基于选择性吸附的两性接枝共聚物构效关系及混凝土超早强作用机制

In traditional knowledge, the graft copolymer dispersants can improve the fluidity of fresh concrete, but have little impact on the hydration and strength of cement and concrete. With the study of grafted comb-like copolymers on the properties of cement going, the impacts of grafted copolymers on the hydration of cement are paid great attentions. Our previous results present that a selective adsorption on cement/water interface occurs with the addition of amphoteric graft copolymer. The charge density in main chain and the side chain length have great influence on the hydration behavior of cement. But there is little study focusing on the relationship between molecular structure of copolymer and the hydration behavior of cement. Therefore, a series of amphoteric graft copolymer dispersants with ultra-long side chain are synthesized in this study. The impact of molecular structure on the hydration behavior of cement and pure cementitious phases (C3S, C3A) were systematically investigated through parameters such as side chain length, charge density, linkage and molecular weight. The main purpose of this study is to understand the relationship between molecular structure of amphoteric graft copolymers and properties of cement such as selective adsorption, dispersion, strength and so on, which gives us a bridge between microscopic structure and macroscopic properties. The mechanisms of amphoteric graft copolymer to enhance the early strength of cement are present based on the study of stucture-activity. This study break the traditional misunderstanding that superplasticizer can affect only the fluidity but not the hydration of fresh concrete. It is in great significance that this study provide theoretical direction for the development of novel copolymer superplasticizer with funtions such as high water-reduction, ultra-high early strength, high durability and so on.

传统观念认为接枝共聚物作为减水剂只能改善混凝土流动性，而对力学性能和水泥水化影响有限。申请人前期研究表明：两性离子共聚物呈现出选择性吸附行为，且主链电荷性质和侧链长度改变了水泥水化行为，但共聚物分子结构如何影响水泥早期水化进程和产物形貌，进而同早期强度发展等宏观性能相关联迄今国内外尚无报道。本项目提出了基于选择性吸附的长侧链两性接枝共聚物作为超早强型混凝土超塑化剂的分子设想，拟从两性共聚物与水泥的相互作用出发系统研究共聚物分子结构（侧链长度、电荷密度、桥接基团、分子量）对水泥及C3S、C3A的水化历程、水化产物形貌的影响规律，从分子层次揭示选择性吸附、分散、早强等宏观性能间的相互关系，进而阐明两性接枝共聚物超早强作用机制，突破减水剂仅仅调控混凝土初期流变性的误区，为具有高减水、超早强、高耐久等协调功能的新型共聚物外加剂的分子构建提供更科学的视角和理论依据。

聚羧酸减水剂具有分散能力高、结构多样可设计等优点，因而被广泛运用于混凝土行业。不同分子结构的聚羧酸减水剂会对水泥基材料的流变性能和水化过程产生不同影响，但是聚羧酸分子结构对于水泥水化的影响机理依然不明确。.本项目合成具有不同分子结构的聚羧酸类接枝共聚物，并采用渗透凝胶色谱、氢谱核磁共振、红外光谱等方法对分子结构进行了系统表征。采用动静态光散射仪等系统研究了接枝共聚物在不同溶液环境中的分子构象与性能，研究结果表明溶液中的阳离子一方面会因静电屏蔽效应使共聚物构象发生蜷曲现象，同时也会与共聚物产生络合效应，改变共聚物的溶液构象，导致共聚物的吸附能力发生变化。主链较长的共聚物更容易发生蜷曲现象，因而在盐溶液环境中的吸附能力较差。.采用分子动力学模拟了不同分子结构的聚羧酸接枝共聚物在溶液环境中的构象，结果表明在盐溶液环境中，接枝共聚物中的侧链容易聚集到一起，主链羧基裸露在外围与Ca2+相互作用，导致其溶液构象发生改变。接枝共聚物主链中的甲基会增加分子的局部刚性，提高分子的耐盐性，随着甲基数量的增加，盐溶液对其构象的影响减小。两性接枝共聚物中主链正负带电基团之间的静电屏蔽作用会直接影响分子的溶液构象，进而改变其吸附能力。.采用宏观测试与微观分析相结合的方法，系统研究了不同分子结构聚羧酸接枝共聚物对于水泥及单矿早期水化的影响规律。结果表明，在相同质量掺量下，随着分子结构中侧链长度的增加，聚羧酸对水泥水化的延缓作用会减弱；但是在相同摩尔掺量下，不同侧链长度聚羧酸对于水泥水化的延缓作用是相近的。聚羧酸分子通过吸附在水泥颗粒的表面，阻碍水泥矿物的溶解和水化产物的成核结晶，从而延缓水泥的早期水化。而长侧链和两性聚羧酸接枝共聚物能在较小的吸附量下通过增加空间位阻的方式提供较好的分散能力，对于水泥水化的延缓作用较小，从而达到提高水泥混凝土早强强度的作用。