Study Of Deterioration Law And Mechanism Of Shotcrete Durability Performance

Shotcrete is concrete which is conveyed under pressure through a pneumatic hose or pipe and projected into place at high velocity,which simultaneous compaction.Since shotcrete as finally support for soft soil at municipal sewer network of Frankfurt in 1970,due to short finally setting time,fast hydration,high early aging strength and easy construction,shotcrete was widely used in civil engineering structure,especially tunnel engineering.As the background of shotcrete permanent single-layer tunnel lining,shotcrete durability performance deterioration law was researched in terms of common atmosphere environment,cold environment,marine environment and Salt Lake encironment.By using X-ray diffraction(XRD),thermal analysis,scanning electron microscope(SEM),mercury intrusion porosimeter(MIP)and infrared spectrum(IR)method,the microstructure of corrosion shotcrete was characterized and the deterioration mechanism of shotcrete durability was discussed.The results are shown as follows:(1)It is obviously different that hydration between shotcrete and normal concrete.Early aging strength was formed from the mesh structure with albite and ettringite.After that,due to high hydration heat,cementitious materials formed hydrated calcium silicate(CSH)gel which filled in mesh structure.However,due to fast hydration,submicron size pores content in CSH gel was high which caused low growth of mechanical properties.Meanwhile,the compressive and splitting tensile strength prediction model was established in terms of water-binder ratio,dosage of fly ash and amount of steel fiber.(2)Aim to analyze the neutralization of shotcrete in the atmosphere environment,the neutralization depth,compressive and splitting tensile strength,pH value and nitrate ions concentration of pore solution were measured in shotcrete with carbonation and coupling influence of nitric acid & carbonation and freeze-thaw & carbonation.Combined with microstructure characterization,the neutralization process of shotcrete was analyzed.Based on experiment date,the neutralization depth prediction model of shotcrete was built under couple effectives.(3)In order to research the performance deterioration procrssing of shotcrete with frozen damage and/or coupling effect of nitric acid & freeze-thaw cycles were studied in terms of macroscopic properties,microstructure,pore structure and nitrate ions concentration.(4)Adopt for potentiometric method,the chloride ion concentration was tested in shotcrete which in under seawater zone,and coupled with freeze-thaw cycles and nitric acid.And the influence of chloride diffusion in shotcrete on freeze-thaw cycle and nitric acid was also investigated.After that,chloride ion diffusion model was established in shotcrete under the couple actions.(5)For researching the shotcrete durability in salt lakes,using dry-wet alternation method,considering the influence of sulfate ion and compositie salt of sulfatemagnesium-chloride,test of durability performance of shotcrete was carried out.For characterizing the physical and mechanical properties,apparent morphology,microstructure,ions concentration and mineral composition,the performance damage process and mechanism of shotcrete in salt lakes were discussed.