An experimental investigation was made to determine the role of gravitational and surface tension forces in the migration of liquid water through fiberglass insulation materials. Straightforward experimental procedures were devised to effectively isolate and quantify flow parameters considered important in describing the flow mechanisms involved. The study was conducted to supplement an earlier investigation into the thermal performance of wetted insulation materials. Darcy's Law was found to apply for the regime of flow encountered in which liquid water flows under the force of its own weight in horizontal rooftop insulation. Experimental determination of the constant of proportionality in Darcy's Law, the hydraulic conductivity, is all that is needed to describe the migration of liquid water in saturated fiberglass insulation. Capillary forces, originally thought to play a significant role in the movement of liquid water through fiberglass insulation, were found to be negligible. Capillary rise up a column of insulation measured no higher than 13 mm. / M.S.

An experimental apparatus and test procedure to measure the sorption isotherm of moisture in porous building materials was developed and tested for its reliability and accuracy. The apparatus shows excellent potential for determining reliable moisture storage property data. The data are used in heat and moisture transport models. The apparatus consists of a small test chamber, with an external forced-air temperature and humidity conditioning system. The conditioning system supplies moist air to the test chamber at 20°C dry-bulb temperature over a range of 0.4 to 85 per cent relative humidity. The new system circumvents problems associated with the use of saturated salt-in-water solutions. Moisture content is determined gravimetrically without removing specimens from their conditioned environment. The mass is monitored in situ such that external ambient conditions have no effect on the data. The control of test chamber relative humidity and dry-bulb temperature is automated. Test results consisting of sorption isotherms and scanning curves for sugar pine, southern pine, and an exterior grade plywood are presented. The maximum uncertainty in moisture content measurement is 0.023 kg/kg-dry mass at 85 per cent RH. Results are compared to data from the literature. The study shows a need for a standard test method for measuring sorption isotherms. Minimum recommendations for such a standard test method are included. A comparison of scanning data to an analytical model from the literature show that further investigation of scanning is needed. The present method is well suited for such a study. / Master of Science

The effect of cyclic moisture infiltration on connections in light-frame wood buildings has received limited research attention. Specifically, the connections between wood-based sheathing materials (OSB, plywood) and solid wood studs are of interest. A comprehensive understanding of connection performance will enhance structure and material design, thereby improving the overall integrity and robustness of light-frame structures. The focus of this research project was to evaluate the strength and stiffness of wood-frame connections exposed to cyclic humidity conditioning. Nailed sheathing/stud connection samples were tested for lateral resistance following various periods of moisture exposure. Elastic stiffness, 5% offset yield load, maximum yield load, and failure yield were computed and analyzed using the data collected. The parameters were compared among connection specimens receiving either 0, 1, 5, 10, 15, 25, or 40 periods of cyclic moisture conditioning. In addition, the bearing resistances of the materials were investigated for application to the general dowel equations for calculating lateral connection values, the current basis for design of single dowel-type fastener connections between wood-based members. An x-ray density profilometer was used to observe the de-densification processes within the composite sheathing materials throughout the moisture conditioning regime. Results indicated moderate to extreme changes in the performance of cycled connections involving lower density sheathing materials. Higher density sheathing materials performed favorably at each cycle test period. Comparisons to the yield model were similar to the control results, but usually differed as cycling increased. Analysis of connection performance following cyclic moisture loading is a vital component in developing a holistic model for service-life prediction of nailed connections in light-frame residential construction. / Master of Science

M.S.

The first objective of this problem - thorough literature review - was conducted on all available references concerning humidity measurement, and visits were made to the American Instrument Company in Silver Springs, Maryland, and the National Bureau of Standards. The survey evaluated the instruments in use today and also explored many of the ideas and concepts that have been suggested in past years as possible means for humidity measurement. A summation of the survey indicated that the electric hygrometer with a ceramic element was a good basic theory for a humidity instrument, but still required development before it,would be of any practical use. The second objective - development of a useful hygrometer - was directed towards the development of the electric hygrometer using a ceramic element. The study that resulted included the evaluation of two methods for determining the change of resistance of the ceramic element, as well as a preliminary investigation of the characteristics of a ceramic element when employed as the sensing element for an electric hygrometer. The element intended for the initial tests, a porous ceramic containing mostly aluminum oxide, was the only material tested, but the tests included elements of the pure ceramic material and the same material after it was soaked in a saturated solution of lithium chloride. With the instruments used, the indications were that both elements were suited for determining the high humidities. The pure element had a lower limit of 50 percent relative humidity, and the coated element a lower limit of 20 percent. Two instruments were used for indicating the change of relative humidity. A vacuum tube voltmeter type instrument was tested, but found unsatisfactory due to variations of readings under the same conditions, drifting of the zero set, and excessive fluctuations of the indicating meter. The other instrument or method used was to apply an A-C voltage across the element, and to measure the resulting current flow. Because the current was maintained above 1 milliampere, heating of the element was caused, resulting in a change of element resistance. However, results with this instrument were sufficient to establish a calibration curve for the apparatus. A comparison of this device and a psychrometer indicated the usefulness of such an instrument, but confirmed that the development was not complete. The overall result of the research indicates that the selection of the ceramic sensing element for an electric hygrometer has merit, but more development is necessary. Two phases of any future work on the problem should be the development of the indicating instrument, and the selection and design of the sensing element. The need for a satisfactory instrument still exists, and the successful development of the type instrument described herein, would undoubtedly meet the requirements. / Master of Science

