Effect of boron doping and cooling condition on polymorph and early strength of dicalcium silicate

Abstract

In order to prepare dicalcium silicate (Ca₂SiO₄, C₂S) with high hydration activity, the effects of boron doping and cooling condition on the early hydration performance of synthesized dicalcium silicate were investigated. The results showed that approximately 20 % of the α′_H-C₂S with high hydration activity existed in clinkers sintered with the addition of boric acid, which was negligibly affected by cooling conditions. In this study, even in the clinker prepared by the slow cooling method and without boron-doping, no water-nonreaction γ-phase was detected, which was mainly attributed to its smaller particle size. Clinkers prepared by the rapid cooling method exhibited smaller particle size and larger specific surface area compared with those prepared by natural cooling process. It was noteworthy that among the two controlled parameters, boron doping was the primary factor influencing the hydration process and mechanical strength. During the initial 28-day hydration process, the microscopic morphology of the hydration product underwent a sequential evolution, starting as a flocculent thin film, then transforming into a needle-like structure, and finally evolving into a short rod shape morphology. After 28 days of hydration, samples doped with boric acid or prepared by fast cooling underwent silicate chains polymerization due to the increase in hydrogen alkali concentration, leading to the formation of hydration products rich in Q²-type silicate chains. The compressive strength after curing for 28 days for samples doped with boric acid was more than twice that of the samples without boric acid doping. Clinker doped with boric acid and prepared by fast cooling method exhibited ultra-high compressive strength after 28 days of hydration, surpassing 50 MPa.