Engineering

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Now showing 1 - 10 of 13
  • (2022) Zheng, Zhaozhi
    Thesis
    Urban stormwater runoff possesses the properties of intermittent occurrence, unexpectable volume and variable pollution which lead to different environmental issues, including flooding and waterlogging, pollution transportation, damage to downstream and contamination of the receiving waters. On the other hand, the low-level contamination (relative to sewerage) and large volume supply of stormwater makes it suitable as an alternative water resource to relieve the water shortage in the urban areas. Stormwater harvesting is under the concept of Water Sensitive Urban Design (WSUD) trying to treat stormwater properly for the different end-uses (like irrigation, toilet flushing and even for the uses close to human contact). Several treatment technologies (e.g., biofilters, constructed wetlands) have already been implemented to purify the stormwater with effective performance prior to reuse. However, the refractory organic micropollutants (especially herbicides) presented resistance to these nature-based solutions by showing variable treatment outcomes. In order to provide harvested stormwater for end-uses with high quality requirement (e.g., close to human contact recreational waters), a reliable treatment technology for organic micropollutants is desired as a post-treatment method in the stormwater harvesting system. This thesis aims to develop advanced oxidation processes (AOPs), in particular, photoelectrochemical oxidation (PECO), as the post-WSUD treatment approach for stormwater using its oxidation capacity towards the refractory organic micropollutants. Following the technology development procedure, three steps have been conducted: (1) testing the feasibility of AOPs for stormwater herbicides treatment; (2) investigating the intrinsic mechanism in the stormwater herbicides degradation process; and (3) assessing the operation conditions impact towards PECO stormwater treatment system. Boron-doped diamond (BDD) anode was used in the preliminary lab-scale tests for the feasibility study of AOPs towards stormwater organic micropollutants (two representative herbicides, diuron and atrazine - selected as the target pollutants in the study). The results showed that the effective herbicides degradation could be achieved by PECO process under 5 V operation (which was regarded as the optimal voltage in the system). The positive impact coming from voltage increase has been found in the study. BDD showed a remarkably durable property with stable removal performance under challenging voltage application (9 V) without observed deterioration. The catalysts loading showed negligible effect in removal performance. While the thermal effect was observed as a supporting factor for the process (higher temperature supported the oxidation process). Since BDD is not a perfect choice for scaled-up implementation due to its high manufacture cost, carbon fiber anode was chosen in the following studies and operated under low voltage (2 V) to avoid the possible anode deterioration under high voltage application. In the mechanism investigation, the superoxide radicals were found to be the major reactive species in PECO process. Meanwhile, hydroxyl radicals and free chlorine also demonstrated supporting impact for the oxidation process. With the identified intermediate products, degradation pathways of diuron and atrazine were proposed for the first time for three AOPs (PECO, electrochemical oxidation (ECO) and photocatalytic oxidation (PCO)) in stormwater herbicides degradation process. PECO was certified to be the preferrable stormwater treatment technology with the ability for further oxidation reactions towards herbicides degradation compared with ECO and PCO. In the third study, a flow reactor was designed and used to test the impacts of operational conditions (flow rate, light intensity, and initial pollutant concentration) for PECO process. An obvious improvement was observed for flow rate towards removal performance, while the light intensity was found to influence atrazine removal only. The initial pollutant concentration study demonstrated the robust performance of PECO flow reactor towards herbicides removal under challenging (240 μg L-1) pollutant concentration condition. The real stormwater experiments suggested the possible impacts coming from the stormwater chemistry towards PECO process. Further based on the energy consumption analysis, high flow rate (610 mL min-1) and normal light intensity (100 mW cm-2) were regarded as the optimal operational conditions for flow reactor system. Also, the effective PECO degradation performance of herbicides under the real stormwater environment has been verified by using the stormwater collected from field as supporting electrolyte in the experiments. Overall, this thesis confirms PECO as a promising stormwater herbicides treatment technology (potentially for all organic micropollutants) to provide further purification for stormwater high-quality targets. It also discusses the implications for the practical implementation and points out the future research directions for the system optimization.

