Effect of synergistic action of C-S-H seeds and liquid accelerator on early hydration of Portland cement

At present, the requirements for liquid accelerators in shotcrete construction were getting more stringent. A major problem was the poor early-age strength of the mortar, caused by the limited levels of hydration products . Recent research showed that introducing C-S-H seeds enriched hydration products and enhanced early-age strength without affecting later-age strength in cement. However, preparing C-S-H seeds was costly and difficult to apply widely. Thus, fly ash (FA) and carbide slag (CS) were used to synthesize C-S-H seeds via hydrothermal methods , which were combined with liquid accelerators to promote the early age strength development of cement and decrease the costs of C-S-H seeds. The research demonstrated that 1 % C-S-H seeds and 7 % liquid accelerator make compressive strengths of 9.73 MPa and 44.39 MPa at 1 d and 28 d, respectively. The analysis showed that the C-S-H seeds promoted the formation of ettringite (AFt) and its uniform dispersion in the cement matrix . They also facilitated tricalcium silicate (C 3 S) hydration, which not only enriched the hydration products but also reduced porosity and significantly enhanced the compressive strength of the mortar. Cost estimates indicated that the synergistic use of C-S-H seeds with a liquid accelerator could save about 8.96 CNY/m 3 construction, providing significant economic benefits for engineering applications . • Successful preparation of C-S-H seeds is achieved using a dual solid waste system (fly ash and carbide slag) under hydrothermal conditions. • The synergistic use of 1 % C-S-H seeds with 7 % liquid accelerator significantly enhances the development of mortar compressive strength, particularly in the early stages. • The cost estimation results demonstrated that the use of C-S-H seeds and liquid accelerator reduced costs by 8.96 CNY/m³ , while maintaining mortar performance, leading to a significant decrease in project expenses.