Study On The Equivalent Method Of Concrete Age Based On Electrical Resistivity

Concrete age is an indicator which could comprehensively reflect the physical properties of concrete and usually described by the time of maintenance under the standard curing conditions or the block’s compressive strength under the standard test. In engineering practice, the curing condition of concrete cannot be exactly the same as the standard curing condition. It is usually require equivalent to get the true age of concrete. But the traditional equivalent method cannot be applied in the area where is the key structural of the building and it also cannot be used for real time monitoring of the age of concrete. Taking into account the internal structure and the composition of concrete determined the macroscopic physical properties of concrete, including the compressive strength, shear strength, resistivity, elastic modulus, ages and so on. Therefore, this paper seeks to establish the relationship between the concrete resistivity and the age of concrete, through the temperature modification of concrete resistivity, to achieve the equivalent method of concrete age under the complex curing temperatures.The main research contents of this paper are as follows:1) Based on the theory of multiphase medium and the series parallel connection of resistance, the Winner boundary principle of porous media is used to derive a concrete resistivity model with multiple variables. The model has a feature of completeness in mathematical, and its parameters have a clear physical meaning, which can include the effect of the physical parameters such as porosity, saturation and other physical parameters on the resistivity of concrete. Through the sensitivity analysis of concrete resistivity model’s parameters, the main factors affecting concrete resistivity are porosity, saturation and the structural parameters. By analyzing the main factors of parameters, we found the function forms of parameters and the solution path.2) Designed a set of concrete resistivity automatic acquisition system, which consists of data acquisition, automatic control and temperature control module. Though the intelligent resistance instrument and the control of the acquisition circuit, this system achieved the real-time and continuous collection of concrete resistivity. The automatic acquisition system has solved the contact problem between the electrode and the concrete and also eliminated the impact of polarization reaction of concrete in the utmost degree by taking measures such as use the aluminum sheet which with small hole, shorten the acquisition time, automatic reverse measurement and so on. The data of concrete resistivity under different curing temperatures were measured by resistivity automatic acquisition system, which provides data support for solving concrete resistivity model.3) Obtaining the data from experiments at different curing temperature which changing with the curing time, using the difference of concrete resistivity that generated by different curing temperature, combining the nonlinear least squares method, this paper has solved the value of model parameters. Through the obtained resistivity model, the value of concrete resistivity under constant temperature and variable temperature curing conditional has been modified, and then using the value equivalent the real age of concrete which is defined under the standard curing condition.