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This dissertation discusses topics related to the performance and long-term durability of glass-reinforced composites. The first portion of this dissertation describes work to assess the effect that post-curing has on widely used E-glass/vinyl-ester composites (E-glass/Derakane 510-A and E-glass/Derakane 8084). It is shown that post-curing can have significant positive effects on the initial material properties of glass-reinforced vinyl ester composites. Furthermore, the post-cure of 82ºC for four hours stabilizes the matrix, and as such reduces matrix-related material property evolution. By stopping or nearly stopping material property evolution due to matrix curing over time, the post-cure regime isolates and allows the study of other time-dependent effects, such as fatigue or hygrothermal degradation, and aids designers by establishing an unchanging base set of initial (undamaged) material design properties. The second portion of this dissertation discusses the effects that mean stress and R-ratio have on the fatigue performance of the same material. Qualitative and quantitative differences are seen in the performance as a function of the loading ratio. A residual strength based life prediction model developed at Virginia Tech is applied to the fatigue data, characterizing the material under constant-amplitude loading. Three curve-fitting parameters are then used along with the model to predict variable-amplitude fatigue lives, with remarkably good results. The final portion of the dissertation concerns the effect of hygrothermal and accelerated aging on glass-reinforced composites. A meta-study is performed on data from the literature, and a glass-degradation-based life-prediction model is applied to the data. It is seen that a static fatigue-based activation energy approach to residual strength can predict activation energies associated with glass-reinforced composite strength degradation in the case of glass-reinforced concrete quite well, predicting values of 80-100 kJ/mol, which are similar to those expected for glass dissolution via silica ring opening. The model may also hold some promise for doing the same for glass-reinforced polymer composites. / Ph. D.

Thermal performance of an insulation material is influenced by the in-service temperature condition. Unlike most other insulation materials, thermal resistance (R-value) of polyisocyanurate (polyiso) foam insulation with ‘captive blowing agent’ varies non-linearly with temperature. Building designers consider constant R-value of different insulating materials for building design and energy calculations, and hygrothermal simulation software packages, such as WUFI, consider linear temperature dependent R-value profiles, even for polyiso. However, neither the linear temperature dependent thermal resistance nor the constant thermal resistance value of polyiso represents the actual thermal performance of the building envelope. This thesis aims to quantify the impact of in-service boundary temperature conditions in Canadian climates on the thermal resistance of polyiso foam insulation board used in EPDM and PVC roof constructions. Hygrothermal simulations were performed using WUFI® Pro, which considers real climate data and hygrothermal properties of constituent roof components for evaluating moisture and temperature conditions in roof constructions. Based on heating degree days (HDD), ten different cities were selected between climate Zone 4 (HDD<3000) to Zone 8 (HDD≥7000). The thermal resistance measurements were conducted using heat flow meter apparatus on four polyiso insulation boards (two new and two aged) of different sizes [thickness - new: 1inch (25mm) and 2 inch (51mm); aged: 2 inch (51mm) and 3 inch (76mm)] at five mean temperatures -4°C (25°F), 4.5°C (40°F), 10°C (50°F), 24°C (75°F), 43°C (110°F) and at a temperature differential of 28°C (50°F). The measured thermal resistance data of the four samples at different mean temperatures were normalized with calculated thermal resistance of each sample at 22°C (72°F). The normalized R-value variation was calculated using in-service boundary temperature conditions determined from hygrothermal simulations and considering linearly varied thermal resistance with temperature, for the selected ten Canadian cities. / Graduate