  • (2022) Shahriari, Siroos
    Thesis
    Time series models are used to model, simulate, and forecast the behaviour of a phenomenon over time based on data recorded over consistent intervals. The digital era has resulted in data being captured and archived in unprecedented amounts, such that vast amounts of information are available for analysis. Feature-rich time-series datasets are one of the data sets that have become available due to the expanding trend of data collection technologies worldwide. With the application of time series analysis to support financial and managerial decision-making, the development and advancement of time series models in the transportation domain are unavoidable. As a result, this thesis redefines time series models for transportation planning use with the following three aims: (1) To combine parametric and bootstrapping techniques within time series models; (2) to develop a time series model capable of modelling both temporal and spatial dependencies in time-series data; and (3) to leverage the hierarchical Bayesian modelling paradigm to accommodate flexible representations of heterogeneity in data. The first main chapter introduces an ensemble of ARIMA models. It compares its performance against conventional ARIMA (a parametric method) and LSTM models (a non-parametric method) for short-term traffic volume prediction. The second main chapter introduces a copula time series model that describes correlations between variables through time and space. Temporal correlations are modelled by an ARMA-GARCH model which enables a modeller to describe heteroscedastic data. The copula model has a flexible correlation structure and is used to model spatial correlations with the ability to model nonlinear, tailed and asymmetric correlations. The third main chapter provides a Bayesian modelling framework to raise awareness about using hierarchical Bayesian approaches for transport time series data. In addition, this chapter presents a Bayesian copula model. The combination of the two models provides a fully Bayesian approach to modelling both temporal and spatial correlations. Compared with frequentist models, the proposed modelling structures can incorporate prior knowledge. In the fourth main chapter, the fully Bayesian model is used to investigate mobility patterns before, during and after the COVID-19 pandemic using social media data. A more focused analysis is conducted on the mobility patterns of Twitter users from different zones and land use types.

  • (2022) Nguyen, Minh Triet
    Thesis
    Singlet fission is a photo-physical process that generates two triplet excitons from one singlet exciton and can potentially enhance efficiency in photovoltaic systems. The combination of photovoltaics and singlet fission is a novel field for solar energy conversion when there is much interest in renewable, non-destructive, and continuously available energy sources. Singlet fission can also overcome thermalization losses in photovoltaics, which happens in traditional cells when the incident photon energy is higher than the silicon bandgap energy, using a carrier multiplication mechanism. This thesis will design, construct, and characterize photovoltaic devices incorporating singlet fission materials to study singlet fission in practical application. The research focuses on materials characterization, spin dynamics, and electron transfers between acene and the semiconductor layer in Au/TiO2 ballistic cells, and the incorporation of singlet fission layers on silicon-based cell structures. In detail, a set of investigations was developed and summarized by implementing singlet fission materials into a state-of-the-art ballistic photovoltaic device and silicon-based solar cell. The studies demonstrate proof of concept and rationally explain the process. The first part of the thesis investigates thin films of pentacene, TIPS-pentacene, and tetracene via crystallinity, morphology, absorption, and thickness characterization. Additionally, Au and TiO2 layers in Schottky device structures were optimized to achieve the best performance for energy transfer from an applied dye layer (merbromin). The drop-casted dye layer influences the device performance by increasing short-circuit current and open-circuit voltage, demonstrating the ability of charge transfer between the device and the applied film. This device structure provides a test bed for studying charge and energy transfer from singlet fission films. The latter part of the thesis describes several investigations to understand singlet fission in a thin film using this architecture. Magneto-photoconductivity measurements were primarily used to observe the spin dynamics via photoconductivity under an external magnetic field. Control experiments with bare Au/TiO2 devices showed no observable magneto-photoconductivity signal. In contrast, devices with pentacene and tetracene singlet fission layers showed a strong magnetoconductivity effect caused by ballistic electron transfer from the singlet fission layer into the TiO2 n-type semiconductor through an ultra-thin gold layer inserted between the layers. A qualitatively different behavior is seen between the pentacene and tetracene, which reveals that the energy alignment plays a crucial part in the charge transfer between the singlet fission layer and the device. The last section investigates the application of pentacene and tetracene evaporated thin-films as sensitizer layers to a silicon-based solar cell. The optimized Si cell structure with the annealing treatment improved the cell's performance by increasing short-circuit current and open-circuit voltage. The deposition of pentacene and tetracene as sensitizer layers into the device showed some results but posed several challenges that need to be addressed. As the current-voltage and external quantum efficiency measurements were taken, it was observed that material interfaces need to be designed to fully achieve the singlet fission of the acene layer into the Si devices.

