Research On Preparation Technology Of Secondary Tunnel Lining Waterproof Fly-ash Concrete

Strength grade of secondary tunnel lining concrete is C25,together with the good workability,waterproof function and crack resistance.Waterproof agent and expansive agent are presently applied to produce the secondary tunnel lining concrete, which increases the cost of the project,and results in the shrinkage and cracking of concrete and serious water leakage of most tunnels due to the relatively high water-binder ratio.With the current problem of production of secondary tunnel lining concrete in practice,the parallel experiment and orthogonal experiment were carried out to study the effects of the waterproof agent and proportion parameters on compressive strength and impermeability of secondary lining concrete.The effect of of waterproof agent show that some waterproof agents can improve impermeability of concrete at a higher water-binder ratio of 0.52,and all the waterproof agents can't improve impermeability of concrete at lower water-binder ratio 0.43,with the low water reducing effect of composite water resistant.The orthogonal experimental result shows that factors affecting the 28d compressive strength and impermeability of concrete are ranked by water-binder ratio＞the exceeding coefficient of fly-ash＞the fly-ash replacement＞unit binder content.It shows that the water-binder ratio seriously affect the 28d compressive strength and impermeability of concrete,together with the relatively low impact of fly-ash replacement.Consequently,the mix proportions of secondary tunnel lining waterproof fly-ash concrete are proposed.That is,the relationship of low intensity,super-flowing and high impermeability of secondary tunnel lining concrete are balanced by reducing water binder ratio with superplasticizer and adding fly-ash replacement,as well as engineering cost is reduced.Proportion parameters of secondary tunnel lining waterproof fly-ash concrete have been optimized.That is,the C25 waterproof fly-ash concrete is prepared byⅡgrade fly-ash and P.O32.5 cement,and the mix proportion is as follows:360kg/m~3 of binder,water-binder ratio 0.46,fly ash replacement 20%,the exceeding coefficient of fly-ash 1.3～1.4。The crack resistance and durability of secondary tunnel lining waterproof fly-ash concrete are researched.The crack resistance of concrete is evaluated by plate test on plastic shrinkage behavior and ellipse ring restrained test technique,brittle coefficient of mortar,the ratio of strength to elastic modulus of concrete,drying shrinkage ratio of concrete.Results show that fly-ash can improve crack resistance of concrete.The results of accelerated carbonation experiment of concrete show that concrete can meet the demand of designed life when the fly-ash replacement is within 30%.The NEL accelerated chloride penetration test show that the secondary tunnel waterproof fly-ash concrete has good chloride ion resistance.The tests of concrete under sulfate corrosion show that the secondary tunnel waterproof fly-ash concrete has a better resistance to the corrosion of sulfate.Finally,the application of secondary tunnel waterproof fly-ash concrete is tested in construction of the Dafengling tunnel secondary lining.The results show that the secondary tunnel waterproof fly-ash concrete has good workability,The formed concrete smooth outside with compacted inside,can meet the demand of designed mechanical property and impermeability.Moreover,the engineering cost is reduced and some economical benefit is acquired.