Control of moisture and heat flow through building enclosure assemblies is a critical component of overall building performance. This thesis shows that significant drying of moisture in wall assemblies is possible and that ventilation of cladding significantly increases the rate of drying in some assemblies without having detrimental impact on the enclosures thermal performance. A review found that thermal and moisture buoyancy, wind pressure gradients and mechanical equipment drive ventilation airflow. This ventilation flow can theoretically increase the effective water vapour permeance and thermal conductivity. Ventilation has the potential to increase outward drying through relatively impermeable claddings at the low flows expected to occur in service. The impact on thermal conductance is much less. A methodology for assessing the complicated airflow resistance characteristics of lap sidings was developed and applied to a representative vinyl siding. Field drying studies showed that the sample tested is well ventilated. Field brick veneer clad wall samples were also tested for system airflow resistance over a range of driving pressures. Theoretical predictions under-estimated the measured flow rate for given steady driving air pressures. Measurements of naturally driven cavity air speeds and smoke pencil testing showed that flow rates were commonly occurring that would in theory significantly affect the hygrothermal performance of the walls. This was confirmed with field drying studies. A field drying study of east-facing test wall with vinyl siding and brick veneer cladding was conducted in Waterloo, Ontario, Canada. Significant amounts of drying and inward moisture redistribution were measured. Wall sheathing dried quickly in hot summer conditions but in some cases significant inward driven moisture flow occurred. In cool and cold weather the wall dried more slowly and much less moisture moved inward. Increased cladding ventilation significantly increased drying rates and reduced internal wall assembly moisture levels. It was concluded that cladding ventilation acts to increase the effective vapour permeance of cladding and to reduce solar driven inward vapour drives. The use of spun bonded polyolefin sheathing membrane in lieu of #15 asphalt impregnated felt was found to improved hygrothermal performance in the test walls. The difference observed was concluded to be due to the higher vapour permeance of the spun bonded polyolefin and may not hold for wall assemblies with lower permeance sheathings (e. g. oriented strand board and foam plastic). Walls clad with vinyl siding dried faster than those clad with brick veneer. It was concluded that the vinyl siding is a well ventilated cladding system.

Polycarbonate (PC) is a glassy engineering thermoplastic that has been used for decades because of its superior mechanical properties such as high toughness and stiffness, and for its general thermal stability. However, the industrial demand for higher performance polymers with faster processing times has caused PC to be gradually replaced by different engineered polymer blends, such as polycarbonate/acyrlonitrile-butadiene-styrene (PC/ABS). Blends combine the advantages of the individual components but because they are a relatively new class of materials, their time-dependent behaviour is less well understood. The goal of the present work is to characterize two primary time-dependent processes in a commercial 75:25 PC:ABS blend that are known to affect the long-term mechanical properties of the individual components. The first is physical aging which is a result of non-equilibrium fast cooling of glassy or amorphous polymers. Physical aging is associated with structural relaxation due to enthalpic and volumetric recovery. The second process is hygrothermal conditioning which is the combined application of thermal aging and moisture absorption. Three sets of characterization tests were conducted using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The enthalpic relaxation results determined from DSC data for aging at nine different combinations of time and temperature showed that aging experiments are best conducted at temperatures between 80 and 90°C. This range is below the glass temperature of the ABS component. The activation energy for enthalpic relaxation for the unaged blend was found to fall between energies for PC and ABS relaxations, but not according to the rule-of-mixtures. The present study attempted to adopt the Tool–Narayanaswamy-Moynihan (TNM) phenomenological model to predict relaxation kinetics but was found to be complicated by multiple endothermic peaks. It was then concluded that the TNM model, although very useful for single polymer systems, is unsuitable for blends. A semi-empirical model was applied instead to fit the experimental data which provided a reasonable estimate of the relaxation behaviour. Aging at 80°C for the period investigated did not reach equilibrium and it is expected that aging times of upwards of 2 years will be necessary to minimize the errors associated with the data fitting to provide a better fit of the model. The FTIR studies revealed that thermal aging at 80°C in dry atmosphere results in oxidation of the butadiene component. However, the addition of moisture to the aging process appears to prevent, or at least impede, oxidation from occurring. The presence of moisture seems to trigger hydrogen bonding, which saturates regardless of the moisture content after approximately 80 days. The initial rate of moisture diffusion in PC/ABS appeared to depend predominantly on temperature while the ambient moisture concentration tends to only affect the final equilibrium content in the blend.

Control of moisture and heat flow through building enclosure assemblies is a critical component of overall building performance. This thesis shows that significant drying of moisture in wall assemblies is possible and that ventilation of cladding significantly increases the rate of drying in some assemblies without having detrimental impact on the enclosures thermal performance. A review found that thermal and moisture buoyancy, wind pressure gradients and mechanical equipment drive ventilation airflow. This ventilation flow can theoretically increase the effective water vapour permeance and thermal conductivity. Ventilation has the potential to increase outward drying through relatively impermeable claddings at the low flows expected to occur in service. The impact on thermal conductance is much less. A methodology for assessing the complicated airflow resistance characteristics of lap sidings was developed and applied to a representative vinyl siding. Field drying studies showed that the sample tested is well ventilated. Field brick veneer clad wall samples were also tested for system airflow resistance over a range of driving pressures. Theoretical predictions under-estimated the measured flow rate for given steady driving air pressures. Measurements of naturally driven cavity air speeds and smoke pencil testing showed that flow rates were commonly occurring that would in theory significantly affect the hygrothermal performance of the walls. This was confirmed with field drying studies. A field drying study of east-facing test wall with vinyl siding and brick veneer cladding was conducted in Waterloo, Ontario, Canada. Significant amounts of drying and inward moisture redistribution were measured. Wall sheathing dried quickly in hot summer conditions but in some cases significant inward driven moisture flow occurred. In cool and cold weather the wall dried more slowly and much less moisture moved inward. Increased cladding ventilation significantly increased drying rates and reduced internal wall assembly moisture levels. It was concluded that cladding ventilation acts to increase the effective vapour permeance of cladding and to reduce solar driven inward vapour drives. The use of spun bonded polyolefin sheathing membrane in lieu of #15 asphalt impregnated felt was found to improved hygrothermal performance in the test walls. The difference observed was concluded to be due to the higher vapour permeance of the spun bonded polyolefin and may not hold for wall assemblies with lower permeance sheathings (e. g. oriented strand board and foam plastic). Walls clad with vinyl siding dried faster than those clad with brick veneer. It was concluded that the vinyl siding is a well ventilated cladding system.

