Crumb Rubber Concrete Durability Research And Application Study As Bridge Deck Pavement

The use of crumb rubber in Portland Cement Concrete (Crumb Rubber Concrete, CRC) has been the growing point of the concrete material research field in the last few years. It has been reported that putting crumb rubber in concrete mixtures compensates the deficiencies of plain concrete and results in low density and plastic shrinkage, significant increase of ductility and toughness, very high damping ratio, and extremely good thermal and sound properties. Recently, Prof. Han Zhu and his research panel in Tianjin University discovered that CRC has the properties of low permeability and low chloride penetration. Therefore, the study on the issue of the durability of CRC is of great importance concerning resolving engineering problem, securing construction quality, enlonging structure's service life, and promoting the application of CRC.This paper focuses on the properties of the permeability under hydraulic pressure, penetration of chloride ions, salt scaling, and steel bar corrosion in salt enviroment of CRC. Moreover, for the purpose of using CRC as bridge deck pavement, a series of material performance have been discussed in the article. The research methods, conclusions, and findings are generalized as follow:(1)The surface physical chemistry theory is adopted to analyze the mechanism of permeability of CRC under hydraulic pressure. Result shows that due to the extremely low polarity and the hydrophobic rough surface, the capillary pressure in concrete is decreased. For the first time, the rubber-water contact angle is experimentally measured, results demonstrated that the contact angle is of 80°-116°, and the angle is influenced by the rubber varieties and the scale of surface roughness. The incorporated rubber decreases the capillary pressure by 38% to 80% compared to the plain concrete. Fourteen groups of specimens, containing five levels of crumb rubber proportion, are tested. Results indicate that all CRC specimens exhibit low permeability.(2)The penetration model of chloride ions into CRC under wetting-drying cycle is established. The mechanism of electro-accelerated penetration is analyzed. CRC specimens are tested using ASTM C1202-97 rapid testing method. Results show that the penetration process is the coupling of pore solution infiltration and the chloride ions diffusion. The electro-accelerated penetration is dominated by electro-migration. Test results indicate that the dielectric flux of CRC is at the round of 1000C, which means a"very low"penetration according to ASTM C1202-97. And the CRC specimens incorporate 1mm~2mm crumb rubber exhibit better penetration resistance than those with 4mm~6mm rubber, which are approximately the same to the controlled group.(3)The electrochemical acceleration method is adopted to investigate the corrosion property of reinforced crumb rubber concrete (CRC). Two levels of water cement ratio were chosen, and a total of 24 beams, which contained four levels of crumb rubber from 0~150kg/m~3 were tested. The weight loss and spalling crack width were measured after the exposure of 5 and 10 days of current flow. To investigate the bearing capacity, deflection, and failure model of CRC beams that had been corroded, the four-point bending test was carried out. Results showed that putting crumb rubber into concrete mixture advanced the steel bar corrosion resistance, and minimized the corrosion while the crumb rubber volume proportion increases. The rust stains area and spalling crack width of CRC beams were much smaller than the controlled group. The shear failure was obsreved in four-point bending test. CRC beams exhibited high bond strength and large ductility. The load-deflection curves presented that CRC beams got lesser bearing capacity loss compared to the controlled group.(4)The FEM is adopted to calculate the stress and strain of pore wall, which is compressed by the spalling of 0~20% NaCl pore solution. The scaling of CRC, 0 ~150kg/m~3 rubber, is experimentally investigated. Results demonstrate that the mean values of stress of C-S-H pore wall of CRC are lower than that of the controlled group. The stress decreases 67.7%, 68.3%, and 72.4% respectively by pure water, 10%, 20% NaCl pore solution. However, the stress of rubber is no more than 0.5MPa. The reason for the pressure relief is the rubber yield large elastic deformation, which releases the expansion of pore solution, and reduces the damage of C-S-H. Test results show that the scaling mass decreases when increasing the rubber content. The scaling mass presents consistence while rubber content exceeding 120 kg/m~3.(5)For the first time, CRC is used as bridge deck pavement. The mechanical properties and impact ductility are tested. Results show that CRC exhibits ductile failure, the flexural and impact ductility is highly improved. A 7m×24m, 120mm thick CRC bridge deck test spot is constructed. The performance of the test site proofs that CRC bridge deck deserves further promotion.