Saudi Cultural Missions Theses & Dissertations
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Item Restricted Structural behaviour of reinforced and prestressed high performance concrete (HPC) structural elements(The University of Adelaide, 2024) Alameri, Mohammad Dhaifallah; Mohamed Ali, Mohamed Sadakkathulla; Sheikh, AbdulConcrete technology has been advanced in various ways to improve current mix designs based on cementitious materials, or by implementing the geopolymer approach, where waste materials are used as the main binder. The development of existing mix designs has led to the creation of ultra-high-performance concrete (UHPC), which exhibits superior mechanical and durability characteristics. However, UHPC is more susceptible to forming cracks due to autogenous shrinkage. Thus, it is necessary to control the formation of cracks to extend the life cycle of the concrete structural members. Moreover, the technology of geopolymer concrete (GPC) is still under development, and there are many variables in this process that increase the uncertainty of producing GPC. Therefore, this thesis consists of several manuscripts (some of them already published and some under consideration by journals) regarding the improvement of the self-healing performance of UHPC, the optimisation of GPC mix design and the structural applications of UHPC and GPC. The first chapter investigates the mechanical, durability and self-healing performance of UHPC with a superabsorbent polymer (SAP) under various curing conditions. The SAP-to-binder ratios used in this study were 0.3% and 0.4%. Two approaches were adopted to examine self-healing performance under repetitive loads and sustained tensile loading for up to 28 days. The results show that incorporating an SAP into UHPC enhances the concrete’s elastic modulus, flexural strength and tensile strength. Also, the mixes exhibited compressive strength above 120 MPa after 90 days. Furthermore, the load recovery of the prisms under repetitive flexural loads and the prisms under sustained tensile loading demonstrated that the self-healing efficiency of the SAP incorporated into the UHPC mixes was higher than that of the control mixes. The second chapter presents a study in which GPC was optimised using the Taguchi method, and it details the mix design to produce ultra-high-performance geopolymer concrete (UHPGC). Utilising an L9 orthogonal array, the investigation was structured into two phases, each examining a distinct set of variables across three levels to ascertain their impact on compressive strength. The first phase analysed the water-to-binder (W/B) ratio, silica-fume-to-binder ratio, potassium-silicate-to-potassium-hydroxide ratio and aggregate-to-binder ratio. The second phase explored the effects of the W/B ratio, fibre content, silicon-carbide-to-binder (SiC/B) ratio and superplasticiser-to-binder (SP/B) ratio. The Taguchi method facilitated a meticulous evaluation of 18 unique mix designs and the identification of an optimal mix that significantly elevated the 28-day compressive strength to 126 MPa. This optimal mix was characterised by a W/B ratio of 0.28, a fibre volume of 3%, a SiC/B ratio of 0 and an SP/B ratio of 2%. Furthermore, the study found a robust correlation between the empirical findings of the second phase and the predictions of the developed mathematical model, which substantiates the effectiveness of the Taguchi orthogonal array in enhancing the compressive strength of UHPGC. The third chapter investigates the mechanical and durability characteristics of fibre-reinforced geopolymer composites (FRGCs). The Taguchi method was employed by using the L9 orthogonal array with four parameters across the three levels of each parameter; the parameters were the percentage of fibre and the W/B, SiC/B and SP/B ratios. The W/B ratio had the most significant impact on the composites’ mechanical and durability characteristics. Analysis of variance (ANOVA) with residual fitting was conducted to derive mathematical models for accurately predicting the compressive strength that exhibited a good correlation with the test results. The fourth chapter studies UHPC-filled double-skin aluminium tube (UHPC-FDAT) columns under combined loading conditions. Four columns under concentric and eccentric loading conditions and a beam were tested. The findings show that increasing the loading eccentricity reduced the ultimate load with an increase in the corresponding mid-height lateral displacement. The specimens tested experimentally were also modelled numerically using the Abaqus software. The numerical results show a very high agreement with the results obtained experimentally. Therefore, a parametric study was conducted by changing one variable among compressive strength, inner tube thickness, outer tube thickness and hollow ratio under the same loading conditions. The outcome of this parametric study shows the dominant influence of the compressive strength of UHPC under axial loading where an increase in the outer tube thickness achieved a higher load while enhancing the loading eccentricity. The fifth chapter examines FRGC-filled double-skin square steel tube (FRGC-FDST) columns. Four columns under concentric and eccentric loading conditions and a beam were tested. An interaction diagram was plotted experimentally and analytically to assess the capabilities of existing models to predict the results for this kind of column. The findings show good agreement between the experimental and theoretical analyses. Furthermore, finite elements modelling (FEM) was conducted with Abaqus to simulate the constructed columns in the experimental program. The numerical and experimental behaviours of the columns also agreed.10 0Item Restricted A STUDY OF THE EFFECT OF