Time-varying Similarity Of Permeability And Mechanism Of Admixture Concrete Under Dry And Wet Cycling Environment

Rebar corrosion is one of the main causes of the damage to the durability of reinforced concrete structures in coastal areas.The reinforced concrete is less durable in a dry-and-wet environment with natural tidal difference.Concrete permeability is one of the important indicators to evaluate the durability of the concrete.Admixtures can reduce the permeability of the concrete to a large extent,thereby improving the durability of it.Therefore,it is of great scientific significance and application value to study the time-varying similarities of admixture concrete when permeated in a simulated environment with tidal differences.The main research contents and outcomes mentioned in this article are as follows:1.Based on the existing research outcomes,we complete the research where the concrete is exposed in an environment with natural tidal difference for 1160 days and analyze how the permeability of the admixture concrete varying from time to time when exposed to water and gases and the correlation between the time and the permeability.The result shows that the more time the admixture concrete is exposed to water and gases,the less the permeated coefficients of the concrete are;the water permeability coefficient and gas permeability coefficient are linearly correlated.2.By using the method of nuclear magnetic resonance,we have traced and tested the main parameters of the microstructure of the admixture concrete;we have analyzed how the admixture has effects on the microstructure parameters of the concrete and the time-varying law;and we have also analyzed the connection between the macro permeability of this concrete and its porosity and ratio of the hole aperture.The result shows that the more the exposed time is,the less the magnitude of the holes of that concrete is in an environment with natural tidal difference;when exposed for the same period of time,compared with the common concrete,the admixture concrete has less holes with the aperture of 100-1000 nm,but it has more holes if the hole aperture is 0-10 nm and 10-100 nm.3.Designed and completed the test where different admixture concrete is exposed in an Ocean environment with tidal difference simulated by humans for 320 days,we have tested the water and gas permeability coefficients of them after different exposure times,and we have also studied the relationship between these two coefficients and the time attenuation coefficient.By means of the NMR,we have traced and tested the microstructure parameter of the tested concrete in the simulated tidal range environment,and analyzed the relationship between the water and gas permeability coefficients of the concrete and the total porosity and other pore structure parameters.The result shows that the water and gas permeability of the admixture concrete tends to be stable in the later period of exposure;the time attenuation coefficient of the water permeability coefficient of the same admixture concrete is larger than the time attenuation coefficient of the gas permeability coefficient;the porosity of the concrete is reduced as the simulated exposed time increases,and the time attenuation coefficient of the porosity of the admixture concrete is less affected by the exposed situation;with the simulated experiment,the permeability and porosity of the concrete are basically the same when exposed for240 days and 360-520 days on site respectively.