Analysis of the influence of material parameters on electrical conductivity of cement pastes and concretes

Abstract

This paper reports investigations on the influence of material parameters on electrical conductivity of cement pastes and concrete mixtures. The influence of cement type, water/cementitious materials ratio (w/cm), and the presence of fly ash as a cement replacement material on the conductivity of cement pastes is studied. The electrical conductivity-time relationships of cement pastes and concretes are expressed using a model that facilitates the extraction of initial and final conductivities, and a characteristic time parameter. These terms can be used to derive information about the microstructural changes occurring with time in cement pastes. A fractional factorial experiment scheme consisting of five factors-w/cm, fly ash content, aggregate-cementitious materials ratio (a/cm), aggregate size, and curing condition (saturated or sealed), with each factor at two levels (+1 or À1 corresponding to high and low levels)-is used for concrete mixtures. The experimental results are subjected to a range analysis to isolate the significant factors and factor interactions that influence the initial and final conductivities as well as the time parameter from the conductivity-time model for concrete mixtures. The a/cm exerts significant influence on both initial and final conductivities, whereas the amount of fly ash in the mixture, aggregate size, and curing condition influence the final conductivity of concretes. The w/cm and fly ash content were seen to influence the time parameter. Analysis of variance is conducted on the test results and the prominent two factor interactions that influence the conductivities and the time parameter are determined. The relationship between these responses and the parameters is expressed in terms of a least squares fit equation using the coded values for the variables.

A Multi-Aggregate Approach For Modeling The Interfacial Transition Zone In Concrete

“…In other words, lowering aggregate volume fraction or using coarser aggregate leads to thicker ITZ. Manchiryal and Neithalath 42 reported that increasing the volume fraction of sand tends to decrease the overall conductivity of mortar. Besides the increased tortuosity, the reduced ITZ extent may also be taken into account when explaining such a phenomenon.…”

Electrical conductivity based microstructure and strength prediction of plain and modified concretes

“…Further details of the experimental set up and measurement details can be found in [7,10]. The electrical impedance measurements of concretes were carried out on cylindrical specimens with steel rods acting as electrodes.…”

“…A more gradual decrease occurs thereafter, as hydration slows. Details on the analysis of the factors influencing electrical conductivity as a function of time, and the use of conductivity-time relationships to infer microstructural changes at early ages can be found in [7,10].…”

“…The impedance spectra can also be used to extract the complex dielectric permittivity and the relaxation times in composite systems. The use of impedance spectroscopy data to understand the response of cementitious systems at early ages [7,10], influence of cement replacement materials [11], and chloride transport and associated microstructural changes in concrete [12,13] have been reported. This paper demonstrates the effectiveness of a generalized effective medium theory, which is a combination of effective medium and percolation theories to predict the porosity of cementitious materials from the effective electrical conductivity obtained from EIS.…”

Prediction Model of Concrete Initial Setting Time Based on Stepwise Regression Analysis

“…The former supposes that the time corresponding to the minimum value point and a turning point on the resistivity development curve is linearly related to the initial and final setting time; while the latter considers that the first peak value of the resistivity differential curve is the turning point of cement paste hardening, which is related to the final setting time of cement paste. Some studies [15,16] proposed using a derivative of the conductivity-time curve to predict the setting time of concrete. They found that the initial setting time corresponds to the highest peak of the conductivity differential curve.…”