Study On The Effect Of Magnesium Phosphate Cement Component On Setting Time And Mechanism Analysis

Magnesium phosphate cement(MPC)is a new type of cement,which has a series of advantages,such as high strength,rapid hardening,excellent adhesion,durability and low energy consumption.However,magnesium phosphate cement has some obvious defects:(1)fast setting;(2)large hydration reaction heat,that result in the poor operating performance of the construction.At present,there are many studies on MPC setting time,but all of which are not able to reach the level of complete control.At the same time,the setting time of the formulating cement is excellent,but the strength and other performance are poor,which cannot play its biggest advantage in the actual engineering application.This paper starts from the analysis of the standard consistency and setting time of MPC,the effect of each component on the standard consistency water and setting time of MPC are been studied.The mathematical relationship between the component content and setting time is been established;Based on the good setting time and economic efficient,the macro and micro performance of MPC with the content of the fly ash is fixed for 60% and different M/P and borax dosage are been analyzed;the study of effect of different component content changes on the hydration properties can not only help explain the hydration reaction mechanism,but also can provide a theoretical basis for the effective control of the exothermic performance of MPC.The experimental results show that:(1)the consistency of MPC is very sensitive to the amount of water,the machine can make the slurry stirring more uniform,which is more scientific;(2)With the increase of M/P and the amount of fly ash,the standard consistency water of MPC will significantly increased,while the effect of borax is on the contrary;(3)the increase of M/P can significantly shorten the setting time,and when the M/P reaches 6/1,the setting time will increase,while the increase of the amount of fly ash and borax can significantly prolong the setting time.(4)there is a significant linear correlation between the component content and setting time,and the regression equation is obtained,and the fitting model of the sample: R2=0.951874,the fitting result is good;(5)The dosage of borax is fixed not more than 8%,the strength of paste get the maximum value,when M/P is 4/1;when borax content exceed 8%,the maximum strength is weakened;fixed M/P not more than 4/1,with the increase of borax content,the paste strength achieved maximum as the borax content is 8%,when M/P is more than 4/1,with the increase of borax content,the strength of the paste sample decrease gradually.the compressive strength and flexural strength of mortar has obvious advantages as M/P is 4/1 and borax content is 8%,reaching to 50 MPa and 8.5MPa,respectively;(6)compared with the sample with the minimal strength,the maximal one has more crystallization and good integrity,after reached to 7d,the growth is not obvious.(7)with the increase of M/P,the induction period and later stages will advance;with the increase of borax content,the induction period and after each stage will be backward;(8)the reaction mechanism of MPC is mainly through the function of the size of the relative content of MgO and borax,the larger amount of MgO,and smaller amount of borax,the first exothermic peak appears earlier,and the the value of the peak is more larger,at the same time,the emergence of the second exothermic peak will advance,the value of the peak is more larger,there is not even second exothermic peaks.