Electrical Resistivity and Electrical Impedance Measurement in Mortar and Concrete Elements: A Systematic Review

Abstract

This paper aims at analyzing the state-of-the-art techniques to measure electrical impedance (and, consequently, electrical resistivity) of mortar/concrete elements. Despite the validity of the concept being widely proven in the literature, a clear standard for this measurement is still missing. Different methods are described and discussed, highlighting pros and cons with respect to their performance, reliability, and degree of maturity. Both monitoring and inspection approaches are possible by using electrical resistivity measurements; since electrical resistivity is an important indicator of the health status of mortar/concrete, as it changes whenever phenomena modifying the conductivity of mortar/concrete (e.g., degradation or attacks by external agents) occur, this review aims to serve as a guide for those interested in this type of measurements.

Electrical Resistivity of Steel Fibre-Reinforced Concrete—Influencing Parameters

“…Mainly due to the pozzolanic or latent-hydraulic reaction of SCMs, such as GGBS, silica fume or fly ash the pore structure becomes finer and less permeable, and thus the conductivity of the pore solution is reduced. The same phenomenon can be observed using finer cements, such as cements with higher strength classes (e.g., [ 42 , 46 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]).…”

“…As stated in several studies (e.g., [ 11 , 26 , 37 , 38 , 41 , 44 , 45 , 46 , 47 , 48 ]), the increase in porosity, which can be a result of a higher w/c ratio or due to an increased binder content, generally led to a reduced electrical resistivity. However, in contrast to [ 41 , 44 , 45 , 46 , 47 , 48 ], both parameters in this study showed interaction effects.…”

“…The same effect of reduced electrical resistivity was detected with the decreasing content of GGBS. Generally, GGBS has a finer pore structure than the concrete, and so the conductivity is reduced by its addition (e.g., [ 42 , 46 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]). In this study, no effect on the electrical resistivity was observed by the replacement of only small amounts of cement by GGBS, but with higher contents of GGBS, 65% of the total binder content, a significant change in electrical resistivity was measured.…”

“…Therefore, for the concrete, if investigated under controlled humidity, especially the pore structure influences the resistivity and in turn is influenced by the process of hydration and the concrete composition (e.g., [ 40 ]). By screening the literature several other parameters become apparent, which affect the pore structure of concrete, such as water/cement ratio, cement content and the concrete ingredients, e.g., type of cement or applied supplementary cementitious materials and aggregates (e.g., [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]).…”

“…At constant cement content, an almost linear decrease in electrical resistivity is visible with increasing water/cement ratios between 0.4 and 0.6, while higher cement contents at a constant w/c ratio also lead to decreasing electrical conductivity. Both parameters are independent of each other and showed no interactions (e.g., [ 41 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]).…”