Graduate Thesis Or Dissertation
 

The Effects of Temperature on Electrical Resistivity Measurements of Concrete

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  • Measuring resistivity as a method to calculate formation factor is becoming a popular way to evaluate transport properties of concrete. Resistivity measurements are dependent on multiple factors including the resistivity of the pore solution, leaching effects, the degree of saturation of the specimen, the age of the specimen (degree of reaction), the microstructural properties of the pore network (porosity and pore connectivity), and temperature. Temperature affects the bulk resistivity measurements of concrete specimens by changing the mobility of the ions in the pore solution. In addition to multiple fitting equations and temperature corrections, numerous values for temperature correction parameters have been proposed for a wide range of materials (i.e., solutions, pastes, mortars, and concretes at different degrees of saturation). In this study, a linear approach (using an α temperature coefficient) and an activation energy type approach (using an Ea-cond temperature coefficient) are examined. These approaches were compared with each other numerically and their predictive capabilities were studied using measured resistivity data from several concrete mixtures. An equation is developed to convert a linear correction (α) to an activation energy type correction, (Ea-cond), given the testing temperature. Using a linear approach might be suitable for solutions and for saturated concrete, which have low values of α and Ea-cond. However, the use of Ea-cond provides better predictive capabilities in sealed concretes, which have higher values of α and Ea-cond, especially at low temperatures. An analysis of literature reveals that Ea-cond values vary from 9 to 39 kJ/mol, for pore solutions, pastes, mortars and concretes with a variety of saturation states. In order to select an appropriate Ea-cond for a specific specimen type, it is important to understand the factors affecting Ea-cond of cementitious materials. Ea-cond increases as degree of saturation of the specimen is reduced with a minimum Ea-cond when the specimen is saturated. This is not due to the dilution of the pore solution, as pore solutions with different ionic strengths have similar Ea-cond. Rather, the increase of Ea-cond upon drying is because of a change in the connectivity of the fluid filled pores. Under certain circumstances, changes in ionic mobility caused by changes in viscosity, may also affect Ea-cond. While it is better to directly measure the Ea-cond of every concrete mixture, this is not always feasible. In such cases, for pore solutions a value of 13.9 kJ/mol can be used, for saturated concretes a value of 15.8 kJ/mol can be used and for sealed concretes a value of 29.8 kJ/mol can be used. For concretes with a varying degree of saturation, the Ea-cond can be estimated if the degree of saturation (DOS) is known using the equation: Ea-cond = 33.3 – 16.3∙DOS.
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  • This work was conducted as part of a multi-laboratory study with mixtures from the Performance Engineered Mixtures (PEM) Champion States and as part of the National Concrete Consortium. Experiments in this study were performed at Oregon State University at the Kiewit Materials Performance Lab and Concrete Performance Lab.
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  • Pending Publication
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  • 2018-01-12 to 2018-08-12

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