导　　师： 韦江雄

学科专业： 080502

授予学位： 硕士

作　　者： ;

机构地区： 华南理工大学

摘　　要： 水泥混凝土是工程建设中应用最为广泛的建筑材料，但其水化硬化过程中体积收缩会导致裂缝的产生，直接影响建筑物的长期耐久性能。因此，如何减少混凝土的收缩，提高混凝土结构耐久性，已成为建筑工程中的普遍存在且最为紧迫的技术难题。目前，使用减缩剂是降低混凝土收缩的方法之一，但其价格昂贵、用量较大，使得混凝土成本提高较多，且存在与混凝土其他外加剂相容性的问题,致使减缩剂的应用推广受到限制。而聚羧酸减水剂因其优异的性能，逐渐成为混凝土外加剂中发展最迅猛的品种。近年来，许多学者尝试将具有减缩功能的基团接枝到聚羧酸减水剂的侧链或者聚合到主链上，以结合减水剂和减缩剂的优点，在不增加成本的情况下，实现减水效果的同时降低混凝土的收缩。本文拟围绕接枝减缩功能基团聚羧酸系减水剂的分子结构与作用机理展开研究，以期为该类材料的设计与生产提供理论指导。 本研究立足于分子结构设计原理，从聚羧酸减水剂的分子结构特点及其作用机理出发，在聚羧酸减水剂的侧链上接枝具有减缩功能的基团，合成出一种具有梳型分子结构的减缩型聚羧酸减水剂/(SRPC/)，并通过分子结构的优化设计，在发挥其高减水率、高保坍性等优点的同时，有效地降低混凝土的收缩率。 首先，探讨了原料配比、反应温度、反应时间等对酯化率的影响。结果表明当酸醇摩尔比为3.5:1，反应温度为130℃，反应时间为4.5h时，酯化率较高；对比了真空抽滤法及减压蒸馏法对酯化物的提纯效果，结果证明采用真空抽滤法提纯酯化物效果较好；并采用红外图谱、核磁共振分析技术表征了酯化物的分子结构，证明合成酯化物的酯化率较高且纯度较好，符合预想的分子结构。同时，考察了单体配比、引发剂用量等实验条件对聚羧酸减水剂流变性能的影响，当n/(APEG/):n/(DGMA/):n/(MAA/):n/(MAS/)=1:2:2:0.125，APS用量为单体总质量的3/%时，减缩型聚羧酸减水剂的流动性能最佳。而当APS用量为单体总质量的3/%，n/(APEG/):n/(DGMA/):n/(MAA/):n/(MAS/)=1:1.2:4.8:0.4时，减缩型聚羧酸减水剂的流变性能较优，且掺流动性能较好的减缩型聚羧酸减水剂的水泥浆体属于牛顿型流体，屈服应力较低。采用红外图谱（IR）、核磁共振/(NMR/)及凝胶渗透色谱/(GPC/)对减缩型聚羧酸减水剂的分子结构进行分析，结果表明，合成的减缩型聚羧酸减水剂成功接枝了目标功能基团，分子量在20000左右。 其次，对比了减缩剂、普通聚羧酸减水剂与减缩型聚羧酸减水剂对砂浆干燥收缩性能及强度性能的影响。结果发现，前12d，掺0.3/%SRPC（减缩型聚羧酸减水剂）的砂浆收缩率与掺2/%SRA（减缩剂）的砂浆相比为高，但14d后SRPC的减缩性能则明显优于掺SRA；而减缩剂SRA在聚羧酸减水剂的辅助作用下表现出更好的抗收缩的能力。 再次，对液相的表面张力，硬化浆体的孔结构及其水化热等进行测试，综合分析减缩型聚羧酸减水剂的减缩机理。结果表明，减缩型聚羧酸减水剂显著降低水的表面张力至45.8mN//m（纯水表面张力为72.6mN//m）；掺SRPC浆体水化28d时的孔结构分布得到优化，并且小于50nm的毛细孔数量比掺SRA的降低得多；且掺SRPC浆体的累计放热量有所降低，与后期SRPC的减缩能力比SRA强有一定关系。结合热分析，结果发现减缩型聚羧酸减水剂和减缩剂对水泥前期的水化均有一定的抑制作用，表明浆体前期水化的延缓能够在一定程度提高抗缩能力。 Although concrete is of great significance to engineering construction, it is a much vexedproblem how to reduce its shrinkage and improve durability of concrete structure.Shrinkage-reducing agent /(SRA/) is one of effective method to prevent shrinkage of concrete.However, SRA cannot be widespread used, because it is expensive and costly. Whilepolycarboxylate superplasticizer /(PCs/) is becoming to be one of indispensable admixtures toconcrete, because of its excellent properties. Recently, many scholars are making an effort tograft reductible groups onto lateral chain of PCs, or aggregate reduced groups on the mainchain of PCs, so that, PCs with excellent performance of SRA can lower the shrinkage ofconcrete without high costs. Our research, according to principles of molecular structuredesign and the molecular structure of PCs as well as its action mechanism, was conducted tosynthesize a kind of shrinkage-reducing polycarboxylate superplasticizer /(SRPC/) withreduced groups grafted to lateral chain of PCs， which can possess high water reducing ratio,high slump loss resistant as well as bring down shrinkage with low-content. Moreover, themolecular structure characterization and properties tests were made. The influences