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 viscoelastic nature of concrete is a topic of much study and the calcium-silicate-hydrate (C-S-H) phase is believed to be largely responsible for this viscoelastic behavior. In this study the viscoelastic properties of synthesized calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) are measured by quasi-static and dynamic nanoindentation. A protocol for synthesizing and preparing samples for chemical and mechanical characterization is presented. The addition of aluminum to C-S-H has been previously shown to modify its molecular structure, a modification that is expected to change the viscoelastic behavior. The results indicate that C-A-S-H behaves more viscously than C-S-H and a number of factors are discussed.

Mortar bars made with silica glass aggregate were tested at 23°C (73°F) to evaluate the applicability of a previously proposed chemical model for the alkali silica reaction (ASR). The model, based on tests at 80°C (176°F), proposes that ASR gel does not form until portlandite (CH) in the hydrated paste is locally depleted and the calcium silicate hydrate (C-S-H) has been locally converted to a more highly polymerized and lower Ca/Si form. SEM-EDX, XRD, and ²⁹Si NMR spectroscopy of the 23°C (73°F) mortars show that the same chemical processes operate at both temperatures. At 23°C (73°F) and up to 60 days, only a small amount (~1%) of ASR gel forms and is confined to cracks entirely within the aggregate grains, but this small amount of gel containing Na, K, and Ca is sufficient to cause substantial expansion. There is no large-scale depletion of CH or increase in the C-S-H polymerization in the paste due to the small amount of gel formed and its confinement in the aggregate grains. Local reduction in both the amount of CH and the Ca/Si ratio of C-S-H in the paste is observed near places where gel-filled cracks in the aggregate contact paste, consistent with the proposed chemical model.

In this study we report on characterization of synthetic calcium silicate hydrate (C-S-H) produced at relatively low Cao to SiO₂ (C/S) mixture ratio of 0.7 compared with C-S-H produced at 1.5 C/S mixture ratio. Synthetic C-S-H slurry was produced by mixing calcium oxide (CaO) to micro-silica (SiO₂) with large amount of deionized water. The slurry was then dried to the standard 11% relative humidity to produce a powder C-S-H. The C-S-H powder was then compacted at compaction pressures of 300 (43.5) and 400 MPa (58.0 ksi) to produce solid C-S-H discs. Modulus-density scaling relationships of C-S-H synthesized at 0.7 and 1.5 C/S ratios were established and compared. Microstructural characterization of C-S-H including Brunauer-Emmett Teller (BET) N₂, thermogravimetric analysis (TGA), and ²⁹Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) were performed. We show that porosity, water content, and silicate polymerization affected the elastic and viscoelastic properties of synthetic C-S-H. We also show that elastic and viscoelastic properties of C-S-H synthesized at 0.7 C/S ratio are more sensitive to porosity than those of C-S-H synthesized at 1.5 C/S ratio.

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.