Experimental Study On Magnesium Phosphate Cement With High Early Strength And Its Applications

Magnesium phosphate cement (MPC) is a new rapid setting material with high early strength, which belongs to the chemically bonded phosphate ceramics. Owning to its excellent performance, such as fast setting time, high early stength, high volume-stability, strong bonding strenth, excellent durability, high deicer-frost resistance, the MPC materials have been attracting more attention in recent years. Now, study of MPC has been becoming the hot research topic because of its superiority properties in recycling wastes, as the constructing a sustainable and economical society becomes more important.In this paper, through analyzing the mineral phases, setting time and the discipline of strength development, the influence factor on the properties of MPC was studied. Based on the experimental results, the raw materials to make MPC were discussed and the calcined MgO, KH₂PO₄ and admixture (borax) were selected. Through orthogonal design method, the influence of molar ratio of MgO and KH₂PO₄, water-cement ratio and borax content on the performance of MPC were analysised and the MPC with compressive strength of more than 40MPa at the age of 3h was made. In addition, the content of high calclium fly ash on compressive strength of MPC has been studied, and the optimum content of high calclium fly ash was got.Based on the micro-testing, such as X-ray diffraction and SEM, the hydration mechanism of MPC was studied. The testing results of X-ray diffraction indicated that major hydration products of MPC were MKP and some unreacted MgO. The pictures of SEM showed that the hydrates MKP was in the form of needles, and they crossed each other and connected into a network structure, which makes the microstructure fully dense. Furthermore, the reaction mechanism of these magnesium phosphate ceramics is also theoretical analyzed by the chemical reaction and thermodynamic principles.In addition, the main properties of MPC composites, such as pH, strength, drying shrinkage, corrosion resisitance, etc., were investigated. Experimental results indicate that, compared with Portland cement, some performances of MPC composites are excellent, including: (1) neutral pH, (2) high strength with rapid development, (3) low drying shrinkage (volume stability), (4) good compatibility and high bond strength with old concrete, (5) resistance to acid alkali and salt. Furthermore, the applications of MPC composites were discussed. The addition of silica fumes and polypropylene fiber in MPC composites to improve its performances were studied by experiment, respectilly. Also, MPC was used to consolidate clay to make block for building.