【作者】 何易；

【导师】 刘加平； 舒鑫；

【作者基本信息】 东南大学 ， 材料科学与工程， 2019， 硕士

【摘要】 聚羧酸系减水剂（PCE,polycarboxylates）是现代混凝土应用最有效最广泛的超塑化剂,可以大幅降低水胶比,改善流动性。然而其与混凝土复杂原材料之间仍旧存在着一系列相容性问题,其原因则在于聚羧酸减水剂与混凝土原材料之间的吸附不匹配。针对该问题,已有学者通过吸附基团改性对聚羧酸减水剂的吸附过程进行调节,但其聚合物模型分子的结构差异较大,并未控制单一结构变量（如:分子量、侧链密度、吸附基团带电荷数）,因此,研究结果未能全面揭示结构参数对聚合物分散性能及其作用机制。本文合成制备了一系列具有相同分子量、相同侧链长度的不同吸附基团（羧基、磺酸基、磷酸基）改性聚合物,以不同的吸附基团取代比例（1/3和2/3）及不同的吸附基团取代方式（等物质的量取代/等电荷量取代）对传统的聚羧酸减水剂进行改性,通过核磁共振和红外光谱对其进行了表征,考察了聚合物的溶液构象与吸附构象、水泥颗粒表面吸附量、分散行为及流变行为,系统地探究了不同吸附基团聚合物对水泥基材料流变行为的影响规律及其作用机制。主要结论如下:（1）不同吸附基团聚合物的溶液构象分别受到聚合物分子内阴离子吸附基团间的静电斥力作用,阴离子吸附基团与Ca²⁺的络合作用以及溶液离子的“屏蔽效应”影响而产生差异,不同吸附基团的络合能力符合:-OPO₃²>-COO^->-SO₃^-。吸附于水泥颗粒表面的磺酸、磷酸基团改性聚合物主链长度较短,单分子占有面积较小,等电荷量取代的磷酸基团改性聚合物侧链密度较高,饱和吸附层厚度较大。在实验条件下,带有较多负电荷、具有较强Ca²⁺络合能力的等物质的量取代的磷酸基团改性聚合物,在1/3和2/3取代比例下的饱和吸附量分别高于传统羧基聚合物76.9%和82.7%,而磺酸基团则因Ca²⁺络合作用较弱较难吸附于水泥颗粒表面,饱和吸附量最低。（2）水泥浆体的流动性结果在较高聚合物掺量下与吸附量结果基本一致,且在实验条件下,1/3等物质的量取代的磷酸基团改性聚合物较羧基聚合物其分散性提高了27.5%;在较低聚合物掺量下,2/3取代比例的磷酸基团改性聚合物由于受到“桥接作用”影响,分散性有所下降,低于传统的羧基聚合物;磺酸基团改性聚合物因吸附能力较低分散性最差。（3）磷酸基团改性聚合物具有显著的抗硫酸盐性能,向聚羧酸减水剂中引入磷酸基团能够有效降低硫酸盐敏感度,在实验条件下,以1/3取代比例等物质的量取代的磷酸基团改性聚合物其硫酸盐敏感度较羧基聚合物降低了约65.4%。本文从微观到宏观系统探究了聚合物吸附基团对水泥基材料流变行为的影响规律及“吸附—分散”作用机制,并探究了磷酸基团改性聚合物对聚羧酸减水剂的硫酸盐相容性的改善效果,在一定程度上为新型高性能超塑化剂的合成制备提供了参考。更多还原

【Abstract】 Polycarboxylate（PCE）superplasticizers are the most widely used superplasticizers in modern concrete,which could greatly reduce the water to binder ratio and improve the flowability.However,a series of compatibility problems still exsist between polycarboxylate superplasticizer and concrete raw materials.Some scholars have adjusted the adsorption process of comb-like polymers by modifying the adsorption groups.Yet,the PCE structure（e.g.grafting density,charge density）and the results might not be comparable between each other and the fundamental effect of different adsorption groups on the rheological properties of cement pastes was still not so clear.In this thesis,a series of PCEs modified with different types（carboxyl group,sulfonate group and phosphate group）and proportions（1/3 and 2/3）of adsorption groups,different substitution methods（equimolar number substitution/equivalent charge amount substitution）,comparable molecular weight and the same side chain length have been synthesized and characterized by NMR and FT-IR.Based on the characterization of the solution and adsorption behavior,dispersion performance,and rheological properties of cement pastes,the effects and mechanism of PCE with different adsorption groups on the flow behavior of cement paste is explored.The main findings are as following:（1）The solution conformation of PCEs with different adsorption groups is influence by the intramolecular electrostatic repulsive force between anionic adsorption groups,the complexation of Ca²⁺and anionic adsorption group,and the“shielding effect”caused by the ions in solution.The results of hydrodynamic radius indicate that the complexing ability of different adsorption groups follows the order（from large to small）:-OPO₃^2-,-COO^-,-SO₃^-.The sulfonate-group-modified polymer and phosphate-group-modified polymer have a short backbone length,a small single-molecule occupying surface area.The phosphate-group-modified polymer synthesized by equivalent subsitituion has a higher side chain density and a larger saturated adsorption layer thickness.The phosphate-group-modified polymer synthesized by equimolar number substitution method has a larger amount of negative charge and strong Ca²⁺complexing ability.Under the experimental conditions,the saturated adsorption amount of PCEs substituted by 1/3 ratio and 2/3ratio of phosphate group with equimolar number substitution method is higher than that of traditional polycarboxylate superplasticizer by 76.9%and 82.7%,respectively.The saturated adsorption amount of sulfonate-group-modified PCE is much lower due to really low complexing ability with Ca²⁺and therefore really low adsorption affinity toward the surface of cement particles.（2）The fluidity of cement pastes is basically consistent with the adsorption amount of PCEs at higher PCE dosage.Compared with PCE with only carboxylic group,the dispersing performance of phosphate-group-modified polymer（substitution ratio 1/3 equimolar number）is improved by 27.5%under the experimental conditions.While at lower PCE dosage,the dispersing performance of phosphate-group-modified polymer with 2/3 ratio of phosphate group is slightly lower than PCE with only carboxyl group due to the“bridge effect”.The sulfonate-group-modified polymer has the worst dispersing performance due to its lower adsorption amount.（3）The phosphate-group-modified polymer has pronounced sulfate resistance.Under the experimental conditions,the sulfate sensitivity of polymer modified with 1/3 ratio of phosphate group characterized by the variety of yield stress is roughly 65.4%lower than that of carboxyl group.The effects of polymers with different adsorption groups on the rheological properties of cementitious material and the“adsorption-dispersion”mechanism is systematically explored from microscopic to macroscopic view.The improving effect of phosphate-group-modified polymer on the sulfate compatibility is further explored.The results provide a constructive reference for the development of new high-performance superplasticizers.更多还原