Georadiological Barrier Gamma Attenuation Model for Waste Containment. I: Model Formulation

Emission of gamma rays from buried and exposed radioactive materials poses health risks at radiologically contaminated sites. Covering the source material with a barrier of adequate thickness and physicochemical composition can reduce the intensity of transmitted gamma rays (γ), thereby reducing such risks. Herein, the Geo-Radiological Barrier Gamma Attenuation Model (GRBGAM) is developed to quantify γ attenuation by earthen covers. The model allows variation of barrier and radioactive source input parameters and comparison of emitted γ intensities and attenuation ratios of different barrier designs for virtually any radioactive isotope decay chain. The model calculates the activities of successive amounts of decaying isotopes within a decay chain and temporally couples the results with an exponential absorption equation to estimate the exit intensity of γ radiation from barriers. A Weibull function integrated into the absorption equation, scales temporal changes in barrier density (ρ′) during long service times. This model can be used to optimize georadiological (georad) barrier mix composition and thickness to increase γ attenuation ratio to acceptable levels.     

Influence of Particle Shape and Surface Friction Variability on Response of Rod-Shaped Particulate Media

Discrete element methods are important tools for the investigation of the mechanics of granular materials. In two dimensions, the reliability of these numerical approaches can be explored using physical tests on rod assemblies. This work highlights the importance of representing the actual distribution of rod shapes and surface friction in numerical simulations. The sensitivity of the response of hexagonally packed rods to minor changes in particle geometry and friction is investigated using a combination of laboratory tests and discrete element simulations. Laboratory test results highlight the influence of small variations in rod geometry on the global response, with the peak friction angle decreasing significantly as the standard deviation of the rod size distribution increased. Small changes in rod shape are also seen to be important. The numerical simulations indicate that the peak friction angle decreases as the standard deviation of the distribution of particle surface friction increases. This paper illustrates the way in which laboratory tests and numerical simulations can be used in a complementary manner to better understand the micromechanics of the response of granular materials.     

Observation on Particulate Matter over a Period of 3 Years at Kaikhali (22.022°N and 88.614°E) inside a Special Mangrove Ecosystem: Sundarbans

Measurement of particulates [respirable particulate matter (RPM or PM10), fine RPM (PM2.5), non-RPM (NRPM), and total suspended particulate matter (TSPM)] were carried out on a campaign basis over a period of 3 years (2003–2006) at Kaikhali (22.022°N and 88.614°E) inside one of the world’s largest mangrove delta region—“The Sundarbans.” Considering the toxic potential of the particulate fractions, the foremost objective of this study was to determine the particulate concentrations during different parts of the year as well as to ascertain the trend of occurrence of the particulate fractions in an area of rich and unique biodiversity. Moreover, as the area had no past records on particulate data over a decade, the other important objective of the study was to prepare substantial database for the area for the present time. The average range of PM10, PM2.5, NRPM, and TSPM for the period from 2003–2006 has been found to be (57–118), (35–80), (10–25), and (73–135)?μg?m?3 respectively. The data obtained for the finer particulate fractions have been compared with some previous studies in India. In addition to the particulate fractions, meteorological parameters such as wind speed, wind direction, and temperature were also recorded to accomplish proper interpretation of the data. The requisite statistical parameters (standard deviation, average, and range) for the particulate fractions have also been calculated.     

Decision-Support Tool for Assessing the Environmental Effects of Constructing Commercial Buildings

Construction of commercial buildings consumes significant amounts of energy and produces lots of emissions and waste. Where should environmental improvement efforts be focused during design and construction? The Construction Environmental Decision-Support Tool allows designers and industry practitioners to quantify energy use, emissions, and waste generation rates due to the construction phase of commercial buildings. A case study of the Bren School at the University of California, Santa Barbara, and several relevant construction scenarios are analyzed. When considering the complete building over its entire life cycle, the construction phase comprised 2% of energy consumption, 1% of CO2 emissions, 7% of CO emissions, 8% of NOx emissions, 8% of PM10 emissions, and 1% of SO2 emissions. This is due to the dominance of the long-term use phase (50?years) compared to a relatively short construction phase (2?years). Scaling up to the national level, however, construction impacts of projects are significant. In each of the categories studied (temporary materials, equipment and materials transportation, equipment use, waste generation), there are actions that can be taken by designers and builders to improve construction phase environmental effects. In structural frame construction, particular areas of concern include material and equipment selection and temporary material use. Energy use and air emissions are primarily due to equipment use, which accounts for at least 50% of most types of emissions. The major contributors are concrete mixer trucks, concrete pumps, cranes, and air compressors. A single feasible decision, such as using a concrete mixer truck with a 335?hp engine instead of one with a 565?hp engine (but having the same capacity) would reduce total construction energy demand by 12%, and the emissions of CO, NO2, PM10, SO2, CO2, and HC by 3, 12, 8, 10, 12, and 10%, respectively. The use of significantly older equipment can have a formidable effect on construction phase emissions. In general, equipment larger that 175?hp made prior to 1996 tends to have significantly greater emissions of HC, CO, and NO2 than more recent models. The majority of waste generated during construction of the structural frame consists of concrete and wood.     

CEM Research for the Next 50 Years: Maximizing Economic, Environmental, and Societal Value of the Built Environment

Construction engineering and management (CEM) research over the past 50 years has focused on extending and applying management and computer science approaches to minimize cost during the implementation phase of construction projects. Three emerging trends suggest the need to broaden the frame of future CEM research in several ways: (1) more integrated delivery of design, planning, construction, and operation of buildings and infrastructure requires us to broaden the focus of construction engineering and management research across the entire facility lifecycle; (2) rapid globalization of the construction industry requires new governance structures for projects that can bridge across the gaps in values, beliefs, norms, work practices, and laws between participants from different countries; and (3) heightened global awareness of, and demands for, enhanced sustainability requires new approaches, methods, and tools to incorporate sustainability issues in the early phases of the facility development process. Building on ASCE’s 2006 Vision for the Future of Civil Engineering. This paper elaborates each of these three trends and draws implications for refocusing and redirecting construction engineering and management research, education, and civic leadership in the next 50 years.