A New Belitic Calcium Sulfoaluminate Cement

A new cement based on belitic calcium sulfoaluminate (BCSA) was investigated, which featured a unique combination of advantages such as fast setting time, increased tensile strength, and net positive expansion over conventional, commercial BCSA and portland cements. These advantages are achieved by combining commercially available BCSA and mixing the cement with pure, finely ground anhydrite. Mortar bars prepared using this new cement (referred to as supersulfated BCSA or SBCSA) achieve nearly seven times the expansion of conventional BCSA at 28 days. SBCSA concrete exhibits restrained and unrestrained expansions greater by nearly eight times compared with standard BCSA concrete at 28 days. The compressive and flexural strengths of SBCSA concretes are nearly 50% and up to 25% higher compared with BCSA, according to standard test methods. The use of cut-sheet continuously deformed steel fibers in the SBCSA concrete mixes at a dosage of 0.75% shows only minor improvements in terms of restrained expansions and flexural strengths. X-ray diffraction (XRD) analysis showed that the amount of ettringite increased by nearly 30%, and the hydration of belite is enhanced in SBCSA at 28 days compared with BCSA. Due to the unique combination of expansive and fast-setting characteristics, SBCSA offers a potential opportunity to improve the structural design of portland cement concrete. For example, the combination of high early strength and expansion allows the concrete to sustain expansions typically destructive in portland-based expansive cements.