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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Bond between two cementitious materials is crucial in applications such as repairs, overlays, and connections of prefabricated bridge elements (PBEs), to name just a few. It is the latter that has special interest to the authors of this paper. After performing a dimensional stability study on grout-like materials commonly used as connections between PBEs, it was observed that the so-called 'non-shrink' cementitious grouts showed a considerable amount of early-age shrinkage. This might have negative effects on the integrity of the structure, due not only to the grout material's early degradation, but also to a possible loss of bond between the grout and the prefabricated concrete element. Many factors affect the bond strength between two cementitious materials (e.g., grout-concrete), the presence of moisture at the existing concrete substrate surface being one of them. In this regard, pre-moistening the concrete substrate surface prior to the application of the grout material is sometimes recommended for bond enhancement. This topic has been the focus of numerous research studies in the past; however, there is still controversy among practitioners on the real benefits that this practice might provide. This paper evaluates the tensile bond performance of two non-shrink cementitious grouts applied to the exposed aggregate surface of a concrete substrate, and how the supply of moisture at the grout-concrete interface affects the bond strength. "Pull-off" bond results show increased tensile bond strength when the concrete surface is pre-moistened. Reasons to explain the observed increased bond strength are given after a careful microstructural analysis of the grout-concrete interface. Interfaces where sufficient moisture is provided to the concrete substrate such that moisture movement from the grout is prevented show reduced porosity and increased hydration on the grout side of the interface, which is thought to directly contribute to the increased tensile bond strength.

Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. Abstract. Many agencies are interested in using a rapid test method for measuring the electrical properties of concrete (i.e., the resistivity or conductivity) since the electrical properties can be related to fluid transport (e.g., ion diffusion). The advantage of electrical testing is that it is relatively easy to perform and the test method is relatively fast (less than a minute). Over the last century, many studies have investigated different approaches for measuring electrical properties. This paper describes the variability associated with measuring the bulk resistivity along the longitudinal axis of a cylinder after placing electrod es on either end. A multi-laboratory evaluation was performed using ten laboratories. Data from this evaluation provided variability data for twelve concrete mixtures at testing ages of 28, 56, and 91 days. Information on the variability is important in the development of precision and bias statements for standard test methods. In addition, this work discusses how the resistivity results obtained from this test can be correlated with surface resistivity measurements made using the Wenner probe. A linear agreement was noticed between the Wenner test and the measurement through the cylinder, but with a factor confirmed by previous research by Morris et al. (1996). Additionally, the effect of electrode resistance was discussed and for high resistivity concrete such as that used in much of the transportation infrastructure, this effect appears to be negligible; however, it can be accounted for easily. 17.

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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