In this study, C-A-S-H nano-seeds with different Al/Si (0.05, 0.10, 0.30) and C-S-H nano-seeds (i.e. Al/Si = 0) were synthesized by co-precipitation using PCE as dispersant and then characterized for particle sizes. Metakaolin blended with 50% reference cement (MK50) was chosen as the cementitious system. Metakaolin is considered to be a low carbon, high Al content and highly potential SCM.

Fig. 12. (a) TG-DTG curves and (b) CH contents of the precipitates.

Technology Overview
C-A-S-H nano-seeds designed for low clinker cements were successfully synthesized. Optimum performances were obtained by C-A-S-H nano-seeds with Al/Si = 0.10. C-A-S-H nano-seeds promoted MK50 hydration more significantly than C-S-H nano-seeds. C-A-S-H nano-seeds can interestingly change the chemical species distribution of Al. The promoting effect of C-A-S-H nano-seeds on pozzolanic reaction has been proved.

Applications & Benefits
The C-A-S-H nano-seeds developed in this study for low clinker cement can effectively solve the problems of slow early-hydration and low early-strength, which has major significance for CO2 reduction in cement industry. In addition, these findings of the C-A-S-H nano-seeds on hydration and pozzolanic reactions provide a theoretical guidance on their engineering applications. Future studies will focus on its applications in the other low clinker cements and even alkali-activated cementitious materials. 

Abstract：
The replacement of cement clinker with supplementary cementitious materials (SCMs) is considered a very effective way of carbon reduction. However, the slow pozzolanic reaction of SCMs weakens the early strength, which hinders its application. In this study, the dedicated nucleating agents for Al-rich SCMs, C-A-S-H nano-seeds, were synthesized by co-precipitation using polycarboxylate superplasticizer (PCE) as dispersant. The performances of four nano-seeds with different Al/Si and their effects on hydration in 50% metakaolin cement (MK50) were investigated in detail. The results showed that C-A-S-H nano-seeds had a greater strengthening effect than C-S-H nano-seeds especially at early ages, and also accelerated setting, with Al/Si = 0.10 being the most significant. The Al/Si = 0.10 nano-seeds advanced the second main exothermic peak by 6.7 h, promoting the production of stratlingite and causing the highest contents of CH and bound water in hydrated samples. It was also demonstrated by 27Al NMR that C-A-S-H nano-seeds enhanced the reaction degree of metakaolin by producing more C-A-S-H than AFt or AFm. The pozzolanic activity was further explored in the reaction between metakaolin and CH. This study aims to develop an efficient strengthening agent (i.e., C-A-S-H nano-seeds) for low clinker cement, and to reveal the mechanistic difference between them and common C-S-H seeds from the perspectives of hydration and pozzolanic reactions, which is of great significance for the carbon emission reduction of cement industries and solid waste utilization.

Effect of calcium alumina silicate hydrate nano-seeds on the hydration of low clinker cement
Author：Liu Xiao, Qifeng Luo, Hui Xie, Shiyu Li, Jiale Zhang, Chunlei Xia, Yungchin Ding, Yichen Chen, Ruijun Gao, Zhongyuan Wei, Wu Zhou, Ziming Wang, Suping Cui
Year：2023
Source publication：Journal of Building Engineering Volume 66, 1 May 2023
Subfield Highest percentage：99%  Architecture # 1 / 189

https://www.sciencedirect.com/science/article/pii/S2352710223000232