Synthesis of C-S-H accelerating admixture and its effect on mechanical and hydration properties of engineering cementious composites

Due to the advantageous tensile ductility and multi-slit cracking characteristics, ECC material has attracted great from scholars. It has demonstrated promising potential in various fields including spray construction, additive manufacturing, building repair, and structural reinforcement. However, it is of note that ECC materials typically contain a substantial amount of low-activity mineral admixtures, which can cause lower initial mechanical properties. To address the existing issue, a hydrated calcium silicate (CSH) suspension was synthesized and added to the ECC material as an accelerating admixture. In this study, mechanical properties and hydration products of the ECC material were explored. The results suggest that CSH effectively enhances the early compressive, flexural, and tensile strength of ECC materials, and makes a positive impact on the later mechanical properties. However, it is of importance to note that CSH increases the fracture toughness of the ECC matrix, which may generate a negative effect on the tensile ductility of ECC. Microscopic analysis indicated that CSH promotes the formation of hydration products such as hydrated calcium silicate, ettringite, and Ca(OH)2, leading to improved hydration of cement clinker. In addition, CSH enhances the bond between the fiber and ECC matrix. In general, the research findings indicate that CSH can serve as a promising accelerating admixture for preparing early-strength ECC materials. The current research is highly significant for the advancement of early-strength ECC materials and expanding the range of applications for CSH accelerating admixture.