PREPARATION PARAMETERS ON THE MECHANICAL PROPERTIES OF FREEZE-DRIED GELATIN-ELASTIN-HYALURONATE SCAFFOLDS(Marquette University, 2024-05) Qamash, Mansour; Tayebi, LobatThis thesis is dedicated to a detailed study of changes in the properties of Gelatin-Elastin Hyaluronate (GEH) tissue engineering scaffold resulting from changes in preparation parameters. More specifically, utilizing a combination of foaming and freeze-drying techniques, this research investigates the effects of different parameters, including agitation speed, duration time, and chilling temperature on the scaffold’s structural integrity, porosity, and mechanical properties. The methodology involves a carefully calibrated process in which the scaffold matrix is initially prepared by incorporating 8% gelatin, 2% elastin, and 0.5% hyaluronate (w/v) into a homogenous aqueous solution, followed by controlled agitation and subsequent freezing at designated temperatures. The freeze-drying stage solidifies the foam structure, creating a porous matrix essential for cell growth and nutrient delivery. The findings reveal that porosity and mechanical properties, such as compressive Young’s modulus, of scaffolds are significantly influenced by fabrication parameters, with higher agitation speeds and longer duration times leading to increased porosity and decreased modulus. Moreover, the degradation rates of the scaffolds processed at both −20 and −80°C were found to be comparable, indicating a similar level of preservation in physiological conditions. Morphological analyses, including laser microscopy and scanning electron microscopy (SEM), indicated optimal pore sizes (100–300 µm) that promote effective cell interaction and tissue regeneration, confirming the successful application of the freeze-drying and foaming methods in creating highly interconnected porous structures. Based on the findings, a decrease in chilling temperature correlates with a slight increase in pore size within the scaffold matrix. The methodical fabrication process developed in this study emphasizes the control of agitation speed and duration to modulate scaffold porosity, which is an essential characteristic for cellular infiltration and vascularization in tissue engineering. The research outcomes demonstrate that scaffold properties can be finely adjusted through the preparation process, offering the potential to match the structural needs of specific tissue engineering applications. The thesis contributes significant advancements in scaffold design, providing a robust framework for the development of tissue scaffolds with controlled porosity and improved mechanical properties. By understanding and harnessing the effects of fabrication parameters, this research offers a pathway to design scaffolds that more accurately replicate the extracellular matrix, promoting enhanced tissue repair and regeneration.18 0Item Restricted Clinical Potential of Three Dimensional (3D) Printed Materials in Restorative Dentistry(Sydney University, 2024-03-13) Alshamrani, Abdullah; Ellakwa, AymanOver the past two decades, rapid prototyping technology, specifically threedimensional (3D) printing, has gained significant popularity in the dental field. It has revolutionized dental restoration processes, leading to improved quality, patient comfort, and overall satisfaction. This thesis explores the integration and benefits of 3D printing technology in various dental applications. The initial chapters provide an overview of the importance of 3D printing technology in dentistry and highlight its advantages over traditional techniques. The focus is on the enhanced production processes, adaptability, and faster fabrication methods offered by 3D printing. Furthermore, the future prospects and limitations of this technology are discussed, with emphasis on the mechanical properties and biocompatibility of 3D-printed dental materials. A key area of investigation pertains to the mechanical properties of 3D-printed dental resin materials. Different printing layer thicknesses and post-printing methods are explored to determine their effects on flexural strength, microhardness, and degree of conversion. Findings reveal that a printing layer thickness of 100 μm yields the highest flexural strength compared to thinner layers. Moreover, post-printing treatments significantly impact the flexural strength and hardness of the 3D-printed resin material. To further enhance the mechanical and biocompatibility properties of dental resin, different nanoparticle additives are incorporated into the resin. Specifically, the addition of zirconia and glass silica nanoparticles is investigated. Results demonstrate that the inclusion of these microfillers significantly improves the flexural strength and biocompatibility of the dental resin material. This finding suggests the clinical application potential of reinforced 3D-printed resin in restorative dentistry. Continuing the exploration of microfillers reinforcement, another chapter focuses on the incorporation of zirconia glass (ZG) ) with an average particle size of approximately 0.4 μm and glass silica (GS) microfillers with an average particle size of approximately 1.5 μm in 3D-printed crown resin materials. Mechanical performance comparable to unmodified resin is achieved, but increased surface roughness needs further optimization to ensure aesthetic considerations are met. In addition to examining resin materials, a separate chapter explores a novel 3D printing technology called lithography-based ceramic manufacturing (LCM), specifically for printing ceramic materials. The mechanical properties of ceramic materials printed using LCM are evaluated, providing insights into their potential applications. Finally, the thesis concludes by summarizing the major