Effects of mixture design parameters on the properties of belitic calcium sulfoaluminate concrete

Belitic calcium sulfoaluminate (BCSA) cement has well-established advantages such as a fast setting time, fast strength gain, long-term strength, shrinkage and sustainability. BCSA cement reaches an initial set in about 15 min at room temperature and can reach compressive strengths of over 27 MPa in about 2 h. While it can be mixed in a similar fashion to Portland cement (PC), a set retarder (such as citric acid) is usually required to achieve adequate working time and the design of mixtures differs slightly from PC designs. This paper provides guidance on establishing mix design criteria for BCSA cement. Slump and compressive strength studies measurements were taken for varying mixture proportions with strengths measured up to 1 year of hydration. For BCSA concrete mixtures, a relationship between water content and slump was established. Citric acid was found to increase the slump, especially at lower water contents. A relationship between setting time and citric acid dosage was proposed on the basis of mortar penetrometer and Vicat needle tests. X-ray diffraction analysis was also conducted on BCSA cement pastes with different water/cement (w/c) ratios. Crystalline structure growth was found to be directly related to the w/c ratio and inversely proportional to compressive strength.