The electrical resistivity of cement-based materials can be used in quality control or service life prediction as an indicator of the fluid transport properties of these materials. Although electrical tests have the advantage of being easy and rapid to perform, several key factors can influence the results: (a) specimen geometry, (b) specimen temperature, and (c) sample storage and conditioning. This paper addresses these issues and compares the measurements from several commercially available testing devices. First, the role of sample geometry is explained with the use of three common geometries: surface, uniaxial, and embedded electrodes. If the geometry is properly accounted for, measurements from different test geometries result in electrical resistivity values that are similar. Second, the role of sample temperature is discussed for both pore solution and uniaxial tests on cylinders. Third, the paper examines the importance of sample curing, storage, and conditioning. Sample storage and conditioning influence both the degree of hydration and the degree of saturation. The role of sample volume to solution volume is discussed, as this ratio may influence alkali leaching and pore solution conduction. This paper is intended to identify factors that influence the results of rapid electrical test measurements and to help identify areas of future research that are needed so that robust specifications and standard test methods can be developed. Standardization will enable electrical tests to provide rapid, accurate, repeatable measurements of concrete's electrical properties.

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The drying of cementitious materials can be influenced by the properties of the fluid in the pores. While there are numerous studies on drying, very few explicitly focus on the properties of the pore fluid. This work investigates the influence of deicing salts on the properties of the pore fluid. The change that deicing salts cause in surface tension and viscosity is described in this study as a function of concentration and temperature. As a relatively limited number of measurements have been reported in literature, it can be difficult to describe the properties over a wide range of concentrations or temperatures. To overcome this limitation, this work provides measurements over concentration and temperature ranges. Semiempirical relationships were successfully fitted to the data confirming the possibility to predict viscosity and surface tension changes with temperature and salt concentration. The implications of the fluid properties on the drying behavior are also discussed as they relate to the diffusion coefficient. The models applied effectively predict the initiation of drying. Further improvements are however necessary to describe the diffusion coefficient as function of the degree of saturation in the presence of deicing salts which appear to be needed to account for the chemical interaction between the matrix and the fluid.

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This paper focuses on examining the pore structure of a cementitious paste made with a calcium silicate (wollastonite) that reacts with carbon dioxide and water to form a hardened solid. The pore structure of the hardened solid has been characterized using vapor sorption and desorption, low-temperature differential scanning calorimetry (LT-DSC), and scanning electron microscopy (SEM). The total porosity was also measured using mass measurement in oven-dry and vacuum-saturated conditions. Evidence exists that support the hypothesis that the solid has two main pore sizes: large macropores (>10 nm) appear to form between the initial calcium silicate particles and small micropores (<10 nm) were found in the reacted silica gel. The bimodal nature of the pore structure was evident from the desorption and LT-DSC responses. The extent of reaction was also investigated and was found to be the result of the function of the raw material particle size: only particles with radius <10 µm were found to have entirely reacted even in highly reacted systems. Moreover, the degree of reaction influenced the uniformity of reaction across the sample. Only the highly reacted system showed a uniform microstructure with continuous reaction products path and low porosity.

Electrical measurements are becoming a common method to assess the transport properties of concrete. For a saturated homogenous system, the surface resistance and the uniaxial resistance measurements provide equivalent measures of resistivity once geometry is appropriately taken into account. However, cementitious systems are not always homogenous. This article compares bulk and surface resistance measurements in cementitious materials intentionally composed of layered materials (i.e., layers with different resistivities). For this study, layered systems were composed of paste and mortar layers, representing the heterogeneity that can exist in the surface layers of field applications as a result of differences in moisture content, segregation, ionic ingress, carbonation, finishing operations, or ionic leaching. The objective of this article is to illustrate that these electrical measures can differ in layered systems (with sharp layer boundaries) and to demonstrate the impact of the surface layer properties on the estimation for the underlying material properties, for both cylindrical and prismatic specimens. Accounting for the effects of a surface layer requires a separate correction in addition to the overall specimen geometry corrections.

Whereas many concrete pavements have exhibited service lives of 30 to 50 years, a portion of these pavements in regions that are exposed to snow, ice, and salt have shown premature distress at the joints. This distress has been observed to occur between 5 and 20 years and requires extensive repair of an otherwise well-functioning pavement. Although there are several potential mechanisms that can lead to this deterioration, a reaction can occur between calcium chloride coming from deicing salt (CaCl2) and the tricalcium aluminate (C3A) and/or calcium hydroxide (CH) in the cementitious matrix. This paper describes the development of a test method that can be used to evaluate the potential for a cementitious binder to react with the calcium chloride deicing salts to form calcium oxychloride (the reaction between CaCl2 and CH). The test method enables the quantity of calcium oxychloride to be determined for each binder system. The results indicate that the amount of calcium oxychloride can be reduced with the replacement of cement with supplementary cementitious materials (fly ash, slag, silica fume, etc.). It is anticipated that the proposed test method could be used to better understand the role of binder chemistry on the calcium oxide formation and to optimize the binder composition to reduce the calcium chloride formation to an acceptable level and ultimately reduce the risk for deterioration.