Study On The High Performance Magnesia-Phosphate Cement Based Composites

Magnesia-phosphate cement(MPC) based material is a new type of cement material, which sets and hardens through acid base reactions and physical actions. It has many advantages such as rapid hydration, high early strength and circumstance suitablity, which has very important military application value, and wide application in rapid repairing of highways and city main roads and impurity solification. Otherwise, previous researches mainly concentrate on its basic abilities, hydration mechanism, and hydration products, while few systematic and basic studies were carried out on its engineering application, especially the special abilities except the rapid hardening and early strength of MPC. The paper focuses on the problems caused by the large-scale application of MPC. The researches has been carried out under the auspice of'the technical research of military engineering rapid repairing materials'of the chief logistics of the China liberation army, and'the research of new phosphate binding materials and its application in road repairing engineering'of Chongqing science committee.Firstly, the paper focuses on the setting time and the strength of MPC, and making sure the direction and the storage workability of MPC. Aiming to meet the demands of the military logistics support and modern economic construction, this paper has a systematic study on the influential factors of MPC's fluidity, the development and improvement of its intensity at sub zero temperature and its durability to the chemical erosion, shrinkage, wearing and its freezing resistance. The research work is mainly on its macro abilities. Meanwhile, it also explains the relationship between the micromechanism and performance by micro methods such as XRD and SEM. According to researches, the following outcomes come out:1. succeeding in using industrial materials to produce MPC, and pointing out that the key to control the setting time and early strength of MPC is to modify the solution velocity of MgO, and so are retarding admixture, specific area, and the ratio between NH4H2PO4 and MgO(P/M).the main reasons that fly ash takes from the strength of MPC are the sorption, the changing of PH and the effect of impurities. 2. The effects of materials, mixing ratio, admixtures and additives on the workability and strength have been systematically researched. And the complex water reducing admixture adjusted to MPC has been worked out for the first time. And this admixture contributes much to the good workability and high strength of MPC, which is in favor of accelerating the engineering application of MPC. 3. To the rapid repairing in cold areas, the rules that how the strength of MPC at sub-zero temperature develops and the how to improve have been researched. It is found that doing pre-curing, reducing water to cement ratio and the amount of retarding admixture, and increasing temperature of mixing water can improve that. For the first time, making sure that ammonia is the good anti-freezing admixture to MPC, which has great military meaning in rapid repairing work of military engineering in cold areas. 4. The results of shrinkage and durability experiments MPC show that the shrinking ratio increases rapidly before 28 days, and slows down after 28 days. The losses of strength and weight of MPC in different erosion solutions have been studied for the first time. It is pointed out that the anti-erosion ability comes from the stability of MgNH₄PO₄·6H₂O in all the solutions. It also shows that MPC based materials have good permeability, reinforcement protection, anti-freezing ability, and interface adhesiveness and abrasion.The paper focuses on not only the basic abilities of MPC based cementious materials, but the exploring research on its probable application field, such as the probability of producing MPC with sea water and sea sand, the erosion of glass fibers in MPC materials, and the adhesiveness of MPC and the strength development contrasting with aluminate cement at sub-zero temperature. The experimental research of practice engineering application had also been done.