Experimental Study On Tunnels Sprayed Concrete Frost-resistance And Durability

Sprayed concrete is the important component of tunnels primary support. Because of requirements of economic and social development, many tunnels in the cold region in China will be built. But the research on frost-resistance and durability of sprayed concrete is relatively rare. This thesis use laboratory experiment method, made two lots of C25 sprayed concrete prismoid test-piece. One group mixed into air entraining. Testing the weight, relative dynamic elastic modulus and ultrasonic wave of C25 Sprayed concrete which bears different times of freeze/thaw cycling. The damage mechanic characteristics of C25 Sprayed concrete which bears different times of freeze/thaw cycling, the air entraining agent influence on sprayed concrete frost-resistance. It uses MIC-840-01 hardened sprayed concrete pore structure instrument testing two lots of sprayed concrete and bubbles characteristic parameter of hardened Sprayed concrete test-piece. and the relationship between frost-resistance and durability of sprayed concrete and bubbles characteristic parameter. The following conclusions are obtained:(1) The average weight of Sprayed concrete test-piece lost 2.82% and 2.27% after bear 400 times of freeze/thaw cycling, less than 5%, relative dynamic elastic modulus dropped to 72.9% and 64.1% respectively, greater than 60%. The average weigh of frost-resistance and durability sprayed concrete test-piece bears 300 times freeze/thaw cycling coefficient is 77.6% and 70% respectively. Greater than 60%. it shows that in the condition of laboratory test through strictly controlling construct match ratio sprayed concrete has a favorable frost-resistance.(2) The average weight of sprayed concrete test-piece mixed into air entraining agent bears 400 times of freeze/thaw cycling relative dynamic elastic modulus dropped to 83.4% and 76.1% respectively. The average weigh of frost-resistance and durability sprayed concrete test-piece bears 300 times freeze/thaw cycling coefficient is 87.1% and 88.2% respectively. Compare with group of normal sprayed concrete, average weight lost are 0.73% and 0.54% less. Relative dynamic elastic modulus is 5.8% and 6.0% more. The average weigh of frost-resistance and durability sprayed concrete test-piece bears 300 times freeze/thaw cycling coefficient is 9.5% and 12.1% more.. It shows that sprayed concrete mixed into air entraining argent could improve frost-resistance and durability of sprayed concrete.(3) The weight of C30 Sprayed concrete test-piece lost 1.2% after bearing 100 times of freeze/thaw cycling, relative dynamic elastic modulus is 62%. The weight of C30 sprayed concrete test-piece mixed into air entraining agent bearing 400 times of freeze/thaw cycling relative dynamic elastic modulus IS 2.76%, relative dynamic elastic modulus is 77.1%. It shows that frost-resistance and durability of sprayed concrete is superior to normal concrete.(4) Bubbles distance coefficient test results between Normal sprayed concrete and sprayed concrete mixed into air entraining argent shows that sprayed concrete mixed into air entraining argent could reduce bubbles distance coefficient. Go through with fitted of sprayed concrete bubbles distance coefficient and frost-resistance and durability coefficient, the result shows that they have linear relation (relation: y=-0.2012x+137.22, Correlation coefficient: R=0.97), with rising of Bubbles distance coefficient, sprayed concrete frost-resistance and durability coefficient goes low.(5) Majority of bubbles in sprayed concrete are innocuous bubbles which less than 200μm in diameter. The results show aerated structure in sprayed concrete is good for frost-resistance and durability.The conclusion indicates that under the condition of laboratory test sprayed concrete has a favorable frost-resistance and durability. Sprayed concrete mixed into air entraining argent could improve frost-resistance and durability of sprayed concrete. With rising of Bubbles distance coefficient, sprayed concrete frost-resistance and durability coefficient goes low. These conclusions offered based methods of frost-resistance and durability of sprayed concrete for further research. The result will be valuable to design and construction of cold region tunnels.