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In this thesis, the carbonation of functionally graded concrete is investigated through a combination of experimental and analytical approaches. The properties of functionally graded concrete vary throughout the cross-section to satisfy performance requirements in a resource-efficient manner. In this research, functional grading of concrete elements is achieved by casting discrete layers of concretes possessing different properties. Layers are cast in the fresh state to prevent formation of a cold joint and associated interface weakness. Carbonation is the process of environmental CO2 diffusing into and reacting with concrete, thereby changing its chemical composition. It is a durability concern for concrete structures, since carbonated concrete does not provide adequate corrosion protection to embedded reinforcement. Increased resistance to carbonation has traditionally been achieved by increasing the cement content in concrete elements, which increases embodied carbon. Carbonation presents as a surface phenomenon. As such, the concrete mix adopted at the outside face is of most concern when designing carbonation-durable elements. Given the ability to relate properties to performance, functional grading presents a promising approach to providing carbonation durability with reduced cement content. In such an element, a high-cement carbonation durability layer could be placed in exposed areas, but retaining low-cement concrete as the material in the bulk remainder. This would have theoretically equivalent durability to a single-mix element cast from the high-cement mix, but significantly lower cement content. The presented research seeks to answer the question "Is layered functional grading a viable method of reducing cement contents in concrete elements without sacrificing carbonation durability?''. This is achieved by first understanding the carbonation behaviour of single-mix concrete specimens, thus establishing baseline processes for accelerated carbonation testing and the influence of material parameters on carbonation performance of different concrete mixes. Next, machine learning is applied to predict properties of concretes from mix composition, such as carbonation performance. Following this, the carbonation of layered functionally graded specimens is experimentally investigated, and the results are used to validate a derived model for the carbonation depth in layers. Finally, it is acknowledged that structural cracking could provide a route for CO2 penetration beyond the depth of a carbonation durability layer. Therefore, a further experimental series investigates the cracking behaviour of layered prisms under loading and their carbonation performance when subjected to simultaneous cracking and carbonation. Digital image processing methods are implemented in multiple areas to improve the detection and analysis of carbonation fronts from phenolphthalein indication tests. Overall, the results demonstrate that layered functionally graded concrete elements offer a viable route to cement reduction, without loss of carbonation durability. Therefore, it is recommended that practitioners consider this approach to design durable structures with reduced cement consumption.

Accumulation of ice or snow on overhead lines can significantly threaten the stability and safety of power systems as a result of the extra weight. This can result in severe damage or the collapse of towers. Surface treatments that claim to be superhydrophobic or icephobic have been attracting a great deal of attention for their anti-icing, self-cleaning, noise- reducing, and anti-corrosion properties. If these surface treatments can be applied to overhead lines in a manner that reduces or delays ice accretion, significant improvements in the stability and durability of existing overhead lines can be achieved. New overhead line designs can also benefit from these surface treatments by reducing clearance requirements to allow lower-cost systems to be built. This research, inspired by the CIGRE TB 631, assesses the viability of the deployment of superhydrophobic surface treatments onto overhead line systems. The wettability performance of superhydrophobic surface treatments was characterised by contact angle measurements. A manual zoomed-in computing method was developed to improve the accuracy of these contact angle measurements. Water drop behaviour on superhydrophobic surfaces was examined under a high-speed camera. The fabrication & application method of various surface treatments were optimised using different parameters to achieve optimal performance with high reproducibility and feasibility. Overall, high levels of superhydrophobicity with low surface hysteresis were achieved on substrates by deploying different protective coatings and laser patterns. Taking into account the need to examine ageing behaviours of surface treatments before deployment, a range of ageing tests were designed and conducted, including thermal ageing/cycling, ultraviolet exposure, corona exposure, and outdoor environmental exposure. The laser patterning technique was proven to be more robust and durable than the protective coatings used in this research. Each laser patterned sample retained a high level of superhydrophobicity after most of the ageing tests, while different levels of degradation were observed on the samples with protective coatings. In addition, the benefits and applications of surface treatments on overhead line systems were discussed, including anti-icing, anti- frosting, audible noise reduction, and heat dissipation improvement.

Suspended vibrating structures play a significant role as basic building blocks for mechanical resonators and form the foundation of modern acoustic transducers. The practical use of mechanical resonators is not limited to acoustic technology but also includes a wide range of applications for sensing and actuation purposes. The ultimate goal of this project has been set to realise highly tunable and sensitive resonators that have operating frequencies covering the audible range (20 Hz - 20 kHz). In this thesis, two distinct types of mechanical resonators have been developed, dedicated mainly to hearing assistive devices and acoustic microphones. The overall performance of mechanical resonators is governed by their structural elements design, material properties, and dimensions. Inspired by their unique mechanical properties, a refractory metal of tantalum and a two-dimensional (2D) material of graphene have been utilised as vibrating structural elements for the developed resonators. In the first parts of this project, mechanical resonators of tantalum tunable to audio frequencies have been developed. First, a comprehensive investigation of the influence of fabrication process parameters on the residual stress of tantalum thin-films has been implemented. Based on the residual stress characterisation, an array of suspended microbeams of tantalum has been created and their mechanical static deflection has been investigated. Accordingly, the design and fabrication process of the resonators have been optimised, and hence straight and undeformed free-standing microbeams with lengths of 1 - 3.4 mm have been created and actuated electrostatically. The resonators have achieved a low resonant frequency (1.4 kHz) tuned over the audio range. Unlike the conventional microphones that have their vibrating membranes made of stressed and stiff materials, the graphene-based resonators developed here from ultra-large and thin bilayer membranes have the advantages of possessing enhanced durability and high frequency tuning sensitivity. A simple and reproducible fabrication process has been demonstrated to create millimetric membranes composed of a multilayer graphene and a thin polymeric film. The novelty of the developed resonators lies in the exceptional area to thickness aspect ratios of ~ 10,000, and the implementation of electrothermal actuation to drive the membranes into resonance and tune their resonant frequencies.

Hydrogen fuel cells, and notably the polymer electrolyte fuel cell (PEFC), present an important opportunity to reduce greenhouse gas emissions within a range of sectors of society, particularly for transportation and portable products. Despite several decades of research and development, there exist three main hurdles to full commercialisation; namely infrastructure, costs, and durability. This thesis considers the latter of these. The lifetime target for an automotive fuel cell power plant is to survive 5000 hours of usage before significant performance loss; current demonstration projects have only accomplished half of this target, often due to PEFC stack component degradation. Health management techniques have been identified as an opportunity to overcome the durability limitations. By monitoring the PEFC for faulty operation, it is hoped that control actions can be made to restore or maintain performance, and achieve the desired lifetime durability. This thesis presents fault detection and diagnosis approaches with the goal of isolating a range of component degradation modes from within the PEFC construction. Fault detection is achieved through residual analysis against an electrochemical model of healthy stack condition. An expert knowledge-based diagnostic approach is developed for fault isolation. This analysis is enabled through fuzzy logic calculations, which allows for computational reasoning against linguistic terminology and expert understanding of degradation phenomena. An experimental test bench has been utilised to test the health management processes, and demonstrate functionality. Through different steady-state and dynamic loading conditions, including a simulation of automotive application, diagnosis results can be observed for PEFC degradation cases. This research contributes to the areas of reliability analysis and health management of PEFC fuel cells. Established PEFC models have been updated to represent more accurately an application PEFC. The fuzzy logic knowledge-based diagnostic is the greatest novel contribution, with no examples of this application in the literature.

Corrosion of reinforcing steel in concrete due to chloride ingress is one of the main causes of the deterioration of reinforced concrete structures, particularly in marine environments. It is therefore important to develop a reliable prediction model of chloride ingress into concrete, which can be used to predict the chloride concentration profiles accurately to help to assess the service life for reinforced concrete structures. Cementitious materials are porous media with a highly complex and active chemical composition. Ionic transport in cementitious materials is a complicated process involving mechanisms such as diffusion, migration, ionic binding, adsorption and electrochemical interactions taking place in the pore solution of the materials. The process is dependent on not only the microstructural properties of the materials such as porosity, pore size distribution and connectivity but also the electrochemical properties of the pore solution including ionic adsorption and ion-ion interactions. This thesis presents a numerical study on the multi-component ionic transport in concrete with the main focus on the microscopic scale. This study first investigated the impact of the Electric Double Layer (EDL) on the ionic transport in cement-based materials. The EDL is a well-known phenomenon found in porous materials, which caused by the surface charges at the interface between solid surfaces and pore solutions. The numerical investigation is performed by solving the multi-component ionic transport model with considering the surface charges for a cement paste subjected to an externally applied electric field. The surface charge in the present model is taken into account by modifying the Nernst-Planck equation in which the electrostatic potential is dependent not only on the externally applied electric field but also on the dissimilar diffusivity of different ionic species including the surface charges. Some important features about the impact of surface charge on the concentration distribution, migration speed and flux of individual ionic species are discussed. Then a new one-dimensional numerical model for the multi-component ionic transport in concrete to simulate the rapid chloride migration test is proposed. Advantages and disadvantages of the traditional methods used to determine the local electrostatic potential, i.e. electro-neutrality condition and Poisson’s equation, are illustrated. Based on the discussion a new electro-neutrality condition is presented, which can avoid the numerical difficulties caused by the Poisson’s equation, and remain the non-linearity of the electric field distribution. This model with the new electro-neutrality condition is employed to simulate the RCM test to prove its applicability. The new model is promising in solving the multi-component ionic transport problems especially in microscopic scale. Lastly, a one-dimensional numerical investigation on the chloride ingress in a surface-treated mortar with considering the penetration of sealer induced porosity gradient was performed. The numerical model was carefully treated to apply governing equations of ionic transport to this situation of two pore structures, with every parameter clearly defined on the microscopic scale.

Crushed or recycled concrete aggregates (CCA/RCA) is an increasingly popular material as a replacement for natural aggregates in concrete due to industry demands for more recycled, lower carbon and responsibly sourced materials. In the UK, the majority of CCA is utilised in non-structural applications such as: a general fill material, road base/subbase or in low-grade concrete. Recycled aggregate producers however, are seeking new ways to incorporate CCA into higher value applications such as structural concrete to increase profits. Opportunities to incorporate CCA into structural concrete may also arise because of project demands for sustainability or in situations where natural aggregates are in short supply. Limited research has been published regarding the effect of coarse CCA on the durability of structural concrete, particularly in respect to water and chloride ion ingress and possibility of corrosion initiation. The aim of this EngD research programme was to investigate the effect of coarse CCA and supplementary cementitious materials (SCMs) on the durability performance of structural concrete, with particular emphasis on the key liquid transport mechanisms within concrete, namely absorption by capillary action, diffusion and migration. This addressed an industry concern regarding the detrimental effect of coarse CCA which has resulted in a limit on replacement levels of coarse natural aggregates in structural concrete, as defined in Eurocodes and local national standards for concrete. In this study, structural concrete was produced with varying levels of coarse CCA replacement (up to 100%), from five different sources and/or structural elements across the UK, with various combinations of SCMs to replace in part the Portland cement. Petrographic analysis was used as an innovative technique to characterise the coarse CCA sources to determine suitability which yielded positive results. The durability performance of the resultant concrete was analysed by exposing the concrete to aggressive chloride environments. The results indicate that the inclusion of coarse CCA, even as low as 20%, had a detrimental effect on the durability performance of structural concrete, in relation to absorption by capillary action, diffusion and migration. This effect however, can be offset through the use of SCMs, which have been shown to outperform control Portland cement concrete with 100% natural aggregates in durability performance tests. The results also suggest that cementitious materials had a greater influence on durability performance than the type and source of coarse aggregates used. It is recommended that the replacement of natural aggregate with coarse CCA be limited to 30% in cases where compliance with the 28 day characteristic strength is of particular importance. If the criterion for compliance at 28 days can be relaxed and the compressive cube strength of concretes with SCMs tested at later ages for conformity (56 or 90 days), then higher quantities of coarse CCA may be incorporated up to 60% to produce a more sustainable structural concrete. It is recommended that Portland cement is partially replaced with 50% ground granulated blast-furnace slag (GGBS) to produce a CEM III/A concrete. This is a significant step towards the potential wider implementation of coarse CCA in structural concrete, provided a suitable quantity of SCM is adopted along with a reliable and consistent source of coarse CCA.

