Research And Application Of Modified Magnesium Phosphate Cement-based Materials

Nowadays,maintenance of concrete structure reinforcement industry is developing rapidly,among which the repair of magnesium phosphate cement based materials has been more and more attention in the field of maintenance.Compared with the abroad study of magnesium phosphate cement,we are still in the preliminary stage.Although in recent years for its hydration mechanism has a theory research,but less in the practical engineering application.This article for magnesium phosphate cement was applied to practical engineering,the use of admixture on the modification research,on the one hand to improve the performance of magnesium phosphate cement,on the other hand also reduce the cost of the engineering application provides a train of thought for the actual promotion.This paper studied the water/cement ratio,the proportion of phosphate and magnesium oxide,dosage of retarder,the ratio of cementing materials and sand on the influence of magnesium phosphate cement paste or mortar compressive strength,fluidity,setting time.By controlling variable method to choose the best proportion,complete magnesium phosphate cement mortar mix proportion design of preliminary;Further use of three kinds of mineral admixture of fly ash and steel slag powder,iron ore tail modification study on magnesium phosphate cement mortar,setting time and compressive strength as reference indicators,identified three kinds of mineral admixtures with the result of the influence of magnesium phosphate cement mortar and the best dosage;Steel slag powder is chosen as the final modification of magnesium phosphate cement mortar admixture on seawater strength,bond strength,dry shrinkage,salt resistant frozen engineering application research,come to a conclusion as follows:(1)For the repair of magnesium phosphate cement mortar mix proportion design,water/cement ratio in the best range between 0.12 and 0.16;Choose a quarter best on the proportion of phosphate and magnesium oxide;Borax content at about 20%,adjusted according to the actual construction situation;Choice of considering the cost of engineering application,the ratio of cementing materials and sand should be 1/1.(2)Mixed with fly ash,can lead to setting time increase;Less than 30% of fly ash mixed is good for magnesium phosphate cement late strength development.(3)The steel slag powder mixed with can make the modified magnesium phosphate cement mortar setting time,less than 20% of steel slag powder adding magnesium phosphate cement strength of late development.(4)The adding of iron ore tail of the benefits of magnesium phosphate cement is not particularly big.(5)The use of steel slag powder modified improve water resistance of magnesium phosphate cement mortar,with 20% steel slag powder repair mortar modified magnesium phosphate cement setting time can be controlled at about 30 min;1 d intensity over 9 MPa;The mortar in the seawater environment at room temperature curing 28 days,the compressive strength,flexural strength loss rate is about 5%.(6)Steel slag powder modified magnesium phosphate cement mortar caking property is very good,28 d bond strength can reach about 3 MPa.(7)Steel slag powder modified magnesium phosphate cement mortar shrinkage rate is small,the dry shrinkage of the 28 d rate only-3.52×10-4.(8)Steel slag powder modified magnesium phosphate cement mortar salt and frozen sex resistant is good,after 25 times freeze-thaw cycle strength loss rate is only 1.4%,and the intensity of 100 times of freeze-thaw cycle loss rate is only 3.5%.