  • (2022) Saavedra Moreno, Yesenia
    Thesis
    Frothers are widely used in flotation to primarily generate air bubbles, aid gas dispersion, and form a stable froth that provides a selective separation of particles. The current frother classification approaches are based on only three characteristics of the frothers. A number of studies have reported the use of characteristics of frothers including critical coalescence concentration and the ability to create an effective foam under dynamic conditions, as well as foam stability to group frothers. Moreover, the majority of studies are based on a two-phase system, ignoring to some extent the effect of particles, which is relevant to flotation. This thesis explores the effect of frother type on foam stability under dynamic and static conditions and provides a framework to classify frothers based on their foam generation ability. Three foam stability variables, dynamic foam stability index, static foam stability index, and decay rate index are quantified for eighteen different frothers. Four more frothers characteristics reported in the literature, MW, HLB, CCC, DL were defined. The hierarchical cluster analysis was conducted to group frothers based on similarity and provide a category system. Based on the similarities, frothers were grouped into four categories as opposed to the binary frother classification reported in the literature. The selectivity of frothers increases from Group 1 to Group 4, whereas frothers decrease their powerfulness from Group 1 to Group 4. To complement the proposed frother classification and assess the relevance to flotation, the effect of particles on the foam generation under dynamic conditions was explored for four frothers from different families. In terms of froth stability, the three-phase system showed a similar frother ranking to the two-phase system, except that TPG behaved as a more powerful frother in the presence of hydrophobic particles than MIBC. It was also found that the proposed frother classification system in a two-phase system translates well to the three-phase system as frothers were clustered in the same groups. Further insight into the changes of foam stability was gained by simulating the coalescence of two air bubbles at various frother concentrations using the volume of fluid method (VOF). It was observed that an increase in frother concentration damped the oscillation of coalesced bubbles by the surface elasticity, suggesting that the bubble surface area moves at a lower velocity, which may reduce the motion of particles attached to the interface and consequently, their detachment during the merging of two bubbles.

