弱碱环境下混凝土石膏型硫酸盐侵蚀机制

Sulfate attack is an important factor for the durability of the concrete. Previous researches mostly concentrated on the ettringite and thaumasite erosion under the strong alkali conditions. Nevertheless, there currently was an increasing number of concrete construction in the weak alkali (pH=7-10) conditions whose corresponding researches on the orientation of gypsum corrosion were fewer. In this project, thermodynamic condition and dynamic characteristic of the gypsum formation, under the weak alkali conditions, were investigated through the effect rules of the temperature, alkalinity and sulfate concentration. And the decalcification and dealumination mechanism and the microstructure evolvement rules of C-S-H were also revealed by the influences of the gypsum sulfate attack on the microstructure of the C-S-H/CH under the weak conditions. What’s more, the internal relations of the gypsum formation, microstructure evolvement and the property degradation were explored according to time-varying rules of the concrete interface, pore structure, and the micro-, macro-properties during the gypsum sulfate attack process under the weak alkali conditions, finally leading to a further revelation of mechanism of the gypsum sulfate attack. on the basis of what is said above, using the dissoluble barium salt and admixture to inhibit the gypsum formation and improve the microstructure, in order to explore the technological approaches to improve resistance of the sulfate corrosion of the concrete under the weak alkali conditions. The project results will enrich the sulfate erosion theory of concrete, and provide the theoretical direction and technological support to the durability design of the concrete.

硫酸盐侵蚀是影响混凝土耐久性的重要因素，传统研究多集中于强碱环境下发生的钙矾石和碳硫硅钙石型侵蚀。现代越来越多的混凝土结构处于弱碱（pH=7-10）环境中，而针对该环境下发生的石膏型硫酸盐侵蚀研究较少。本项目拟研究温度/碱度/硫酸盐浓度对水泥石中石膏相形成的影响，探明弱碱环境下水泥石中石膏相形成的热力学条件和动力学特征；研究弱碱环境下石膏型硫酸盐侵蚀对C-S-H/CH结构的影响，揭示胶凝组分脱钙/铝及C-S-H结构损伤机制；研究弱碱环境下石膏型硫酸盐侵蚀过程中混凝土界面、孔结构和微细-宏观性能的时变规律，探明石膏相形成-微结构演变-性能劣化之间内在关系，揭示弱碱环境下混凝土石膏型硫酸盐侵蚀机理。在此基础上，采用可溶性钡盐/掺合料抑制石膏相形成、改善微结构，探索弱碱环境下提高混凝土抗硫酸盐侵蚀性能技术途径。成果将丰富混凝土硫酸盐侵蚀理论，为混凝土结构耐久性设计提供理论指导和技术支撑。

传统混凝土硫酸盐侵蚀研究多集中于强碱环境下发生的钙矾石和碳硫硅钙石型侵蚀的情况，本项目从弱碱环境入手分析了pH值对石膏形成的影响，指出低pH条件下形成石膏需要的硫酸根浓度明显降低，阐明了弱碱环境下硫酸盐侵蚀下石膏容易形成的原因和形成机制。项目揭示了弱碱硫酸盐环境下C-S-H、C-A-S-H脱钙、脱铝机制并探明了C-S-H、C-A-S-H分子链长、聚合度等微结构的演变过程。在此基础上，进一步发现弱碱环境下在界面处CH变成的石膏会引起浆体和骨料的剥离，为维持体系平衡C-S-H、C-A-S-H脱钙则会引起胶凝能力的丧失，引起混凝土的软化和溃散，揭示了石膏型硫酸盐侵蚀过程中混凝土界面、孔结构和微细-宏观性能的时变规律，探明了石膏相形成-微结构演变-性能劣化之间内在关系，揭示弱碱环境下混凝土石膏型硫酸盐侵蚀机理。最后项目组采用硅灰、钡盐等手段消耗氢氧化钙和迁移进入的硫酸根离子，提升水泥基材料的密实度，抑制石膏相的形成，从而有效提高水泥基材料抗石膏型硫酸盐侵蚀的能力。成果将丰富混凝土硫酸盐侵蚀理论，在弱碱环境下对混凝土结构耐久性设计提供理论指导和技术支撑。