Geopolymers are a subset of alkali-activated materials, synthesised from by-products of low-calcium aluminosilicates such as fly ash (FA) and metakaolin (MK). These clinker-free binders have been developed as a potential partial replacement of CEM I (ordinary Portland cement) in order to help reduce the environmental footprint of concrete. Geopolymer concretes (GCs) can also provide mechanical properties comparable to those of CEM I concretes. The inclusion of ground granulated blast-furnace slag (GGBS) offers benefits in improving the hardening process of the concrete at ambient temperature and reducing the permeability of the binder. However, there have been a limited number of studies on the durability of FA-based GC for structural applications, in particular GGBS/FA blended GCs with up to 50 % GGBS. The current study hence aimed to investigate the durability properties for the structural construction of GCs optimised for the compressive strength. It is also essential to improve understanding regarding the fresh state of GC in order to develop effective preparation and casting processes. The factors influencing the compressive strength and consistency of FA-based GCs were investigated, including varying the constituents, the initial curing temperature and the additional GGBS. The relationships between the compressive strength and water content of both blended GCs with GGBS/FA ratios of 0/100, 20/80, 35/65 and 50/50, and the initial curing temperatures of 10, 20, 30 and 75 oC, as well as CEM I concretes as references were evaluated in order to identify the mix designs targeted at 35 MPa and 60 MPa. The durability properties of these concretes were then investigated at 91 days using several selected testing methods standardised for analysis of CEM I concretes including water permeability, rapid chloride migration, concrete resistivity, carbonation and steel reinforcement corrosion. An effective combination coating process for the steel mould using Z30 Fluid and Waxoyl was developed. The consistency of GCs increases with the water content, but decreases with the increase of GGBS proportion. The flow table is recommended to indicate the consistency of GCs (compared to the slump) because the flow diameter distributed equally and linearly over an appropriate range from a low to medium workability, as classified for CEM I. Prolonged curing at 10 oC for 28 days is sufficient for blended GCs with at least 20 % GGBS to achieve a compressive strength of 33 MPa. The presence of GGBS increases the compressive strength of blended GCs cured at either 20 or 75 oC to above 80 MPa. Whereas, the optimal mix design of the FA-based GC with an alkaline to binder ratio of 0.3 can be obtained when using the total aggregate to GC ratio of 0.77; fine aggregate to total aggregate ratio of 0.35; sodium hydroxide molarity of 12 M; sodium silicate to sodium hydroxide ratio of 2.5; superplasticizer to binder ratio of 1.5 %; and initial steam curing temperature of 75 oC for 24 h. However, an alkaline to binder ratio of 0.6 exhibited the maximum 7-day compressive strength of 82 MPa for the FA-based GC. The compressive strengths of the GCs decrease with the increased water content and become more sensitive at the higher water to solid ratios, on which the effect of increasing temperatures from 10 to 30 oC becomes insignificant. Moreover, the compressive strength Durability of reinforced GGBS/FA geopolymer concretes vi development of the GCs shows an insignificant increase at the age of 91 days, except for 35 % GGBS specimens and cured at 20 oC or higher with a slight decrease. In general, increasing the compressive strength of GCs from 35 MPa to 60 MPa reduced the durability properties by factors of 1.5 to 2, except for the porosity (VPV) with a slight decrease. According to the VPV results, the porosity of the GCs is comparable to that of the equivalent CEM I concretes regardless of the curing temperature and GGBS content. Meanwhile, the GCs cured at more ambient temperatures seem to have either a coarser or more interconnected pore structure leading to a higher sorptivity coefficient than the CEM I counterparts by a factor of 2 to 5. However, at the elevated curing temperatures of 75 oC, the sorptivity of GCs became comparable with the CEM I concretes. Besides, the inclusion of GGBS up to 50 % shows inconclusive influences on the porosity and pore interconnectivity but it hinders the chloride migration coefficient. The time to failure inferred from the current and time relationship monitored in the accelerated corrosion test takes up to 5 times longer for the GCs than the CEM I equivalents. Conversely, the GGBS/FA blended GCs appear to be more susceptible to carbonation, even in the natural atmospheric condition. Moreover, 1% CO2 concentration seems to be aggressive to FA-based GC cured at 75 oC with a carbonated depth of more than 5 cm after 54 days, whereas in the natural condition, the carbonation depths of these samples were very low and similar to that of the high strength CEM I concretes after 147 days. It can be concluded that care must be taken when using the GCs with 50 % GGBS and cured at more ambient curing temperatures for the structural concrete, in particular in aggressive environments containing extensive chlorides and/or carbon dioxide, in which an elevated curing temperature of 75 oC is recommended.

The study investigates how museum and gallery buildings can be designed to give functional longevity and appeal. It considers this in terms of their design and relation to their surroundings and use in the context of changing social, cultural, political and economic factors. Post World War II the typological design and layout of these buildings was challenged; partly as a result of the influence of modernism and also as new modes of art production challenged the spaces and display modes. Financial instability and class perception have always been problematic and increased public expectations add to issues that need addressing. The study investigates how these factors have impacted on these buildings and if this has influenced their design and use. It considers the regional context of the West Midlands and also draws comparisons to other areas in England to investigate ways of addressing contemporary issues to achieve longevity of use. The study considers the historical influence of the typological developments. Examples from the West Midlands and investigation of the area’s historical background are used to identify if regional idiosyncrasies exist and if these influence a building’s longevity. This establishes their contemporary context and objectively reviews the resulting implications of appearance and function in relation to the social, cultural and economic issues that may be dominant within this region. A qualitative interview methodology and analysis is used to examine the views of a multidisciplinary group of museum and gallery users, capturing a snapshot in time of their views on the appearance, understanding and use of these buildings. This information is analysed and discussed in conjunction with the findings of the relevant literature. The comparison of the information researched raises regional and national issues associated to design and use of these buildings. Four key themes related to the longevity of use emerged; architectural design, location, economic viability and inclusivity.

This report describes a 3 year study carried out to determine the effects of modern coal power generation technologies on the properties of fly ash and how these may affect the use of the material in concrete. A total of 18 fly ashes, from 11 different sources, produced under a range of conditions and technologies were investigated. These primarily included co-combustion, low NOx, supercritical and oxy-fuel technologies, although other available materials (run-of-station, air-classified, processed and stockpiled fly ashes) were included for comparison. The initial experimental work involved physical and chemical characterization of the fly ash samples. Thereafter, tests covering fresh properties, strength development and durability were carried out on selected concretes. A fly ash level of 30% was used with w/c ratios covering the practical range considered (0.35 to 0.65). Equal strength comparisons were also made where appropriate. Finally, granular (unbound fly ash) and monolithic (fly ash concrete) leaching tests were carried out to assess the environmental implications of using the fly ashes. The results from the physical and chemical characterization tests suggest that modern technologies used for coal fired power generation can have an influence on the properties of fly ash produced. The co-combustion, oxy-fuel and in-combustion low NOx fly ashes had reduced fineness and greater LOI, which had a negative effect on foam index and water requirement of the materials. However reactivity was largely unaffected. The post-combustion low NOx and supercritical fly ashes appeared to be unaffected by their production methods compared to that produced by conventional/establish means. Tests on fresh concrete properties showed that fly ashes with high LOI and low fineness required higher SP doses than the reference PC concrete. However, fly ashes with high fineness and low surface area were found to require a lower SP dose than the PC concrete. The concrete compressive strength tests indicate that, in general, finer fly ash concretes tended to have higher strengths than those containing coarser material. However, there did not appear to be any significant difference in performance between fly ash concretes, which suggests that, although modern technologies can have an impact on fly ash properties, if account is taken of these they should not have any significant influence on strength development. Comparison with an earlier study from the 1990s considering BS EN 450-1 fly ashes showed general agreement between the data. The durability study showed that finer, low LOI fly ashes had higher chloride resistance and at equal strength fly ash concretes performed better than those with PC. Equal strength fly ash concretes covering the modern technologies were found to have similar levels of durability for sulfate attack, abrasion and carbonation. High alkali concrete (following the BS 812-123 method) gave similar expansion levels and good resistance with respect to AAR. With air-entrainment, it was found that the fly ash concretes required high doses of AEA (relative to the PC concrete), with high LOI/BET fly ashes requiring greatest quantities. At equal strength, the fly ash concretes had poorer freeze-thaw scaling resistance than PC concrete. However, the majority of the fly ashes did manage to achieve acceptable scaling resistance according to the Swedish criteria. In general, the findings of the durability study are in agreement with the earlier study from the 1990s. Overall, no effect of production technology on the durability of concrete was observed. The leaching studies showed that, in general, in both granular and concrete form, modern fly ashes met the non-hazardous waste requirements in the WAC for all components tested except chromium. For the granular test, there were instances where elevated chromium levels were observed. Similarly, the fly ash concretes failed to meet the non-hazardous limit for chromium. However, chromium from the cement may have contributed to this, since the PC reference also failed to meet this requirement. Based on the results, there is no effect of production technology on the leaching characteristics of fly ash or concrete and the materials do not appear to pose a significant environmental risk. The practical implications of the study have been considered and overall, it has been shown that modern fly ashes behave in much the same way as traditional materials, and therefore, if these materials meet the requirements of BS EN 450-1, and their properties are taken into account in the proportioning of concrete, they should give satisfactory performance.

