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In the paper, the effect of transverse cracks on the corrosion length of steel bars in concrete under the dry-wet circulation environment has been studied. Specimens of reinforced concrete with different width of transverse cracks were used in the drywet circulation environment test. After a certain number of cycles, carry out the study on the state of reinforcement corrosion in concrete. Main results are as follows: the steel corrosion length in the specimens soaked in chloride solution was much longer than the steel corrosion length of those specimens soaked in water. Besides, the corrosion length of steel bars increased along with the increase of crack width. When the crack width was more than 0.3mm, the reinforced steel showed the sustained corrosion mechanism; but when the crack width was less than 0.3mm, the reinforced steel showed the crack sealing mechanism. The phenomenon illustrated that the corrosion rate was fast at the early stage, and slowed down or even stopped later. The relationship between steel corrosion length and the period of dry-wet circulation applied to the linear relationship. In the paper, the prediction model of steel corrosion length has been built after the relationship between steel bars corrosion length and the dry-wet cycles has been analyzed.

The chloride ion concentration distribution and crack influence area in concrete crack area under dry-wet cycle are studied. Test blocks of concrete with different width of transverse crack are made; accelerate chloride ion erosion of concrete by using dry-wet cycle; the chloride ion concentration in the side of the crack and from the surface of the specimen to the direction the steel bar of different erosion cycles is regularly detected. The test results show that chloride concentration decreases with the increase of transmission depth, and achieve stability at 20mm. With the dry-wet cycle progressing, after 20 dry-wet cycle periods, chloride concentration in the specimen with crack width from 0.1mm to 0.5mm is over 0.1% on the side of crack by 30mm, which means the steel in this section is in danger of corrosion. Meanwhile, because of the interplay between the two-dimensional transmissions, the greater the crack width is, the higher will the chloride concentration of same transmission depth be.

The auto efficiently hydration heat arrangement and the non-contacting electrical resistivity device were used to test the thermology effect and the resistivity variation of Portland cement hydration. The structure forming model of Portland cement initial hydration was established through the systematical experiments with different cements, the amount of mixing water and the chemical admixture. The experimental results show that, the structure forming model of cement could be divided into three stages, i e, solution-solution equilibrium period, structure forming period and structure stabilizing period. Along with the increase of mixing water, the time of inflexion appeared is in advance for thermal process of cement hydration and worsened for the structure forming process. Comparison with the control specimen, adding Na2SO4 makes the minimum critical point lower, the flattening period shorter and the growing slope after stage one steeper. So the hydration and structure forming process of Portland cement could be described more exactly by applying the thermal model and the structure-forming model.