Abstract:
Based on the comprehensive consideration of the complex climatic characteristics and corrosion environment along the metro line, simultaneously considering ultraviolet radiation, wet and dry cycles, freeze-thaw cycles, sulfate and magnesium salt corrosion, a large cycle indoor test is designed and durability tests are carried out on 5 kinds of concrete including 3 water binder ratio and 3 fly ash content. The durability of the subway concrete is evaluated through the apparent phenomenon, compressive strength value, the relative quality evaluation parameters, the relative dynamic elastic modulus evaluation parameters, and the comprehensive damage assessment parameters. The damage degradation mechanism of concrete under multi-factors is analyzed by means of X ray diffraction (XRD) and scanning electron microscopy (SEM) with considering the quality and dynamic elastic modulus and the micro image. The results show that concrete specimens under indoor large cycle have complex physical and chemical reactions, generate expansive products, i.e. ettringite and gypsum crystals, and products without cementing performance, i.e. M-S-H. And the same time, they are subjected to the combined action of temperature stress, expansion and contraction stress, swelling pressure and salt crystal pressure and take on the erosion characteristics of initial strengthening, preliminary deterioration and accelerated degradation later. The comprehensive damage evaluation index of quality and dynamic elastic modulus can more objectively and accurately demonstrate macro performance and microstructure of concrete. The durability of the specimen with water cement ratio of 0.35 and fly ash content of 30% is the best.