Lime stabilisation is a ground improvement technique used to improve the engineering properties of cohesive fill materials. During earthworks operations, specialist plant is used to rotovate the clay fill material and intermix lime binder around clay clods. After completion of the lime treatment, the layer is compacted in the usual way. Immediately after mixing, the lime instigate a series of physico-chemical reactions within the clay soil. Where the chemical reactions are favourable and with time after compaction (curing) the material becomes progressively stronger and durable to environmental influences, e.g. inundation by surface or ground water. However, where sulphate is present within the soil, the reactions may change and the ingress of water into the layer can result in the expansive growth of deleterious minerals e.g. ettringite. While sulphate swell issues are relatively rare, when they do occur the degree of expansion can be very high. A high profile sulphate swell failure developed during the construction of the M40, Oxford, UK in 1989. Over the winter period after the lime stabilisation works, a 250mm deep lime treated layer heaved by up to 150mm - destroying the overlying road construction. Since the M40 failure, a substantial amount of effort has been undertaken to better understand the sulphate swell reactions and in this regard the state of scientific knowledge is relatively strong. A fundamental issue for field applications of lime stabilisation is that the vast majority of research has been undertaken on laboratory specimens prepared using methods which do not reflect site practice. Laboratory studies often use oven dried and finely crushed clay, whereas site operations will treat much larger clay clods to result in a more heterogeneous distribution of lime through the compacted soil body. With large clay clods, the chemical reactants must migrate through clods and this may cause the sequence of chemical reactions to change. A further challenge is that laboratory studies are typically undertaken with cure temperatures of 20°C, whereas a typical near surface temperature in the UK is <10°C. This is of particular relevance to sulphate swell failures which are reported to coincide with a reduction in ambient temperature over winter periods. Thus, the direct relevance of laboratory studies to site application was unclear. A series of laboratory experiments using a preparation method which reflects field applications of lime stabilisation was used to investigate the influence of large clay clods on the durability of lime stabilised clay soil. This method was applied to both low and high sulphate clay soils. A fundamental discovery from work on low sulphate clay is that the addition of lime binder to the surface of the clay clods causes a physico-chemical boundary to form. This boundary develops due to the rapid increase to the plastic limit of the clay preventing adjacent clods from joining together during compaction. This causes the engineering properties of each individual clod to develop independent to its neighbours and for each clay clod to be separated by an inter-clod pore space. The strength of each individual clay clod will increase with curing as the added lime dissociates into Ca2+ and OH- and migrates to form C-S-H deep within the clods. Where the material is compacted wet of the optimum water content, this condition improves ion migration and enables development of diffuse cementation deep within clods. The inter-clod porosity remains as a weakness throughout curing especially during specimen soaking, where the pore channels comprise a pathway, accelerating the ingress of soaking water. With low sulphate soil, the soaking water softens the treated material, however, with high TPS soil substantial sulphate swelling may develop. Thus, efforts to minimise this porosity during preparation is important and the use of quicklime with longer mellowing periods can cause the clay clods to develop high strength before compaction. The high strength clods resist compaction and the degree of inter-clod porosity in the compacted mass increases, worsening specimen durability to water ingress. The investigations into high sulphate clays included the development of a Novel Swell Test (NST) to assess volume change. A unique aspect of the NST was that the sulphate swell response of the lime treated material was investigated at site realistic temperatures of 8°C. It was identified that, when compared with standard laboratory test temperatures of 20°C the rate of sulphate swell is substantially higher at the low temperature. The mineralogical testing has permitted the hypothesis that, at 8°C the growth of crystalline ettringite becomes slower and the ettringite precursor, which has a high affinity to imbibe water, remains in this state for much longer. Thus, laboratory swell tests at 20°C may substantially underestimate the degree of swell that may develop in the field. As a pressing need, it is recommended that the industry adapt sulphate swell test methods to appraise the degree of swell at field realistic temperatures i.e. < 10°C. The work also identifies that the primary defence against sulphate swell is to condition the fill so that the risk of post compaction water ingress, via inter-clod porosity, is minimised. The use of GGBS and water addition during extended mellowing periods also reduces the degree of sulphate swell in natural clay soils. This work concludes that working methods for lime stabilisation of medium high plasticity soils of a potentially high sulphate content, should be adapted to encourage diffuse cementation and minimise the degree of (post compaction) inter-clod porosity. Practically this involves the use of hydrated lime and the addition of mixing water throughout extended mellowing periods. Fundamentally, the study recommends that where construction programmes allow, the long term durability of a fill material should be the priority over immediate strength.

The main theme of this research was to investigate the durability of concrete made using waste materials as a cement replacement. This is a method to produce green sustainable concrete. The objective was to use locally available wastes to produce a concrete that could be used by the local authority. The mechanical, physical and chemical properties of concrete made predominantly with IFA as a partial cement replacement have been tested. The IFA was won locally from the domestic waste incinerator at Coventry, UK. The other materials used in the mixes included Ground Granulated Blast Furnace Slag (GGBS), silica fume and by-pass dust, which was used as an activator and was also won locally from the Rugby cement plant. Compressive strength and tensile strength, workability, corrosion of embedded steel, shrinkage and expansion, freeze and thaw, corrosion and chloride ingress were studied. Water permeability was studied by the author on mortar samples during one year and on concrete samples during the following. Carbonation was studied on concrete samples and finally mechanical experiments were carried out on concrete beams and slabs. Two further experiments were carried out to complete the study of durability of concrete made with waste materials being, the ASR (Alkaline Silica Reaction) and sulphate attack experiments. One main physical experiment, in the form of a trial mix, was carried out in one of the waste recycling sites of Warwickshire in September 2013. Subsequent to observations during the site trial, the author compared results of setting time, heat of hydration and strength of the trial mix and control mixes. The outcome of this research was a novel mix that had more than 30 percent waste material and a further 40 percent of secondary materials, making it as sustainable as possible. Both laboratory and site trial results have achieved compressive strength which are higher than 30 MPa, indicating that the novel mix concrete could be used for structural purposes. Most of the durability results of the novel mix were comparable with the control OPC mix and the novel mix concrete, in terms of transport properties, induced less electrical current seepage. Furthermore the tensile strength of the novel mix concrete was higher than the control OPC concrete and this is due to the higher ductility index of the novel mix.

Durability is a term that is used to describe and measure a regime's ability to survive and its longevity. It also can be defined as the overall strength derived from the accountability to a state’s population. Many Authors have discussed durability and how and why regimes stay in power for so long. Also, a big factor that is discussed within the literature is foreign intervention in the form of financial, fiscal, and military aid. What I seek to understand is how foreign financial aid along with military intervention, and continuous fiscal support affects regime stability and longevity over time within my case studies of Jordan and Saudi Arabia. I am going to add to the discourses surrounding how foreign aid, military intervention, and fiscal support either positively or negatively affect the durability of regimes and I am to answer the question of if aid is the main factor that affects regime survivability and with the cases of Jordan and Saudi Arabia, I aim to create a linear spectrum of durability where the previous cases that Dr. Yom discusses and where my cases fall on the spectrum of durability. From the literature discussed by the various authors on durability, survivability, and infrastructural power. I aim to find where my case studies of Jordan and Saudi Arabia fall as they relate to geopolitical seclusion (durable), geopolitical subsidization (tenuous survival), and geopolitical substitution (total regime change) and seek to chart a spectrum of durability.

Adhesive joining is an attractive alternative to conventional joining methods, such as welding and mechanical fastening. The benefits of adhesive bonding include: the ability to form lightweight, high stiffness structures; joining of different types of materials; better fatigue performance, and reduction in the stress concentrations or the effects of the heat associated with welding. However, concerns about the durability of adhesive joints still hinder their widespread use in structural applications. Moisture has been identified as one of the major factors affecting joint durability. This is especially important in applications where joints are exposed to varying moisture conditions throughout their useful life. The aim of this research is to develop models to predict degradation in adhesive joints under varying moisture conditions. This was achieved by a combination of experimental and numerical methods. Experiments were carried out to characterise the moisture uptake and mechanical properties of the single part epoxide adhesive, FM73-M. Single lap joints were manufactured from aluminium alloy 2024 in heat treated (T3) and non heat treated (O) states using the FM73-M, BR127 adhesive-primer system. Tensile testing of the single lap joints was carried out after the joints had been exposed to hot-wet conditioning environments. Models were developed for predicting moisture concentration in the adhesive under cyclic moisture absorption and desorption conditions. A finite element based methodology incorporating moisture history was developed to predict the cyclic moisture concentration. In the next step, a novel finite element based methodology, which was based on moisture history effects, was developed to determine stresses in bonded joints after curing, conditioning and tensile testing. In the final step, a moisture history dependent cohesive zone element based damage and failure criterion was introduced to predict damage initiation, crack growth and failure under variable moisture and temperature conditions. The methodology proposed in this work and its implementation by finite element method provides a systematic approach for determining the degradation in adhesive joints under varying environmental conditions and accomplishes the aim of this research.

Self-consolidating concrete (SCC) is a relatively new concrete technology which allows the concrete to be placed without the need for manual or machine vibration. This innovation reduces labor costs, construction times, and can provide a smooth, finished surface. However, this technology is used in the United States primarily in the precast and prestressed concrete industry. The utility of SCC in structural applications, such as areas of dense reinforcement or locations where complex geometry makes consolidation impossible, is also advantageous. In this study, a series of SCC mixtures were developed both with and without fly ash replacement. These mixtures were then used to compare how SCC performed relative to traditional slump concrete in drilled shaft applications. The SCC mixtures also contained different aggregate sizes (#7 and #57), blended in multiple ratios. The impact of these mix proportions was evaluated based on the fresh properties and strength of the SCC. Fresh property testing was performed using specialty test methods developed for use with SCC. To examine the performance of these mixtures in underwater placements, a washout test was performed. A viscosity modifying admixture (VMA) was included for these tests to improve the resistance to washout. Finally, seven simulated drilled shafts were placed in wet and dry environments to test how each SCC mixture performed. These shafts were compared to two shafts (one placed underwater and one placed dry) made with a traditional slump concrete mix. The #7 aggregate showed superior performance in fresh property testing compared to both #57 aggregate mixes and blended #7 and #57 aggregate mixes. VMA was found to improve washout resistance of SCC but was detrimental to other fresh properties. Fly ash negatively affected the early-age strengths (threeday and seven-day), but significantly improved ninety-day strengths compared to the standard SCC mixture. Higher fly ash replacements also resulted in significant decreases in peak concrete temperatures and increased the time to reach these peak temperatures. SCC mixes performed significantly better during the drilled shaft placements due to its deformability and flowability compared to traditional slump concrete. The wet environment placements showed that SCC provides an improved finished product and has incredible promise for use in drilled shaft applications and other structural elements.

Some asphalt mixes, following the Superpave mix design procedure, have been reported to be too stiff, making cracking a prevalent form of pavement distress. Additionally, cracking has been reported to be the main form of distress of asphalt pavements in the State of Arkansas. These facts have heightened state agencies’ interest in better performing asphalt pavements, with Arkansas resolving to explore performance-based balanced mix designs (BMD), not yet explored in the state. The primary objective of this document is to present the completed study of balanced mix designs, based on the rutting and cracking potential of asphalt pavement mixtures through Asphalt Performance Analyzer (APA) and IDEAL-CT testing. The research matrix for the study helped provide a template for exploring the impact of parameters such as number of gyrations, and binder content in the performance of the mix. Findings were used to determine poor, moderate, good, and excellent performance zones for the mix. It was found that higher binder contents and lower gyration mixes perform best when compared to lower binder content and higher gyration mixes.

This thesis presents the experimental and analytical results to investigate the effect of corrosion on the mechanical properties of reinforcing bars and concrete beams, with particular reference to their ductility. In the experimental works, specimens were electrochemically corroded, before they were loaded to failure. In the finite element analysis, the corrosion of reinforcement was modelled as either internal pressure or radial expansion around corroded bars. The study indicates that the amount of corrosion to cause cracking at the bar and concrete surfaces almost linearly increased with the bar diameter and ratio of cover to diameter, respectively. No matter whether concrete cover c increased or bar distance S decreased, once the ratio of S / c became less than 2.5, corrosion cracks first propagated internally between the bars and caused delamination. Although corrosion did not alter the shape of force-extension curves substantially, it decreased bar strength and, especially, ductility greatly. Furthermore, although the reductions of strengths were identical, the ductility of bars corroded in concrete decreased more rapidly than that of bare corroded bars. Corrosion decreased beam strength and altered its ductility and failure mode. When the cracking of compressive concrete or the reduction of tensile bar area dominated beam response, corrosion increased beam ductility and caused a beam to fail in a less brittle and even ductile manner. When the deterioration of bond strength or the reduction of steel ductility controlled beam behaviour, however, corrosion decreased beam ductility and led the beam to fail in a less ductile and even brittle manner. There is a concern regarding the ductility of reinforcing bars and under-reinforced beams if the amount of corrosion exceeds 100/0, since bar ultimate strain decreased below the minimum requirements prescribed in the Model Code 90 for situations requiring high ductility.

