The Reinforced Concrete Cover Cracking Prediction Model Of Metro Shield Segment

Currently, metro is used to ease the increasingly heavy pressure on urban traffic with having many advantages as lager passenger and fast. The chloride ions is easy to produce in the subway process, coupling with chloride ions accelerated steel corrosion in reinforced concrete, then expansion force is rusted, resulting in the protective layer of reinforced concrete structures cracked prematurely, which is a serious threat to the underground structure,s normal service life.Based on the project of the national natural science fund: the research of multiple scale corrosion fatigue damage and failure mechanism of underground reinforced concrete interface(51478183), in order to study the problems in the amount of steel corrosion quantity change over time in the process of the protective layer cracking of reinforced concrete structures in metro shield segment, and the prediction and the evaluation of the protective layer cracking, adopts the method of the thermal infrared imager and electrochemical workstation PS-268 A to do the research. The main research results are shown as follows:(1) The electrochemical workstation is used to research the condition of steel corrosion quantity change over time in concrete structures under the underground environment.Research shows that: Compared with single factor, coupled with the effect of stray current and chloride ions obviously accelerate the steel corrosion. The stray currents intensity greater, the chloride ions concentration higher, the steel corrosion rate will be greater, but the steel corrosion rate gradually stabilized with the extension of corrosion time.(2) Based on the electrochemical corrosion principle, through comparing the factors of stray current quantity and chloride ion concentration effect on the evolution of steel corrosion degree, and the degree of influence of each factor on steel corrosion rate is clear. Based on this basis, the prediction model of steel corrosion quantity in concrete is established.(3)The factors of stray current strength and chloride ion concentration on the influence of the reinforced concrete structures protective layer cracking in the subway environment is researched by combining the knowledge as elasticity and Faraday,s law with the experimental results, then the protective layer cracking of reinforced concrete structure prediction model is established under the simulated environment, which is based on the prediction model of the steel corrosion quality.(4) Based on infrared image technique, the evaluation method of reinforced concrete cover cracking is established with the indicator of average temperature rise. The theoretical analysis and experimental results show that: The evaluation method of concrete cover cracking basing on infrared technology has many advantages as high speed, accuracy andreproducibility, which can evaluate the crack depth development in concrete with the metro environmental erosion scientifically.