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Master of Science / Civil Engineering / Kyle Riding / The Kansas Department of Transportation (KDOT) currently practices a six-month procedure for determining freeze-thaw durability of coarse aggregate intended for use in concrete pavement. In addition to the excessive amount of time required to conduct this procedure, the testing conditions fail to replicate the accelerated rate of concrete deterioration commonly caused by deicer salt exposure in freeze-thaw environments. An experimental study was conducted in an attempt to reduce the duration of this aggregate qualification procedure. Limestone course aggregates from different quarries were used to batch concrete specimens. These specimens were subjected to curing regimes of different durations before being exposed to repeated cycles of freezing and thawing. The effects of the curing methods on freeze-thaw durability were then investigated. Another segment of this study entailed the immersion of coarse aggregate in salt brine solution prior to concrete batching. Salt-treated and non-salt-treated specimens were subjected to two different methods of freeze-thaw cycling to determine if the presence of salt could differentiate between aggregates with high and low performance. This study found that shorter curing methods, along with adjusted performance requirements, could be used to develop a shorter aggregate qualification procedure. It also found that shorter periods of time in more severe freeze-thaw conditions produced comparable concrete durability results to those of the current test method. Salt treatment of aggregates could indicate a difference in performance of aggregates when exposed to salts in freeze-thaw conditions. It could also be useful in determining frost resistance of hardened cement paste.

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Freeze-drying is the process of removal of water or organic solvent from a desired product by means of sublimation at a low temperature and low pressure. It is commonly employed for drying samples which are heat labile and require sensitive treatment, and is mainly used in the pharmaceutical and food industries. It is an expensive process, requiring vacuum, refrigeration and long cycle times, but does yield quality benefits due to the low temperatures involved and the porous nature of the product. Reducing drying times is important to manufacturers, and this depends on optimising rates of heat and mass transfer in the system without the sample losing its porous structure. However, freeze drying is difficult to study experimentally due to the low temperatures and pressures involved. The quality of the final product mainly depends on the sublimation rate and an optimum lyophilisation requires identification of the parameters which influence the process. The main aim of this study is to employ freeze drying microscopy (FDM) as a useful tool to identify these process parameters and help optimise primary drying phase of the freeze drying process for two systems: lactose (relevant to pharmaceuticals) and coffee (the most widely freeze-dried food product). This equipment allows the movement of sublimation fronts to be directly visualised in-situ under carefully controlled (and isothermal conditions), but has scarcely been used in the literature for this purpose. An image analysis method is developed to automatically track the movement of sublimation fronts, and the frontal data fitted to a simple mass transfer model employing surface and bulk resistances. Initial experiments with lactose solution show poor reproducibility in nucleation temperatures during the freezing step and thus primary drying rates. To improve reproducibility, a small amount of silver iodide (AgI) was added to samples which acts as a nucleating agent and increases the nucleation temperature. This addition of AgI also increases the mean ice crystal size in the samples and are easily visible under the freeze-drying microscope, and in many cases show a distinct orientation with respect to direction of sublimation front. Furthermore, the orientation greatly influences sublimation rates, being approximately factor of two faster when crystals are oriented in the direction of mass transfer. FDM experiments with coffee were less straightforward as nucleation temperatures could not be reliably controlled, even with AgI added. Nevertheless there was a clear decrease of bulk resistance with increasing nucleation temperature. An experimental programme was then undertaken to examine the impact of initial solid content, cooling rate, the addition of an annealing step, freeze drying temperature and aeration (for coffee samples). Frontal data were fitted to a simple mass transfer model comprising surface and bulk (per unit depth) resistances and good fits to data were obtained. FDM experiments with lactose and coffee clearly showed the presence of a surface resistance which could also be seen as a surface layer which was devoid of ice crystals (and hence not porous when sublimed). The edge resistance first increased and then decreased with solids content. The resistance per unit depth increased exponentially with solids content, so much so that there is an optimal solids content (around 10% solids) in relation of the rate of production of dried material. Cooling rates were mainly found to affect the surface resistance rather than bulk resistance and this may be due to different levels of surface drying when the samples are being cooled for different lengths of time. Annealing substantially changed the ice crystal sizes, and had a beneficial effect on freeze drying rates and had a similar effect to adding AgI. Freeze drying rates also increased with increasing temperature approximately in line with the saturated vapour pressure (SVP) of ice which is widely held to constitute the driving force for mass transfer. It was possible to make drying time calculations for conventional vial (lactose) and tray (coffee) drying using the frontal rate data obtained from FDM. For 10% lactose and 10% coffee (annealed) there was good agreement between the vial and tray data and predictions based on a microstructure oriented parallel to the direction of mass transfer. This was the only case where agreement was found, but also the only case where directionality was observed in FDM. The much faster drying times observed in the vial and tray experiments are thus attributed to directional solidification occurring in these systems, and this was borne out by SEM imaging. Aeration of the coffee samples was also found to substantially reduce drying times. The influence of microstructure on freeze drying rates is thus very clear.

