Editors: Mohammad Pour-Ghaz, Aali R. Alizadeh, and Jason Weiss

With the recent quest for developing sustainable infrastructure materials, there is a need for more advanced material characterization techniques at different length scales that can provide insight to the nature and fundamental behavior of the new classes of cementitious materials as they are becoming available. These methods can be used to predict the mechanical properties, microstructural aspects, and long-term performance of different cementitious systems. Examples of these novel techniques that have been recently used for material characterization include nuclear magnetic resonance spectroscopy, nano- and micro-indentation, X-Ray tomography, and atomic force microscopy. Recently, major progress has also been made in the development of novel cement-based systems such as C-S-H/polymer nanocomposites and self-healing materials. This Special Publication aims at providing a treatise on the current research in the areas related to innovative characterization methods and analytical techniques used in the cement and concrete research, as well as the development of novel basic and composite cementitious materials. This Special Publication is developed to honor the significant contributions made by Dr. James J. Beaudoin over the past four decades to the advancement of cement and concrete science. Dr. Beaudoin, a Researcher Emeritus, Fellow of the Royal Society of Canada, and Fellow of the American Ceramic Society, has authored more than 500 publications, including five books, 20 book chapters, encyclopedia contributions, more than 270 research journal papers, 17 patents, and numerous discussions and book reviews. He is the recipient of numerous prestigious awards, including the Della Roy Lecture Award on applications of nanotechnology in cement science (American Ceramic Society, 2005), the Wason Medal for Materials Research (American Concrete Institute, March 1999) and the Copeland Award (American Ceramic Society, 1998). The papers included in this Special Publication were presented in two sessions in ACI Fall 2014 Convention, Oct 26-30, 2014.

The durability performance of cement-based materials is directly related to the rate of moisture ingress in them. Moisture ingress in cement-based materials can be assessed using electricallybased methods. Traditionally, the electrically-based assessment of the moisture transport in cement-based materials has relied on two or four-point measurements, enabling onedimensional (1D) moisture flow monitoring. However, moisture ingress in cement-based materials is most often three-dimensional (3D). The objective of this paper is to investigate the feasibility of 3D electrical imaging of moisture ingress in mortar using Electrical Impedance Tomography (EIT). The EIT reconstructions are compared with the results of unsaturated moisture transport simulations using 3D Finite Element Method. The results of this study support the feasibility of EIT for 3D imaging of moisture flow in cement-based materials.

Many analytical surface characterization techniques exist to study steel passivity and corrosion in concrete. Some of these techniques, such as EIS and polarization resistance methods, have been used for decades to provide macro-scale data to characterize electrochemical activity on metal surfaces. More recently, advanced nanoscale spectroscopic methods, such as XPS and EELS, as well as analytical TEM have been shown to be quite useful to study compositional and crystallographic structures of oxides that form on steel. Despite these advances, researchers studying the interface between reinforcing steel and concrete in different scales are faced with several challenges with respect to the selection and the utilization of the available techniques. Each technique has advantages and disadvantages when compared with others; however, literature on these are quite limited in the study of steel/concrete interface. Since most of these techniques are not performed in situ, the interpretation of the data they provide requires careful examination. In addition, since most analytical studies to study passivity and corrosion in concrete are conducted in simulated environments, representativeness of the test setups are generally questioned. This paper presents a review of the commonly-used electrochemical as well as more recent analytical surface characterization techniques for the study of steel passivity and corrosion in concrete structures. The paper addresses the challenges with respect to the selection and the use of these techniques, pitfalls related to interpretation of the data, and common errors in test setups.

The evaluation of steel corrosion in reinforced concrete is commonly carried out using techniques like half-cell potential (HCP) and linear polarization resistance (LPR) measurements. The latter is however the subject of interrogations concerning the relevance of the method and the actual steel area polarized by the external current I_ce applied from a surface counter-electrode. To control the path of the polarizing current I_ce towards a specific steel area, a current-confining device (guard-ring) is used in some LPR instruments, which imposes an additional current I_gr around the counter-electrode. The impact of this guard-ring on LPR measurements is deduced from the uniform corrosion assumption. However, previous works have shown that the polarizing current spreading in macrocell corrosion systems is more complex and does not verify the uniform corrosion hypothesis. This paper presents the results of a 2D numerical study providing new insights on the theoretical impact of a guard-ring in case of galvanostatic pulse measurements performed on a macrocell corrosion system. The polarizing and confining currents are spread in a similar way over the macrocell system. In the case of an anodic polarization, both I_ce and I_gr are collected by the active steel area. In the cathodic direction, both I_ce and I_gr are spread over the passive areas. Consequently, numerical results show that the assumed confining effect cannot be achieved in presence of corrosion macrocells and it is actually impossible to define a specific polarized area. Moreover, since polarizing and confining currents have similar distributions, the confining current fully contributes to the system polarization, while it is not considered in LPR measurement analyses.

Development of a new composite technology for programmed delivery and control of admixture effects in concrete and other cement-based materials present is described. A series of new organo-mineral phases have been developed by a “chimie douce” technique and analyzed using a combination of analytical techniques: X-ray diffraction (XRD), infrared spectroscopy (IR), and scanning electron microscopy (SEM). Conduction calorimetry was utilized to monitor the effect of modified admixture on the hydration reactions. The slump loss characteristics of cement paste and mortar samples containing different amounts of these additives were investigated. The results showed that a good workability of the fresh mix was maintained over a relatively longer period.