Effects of Tensile Stress on Carbonation of Multilevel Concrete with Low Water-Binder Ratio

摘要

Two tensile loading devices were developed to investigate the effect of tensile stress level on carbonation rate of concrete specimen and girder respectively. The influence of tensile stress level on air permeability by TORRENT instrument and microstructures of concrete with SEM-BSE image were also studied. The results show that the relationship between accelerating-carbonation coefficient of concrete and tensile stress level is in agreement with exponential growth mode; Carbonation rate of small specimen is higher than that of corresponding girder suffering from the same tensile stress level and the difference gets much higher with growth of tensile stress level. The bottom concrete close to main steel in girder possesses higher anti-carbonation capability by 12.5%, compared to the lateral concrete of girder. Furthermore, the relation between tensile stress level and air permeability coefficient is also in exponential growth mode and the SEM-BSE images once again prove that certain tensile stress level induces irreversible micro-cracks inside the concrete matrix and enhances the diffusivity of CO_2 in concrete, which eventually results in higher carbonation rate of concrete.