| Magnesium phosphate cement(MPC) is a kind of gas cementing material, it has rapid hardening, strong early strength, adhesive force strong, good durability and other advantages, but the cost of traditional MPC’s preparation is very high, limiting its application in engineering.This paper use the Saline Lake lithium by-product Magnesium Oxide containing boron as an alternative raw material for heavy firing Magnesium Oxide to prepare MPC. The best three optimal ratio of MPC researched by our subject group were prepared for the basic physical and mechanical performance of MPC, and study the MPC’s setting time, fluidity, compressive strength at different ages, the flexural strength and adhesion strength in optimal ratio. In addition, in the optimal ratio by repairing the concrete defects of different types and test the mechanical properties related, to repair evaluate the performance of MPC material. Finally we studied the MPC’s durability after repairing defects of concrete. The MPC material achieve Saline Lake resources recycling, also provides a theoretical basis for the use of boron containing Magnesium Oxide in project. The main achievements of this dissertation are as follows:(1) the basic mechanical properties of MPC materials in the optimal ratio. To study the setting time, fluidity, compressive strength at different ages, the flexural strength and bond strength as index, in the case of not adding boron, the systematic study of the influence law of water binder ratio, mineral admixtures, cement ratio on the performance of MPC.The results show that: the optimal ratio for preparation of low cost and high performance of MPC paste: Magnesium Oxide and phosphate molar ratio(M/P) 6:1 ratio, water cement ratio is 0.16, the compressive strength of 3h is very high, up to 36.1MPa. When adding 40% fly ash(FA) or 20% slag(SG), the 3h compressive strength reached 27.3MPa and 32.5MPa, 24.4% and 10% lower than the benchmark MPC paste. But, it still has high early strength, the compressive strength of 1d are still up to 35.5MPa and 43.6MPa. The optimal ratio of preparing mortar MPC with high performance and low cost is: M/P ratio of 6:1, cement sand ratio is 1:1, water cement ratio is 0.18, the benchmark MPC 3h mortar compressive strength reached 30.5MPa, addition of 40% FA or 20% SG, also has the advantages of quick coagulation, strong early strength and high strength property.(2) technology and performance of MPC rapid repairing material to repair concrete defects. Method was studied by using the reference MPC, adding 40%FA MPC(FAMPC) and adding 20%SG MPC(SGMPC) to repair airport pavement concrete of crack and surface spalling in different types of defect repairing materials, and through the flexural bond strength, splitting tensile bonding strength, surface tensile strength and fracture toughness to evaluate the performance of MPC. Cracks in concrete pavement were repaired by MPC paste, 3h splitting tensile bonding strength reached 1.56 MPa, up to the original matrix strength’s 61.6%, 28 d can achieve the original matrix’s 87.3%; crack repaired by FAMPC paste 3h and 28d’s splitting tensile bonding strength are slightly lower than the reference MPC paste repaired, reduces the amplitude of respectively 21.7% and 5.4%. Crack repaired by SGMPC paste after 3h and 28 d splitting tensile bonding strength than the base MPC paste repaired increased by 3.2% and 3.1%. MPC fracture toughness crack repaired after 3h reached 0.3941 2MPam-×, up to the original matrix strength‘s 56.2%, 7d and 28 d to achieve the original matrix’s 89.6%. Using 3h, 7d and 28 d fracture toughness FAMPC and SGMPC paste to repair cracks is lower than the benchmark MPC paste patch decreased, but the latter decreasing amplitude is smaller. Through repairing the surface spalling by MPC mortar, the surface‘s 3h drawing strength reached 0.34 MPa, 28 d to 0.66MPa; 3h and 28 d surface drawing strength declined by using FAMPC and SGMPC mortar to repair the concrete.however, the latter decreased less. Because of MPC and SGMPC high early strength, rapid repairing is more suitable for the surface crack and spalling. The effect of MPC repairing material in repairing cement concrete is related to the performance of MPC repairing materials and it have nothing to do with raw materials,the ratio and so on.(3)the durability of MPC concrete defects repaired. The anti seawater corrosion performance of water resistance and concrete substrate surface mortar repair of concrete surface defect repaired were studied, we selected Sodium Chloride Solution as corrosive medium. The results show that: the surface spalling of concrete by MPC mortar after repairing has good water resistance and excellent performance. After concrete repaired by the benchmark MPC mortar, its 3h surface absorption rate is 8 1 23.13 10 g s mm- - -′ ×. After the concrete surface repaired, simulated seawater erosion after 28 d, the corrosion resistance coefficient is 0.843, the corrosion resistance coefficient after repairing by FAMPC and SGMPC is 0.764 and 0.849, In simulated seawater erosion after 60 d, the diffusion coefficient of the free chloride is 6 2 19.03 10 mms- -′ ×, the diffusion coefficient of the free chloride of FAMPC mortar and SGMPC mortar after repairing are respectively 6 2 19.997 10 mms- -′ × and6 2 18.771 10 mms- -′ ×, and they decrease as the exposure time increasing, it shows that the MPC material can be used in the coastal area of the airport pavement rapid repairing.(4) discusse the repairing method of construction technology of MPC material and its application in rapid repairing airport pavement in engineering. |
