Technical Measures Of The Railway Tunnel Lining Concrete Resistance To Sulfate Attack

In the southwestern regions of China, the lining concrete of railway tunnels is and has been being severely attacked by the sulfate ions dissolved in the complex geologic environment. It is an urgent and important mission to study the durability of tunnel lining concrete in the sulfate environment to improve the long-term service function of new tunnel lining concretes and repair and reinforce the damaged ones.Based on the survey results of damaged tunnels in the southwestern regions, the tests concerning the sulfate attack on intial supporting shotcrete (ISC) and secondary lining concrete (SLC) were carried out using fully buried, partially exposed and wetting/drying cycles methods, and two inhibitors used in ISC and SLC were made. At last, the effects of DPS (Deep Penetration Sealer) and RMO (Repair Mortar Overlay) on the sulfate resistanc of concrete were studied respectively.The mains results of this paper are shown as follows:(1) according to the analysis results of XRD, EDS and XRD, the main mechanism resulting in the damage of lining concrete of tunnel in southwestern regions of China is the chemical and physical sulfate attack occurring in the sulfate environment with high concentration. (2) InhibitorⅠand InhibitorⅡ, whose main compositions are fly ash and silica fume, can significantly improve the sulfate resistance of ISC and SLC. After 240 days immersion in the 5% Na2SO4 solution, the strength loss of ISC with 20% dosage of InhibitorⅠwas 7.2% and the normal concrete was 71.7%, on the other hand, the sulfate resisting class of SLC with 30% dosage of InhibitorⅡcan be promoted from KS90 to KS150. (3) The results of practical engineering applications showed that the ISC with InhibitorⅠhad super spraying performance and the SLC with InhibitorⅡgood pumping workability, this supports that InhibitorⅠandⅡhave excellent applicability. (4) The depth of penetration of sulfate ions in the concrete could be significantly decreased if the surface of concrete in contact with water was coated by RMO and DPS, the reason is that the surface coating can prevent sulfate ions to go into concrete and reduce the harmful effect of sulfate attack; the same appearance could be found in the concrete whose surface in contact with air coated by RMO and DPS, the mechanism is that surface coating can prevent the evaporation of water and decrease the capillary suction of concrete resulting in light damage by sulfate attack.