Research On The Bonding Properties Of Magnesium Phosphate Cement Based Materials

The concrete structures are widely used under various circumstances, and sometimes degradation occurs thus need to be repaired. Phosphate cementious materials are bonded from a certain ratio of metal oxide, soluble phosphate (MH2PO4, M=NH4or K) and retarding agent. The main cementious hydration product of the new inorganic cementitious material is phosphate cement. This material shows a favorable performance of volume stability and durability, besides, it can set in a short time and harden quickly. These properties make its possible of being an excellent and promising repairing material with Portland cement. This paper investigates the characteristics of phosphate cement based material bond from dead burnt MgO and mono-potassium phosphate with retarding composite. The work and main conclusions of the research are listed as follows:The hydration properties of magnesium phosphate cement have been studied. The result shows the pH value of the magnesium phosphate cement is relative lower than that of Portland cement and its between6-10. The hydration reaction rate is much higher and it releases a large of heat which allows it set and harden in negative temperature. Adding the composite retarder into the hydration system can suppress the hydration heat flow and lower the reaction rate, leading to prolong the setting time.The effect of mineral admixtures on the properties of magnesium phosphate cement has been investigated and it has been found that the admixtures can improve the fluidity of cement paste. The fly ash can prolong the setting time moderately, while the early strength is reduced and the strength in later age is improved. On the contrary, the addition of slag and cement shortens setting time but improves the early strength of magnesium phosphate cement paste. The strength of the specimen in natural curing condition is the highest compared to the paste curing in high/low temperature and water condition.Through the research on the sand to binder ratio and kinds of aggregates on the fluidity and strength of magnesium phosphate cement, with the analysis of interfacial transition zone, the favorable sand to binder ratio is1:1. With this ratio, the fluidity can meet the requirements and the compressive strength is the highest. The crushed gravel is favorable to act as the fine aggregate of magnesium phosphate cement. The magnesium phosphate cement is comparable to the Portland cement. This study investigate the influence of different strength grades of repairing material and Portland cement matrix, the treatment and moisture condition of interface and the curing conditions on the bonding properties. The reason of good bonding strength is divided into two parts, which is physical and chemical, i.e., the good volume stability and chemical activity of magnesium phosphate cement.The study on the bonding properties between different shape of steel fibers with different matrix also have been carried out. Analysis from the load-displacement curves shows that the shape of steel fiber has significant influence on the bonding strength. Due to the anchoring effect, the specimens reinforced by deformed steel fiber demonstrate much higher bonding strength and more pullout energy. Adding the mineral admixtures, such as lime powder and slag, to the matrix have positive effect on the pullout behavior as the admixture is denser and partial size is smaller.