Study On Deterioration Law Of Tunnel Lining Concrete In Saline Dry And Cold Region Of Northwest China

Due to the mismatch between water resources and population distribution in Northwest China,a large number of water diversion projects need to be built to regulate water consumption.However,the durability of concrete works will be affected in the service process under the harsh erosional environment in the dry and cold saline area in Northwest China.As an indispensable part of water diversion project,it is crucial to ensure that the concrete lining of tunnel will not be degraded during the operation period.In this paper,through theoretical analysis and investigation of service environment obtained the main erosion damage factors of tunnel lining concrete in this area are dry and wet,freeze-thaw and salt erosion,and the erosion ion is determined.This article designed three different erosion environments（The three erosion factors are respectively dry and wet+freeze-thaw,dry and wet+freeze-thaw+5%Na₂SO₄solution,dry and wet+freeze-thaw+5%double salt solution）to simulate the harsh environmental conditions in the dry and cold region of Northwest China,and made eight kinds of modified concrete by adding fly ash,polypropylene fiber and applying polyurea coating.And analysis mass loss rate,compressive strength loss rate and relative dynamic modulus of modified concrete under different erosion environment,obtained the deterioration rule of indoor accelerated test,determined the life of indoor accelerated test,and through the economic analysis method to determine the best value of modified concrete as a method to improve the durability of tunnel lining concrete in the region.The purpose of this study is to provide a theoretical basis for the design,construction and later operation and maintenance of tunnel lining in the dry and cold saline region of Northwest China.Summarize the research results and draw the following conclusions:（1）For the test group with add fly ash,adding 15%fly ash improve the overall performance of lining concrete in the case of only dry,wet and freeze-thaw damage.In the area of serious salt erosion,it is not recommended to add appropriate amount of fly ash to improve the durability of concrete.Adding 0.9kg/m³polypropylene fiber can effectively improve the compactness of concrete,increase the permeability resistance of water and salt ions,and resist the effects of dry-wet,freeze-thaw and salt erosion.（2）Through the analysis of three different kinds of modified concrete coated with polyurea coating,it was found that the test group with 30%fly ash and coated with polyurea coating had the best performance in the clear water solution,and the test group with 0.9kg/m³polypropylene fiber and coated with polyurea coating had the best performance in the salt solution.The early damage of concrete coated with polyurea coating mainly depends on the durability of the polyurea coating.It is found by the test that the durability of the polyurea coating under different erosion solutions is from good to poor:clear water solution,5%Na₂SO₄solution,5%double salt solution.For uncoated polyurea concrete,under different erosion solutions,the durability from good to bad is:clear water solution,5%double salt solution,5%Na₂SO₄solution.（3）Based on the self-adaptive characteristics of the full-order time power grey prediction model,this paper selects the optimal structure form to predict the accelerated test life of the experimental group which has not reached failure after eight major cycles,and realizes the prediction of the future change trend of different modified concrete.（4）Through eight different modified concrete under three different erosion solution analysis of the value found in the water,5%Na₂SO₄solution and 5%double salt solution a maximum value in the experimental group are:ANF3,BNJ3,CNJ3,and all of those are daub polyurea coating concrete,but late daub polyurea coating can increase the quantities,so can consider adding 15%fly ash or 0.9 kg/m³polypropylene fiber resistance the effect of dry-wet and freeze-thaw,adding 0.9 kg/m³polypropylene fiber to resist salt invasion,dry-wet and freeze-thaw effects.For the dry and cold areas with high engineering quality requirements and severe erosion,suggested that in the early stage mixed 0.9kg/m³polypropylene fiber,and in the later stage of operation and maintenance,polyurea coating should be applied for protection after cleaning the surface residue of the places with severe erosion.This can not only improve the durability of concrete,but also achieve economic effect.