Drought is one of the most severe natural disasters and detrimentally impacts water resources, agricultural production, the environment, and the economy. Climate change is expected to influence the frequency and severity of extreme droughts. This dissertation evaluates drought conditions using a variety of hydrologic modeling approaches include short-term drought forecasting, long-term drought projection, and a coupled surface-groundwater dynamic drought assessment. The economic impacts of drought are also explored through a linked economic impact model. Study results highlight the need for various drought assessment approaches and provide insights into the array of tools and techniques that can be employed to generate decision-support tools for drought mitigation plans and water resource allocation. For short-term drought forecasting, the Soil and Water Assessment Tool (SWAT) and Variable Infiltration Capacity (VIC) models are used with a meteorological forecasting dataset. Results indicate that eight weeks of lead-time drought forecasting show good drought predictability for the Contiguous United States (CONUS). For the drought projection at a finer scale, both SWAT and VIC models are applied with Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model outputs to derive multiple drought indices for the Chesapeake Bay watershed and five river basins in Virginia. The results indicate that current climate change projections will lead to increased drought in the entire Chesapeake Bay watershed and Virginia river basins because of increases in the sum of evapotranspiration, and surface and groundwater discharge. The impacts of climate change on future agricultural droughts and associated economy-wide implications are then evaluated using the VIC and IMPLAN (IMpact analysis for PLANning) model for the several congressional districts in Virginia. The result indicated that increases in agricultural drought in the future would lead to decreases in agricultural productions and job losses. Finally, a coupled framework using the VIC and MODFLOW models is implemented for the Chesapeake Bay and the Northern Atlantic Coastal Plain aquifer system, and the results of a drought index that incorporates groundwater conditions performs better for some drought periods. Hydrologic modeling framework with multiple hydrologic models and various scales can provide a better understanding of drought assessments because the comparisons and contrasts of diverse methods are available. / PHD / Drought is one of the most severe natural hazards and negatively impacts the water resources, agricultural production, the environment, and the economy. Climate change influences the frequency and severity of extreme droughts. This dissertation assesses drought conditions using various hydrologic-modeling methods, which are drought forecasting, climate change impacts on drought, economic influences of droughts, and a coupled model approach. Study results highlight the need for various drought evaluation techniques that can generate decision-support tools for drought mitigation plans and water resource management. For short-term drought forecasting, two hydrologic models are used with a meteorological forecasting dataset. Results indicate that eight weeks of lead-time drought forecasting show good drought predictability for the Contiguous United States (CONUS). For the drought projection at a finer scale, two models are also used with multiple climate models for the Chesapeake Bay (CB) watershed and five river basins in Virginia. The results indicate that current climate change projections will lead to increased drought in the entire CB watershed and Virginia river basins. The impacts of climate change on future agricultural droughts and associated economy-wide implications are then evaluated using the hydrologic and economic models for the several congressional districts in Virginia. The results indicate that increases in agricultural drought in the future would lead to decreases in agricultural productions and job losses. Finally, a coupled model is implemented for the CB and the Northern Atlantic Coastal Plain (NACP) aquifer system, and the results of a drought index that incorporate groundwater conditions performs better for some drought periods. Hydrologic modeling framework with multiple hydrologic models and various scales can provide a better understanding of drought assessments because the comparisons and contrasts of diverse methods are available.

Yes / The major concern of the physical and chemical instability of effervescent products during manufacturing and storage is addressed through a co-crystallization strategy. Citric acid (CA) and sodium bicarbonate (SBC) are the essential components of effervescent products. CA is hygroscopic and led to an uncontrollable autocatalytic chain reaction with SBC in the presence of a small amount of moisture, causing product instability. The acid···amide dimer bond and layered structure of the citric acid-nicotinamide co-crystal restricts interaction of moisture with CA, making it nonhygroscopic, and improves the stability of effervescent products. The comparative study of effervescent products containing CA in its free form and as a co-crystal suggests a significant advantage of the use of co-crystal in effervescent products. This finding is supported by the mechanistic understanding developed through GAB and Y&N models obtained from moisture sorption data along with the computational investigations into moisture interactions with different crystal surfaces.