In Europe, clay roof tiles are manufactured by pressing in 'open' moulds whereas in South East Asia 'closed' moulds are commonly used. The European products are more complex, having a greater degree of detail. Closed mould pressing could, however, be advantageous as it would minimise scrap recycling but the products would need to have equivalent or superior durability to existing tiles. The aim of this work was to investigate the feasibility of using a closed mould for the manufacture of European tiles by examining the relationship between the type of pressing and subsequent durability, in terms of resistance to repetitive freeze-thaw cycles. One specific clay type, the Marseille rose blend, was investigated over a range of forming water contents. Preliminary data relating to plasticity and friction were obtained through an empirical (Pfefferkorn) plasticity test, uniaxial compression of cylinders and friction ring experiments. Clay cylinders containing 16-21 wt % water were deformed at a compression rate of 240 mm/min. The yield stress was found to increase with decreasing moisture content. The plastic ranges of the stress-strain curves were well represented by a plastic deformation equation of uniaxial compression under sticking friction conditions. A laboratory-scale pressing rig was designed to make profiled specimens which would reproduce the essential features of a European tile. Comparison of the microstructures of the laboratory and factory samples showed that there was sufficient resemblance to validate the replication of the Marseille products in the laboratory tests. Bats of three moisture contents of 16.4, 18.4 and 20.6 wt % and different geometries were pressed in open, partially closed and closed rubber lined resin moulds in a mechanical testing machine using a cross-head speed of 240 mm/min. This was lower than a typical pressing operation but the speed of pressing had been found to not be a significant variable over the range commonly encountered. Clay was trapped in the features as the mould closed and flowed mainly within the flat part of the samples during pressing. For the open and partially closed moulds excess material was extruded through the gaps at the sides, a process referred to as flashing. The shape of the load-displacement curves was characteristic of the stages of the pressing process. The stress-strain curves for the pressing in open moulds showed good qualitative agreement with the results from uniaxial compression of cylinders. The open porosity of the samples after firing was strongly related to the forming moisture content of the clay with the open porosity increasing with increasing water content. Comparison of extruded bats and pressed bars showed that the influence of the pressing processes was not significant. Likewise, in freeze-thaw testing, the effect of the moisture content was again the overriding parameter, with acceptable durability always being obtained from the lowest open porosity samples. Given the marginal differences, the pressing processes investigated in this study were assumed to be equivalent in terms of the quality of the samples produced. Thus, closed mould pressing is feasible but does not lead to product improvement and hence may not be economically viable.

Recycled concrete aggregates (RCA) and lightweight aggregates (LWA) are popular alternative aggregates for concrete. However, due to their highly porous structure, concrete with RCA and LWA shows a different microstructure and higher permeability than conventional concrete. Thus, the existing relationships used to evaluate the permeability and, consequently, the durability of concrete are not applicable in concretes with RCA and LWA. This research examined the permeation properties of recycled aggregate concrete (RAC) and lightweight aggregate concrete (LWAC). The relationships between electrical resistivity-based measurements in RAC and LWAC and their permeation properties were determined and compared to that of normal weight aggregate concrete (NWAC). At the same electrical resistivity, RAC has higher chloride permeability than LWAC and NWAC. But at the same formation factor, LWAC has higher water permeability than RAC and NWAC. Permeability prediction models for RAC and LWAC were generated using multiple linear regression. Lastly, image analysis was used to determine the air void structure and material composition of the concretes. The air void structure and paste content were found to have significant effects on most permeability measurements.

The extraction of natural resources for building and construction materials is growing exponentially. Concrete and mortar materials require cement as the primary binder, but cement production negatively impacts the environment. Cement substitution has been studied by many researchers over the years, primarily focusing on industrial wastes as a partial replacement. However, the accumulation of common waste materials is a challenging problem due to the abundance of waste generated across all economic sectors. Due to recent exportation bans, countries are now searching for alternative methods to recycle their common household waste products. Cardboard materials have a limited recycling rate due to the contamination and weakening of the constituent fibres (kraft fibres). This leads to the disposal of cardboard contributing approximately 2.2 million tonnes of waste annually to landfills across Australia. To reduce cardboard waste accumulation, there is potential for kraft fibres (KFs) to be further incorporated into cement-based composite materials. Nonetheless, limited research outputs have been conducted on the successful integration of KFs. KFs are natural fibres which are susceptible to degradation in high alkaline environments, such as cement-based materials. When fibres degrade, the mechanical integrity of the material is compromised, and the service life of the application is often reduced. For the application to be widely accepted in the construction industry, further research is required. As the drive toward the circular economy framework becomes prominent, this research addresses the issue of cardboard waste accumulation and reducing cement consumption in concrete and mortar materials. This thesis presents a study that integrates matrix and fibre modification techniques on KFs derived from cardboard waste. Silica fume (SF) is used as a fibre pre-treatment, creating silica fume kraft fibres (SFKFs) and metakaolin (MK) as a matrix modifier. Integrating both SF and MK with KFs is a novel concept for minimising the degradation caused by calcium hydroxide in concrete on natural fibres. The target compressive strength was 25MPa, with KFs replacing 5-20% of cement in concrete. Compressive, tensile, and flexural testing was conducted to determine the mechanical capabilities of the novel mix designs. As expected, density and compressive strength declined with increasing fibre integration. However, matrix modification with 5% MK alongside 5% SFKFs increased the tensile strength by 10%. To ascertain the long-term effects of the novel composite, durability experiments were required. These included accelerated ageing simulations of wet and dry cycles, as well as water absorption, water immersion, carbonation, and chloride ion permeability experiments. The ageing simulation results produced a lower mechanical strength for all composite materials, including the control. The integration of 5% MK increased the surface absorption of the fibre composites, whereas 10% SFKF composites exhibited the lowest water absorption at 365 days. Raw KFs had a lower carbonation rate than matrix and modified fibres due to the morphology of the supplementary cementitious materials. The morphology and microstructure of the fibres were analysed using a scanning electron microscope (SEM) and energy dispersion x-ray spectroscopy (EDS). This application of SF revealed less degradation on the outer fibre walls, thus increasing service life of the fibre and the corresponding composite. A Fourier transform infrared spectroscopy (FT-IR) was employed to gain insights into the fibres chemical nature. The thermal, calorimetric and combustion attributes of the fibres were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and pyrolysis combustion flow calorimetry (PCFC). SFKFs showed a lower heat release capacity, demonstrating a lower combustion propensity compared to raw KFs. Furthermore, a 45% decreased peak heat release rate of SFKFs highlighted the overall reduction in the fire hazards associated with these materials. Moreover, SEM images illustrated advanced petrification on raw KFs compared to SFKFs within the composite. The increase of cement products on the fibre wall contributes to the associated mechanical strength reductions. In conjunction with the experimental data, life cycle assessments (LCA) and mix design optimisation were used to determine the environmental and economic effects when using waste cardboard KFs. The LCA determined the environmental effect of waste cardboard integration. A sensitivity analysis using a Monte-Carlo (MC) simulation investigated the transportation and energy manufacturing greenhouse gas (GHG) emission variables. Two KF composites were subsequently evaluated. SFKF5 mix design contained 5% KFs and SFKF105 contained 10% KFs with 5% MK. Both composites integrated SF as a fibre modification technique for durability purposes. LCA results of SFKF105 showed savings of 11%, 8%, 4% and 1% for terrestrial acidification potential, global warming potential (GWP), terrestrial ecotoxicity potential (TEP) and human toxicity potential, respectively. SFKF5 revealed savings of 3%, 2% and 4% for GWP, TEP and marine eutrophication potential, respectively. The additional travel requirements of KFs and MK to the cement batching plant for composite production did not surpass the embodied energy and travel emissions of the control. However, this was negated due to the additional energy requirements to manufacture KFs. Optimising the economic and environmental trade-offs via the use of a nondominated sorting genetic algorithm revealed three key regions. Region 1 was the most economical but also created the most carbon emissions. Region 2 was a compromise between both economical and environmental factors and region 3 demonstrated the lowest carbon emissions but also produced the highest costs. Utilising the acquired data from the associated regions produced additional mix designs for mechanical analysis. The findings of this study provide a detailed understanding of the effect of KFs on cementitious composites when integrated with SF and MK. As a result, material engineers may use the results described herein to incorporate cardboard waste materials into composite designs. The results provide opportunities to utilise the novel composites within low stress grade concrete such as non-structural civil applications, residential slabs, and driveways. In addition, researchers may use similar concepts to integrate other novel waste materials, contributing to the circular economy and enhancing the sustainability of the building and construction sector.

Military airbases face challenges such as high temperatures from jet exhaust, spills of aviation oil during refuelling and maintenance, and other factors. The combination of these factors leads to spalling, which is the deterioration of the concrete pavement. Spalling creates debris that poses a risk to jets and maintenance crews. This research aims to understand the causes of spalling in military pavements and develop suitable cementitious materials by adjusting the binder, aggregate, and incorporating different types of fibres. To simulate airfield conditions, the laboratory used an electric oven to generate heat similar to jet exhaust and spills of aviation fuel, engine oil, and hydraulic oil on the pavement. Various concrete specimens like cylinders, cubes, and beams were tested for their mechanical and thermal properties. The research focused on creating spalling-resistant cementitious composites by adjusting the Portland cement concrete mix ratios, geopolymer concrete, aggregates, silica fume, and steel/polyvinyl alcohol fibres. The degradation and decomposition of concrete mineral components were assessed using FTIR, XRD, and TG/DSC tests. The chemical composition of aviation oils was also analysed. The presence of fatty acid esters and phosphates in aviation oil react with concrete, forming harmful salts and reducing mechanical properties at high temperatures. Since aggregates make up a significant portion of concrete, lightweight aggregates, which perform better under high temperatures, were evaluated alongside normal-weight aggregates. Geopolymer concrete, incorporating 20% silica fume and hybrid fibres, was tested for its resistance to spalling due to its excellent fire resistance. The addition of hybrid fibres significantly enhanced the performance of the concrete. Overall, this cementitious matrix demonstrated the best performance under simulated airfield conditions. Therefore, the study recommends using geopolymer concrete with 20% silica fume, partially replacing basalt aggregate with lightweight brick chips, and incorporating 0.7% hybrid fibres for cementitious matrices in military airbases.

