Influence of gypsum on composition and performance of hardened paste of belite-barium

Belite-barium calcium sulphoaluminate cement is a new kind of binding material. The mineral phases of the cement clinker are mainly C₃S, C₂S, C₃A, C₄AF and C_2·75B_1·25A₃S. The influence of gypsum on the composition and performances of hardened cement paste was studied. The composition and structure of hardened cement paste were analysed by means of X-ray diffraction and scanning electron microscopy. The results show that the compressive strengths of belite-barium calcium sulphoaluminate cement with 10% gypsum addition at 3, 7, 28 and 90 days curing age were 45·0, 61·9, 82·1 and 85·6 MPa. The hydration products of the cement were mainly AFt, Ca(OH)₂ and C–S–H gel. With increasing addition of gypsum, the amount of AFt and C–S–H gel increased and the amount of Ca(OH)₂ decreased gradually at later hydration age. In comparison with belite cement, the hardened paste of belite-barium calcium sulphoaluminate cement has more C–S–H gel and a denser structure.