Preparation And Properties Of Modified Cellulose-Based Polycarboxylic Superplasticizers

Superplasticizers can improve the workability of mixed concrete.It is an indispensable additive for high-performance concrete.The polycarboxylic superplasticizers is third generation superplasticizers after lignosulphonate superplasticizers and naphthalene superplasticizers.It is extensively used in bridges,high-speed railways,freeways,airports and other engineering projects due to its advantages of high water-reducing rate,low dosage,high slump resistance,molecular adjustable,green and environmental protection.With the development of green chemicals and sustainable economy,the preparation of concrete admixtures using natural polymers as raw materials has become one of the research hotspots of polycarboxylic superplasticizers.Based on the designable molecular structure of polycarboxylic superplasticizers,this paper prepared two functional cellulose-based polycarboxylic superplasticizers using cellulose hydrolysates as starting materials and grafting different functional monomers,and its performance and action mechanism were explored.To make it to be polycarboxylic superplasticizer which have excellent comprehensive property and high cost effective.The main work is as follows:（1）The retarded cellulose-based polycarboxylic superplasticizers were prepared by free radical polymerization in aqueous solution using isoprenol polyoxyethylene ether（TPEG-2400）,acrylic acid（AA）and cellulose maleate as monomers.Then,the influence of synthesis conditions on its dispersibility was studied.Through orthogonal experiments,the optimum synthesis process was as follows:the synthesis temperature was 45℃,the synthesis time was 3h,the ratio of acid to ether was 3:1,the content of cellulose maleate was 10%,the content of thioglycolic acid（TGA）and hydrogen peroxide（H₂O₂）was 0.55%and 0.45%,respectively.The polycarboxylic superplasticizers prepared by this process had an initial fluidity of 285 mm for cement paste,reached 298 mm in 30 minutes and 305 mm in 60 minutes.It exhibited good slow-release and water reduction performance.（2）The test results of different retarded cellulose-based polycarboxylic superplasticizers showed that when the dosage of cellulose maleate was 10%,the polycarboxylic superplasticizers not only showed good retarding effect of cement,but also improved the strength of cement hydrate.Specifically,0.5%of the polycarboxylic superplasticizers was added into the cement,the water-reducing rate achieved 28.3%and the setting time was extended 69 min.The compressive strength of cement mortar at 3 d,7 d and 28 d were increased by 35.4%,70.0%and 25.2%,respectively.The bending strength of cement mortar at 3 d,7 d and 28 d were increased by 73.4%,25.0%and 18.0%,respectively.The XRD and SEM analysis showed that the retarded cellulose-based polycarboxylic superplasticizers inhibited the hydration of C₃S,which confirmed the retarded property.（3）The early strength cellulose-based polycarboxylic superplasticizers were prepared by free radical polymerization in aqueous solution using AA,TPEG-2400,cellulose hydrolysate and sodium methacrylate sulfonate（SMAS）as monomers.Then,the influence of synthesis conditions on its dispersibility was studied.Through orthogonal experiments,the optimum synthesis process was as follows:the synthesis temperature was 55℃,the synthesis time was 3h,the ratio of acid to ether was 3.5:1,the content of SMAS was 2%of the mass of large monomer TPEG-2400,and the amount of H₂O₂ was 1%.（4）The test results of different early strength cellulose-based polycarboxylic superplasticizers showed that the best performance was when the dosage of SMAS was 2%.Specifically,when 0.5%of the polycarboxylic superplasticizers was added to the cement,the water reducing rate could reach 27%.The compressive strength of the cement mortar at 1 d,3d,7 d and 28 d were increased by 96.9%,129.2%,105.5%and 71.6%,respectively.The bending strength of cement mortar at 1 d,3 d,7 d and 28 d were increased by 103.5%,44.9%,110.6%and 74.5%,respectively.The SEM and XRD analysis showed that the addition of early strength cellulose-based polycarboxylic superplasticizers could accelerate the hydration rate of cement and improved the early strength of the mortar.