  • (2022) Idris, Nur Fadhilah
    Thesis
    Odours from the drying process at rubber processing plants have been identified as a major malodour contributor. The increasing number of complaints from these operations has resulted in the suspension and/or shutdown due to environmental impacts by local communities. Previous studies have indicated that packed-bed wet scrubber typically adopted as an odour abatement technology is ineffective at treating odours from these plants. Literature review reveals there is various chemical groups of volatile organic compounds emitted from the raw rubber processing. To date, no comprehensive analytical study was conducted on the effectiveness of wet scrubber in removing the VOCs. This research aims to understand the composition of VOCs emitted at full-scale drying processes in Malaysian rubber processing plants in terms of their chemical composition and sensorial profile. This led to the identification of key odorants responsible for the malodour issue. The wet scrubber performance to remove the VOCs was investigated as well as the operation optimisation to improve its performance. The adsorption by activated carbon was explored as a potential secondary treatment to improve the overall VOCs removal for emissions from rubber drying processes. Lastly, the sustainability of all options to upgrade the wet scrubber system was studied. The VOCs emissions samplings were performed at two typical commercial rubber processing plants in Malaysia. VOCs samplings were collected at both inlet and outlet of the wet scrubbers using a nalpohan bag attached to a vacuum drum and subsequently transferred to sorbent tubes at dry and wet seasons as well as at different operational times. The VOCs quantification was performed using a gas chromatography-mass spectrometry/olfactometry (GC-MS/O). Additionally, the presence of hydrogen sulfide (H2S) was determined using a H2S analyzer (Jerome 631-X) in one of the sampling periods. For the optimisation, the design and operating conditions of one of the plants were used in simulation and experimental studies. Meanwhile, the adsorption behaviour of selected VOCs was investigated on two types of virgin activated carbon (AC) namely coconut-based AC (CSAC) and palm kernel-based AC (PKSAC) manufactured in Malaysia. The ACs were characterised accordingly to determine their surface characteristics. The environmental impact of the proposed improved odour abatement technologies was compared by Life cycle Assessment (LCA). A total of 80 VOCs from various chemical functional groups was frequently detected by GC-MS/O with 11 new compounds not previously reported. 50 % of the chemical concentration of the emissions was dominated by the volatile fatty acids (VFAs) and 16 critical VOCs were identified including key odorants. H2S was detected in the emissions and potentially contributes to the odour impact. The composition of the emissions was observed to be influenced by the seasonal variation in terms of the number of VOCs detected for each season. Odour wheels were developed for the first time based on the sensory analysis of full-scale rubber emission before and after treatment by the wet scrubber as a management tool for on-site plant operators and regulatory authorities to assess the malodour impact on surrounding communities. The performance analysis of the existing wet scrubber technology revealed that it was ineffective at removing VOCs, indicated by the high chemical concentration and odour activity value (OAV) detected at the outlet emissions of the wet scrubber except for single-chain VFAs. The comparable odour categories and the number of sensory-related VOCs in both inlet and outlet emissions further revealed the wet scrubber’s poor sensory removal. The wet season observed a higher wet scrubber performance because of the greater VFAs concentration detected in the emissions. However, the wet scrubber is not suitable to remove the H2S due to its poor and inconsistent removal. The study demonstrated that the combination of sensory and quantitative analysis improved the accuracy to identify the odorants from rubber emissions and investigated wet scrubber poor performance. The simulation study revealed that the performance of the wet scrubber can be optimised (> 80 % chemical concentration removal) by modification of some of the operating conditions, namely the application of a higher liquid/gas ratio and greater interfacial area of packing to remove water-soluble VOCs and subsequently, reduce the odour impact (> 90 % OAV reduction). Laboratory-scale optimisation experiments demonstrated that the VOCs solubility is highly correlated with their absorption efficiency. Furthermore, the absorption of the VOCs is best at higher gas temperature (> 45 C) and low liquid temperature (< 10 C). The experimental results show the condition in the gas phase has a greater influence on the removal efficiency compared to the liquid condition. Optimal removal of the key odorants and other critical VOCs at this stage is necessary to minimise the odour impact and organic loading before subsequent treatment. The adsorption by activated carbon has the potential to be incorporated as a secondary treatment to remove the remaining low water-soluble VOCs that are inefficient to be removed by the wet scrubber. The boiling point of the VOCs was found to be the primary factor that influences AC adsorption behaviour whereas polarity and molecular structure were secondary factors. The emissions consist of multi-component VOCs, an adsorption competition has been observed where higher boiling point VOCs have a stronger affinity with the AC and displace the weaker adsorbed lower boiling point VOCs. The presence of high relative humidity (RH >70 %) was found to shorten the breakthrough times greatly and adversely