Edward J. Garboczi

Experimental limitations in impedance spectroscopy of materials systems

Using resistor-capacitor networks, sources of experimental artifacts in impedance spectroscopy were investigated, such sources include machine limitations, rig/cabling contributions at high frequencies, and artifacts due to high impedance reference electrodes and their geometrical placement. In the instance of electrode placement, computer simulations with a pixel-based model were in agreement with the experimental observations. Remedies for these artifacts such as rig shielding/grounding, geometrical adjustments, and null corrections are also discussed.

Standards Development for Gas Phase Air Cleaning Equipment in Buildings

Concerns about building security have resulted in increasing interest in gas phase air cleaning (GPAC) and the need for standard methods to determine the effectiveness of these systems. Similarly, the ability to predict their installed performance, based on such standard test data, is becoming increasingly important. The development and application of these standards and prediction tools will provide better protection of building occupants against chemical agents and improve the ability of designers and building owners to identify and specify air-cleaning equipment with a realistic expectation as to installed performance. The National Institute of Standards and Technology (NIST) has conducted an effort to facilitate the development of these standards and predictive tools under a project funded by the Department of Homeland Security. This report describes the following tasks that were carried out as part of this project: an evaluation of gas phase air cleaning technology; an assessment of existing and proposed standards, as well as relevant guidance documents; design of a laboratory-scale microreactor to evaluate media consistent with current and proposed industry approaches; micro-scale modeling to understand the interactions between the media and gaseous contaminants and, building-scale modeling to understand the impacts of air cleaning systems in controlling occupant exposure.

Measurement Science Needs for the Expanded Use of Green Concrete

Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. ACKNOWLEDGMENTS The Inorganic Materials Group at the National Institute of Standards and Technology would like to thank everyone who contributed their time and expertise by participating in the Measurements Science Needs for the Expanded Use of Green Concrete workshop. This report is based on the presentations and discussions that took place at the workshop. Special thanks are extended to plenary speakers, listed below, and to the many expert participants, shown on the next page. Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose.

Microstructure-Electrical Propertyrelationships in Cement-Based Materialss

There has been much recent progress on the application of impedance spectroscopy (IS) to the study of microstructure and transport in cement-based materials. The IS spectrum allows for the precise determination of bulk resistance, which is a measure of the pore phase interconnectivity, and calculation of the relative dielectric constant, which is related to the capillary pore size and distribution. High values of the relative dielectric constant (σ10 5 ) observed in cement paste at early hydration times are the direct result of the microstructure inducing dielectric amplification. Solvent exchange and freezing experiments, combined with digital-image-based computer modeling, have confirmed the role of large capillary pores in the dielectric amplification in young pastes. The conductivities (σ) and relative dielectric constants (e r ) of ordinary portland cement (OPC) pastes were monitored during cooling and solvent exchange with isopropanol and methanol. Dramatic decreases in σ and e r , in some cases over two orders of magnitude, occurred at the initial freezing point of the aqueous phase in the macropores and large capillary pores. The same dramatic decreases in a and er were observed at the onset of solvent exchange. Both effects provide experimental support for the dielectric amplification mechanism within the microstructure on the μm-scale. A secondary dielectric amplification was observed in the frozen and solvent exchanged pastes, which produced dielectric constants on the order of 10 3 . This effect is attributed to amplification on the nm-scale within the layered calcium silicate hydrate (C-S-H) gel microstructure. Additional insight into the variable nature of the C-S-H microstructure was obtained by comparing the dielectric behavior of methanol-exchanged OPC pastes to isopropanolexchanged OPC pastes.