含石膏质集料混凝土内部硫酸盐侵蚀机理

Aggregates in many parts of China are contaminated with sulfate, particularly with calcium sulfate. The existence of an excessive amount of sulfates in aggregates may lead to internal sulfate attack(ISA) in the concrete,which had happened in many concrete constructions. However, the mechanism of internal sulfate attack in concrete is lacking of system research now. In this project, the effect of the temperature, alkalinity, curing methods and sulfate concentration in the pore solution on the formation of the ISA corrosion products were researched. Then the thermodynamic condition and dynamic characteristic of the formation of corrosion products during the process of ISA were investigated. By the above study results, the microsturcture evolutiong during the process of the ISA was studied. And the relations of the corrosion products formation, stress distribution, microstructure and the performanc deterioration of the concrete were presented in order to provide the informance about the mechanism of ISA in concrete. Besides, several methods were used to inhabit the corrosion products formation and improve the microstructure of the concrete for boosting the resistance of internal sulfate attack in concrete, such as changing the curing system, using the dissoluble barium salt and mineral admixture. The project results will enrich the sulfate corrosion theorys of the concrete, and provide the theoretical direction and technological support to the durability design of the concrete.

我国低工业价值石膏质集料资源丰富，实际工程中时常发生因使用石膏质集料而导致混凝土结构破坏的案例。目前，对混凝土硫酸盐侵蚀的研究多集中于外部硫酸盐侵蚀，对于内部硫酸盐侵蚀机理仍缺乏系统研究。本项目拟研究温度/碱度/孔隙溶液硫酸盐浓度/养护制度对内部硫酸盐侵蚀过程及主要侵蚀产物相形成的影响，探明侵蚀过程中各侵蚀产物相的热力学条件和动力学特征；研究各侵蚀产物相形成过程对混凝土界面、孔结构和微细观-宏观性能的时变规律，探明侵蚀产物相形成-内应力分布-微结构演变-性能劣化之间的内在关系，揭示石膏质集料引起的内部硫酸盐侵蚀机理。在此基础上，采用改变养护制度/掺合料/可溶性钡盐抑制侵蚀产物相形成、改善微观结构，探索提高混凝土抗内部硫酸盐侵蚀的技术途径。成果将丰富硫酸盐侵蚀理论，为混凝土结构耐久性设计提供理论指导和技术支撑。

我国低工业价值石膏质集料资源丰富，实际工程中时常发生因使用石膏质集料而导致混凝土结构破坏的案例。目前，对混凝土硫酸盐侵蚀的研究多集中于外部硫酸盐侵蚀，对于内部硫酸盐侵蚀机理仍缺乏系统研究。本项目研究了多因素条件下，水泥基材料内部硫酸盐侵蚀机理。研究认为：溶液的pH值对石膏集料的溶解速率有很大影响；孔隙溶液pH值直接影响内部硫酸盐侵蚀产物种类和结构的形成。整个劣化过程可以分为两步:首先混凝土出现膨胀，强度有略微的提升，浆体中无明显裂纹；随着龄期的增加，侵蚀产物进一步增多，混凝土试件强度出现下降，石膏周围的浆体出现裂纹，浆体与集料也出现裂缝。