| The groundwater of the Linhuan Mining Area contains high concentrations of SO42- and Ca2+, and several vertical shafts at the bedrock section have been seriously corroded. At those shafts, the sidewall has varying degradation degrees in different parts. The part on which water flowed is barely corroded, whereas the moist part near the pouring joints is seriously corroded. After the mechanism of this phenomenon was studied, based on accelerated corrosion experiment, a remaining life prediction method for corroded sidewall was established.Taking the auxiliary shaft of the Tong-ting Coal Mine as the research object, the corrosion degree of typical parts was tested by ultrasonic and rebound test, and the corrosion mechanism was studied by chromatography, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The results showed that gypsum in corrosive water was supersaturated. The part on which water flowed was protected by the crystallized precipitation on the concrete. By contrast, the corrosion of the part where water flowed through pouring joints was aggravated by internal crystallization.When a sidewall is corroded by sulfate attack, the reliability and remaining service life are both essential questions. In order to solve those problems, accelerated corrosion experiment is usually needed to obtain the degeneration law of strength parameters and the acceleration corrosion factor. In accelerated corrosion experiment, there were two kinds of specimens, three point-bending beams and cube specimens.The corrosion environments of the three point-bending beams included immersing (0,9 and 15 wt% sulfate solution) and drying-wetting (15 wt% sulfate solution).The phase analysis indicated that the corrosion reaction in accelerated corrosion experiment and corroded sidewall were similar. After a predictive function of the corrosion layer in drying-wetting accelerated corrosion experiment was built by GM(1,1) model, by comparing to the corroded sidewall, the acceleration corrosion factor of drying-wetting accelerated corrosion experiment was obtained. After the predictive functions of elastic modulus were built by GM(1,1) model, the corrosion speed rate between immersing and drying-wetting accelerated corrosion experiment was acquired. Then, the acceleration corrosion factor of immersing accelerated corrosion experiment was obtained.After the cube specimens were divided into three groups, and separately loaded 0,14 and 21 MPa, they were immersed in 0 or 15 wt% sulfate solution. As we assumed that the acceleration corrosion factor based on corrosion depth, elastic modulus and compressive strength are equal, combining with the acceleration corrosion factor and the predication functions of the axial compressive strength of the corroded pre-damaged and normal cube specimens built by GM(1,1) model, a predictive function of the axial compressive strength of corroded sidewall was established.When a sidewall is corroded, the degeneration of the elastic modulus may cause stress redistribution. Thus, simplified models was built to analyses how increasing corrosion degree affects stress distribution. The results showed that, as to the auxiliary shaft of the Tong-ting Coal Mine, corrosion barely influent on stress distribution. Based on the predictive function of the axial compressive strength and the elasticity solution of the circular sidewall, a predictive functional of the reliability index for corroded sidewall was established.As to the auxiliary shaft of the Tong-ting Coal Mine, the service life is 47.3 years. In 2014, the residual life was 24.7 years, and the degradation parts have no need of immediately reinforcement. But if the pre-damaged degree of the sidewall was equivalent to 14MPa or 21MPa, the service life decreased to 24.4 or 20.2 years. It shows that damge by early loading on young concrete should be avoided during construction period, especially in sulfate corrosion environment. |
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