Study On The Synthesis Technology Of Polycarboxylate Superplasticizer At Normal Temperature

With the rapid development of domestic construction industry,the polycarboxylate superplasticizer has become the main variety of concrete water reducing agent.Compared with high temperature synthetic the polycarboxylate superplasticizer,the synthesis process of the polycarboxylate superplasticizer at room temperature has lower energy consumption、faster reaction rate、simple equipment and other advantages.So the polycarboxylate superplasticizer have been widely paid attention to and become the main research direction of production.In this paper,the effects of different molecular weight and different kinds of comonomer on the properties of the polycarboxylate superplasticizer in room temperature process are discussed in detail.The fluidity of the initial、1 h、2 h cement paste,on cement hydration rate and the strength of cement paste at 1 d and 3 d were investigated.And the infrared spectra of the functional groups of water reducer were test.As indicated by the results,under normal conditions,using methyl allyl polyoxyethylene ether(HPEG),acrylic acid(AA)as the main raw material,hydrogen peroxide(H2O2)-ascorbic acid(Vc)as initiator,mH2O2;mvc=20:1,nacid:nether=4:1,and dropping time is 1h,the synthesis of polycarboxylate superplasticizer is the best sample to choose.The application of polycarboxylate superplasticizer on cement paste,water reducing agent can have good dispersibility and early strength.Under this condition,the research for the synthesis of different molecular weight reducing agent,for HPEG 2400-APEG 700 and HPEG 2400-APEG 1000 compound system of two polycarboxylate superplasticizer,cement hydration exothermic rate with the increase in the rate of small molecular weight APEG instead of first increased and then decreased.Respectively when the substitution rate of APEG 700 is 30%and APEG 1000 is 20%,the cement hydration rate reaches minimum value.When the substitution rate of APEG 700 is 30%,the fluidity of cement paste reaches the maximum value,that means the dispersing performance of the superplasticizer is optimal.The early strength of the slurry gradually decreases with the increase of the APEG of the small molecular weight,and the functional groups such as carboxyl group(-COOH),ether group(-O-),hydroxyl(-OH)and C-H bond in the molecular structure of the polycarboxylate superplasticizer of different systems are confir-med by infrared spectrum test.In addition,the polycarboxylate superplasticizer was synthesized from three kinds of comonomer HPEG-AM-AA,HPEG-SMAS-AA and HPEG-MMA-AA,when the substitution rate of AM、SMAS、MMA increase,that means the hydration heat release rate of cement increases gradually.The fluidity of cement paste increased first and then decreased,and when the substitution rate of AM is 10%、the substitution rate of SMAS is 5%、the substitution rate of MMA is 5%and the fluidity of cement paste reaches the maximum value.That means the superplasticizer synthesized under the condition of doping has the best dispersion property.Early strength of cement paste increases slightly but the change is not obvious.By infrared spectrum test,it is found that carboxyl group(-COOH),ether group(-O-),hydroxyl group(-OH)and C-H bond exist in functional groups of polycarboxylate superplasticizer,but there are functional groups such as amide group(-CO-NH-),sulfonic group(-S03H),ester group(C-O-C)and so on.