Effect Of Sucrose On The Performance Of Potassium Magnesium Phosphate Cement And Its Mechanism

Magnesium phosphate cement(MPC,Magnesium Phosphate Cement)is a new type of special cementitious material,with short setting and hardening time,high early strength,strong bond,small dry shrinkage deformation,wear resistance,and other advantages,in emergency repair,reinforcement repair,and other engineering has a relatively broad application prospect.However,due to its short setting time,rapid exothermic hydration,short operable time,etc.,can not meet the actual construction needs,and an increase in the amount of borax retarder dosing will lead to a significant decline in the early strength,late strength is affected.In addition,the performance of MPC is largely affected by the temperature,with the increase in ambient temperature,MPC coagulation speed up,and strength development may first increase and then decline.Therefore,in this study,borax sucrose binary compounding was used to prepare magnesium potassium phosphate cement(MKPC),and the effect of binary compounding on the setting and hardening,physical evolution,exothermic hydration,and microstructure of the MKPC system was systematically investigated to reveal its effect on the regulation of hydration history and early strength enhancement of MKPC,to provide new ideas for the performance regulation of MKPC system.(1)Firstly,the effects of borax and sucrose as retarders and their binary compound on the hydration and hardening properties of MKPC and the mechanism of the study were investigated.It is found that borax and sucrose have certain retarding effects on MKPC,but the best effect of binary compounding;compared with the same setting time of a single borax sample,the hydration exothermic peak of binary compounded potassium magnesium phosphate cement is significantly delayed,but the exothermic rate and total exothermic heat are greater,the 3h strength is increased by 109%,and the late strength is comparable to that of single borax sample;binary compounding has no effect on the type of hydration products,but can effectively Promote the system early and late crystal hydration products K-struvite content,and promote the development of strength;after compounding the sample microstructure densification is higher,which may be related to the amount of retarder adhesion,the difference in the ability to inhibit product growth.(2)Secondly,the effect of sucrose dosing on the MKPC system was investigated under the binary compounding method.The study shows that the ability of sucrose to retard the hydration is greater than that of borax under the binary compounding method;sucrose can significantly delay the second exothermic peak of hydration and slow down the exothermic rate,which has a significant inhibition effect on the early 3h hydration,resulting in a significant reduction of K-struvite production in the early hydration products and a corresponding increase of amorphous content in the system,with less inhibition effect on the late strength;and with the increase of sucrose dosing,the hydration products of MKPC The hydration product of MKPC transitions from well-crystallized slab-like to bloom-like and amorphous shape,and the particle size gradually becomes smaller,resulting in the formation of cavities and cracking phenomenon;combined with the work performance and mechanical strength,the best doping of borax and sucrose compound are B/M=1.5%～2.5%and S/M=4%～8%.(3)Finally,the effect of ambient temperature on the performance of MKPC under binary compounding was investigated in combination with ambient temperature.It was shown that 0～20℃ is a more suitable preparation temperature for MKPC;compared to 20℃,the decrease in temperature leads to a decrease in mortar flow of about 15%,slower early hydration rate,11%decrease in 3h strength,and 4～8MPa loss in late strength,while the increase in temperature to 40℃ leads to a shortening of MKPC setting time to 7～8min,but the second exothermic peak of hydration is significantly delayed and the transition phase transition was delayed,leading to a significant lack of strength development as well,which adversely affected the microstructure.On this basis,binary compounding is adopted to prepare potassium-magnesium phosphate cement.And the engineering application practice on the campus,to provide new ideas for the improvement of the existing ratio,will also help the actual promotion of the application of magnesium phosphate cement.In summary,this study starts by coordinating the relationship between the set time and early strength of MKPC and achieves the dual enhancement of slow setting and early strength of MKPC by binary compounding of sucrose and borax.Meanwhile,the binary compounding method can meet the performance requirements of MKPC at room temperature and lower ambient temperature,but it is difficult to guarantee working performance and strength development at a higher temperature.