Neutralization Study On Shotcrete Under The Nitric Acid Attack And Carbonation

In recent years,single permanent shotcrete lining structure has been gradually used in tunnel engineering.There are high concentration nitrogenoxide and CO₂ in the tunnel environment and the nitrogenoxide turnes into HNO₃ with water.The HNO₃ and CO₂result in the neutralization of the shotcrete,which causing the shotcrete p H lowered,steel of the lining structure corrosion and the bearing capacity degradation.Nitric acid attack and rapid carbonation tests have been carried out to research the neutralization of shotcrete under the effect of vehicle exhaust and CO₂.（1）An alternate test of nitric acid immersion and rapid carbonation was carried out to analyze the change law of the macroscopic properties.The impact of water-binder ratio,fly ash content and steel fiber content on shotcrete quality,relative dynamic elastic modulus,neutralization depth and compressive strength were researched.The relationship model of compressive strength and neutralization depth was established.（2）The basic performance variation of the eroded ordinary concrete and shotcrete was analyzed.The influence of construction technology on concrete neutralization was researched.In addition,the quantitative relation of neutralization depth and compressive strength variation coefficient between ordinary concrete and sprayed concrete were established.（3）The mineral composition and microstructure of the shotcrete specimens for different erosion time were analyzed for the further study about the erosion process and mechanism by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.