The influence of calcium sulphoaluminate on the properties of low-cost magnesium phosphate cement mortars

Magnesium phosphate cement (MPC) exhibited many excellent performances, however, the high cost of raw materials of MPC limited its application in construction areas. Calcined dolomite powders containing CaO could not be applied in MPC production. The dolomite-bauxite-gypsum powders after calcination were used to replace dead burned MgO and the free-CaO in dolomite was transferred into calcium sulphoaluminate (ye'elemite, C4A3 S). This study intends to investigate the performance of the low-cost MPC mortars prepared with calcined dolomite-bauxitegypsum powders containing C4A3 S. The setting times, fluidities, hydration temperature developments, compressive strength developments and volume changes of MPC mortars with C4A3 S were investigated. Furthermore, the differences in compressive strength, flexural strength and bond strength development of MPC mortars with C4A3 S in air and water curing were compared. Phase developments, microstructures and pore diameter distribution of MPC mortars with ye'elemite were also investigated. MPC mortars prepared with the calcined dolomite powders containing 51% C4A3 S and 26% MgO showed a setting time of 27 min, free-fluidity of 150 mm, 3-h compressive strength of 41 MPa, 7-d compressive strength of 58 MPa and 180-d compressive strength of 74 MPa. C4A3 S in MPC mortars could form some amorphous hydration products and its hydration may be promoted in water curing. The new amorphous phases may have filling and cementitious effects, leading to denser structures and higher strengths.