Effect of Calcium Sulfoaluminate Cement on Properties of Formwork Shell Concrete with Good Toughness

A concrete formwork shell is a low-carbon tough prefabricated composite formwork that does not require disassembly. Good workability is the premise of its forming compactness, and good mechanical properties, toughness, and deformation resistance are the guarantee of its engineering application. The composition of the cementitious material is a key factor influencing the performance of formwork shell concrete (FSC). In the paper, FSC was prepared by mixing ordinary portland cement (OPC) and calcium sulfoaluminate cement (CSA). The properties of plastic state, mechanical properties, flexural toughness, and deformation resistance were studied. The hydration products and microstructure of FSC was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the early mechanical properties and flexural toughness of FSC are greatly improved by high CSA content, whereas the late mechanical properties and flexural toughness are improved by low CSA content. The deformation resistance of FSC at both early and late stages is improved by high CSA content. The main hydration products of the composite cementitious system are ettringite (AFt), monosulfate (AFm), portlandite (CH), C-S-H gel, and AH3 gel. An increase in CSA content and hydration age promotes the formation of AFt. When CSA is 40%–50% and the age exceeds 7 days, more AFm is formed. The crystal structure of lamellar AFm is loose, which is not conducive to the development of mechanical properties and flexural toughness of FSC. When CSA is 10%, the workability, mechanical property, toughness, and deformation resistance of FSC at early and late stages are good.