Solid oxide cells (SOCs) have emerged as a promising electrochemical energy conversion and storage device, especially for large-scale applications, due to their high efficiency, fuel flexibility, and reversibility between fuel cell and electrolysis modes. However, the high operational temperature poses durability challenges, and lowering the operating temperature significantly reduces the catalytic activity, particularly in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurring in air electrodes. La-based perovskites with an A-site dopant (La1-xA'xBO3) are commonly employed as the air electrode owing to their high electrochemical kinetics and decent chemical stability in oxidizing environment. In this dissertation, I demonstrate that an atomically thin oxide overcoat on perovskite-based air electrodes can simultaneously address two key degradation processes: agglomeration and dopant segregation, while enhancing the electrode surface kinetics for both ORR and OER. The overcoat provides mechanical stabilization and suppresses the agglomeration of the perovskite nanoparticles, while simultaneously limiting A-site dopant segregation toward the electrode surface.Firstly, I show that an atomic layer deposition (ALD) overcoat facilitates the ORR kinetics and improves cell durability. By employing an angstrom-level CeO2 and Y2O3 overcoat via ALD on a ceria nanodot-decorated LaNi0.6Fe0.4O3- (LNF) air electrode, we demonstrate that the angstrom-level metal oxide overcoat is highly effective in suppressing the nanodot agglomeration and enhancing the ORR kinetics. Secondly, I demonstrate that an ALD overcoat of a specific type of oxides suppresses A-site dopant segregation effectively. I apply a ~ 2 Å thick metal oxide ALD coating (ZrO2, Y2O3, CeO2 and TiO2) on a La0.8Sr0.2MnO3- (LSM) air electrode and quantify the Sr segregation behavior and ORR kinetics for 250 h at 750 ºC. Results reveal that a coating of metal oxide with multi-valent cations lead to a suppression of surface segregation or even de-segregation of Sr from the electrode surface. The oxygen vacancies formed on the perovskite surface by the ALD treatment are identified as the key to controlling Sr segregation. Lastly, I demonstrate that an ALD overcoat with metallic Ru catalyst (7.5-20 Å in nominal thickness) enhances both ORR and OER kinetics and preserves cell durability under electrolysis mode when applied on a conventional La0.6Sr0.4Co0.2Fe0.8O3- (LSCF) air electrode via plasma-enhanced ALD (PE-ALD). The Ru catalyst reacts with surface-segregated Sr species, forming a secondary perovskite phase that suppresses further Sr segregation and improves cell stability. These findings highlight the potential of surface engineering to effectively enhance the performance and durability of both solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs).

Continuously expanding urban environments compete with and negatively impact natural ecosystems. Building processes consume numerous resources including materials which need to be extracted, transported, shaped, and disposed of. To reduce this negative impact and instead potentially positively affect natural ecosystems, the built environment needs to perform ecosystem services originally in place and sustainable building practices should be employed for their entire life cycle. The principle of biological growth has architectural potential including adaptation, resilience, dynamics, differentiation, and continuous functionality. Biotechnology and biomimicry serve as integrated bioscience methods to transfer biology into architecture by integrating living organisms into the manufacturing process and applying abstracted biological principles into technological systems. This PhD explores the solidification of aggregate materials through both methods to show their potential and limitations: growth of fungal mycelium on agricultural byproducts to produce building materials and design of foundation systems inspired by tree roots. Mycelium-based materials are of increasing interest for their potential in generating biodegradable building materials with tunable properties from waste products through clean manufacturing processes. Before their implementation into permanent buildings, numerous aspects have yet to be researched. This PhD primarily focuses on: the optimization of large-scale manufacturing processes, effects of the manufacturing process and material compositions on mechanical properties and outdoor durability, and utilization of local species.Root-inspired foundation systems can enhance traditional foundations by reducing resources utilized and integrating new functions to serve the built environment and natural ecosystems. Conceptual designs present how root strategies are abstracted and transferred towards the future of building foundations. Biological research on tree roots is performed to gather emerging knowledge about morphological adaptation across species and environments. An innovative process is employed to generate 3D models of tree roots in the field and develop an algorithm which extracts morphological traits. Civil engineering tests are performed to evaluate the effect of various root traits on foundation.Overall, this research serves the fields of integrated bioscience by providing new methods and insights of biological knowledge while abstracting and applying it towards the future of architecture.

Different batches of repair lime rendering mortars were designed by mixing microencapsulated Phase Change Materials (PCMs) and other additives. The final aim of these renders is to improve the thermal efficiency of the envelope of the Built Heritage, while allowing the practitioners to apply a render with positive final performance. The combinations of the PCMs in different weight percentages, a superplasticiser (to increase the fluidity of the render keeping constant the mixing water), an adhesion improver and a pozzolanic additive were studied. The adhesion of these renders onto bricks and limestone specimens and the shrinkage and cracking of the mortars were studied in detail. X-ray diffraction technique was used to study the composition and evolution of the carbonation process. Compressive strength measurements were studied in hardened specimens. In addition, the porous structure of the rendering mortars was studied by mercury intrusion porosimetry to assess the effect of the PCMs' addition. Samples underwent accelerated climatic ageing to study their durability and the preservation of the thermal efficiency. Results have shown that these thermally enhanced mortars are feasible materia Is for real-life application in the context of architectural heritage restoration and conservation.

The asphalt concrete (AC) base course contributes largely to the structural capacity of a layered asphalt pavement system. Due to its location in the cross-section, a failure of the AC base would require costly repairs. Therefore, it is important to use AC base courses that are durable. However, durability of AC bases courses seems often overlooked in flexible pavement research.This dissertation demonstrates the potential of a very practical approach to evaluate the durability of asphalt concrete base courses. Additionally, it presents the most reliable of the latest fracture parameters to be used for cracking characterization of AC base courses. Furthermore, provides an approach to evaluate the segregation potential of AC base courses. This dissertation addresses the lack of research on AC base course evaluation and provides the state agencies and construction companies with guidelines of more practical, inexpensive and time-efficient approaches to assess the design and quality of AC base mixtures. To achieve this, a four phases research was developed: 1) more than 50 projects, with different mixture composition and age range, were selected from all over the State of Ohio in order to collect pavement cores for laboratory testing; 2) an evaluation of the AC base mixtures fundamental material properties such as in-place density, moisture-induced damage and disintegration susceptibility (estimated from tensile strength ratio (TSR) and Cantabro mass loss (ML) test), and flexibility index (FI) and cracking resistance (obtained from Illinois semi-circular bending test, IL-SCB) was conducted; 3) a more time-efficient and sensitive procedure to characterize coarser AC base mixtures based on their cracking tolerance (estimating CTindex, using TSR data) was evaluated; 4) an approach to assess the segregation potential of AC base courses was explored.Cantabro mass loss was found to have potential as an approach to characterize the durability of AC base courses. New guidelines for design of more durable AC base courses (i.e. potential threshold values for in-place air voids, asphalt content, and VMA) have been introduced. Findings regarding the reliability of cracking characterization methods have been presented. Finally, considerations to reduce the segregation potential of AC base courses have been identified and recommendations have been drawn.

Ultra-high-performance-concrete (UHPC) is a cementitious material with a high compressive strength, densely packed structure resulting in near zero permeability, small crack opening, and significant post-cracking tensile strength. UHPC has both mechanical properties and durability exceeding those of normal strength concrete. However, these properties come with a substantial material cost, with most of the cost associated with the fiber amounts. In this research, the effect of both fiber content (1, 2, 4 and 6% by volume) and type (0.5 in. straight microfibers and 1.2 in. hooked-end fibers) on UHPC properties has been studied in a non-proprietary UHPC mix developed at the University of Oklahoma (J3). Compression, flexure, direct tensile, and splitting tensile behaviors emphasizing strain responses of J3 concrete have been examined in this study to better understand the linear-elastic response, fiber bridging property and failure mode. Also, the study of flexure behavior of J3 concrete with hooked-end fibers subjected to freezing-thawing cycles in both pre-cracked and uncracked specimens was undertaken to better understand the effect of initial cracking on durability and actual damage of rapid freezing and thawing on the concrete matrix. Furthermore, UHPC was used to retrofit a half-scale AASHTO Type-II prestressed girder which was failed using a point load positioned to induce bond shear failure. The beams were then repaired by encapsulating the failure zone using J3 mix with 2% straight microfibers. Though this process did not restore the prestress, it successfully restored original shear capacity and created an impermeable layer to prevent water ingress into the existing cracks.

Ultra-High Performance Concrete (UHPC) is an advanced concrete material with superior mechanical strength, high tensile ductility, and exceptional durability, including negligible permeability. Despite these excellent material properties, the use of UHPC in structural applications is limited because of the high cost of commercially available UHPC products. Therefore, developing non-proprietary UHPC mixtures using local materials is a viable way to reduce the initial cost of UHPC.In this research, sustainable and cost-effective UHPC mixtures were developed using locally sourced materials so that UHPC may be more affordable to a wider variety of applications. Specifically, locally available Type I-II cement, local sand with a top size of 4.75 mm (0.187 inch), high range water reducing admixture, domestic steel fibers, and Class F fly ash were used in this research. These material selections improved the sustainability of UHPC. Two final mixtures (plain and fiber reinforced) were recommended as the UHPC mixtures. The greatest compressive strengths obtained in this research were 138.1 MPa (20,030 psi) for plain UHPC and 165.8 MPa (24,030 psi) for fiber reinforced mixture. The greatest flexural strengths were 12.95 MPa (1,230 psi) and 14.35 MPa (2,080 psi) for plain and fiber reinforced UHPC, respectively.After developing the UHPC mixtures, physical properties: drying shrinkage and permeable porosities of plain and fiber reinforced mixtures were investigated. The drying shrinkage of plain UHPC was greater than that of fiber reinforced UHPC by 27%. The lowest permeable porosities obtained were 2.4% and 2.6% for plain and fiber reinforced mixtures, respectively.In addition to mechanical and physical properties, the durability of UHPC mixtures was also studied. Rapid chloride permeability testing was performed on plain UHPC which showed very low chloride ion penetrability. Resistance of plain and fiber reinforced UHPC mixtures to freeze-thaw cycles was studied and observed no damage due to frost action with a durability factor of 100. Additionally, sulfate resistance of the final two mixtures was evaluated by submerging the specimens under 5% sodium sulfate for one year. The maximum expansions in plain and fiber reinforced specimens were 0.07% and 0.06%, respectively, which indicated excellent resistance to sulfate attack.

Pallet durability is a key characteristic with significant impact on a company's supply chain. Physical durability is defined as the number of trips that the pallet will accomplish before requiring repairs. Numerous studies have focused on understanding how durability is affected by different pallet components and warehouse environment characteristics. The VPI FasTrack is a testing sequence created to predict the performance of a pallet in a warehouse environment through different handling modes. However, this simulation has not been updated since its creation in 1993; therefore, a revision is needed to make it more closely reflect the behavior of a pallet in terms of durability. The objective of the current research was to investigate the ability of the FasTrack procedure to replicate the damages caused by material handling and storage systems in modern warehouses. This investigation was conducted through visual inspections of the damages seen on pallets used in the field, and pallets tested with FasTrack. The results of this study show the differences between the simulation-tested pallets and those from the field. The FasTrack simulation focuses heavily on top lead deckboard and stringer damage. The occurrence of damage modes such as splits and missing wood, were identified for these components. It was found that most of the damages from this simulation are created due to forklift handling. Because of substantial forklift handling damages, an experimental design was developed to investigate the effects of entry speed, payload, forklift type, and pallet design on the stresses exerted on a pallet, measured in terms of peak acceleration. The factors with the greatest effect on forklift peak acceleration and pallet peak acceleration were identified. The research shows that the acceleration in the pallet is approximately 4.4 times greater than the acceleration recorded in the forklift; however, the model of pallet acceleration based on forklift acceleration as a predictor shows poor performance. Different modifications to FasTrack are proposed according to the findings of this research. It is advised that they continue the FasTrack procedure past the point of repairable damage in a pallet, which is the usual practice when pallets are handled in the field. Further investigation of steps such as the flow rack and the stack storage are proposed, due to their low damage output during the simulation. The experimental design also showed that different damage severity levels from the FasTrack simulation are possible with variations in top load and entry speed. These changes could improve the ability of the VPI FasTrack to replicate the damages that pallets experience in the field.

