Study On Mechanical Properties Of RC Beams With Degraded Before And After Reinforcement By Carbon Fiber Reinforced Cement-based Materials

At present,coal is still the main body of energy in China.The safety production of coal mine and the secondary utilization of abandoned space have higher requirements on the bearing capacity and durability of surface buildings of coal mine.It is very important to evaluate the reliability of RC beam structure in coal mine environment and to repair and reinforce it in time to avoid economic loss and casualties caused by structural damage.In this paper,based on existing discovers the test data,the use of physical experiment and numerical calculation comprehensive to analysis the light and moderately degraded RC beam law of concrete and reinforcement mechanics performance degradation,the law of RC structural behavior degradation and carbon fiber reinforced cement-based composites after strengthening RC structural behavior enhance law,main conclusions and innovations are as follows:1.The degradation law of mechanical properties of light and moderately degraded RC beams concrete are revealed.It fit the time function of concrete neutralization depth and core compressive strength;With the extension of the deterioration cycle,the neutralization degree of RC beam concrete in coal mine environment shows a trend of “fast and slow alternate”;Continuing growth of corrosion elements and corrosion products from the surface;The compressive strength of the core sample increases first and then decreases with the extension of the cycle.2.The Law of degradation of mechanical properties of light and moderately degraded RC beam corroded steel bars is obtained..The relationship between the strength of corroded steel bars and the corrosion rate of steel bars was established;It fit the time function of the corrosion rate of steel bars at different locations;The corrosion rate of steel bars increases slowly and then increases rapidly and damaged steel bars increases faster than that of deteriorated beams;The yield strength and ultimate strength of steel bars decrease with the increase of corrosion rate and the development of steel strength has fluctuations and the strength loss is not big;3.The Change law of light and moderately degraded RC beam degradation state and failure process and failure characteristics evolution are revealed.The degree of deterioration of RC beams in coal mine environment deepens with the increase of cycle;The failure process and failure characteristics of the beam in the 7-8 cycle test are basically the same;The ultimate bearing capacity of the damaged beam with the same period is obviously smaller than the ultimate bearing capacity of the deteriorated beam;The decrease of the effective height of the section and the decrease of the concrete strength grade are the main factors affecting the rate of deflection of the light and moderately degraded RC beam.4.Theoretical calculation model for flexural capacity of light and moderately degraded RC beams is established.The change of ultimate bearing capacity of light and moderately degraded RC beams shows a trend of first fast and then slow down with the extension of corrosion cycle;The deformation capacity increases with the increase of the corrosion cycle.With the increase of cycle,the failure mode of RC beam changes from compression shear failure to bending failure.Based on the degradation law of mechanical properties of 0-8 cycles RC beams in coal mine environment,considering the multiple corrosion factors,the calculation method of flexural capacity is improved.5.The different effects of CFRCM bonded carbon fiber cloth and fiber woven mesh after reinforcement are obtained.CFRCM paste carbon fiber cloth enhances the section bending stiffness,and the bearing capacity enhancement effect is better than the bonded carbon fiber woven mesh,which has a rigid reinforcement effect.CFRCM paste carbon fiber woven mesh effectively improves the ultimate displacement of the component,and the toughening effect is better than the bonded carbon fiber cloth,which provides a flexible reinforcement effect.6.The calculation method for the flexural capacity of moderately degraded RC beams by carbon fiber reinforced cement-based composites is proposed.Based on factors such as RC beam material degradation and effective utilization of carbon fiber composite materials and the enhancement of mechanical properties of RC beams strengthened with carbon fiber reinforced cement-based composites,the calculation method of flexural capacity is revised.The ultimate bearing capacity and deformation capacity of CFRCM bonded carbon fiber cloth or fiber woven mesh reinforced RC beams have been significantly improved,which deserves further study.