No description available.

The results of this investigation indicate: 1. The deterioration rate in the lateral direction of the uniaxially prestressed members subjected to the deep-seated type of freeze-thaw damage increased as the level of the compressive stress field increased. 2. Under all levels of uniaxial compression, cracks formed parallel to the direction of the applied stress field and in any plane parallel to this direction when the members were subjected to freeze-thaw damage. 3. The cracks are assumed to start at the boundary of a capillary within the aggregate and propagate through the aggregate to the aggegate- mortar interface. 4. Due to previous investigations, bond and mortar cracks are assumed to exist in the concrete. These cracks increase for increasing stress levels. 5. For the prestressed direction of any uniaxially prestressed member, there was a certain prestress level for which the change in length due to internal freeze-thaw damage equaled the change in length due to the applied prestressing force plus any longitudinal creep effects. This resulted in a total zero change in length. This zero change in length condition is called the "stress equilibrum condition" and the level of prestress which causes this condition is called the "prestress stability level." However, this condition can only last a short while before equilibrium is destroyed, since freeze-thaw daamage and and creep are continuously changing. / Master of Science

No description available.

Master of Science / Department of Civil Engineering / Kyle Riding / Concrete is most widely used material in construction industry, which is made up of cement, water and aggregates as its major ingredients. Aggregates contribute to 60 to 75 % of the total volume of concrete. The aggregates play a key role in the concrete durability. The U.S Midwest has many aggregates that can show distress in the field under freezing and thawing conditions. The objective of this research was to determine if the Test Method for the Resistance of Unconfined Coarse Aggregate to Freezing and Thawing, method CSA A23.2-24A, could be used to differentiate good from poor performing aggregates in concrete. In this study fifty one KDOT aggregates (including twelve ledge and thirty nine production samples) were tested for freeze thaw resistance using CSA A23.2-24A test method and were compared to the results of the standard KDOT aggregate qualification tests. In addition to performing the CSA test method using a 3% sodium chloride solution, a subset of the aggregates were tested using either a 3% magnesium chloride or calcium chloride solution to determine the effects of the salt type on the aggregate performance. No correlation was found between the CSA A23.2-24A test method results and the standard KDOT aggregate qualification tests. The results also indicated that the mass loss in the CSA A23.2-24A was similar for the aggregate sizes tested. The use of alternate salt solutions like MgCl2 and CaCl2 resulted in increased freeze thaw mass loss in limestone aggregates.

Wastewater sludge is considered a valuable source of nutrients and energy. Freeze/thaw treatment is an efficient dewatering method for wastewater sludge management in First Nation communities located in cold climate conditions. Natural freeze/thaw is a simple, practical and low cost method, which can effectively dewater sludge. The objective of this research is to evaluate dewatering, nutrient recovery and organics separation of wastewater sludge originating from different wastewater treatment processes using freeze/thaw processing. The results of experiments showed the effectiveness of this method in sludge dewaterability and solubilisation of organics and nutrients. The sludge solid content increased by approximately 10-fold after treatment. It was effective in solubilisation of about 15.2%, 33.5% and 21.5% of total nitrogen, total phosphorus and total chemical oxygen demand to soluble one, respectively for the non-BNR sludge. However, anaerobic digestion of the solid cake post freeze/thaw treatment did not show enhanced methane yield compared with fresh sludge. / February 2017

The freeze-thaw process controls several hydrologic processes including infiltration, runoff, and soil erosion. Simulating this process is important particularly in cold and mountainous regions. The Soil and Cold Regions Model (SCRM) was used to simulate, study, and understand the behavior of 12 homogenous soils, subject to a freeze-thaw process based on meteorological data at a snow dominated forest site in Laramie, WY, from 2010 and 2012. To complete a simulation, which accounts for all three phases of water (liquid, vapor, and ice), the model requires meteorological data, canopy characteristics, soil physical properties including the van Genuchten-Mualem parameters, and the initial state of the soil profile. Different model conditions were applied included the relationship between soil pore size, soil particle contact, soil thermal conductivities, soil ice/water content, snow cover, and meteorological data. Analysis of the simulations used metrics such as soil frost depth, days with ice, and maximum ice content. The results showed a threshold in snow depth ranging from 20 to 40 cm to fully insulate the soil from the atmosphere. Additionally, the model showed that the freeze-thaw process was strongest in the period with a shallow snow pack and that particle packing within the soil profile was an important factor in this process. Soil texture and water content controlled soil thermal properties. Water movement towards the freezing front was especially important in fine textured soils, where water and ice was concentrated in the upper layers. In coarser textured soil, frost also occurs, but not to the same extent. Based on these results, future research that combines a broader set of soil conditions with an extended set of field meteorology data could elucidate how soil texture controls thermal properties related to soil frost.