affect the AC adsorption performance. The breakthrough of VOCs categorised as odorant is more critical because of the greater odour impact contribution than its chemical concentration. CSAC demonstrated greater adsorption capacity (average 38 %) than PKSAC (average 11 %) due to the different surface characteristics. However, both ACs showed comparable adsorption behaviour. Therefore, AC adsorption could be employed as a polishing (or secondary) stage after full-scale wet scrubber abatement to improve the overall odour mitigation from rubber drying processes. Life cycle assessment (LCA) was performed on the existing wet scrubber (WS), optimised wet scrubber (OWS) and a hybrid of the optimised wet scrubber with activated carbon (OWS+AC) at full-scale operation. It was found that the impact of malodorous emissions was the greatest for the direct emissions (> 99 %) of WS due to its lower efficiency in removing the malodour. 3-methylbutanal and 3-methylbutanoic acid have the greatest contribution from the direct emission of WS whereas H2S has a greater contribution from additional components used in OWS and OWS+AC. Electricity was found to be a major contributor to global warming and either ozone formation or human health potential impact categories with the increasing trend in WS, OWS and hybrid OWS+AC, accordingly. Meanwhile, the upgrading of the wet scrubber has also impacted the operational cost. In general, the environmental impact contributed by WS primarily came from direct emissions whereas the whole supply chain of OWS and hybrid OWS+AC has a greater environmental impact than their direct emissions. Nevertheless, the application of renewable energy is a good option to reduce the environmental impact.

  • (2020) O'Neill, Daniel
    Thesis
    This thesis examines the impacts of Electric Vehicles (EVs) and Vehicle-to-Grid (V2G) technology on residential microgrid environments. EVs are rapidly growing technology which play a major role in lowering Greenhouse-gas emissions in the transport sector. Additionally, EVs can also reduce emissions in the energy sector while also improving grid stability. This can be implemented by V2G technology supporting variable renewable generation (as additional storage) and by providing ancillary services. While some studies have presented specific instances of V2G implementation, long-term operation of the technology is still not well researched. Past research indicated financial barriers and availability as concerns which deter the implementation of V2G. Recent advancements in battery technology present new opportunities to make the technology viable. Using current and predicted EV technology trends, new EV load and V2G availability profiles were developed and used to evaluate the long-term operation and benefits of EVs and V2G in a residential microgrid environment. Simulation results indicate that the operation of V2G in a microgrid environment improves the economic operation of the system and reduces the levelized cost of energy by up to 5.7%. These results suggest the latest advancements in EV technology have improved the economic viability of V2G as well as its potential for further improving grid efficiency by providing energy services like peak demand shaving and additional storage capacity.

  • (2022) Fan, Hui
    Thesis
    The integration of variable distributed energy resources and vehicle electrification has come to focus over the last few years. While much work has been done to address the challenges that arise in modern distribution system planning and operation, continuous improvement to the models with the change is essential. The objective of this thesis is to improve the distribution network planning and operation models in the presence of distributed generation and electric vehicles. It aims to build stochastic models including the power generation and the charging demand, determine the location and sizing of the energy resources and charging stations in the coupled systems, and evaluate the impacts of the new low-carbon technologies on the network. Using a mixed-integer nonlinear programming framework through an optimal power flow analysis, this thesis presents three major methodological contributions including uncertainty modelling, coordinated mathematical formulation, and conflicting objective solutions. First, a multivariate stochastic process based on the notion of copula is applied to derive probabilistic charging patterns and to obtain the stochastic charging profiles. Second, a two-stage stochastic program based on statistical analysis and numerical simulation is introduced to generate synthetic time series of solar and wind power generation. The continuous distributions are discretized to generate the scenarios and the number of scenarios is reduced using Kantorovich metrics. Third, a two-dimensional Pareto front of dominant solutions is given for the competing objectives using a multiobjective Tchebycheff decomposition-based evolutionary algorithm. Case studies are conducted to evaluate the effectiveness of the proposed methods. An optimal charging scheduling problem is formulated to assess the stochastic charging models. The problem is formulated as a conic quadratic optimal power flow model and solved with a convex optimization algorithm. Network expansion planning problems are presented with carsharing and non-carsharing models, as well as the distributed energy generations. Overall, these problems aim to minimize the planning and operational cost of feeder routing, and substation alterations while maximizing the utilization of charging stations. It is found that an accurate estimation of the randomness intrinsic to the network is critical to ensure the secure and economic operation and planning of the distribution system intertwined with the transport network.

