Fundamental design of low-carbon ordinary Portland cement-calcium sulfoaluminate clinker-anhydrite blended system

Calcium sulfoaluminate (CSA) cements have lower carbon dioxide (CO2) emissions during production compared with conventional ordinary Portland cement (OPC). However, the high cost of production is a significant limi-tation of the application of CSA cements. This paper aims to improve the use efficiency of CSA clinker by adding OPC , anhydrite. The low-carbon OPC-CSA clinker-anhydrite system is expected to contain less CSA clinker while showing excellent performance. A design methodology was developed to optimize the component of the OPC-CSA clinker-anhydrite blended system. The hydration mechanism of the ternary system was investigated using isothermal conduction calorimetry, X-ray diffraction (XRD) , thermogravimetric analysis (TGA), and thermodynamic modelling was used to predict the amount of hydration products. The results showed that ettringite is the main hydration products of the OPC-CSA clinker-anhydrite system, and the addition of OPC provides portlandite for the formation of ettringite. The ternary system is characterized by rapid development of strength and low CO2 emissions. The compressive strength at 4 h and the CO2 emissions are about 10 MPa and 500 kg/t, respectively. In addition, the ternary system, composed of 27.9 wt% CSA clinker, 32.5 wt% anhydrite, and 39.6 wt% OPC has the highest compressive strength at 28 d and the lowest CO2 intensity.