Polycarbonate (PC) is a glassy engineering thermoplastic that has been used for decades because of its superior mechanical properties such as high toughness and stiffness, and for its general thermal stability. However, the industrial demand for higher performance polymers with faster processing times has caused PC to be gradually replaced by different engineered polymer blends, such as polycarbonate/acyrlonitrile-butadiene-styrene (PC/ABS). Blends combine the advantages of the individual components but because they are a relatively new class of materials, their time-dependent behaviour is less well understood. The goal of the present work is to characterize two primary time-dependent processes in a commercial 75:25 PC:ABS blend that are known to affect the long-term mechanical properties of the individual components. The first is physical aging which is a result of non-equilibrium fast cooling of glassy or amorphous polymers. Physical aging is associated with structural relaxation due to enthalpic and volumetric recovery. The second process is hygrothermal conditioning which is the combined application of thermal aging and moisture absorption. Three sets of characterization tests were conducted using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The enthalpic relaxation results determined from DSC data for aging at nine different combinations of time and temperature showed that aging experiments are best conducted at temperatures between 80 and 90°C. This range is below the glass temperature of the ABS component. The activation energy for enthalpic relaxation for the unaged blend was found to fall between energies for PC and ABS relaxations, but not according to the rule-of-mixtures. The present study attempted to adopt the Tool–Narayanaswamy-Moynihan (TNM) phenomenological model to predict relaxation kinetics but was found to be complicated by multiple endothermic peaks. It was then concluded that the TNM model, although very useful for single polymer systems, is unsuitable for blends. A semi-empirical model was applied instead to fit the experimental data which provided a reasonable estimate of the relaxation behaviour. Aging at 80°C for the period investigated did not reach equilibrium and it is expected that aging times of upwards of 2 years will be necessary to minimize the errors associated with the data fitting to provide a better fit of the model. The FTIR studies revealed that thermal aging at 80°C in dry atmosphere results in oxidation of the butadiene component. However, the addition of moisture to the aging process appears to prevent, or at least impede, oxidation from occurring. The presence of moisture seems to trigger hydrogen bonding, which saturates regardless of the moisture content after approximately 80 days. The initial rate of moisture diffusion in PC/ABS appeared to depend predominantly on temperature while the ambient moisture concentration tends to only affect the final equilibrium content in the blend.

There is a growing interest in straw bale construction for its low embodied energy and insulation value. Early studies of its structural behaviour and fire resistance have shown it to be a viable alternative to traditional building techniques. However, the biggest remaining obstacle to widespread acceptance is the moisture behaviour within the straw bale walls, especially as it concerns mould growth. The uncertainty of this behaviour leads to the hesitation of building officials and insurance providers to freely accept straw bale construction. Therefore, this study investigates the moisture, temperature and mould growth in straw bale walls, through a combination of analysis, dynamic modeling and field studies. A study of mould is presented along with the current methods available for predicting mould growth. Moisture is the primary controllable factor to mould growth in buildings. Therefore, an understanding of moisture accumulation within straw bale walls is necessary to provide a safe design that precludes mould growth. This study compiles the current state of knowledge of the hygrothermal properties of the materials used in straw bale walls. Then a parametric steady-state analysis is conducted to show the expected behaviour of vapour diffusion and the effects of the material properties. Two 14”thick x 6’ wide x 8’ high straw bale test walls were constructed: one was rendered with a typical cement-lime plaster and the other with a clay plaster. Temperature and moisture were monitored throughout the walls for over a year. These test walls provide more information on the macro behaviour of the walls to both vapour diffusion and, more importantly, rain. Hygrothermal computer modeling was conducted and compared to the test data to assess its accuracy. Thermal modeling was successful, while moisture modeling was found to be more difficult due to a lack of accurate rain data. With better climate data it is expected that accurate hygrothermal modeling of straw bale walls is possible. The result of this work is a general starting point for more detailed studies of the hygrothermal behaviour of straw bale walls with the ultimate goal of assessing the mould risk for various construction techniques and locations.

