Location
University of Leeds
Keywords
Sulfate attack, temperature, calcium leaching, multi-ion interaction, numerical model
Abstract
Sulfate attack is one of the major durability problems of concrete structures, which is manifested by expansive cracks and deterioration of cement paste. In this study, a numerical model is proposed to predict the process of ionic diffusion into concrete under external sulfate attack. The chemical reaction and diffusion processes are considered in this model. Furthermore, the influence of calcium leaching, chemical activity of multi-ions, temperature and changes in porosity are also taken into account. The initial porosity and tortuosity are assumed to be homogeneous in concrete, and the chemical potential gradient is regarded as the driving force for ions migrating in pore solution. The modified Davies equation is employed to quantize interaction effect among different ions in solution. A temperature dependent parameter is introduced in the diffusion process of sulfate ion. The dissolution of solid calcium is divided into two stages referring to solid-liquid equilibrium curve of calcium ion. One is the dissolution of the calcium hydroxide, and the other is the decalcification of the calcium silicate hydrate. The influence of calcium leaching on porosity is further considered in diffusion coefficient. Moreover, changes in porosity due to formation of expansive ettringite are also reflected in the diffusion coefficient. Finally, a new numerical model is established and a comparison of the model prediction with the experimental results has been conducted. It is demonstrated that the established diffusion-reaction model can provide a better deterioration assessment of concrete structures exposed to sulfate attack.
Included in
Establishment of a Numerical Model for Sulfate Attacked Concrete Considering Multi-factors
University of Leeds
Sulfate attack is one of the major durability problems of concrete structures, which is manifested by expansive cracks and deterioration of cement paste. In this study, a numerical model is proposed to predict the process of ionic diffusion into concrete under external sulfate attack. The chemical reaction and diffusion processes are considered in this model. Furthermore, the influence of calcium leaching, chemical activity of multi-ions, temperature and changes in porosity are also taken into account. The initial porosity and tortuosity are assumed to be homogeneous in concrete, and the chemical potential gradient is regarded as the driving force for ions migrating in pore solution. The modified Davies equation is employed to quantize interaction effect among different ions in solution. A temperature dependent parameter is introduced in the diffusion process of sulfate ion. The dissolution of solid calcium is divided into two stages referring to solid-liquid equilibrium curve of calcium ion. One is the dissolution of the calcium hydroxide, and the other is the decalcification of the calcium silicate hydrate. The influence of calcium leaching on porosity is further considered in diffusion coefficient. Moreover, changes in porosity due to formation of expansive ettringite are also reflected in the diffusion coefficient. Finally, a new numerical model is established and a comparison of the model prediction with the experimental results has been conducted. It is demonstrated that the established diffusion-reaction model can provide a better deterioration assessment of concrete structures exposed to sulfate attack.
