Expansion stress during sulphate attack on concrete - effect of additions containing aluminium

与含硫酸盐的地下水接触的混凝土结构的外部硫酸盐侵蚀可导致由钙矾石的形成引起的损坏，从而导致损坏和高维修成本的膨胀应力。在第一个资助期内，用储存在硫酸盐溶液中的试样测量了含有生态和经济上有利的富铝矿物添加剂的波特兰水泥粘合剂组合物中的铝含量对膨胀应力的影响。结果表明，铝含量相比，孔径distribution.The调查只起次要作用还表明，外部硫酸盐侵蚀过程中发生的反应前沿可以可靠地监测使用现代空间分辨分析技术。在具有增强的抗硫酸盐性的波特兰水泥的情况下，观察到石膏形成跟随产生高度膨胀的钙矾石的形成。虽然对钙矾石层的损害机理已有深入的认识，但石膏层对损害发展的影响尚不清楚。由于在常规抗硫酸盐性测试期间由于所使用的高硫酸盐浓度而经常发生石膏形成，因此需要更深入地理解石膏形成的后果，特别是关于具有增强的抗硫酸盐性的抗硫酸盐波特兰水泥。令人惊讶的是，调查还显示，试样与抗硫酸盐波特兰水泥不表现出宏观裂纹，尽管一个非常高的自由膨胀。这种现象是否与石膏形成的增加直接相关，是本研究应用的主题。可以想象，由于钙矾石形成的新的微裂纹填充有石膏，抑制裂纹growth.The拟议的工作方案，包括在不同的低硫酸盐浓度的膨胀战线的空间分辨调查，以便石膏沉淀的效果可以系统地确定。在抗硫酸盐性增加的波特兰水泥的情况下，如果石膏沉淀较少，则这将导致更多的宏观裂纹。工作方案包括有约束和无约束的空心圆柱硫酸盐储存试验，因为目前的结果表明，约束抑制石膏的形成。与第一个供资期一样，使用有限元建模和热力学计算来帮助解释实验结果。该研究项目的结果旨在帮助设计更精确的抗硫酸盐性测试方法。

External sulfate attack on concrete structures in contact with sulphate-containing groundwater can lead to damage caused by the formation of ettringite and thus an expansive stress resulting in damage and high repair costs. In the first funding period, the effect of the aluminium content in Portland cement binder compositions containing ecologically and economically advantageous aluminium-rich mineral additions on the expansion stress was measured with test specimens stored in sulphate solutions. The results indicate that the aluminium content plays only a minor role compared with the pore size distribution.The investigations also showed that the reaction fronts occurring during external sulphate attack can be reliably monitored using modern spatially resolved analysis techniques. In the case of Portland cement with enhanced sulphate resistance, gypsum formation was observed to follow the formation of ettringite which produces a high degree expansion. While in-depth knowledge has been obtained on the damage mechanism of ettringite formation, the effect gypsum formation on damage development is unknown. Since gypsum formation often occurs during conventional sulphate resistance tests due to the high sulphate concentrations used, a deeper understanding of the consequences of gypsum formation, particularly with regard to sulphate-resistant Portland cements with enhanced sulphate resistance, is desirable. Surprisingly, the investigations also revealed that specimens with sulphate-resistant Portland cements do not exhibit macroscopic cracks despite a very high free expansion. Whether this phenomenon is directly related to the increased gypsum formation is the subject of this research application. It is conceivable that new micro cracks due to ettringite formation are filled with gypsum which inhibits crack growth.The proposed work programme includes the spatially resolved investigation of the expansion fronts at different low sulphate concentrations in order that the effect of gypsum precipitation can be systematically determined. In the case of Portland cements with increased sulphate resistance, this should lead to more macroscopic cracks if less gypsum precipitates. The work programme includes sulphate storage tests with hollow cylinders, with and without restraint, because the present results have shown that restraint inhibits gypsum formation. As in the first funding period, finite element modelling and thermodynamic calculations are used to aid the interpretation of the experimental results. The findings of the research project are intended to assist the design of more precise sulphate resistance test methods.