Durability And Service Life Prediction Of Concrete Exposed To Harsh Environment In West Of China

In the West of China, especially in slat lake area, where many concrete constructions is severely deteriorated and lost its function only in several years, which is mainly caused by the concentrated salts solutions such as chloride, sulfate and magnesium ions, and the harsh climate environment that is both dry and hot or cool. In the paper, a new suit of durability testing research system is established to simulate damage and deteriorated process of concretes under the interaction of loading and harsh environment in the West of China. Based on durability experimental results, the damage process of concretes with different compressive strength is systematically investigated under single factor, double factors and multi-factors with sulfate-chloride-magnesium-bending loading. And a damage function considering the bending loading, environment factors and types of concrete, is proposed. The diffusion of chloride in concretes is in detail studied under a factor, double factors and multi-factors with chloride- sulfate-magnesium-bending loading. And the chloride binding capacity of different concretes in different environments is also investigated. According to experiment results of damage and chloride diffusion into concretes immersed in Qinghai slat lake solution, mixing proportions of concretes are optimized for construction engineering in slat lake areas. In order to elucidate the above experimental results, the mechanism, which effect of sulfate on diffusion of chloride in concrete, is also investigated by the modern microanalysis techniques and theoretical analysis. The relationship between chloride diffusion coefficient and concentration of sulfate and chloride, as well as corrosion period is mathematically modeled. Moreover, corrosion production of pastes, immersed in different corrosion solutions and different immersion time, is quantitative analysis by XRD, TG-DSC. Microstructural and macrostructural changes of concretes exposed to composite solution are systematical investigated. The micro-expansion strength resulted of sulfate corrosion in concrete, and critical tensile strength of concrete is theoretical calculated. Base on the above calculated results; the cracks formed rule is determined for concrete exposed to composite solution. In the paper, two sets of service life prediction model are proposed. The one is multi-factors carbonation modeling for concretes in atmosphere environment, which considered carbonation, bending loading, content of fly ash, curing age, variability of concrete cover, and temperature. Another is multi-factors service life prediction modeling for concretes in salt lake area, which covered the sulfate and chloride ions mainly. The new modeling is based on Fick's second diffusion law, considering chloride binding capacity and bending loading, especially the interaction of sulfate and chloride, and the interaction of loading, sulfate and chloride. Based on the new service life prediction modeling, effect of concentration of sulfate and chloride, bending loading, and chloride binding capacity on service life prediction is calculated.(1)　Establishment of New multi-factors durability experiment system. In the paper, two corrosion regimes are employed in this study: naturally immersion (immersion in corrosion solution for long duration), drying-immersion cycles. The corrosion solution includes: NaCl solution, Na₂SO₄ solution, MgSO₄ solution with a concentration, and a set of composite solutions of 10%Na₂SO₄ (or 10%MgSO₄) and NaCl with different concentration, and a set of composite solutions of 3.5%NaCl and sulfate slat with different concentration, as well as Qinghai slat lake solution. The stress ratios, i.e. the ratios of flexural loading externally applied to the ultimate flexural loading of concrete, included 25%, 35% and 50%, are...