Study On The Synthesis And Properties Of Polycarboxylate Superplasticizer With Early-age Strength

Polycarboxylate superplasticizer have been widely applied in concrete engineering duing to its advantages such as high water reduction,low dosage,slump resistance,strong molecular structure and environmental protection during production.Polycarboxylate superplasticizer with early-age strength can promote the hydration of cement,shorten the setting time of cement,improve early strength of concrete,accelerate the turnover of templates of precast concrete products,increase economic benefits,and have wide application prospects,which is one of the research hotspots at home and abroad.In this paper,polycarboxylate superplasticizer with early-age strength(PA)were prepared with QX-M and AA as the main raw materials by aqueous solution free radical polymerization under the action of redox initiator system.In order to compare with PA,the common polycarboxylate superplasticizert(PN)were synthesized with 203 monomers and acrylic acid as the main raw materials.The optimum synthesis conditions of two kinds of polycarboxylate superplasticizerts through the experiment of cement paste fluidity are:n(AA):n(QX-M)=6,the raw ratio of AA(the base of AA)wasw 50%,n(AA):n(203)=5,polymerization without heat,the reaction time is 3h and when the reaction ends the heat preservation 30min.In addition,the effect of small molecule monomer AM and AMPS on the early strength of polycarboxylate superplasticizer was also investigated.The uniformity of the polycarboxylate superplasticizer was tested by the solid content test,the water reduction test and fluidity of the cement paste test.The molecular characterization and microscopic analysis of the synthesized polycarboxylate superplasticizer were carried out by gel permeation chromatography(GPC),infrared spectroscopy,X ray diffraction(XRD)and scanning electron microscope(SEM).The application performance and action mechanism of the synthesized polycarboxylate superplasticizer were studied by setting time test,mortar compressive strength test,concrete compressive strength test and hydration heat test.Based on the experiments above,the early strength mechanism of the polycarboxylate superplasticizer with early-age strength was preliminarily analyzed.The test results showed that no matter the ratio of AM and AMPS,the compressive strength of each age samples were higher than test blocks of polycarboxylate superplasticizer with early strength.The compression strength of blocks with polycarboxylate superplasticizer with early-age strength,which is mixed with different acid and ether ratio,decreases first and then increases,last decreases.When the ratio of acid to ether is 6,the compressive strength of the 1 days,3 days and 7 days of the test block reaches the maximum value.At this time,the compressive strength of 1 day of the sample mixed with polycarboxylate superplasticizer with early-age strength is increased by 23%,the compressive strength of 3 day is increased 21%,and the compressive strength of 7 day is increased by 17%.The polycarboxylate superplasticizer with early-age strength(PA)showed excellent performance in the early strength.Compared with the blank sample,the initial setting time of the sample with PA is prolonged by 59min,and the end setting time is shortened by 33min.Compared with the sample with ordinary polycarboxylate superplasticizer,the initial setting time was prolonged by 22min,and the end setting time was shortened by 27min.Therefore,the polycarboxylate superplasticizer with early-age strength can prolong the initial setting time while shortening the final setting time,which is more suitable for the construction requirements of precast concrete.The early strength mechanism analysis of polycarboxylate superplasticizer with early-age strength PA showed that:the polycarboxylate superplasticizer with early-age strength and ordinary polycarboxylate superplasticizer have a certain retarding effect on the initial hydration of cement,while the polycarboxylate superplasticizer early-age strength has a smaller delay.Our polycarboxylate superplasticizer with early-age strength not only promote the hydration of cement,but effectively control the severe hydration in the early stage of cement,which make the cement initial hydration more stable,the formation of hydration products closer,and reduce the pores of the sample,so as to improve the early strength.