The crystallization of ice in porous materials can lead to a significant decrease in durability. This is particularly important for reinforced concrete structures where ice formation can compromise the civil infrastructure. Much progress has been made in how to reduce the damage, but to develop new improvements, it is necessary to characterize the multi-scale dimensional structure of air-entrained concrete exposed to low temperatures. Synchrotron radiation laboratories supply their equipment with high flux high brightness light, offering phenomenal and varied exploration for fine-tuned and precise characterization techniques that are unafforded, in comparison, by standard stand-alone laboratory equipment with significantly limited source illumination. The use of synchrotron radiation has opened exciting new lines of research, and this dissertation uses cutting-edge techniques to image, for the first time, the in-situ ice formation inside a hydrated air-entrained cement paste using hard x-ray synchrotron microtomography (µCT). The results provide clear evidence of the importance of air-entrainment to mitigate freezing damage, and the ability to observe undisrupted internal paste ice formation opens the possibility to non-destructively observe and evaluate air entrainment variables in action. This novel technique opens new lines of research on the in-situ quantification of ice crystallization, a critical information for the micromechanical modeling, including cryo-suction of porous materials exposed to freezing conditions. Using a custom-made loading device mounted on the loading stage of the µCT, it was possible to record, for the first time, the in-situ formation and propagation of microcracks in entrained air void mortar pastes subjected to compression and tension. It is well-known that the presence of distributed small air voids in paste protects the matrix against ice expansion, but the enhanced durability comes at a cost of reduced mechanical strength. However, the mechanism of the reduction of strength has not been studied. The in-situ mechanical tests clearly show how the cracks form near or at the air void and develop a complex cracking pattern connecting the voids. The studies provide physical evidence for improvement of topology of the air void system in the cementitious matrix. Even though the use of surfactants has been used to successfully entrain air in concrete, the understanding of their mechanism is far from complete. This lack of understanding prevents the development of optimized surfactants. For this reason, this dissertation presents a sub-micron scale chemical speciation of the shell structure formed around entrained air voids in hardened entrained cement paste using scanning transmission x-ray microscope (STXM). Some detailed location specific information is revealed in this study, such as the state of carbonation, the identification and composition of the hydration products, and the level of hydration at and near the air void shell. It is found that the air void shell is made mostly of calcium silicate hydrate (C-S-H) with higher Ca/Si ratio in composition than the C-S-H that exists in the matrix, which contradicts previous studies performed using a scanning electron microscope energy dispersive spectroscopy (SEM-EDX). The study of ancient Roman concrete has been receiving attention because of its long durability. One of the open questions is how the Roman concrete survived frost action. For this reason, ancient concrete samples collected both from marine and land structures were collected and subjected up to 20 cycles of freeze-thaw. Their varied resistance to freeze damage was documented using µCT and while some patterns were identified, it was not possible to establish a universal law to predict the frost resistance of Roman concrete.

The development of alternative binders as a replacement for Portland cement can be one of the means to meet both the growing demand and sustainability of cement in the construction industry. Alkali-activated materials (AAMs) are increasingly attracting attention as a promising sustainable alternative to Portland cement-based materials. However, the manufacturing process of alkaline activators is energy-intensive that leads to an increase in the overall embodied energy and greenhouse gas emissions of AAM systems. Waste-derived activators have been promoted as an effective way not only to reduce the greenhouse gas emissions but also to reprocess wastes into valuable activators that can substitute the conventional alkali-silicate activators. To advance the understanding of the performance of AAMs and the synthesis of waste-derived activators, the present research focuses on three aspects: (a) fundamental differences in rheological properties between AAM and cement systems, (b) systematic synthesis and characterisation of rice husk ash (RHA) derived sodium silicates (SSs), and (c) the effect of RHA derived SSs on the rheology, structural build-up and durability of AAMs compared to commercially available SS. An alternative SS solution was synthesised by mixing RHA with NaOH solution. The influence of different parameters, including the processing duration (1 to 5 h of stirring) and temperature (60 to 100 °C), on the dissolution efficiency of silica from RHA was examined. The results showed that the extraction of silica from RHA was effective using the hydrothermal process (heating and stirring). The proper selection of the raw RHA and the extraction conditions allow for maximising the yield of silica, where most of the amorphous silica in RHA was dissolved within 1 h at 80 °C. The silicate species in the activator is a determinant component that affects the overall performance of AAMs. First, a test program was designed to understand the distinctive rheological and temporal viscoelastic behaviour of AAMs compared to cement pastes. After that, the effect of RHA-derived SSs on the structural build-up of AAM pastes was investigated. The results revealed that the high viscous activator increased the plastic viscosity of AAM pastes by 4 – 8 times higher than that of cement paste and drastically decreased the yield stress due to viscous effects and weak inter-particle interactions. Temporal changes in viscoelasticity showed that the negligible colloidal interactions between particles in AAM paste made the system non-percolated until the initial setting. This behaviour was very different from the well-percolated network that forms in cement paste a few minutes after mixing. In AAMs activated with RHA SSs, filtered and unfiltered solutions were used from the optimised process (1 h at 80 °C) to study the evolution of the viscoelasticity, ultrasonic pulse waves, infrared spectra, and flowability. The overall structural build-up of AAM paste activated using RHA SS was very comparable to the one activated using commercially available SS. This suggests the formation of identical reaction products and the minor effect of the nature of the silicate species in the activator. In terms of flowability, the residues in the unfiltered RHA SS increased the yield stress and reduced the flowability of the paste. Finally, the ability of AAMs made of RHA SSs to resist aggressive media was evaluated using various tests, including water absorption, sorptivity, acid attack, sulphate attack, rapid chloride-ions penetration, chloride migration and chloride diffusion. The durability performance was comparable between the AAMs activated by the filtered RHA and commercial SSs. On the other hand, the unfiltered RHA SS showed some adverse effects on some durability properties. For instance, the residues in the unfiltered RHA SS resulted in a slight increase in the expansion caused by sulphate attacks. However, these residues had insignificant impacts on the compressive strength when using identical SiO2/Na2O and Na2O/binder ratios in the mix design. It is believed that the results of this research will provide an advanced understanding of the early-age evolution of the AAM paste from the fresh condition to the initial setting. In addition, better insights were described on the effect of various processing parameters on the availability and structure of silicate species during the preparation of RHA SSs. Moreover, this research proved that the use of unfiltered RHA SS containing undissolved particles is still practically viable, but special attention should be paid to flowability and some durability properties.

Water accelerates various modes of degradation in silicon photovoltaic (PV) modules including encapsulant yellowing, delamination, and contact corrosion. Moisture primarily enters silicon PV modules through the polymeric module components (encapsulant and backsheet). To mitigate moisture-induced degradation, we must understand the dynamics of moisture in state-of-the-art encapsulants and module architectures. In this work, we present a robust optical method to quantify water content on the front and rear side encapsulants in bifacial silicon PV modules and use such measurements to validate a model for simulating water concentration in these modules. First, we quantify the solubility and diffusivity of water in four modern encapsulants: ethylene vinyl acetate (EVA) and polyolefin (POE) both with and without UV-blocking additives. Second, we measure water concentration within glass-glass and glass-backsheet using water reflectometry detection (WaRD), tracking the diffusion of moisture throughout the modules as a function of time and environmental condition. Crucially we separate the water content from the front encapsulant and rear encapsulant and backsheet within the glass-backsheet modules. Third, we present a model of moisture dynamics in bifacial silicon PV modules and show it to be consistent with our measurements. Finally, we apply this model to simulate the concentration profile of water typical fielded climates as a function of time, environmental conditions, cell size, and module architecture. Overall, our work presents: 1) a quantitative picture of water dynamics in industrially relevant module architectures and field conditions, and 2) a framework to extend this approach other encapsulants and module designs.

The supplies of concrete aggregates from natural sources are rapidly reducing. Recycled concrete aggregates (RCA) are produced by crushing the concrete obtained from demolished concrete structures. The purpose of this study is to determine the durability properties of concrete with 100% recycled concrete coarse aggregates and relate the durability of such concrete to the physical, mechanical, and durability properties of RCA and the RCA parent concrete. The correlations of several properties are determined by developing model equations to predict RCA properties. The parent concrete is crushed and graded at two nominal maximum sizes, 1" and 0.75", to determine the RCA production effects on new concrete. Six varieties of RCA were manufactured for the study. Concrete mixtures with RCA coarse aggregate have water-to-cement ratios of 0.38 and 0.48. Physical properties of aggregates tested in the lab include bulk density, specific gravity, absorption, and residual mortar. The concrete durability is obtained by measurement of resistance to degradation, resistivity test, density, absorption, and voids in the hardened concrete. A regression model for the surface resistivity of RCA showed that the surface resistivity increases when the absorption of RCA, w/c of concrete, and the volume of mortar decrease. The research results contribute to increasing RCA use through an improved understanding of its influence on concrete durability.

The suspension system in vehicles supports the vehicle's road stability and ride quality by scaling down the vibration responses resulting from road surface's roughness. This research focuses on fatigue life analysis of coil spring component. Static linear analysis is conducted on the 3D model of helical coil spring to investigate deformation and stress responses. Modal analysis evaluates the characteristics of vibration, i.e. natural resonance frequencies and corresponding mode shapes. The stress frequency response is generated after performing the harmonic analysis on the spring. Dynamics and performance of spring are analyzed over practical frequency range of 0 Hz to 200 Hz. Fatigue life estimation of vehicle suspension spring is performed using the stress data obtained from frequency response analysis. The stress-life (S-N) approach is utilized for fatigue life assessment of suspension spring. This durability analysis technique can be utilized in the automotive industry to improve reliability of vehicles. The outcome of this research can contribute in analysis and design of modern smart vehicles.

Experimental results demonstrate that droplet vaporization on metal surfaces can be significantly enhanced with the application of a nanoporous, superhydrophilic surface coating. A thin layer of ZnO nanopillars can be easily seeded and grown on most metallic surfaces to achieve nanoscale pores between pillars, and ultra-low apparent contact angles. Such surfaces have immense potential to improve spray cooling processes, however, little durability testing of the surface has been performed. In spray cooling applications, as water evaporates, any impurities in the water will be deposited onto the surface. This investigation serves to demonstrate how minerals in hard water deposit on the surface and interact with the ZnO nanopillars of the superhydrophilic surface. Micrographs of the surface demonstrate that minerals deposit nonuniformly, and quickly fill the porous nanostructure. Scale tended to build up on previously deposited scale, leaving largely uncoated areas where droplets chose to preferentially spread, resulting in a continued low contact angle. Maintaining these uncoated areas, and reducing the contaminants present in the water will extend the life and performance of the nanostructured surface. Experiments briefly explored potential chemical cleaning methods but none were found to preserve the nanostructure. It is also important to have a clear model of droplet vaporization on such surfaces and understand the vaporization dependence of surface parameters. Surface and impact parameters such as the surface contact angle, wicking speed and impact velocity all interact to affect the maximum spread of the droplet and the speed at which the droplet reaches its full spread. Along with variations in droplet volume and wall superheat, the model for droplet vaporization becomes more complex and nonlinear. Machine learning tools can be utilized to determine the dependence of droplet evaporation time on these parameters simultaneously. A genetic algorithm and a neural network were used to develop a droplet evaporation model for these superhydrophilic surfaces. Results from the genetic algorithm and neural network were also compared with results from a standard optimization function, the downhill-simplex algorithm. Comparison with the downhill-simplex algorithm is meant to demonstrate the necessity of the other two machine learning techniques in solving this problem. These machine learning techniques were also used to investigate boiling heat flux dependencies of a binary mixture on wall superheat, gravity, Marangoni effects, and pressure. Each algorithm demonstrated clear advantages depending on whether speed, accuracy, or an explicit mathematical model was prioritized. The downhill-simplex algorithm is highly optimized and is most useful when given a highly tailored initial guess. The artificial neural network provides the highest accuracy, but the black box approach prevents the extraction of a simple mathematical model. Finally the genetic algorithm provides sufficiently high accuracy while also being able to produce an explicit model.