This thesis analyzes the implementation of surface bonded piezoelectric actuators to control or minimize the deformation in elastic or viscoelastic cantilever beams due to simultaneous heat and moisture diffusion. The problem is addressed in the context of linearized elasticity and linearized viscoelasticity. The constitutive equations are derived from the balance laws for mass, linear and angular momenta, energy, entropy and the second law of thermodynamics. The constitutive equations for linearized elasticity are then obtained as a consequence of small deformation assumption. The temperature and moisture induced deformation is introduced through the coefficient of thermal expansion CTE and coefficient of moisture expansion CME. The constitutive equations for linearized viscoelasticity are obtained by correspondence principle. The coupled temperature and moisture diffusion equations are obtained as a consequence of Clausius-Duhem inequality. The extent of coupling between heat conduction and moisture diffusion phenomena is studied by varying the ratio of their diffusivities and a non-dimensional coupling parameter. The effect of coupled unsteady heat conduction and moisture diffusion phenomena on the short and long term response characteristics of the beam such as displacement, stress and strain fields is studied. Based on these response characteristics, the magnitude of external actuating voltage required to minimize deformation is predicted. This is followed by a comparative study of the field variables in cases of actuated and unactuated beams. Four materials are chosen for this study; aluminium, epoxy, carbon fiber reinforced polymer with fiber volume fraction of 60 percent, and an epoxy-like viscoelastic material. The viscoelastic material is assumed to be thermorheologically simple. The shift factor is assumed to be a linear function of temperature and moisture fields. To address this problem numerically, a finite difference formulation is presented for the field equations and boundary conditions. This numerical scheme is validated by solving the problem of uniformly loaded cantilever beam and comparing the results with the analytical solution known a priori. The results obtained numerically are validated by comparison with experimental results. It is observed that the under the effect of external actuation, the stress and displacement fields are largely minimized in all four cases chosen for study. The bending in the unactuated viscoelastic beam is more pronounced than bending in the unactuated elastic beam. This is due to the softening of the material with time due to evolving temperature and moisture fields. However, relatively lesser external actuating voltage is necessary to minimize bending in the former case compared to the latter. The magnitude of actuating electric field required in the piezoelectric layer suggests a need to address the problem with in a non-linear framework, no such attempt is made in this study.

There is a growing interest in straw bale construction for its low embodied energy and insulation value. Early studies of its structural behaviour and fire resistance have shown it to be a viable alternative to traditional building techniques. However, the biggest remaining obstacle to widespread acceptance is the moisture behaviour within the straw bale walls, especially as it concerns mould growth. The uncertainty of this behaviour leads to the hesitation of building officials and insurance providers to freely accept straw bale construction. Therefore, this study investigates the moisture, temperature and mould growth in straw bale walls, through a combination of analysis, dynamic modeling and field studies. A study of mould is presented along with the current methods available for predicting mould growth. Moisture is the primary controllable factor to mould growth in buildings. Therefore, an understanding of moisture accumulation within straw bale walls is necessary to provide a safe design that precludes mould growth. This study compiles the current state of knowledge of the hygrothermal properties of the materials used in straw bale walls. Then a parametric steady-state analysis is conducted to show the expected behaviour of vapour diffusion and the effects of the material properties. Two 14”thick x 6’ wide x 8’ high straw bale test walls were constructed: one was rendered with a typical cement-lime plaster and the other with a clay plaster. Temperature and moisture were monitored throughout the walls for over a year. These test walls provide more information on the macro behaviour of the walls to both vapour diffusion and, more importantly, rain. Hygrothermal computer modeling was conducted and compared to the test data to assess its accuracy. Thermal modeling was successful, while moisture modeling was found to be more difficult due to a lack of accurate rain data. With better climate data it is expected that accurate hygrothermal modeling of straw bale walls is possible. The result of this work is a general starting point for more detailed studies of the hygrothermal behaviour of straw bale walls with the ultimate goal of assessing the mould risk for various construction techniques and locations.