findings and conclusions derived from the previous chapters. Future directions and challenges in the field of 3D-printed dental materials are also discussed, emphasizing the need for further research to optimize nanoparticle concentrations, evaluate long-term clinical outcomes, and enhance the overall effectiveness and suitability of these materials in restorative dentistry. In summary, this thesis contributes to the advancement of 3D-printed dental materials, offering valuable insights into their mechanical properties, biocompatibility, and potential applications. The integration of 3D printing technology in dentistry has transformed the field, paving the way for more effective and durable dental restorations.14 0Item Restricted Understanding the Structural and the Mechanical Properties of Bone(Saudi Digital Library, 2023-12-12) Almoshawah, Yasser Ali H; Rehman, Ihtesham Ur; Dall’Ara, EnricoOsteoarthritis (OA) is one of the most common chronic diseases characterised by a disorder in the subchondral bone (SB), cartilage damage, and osteophyte formation. Due to an inadequate understanding of the mechanism of disease pathology, no treatment is currently available to effectively prevent the initiation or progression of OA, and severe treatment modalities, such as hip joint replacement, are currently available. A better understanding of the chemical and mechanical properties of bone will also help improve OA’s diagnosis. This study aims to investigate the chemical properties of SB from the femoral head (FH) of patients with OA through an invasive and label-free approach. Vibrational spectroscopy has shown the potential to provide diagnostic information. A combination of Raman, Fourier-Transform Infrared (FTIR) spectroscopic, and Photoacoustic Fourier Transform Infrared Spectroscopy (FTIR-PAS) methods were used for the chemical analysis of samples. Principal Component Analysis (PCA) was used to identify variations within different tissue of OA bone. Linear Discriminant Analysis (LDA) was used to predict pathogenic markers with high sensitivity (Sn) and specificity (Sp). The combination of Infrared and Raman spectroscopy with chemometrics were very helpful in identifying new spectral markers to differentiate OA bone samples. Initially, preliminary studies were conducted on bovine bones, which are almost comparable to human bones. They were applied on Raman and FTIR to study the chemical composition concerning the different cutting directions to prevent mistakes and enhance the primary study. For Raman, the PCA bovine result showed a perfect clustering, with PC-1 and PC-2 accounting for 92% of the variation, resulting in excellent Sn and Sp of 100%. The results for FTIR also exhibited perfect clustering, with PC-1 and PC-4 accounting for 80% of the variance, resulting in 100% Sn and Sp. Raman, FTIR and FTIR-PAS have identified structural and compositional changes in OA compared to tissue-specific (subregion). Significant statistical differences were detected among the bone types, including organic and inorganic composites. The results of the PCA in all vibrational spectroscopy showed that the PCA had good clustering, accounting for 74, 75, and 86% of the variation for Raman, FTIR and FTIR-PAS, respectively, leading to excellent Sn and Sp of 100%, representing the whole spectrum. Furthermore, as the aetiology and pathogenesis of OA are not fully understood, measuring the mechanical properties of bone by applying nanoindentation to FH to extract the mechanical properties is essential in order to understand the disease profile. The mechanical results show that the reduced modulus (𝐸𝑟) and the hardness (H) averaged out to be (16.07±3.05 GPa) and (0.56±0.107 GPa), respectively. The average elastic modulus (𝐸𝑏) of bone was measured to be (14.84±2.85 GPa), whereas the indentation modulus (E_ind) was (16.31±3.14 GPa). Compared to the other bone types, the osteophyte (Osteo) bone has the lowest value, while the cortical bone (Cort) has the highest value. The parameters in RS and FTIR confirm that increasing mineralisation ratios in bone types were correlated with a decreased 𝐸𝑏 and vice versa. In conclusion, vibrational spectroscopy is a highly effective method for identifying chemical changes associated with different subtypes of bone tissue disease. This study confirms its significance in evaluating both chemical and mechanical changes in cases of severe OA affecting the human FH helping to understand the reasons for the disease process and enable an improved treatment modality. Furthermore, these findings will assist the research community in identifying regions of the skeleton where the local physical and chemical properties of bone, in addition to the mechanical properties, should be characterised during the preclinical optimisation process of treatments for skeletal diseases.31 0Item Restricted Development of 3D printed resin-based nanocomposites for dental prosthetic restorations(Saudi Digital Library, 2023) Aati, Sultan Yahya A; Fawzy, AmrProsthetic dentistry is an essential practice for maintaining the structure of the oral cavity. Resin-based materials have been clinically recognized as substitutes to restore lost teeth and function. 3D printing technology has significantly strengthened the production of dental prostheses due to its precision and economic advantages. The oral environment commonly subjects synthetic substitutes to excessive functional stress, causing degradation and clinical failure due to insufficient material integration and toughness. Additionally, the inherent physical properties of dental materials promote microbial adhesion and biofilm formation. Therefore, the development of 3D printed resin is imperative to enhance the clinical performance of dental restorations.42 0