X-ray microtomography (microCT) of the progression of sulfate attack of cement paste

High-resolution X-ray computed tomography (i.e., microCT or microtomography) was used to study the sulfate attack of cylinders of Type I cement paste cast with water-cement (w/c) ratios of 0.45, 0.50 and 0.60. Damage levels in samples exposed to a Na₂SO₄ solution with 10,000 ppm sulfate ion concentration were qualitatively rated from 0 (no damage) to 4 (extreme damage) based upon visual examination of the samples' exteriors and microtomography of the samples' interiors. The greater the w/c ratio, the more rapid the onset of sulfate damage. The corners of the cylinders appeared to be particularly susceptible to spalling, and damage may have continued into the cement paste by formation of subsurface cracks.     

The ATSC Digital Television System

The ATSC digital television standard describes a system designed to transmit high-quality video and audio, and ancillary data within a single 6-MHz terrestrial television broadcast channel. This paper outlines the overall architecture of the system and serves as an introduction to the papers that follow in this special issue of the Proceedings of the IEEE.     

Creep of UHPC in tension and compression: Effect of thermal treatment

Steel fiber-reinforced ultra-high performance concrete (UHPC) is of increasing interest for use in precast prestressed concrete highway bridge girders due to its superior durability and the potential for reducing or eliminating shear reinforcement, due to the presence of steel fibers. However, the contributions of creep, and especially tensile creep, to long-term performance must be better understood to develop appropriate design specifications. Due to practical considerations, it is also of interest to investigate the influence of varying thermal treatment, including temperatures lower than those recommended by the manufacturer (i.e. 90 °C), on the creep of UHPC. In this 1-year study, the effects of three different thermal treatment regimes on tensile and compressive creep performance of UHPC are examined, with complementary characterization by nanoindentation and scanning electron microscopy. Results show that UHPC creeps phenomenologically differently in tension and compression. Both thermal treatments examined resulted in similar tensile creep behavior, suggesting that a lower temperature applied over a longer period could effectively cure UHPC. For the non-thermally cured UHPC, a 10 μm wide region observed at the fiber/matrix interface was characterized by reductions in elastic modulus as well as greater porosity and microcracking than the bulk paste. It is suggested that the quality of the fiber/matrix interface is a major contributor to the measured increased creep of non-thermally treated UHPC as compared to UHPC treated at 60 °C or 90 °C.     

Indoor exposure to particulate matter and the incidence of acute lower respiratory infections among children: A birth cohort study in urban Bangladesh

Approximately half of all children under two years of age in Bangladesh suffer from an acute lower respiratory infection (ALRI) each year. Exposure to indoor biomass smoke has been consistently associated with an increased risk of ALRI in young children. Our aim was to estimate the effect of indoor exposure to particulate matter (PM_2.5) on the incidence of ALRI among children in a low‐income, urban community in Bangladesh. We followed 257 children through two years of age to determine their frequency of ALRI and measured the PM_2.5 concentrations in their sleeping space. Poisson regression was used to estimate the association between ALRI and the number of hours per day that PM_2.5 concentrations exceeded 100 μg/m³, adjusting for known confounders. Each hour that PM_2.5 concentrations exceeded 100 μg/m³ was associated with a 7% increase in incidence of ALRI among children aged 0–11 months (adjusted incidence rate ratio (IRR) 1.07, 95% CI 1.01–1.14), but not in children 12–23 months old (adjusted IRR 1.00, 95% CI 0.92–1.09). Results from this study suggest that reducing indoor PM_2.5 exposure could decrease the frequency of ALRI among infants, the children at highest risk of death from these infections.     

Water Efficiency and the Professional Plumbing Sector: How Capacity and Capability Influence Knowledge Acquisition and Innovation

Professional plumbers play an essential role in the implementation of water efficiency. If North America is to achieve high water efficiency standards and more ambitious plumbing codes, plumbers will need to be actively included in the water efficiency discussion. Repositioning the industry will required a cultural shift because the plumbing community has been mostly ignored in discussions of the larger environmental agenda and priorities. This repositioning will require substantial rethinking and retraining. New knowledge will need to be transmitted about emerging water efficient technologies, public policies and practices, as well as the rationale for use in residential and Industrial, Commercial, and Institutional (ICI) sectors. The GreenPlumbers Program (GPP) initiated this knowledge transfer process. Originating in Australia and expanded to the United States, the GPP is a national training and accreditation program for professional plumbers. Their focus has been on upgrading skills and awareness of water efficiency, conservation, and the professional plumbers’ roles in the contemporary environmental context. In this paper we report on the efficacy of the GPP’s curriculum and the process of transferring explicit water efficiency knowledge. Semi-structured interviews and a survey were used to gather the data. We considered how the program participants incorporated the GPP curriculum into their ‘day-to-day’ practices and operations post-certification. We also investigated participants’ motivating factors and cross-referenced these findings to their overall assessment of the program. Recommendations focus on how the GPP can best influence and contribute to a more comprehensive water efficiency agenda.     

Plastic design of two-way structures and elements

This is an introductory paper outlining the background to the plastic design of two-way spanning systems such as (some) space frames, bridge decks and steelwork connection components. The approach draws on the now well-established British (Baker) methods for the plastic design of one-way systems and upon the Scandinavian (Johansen, Hillerborg) proposals for two-way systems. What emerges is a new concept for a stress-resultant to be called a ‘Bimoment’. Bimoments seem to have a significance for some two-way systems comparable to the significance that ordinary bending moments have for one-way systems. Thus they do permit comprehensive direct equilibrium relationship between total loads and stresses for portions of plates or grillages which are large in one or both directions.     

A quasi-two-dimensional electrochemistry modeling tool for planar solid oxide fuel cell stacks

A quasi-two-dimensional numerical model is presented for the efficient computation of the steady-state current density, species concentration, and temperature distributions in planar solid oxide fuel cell stacks. The model reduction techniques, engineering approximations, and numerical procedures used to simulate the stack physics while maintaining adequate computational speed are discussed. The results of the model for benchmark cases with and without on-cell methane reformation are presented with comparisons to results from other research described in the literature. Simulations results for a multi-cell stack have also been demonstrated to show capability of the model on simulating cell to cell variation. The capabilities, performance, and scalability of the model for the study of large multi-cell stacks are then demonstrated.     

Laser scanning confocal microscopy for in situ monitoring of alkali–silica reaction

Alkali–silica reaction (ASR) occurs in concrete between reactive siliceous components in the aggregate and the strongly alkaline pore solution, resulting in the formation of a potentially expansive gel product. Lithium additives have been shown to reduce expansion associated with ASR, but the mechanism(s) by which lithium reduces expansion have not been understood. Therefore, development of an in situ method to observe reactions associated with ASR is highly desirable, as it will allow for non‐destructive observation of the reaction product formation and damage evolution over time, as the reaction progresses. A technique to image into mortar through glass aggregate by laser scanning confocal microscopy (LSCM), producing three‐dimensional representations of the sample was developed. This LSCM technique was utilized to monitor the progress of alkali–silica reaction in mortar samples prepared with alkali‐reactive glass aggregate both in the presence and in the absence of lithium additives: LiNO₃, LiCl or LiOH. The method proved to be effective in qualitatively monitoring crack formation and growth and product formation, within cracks and at the paste/aggregate interface. In particular, dendritic products were observed at the paste/aggregate interface only in those samples containing lithium, suggesting that these products may play a role in ASR mitigation.