Preparation Technology And Performance Study Of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer has become the first choice for concrete because of its advantages such as low content,good dispersion,high water reduction rate,environmental protection and molecular regulation.In order to meet these requirements,it is of great significance to develop a series of high-performance polycarboxylate superplasticizer.In this paper,the synthesis process of standard and sustained-release polycarboxylate superplasticizer was optimized and improved,and a polycarboxylate superplasticizer with super long sustained-release and slump protection effect was developed.In this paper,acrylic acid（AA）,isobutenyl polyethylene glycol ether（HPEG-2700）or isopentenyl polyethylene glycol ether（TPEG-2700）as the main polymerization monomer,under the action of initiator using free radical polymerization method to synthesize standard polycarboxylate superplasticizer.The optimum preparation process of standard polycarboxylate superplasticizer was determined by single factor test and orthogonal test.The water reduction rate of the standard polycarboxylate superplasticizer synthesized by the optimum preparation technology is 38.52%,when the content of the superplasticizer is 0.17%.The cement dispersion characteristics of HPEG type and TPEG type polycarboxylate superplasticizer were compared through the fluidness test of cement paste.It was decided to prepare standard polycarboxylate superplasticizer with HPEG macromonomer,and prepare slow release polycarboxylate superplasticizer with TPEG macromonomer.The sustained-release polycarboxylate superplasticizer was synthesized by free radical polymerization with isopentenyl polyethylene glycol ether（TPEG-2700）,acrylic acid（AA）,hydroxyethyl acrylate（HEA）as the main monomer and a compound,REDOX system of ammonium persulfate（APS）,hydrogen peroxide（H₂O₂）and L-ascorbic acid（Vc）as the initiator.The optimum synthesis process of sustained-release polycarboxylate superplasticizer was determined by orthogonal test and single factor test.The results of IR and GPC analysis showed that the molecular structure was in line with the expected design,Mw=100096,Mw/Mn=1.902.The experimental results of concrete show that the slow-release polycarboxylate superplasticizer synthesized by the best technology has better initial dispersion performance compared with the same type of superplasticizer on the market,but neither of these two kinds of slow-release superplasticizer has slump protection performance for a long time,and the concrete loses fluidity after 4h.In order to reduce the time-lapse loss of concrete slump and improve its later fluidity.Using polyether monomer（TPEG-2700）,acrylic acid（AA）,hydroxyethyl acrylate（HEA）as the main raw materials,under the condition of a certain mole ratio of AA to HEA,sodium methyl propylene sulfonate（SMAS）was used to replace part of AA,butyl acrylate（BA）was used to replace part of HEA.A polycarboxylate superplasticizer agent with long sustained release was synthesized at room temperature under the condition of aqueous solution polymerization.Through orthogonal test and single factor test,the effects of the proportion of each small monomer and the addition process on its properties were studied.Meanwhile,the molecular structure was characterized by IR and GPC.The results showed that when the reaction temperature was 28,the acid-ether ratio was 5.01,n（AA）:n（HEA）was 3.5:6.5,the substitution rate of SMAS was 7.5%,the substitution rate of BA was 20%,the mixed monomer was 50%,the time of drip of A was 2 h,and the time of drip of B was 2.5 h,the dispersibility and retention of the synthetic water-reducing agent was the best,after 4 h,the concrete slump loss is only 37mm.