Synthesis Of Polycarboxylate Superplasticizer And Application In Shotcrete

As an environmental friendly materials, polycarboxylate superplasticizers were favored by the construction industry increasingly and became a focus of research recently. Until now a lot of research were focused on how to improve the performance of polycarboxylate superplasticizers. Through the use of low-cost polyethylene glycol as synthetic monomer and the reasonable ratio selection of small monomers and synthesis process, variety of ways had been employed to achieve the purpose of decreasing the synthesis cost of the polycarboxylate superplasticizers. It was of great significance in the age of scarce natural resources and the rising cost of industrial production increasingly. Shotcrete was important manner in many projects such as: the road slope stability, tunnel support, geotechnical and building repairing and reinforcing and so on. The engineering performances of shotcrete were studied through doped polycarboxylate superplasticizers and fly ash which provided experiment evidence for the polycarboxylate superplasticizers applied in shotcrete.In this study, polyethylene glycol400and methacrylic acid as the main raw materials, the polyethylene glycol methacrylate monomers had been syntheszed by the direct esterification. The following factors on the esterification rate were discussed: molar ratio of acid and alcohol, reaction temperature and the amount of inhibitor, catalyst and absorbent. The esterification rate of esterification actions was the main assessment of the selection of the process conditions. The optimum process conditions were:PEG400, the acid to alcohol molar ratio was1.1:1, the amount of the catalyst, inhibitor, water absorbent were1.0%,0.5%and15%of the total mass of the acid and alcohol, respectively. The reaction were stop when the esterification rate was between40%-60%. The esterified monomer was the raw materials of polycarboxylate superplasticizer copolymer. The free radical copolymerization reactions had been carried out in the aqueous solution with the use of homemade esterification macromer PEGMAA and the functional monomers, methacrylic acid, methacrylamide sulfonate, acrylamide under excitation of ammonium persulfate and hydrogen peroxide. Three best synthetic processes were obtained after studying persulfate-hydrogen peroxide initiator system, the reaction temperature and different proportion of monomer, respectively. The following synthesis process was selected as the final synthesis program:10g PEGMAA,1.0g MAA,0.5g SMAS, the initiator was0.1g of thioglycolic acid, the APS and H2O2were4%o and4%o of the total mixed monomer, the temperature was80℃and the reaction time was3-5h. The products were characterized by IR spectra. Superplasticizer solid content was38.2%, the saturation dosage point of water reduction rate was0.3%. When folding solid dosage was0.3%, water reduction rate of cement paste was34.4%, the initial flow was280mm, the flow for1h was285mm.Many effect factors of shotcrete had been comprehensively studied:the amount of accelerating agent and fly ash, relationship between accelerating agent and the plastic material, the excitation of sodium sulfate. The flexural strength and compressive strength of shotcrete doped fly ash and superplasticizer had been studied also. The conclusion as follows:The accelerating agent content had the proper range. The mixing ratio of fly ash could not exceed30%of the total plastic material. There was a positive relationship between accelerating agent with cement. Sulfate could improve the compressive strength and the working properties of shotcrete doped fly ash. Fly ash or superplasticizers could improved the performances of shotcrete, such as flexural strength, compressive strength and resistance to sulfate corrosion. Compared with two commercially available superplasticizers, The shotcrete doped homemade polycarboxylate superplasticizers had better performances in flexural strength, compressive strength, resistance to sulfate corrosion rate.