Abstract
Nondestructive methods to obtain the electrical conductivity (σ) or resistivity (ρ) of concrete are gaining popularity for durability evaluation. However, these methods are susceptible to the effects of curing and conditioning, primarily temperature and degree of saturation. Before σ of concrete at varied temperatures can be used for durability assessment, appropriate corrections must be made to account for the effect of temperature (T). In this study, two existing and one new temperature correction methods were evaluated for 12 mortar mixtures varying in water-to-cementitious material ratio (w/cm) and the content and types of supplementary cementitious materials (SCM). Mortar specimens instrumented with embedded sensors were cured in sealed conditions for 11–13 months. After this period, the sealed specimens were subjected to stepwise temperature change in 5–50°C range while σ was recorded using the embedded sensors. Linear, bilinear, and Arrhenius temperature correction (LTC, BLTC, and ATC, respectively) were fitted to the obtained σ-T datasets and were evaluated for fitness. LTC provided an acceptable fit to the σ-T data (R2 > 0.81) but was found the most suitable in 5–30°C temperature range. BLTC was defined as a combination of two distinct LTC below and above the reference temperature at 23°C and had a better fit to the data (R2 > 0.96). Lastly, ATC showed the best fit among the tested methods (R2 > 0.98) and was found applicable for the full tested temperature range. Comparison of correction coefficients among the mixtures indicated that increase in w/cm results in less sensitivity of σ to temperature. Mixtures with SCM generally exhibit higher temperature sensitivity compared to the corresponding plain mixture. Since the variations in correction coefficients were not substantial (less 18% variation among 10 of 12 mixtures), a single value of activation energy of conduction (Ec) at 32 kJ/mol was identified as the general recommendation for all the tested mixtures.
Highlights
In recent years, nondestructive techniques for indirect assessment of concrete transport properties and durability by measuring electrical conductivity (σ) or resistivity (ρ) have gained popularity [1]. e measurements are taken by several available methods based on uniaxial or bulk resistivity, surface resistivity, electrical impedance spectroscopy, and noncontact resistivity measurements based on the transformer principle [1,2,3,4,5]
An experimental study was conducted with the primary objective to evaluate existing temperature correction methods for electrical conductivity (σ) of concrete
Twelve mortar mixtures were kept in stepwise temperature change in 5–50°C range. ree methods of linear, bilinear, and Arrhenius temperature correction (LTC, Bilinear Temperature Correction (BLTC), and Arrhenius Temperature Correction (ATC)) were evaluated
Summary
Nondestructive techniques for indirect assessment of concrete transport properties and durability by measuring electrical conductivity (σ) or resistivity (ρ) have gained popularity [1]. e measurements are taken by several available methods based on uniaxial or bulk resistivity, surface resistivity, electrical impedance spectroscopy, and noncontact resistivity measurements based on the transformer principle [1,2,3,4,5]. Typical values of Ec from the literature range from 12.54 to 42.47 kJ/mol and primarily depend on the degree of saturation, with sealed specimens presenting higher Ec compared to the saturated ones [3, 8, 16, 17, 20, 21]. Due to higher temperature sensitivity of the sealed specimens, ATC was recommended as the reliable temperature correction method [17]. Sensor-based σ data are used from a variety of mortar mixtures over a wide temperature range from 5 to 50°C to investigate the effectiveness of both the LTC and ATC methods. Recommended values for the correction parameters of each method are developed based on the tested mixtures
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