【作者】 张海彬；

【导师】 楼宏铭；

【作者基本信息】 华南理工大学 ， 应用化学， 2010， 硕士

【摘要】 我国正值大规模建设时期,对混凝土高效减水剂的需求巨大,2009年其用量达484万吨。高效减水剂的应用推进了建筑节能降耗,提高了混凝土工程的耐久性,具有重大的经济和社会效益,但是对混凝土高效减水剂的分子结构及其吸附分散作用机理还缺乏深入系统的研究。本文针对高效减水剂具有水溶性高分子表面活性剂的结构特点和表面物化行为,采用超滤膜技术将高效减水剂按分子量大小切割成3～4个级分,然后对各个级分进行结构表征和分散性能研究,最后结合其在水泥颗粒上的吸附动力学、热力学、吸附膜厚度及吸附后形成zeta电位探讨了分子量对高效减水剂的吸附分散作用机理的影响规律,为进一步优化高效减水剂的合成工艺和深入理解其分散作用机理提供了方向和参考。本文研究了五种高效减水剂,包括改性造纸黑液高效减水剂(GCL1-JB)、萘系高效减水剂(FDN)、脂肪族高效减水剂(SAF)、氨基磺酸系高效减水剂(ASP)和聚羧酸高性能减水剂(PC)。研究结果表明:(1)不同分子量级分的特性粘度差距较大,GPC的测试结果也表明超滤实现了按分子量切割为不同级分的目的,并且各级分的分子量分布变窄。元素分析测试结果表明,随着级分分子量的增大,单位质量磺化度降低,单分子磺酸根含量增加。(2)上述五种高效减水剂对水泥的分散性能都是随级分分子量的增大而增强。不同类型的减水剂随着级分分子量的增大,分散性能提高的程度不同,脂肪族减水剂的提高程度最大。0.5%掺量下,达到流动度250 mm左右,掺SAF所需水灰比为0.31,掺大分子量级分(SAF-D)所需水灰比仅为0.21。达到同样流动度,掺0.2%的聚羧酸高性能减水剂所需水灰比约为0.25。水灰比为0.21时,掺0.2%大分子量聚羧酸高性能减水剂级分(PC-C)的水泥净浆流动度为268 mm。(3)随着级分分子量的增大,SAF、FDN、和ASP的吸附量增大,zeta电位绝对值和吸附膜厚度增加。大分子量分子吸附到水泥颗粒表面能够产生较大的静电斥力和空间位阻,因而具有较强的分散性能。研究表明,大分子量脂肪族减水剂分子吸附的吉布斯自由能绝对值较大,优先吸附到水泥颗粒表面,具有较高的zeta电位和较厚的吸附膜厚度与其分子结构和吸附形态有关。大分子量分子具有较多的单分子磺酸根和较好的分子链柔性,因而分子在溶液中蜷曲,能在水泥颗粒表面形成多点的环圈式构型和具有多层电荷的空间结构,产生较高的静电斥力和较强的短程空间位阻,对水泥颗粒的分散性能更强。更多还原

【Abstract】 Recently, demand of concrete water reducer become huge as large-scale of constructionin China is doing. For example, the consumption of water reducer reached 4.84 million tons in2009. The application of superplasticizer can reduce building energy consumption andimprove the durabilityof the project, so it brings significant economic and social benefits. Butthe study of synthesis and dispersion mechanism of superplasticizer is not enough.Superplasticizer is water-soluble polymer with structural characteristics and surfacephysico-chemical properties of surface active agents. In this paper, superplasticizer was cuttedinto 3~4 fractions by ultrafiltration membrane technology, then the structure of fractions arecharacterized and dispersion propertities of each fraction were also studied. Adsorptionkinetics, thermodynamics, zeta potential and adsorbed layer thickness data of differentfractions after being adsorbed on cement particles were to sheld light on dispersionmechanism of superplasticizer fractions. Conclusions here may provide useful direction andreference for optimizing the synthesis craft and in-depth understanding dispersion mechanismof superplasticizer.In this paper, five superplasticizers, including the modified pulp black liquorsuperplasticizer (GCL1-JB), naphthalene sulfonate formaldehyde condensate superplasticizer(FDN), sulfonated acetone formaldehyde condensate superplasticizer (SAF), amino acidphenol formaldehyde condensate superplasticizer (ASP) and polycarboxylate superplasticizer(PC) were studied.The results show that:(1) Different molecular weight fractions of superplasticizer had distinct difference inintrinsic viscosity. GPC test result showed that dividing the superplasticizers into fractions ofdifferent molecular weight was achieved by ultrafiltration membrane technology, andmolecular weight distribution of fractions got narrower. Elemental analysis result showed thatfractions’molecular weight were higher, degree of sulfonation would be lower, and thesingle-molecule sulfonic group content was higher.(2) From the results obtained from the study on the effect of fractions of fivesuperplasticizers on the dispersion of cement paste, it was found that the higher molecularweight fractions, the better the water-reducing dispersion performance. SAF fractions of high molecular weight enjoyed better dispersion performance than other type superplasticizers。When dosage of water reducers was 0.5%, and fluidity of cement paste reached 250 mm,water-cement ratio of SAF was 0.31, but water-cement ratio of high molecular weight SAFfraction (SAF-D) was only 0.21. When fluidity of cement paste was up to 250mm and dosageof polycarboxylate superplasticizer was 0.2%, corresponding water-cement ratio was 0.25.And when water-cement ratio was 0.21 and dosage of polycarboxylate superplasticizer withhigh molecular weight was 0.2%, fluidityof cement paste was up to 268 mm.(3) From the results obtained from the study of adsorption characteristics of SAF, FDNand ASP fractions, it was found that the higher molecular weight fraction, the larger amountof it on cement particles would be adsorbed, and so were zeta potential and adsorbed layerthickness. High molecular weight fraction adsorbed to the surface of cement particles inducedgreater electrostatic repulsion and steric hindrance, so the cement system would show betterdispersion performance. Further study of SAF showed that high molecular weight fractionwas of higher absolute value of Gibbs free energy, zeta potential and adsorbed layer thickness,and might preferentially adsorbed onto the cement particles, which was related to it’smolecular structure and adsorption configuration. High molecular weight molecule withhigher sulfonic group content per chain and better molecular chain flexibility, was proposed tobe coil configuration in solution, which enhanced interaction with the cement particles. Andhigh molecular weight molecule adsorbed on cement particles formed loop on cementparticles to show multi-charge structure which induced higher electrostatic repulsion andstrong short-range steric, and as a result dispersion performance of cement paste was greatlyincreased.更多还原