of raw material ratio, reaction temperature and time on esterification rate wereinvestigated firstly. The results showed that the raw material ratio, reaction temperature andtime were3.5:1,130℃and4.5h respectively for the optimum esterification rate. Contrastedvacuum distillation with vacuum infiltration, it was found that the method of vacuuminfiltration was more effective and scientific. And it was showed that the molecular structureof compound ester was the expected one and the ester was of high conversion rate and purity,after the molecular structure of compound ester was characterized by infrared spectrum /(IR/)and nuclear magnetic resonance /(NMR/). Moreover, the effects of monomer ratio and initiatordosage on rheological property were studied, and the results showed that the optimal mixingproportion for flowability of SRPC was n/(APEG/):n/(DGMA/):n/(MAA/):n/(MAS/)=1:2:2:0.125and the dosage of initiator was3/%of grass mass of monomer, while best mixture ratio forrheology was n/(APEG/):n/(DGMA/):n/(MAA/):n/(MAS/)=1:2:4:0.33with the same dosage of initiator. The rheological model of cement with ideal SRPC whose yield stress was very lowwas proved to be Newton-type. The molecular structure of SRPC was represented by IR,NMR and GPC. And the results found that SRPC was grafted successfully shrinkage-reducinggroups on having expected group. Meanwhile, the molecular weight distribution of SRPC wastemperate. In contrast, SRPC, PCs and SRA sold in market possess the same mainfunctional groups. Besides, the effects of PCs, SRA and SRPC on shrinkage reducing property as well asstrength performance of cement mortar were also researched. It is found that shrinkagereducing ability of0.3/%SRPC was much better than2/%SRA until the day cement mortarscured for14days, and SRA doped with PCs demonstrated more excellent shrinkage reducingperformance than that without PCs. Furthermore, the influence of the surface tension of capillary pore solution, pore structuresand hydration of cement pastes on the shrinkage reducing properties was analyzed, accordingto the shrinkage mechanism. There were some results as follows: the surface tension ofwater was decreased to45.8mN//m by SRPC; the quantity of capillary below50nm of cementpaste with SRPC cured for28days decreased more than that with SRA, and the former hadmore optimal pore size distribution; the accumulative hydration heat of cement doped withSRPC was cut down, which might be related to the better shrinkage reducing performanceafter14days; with integration of TG-DTA it came out that both SRPC and SRA could delaythe early hydration of cement, which could be beneficial to enhance the anti-shrink efficiency.

关 键 词： 聚羧酸 分子结构设计 减缩 减水 表面张力

分 类 号： [TU528.042.2]

领　　域： [建筑科学]