Understanding of moisture behavior in cross laminated timber (CLT) is critical to the widespread use of CLT in construction in the United States. Currently, very little data exists on the long-term impact of moisture on CLT. The objective of this research is to collect data regarding the long-term moisture variation in the CLT panel at the University of Arkansas Adohi Hall residence hall. The climate of Northwest Arkansas is different from previously monitored buildings, as they were in the Pacific Northwest. Comparatively, Northwest Arkansas has a warmer climate with higher average annual precipitation. Waterproofing efforts are usually employed to prevent the intrusion of moisture into wood products, regardless of their application. These efforts are seen in roofing materials and insulation, among others. In the case of Adohi Hall, several layers of waterproofing membranes and insulation protect the CLT panel roof from exterior moisture intrusions. Moisture sensors were installed in 45 locations throughout the building to provide a comprehensive evaluation of the building. Locations were selected to represent different base conditions such as building envelope, communal bathrooms, interior locations, and trash rooms. Results indicate that on interior floors of the building, i.e., not the roof, CLT panels have not encountered moisture intrusions. At the roof level, moisture intrusions during construction were trapped in the CLT panels by waterproofing. This trapped moisture resulted in slow (approximately one year) drying to below acceptable levels of moisture.

High density polyethylene (HDPE) is increasingly being used in infrastructure applications with a design service lifetime of several decades. In many cases, the member is exposed to a corrosive environment, such as in pipes carrying potable water, where the dissolved bleach selectively attacks the loosely packed amorphous phase of the polymer. The failure mode of HDPE transitions from a ductile to a brittle mode as the corrosion level increases. This leads to subcritical crack propagation that deteriorates the load capacity and long-term behavior of HDPE structure exposed to a chlorinated environment. In this study, we develop a coupled chemo-mechanical model to simulate stress corrosion cracking (SCC) of HDPE members in a bleach solution. The mechanical response of the polymer is described by a constitutive model to considers the individual deformation and damage mechanisms of the amorphous and crystalline phases. The model accounts for the intermolecular deformation and homogeneous void growth in the crystalline and amorphous phases, along with entangled network resistance and craze damage in the amorphous phase. The embrittlement due to corrosion is captured by relating the amorphous phase parameters to the polymer molecular weight which decreases with corrosion level. The proposed model is calibrated using uniaxial tensile tests at different deformation rates, crystallinities, and corrosion levels. The model is used to simulate the double-edge notched (DEN) tension specimens at different corrosion levels. The constitutive model can capture the rate-dependent elasto-viscoplastic behavior of HDPE under the unexposed condition as well as the brittle failure behavior after exposure to a highly corrosive environment. The decrease in the molecular weight of HDPE due to exposure to bleach environment is captured by a reduced-order corrosion kinetics model. The selective diffusion and chemical reaction of bleach into the amorphous phase lead to polymer chain scission that reduces the molecular weight. The corrosion kinetics model describes this diffusion-chemical reaction of bleach and expresses the extent of chain scission as a function of the bleach concentration. The proposed material constitutive model and the diffusion-reaction model are combined in a single finite element (FE) code to investigate the SCC behavior of double edge notched HDPE specimens. The simulation yields the stress-life curves which qualitatively match the measured stress-life data of polymer pipes. The stress-life curve is shown to exhibit different regimes corresponding to distinct failure mechanisms, as indicated by the stress and strain distributions in the specimen. The simulations also provide the fracture kinetics under different environments, which can be used to predict the service life of an HDPE specimen with any geometry and applied load.

The proper maintenance and long-term durability of the building envelope are two of the most important factors in achieving adequate serviceability of a building. However, products and components are typically tested using fresh and unweathered specimens, leading to a lack of data concerning long-term durability of these components. This thesis investigates various waterproofing material components and assemblies including more elastomeric sealants, clear penetrating water repellent products, and a weather-resistive barrier in the presence of surfactants. These projects are being pursued in an attempt to fill the gap between fresh state material testing and the performance of materials under weathering exposure and a variety of conditions to assess the many factors that contribute to the building envelope’s durability. The data and analysis included in this thesis is a small subset of projects currently in progress at the University of Texas at Austin which also include ongoing investigations into 30+ different materials and components of the building envelope. In this study, more than two dozen elastomeric sealant products from three distinct chemistries were analyzed and their performances compared to assess the influence of product chemistry and starting position (compression vs. extension). It was observed that sealants experiencing early-life compression showed distress sooner than those experiencing early-life tension, but long-term performance is comparable for those products able to withstand initial cycles of compression/extension stresses. Additionally, third-party validation may help a specifier in choosing a product, but this alone may be insufficient in determining products best suited for long-term durable performance. Furthermore, round-robin testing is required to assess the current testing protocols and whether they are truly reflective of performance when installed in real building envelopes. 28 clear penetrating water repellent products from 7 different chemistries were tested for depth of penetration. Silanes tend to penetrate much deeper than siloxanes, silane-siloxane hybrids, and other silicone-based products, with marginal increases in penetration depths with greater active contents. Further long-term testing is required to assess DoP influence on overall durability in preventing water absorption into various substrates. Literature review regarding effects of surfactants in stucco wall assemblies is presented, and bench tests were developed which showed deleterious effects of surfactants on common polyethylene sheet weather-resistive barriers (WRBs). A full-scale testing wall is under construction to investigate mechanisms by which surfactants present in stucco mixtures may affect water-resistive properties of stucco and the underlying WRBs, and a future testing protocol is presented to assess active life of surfactants in hardened stucco to assess potential leaching of the surfactants in hardened stucco.

Thermally modified wood (TMW) contains no toxic components and is recommended for its durability, levels of equilibrium of moisture content, and dimensional stability performance. A limitation of TMW is the lack of market acceptance and products due to insufficient information regarding the performance of commercially available products. The goal of this project was to improve the market penetration and industrial processes of TMW. The first objective was to study the perception of TMW products from architects in North America using a survey instrument. Results revealed that information regarding TMW is not reaching the audience for TMW, and that providing knowledge regarding technical and marketing aspects of TMW is essential to increase the market share. The second objective consisted of the evaluation of the variability of the physical and mechanical properties of three thermally treated species manufactured in North America. Results showed that the performance of the commercially produced material was similar among the three companies, where only in seven out of 24 properties had statistical differences. Properties that were significantly different, did not have large enough differences in means to be realistically noticed by customers and all were highly different from untreated wood. The final objective involved the implementation of Lean thinking to the manufacturing process of TMW with the goal of improving the process with a direct impact on cost and waste reductions. Three companies were used as case studies for the production process. The implementation of Lean thinking in the process proposed a reduction in lead times from 55.47 days to 23.20 days, with an increase in value-added activities from 1% to 6%. Most of these gains were obtained through a reduction in inventory levels.

During operation, proton-exchange-membrane fuel cells (PEMFCs) are subjected to mechanical and chemical stressors that contribute to membrane degradation, performance loss, and eventual failure. Together, synergistic effects between mechanical and chemical degradation mechanisms lead to accelerated degradation. A physics-based model is developed to understand the synergistic effects of chemical and mechanical degradation and the coupled nature of performance and durability in PEMFCs. The model includes pinhole existence and growth in the membrane, which increases crossover of reactant gases as well as subsequent formation of chemical-degradation agents that impact both transport and mechanical properties of the membrane. The underlying performance model accounts for the multi-component gas diffusion, reaction kinetics, and transport across the membrane. The membrane mechanical model assumes that a circular pinhole is present in the membrane and calculates the swelling strains and the elastic or plastic stresses on the pinhole. Additionally, an empirical model for the chemical degradation of the membrane via hydrogen peroxide and subsequent hydrogen fluoride generation is used to modify the mechanical properties as a result of chemical degradation. The fuel-cell model is fully coupled with a mechanical model to determine the stresses on the membrane and subsequent growth of pinholes during transient operation. Simulation results show pinhole growth under humidity cycling conditions and an increase in gas-crossover fluxes and decrease in performance. Sensitivity studies show how the membrane mechanical properties impact both the performance and degradation behavior of the membrane.Multiphase effects are incorporated into the model to account for the effects of flooding on membrane degradation. Liquid condensation in the fuel cell can cause defects such as pinholes to close. Modeling results analyze the conditions under which water condensation will occur in pinholes, which is determined by calculating the critical radius. As the surface of Nafion can change from hydrophobic to hydrophilic, a sensitivity analysis on the critical angle is carried out. In addition, liquid water also reduces the amount of catalyst surface area available and therefore slows down the formation of hydrogen peroxide that drives chemical degradation. The decrease in chemical degradation at high RH values is demonstrated.Cerium ions are added to the membrane to extend its lifetime by scavenging radicals produced by crossover of reactant gases during PEMFC operation. The cerium ions also lead to a decrease in performance due to changes in the PEM transport properties and possible site blockage in the catalyst layers. The PEMFC performance and durability model is extended to include micro-kinetic framework that accounts for gas-crossover-induced degradation and concentrated-solution theory describes transport in the PEM. The transport model takes into account the coupled nature of the electrochemical driving forces that cause transport of cerium ions, protons, and water. The cell model predicts the migration of cerium out of the membrane and into the catalyst layers and its impact on performance. A comparison of dilute-solution-theory and concentrated-solution-theory approaches illustrates the interactions between water and cerium transport in the cell. Transient simulations show that low concentrations of cerium in the membrane (less than 1% of membrane sulfonic acid sites occupied by cerium) are required to optimize these design tradeoffs.Combining the mechanical and chemical degradation models, the mitigation effects of cerium on the coupled degradation methods can be shown. The model results show how the presence of a pinhole in the membrane shifts the distribution of cerium in the cell from the cathode into the anode and membrane. As the presence of cerium slows down the chemical degradation rate of the membrane, the rate of change of the mechanical properties of the membrane decreases. The model also shows how cerium modifies the mechanical and chemical degradation rates of the membrane under humidity- and voltage-cycling conditions.Finally, three approaches for modeling the electrochemical impedance response of a PEMFC are compared using two case studies: a porous electrode with linear kinetics and a fuel cell cathode with Tafel kinetics. These approaches may be applied to the development of a physics-based electrochemical impedance model for a full fuel cell model. The first approach uses a transient-model approach, which is much slower and more prone to errors. However, this approach requires no additional modification of the time domain equations describing the system. The second and third approaches transform the transient model into frequency space and linearizing around the steady-state conditions. This approach is quick and accurate, but is impractical for highly coupled, nonlinear systems of equations. This approach applied to the fuel cell cathode with Tafel kinetics allows for analysis of system properties that change over time as a result of membrane degradation.

The growing need for high-performance electrode materials in electrochemical conversion and storage applications requires further fundamental investigation on the working and degradation mechanisms of these materials. Among various functional materials, transition metal oxides are still one of the main choices due to their tunable chemical compositions and diverse crystal structures in most aqueous and organic electrolytes. The charge transfer process mainly occurs at the electrode-electrolyte interface, and controlling the electrochemical interfacial stability represents a key challenge in developing sustainable and cost-effective electrochromic materials. The present thesis focuses on classical tungsten trioxide (WO3) materials as the platform to uncover the previously unknown interrelationship between phase transformation, morphological evolution, nanoscale color heterogeneity, and performance degradation in these materials during 3,000 cyclic voltammetry cycles. Through the application of novel cell design, synchrotron/electron spectroscopic, and imaging analyses, we observe that the interface between the WO3 electrode and 0.5 M sulfuric acid electrolyte undergoes constant changes due to the tungsten oxide dissolution and redeposition. The redeposition of dissolved tungsten species provokes in situ crystal growth, which ultimately leads to phase transformation from the semicrystalline WO3 to a nanoflake-shaped, proton-trapped tungsten trioxide dihydrate (HxWO3·2H2O). The multidimensional (surface and bulk) quantification of the electronic structure with X-ray measurements reveals that the tungsten reduction caused by proton trapping is heterogeneous at the nanometric scale and is responsible for the nanoscale color heterogeneity. The Coulombic efficiency, optical modulation, apparent diffusion coefficients, and switching kinetics are gradually diminished during 3,000 cyclic voltammetry cycles, resulting from the structural and chemical changes of the WO3 electrode. We hypothesize that the high interfacial reactivity in the electrode-electrolyte interfacial region could be the universal underlying mechanism leading to undesired bulk structural changes of inorganic electrochromic materials.