Highway subsoils in cold countries are subject to increased thermal conductivity, disruption of natural moisture circulation as well as dynamic loading and application of de-icing chemicals in the winter months. In this work, the moisture mass transfer in a state of vapour flow and the de-icing chemical migration were considered during unidirectional freezing. The moisture mass transfer in a gaseous state was previously widely neglected in the exploration of frost heave. To conduct freeze-thaw cycles with increased lengths of soil samples and a modified slow freezing technique, an environmental chamber of nine samples capacity was designed. Supplying the non-saline samples with either 11 or 22 g/L sodium chloride solution signified chemical mass transport over the sample length and a significant change in temperature-moisture distribution when compared to deionised water supplied test results. The presented conceptual model with vapour mass transfer was based on the thermodynamic equilibrium of vapour density with temperature change and the phase transition to ice during thermal energy withdrawal. Compared to the widely used coupled heat-mass models, the vapour flow based model clearly explained the driving forces and presented a much easier algorithm for calculation. The de-icing chemical displacement was explained as the migration of the dissolved ions together with hygroscopic water transport, which in turn, was driven by cryosuction forces. The reduction of hydraulic conductivity during the secondary salinisation with sodium chloride was caused by chemical osmosis, which tended to equalise the solute concentration in pore water over the sample length. The research outcomes indicate a significant contribution to the future perspectives on frost heave modelling and prognosis. Further research could extend this work by inclusion of the vapour mass transfer in quantitative analysis for soil freezing. The effect of secondary salinisation should be also foreseen in the long term prognosis for highway subsoils exploitation.

High quality, mature sour cherries (Prunus cerasus L., cultivar Montmorency)were freeze-dehydrated, conditioned with one thousand part per million of sulfur dioxide solution spray followed by dry heat at 200 F for 1 minute and compressed with a pressure of 400 pounds per square inch. The samples were vacuum sealed in cans and stored at 100 F and 70 F for 6 months. The samples were analyzed every 2 months for compression characteristics, changes of color, acidity, anthocyanins, and ascorbic acid. Organoleptic evaluations were made for flavor, texture, and appearance of the rehydrated products prepared as pies. The results indicated that freeze-dehydrated sour cherries stored at 70 F maintained higher quality and had a slower rate of change than those samples stored at 100 F. The sulfited sample had a higher quality rating than the control sample.

Fibre reinforced polymer (FRP) materials have emerged as an innovative tool within the civil engineering community for the strengthening and rehabilitation of existing reinforced concrete structures. Research has taken place over the past decade that has demonstrated the benefits of FRPs, and it is evident that there is a need for their usage given the status of the deteriorated North American civil infrastructure. However, in order to increase confidence in the application of these materials in Canada, further information is required to fully understand their behaviour in cold climates. This thesis expands on the previous research that has taken place at Queen’s University, investigating the freeze-thaw behaviour of FRP strengthened reinforced concrete. The research program herein studies the combined effects of freeze-thaw cycling and sustained loading on the flexural performance of 45 small-scale beams strengthened with glass FRP sheets, carbon FRP sheets, or carbon FRP plates. In an attempt to attain failure of the beams due to FRP rupture, the anchorage of the beams was increased and a theoretical model was produced to select the beam design for this failure mode. The model also predicted the performance of the strengthened beams in order to determine appropriate sustained loading levels. After being subjected to 300 freeze-thaw cycles and almost 3 months of sustained loads, the beams were tested to failure. It was found that the beams subjected to combined loads encountered virtually no losses in average ultimate strength. However, the greater inconsistency of the results for these beams relative to the control beams implies that lower guaranteed strengths should be used for design in situations where these conditions are present. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-02-29 14:19:29.954

In recent years, a modified method to strengthen reinforced concrete (RC) structures has emerged involving application of fibre reinforced polymers (FRPs) in the ‘near surface’ of a member. The near surface mounted (NSM) method entails placing a pre-cured FRP bar, rod, strip, or plate, along with an adhesive into a pre-cut groove or slot in the cover of a member. Advantages of the NSM technique over externally bonded (EB) systems include minimal surface preparation and installation time, the ability to anchor the FRP into an adjacent member, superior protection from mechanical and environmental damage, and superior bond properties. Although a number of laboratory studies, field applications, and experimental field projects have employed the NSM FRP strengthening technique, none of these have been performed in a climate where cold environments and freeze-thaw cycling could cause adverse effects. This thesis presents the results of an experimental program to investigate the flexural and bond performance and freeze-thaw durability of a specific NSM carbon/vinylester FRP tape strengthening system through a series of tests on strengthened slab strips and a series of pull-out bond tests. The effects of adhesive type (cementitious or epoxy) and exposure condition (room temperature, freeze-thaw, sustained load, or freeze-thaw under sustained load) are examined. The results indicate no discernable negative impacts on the performance of the grout strengthened members after exposure to freeze-thaw cycles and/or sustained load. The slab strips strengthened with epoxy adhesive displayed minor changes in ultimate load (less than three percent) after exposure to freeze-thaw cycles or a period of sustained load, while the combined effect of freeze-thaw cycles and sustained load produced an average reduction in ultimate load of eight percent. The epoxy adhesive strengthened pull-out bond tests experienced a 27% average drop in ultimate load after 150 freeze-thaw cycles. These results suggest that additional research on the combined effects of sustained load and freeze-thaw cycling are warranted, particularly for NSM strengthening applications using epoxy adhesives. / Thesis (Master, Civil Engineering) -- Queen's University, 2010-04-30 18:11:56.424