Conductivity/activation energy relationships for cement-based materials undergoing cyclic thermal excursions

Abstract

The electrical conductivity of a range of concrete mixes, with and without supplementary cementitious materials (SCM), is studied through multiple cycles of heating and cooling over the extended temperature range -30/?70°C. When presented in an Arrhenius format, the experimental results display hysteresis effects at the lowtemperature end of the thermal cycle and, in those concretes containing supplementary cementitious materials at higher water/binder ratios, hysteresis effects were evident over the entire temperature range becoming more discernible with increasing number of thermal cycles. The depression in both the freezing and thawing point could be clearly identified and was used to estimate pore-neck and pore-cavity radii. A simplified approach is presented to evaluate the volumetric ratio of frozen pore water in terms of conductivity measurements. The results also show that the conductivity and activation energy of the concrete specimens were related to the water/binder ratio, type of SCM, physical state of the pore water and the thermal cycling regime.

Estimation of Ice Content in Mortar Based on Electrical Measurements under Freeze-Thaw Cycle

“…5, the electrical resistivity becomes almost constant when the temperature becomes 10℃, which means that the temperature hysteresis change due to the frost damage was negligible. In addition, the temperature variation of concrete samples with FTCs was measured in (McCarter et al 2015). Their temperature hysteresis results show little difference between two temperature cycles, which can also confirm that the change of thermal conductivity coefficient is not obvious after one cycle of frost damage.…”

“…McCarter et al (2015) also proposed a model to predict the ice content based on electrical measurement with a similar equation to Cai and Liu's, but it considers the effect of temperature on pore solution. Nevertheless, in their study the contributions of porosity and connectivity to the electrical conductivity of the specimen are ignored and the ice formation process is instant rather than continuous.…”

Experimental Examination of Electrical Characteristics for Portland Cement Mortar Frost Damage Evaluation

“…Because ice formation is essential for understanding the frost damage of concrete [33], electrical measurements have been applied to estimate the ice content below freezing point [34][35][36][37][38]. To estimate the ice content of mortar sample saturated with NaCl solutions, the relationships between the combined effects of saturation degree, temperature and solution ions concentration and the electrical conductivity of mortar samples were clarified [37].…”

“…The results from pulse velocity were used for comparison rather than that from mechanical tests. Besides, McCarter et al [35] concerned the activation energy and depression in both freezing and thawing points for different cement-based materials under FTCs because these parameters are related to the microstructure of the porous media. Recently, Kim et al [13] further studied these parameters by complex impedance with regard to a wide range of frequency and temperature.…”

A new model for the electrical conductivity of cement-based material by considering pore size distribution

“…When CBMs are subjected to freeze-thaw cycles, frost damage may occur due to frost heave of the pore liquid phase. To alleviate this problem, higher porosity is needed to offer a 'cushion space' during freeze-thaw cycles and higher conductivity of CBMs in the saturated surface dry state is then required (McCarter et al, 2015;Wang et al, 2014b). Due to capillary condensation in the pores and adsorption on pore surfaces, the existing liquid phase in the pores and the saturation of CBMs are related to the relative humidity (RH) (Zeng et al, 2014).…”