The demand for concrete has been overwhelming nowadays due to globally booming economy and population, which induces environmental and social issues including the increase in anthropogenic CO2 emission from cement production and natural sand rarefaction by excessive exploitations. A new supplementary cementitious material (SCM) known as a combination of flash calcined clay and limestone has been promoted as promising alternatives to fulfil the development of sustainable concrete. Ferronickel slag sand is also a potential option to replace natural sand in concrete. However, performance in terms of durability is always a concern for the industry delaying the widespread adoption of new low-carbon concrete. This study aims to investigate the durability performance of concrete containing flash calcined clay, limestone as binder replacement (LC3 concrete) and ferronickel slag as natural fine aggregate replacement (FNS concrete). The influence of flash calcined clay, limestone and ferronickel slag on the deterioration of concrete structure including alkali-silica reaction (ASR), reinforcement corrosion in initial and propagation phases were evaluated. The variation of mechanical, physical and durability properties of LC3 concrete with various amounts of calcined clay and limestone and FNS concrete with fly ash as SCM was investigated. The performance of both LC3 and FNS concretes in the initial phase of reinforcement corrosion relating to carbonation and chloride diffusion resistance was investigated through accelerated and natural test protocols. The propagation stage of rebar corrosion of LC3 concrete was monitored and the electrochemical testing methods developed for Ordinary Portland Cement (OPC) concrete were validated for LC3 concrete. The mitigation effect on ASR expansion of flash calcined clay and limestone was systematically evaluated using the accelerated mortar bar test, scanning electron microscopy (SEM) analysis and model reactant experiments. The expansion due to ASR of FNS concrete which is the major concern to adopt manufactured sand into concrete industry was monitored and evaluated by using concrete prism test (CPT) and SEM. Results show that the use of flash calcined clay, limestone and ferronickel slag sand in concrete not only allows to produce low-carbon concretes but also to enhance the durability performance, except for carbonation penetration in LC3 concrete.

Abstract: The most common detrimental processes that lead to reduction in durability in reinforced concrete elements are shrinkage, sulphate attack and chloride attack. Shrinkage is a dimensional instability chiefly caused by a loss of moisture in the hydrating cement paste. Soluble sulphate ions take part in ettringite-induced expansive reactions in concrete, while chloride ions trigger the corrosion process in embedded steel reinforcement. Cellulose nanofibrils (CNFs) possess unique characteristics, including hydrophilicity, nano-dimensions, and excellent chemical tunability. These features confer upon CNF the ability to control internal moisture movement and also mitigate the ingress of harmful agents, including sulphate and chloride ions, into the cementitious system. A thorough review of the literature confirms that the proposed study is a novel scientific approach. This study explores the feasibility and demonstrates successfully the ability of CNF to address these three durability concerns. Three types of CNFs were used in the study, each one with a distinct amount of carboxylate grafted upon the fibre surface. The CNF was incorporated in cement-based paste and mortar mixtures at various volume fractions. The mixtures were cast to the same workability and water-to-cement ratio, and the mortars had a fixed cement-aggregate ratio. Results show that adding CNF moderately increased the shrinkage as measured at 2-days using image analysis. Similar growth in the drying shrinkage was observed in 90-day trials performed according to ASTM C596. However, CNF additions significantly alleviated bleeding and the shrinkage behavior was strongly influenced by CNF's ability to retain water in the early hours of hydration. Further evidence from the gas-sorption analyses reveals that this water accumulated in fresh mixtures due to CNF led to a larger volume of capillary pores and an increase mainly in the pore gel phase. As seen in the long-term trials, when this cumulative water was lost, there was a rise in shrinkage. This study reveals a retardation in hydration upon adding CNF. However, the samples containing CNF uniformly showed less cracking, which is likely due to fibres bridging the micro- and nano-cracks. The mortars mixtures when dosed with CNF uniformly exhibited noticeable reduction in the ingress of sulphates ions and again, for chlorides ions. Under sulphate exposure, the CNF visibly reduced the penetration of sulphate ions and effected a marked reduction in ettringite as well as the associated ettringite-induced expansion, measured as per ASTM C1012/C1012M. The decrease in the ettringite content (as measured by X-ray analysis) in the CNF-loaded Type GU Portland cement paste mixtures even after 90 days in sulphate solution was comparable to that seen with Type HS Portland cement. At the same time, the compressive strength of CNF-cement mortars was enhanced. Similar improvement was observed in the resistance of mortars loaded with CNF against chlorides ion ingress, as substantiated by the results of the rapid chloride penetrability test (as described in ASTM C1202) and the silver nitrate-based colorimetric method. The performance verified here can be credited to physical and chemical mechanisms trigged by CNF. Despite a slight increase in the capillary pores ranging from 100 nm – 10 μm as seen from the analysis of SEM images, the porosity in the range of 10 nm to 140 nm was moderately reduced as increasingly amounts of CNF were added to cement pastes. As a result, the pore network in this range experienced a rise in the tortuosity and a reduction in the connectivity, which ultimately hindered the ingress of sulphate ions and chloride ions. Concurrently, the negatively charged ionic groups of CNF chemically scavenged some of the calcium cations soluble in the aqueous phase (as evident from the thermogravimetric analysis), which are essential to the ettringite phase formation. This further explains why CNF loadings slowed down the ettringite content. However, the pH of CNF-cement pastes remained unaltered, notwithstanding the reduction in the calcium content in the pore solution. It is safe to say that CNF will not break the protective passive film of the embedded steel bars. The results show CNF as an all-round promising additive to hamper the ingress of deleterious agents in cement-based systems.

Ultra-high performance concrete (UHPC) is one of the new, cutting edge concepts in the world of concrete. Boasting significantly higher compressive and tensile strengths, longer service life, and significantly increased durability, UHPC has a considerable level of appeal over conventional concrete mix designs. This result is accomplished through three main changes to the conventional concrete mix design: an extremely low water-to-cementitious material ratio, elimination of coarse aggregate to allow for dense particle packing, and the addition of steel fibers to significantly increase tensile strength. Unfortunately, these additional advantages come at a significant cost. All commercial UHPC mixtures currently on the market are close to 20 times the price of a traditional concrete mix, pricing most people out of the UHPC market. The Oklahoma Department of Transportation (ODOT), however, is hopeful and looking for a way to be able to use UHPC for both full and partial bridge deck repairs. Currently, the University of Oklahoma has completed extensive research into developing their own nonproprietaryUHPC mix, titled “J3”, and found it to be sufficient for all strength and bonding requirements. Still, there is need for research on the durability of J3 before it can be utilized in the field. Quantifying the durability of J3 in comparison to conventional concrete (ODOT class AA), as well as commercially available UHPC (Ductal®), was the primary goal of this study. Testing was broken up into two parts: durability and corrosion. Durability testing included freeze-thaw resistance in accordance with ASTM C666, scaling resistance in accordance with ASTM C672, and chloride ion penetration in accordance with ASTM C1202. Corrosion testing included both small-scale specimen testing to focus solely on the response of each of the different concrete mixtures due to the “Halo Effect”, as well as large-scale specimen testing on previously corroded slabs (provided by ODOT) to analyze the overall impact of using different concrete mixtures to repair existing concrete structures with previously corroded steel rebar. Durability results for J3 included a Relative Dynamic Modulus (RDM) value of 103% after 350 freeze-thaw cycles, a visual rating of 0 after 50 scaling cycles, and an average chloride penetration rating of very low and negligible at 28 and 90 days, respectively. Corrosion testing resulted in minimal corrosion of steel reinforcing bars in both the small- and large-scale corrosion specimens. Additionally, significant surface corrosion occurred along the joint of the large-scale Ductal® specimen, which was not experienced by the J3 specimen, proving a superior response to the Halo Effect and overall corrosive attack. The results of this study show J3 to have exceptional durability properties and corrosion resistance, making it ready for trial use as a bridge deck or bridge girder repair material in the field.

The purposes of this study were to (a) design concrete pavement mixtures with recycled concrete aggregates using ternary blends of cementitious materials and a low water-to-binder ratio, (b) measure the fresh and hardened properties of the proposed concrete mixtures and (c) assess the long-term performance of the concrete implementing the use of recycled coarse aggregates. Preliminary investigation into ternary blend combinations via the compressive testing of mortar cubes and isothermal calorimetry was used to predict an optimal blend of cementitious material. Mixes using recycled concrete aggregates at varying replacement rates were tested for fresh and hardened properties using the proposed blend. It was found that a blend of portland cement, Class C fly ash, and ground granulated blast furnace slag produced the highest strength of ternary binder. Ternary blended cement mixtures showed improvement in hardened properties in late-age testing. At 50% replacement of virgin aggregates, specimens showed comparable mechanical performance to the control mix.

Recently, Carbon Nanotubes (CNTs) are drawing considerable attention of researchers for reinforcing cementitious materials due to their excellent mechanical properties and high aspect ratio (length-to-diameter ratio). However, CNTs might not disperse well within the cement matrix, resulting in little improvement or even degradation of concrete properties. The uncertainty in producing the consistent results in different studies might be attributed to multiple interactions between the experimental variables affecting the nanotube dispersion and the final properties of CNT-cement nanocomposites. Therefore, this research mainly focused on proposing equations that can reliably capture these interactions in order to correlate CNT dispersion with the mechanical properties. The main experimental variables studied included CNT concentration, aspect ratio, ultrasonication energy, ultrasonication amplitude, surfactant-to-CNTs ratio, water-to-cement ratio, sand-to-cement ratio, and hydration age of specimen. The study reported in this research was conducted in two parts: experimental program and modeling. In the experimental part of this research, a total of 63 different mix proportions were used to evaluate the flowability, mechanical properties, and durability characteristics of cement pastes and mortars containing CNTs. Using experimental test results reported in this study and the literature, three critical relations were proposed to consider the CNT dispersion, cement matrix composition, and hydration age of cement. The proposed critical relations were then added to available theoretical models in the literature. The flexural strength and elastic modulus of CNT-cement nanocomposites were predicted through a state-of-the-art probabilistic model using a Bayesian methodology. Finally, the developed probabilistic models were used to identify the optimum ranges of the experimental variables to maximize the mechanical properties. This was done through computing the conditional probability of not meeting the specified design requirement. The experimental results indicated that addition of CNTs could significantly improve different properties of cementitious materials, if the optimum range of each variable was used. Also, to achieve the desired mechanical properties, various combinations of the experimental variables might be used. The proposed prediction models were shown to capture the interactions between the experimental variables for predicting the mechanical properties within ±15% and ±18% of the experimental test results for flexural strength and elastic modulus, respectively. Based on the findings of this research, contour plots were developed to provide practical guidelines for future engineers to design CNT-cement nanocomposites.