Influence of Carbonate Environment on Performance and Microscopic Characteristics of Tunnel Concrete
To investigate the erosion and deterioration of railway tunnel lining concrete in karstic areas,this study focuses on ordinary Portland cement concrete and calcium sulfoaluminate cement concrete,as well as shotcrete.An environment of accelerated corrosion through carbonate exposure was simulated.The impact of carbonate environment on the macroscopic properties and microscopic characteristics of different types of tunnel concrete was studied using macroscopic performance testing and microscopic testing methods such as X-ray diffraction analysis,Fourier-transform infrared spectroscopy,thermogravimetric analysis and scanning electron microscopy.The mass,relative dynamic modulus of elasticity and compressive strength of concrete show an initial increase followed by a subsequent decrease with the increase of immersion duration.The decline starts after 180 d of immersion,in which the compressive strength of calcium sulfoaluminate cement concrete is lower than the initial value after immersing for 360 d.Microstructural analysis of the concrete reveals that after 360 d of erosion,the crystals and gels in the original hydration products of the samples sharply decrease,giving rise to a significant amount of calcium carbonate.In the samples of calcium sulfoaluminate cement concrete,[Si(OH)6]2-octahedral groups are detected,confirming the formation of thaumasite.The calcium sufoaluminate cement-based concrete with ettringite as the main hydration product is more significantly affected by carbonate erosion.
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