical properties of LC3. The results showed that the addition of CS significantly enhances the early age strength of LC3, enabling the system with 54% and 38% cement content to reach strength level comparable to the pure cement system at 1 and 2 days, respectively. The enhancement is due to the accelerated reaction of alite and tricalcium aluminate as well as the pozzolanic reaction of metakaolin, which results in a lower porosity of the CS added samples compared to the reference (without adding CS). Nevertheless, CS negatively affects the development of later age strength of LC3, indicating the imperfection of this technique. Therefore, further studies are needed to improve this shortcoming.