Transient Resistivity-based Concrete Performance Characterization And Pore Structure Analysis

Concrete resistivity,as an electrical parameter,reflects the ability of concrete to block the flow of electric current per unit length.It also reflects the micro structure of concrete.It can be used to characterize the structure and performance of concrete.Resistivity is closely related to permeability,which in turn is closely related to durability,so it plays an important role in concrete durability evaluation.The concrete resistivity measurement method can be roughly divided into DC(directcurrent)test and AC(alternating current)test in principle.DCtestis relatively simple,but errors will occur during testing due to polarization effect.compared to DCtest,AC testing is simpler,but the testing process is also more complex.In this study,the concrete transient resistance tester developed based on the principle of DC-step input is used to test the concrete resistivity.This test method is simple,fast.The test returns several data at one test,make results more reliable.At present,the research on the influencing factors of concrete resistivity mainly focuses on the water-cement ratio and mineral admixtures.In addition to the above factors,this paper also studies the effect of concrete saturation rate,the resistivity of pore solution and the temperature of the test environment on the concrete resistivity.After discovering the influencing factors of concrete,this paper establishes the relationship between concrete resistivity and various properties of concrete,the feasibility of using the test results of transient resistance to characterize the strength,capillary water absorption rate,water permeability and chloride ion permeability of concrete at various ages is studied.Finally,the relationship between macroscopic resistivity and microscopic pore structure of cement-based materials was explored based on GEM model based on the transient resistance test and thermogravimetric test results.The main results of the experiment are as follows:(1)Water cement ratio,water saturation rate,temperature of test environment are the biggest factors affecting the resistivity of concrete.In this paper,the growth law of concrete resistivity with water-cement ratios from 0.30 to 0.60 is studied.The resistivity of concrete decreases with the increase of water-cement ratio.The resistivity of concrete with 0.3 water-cement ratio is much higher than that of concrete with 0.6 water-cement ratio,and the former is about twice of the latter.The increase of temperature will also reduce the resistivity of concrete.This paper tested the resistivity of concrete at different temperatures between 5℃ and 35℃,and the resistivity of concrete decreased by nearly200Ω·m.The saturation rate can be the biggest factor affecting the resistivity of concrete,and the resistivity of completely dry concrete can reach 2500Ω·m.After analyzing the variation law of concrete resistivity with age under different influencing factors,a concrete resistivity calculation model based on different influencing factors is deduced according to the test results.(2)When it comes to the characterization of concrete properties,the correlation coefficient between the resistivity test results and the permeability test results is generally high.The Impermeable label increases with the increase of concrete resistance,which shows a linear relationship with a correlation coefficient of 0.78.The electric flux decreases with the increase of concrete resistivity,they are inversely proportional to each other,and the correlation coefficient is 0.91.The diffusion coefficient of chloride ion decreases with the increase of concrete resistivity,which is also inversely proportional with a correlation coefficient of 0.72.The correlation between resistivity and RCM test results is slightly lower,which may be results of higher mineral admixture content.(3)Based on GEM model,the macro-resistivity of concrete is used to characterize the micro-structure of concrete in this paper.The effect of interfacial transition zone on the porosity of the whole slurry is considered,and the relationship between concrete resistivity and porosity and pore connectivity is discussed.The resistivity of concrete is quite sensitive to the change of porosity and connectivity,and decreases with the increase of porosity,while increases with the decrease of connectivity,which further verifies the research results of the first two chapters.In the process of analysis,the solid phase resistivity of concrete at three different scales,namely CSH gel phase,cement slurry phase and solid phase including aggregate,is also discussed.Through the analysis and summary of the above results,the transient resistance test method has a certain potential in the characterization of the macroscopic properties and microstructures of concrete structures.Especially in the aspect of permeability characterization,the transient resistance method not only has high correlation,but also has the advantages of short test time,simple test method,good stability of test results and low test cost compared with the traditional test method.