Study On The Mechanism And Life Prediction Of New Corrosion Resistance Measures For Early Age Concrete In Saline Soil Area

With the implementation of a series of national policies such as China’s "Belt and Road" and "West-to-East Gas Transmission",more and more construction facilities of national strategic significance have been approved,which puts forward higher requirements for the construction industry in western China.However,there are a large number of salt lakes and saline land areas distributed in the western region of China,and these regional environments contain a large number of sulfate corrosion ions,which will cause serious physical and chemical erosion of the service concrete structure.In particular,the pile foundation is often in direct contact with the corrosive medium,and the poured pile concrete is not completely set and hardened in the early stage,which is more susceptible to sulfate erosion.Based on this background,combined with the construction characteristics of poured pile concrete,this paper takes different anti-erosion measures to carry out erosion tests on early concrete,analyzes the deterioration of concrete under different erosion resistance countermeasures,and predicts the service life of concrete under different erosion resistance measures based on the evolution equation of concrete damage degree,and the main research conclusions are as follows:(1)Using styrene and polyionic liquid as wall materials,calcium oxide and polyacrylamide were selected from the core materials to synthesize two microcapsules suitable for different scenarios.The polyionic liquid in the wall material has a certain sulfate ion response ability,the polyionic liquid can react with sulfate ions to form a hydrophilic channel in the microcapsule shell to release the internal core material,and the microcapsule with polyacrylamide as the core material is used as an example to test the microcapsule wrapping rate and ion response ability.Under the ambient conditions of 75 °C,the encapsulation rate of synthetic microcapsules was higher than that of 65 °C and 85 °C environmental conditions,and the microcapsules synthesized under the three temperature conditions stood in6% sodium sulfate solution for 20 min at room temperature,and the trigger rate of corrosion ions was between 28.6%～30.5%,and the trigger rate of corrosion ions could reach 100% after full reaction in 6% sodium sulfate solution.(2)Concrete with a microcapsule content of 1%,3% and 5% was tested for sulfate erosion resistance,and after 40 dry and wet cycles,the concrete with a microcapsule content of 3%and 5% was not eroded by sulfate ions at a depth of 20 mm.However,the unwrapped polyacrylamide in the later stage of concrete hydration will lose water and shrink,resulting in a decrease in concrete compactness,and excessive microcapsule content will adversely affect the durability of concrete structures,and the optimal microcapsule content in this test is 3%.(3)External protection is based on the engineering background of a layer of mud between the concrete and the rock layer after the construction of the poured pile concrete,if some anti-corrosion chemical reagents are added to the mud,it can form a good protective effect on the poured pile concrete.The mud configuration was carried out by the four-factor three-level orthogonal test,and the viscosity value with the greatest influence on the formation of mud skin was selected as the evaluation index,and the viscosity value of the mud was directly proportional to the sodium carboxymethylcellulose and bentonite content,and inversely proportional to the sodium lignosulfonate content.(4)The test piece mixed with fly ash,with the increase of fly ash content in the early stage,the compressive strength and dynamic elastic modulus of the test piece are reduced,if the fly ash content is too high,it has a certain adverse effect on the sulfate erosion resistance of early concrete.In this test,the proportion of fly ash incorporated from weak to strong protective effect is: 10%,30%,20%.(5)The test piece with mud protection,the thicker the mud protective layer,the better the protection ability.However,based on the direct shear test,the presence of mud will reduce the friction between concrete and soil,and the shear stress of the test group with mud skin will decrease rapidly under the same shear displacement compared with the test group without mud skin,and the decline will gradually increase with the increase of mud thickness.(6)Based on the test results,the evolution equaton of concrete damage degree was established,and the accelerated test method was selected as the method of life prediction,the actual engineering environment was compared with the indoor test environment,the acceleration constant of the indoor test was determined,and finally the life of concrete specimens under different erosion resistance measures was predicted.