Research On Feasibility Of AC Impedance Monitoring Concrete Expansion And Cracks

Expansive crack is one of the cracks caused by non-load force, which is caused by the expansion uniformity of expansion source, expansive crack happen when the partial tensile stress exceeds the limit. Delayed ettringite formation(DEF) is a kind of concrete expansion damage of which source is ettringite in the concrete, it is difficult for damage assessment. Since DEF always occurs after concrete structures have been put into use for a long period of time.AC impedance spectroscopy(ACI) is a method of analyzing material properties or reaction process with AC signal, there will be a response when applying perturbation on an object, plural forms of the two signals(i.e. the impedance) in different frequency make up the AC impedance spectrum. We can get the percolation structure parameters(PSP) of concrete structure when impedance spectra information is translated into a quantitative representation with equivalent circuit diagram.The purpose of this paper is to assess the feasibility of AC impedance monitoring concrete expansion and cracks, which will be proposed through the analysis of the concrete expansion characteristics, ACI and PSP of the cracking process, the monitoring can be achieved with this connection obtained via the analysis. If the ACI spectrum can be put into practical application, it will be easy to conduct fast and lossless evaluation to concrete expansion and cracks like DEF.By adding expansion component(FBC ashes, dihydrate gypsum) to the concrete, and providing the internal and external conditions of DEF, expansion and surface cracking in some of the specimens were observed. There was a high frequency semicircle mutation in the ACI of surface-cracked concrete, the trend of some PSPs(rh, Rct, and T) changed at the time point of cracking. It is believed that concrete cracking will both affect ACI and PSP.it is not the same effect on the ACI and PSP because the internal structure changes of concrete before and after cracking are not the same, The experimental results indicate that the concrete cracking, ACI and PSP are interrelated, it is feasible to monitor the expansion and cracking of concrete by means of ACI.According to the Model of concrete expansion and cracking, the relationship of ACI and PSP with expansion and cracking can be indirectly established through the three effects in the process of cracking, Further study is needed since the relationship is very ambiguous, according to the mutation of ACI high-frequency semicircle, the Rct value and the highest point of high-frequency semicircle are considered to be applicable for early warning of the concrete surface cracking.