Preparation of C-S-H seeds from solid waste and its application as Portland cement accelerator

C-S-H seeds are expected to be a new type of accelerator to cope with the challenges of reduced strength and poor durability of concrete in the later stage caused by high dosage of accelerator. In this study, two solid wastes, rice husk ash and carbide slag, were used as silicon and calcium sources to synthesize C-S-H seeds. By screening the particle size and solid content of C-S-H seeds, the optimum synthesis condition was determined to be stirring at 25 °C for 2 h. The average particle size of synthesized C-S-H seeds approximates this to 320 nm and was mainly composed of C-S-H gel, PCE and sodium nitrate. The effects of C-S-H seeds on the properties of cement paste were studied by experiments such as fluidity, setting time, compressive strength, heat of hydration, XRD, TG and MIP. The results showed that the addition of C-S-H seeds improved the fluidity of cement paste, shortened its setting time, accelerated its early hydration, especially the NG process, and significantly improved its early compressive strength. Meanwhile, it densified the cement paste and improved the compressive strength in the later stage. The C-S-H seeds synthesized in this study not only showed excellent acceleration, but also were based on solid waste as raw material, while the reaction time was short and the equipment requirements were low.