蒸汽养护影响水泥基材料氯离子固化性能机理研究

There is an obvious influence of steam curing on the chloride ions binding capacity of cement based materials, which leads to great differences between steam curing and normal curing cement based materials on this. In order to reveal the above influence mechanism, this project will be conducted from binding and release of chloride ions. The chloride ions binding characteristics of steam curing cement based materials will be researched with the isotherm equilibrium method. The chemical corrosion method will be introduced to determine the contribution of physical absorption and chemical binding of chloride ions on the binding capacity of steam curing cement based materials. Otherwise, the relationship between the change on Ca/Si of C-S-H gel and curing temperature will be cleared and the influences of polymerization degree, chain length and density of C-S-H gel on its’ absorbing chloride ions capacity will also be verified. Based on these results, the relationship between “influence degree” of steam curing and the change of absorbing chloride ions capacity of C-S-H gel will be discussed. The change rule of thermal stability of AFt will be researched to analysis the influence of decomposition of AFt on the formation of Friedel’s salt, and the relationship between “influence degree” of steam curing and the change of chemical binding chloride ions capacity of AFm will also be discussed. The macro critical conditions of the release of bound chloride ions under no chemical corrosion environment will be stated. Otherwise, the change rules of contents on SO42-、OH- ¬and Cl- are going to be stated from micro perspective to reveal its’ influence on the formation and decomposition of Friedel’s salt will be researched, and propose the transforming equilibrium model among AFt, AFm and Friedel’s salt. The results from this project will prove theoretical basis for the optimum durability design and predicting service life of steam curing concrete structure.

蒸养对水泥基材料氯离子固化性能有明显影响，使得其与常温养护水泥基材料存在较大不同。项目拟从氯离子固化和解固两方面入手，揭示该影响机理。采用等温吸附平衡方法，研究蒸养水泥基材料氯离子固化特征；利用化学腐蚀法确定物理吸附和化学结合氯离子对材料氯离子固化性能“贡献”。确定凝胶钙硅比变化与养护温度的关系，及聚合度、链长、密度变化对其氯离子吸附性能影响规律，论述蒸养“影响程度”与其物理吸附氯离子性能变化关系；研究AFt热稳定性变化规律，分析AFt分解对Friedel（F）盐形成影响机制，论述蒸养“影响程度”与AFm相化学结合氯离子性能变化之间关系。研究无化学腐蚀情况下，固化氯离子解固的宏观临界条件，从微观角度阐明SO42-、OH-和Cl-浓度变化规律和原理，及其对F盐形成和分解的影响机制，提出AFt-AFm-F盐转变平衡理论模型。项目成果将为蒸养混凝土结构耐久性优化设计和寿命预测提供理论基础。

蒸养对水泥基材料的氯离子固化性能有明显影响，使得其与常温养护水泥基材料存在较大不同。鉴于此，项目对蒸养水泥基材料氯离子固化特征进行了研究，分析了水泥基材料物理吸附和化学结合固化氯离子量变化特征。与此同时，还研究了不同腐蚀环境下蒸养水泥基材料中固化态氯离子稳定性变化特征，研究了蒸养对C-S-H凝胶和Frielde盐形成影响。结果表明：蒸养对水泥石氯离子固化性能存在明显不利影响，随着静养时间延长，水泥石氯离子固化性能呈先增大后减小趋势，增大恒温温度，会导致水泥石氯离子固化性能下降，延长恒温时间同样会对其产生不利影响。蒸养对水泥石氯离子固化性能不利影响是长期性，也即蒸养结束后，随着养护龄期延长，固化性能会持续下降。在标养条件下纯水泥石氯离子固化以化学结合占主导，而蒸养以物理结合为主导。与普通养护相比，蒸养水泥石中已固化氯离子在硫酸钠侵蚀和碳化反应条件下，更易发生解固，增大恒温温度可提高已固化氯离子在上述腐蚀环境中稳定性，但温度不宜高于70℃。蒸养条件下C3S前期水化速度快，后期水化速度慢，与标养相反。蒸养阶段，C3S水化生成的C-S-H凝胶C/S和H/S受养护温度影响，随养护温度增加，二者同步增加。当蒸养结束时，C-S-H凝胶组成与标养相同：C/S=1.63，H/S=5.76，即C3S水化生成的C-S-H凝胶与养护历史无关，仅与最后阶段养护温度有关。标养C3S水化产物氯离子固化能力大于蒸养。随水化龄期增加，C3S水化产物氯离子固化能力降低；蒸养对化学结合氯离子，也即Friedel盐形成影响较大，其表现为不但会抑制水化早期Friedel盐形成，且蒸养结束后，随着养护龄期延长，硬化水泥石体系中AFm相（SO42-）会逐渐减少，Friedel盐形成一进步受到限制。本项目的研究成果对进一步探明蒸养混凝土耐久性劣化机理，优化蒸养混凝土结构耐久性的设计和寿命评估方法具有重要科学和实践意义。