Study On The Properties Of Mineral Admixture And Portland Cement Modified Magnesium Phosphate Cement

With the rapid development of social economy, the concrete is more and more widely used in the construction of high buildings and large mansions, airports, factories, ports, highways, bridges and so on. However, under the influence of various factors, some concrete buildings have been seriously damaged, can not work properly. In order not to affect normal use of the building, in order not to hinder the rapid development of social economy, these damaged buildings need to be repaired as early as possible, and restore its use function. Among the various types of repair materials, inorganic repair materials are considered to be the most suitable materials for the repair of concrete structures with good adaptability and economy. Because of the performance of fast setting, high early strength, high bonding strength with old concrete, small volume deformation, wear-resistance and freezing resistance performance, magnesium phosphate cement(MPC) is widely used in the repair of concrete structures. But for the disadvantage of fast seetting, poor water resistance, high price, MPC can not be widely used. In view of the above problems, this paper aims to improve the performance of magnesium phosphate cement by adding the admixture and the external admixture on the basis of previous studies.Firstly, The influences of the single doped amount of fly ash, slag and Portland cement on the paste setting time, mortar compressive strength and water resistance of MPC were studied in this paper; Secondly, on the basis of single doped, the influences of the complex doped amount of Portland cement-fly ash and Portland cement-slag on paste setting time, mortar compressive strength and water resistance of MPC were studied; Finally, the hydration products of MPC with fly ash, slag, Portland cement by X-ray were analyzed. The experimental results are as follow:(1)With the increase of fly ash, slag, Portland cement-fly ash and Portland cement-slag content, the setting time of MPC pastes presented the trend of decreasing, but with the increase of Portland cement content, the setting time of MPC pastes presented the trend of increasing slowly firstly and then decreasing sharply.(2)With the increase of fly ash, slag, Portland cement, Portland cement-fly ash and Portland cement-slag content, the compressive strength of MPC mortars presented the trend of increasing firstly and then decreasing.(3)The order of contribution of fly ash, slag, Portland cement to the compressive strength of MPC mortar is: slag > fly ash > Portland cement, but the order of contribution of Portland cement-fly ash and Portland cement-slag to the compressive strength of MPC mortar is: Portland cement-slag > Portland cement-fly ash.(4) Fly ash, Portland cement, Portland cement-fly ash and Portland cement-slag improved the water resistance of MPC, but the slag decreased the water resistance of MPC.