  • (2022) Liu, Tongming
    Thesis
    The level of electricity consumption usually can reflect the level of development of a society. With the development of social industrial technology, the demand for electricity and other energy sources is increasing. Meanwhile, the control measures for carbon emissions have become an important social issue that needs to be solved urgently cause a series of problems such as environmental pollution has become more and more serious with the large-scale use of traditional fossil energy. Renewable energy provides new ideas for solving this issue. Recently, some renewable energy sources, including solar and wind energy, have been widely used. However, as renewable energy has some shortages such as instability, inflexibility, it can not replace traditional fossil energy completely. Due to consumers usually having different energy demands, the concept of an integrated energy system including traditional fossil energy and renewable energy has been proposed. The efficiency of energy usage can be improved, and energy losses can be reduced through coordinated planning and optimal operation method. Thus, integrated energy systems become an effective method to solve the current social issues. With the increasing penetration of renewable energy injection in the electric power grid, the impact of uncertainty and fluctuation in renewable energy generation on the grid performance cannot be ignored. Integrated energy networks with the Power-to-Gas (PtG) system have been used to maintain the stability of the system by employing the efficient conversion of different energy forms (electricity and gas) and massive energy storage. Meanwhile, the wave energy converter system can make full use of wave energy to improve the use of renewable energy in the integrated energy system. An economic receding horizon control strategy that solves the constrained optimization problem of the wave energy converter system is analyzed in this research. The Model Predictive Control (MPC) method is adopted to focus on tracking system cost function, and the system state is steered to the steady-state at the end of the optimization horizon by using terminal equality constraint, and the non-convex optimization problem is solved by the controller in real-time. As a form of a hybrid multi-energy system, the integrated energy system usually contains different forms of energy such as electric power, thermal, and gas while meeting the load of various energy forms. Therefore, the model building and optimal operation of the integrated energy system are the key points of the research. The appropriate models established for the integrated energy system can not only reduce the calculation and power dispatch times but can help the entire system reach the optimal state faster. The main work of this thesis is as follows: In chapter 2, various energy conversion systems, including power-to-gas systems and combined heat and power (CHP) systems have been analyzed. A method for optimal operation of a microgrid that contains the PtG system with rolling horizon strategy is proposed, and it applied the power and gas cooperative accommodation to solve the deviation between the forecast load and real load as well as reduce the overall microgrid operation cost in a corrective manner. Models of various components in a microgrid are introduced, and a mixed-integer linear program (MILP) mathematical optimization problem is formulated to describe the day-ahead operation problem. The rolling horizon strategy is adopted to reduce the impact of intermittence natural of the renewable energy sources, and the benefits of cooperative accommodation of electric power and gas in a corrective manner are discussed as well. In chapters 3 and 4, the different energy models in the integrated energy system have been analyzed. The dist-flow method is applied to quickly calculate the power flow, and the gas system model is built by the analogy of the power system model. Meanwhile, the piecewise linearization method is applied to solve the quadratic Weymouth gas flow equation, and the Alternating Direction Method of Multipliers(ADMM) method is applied to narrow the optimal results of each subsystem at the coupling point. Simulation-based calculations and comparison of results under different scenarios are proved that the power-thermal-gas integrated energy system enhances the flexibility and stability of the system as well as reduces system operating costs to some extent. In chapter 5, an economic receding horizon control strategy that solves the constrained optimization problem of the wave energy converter system is proposed. Generally, the standard Model Predictive Control focuses on tracking system cost function. However, in economic MPC, a general economic cost function is established, which contains the objective of maximizing the energy extracted from ocean waves and minimizing the operation cost, as well as directly reflecting the economic indicators of the Wave Energy Converter (WEC). Meanwhile, the system state is steered to the steady-state at the end of the optimization horizon by using terminal equality constraint, and the non-convex optimization problem is solved by the controller in real-time. The auxiliary optimization problem is applied to the stability analysis, while the convergence of the system can be proved by the Lyapunov technique. And several numerical simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

