Mix Proportion Design And Application Research On Concrete Of Huang Jiatai Tunnel Engineering In Qian Zhangchang Railway

Based on Huang Jiatai tunnel engineering of Qiang Zhangchang railway,the influences of sand percentage,water reducer and accelerating agent on the properties of tunnel shotcrete are studied by orthogonal design.Meanwhile,the influences of W/B,fly ash and water reducer on the properties of secondary lining concrete are studied by the similar method.The microstructure of tunnel shotcrete and secondary lining concrete under different experimental conditions are studied by SEM.Combined with quality control of concrete construction in tunnel engineering as a key technology,the conclusions are outlined as follows:(1)The dosage of accelerating agent in the range of 1%~7%,the initial setting and final setting time of cement decreases gradually with the increase of the dosage of accelerating agent,and the setting time becomes longer when it is higher than 7%.Therefore,the proportion of accelerating agent should be controlled between 5% and 7%.(2)For tunnel shotcrete,under the condition of W/B fixed to 0.45,the proportion of water reducer is the main factor influencing its slump,while sand percentage is the main factor influencing its compressive strength and impermeability,so in the preparation of tunnel shotcrete,we should choose reasonable dosage of water and sand percentage.With comprehensive consideration of its performance,economy and construction technology,the best mix proportion of tunnel shotcrete which obtains by orthogonal is that W/B is 0.45,sand percentage is 48%,water reducer is 1%,accelerating agent is 5% and unit water dosage is 190kg·m-3.As a result its performance index meets the design requirements and its economy is reasonable.(3)For secondary lining concrete,W/B is the main factor influencing its slump and impermeability,and fly ash is the main factor influencing its compressive strength,so in the preparation of secondary lining concrete,we should choose reasonable W/B and proportion of fly ash.With comprehensive consideration of its performance,economy and construction technology,the best mix proportion of secondary lining concrete which obtains by orthogonal is that W/B is 0.45,the proportion of fly ash is 20%,sand percentage is 39%,water reducer is 1% and total cementing material is 400kg·m-3.Consequently its performance index meets the design requirements and its economy is reasonable.(4)SEM observations show that for tunnel shotcrete,the microstructure of the concrete number of P-A is less pore,higher density than that of the concrete number of P-3,P-8,P-14,and has little difference with the concrete number of P-9 and P-10,so the concrete number of P-A is optioned as the best mix proportion of tunnel shotcrete.For secondary lining concrete,the microstructure of the concrete number of C-4 is less pore,higher density than that of the concrete number of C-6 and C-9,and has little difference with the concrete number of C-2,C-7 and C-A,so the concrete number of C-4 is optioned as the best mix proportion of secondary lining concrete.(5)In the actual construction of the engineering,for tunnel shotcrete,the dosage of water reducer which changes from 1.0% to 1.2% can improve its slump and solve some problems such as serious losses because of excessive pouring time.When pouring each vehicle tunnel shotcrete,the dosage of accelerating agent should be used 7% in the former 5 m3,then the dosage of accelerating agent should be used 5% in the later 5 m3,hence it can solve the problem such as concrete rebound is too large.For secondary lining concrete,when pouring arch,W/B which changes from 0.40 to 0.42 and the dosage of water reducer which changes from 1.0% to 1.2%,can solve the problems such as dense,void and shrinkage cracking of arch.