Research On The Durability Of High-temperature Rock-wall Tunnel Lining Concrete

In the construction of the deep-lying long tunnels, due to the formation lithology,geological structure, recent magmatism, groundwater activities and other factors,problems like high rock wall temperature and high-temperature water gushing oftenappear, which poses a serious impact on the tunnel lining construction. Differentdegrees of researches on effect of high temperature of rock-wall on the properties ofconcrete have been done by some scholars, which is still not systematic, and it’s also notclearly defined in tunnel codes. In view of this condition, through laboratory simulationof construction environments of high temperature of rock-wall and low-humidity thatexist in some geothermal abnormal lots of Lasa-Rikaze railway tunnel construction, theinfluencing laws and mechanisms of effect of high temperature of rock-wall on thedurability of tunnel lining concrete were investigated.There are two stages in the laboratory to simulate the curing system of thehigh-temperature rock wall tunnel lining concrete: the high-temperature curing stageand standard-curing stage. After molding, cure the specimens with molds under thecondition of high temperature for24hours. Then remove the molds, and cure thespecimens under the stander-curing condition to required ages. The temperatures ofhigh-temperature curing stage are50℃,60℃,80℃; The humidities ofhigh-temperature curing stage are50%RH,75%RH,100%RH.The influences of different temperatures and humidities of high-temperature curingstage on the durability of concrete have been studied. The results show that under thecondition of50%RH of high-temperature curing stage unchanged, the resistance of concrete to chloride ion penetration and carbonation is weakened as the curingtemperature rising; Under the condition of80℃of high-temperature curing stageunchanged, the resistance of concrete to chloride ion penetration and carbonation arestrengthened with the curing humidity rising.The effects of curing agent on the durability of concrete cured under simulationcondition of tunnel of high temperature of rock-wall were investigated. The resultsindicate that under the high-temperature curing stage of80℃and50%RH, theresistance to chloride ion penetration and carbonation of the concrete sprayed bysodium silicate curing agent is better than that of the concrete sprayed by paraffinemulsion curing agent.The influences of mineral admixtures on the durability of concrete cured underdifferent simulation curing regimes were studied. Based X-ray diffraction and SEManalysis of binder pastes at different ages, the influencing mechanisms of differentcuring temperatures on the resistance of concrete to chloride ion penetration andcarbonation were discussed from the microscopic point of view. The results show that athigh-temperature curing stage, the rate of cement hydration and water evaporationimprove, causing the uneven hydration products, which is one of the reasons that theresistance to chloride ion penetration and carbonation of the concrete cured undersimulation condition of tunnel of high temperature of rock-wall are better than thatcured under standard-curing system. When the temperature of high-temperature curingstage is below80℃, the resistance to chloride ion penetration and carbonation of theconcrete singly mixed with fly ash are worse than that of concrete singly mixed withslag powder. As the curing temperature rising, the fly ash particles begin to etch andcrack, and the activity of fly ash is significantly enhanced. The resistance to chloride ionpenetration and carbonation of the concrete singly mixed with fly ash are better thanthat of concrete singly mixed with slag powder, when the temperature ofhigh-temperature curing stage is at80℃.