A study on improvement of early - age strength of super sulfated cement using phosphogypsum

Supersulphated cement (SSC) is a newly developed non-burned cementitious material. It is a kind of environmentally-friendly cementitious material due to its energy-saving, low-carbon emission, and waste-utilization. Compared with ordinary Portland cement (PC), SSC has many advantages such as low hydration heat, excellent property of resistance to sulfate, using less clinker but more gypsum. However, the setting time of this binder is quite long, so the strength development is slow at early age. The aim of this paper is to improve the early-age strength for SSC binder samples with 30% Phosphogypsum, 60% ground-granulated blast-furnace slag, the rests are cement or lime and activator Na2SO4 with different content. The research results show that compressive strength at 3-day age can be improved almost twice. Microstructural analysis by infrared spectroscopy revealed that ettringite formed earlier in the case of using activators and improved the microstructure and strength at early age of the binder. However, the strength of the SSC at the later age was reduced when compared to the control sample without activator. The results also show that the optimum content of activator Na2SO4 for improving SSC strength at early age is 1%.