Determination of the transport properties of a blended concrete from its electrical properties measured during a migration test

Abstract

The Nernst-Planck equation describes ionic movements in saturated porous materials subject to chemical concentration gradients in the pore fluid and applied electric fields. When applied to a macroscopic system the equation supposes that the flux of each ion is independent of every other one. However, owing to the ionic exchange among different or similar species, there are ionic potentials that affect the final flux. These will distort the applied electric field and thus keep the electroneutrality of the sum of all the ionic species involved. The applied potential will fall linearly across the sample but an additional 'membrane' potential will change with position and time. This paper summarises a theoretical and experimental investigation into the application of the non-linear electric membrane potential to the simulation of the migration of chlorides in concrete. A new electrochemical test has been developed and carried out with different samples of concrete blended with pulverised fuel ash (PFA) and ground granulated blastfurnace slag (GGBS). During the tests the transient current and the electrical membrane potential were measured. A numerical model developed previously using the classical equations, but including changes in the concrete membrane potential, was optimised using an artificial neural network (ANN). Based on the experimental results and the simulations, the intrinsic diffusion coefficients of chloride, hydroxide, sodium and potassium were obtained. Also, the initial hydroxide composition of the pore solution, the porosity, and the chloride binding capacity were determined. The results showed good agreement with the theory and can help to explain the complex phenomena that occur during a concrete migration test.

Modelling chloride penetration in concrete using electrical voltage and current approaches

“…Additionally, the voltage membrane potential was calculated using a salt bridge in a drilled hole in the top of the sample giving readings of the actual voltage in the sample during the test (Figure 3). These readings confirmed that the voltage drop across the sample is not linear and varies with time 10,11 .…”

“…The chloride related transport properties needed to simulate the chloride effects on a voltage or current control test for the mixture proposed were obtained from the experimental voltage control results by feeding an artificial neural network with results from the electrochemical model 10,11 . Table 2 is a summary of the principal transport properties and variables obtained following that methodology.…”

Research on Interlayer Bonding Quality Control Method of Dam Concrete Based on Equivalent Age

“…There are two methods to test the chloride ion penetration resistance of concrete, which are the fast chloride ion migration coefficient method [ 34 , 35 ] and the electric flux method [ 36 ]. Electric flux is a parameter to evaluate the resistance of concrete to chloride ion penetration.…”