| Polycarboxylate superplasticizer (PCE) was widely used to prepare highperformance concrete of major engineering projects, such as high-speed railways,bridges and airports, because it has good performances, such as low dosage, highwater reducing ratio, low slump-loss and excellent safety and environmentalprotection. However, PCE was obtained by synthesis of petroleum productswhich were non-renewable fossil resources. The application of PCE was limitedto a certain extent because of higher cost. Therefore, developed moreenvironmentally friendly raw materials or substitutes and reduced costs havebecome one of the research hotspots of PCE. For this reasons, the reed pulp wasmodified by chemically to prepare modified product which composited with PCEto partly replace PCE, and made it to be composite water reducing agent whichhad good comprehensive performances and high cost-effective in this paper.Microcrystalline cellulose (MCC) was prepared by hydrolysis from reedpulp, and hydrolysis processes were studied by orthogonal experimental design.Sulfopropylated cellulose ether (SPC) was prepared by alkalization andetherification from MCC to improve its solubility in water, and preparationprocesses of water-bath heating were studied by uniform experimental design.The structure of MCC and SPC was characterized by infrared spectroscopy andX-ray diffraction analysis. SPC-Ⅰ/PCE, SPC-Ⅱ/PC and SPC-Ⅲ/PCE compositewater reducing agents were obtained by PCE compound with SPC which wasprepared by water-bath heating, ultrasonic heating and microwave heating,respectively. The performances of composite water reducing agents wereinvestigated by measuring the fluidity of cement paste and water reducing ratio.The results showed that the optimal preparation conditions of MCC were1h of ultrasonic pretreatment time,6wt%of hydrochloric acid concentration,30:1of the liquid-solid ratio,100℃of the reaction temperature and2hrs of thereaction time. The yield of MCC was84.9%in this condition. The study of thestructure of MCC showed that pretreatment and hydrolysis process were almostno effect on the molecular structure of MCC. The crystallinity of MCC increasessignificantly during hydrolysis, but it declined slightly in the ultrasonicpretreatment process. The preparation technology of SPC by water-bath heatingwas divided into alkalization and etherification. The conditions of alkalizationwere2.7of the NaOH/AGU (anhydroglucose unit) molar ratio,10℃of thealkalization temperature and1h of the alkalization time. The conditions ofetherification were1.5of the PS (1,3-propyl sultone)/AGU molar ratio,95℃of the etherification temperature and4hrs of the etherification time. Differentpreparation methods of SPC have been contrast studied. Compared with thewater-bath heating, ultrasonic heating and microwave heating can make theetherification time reduced to2hrs and1h, respectively. The results of SPCshowed that the etherification reaction taking place between PS and hydroxylgroups on the cellulose molecular chain to introduce sulfopropyl group. Thesubstitution degree and the intrinsic viscosity of SPC were0.355and44.03ml/g,respectively. The degree of substitution had a greater impact on the fluidity ofcement paste, and the intrinsic viscosity had little effect. With a high degree ofsubstitution and low intrinsic viscosity of SPC showed good water-reducingeffect to cement paste. Modified cellulose/polycarboxylate composite waterreducing agent was investigated and indicates that the optimum weight ratio ofSPC-Ⅰ/PCE, SPC-Ⅱ/PCE and SPC-Ⅲ/PCE composite water reducing agentswere10/90,15/85and15/85, respectively. And water reducing ratio was29.5%,26.6%and29.1%, respectively. It was close to water reducing ratio of PCE(30.5%). The comprehensive effect of SPC-Ⅲ/PCE was the best. The time-lossratio of cement paste fluidity was lower over time. The average value of the time-loss ratio of cement paste fluidity in120min was18.7%, lower4.9%than PCE.At the same time, it can reduce the cost of9.2%. |
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