This project addresses two main subjects of moisture-cure polyurethane (PUR) wood adhesives: wood/PUR interactions and structure-property behavior emphasizing on weather durability. For these purposes, one simplified model PUR (MPUR) and three more commercially significant PURs (CPURs) with different hard segment contents were prepared. Separately, an early side project involved the synthesis of a 13C and 15N double-labeled polymeric methylenebis(phenylisocyanate) (pMDI) resin; this was used for the solid-state NMR characterization of isocyanate cure chemistry in wood bondline. MPUR and a CPUR were employed to investigate whether wood/adhesive interactions influence PUR properties. Wood interactions significantly altered PUR hard/soft domain size distribution (atomic force microscopy, AFM), thermal transition temperatures (dynamic mechanical analyses, DMA), and urethane/urea hydrogen bonds (Fourier transform infrared spectroscopy, FTIR). The effects of hard segment content on properties of PUR prepolymers, and cured PURs (films and wood composites) were studied. Hard segment content largely influenced the PURs’ molecular weights, viscosity, penetration, thermal transitions, and hard segment hydrogen bonds, but only slightly altered the dry (unweathered) bondline toughness. Three accelerated weathering procedures were developed to evaluate CPUR bondline weather durability through mode-I fracture testing. Both hard segment content and weathering conditions were found to significantly influence the bondline weather durability. Among these weathering procedures, only one (VPSS) was able to effectively distinguish weather durability of PUR adhesives, and therefore it was selected for detailed structure-weather durability studies. PUR weather durability was found to correlate with its moisture sensitivity and hard segment softening temperature; both were provided by water-submersion DMA. Much attention was directed to the investigation of weather-induced PUR molecular changes. FTIR studies provided evidences of post-cure, hydrolytic degradation, and variation of urethane/urea hydrogen bonds. DMA presented weathering effects on PUR thermal properties. Special efforts have been made to correlate these analytical results with PUR weather durability. A 13C and 15N double-labeled pMDI resin was synthesized and used for solid-state NMR characterization of isocyanate cure chemistry in wood bondline, particularly to detect the evidence of urethane formation. Rotational echo double resonance (REDOR) NMR clearly revealed the formation of urethane linkages, but largely overestimated their content. / Ph. D.

Green building standards recommend use of a variety of new thermal insulation products. However, durability of wooden framing used in conjunction with new insulation materials has not been thoroughly examined, specifically in reference to interstitial condensation. This research used a single-sided hot-box design to measure moisture content of wood framing during a 60-day period. The resulting moisture content of the wood framing was compared as tested with spray-applied cellulose and polyurethane versus fiberglass batt insulation. The average moisture content of framing insulated with cellulose and polyurethane was greater than framing insulated with fiberglass. Based on the results from this research, the use of spray-applied cellulose and polyurethane insulation materials may increase the risk of structural durability. Green building standards, such as LEED for Homes or the National Green Building Standard, emphasize creating energy efficient structures to limit negative impact on the environment. Green building practices employed to increase energy efficiency of the building enclosure may overlook possible adverse effects that these practices may have on structural durability. Because spray-applied cellulose and polyurethane insulation increase moisture content of wooden framework within building enclosures, it can be deduced that energy efficient insulation may increase risk of moisture-related biodeterioration of the building enclosure. After review of points awarded for insulation materials within LEED for Homes and the National Green Building Standard, results from this study imply that the National Green Building Standard does not emphasize durability of wooden structures in their guidelines at the present time. / Master of Science

An instrument (differential flow water meter) to measure the water vapor concentration in stack gases was developed. This is intended for use as a standard reference as well as a practical method for the determination of the moisture content of stack gases from wood stoves. The accuracy of the instrument was tested by generating gas mixtures with known water vapor content and comparing the measured concentrations with the actual values. Several tests were made under actual operating conditions, i.e., testing the water vapor concentration of stack gases from a wood stove under different firing conditions. The accuracy of the results was further checked by weighing the condensed catch and comparing the measured and predicted values. For each of the tests a wet and dry bulb technique was also used to measure the stack gas moisture content. A comparison of the results obtained using these two methods and the WHA (Wood Heating Alliance) standard method was also done. The results show that the wet and dry bulb method overpredicts the moisture content as compared to the differential flow water meter. / M.S.