Synthesis And Performances Study Of Functional Polycarboxylate Superplasticizer

As a third-generation superplasticizer,polycarboxylate superplasticizer?PCs?is widely used in expressway?high-speed rail projects and commercial housing construction due to its excellent performance:Low dosage,high water reduction rate,high dispersion of cement and environmental protection.Although PCs own many advantages on performance,they are used more and more widely in the concrete industry and usage amount is increasing,there are still some problems in the production and practical application of PCs,such as large slump loss,adaptability to cement,corrosion of reinforced concrete,etc.In view of the design characteristics of the molecular structure of PCs,several functional PCs were synthesized to solve the problems in practical application,and then explore their performance and mechanism,as follows:1.The introduction part mainly introduces the types and main functions of concrete admixtures,the mechanism of action,development history and the research status in domestic and foreign of PCs.Finally,the application and production problem of PCs are presented.2.For the reinforced concrete corrosion problem,improve rust resistance of PCs by introducing a quaternary ammonium functional group,allyl trimethyl ammonium chloride?ATMC?is used as a functional monomer.A rust-inhibiting PCs were synthesized by free radical polymerization which use methyl allylate polyoxyethylene ether?TPEG-2400?,acrylic acid?AA?and ATMC as monomers.The performance test found that the functional monomer doesn't have much effect on dispersion of PCs,the new rust-inhibiting PCs were roughly equivalent with the commercially available PCs in terms of liquidity,water reduction and compressive strength,reach the required national standards of GB 8076-2008"Concrete Admixture Specifications"about high performance PCs.The rust resistance test and analysis shows that rust-inhibiting PCs can improve the corrosion resistance of steel bars greatly,by forming a protective film on the surface of the steel bar.And restrain the corrosion reaction of the anode and the cathode simultaneously,mainly for anodic corrosion reaction.Finally,the optimal reaction conditions were explored,it was found that when the monomer molar ratio of TPEG:AA:ATMC was 1:3:1.2,initiator mass fraction was 1.4%,reaction time was 2.5 h,and reaction temperature was 70°C,the modified PCs own the best dispersion and retention properties for cement.3.In view of the large slump loss of concrete,poor dispersion and retention performance of cement,using maltitol as raw material,acyl chloride reaction was carried out which in an N₂ atmosphere and ice-water bath,obtain acid maltitol ester?AGE?,then use methyl allylate polyoxyethylene ether?TPEG-2400?,acrylic acid?AA?and AGE as monomers,finally obtain modified PCs by free radical polymerization.Then the effect of reaction conditions on the properties of modified PCs was investigated.The results showed that when the molar ratio of TPEG,acrylic acid and AME was 1:3:0.8,the reaction temperature was 60°C,reaction time was 3.5h,and the initiator dosage was used at 1.6%,the synthesized PCs own best performance of dispersion and retention.The test result show that the cement fluidity of modified PCs can reach up to 290 mm within 1h.Through the concrete slump test,it was found that the slump retention performance of the modified PCs was better than that of the unmodified PCs.Moreover,it can improve the compressive strength of concrete in the later stage.Combined with scanning electron microscopy?SEM?,it was found that the maltitol modified PCs can promote the growth of acicular Ca?OH?₂,enhance the compressive strength and improve the strength of concrete in the late stage significantly.