Durability of Green Concrete in Severe Environment

In this paper,the effects of different mineral admixtures and sulfate solution types on the appearance,mass change rate,relative dynamic elastic modulus,and corrosion resistance coefficient of concrete were systematically studied.X-ray Diffraction(XRD),Mercury Intrusion Porosimetry(MIP),Scanning Electron Microscopy(SEM),and X-ray Computed Tomography(X-CT)were used to explore and analyze the changes in the microstructure and the corrosion products of concrete in the sulfate solution.The results show that the existence of magnesium ions accelerates concrete deterioration.There is a critical dosage of fly ash for magnesium sulfate resistance of concrete.The magnesium sulfate resistance of concrete is improved when the fly ash content is less than 20%.Slag can significantly improve the corrosion resistance of concrete to magnesium sulfate.The diffusion of sulfate ions into concrete is a gradual process.In the early stages of corrosion,sulfate ion content in the concrete immersed in the magnesium sulfate solution is slightly less than that of the concrete immersed in the sodium sulfate solution.However,in the later stage of corrosion,the sulfate ion content in the concrete immersed in the magnesium sulfate solution is significantly higher than that of the concrete immersed in the sodium sulfate solution.

Bond behavior of the interface between concrete and basalt fiber reinforced polymer bar after freeze–thaw cycles

The shear bond of interface between concrete and basalt fiber reinforced polymer(BFRP)bars during freeze–thaw(F–T)cycles is crucial for the application of BFRP bar-reinforced concrete structures in cold regions.In this study,48 groups of pull-out specimens were designed to test the shear bond of the BFRP-concrete interface subjected to F–T cycles.The effects of concrete strength,diameter,and embedment length of BFRP rebar were investigated under numerous F–T cycles.Test results showed that a larger diameter or longer embedment length of BFRP rebar resulted in lower interfacial shear bond behavior,such as interfacial bond strength,initial stiffness,and energy absorption,after the interface goes through F–T cycles.However,higher concrete strength and fewer F–T cycles were beneficial for enhancing the interfacial bond behavior.Subsequently,a three-dimensional(3D)interfacial model based on the finite element method was developed,and the interfacial bond behavior of the specimens was analyzed in-depth.Finally,a degradation bond strength subjected to F–T cycles was predicted by a proposed mechanical model.The predictions were fully consistent with the tested results.The model demonstrated accuracy in describing the shear bond behavior of the interface under numerous F–T cycles.