Rapid CO₂ catalytic activation of binary cementing system of CSA and Portland cement

This study presents a novel approach to activating a binary cementing system composed of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) using an instant CO₂ catalysis. The activation led to significant and rapid strength enhancement, with the binary cement achieving a strength of 15.42 MPa immediately after activation, all within 1 min. The rapid CO₂ activation catalyzed a notable heat release, accelerating the hydration of ye'elimite to form ettringite, which is a crucial component capable of bridging gaps and imparting high initial strength. Simultaneously, the CO₂ activation catalyzed the increase in sulfur concentration, which in turn, also facilitated the formation of ettringite at an early age. Subsequent strength development was attributed to belite hydration. Apart from the rapid strength gain, employing CO₂ activation facilitated control over the pH value of the pore solution, thus enabling the manipulation of ettringite's crystal morphology to strategically enhance the microstructure. Samples with lower pH values exhibited needle-like ettringite formations, whereas samples with higher pH values yielded rod-like and column-like ettringite crystal structures. Comprehensive analytical investigations were analyzed using XRD, FTIR, TGA, ²⁷Al NMR, MIP, SEM, and ICP-OES. The present study provides a new perspective on the potential application of CSA-based cement, such as precast concrete element, instant concrete product delivery, and urgent reconstruction.