  • (2022) Fu, Jiayi
    Thesis
    The increasing focus on sustainability has driven manufacturers to develop greener cementitious products in order to reduce the associated carbon dioxide emissions. Supplementary cementitious materials (SCM) such as ground-granulated blast furnace slag (GGBFS) are commonly used in the development of low carbon, blended cement formulations. The reduced strength development due to the addition of slag can be improved by the addition of chemical activators such as sodium sulfate (Na2SO4). The reactivity and early strength of cement:slag binders is significantly enhanced by the addition of Na2SO4 though the mechanisms underlying the relationship between the enhanced hydration reactions and the strength behaviour remain unclear. This thesis explores the impact of Na2SO4 on the early age chemical reaction mechanism in blended systems containing a high percentage of blast furnace slag. Early hydration reactions and resultant compressive strength in a 50:50 slag:cement binder in the presence of Na2SO4 were investigated. Early strength increases in the presence of Na2SO4 were shown to be due to a combination of increased alite hydration and increased slag dissolution. Increased alite hydration was due to neither reduced dissolved Al concentration nor increased alite under-saturation, but related to increased ionic strength due to the presence of Na2SO4. Increased slag dissolution was associated with both increased pH and decreased Ca activity with the two being connected through the portlandite solubility limit. Na2SO4 was shown to substantially enhance slag dissolution at fixed pH 13 with this action attributed to greater under-saturation of slag as a result of ettringite formation. Na2SO4 was shown to be superior to alternate activators in a slag:cement binder. Microstructural development in the presence of Na2SO4 was investigated utilizing mercury intrusion porosimetry (MIP), NMR relaxometry, and XRD. Increased rates of early strength development and decreased rates of late strength development due to the presence of added Na2SO4 were linked to effects on capillary porosity refinement. While the degree of hydration at later age was shown to have been lower in the presence of Na2SO4, and may have been responsible for the higher capillary porosity, a clear alteration in the pathway of microstructural development had occurred with inhibition to hydration of the slag component due to earlier microstructural development. Subsequently, different cement types with varying clinker chemistry were used to investigate which clinker phase was primarily responsible for the acceleration reaction with Na2SO4. Early hydration reactions were examined and monitored utilizing mercury intrusion porosimetry (MIP), calorimetry, and XRD while the resultant compressive strength in a 50:50 slag:cement binder in the presence of Na2SO4 was investigated for up to90days. Forallcementsexamined,astronginversecorrelationbetweenearlystrength development and late age strength was apparent with results suggesting that the retardation of the early hydration reactions due to the presence of sodium sulfate resulted in a higher late age strength development. Previous studies indicate that Na2SO4 activation improves the early strength of blended cements due to enhanced ettringite formation. In this study, we examine whether triethanolamine (TEA) provides further early strength increase through additional ettringite formation by investigating the effect of TEA at 0 to 0.5% w/w of cement in a 2.5% w/w sodium sulfate activated 47.5:50 GGBFS:Portland cement blend. Results of XRD analyses indicate that TEA encouraged ettringite formation through enhanced calcium aluminoferrite (ferrite) and gypsum consumption, and, to a lesser extent, enhanced tricalcium aluminosilicate (C3A) consumption. Increased porewater Fe(III) concentrations provided further evidence of TEA-facilitated ferrite dissolution. Compressive strength results correlated with the degree of calcium silicate hydration and ettringite transformation, being highest in the 0.2% TEA blend but lowest in the 0.5% TEA blend. Finally, the effect of higher gypsum content in blended cement:slag can led to C3A dissolution retardation. Associated early age strength development was examined using calorimetry, pore solution chemistry, XRD, and MIP. Gypsum was found in these cements to exert no effect on alite hydration as it is consumed during C3A hydration and ettringite formation. Compressive strength measurements in the “gypsum studies” reinforced the inverse relationship between early and late strength development and the critical role of alite during early hydration towards late age strength development. This work hopes to contribute a more comprehensive understanding of the effect of Na2SO4 on the early hydration stages of GGBFS incorporated Portland cement blend systems from a geochemical approach in effort to achieve greater sustainability through higher cement replacement.