Soil moisture and ground thaw state are both indicative of a hillslopes ability to transfer water. In cold regions in particular, it is widely known that the wetness of surface soils and depth of ground thaw are important for runoff generation, but the diversity of interactions between surface soil moisture and ground thaw themselves has not been studied. To fill this knowledge gap, detailed shallow soil moisture and thaw depth surveys were conducted along systematic grids at the Baker Creek Basin, Northwest Territories. Multiple hillslopes were studied to determine how the interactions differed along a spectrum of topological, typological and topographic situations (T³ template). Results did not show a simple relationship between soil moisture and ground thaw as was expected. Instead, correlation was a function of wetness such that the correlation between soil moisture and ground thaw improved with site wetness. To understand why differences in soil moisture and ground thaw state arose, water and energy fluxes were examined for these subarctic study sites to discern the key processes controlling the patterns observed. Results showed that the key control in variable soil moisture and frost table interactions among the sites was the presence of surface water. At the peatland and wetland sites, accumulated water in depressions and flow paths maintained soil moisture for a longer duration than at the hummock tops. These wet areas were often locations of deepest thaw depth due to the transfer of latent heat accompanying lateral surface runoff. Although the peatland and wetland sites had large inundation extents, modified Péclet numbers indicated that the relative influence of external and internal hydrological processes at each site were different. Continuous inflow from an upstream lake into the wetland site caused advective and conductive thermal energies to be of equal importance to ground thaw. The absence of continuous surface flow at the peatland and valley sites led to the dominance of conductive thermal energy over advective energy for ground thaw. A quantitative explanation for the shallow soil moisture-ground thaw patterns was provided by linking hydrological processes and hillslope storage capacity with the calculated water and energy fluxes as well as the modified Péclet number. These results suggest that the T³ template and the modified Péclet number could be very useful parameters for differentiating landscape components in modeling soil moisture and frost table heterogeneity in cold regions.

Soil moisture and ground thaw state are both indicative of a hillslopes ability to transfer water. In cold regions in particular, it is widely known that the wetness of surface soils and depth of ground thaw are important for runoff generation, but the diversity of interactions between surface soil moisture and ground thaw themselves has not been studied. To fill this knowledge gap, detailed shallow soil moisture and thaw depth surveys were conducted along systematic grids at the Baker Creek Basin, Northwest Territories. Multiple hillslopes were studied to determine how the interactions differed along a spectrum of topological, typological and topographic situations (T³ template). Results did not show a simple relationship between soil moisture and ground thaw as was expected. Instead, correlation was a function of wetness such that the correlation between soil moisture and ground thaw improved with site wetness. To understand why differences in soil moisture and ground thaw state arose, water and energy fluxes were examined for these subarctic study sites to discern the key processes controlling the patterns observed. Results showed that the key control in variable soil moisture and frost table interactions among the sites was the presence of surface water. At the peatland and wetland sites, accumulated water in depressions and flow paths maintained soil moisture for a longer duration than at the hummock tops. These wet areas were often locations of deepest thaw depth due to the transfer of latent heat accompanying lateral surface runoff. Although the peatland and wetland sites had large inundation extents, modified Péclet numbers indicated that the relative influence of external and internal hydrological processes at each site were different. Continuous inflow from an upstream lake into the wetland site caused advective and conductive thermal energies to be of equal importance to ground thaw. The absence of continuous surface flow at the peatland and valley sites led to the dominance of conductive thermal energy over advective energy for ground thaw. A quantitative explanation for the shallow soil moisture-ground thaw patterns was provided by linking hydrological processes and hillslope storage capacity with the calculated water and energy fluxes as well as the modified Péclet number. These results suggest that the T³ template and the modified Péclet number could be very useful parameters for differentiating landscape components in modeling soil moisture and frost table heterogeneity in cold regions.

Freshwater ecosystems have long been neglected as an important part of the global carbon cycle. However, research shows that most of the world’s lakes are net-heterotrophic and consequently emitters of greenhouse gases to the atmosphere. In many boreal and north-temperate lakes, most of the yearly emissions usually occur in spring, shortly after ice-thaw. The aim of this study was to quantify the flux of carbon dioxide (CO2) and methane (CH4) in three boreal lakes, during this annual event. In order to do this, water samples were collected before and after ice-thaw, and the flux was estimated as the difference in mass of carbon between the two sampling occasions. The results showed that the lakes had accumulated high amounts of carbon over the winter, with higher concentrations generally at higher depths. The fluxes during ice-thaw ranged from 234–380 (mean: 302) and -1.15–15.12 (mean: 8.64) mmol m-2 y-1 for CO2 and CH4, respectively. Given their small sizes, the lakes emitted less carbon, per unit area, than expected. This was assumed to be due to the lakes’ rather isolated locations and since the heating of the water rapidly caused them to become highly stratified, thus preventing the wind from releasing deeper stored carbon. Presumably, this holds true for other similar boreal lakes as well, which suggests that attention – in such ecosystems – also needs to be brought to other mixing periods.

A field experiment was carried out in Ontario, Canada to compare independently measured soil N2O profile concentration and surface N2O flux measurements overwinter and at spring thaw, to estimate the soil N2O content accumulation overwinter, and to estimate the magnitude of the contribution of the physical release of trapped N2O to surface fluxes at spring thaw. Gas samples at various depths were taken and N2O concentrations determined, soil profile gaseous N2O content was calculated by estimating the air-filled pore-space from soil condition measurements, and soil aqueous N2O content was calculated using liquid water content measurements and applying Henry’s Law. Soil N2O content was found to reach a maximum of ~25 mg N2O m-2, and by comparing changes in soil N2O content to surface fluxes measured using the micrometeorological flux-gradient technique, the physical release of previously produced N2O was estimated to contribute up to 47% of spring thaw N2O surface fluxes.