Water Stability Of Magnesium Phosphate Cement-based Materials And Its Influencing Factors

Magnesium phosphate cement is usually composed of acid phosphate,dead-burned magnesium oxide,retarder and modified components.It has excellent properties such as rapid early strength development,good volume stability and high bonding strength.Municipal main roads and other rapid repair projects that have strict requirements on time have a wide range of applications,and they are also the first choice materials in the repair and repair of military projects.However,with the extensive research and application of magnesium phosphate cement,the water resistance of magnesium phosphate cement has received more and more attention.The increase shrinks,and the magnesium phosphate cement is considered water-resistant.However,there are also studies found that the strength of magnesium phosphate cement-based materials in water curing,although lower than dry air curing,can still maintain strength growth or maintain stability.Whether magnesium phosphate cement-based materials can be used in the water environment for a long time and maintain stable performance is a problem that needs to be clarified and resolved.The article studies the water stability performance of magnesium phosphate cementbased materials,and according to the existing research mechanism,by reducing the unreacted phosphate in the material and improving the early reaction degree of the hydration system,exploring the factors that affect the water stability of magnesium phosphate cement-based materials.First,the concept of water stability of magnesium phosphate cement-based materials is clarified.The water stability of magnesium phosphate cement-based materials refers to the ability of the material to maintain stable performance or development under water environment.The strength development of the material in water should be used as the main evaluation index to evaluate the performance stability of the material in water,supplemented by the softening coefficient or strength retention rate to evaluate the performance gap of the material under air and water curing.Secondly,Tests on commercially available magnesium phosphate cement products found that the specimens cured in fresh water and sea-water can maintain a stable development of strength,and the strength retention rates at 180 days of age are 95.13%and 102.26%,indicating magnesium phosphate cement The base material itself does not have the problem of poor stability in water.Further,using products’ raw materials,we explored the factors influencing the water stability of magnesium phosphate cement-based materials from the two aspects of raw materials and mix ratios.Among them,the influence of phosphorus-magnesium ratio,water-binder ratio,phosphate type and phosphate quality on the water stability of magnesium phosphate cement-based materials is more significant.When P / M = 1/3,the strength of the test piece was the highest under the conditions of air culture and water culture,and the retention rate of intensity remained above 90% at age of 180.The choice of water-binder ratio needs to consider the theoretical water requirement of the hydration system(W/ADP=0.782,W/KDP=0.661)and the working performance of the slurry.Too high or too low water-binder ratio is not conducive to the development of underwater performance of magnesium phosphate cement-based materials.The amount of borax has little effect on water stability.The water stability of the ammonium magnesium phosphate cement system is superior to the potassium magnesium phosphate cement system,and the water stability of the magnesium phosphate cement prepared with high-quality phosphate is betterFinally,the effects of the slurry stirring time of magnesium phosphate cement during construction and the air pre-curing time after hardening on the water stability of magnesium phosphate cement-based materials were explored.The results show that in actual engineering,in order to furthering improve the stability and development speed of magnesium phosphate cement-based materials in water environment,the slurry mixing time can be appropriately extended within the range of 3 to 6 minutes.The pre-curing time in the air after hardening of the material should be extended as much as possible.