  • (2022) Tao, Congyuan
    Thesis
    The mesoscale failure behaviour of textile Carbon Fibre Reinforced Polymer (CFRP) is investigated using in-situ CT scan. The research focused on the potential of using CT acquired geometries, deformation, and failure information to validate traditional modelling techniques and improve the accuracy of future modelling. Carbon Fibre Reinforced Polymer (CFRP) has been widely used in aerospace, automobile, and sporting industry due to its high strength to weight ratio, high stiffness and resistance to fatigue or corrosion. Textile CFRP is a fabric weaved from fibre bundles. Compared to traditional unidirectional CFRP, textile CFRP is usually easier to handle and to form into complex shapes during manufacturing. Due to the yarn interlacing, textile CFRP is also more stable and damage tolerant. However, the interlacing fibre bundles (yarn) introduced additional layer of complexity when predicting the strength and failure of textile composite parts. The main approaches used in current modelling techniques, assume the textile fabric has a regular and repeating structure, failed to capture the irregularity in mesoscale structure introduced during the manufacturing process. As experimental observation shown, the irregularity in mesoscale structure initiates micro crack and failure and has a considerable influence on the properties and failure behaviour of textile CFRPs. The ability of capturing a textile CFRP meso-structure and reconstructing it for FE modelling improves the accuracy of numerical analyses and result in a more reliable and efficient CFRP structure. This research demonstrated the potential of using computer tomography (CT) to improve the understanding of CFRP mesoscale failure behaviour both numerically and experimentally. A more realistic numerical model was constructed using the geometry extracted from the CT image. The CT image volume was classified based on the tow direction and the material property was adjusted based on the fibre orientation. Irregularities in the specimen could be fully reflected in the finite element model. This improves the ability of predicating the onset and progression of failure of textile CFRP. In-situ CT scan was used to investigate the failure mode and crack propagation in several textile CFRP tensile specimens. An in-situ tensile testing rig was designed and manufactured to allow a reliable CT scan of textile CFRP specimens while under tension. One major challenge identified in mesoscale CFRP study is to have a specimen large enough to encompass complete meso-structures while have sufficient resolution. Tensile specimens with a gauge width of 10mm was found to be large enough while providing a good CT image result when scanned using the lowest voltage of 60 kV with 6 accumulations. This resulted in a CT image resolution of 3.2μm. The CT results showed cracks that were usually not visible under conventional scanning technique. Digital volume correlation (DVC) was used to calculate the 3D displacement field by comparing the pre and peri load CT images, providing a quantitative understanding on the failure process. Strain fields were calculated using the forward difference of the displacement field and were used to validate the result of numerical models. The original contribution of this project is the use of CT scan to improve the procedure of obtaining the numerical and experimental results, thus improve the understanding of textile CFRP failure behaviour. A novel in-situ testing rig and the corresponding specimens were manufactured to allow the observation of textile CFRP failure under load. The novel algorithm developed during the project provided a more detailed and accurate geometry of the specimen and allowed for a more accurate model. These contributes to the significant improvement in the understanding of textile composite failure behaviour, both experimentally and numerically.