SMARTech Community: School of Civil and Environmental Engineering (CEE)

Diatomaceous silica as an admixture in mortars and concrete

Mon, 28 Apr 1930 22:58:59 GMT

Title: Diatomaceous silica as an admixture in mortars and concrete

Authors: Weber, Homer Squire

Sensitivity and uncertainty analyses of impacts of climate change on regional air quality

Wed, 11 Jun 2008 22:58:59 GMT

Title: Sensitivity and uncertainty analyses of impacts of climate change on regional air quality

Authors: Liao, Kuo-Jen

Abstract: Climate change is forecast to affect ambient temperatures, precipitation frequency and stagnation conditions, all of which impact regional air quality. An issue of primary importance for policy-makers is how well currently planned control strategies for improving air quality that are based on the current climate will work under future global climate change scenarios. The US EPA s Regional Air Quality Modeling System, CMAQ, with DDM-3D are used to investigate sensitivities of ozone and PM2.5 to emissions for current and future scenarios. Sensitivities are predicted to change slightly in response to climate change. In many cases, mass per ton sensitivities to NOx and SO2 controls are predicted to be greater in the future due to both the lower emissions as well as climate, suggesting that current control strategies based on reducing such emissions will continue to be effective in decreasing ozone and PM2.5 levels. Impacts of climate uncertainties on regional air quality predictions are investigated using multiple climate futures in order to evaluate the robustness of currently planned emission controls under impacts of climate change. The results show that planned controls for decreasing regional ozone and PM2.5 will continue to be effective in the future under the extreme climate scenarios. However, the impact of climate uncertainties may be substantial in some urban areas and should be included in assessing future regional air quality and emission control requirements. Furthermore, daily cross-responses of ozone and PM2.5 to emissions are investigated for current and future scenarios. Planned controls of NOx emissions are predicted to lead to more positive responses in reducing urban ozone and PM2.5 levels in the future. Based on present emission control technologies, cost optimized emission reductions for offsetting impacts of climate change on regional peak fourth-highest daily maximum 8-hr average ozone and yearly average PM2.5 are predicted to range from $27 million to $5.9 billion (1999$) per year in 2050s for the cities examined in this study.

Thermoelastic stress analysis techniques for mixed mode fracture and stochastic fatigue of composite materials

Sun, 04 May 2008 22:58:59 GMT

Title: Thermoelastic stress analysis techniques for mixed mode fracture and stochastic fatigue of composite materials

Authors: Wei, Bo-Siou

Abstract: This study develops new quantitative thermoelastic stress analysis (TSA) techniques for fracture and fatigue damage analysis of composite materials. The first part deals with the thermo-mechanical derivation of two quantitative TSA techniques applied to orthotropic composites with and without a transversely-isotropic surface coating layer. The new TSA test procedures are derived in order to relate the thermal infrared (IR) images with the sum of in-plane strains multiplied by two newly defined material constants that can be experimentally pre-calibrated. Experiments are performed to verify the TSA methods with finite element (FE) numerical results along with available anisotropic elasticity solution. The second part of this study applies the quantitative TSA techniques together with the Lekhnitskii's general anisotropic elasticity solution to calculate mixed-mode stress intensity factors (SIFs) in cracked composite materials. The cracked composite coupons are subjected to off-axis loadings with respect to four different material angles in order to generate mixed-mode SIFs. A least-squares method is used to correlate the sum of in-plane strains from the elasticity solution with the measured TSA test results. The mode-I and mode-II SIFs are determined from eccentrically loaded single-edge-notch tension (ESE(T)) composite specimens. The FE models and virtual crack closure technique (VCCT) are utilized for comparisons. In the third part, a new stochastic model is proposed to generate S-N curves accounting for the variability of the fatigue process. This cumulative damage Markov chain model (MCM) requires a limited number of fatigue tests for calibrating the probability transition matrix (PTM) in the Markov chain model and mean fatigue cycles to failure from experiments. In order to construct the MCM stochastic S-N curve, an iterative procedure is required to predict the mean cycles to failure. Fatigue tests are conducted in this study to demonstrate the MCM method. Twenty-one open-hole S2-glass laminates are fatigue-cycled at two different stress levels. The coupon overall stiffness and surface-ply TSA damage area have been used as two damage metrics. The MCM can satisfactorily describe the overall fatigue damage evolution for a limited number of coupons (less than 6) subjected to a given specific stress level. The stochastic S-N curve can be constructed using at least two sets of fatigue tests under different stress levels. Three available fatigue tests for different E-glass laminates from the literature are also investigated using the proposed MCM approach. The results show the MCM method can provide the stochastic S-N curves for different composite systems and a wide range of fatigue cycles.

Dispersion of fullerenes in natural water and their behavior in water treatment process

Mon, 30 Jun 2008 22:58:59 GMT

Title: Dispersion of fullerenes in natural water and their behavior in water treatment process

Authors: Hyung, Hoon

Abstract: Environmental impact of fullerenes such as C60 and carbon nanotubes is of great concern due to the projection for widespread application and mass production in near future. Understanding their fate in the aqueous phase is prerequisite for accurate assessment of their ecotoxicological and human health effects upon unintended release to environment. This research addresses outstanding questions related to the behavior of fullerenes in natural and engineered water environments. Specifically, this research focuses on investigating: 1) the stability of fullerenes in the natural water, 2) interaction between fullerenes and natural organic matter (NOM), and 3) treatability of water stable fullerenes by conventional water treatment process. The experimental results suggested that NOM readily interacts with fullerenes leading to the formation of water stable fullerene suspensions. The adsorptive interaction between NOM and fullerenes was largely affected by NOM characteristics as well as water quality parameters. The fate of fullerenes in water environments was also greatly influenced by the types of fullerenes (e.g., single walled carbon nanotubes, multi-walled carbon nanotubes, and C60) and the pathway they are introduced into the aqueous phase. These water stable fullerene suspensions were found to be relatively well removed by conventional water treatment processes while the presence of NOM could negatively impact the removal efficiency. The outcomes of this study collectively imply that the dispersion of fullerenes in the natural water can occur beyond the level predicted only based on their extreme hydrophobicity and NOM plays a critical role on the fate of fullerenes both in natural and engineered water environments.