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Electrical tests have been used to characterize the microstructure of porous materials, the measured electrical response being determined by the contribution of the microstructure (porosity and tortuosity) and the electrical properties of the solution (conductivity of the pore solution) inside the pores of the material. This study has shown how differences in concentration between the pore solution (i.e., the solution in the pores) and the storage solution surrounding the test specimen leads to significant transport (leaching) of the conductive ionic species between the pore solution and the storage solution. Leaching influences the resistivity of the pore solution, thereby influencing electrical measurements on the bulk material from either a surface or uniaxial bulk resistance test. This paper has three main conclusions: 1.) Leaching of conductive species does occur with concentration gradients and that a diffusion based approach can be used to estimate the time scale associated with this change. 2.) Leaching of ions in the pore solution can influence resistivity measurements, and the ratio of surface to uniaxial resistivity can be used as a method to assess the presence of leaching and 3.) An estimation of the magnitude of leaching for standardized tests of cementitious materials.

The service life of many concrete structures depends upon their resistance to chloride ingress. Service life models estimate the time required for chloride ions to reach the reinforcing steel, to build up a critical concentration, and to initiate corrosion. Fick’s second law and the Nernst–Planck equation are two of the more popular methods that are used to estimate chloride ingress. While chloride ions are usually the primary consideration, in general they are not present by themselves. The co-present cations and anions can influence the rate of chloride ingress. This paper discusses how the apparent chloride diffusion coefficient, based on Fick’s second law, is dependent on the chemical composition and concentration of the ponding solutions. This study examines the influence of the chemical composition and concentration of solutions on the chloride binding capacity, on the consequential microstructural changes as determined with scanning electron microscopy using energy dispersive X-ray spectra (SEM-EDS), on the surface charges of the pore walls, and on the overall chloride ingress of the concrete materials. Chloride ingress predictions based on the Nernst–Planck equation were also compared with the experimental chloride profiles. The Nernst–Planck approach provided good predictions at low salt concentrations (less than 1.0 mol/L NaCl) using a single porosity, tortuosity, and binding approach. At higher concentrations, the binding and change of microstructure was under-predicted, and thus the chloride ingress was over-estimated.

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Calcium hydroxide (CH) typically comprises 20-25 % of the volume of ordinary portland cement (OPC) paste. CH is generally considered as an elastic phase that restrains the viscoelastic responses of calcium silicate hydrates (CSH). In this study, nanoindentation was used to study both the indentation modulus and the short-term viscoelastic responses of CSH/CH mixtures using an OPC paste made using a low water to cement ratio. A scanning electron microscope, equipped with energy dispersive X-ray spectroscopy, was used to identify the phase compositions in the matrix at the individual indentation locations. This study showed that CH increased both the indentation modulus and the contact creep modulus of the CSH/CH mixtures when compared with more pure CSH phases. However, such enhancement did not depend strongly on the volumetric concentration of CH. When the CH volume exceeded 20 %, no further enhancement of the indentation modulus and contact creep modulus was observed.

Air entrainment is commonly used to improve the durability of concrete materials exposed to freezing and thawing. While the influence of air voids on freeze/thaw damage and salt scaling is frequently studied, the influence of entrained air voids on ionic transport has been studied less frequently. Since ionic transport in concrete materials relies on pore fluid as the medium of conduction, only saturated or partially saturated air voids participate in the transport processes. This paper discusses the conditions under which air voids could become saturated. Specifically, the saturation condition of entrained air voids in laboratory tests and in service is discussed. This paper compares the results of steady and non-steady state migration tests on concrete specimens when air voids are saturated and when air voids are primarily empty. The implications of the observed difference are discussed to provide a better understanding of the direct application of laboratory test results to predict the service life of concrete materials in the field. The saturation of air voids is observed to also influence the electrical resistivity of concrete materials.

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