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.12 0Item Restricted Behavior and Design of Composite Rebars Interfaced with Concrete(university of colorado Denver, 2024) Alatify, Ali; Kim, JimmyAbstract This dissertation studies different aspects of the interfacial behavior of composite reinforcement embedded in concrete. GFRP rebars are known for its none-corrosiveness, light weight, and high strength compared to conventional steel rebars, and became predominantly employed in different structural applications such as bridge construction. Thus, the serviceability and interfacial behavior of GFRP bars in different structural applications is investigated in four phases in this research. Chapter three presents an experimental study on the residual bond of glass fiber reinforced polymer (GFRP) rebars embedded in ultra-high performance concrete (UHPC) subjected to elevated temperatures, including a comparison with ordinary concrete. Based on the range of thermal loading from 25oC (77oF) to 300oC (572oF), material and push-out tests are conducted to examine the temperature-dependent properties of the constituents and the behavior of the interface. Also performed are chemical and radiometric analyses. The average specific heat and thermal conductivity of UHPC are 12.1% and 6.1% higher than those of the ordinary concrete, respectively. The temperature-induced reduction of density in these mixtures ranges between 5.4% and 6.2% at 300oC (572oF). Thermal damage to GFRP, in the context of microcracking, is observed after exposure to 150°C (302°F). Fourier transform infrared spectroscopy reveals prominent wavenumbers at 668 cm-1 (263 in.-1) and 2,360 cm-1 (929 in.-1), related to the bond between the fibers and resin in the rebars, while spectroradiometry characterizes the thermal degradation of GFRP through diminished reflectivity in conjunction with the peak wavelength positions of 584 nm (2,299×10-8 in.) and 1,871 nm (7,366×10-8 in.). The linearly ascending bond-slip response of the interface alters after reaching the maximum shear stresses, leading to gradual and abrupt declines for the ordinary concrete and UHPC, respectively. The failure mode of the ordinary concrete interface is temperature-sensitive; however, spalling in the bonded region is consistently noticed in the UHPC interface. The fracture energy of the interface with UHPC exceeds that of the interface with the ordinary concrete beyond 150oC (302oF). Design recommendations are provided for estimating reductions in the residual bond of the GFRP system exposed to elevated temperatures. The interface shear between ordinary concrete and ultra-high-performance concrete (UHPC) connected with glass fiber reinforced polymer (GFRP) rebars is presented in chapter four. Following ancillary tests on the fracture of the rebars under in-plane shear loading, concrete-rebar assemblies are loaded to examine capacities and failure modes that are dependent upon the size, spacing, and number of the rebars. While the transition of load-resisting axes in the glass fibers and their quantity dominates the shear behavior of the bare rebars, the size and spacing of the reinforcement control the capacities of the interface by altering load-transfer mechanisms from the rebar to the concrete. The degree of stress distribution affects the load-displacement response of the interface, which is characterized in terms of quasi-steady, kinetic, and failure regions. The primary failure modes of the interface comprise rebar rupture and concrete splitting. The formation of cracks between ordinary concrete and UHPC results from interfacial deformations, leading to spalling damage when applied loads exceed service levels. An analytical model is formulated alongside an optimization technique. The capacities of the interface in relation to the rebar rupture and concrete splitting failure modes are predicted. Furthermore, a machine learning algorithm is utilized to define a failure envelope and propose practice guidelines through parametric investigations. The serviceability of concrete beams with continuous and spliced glass fiber reinforced polymer (GFRP) rebars is investigated and detailed in chapter five. An experimental program is undertaken using 18 beams incorporating various reinforcing schemes to examine the effects of rebar distribution and spacing on flexural and cracking responses. The cracking load of the beams with the continuous rebars (Category C) is 24.2% higher than that of the beams with the spliced rebars (Category S) experiencing stress concentrations. The distributed configuration of the rebars enhances interactions between the concrete and reinforcement, thereby increasing bond transfer in the beams. Contrary to the linear load-displacement behavior of the C-category beams after cracking, parabolic trends are observed in the S-category beams owing to the slip of the spliced rebars, which degrades composite action at the rebar-concrete interface and reduces the flexural rigidity of the beams. The crack opening of the C-category beams under service loading is within the tolerable limits of published guidelines, whereas the opening of the S-category beams exceeds the limits. Through statistical characterization, the significance of the rebar distribution in crack opening and depth is demonstrated at a 5% significance level (95% confidence interval). Design recommendations include a slip multiplier of 0.63 for calculating the stress of spliced GFRP rebars and a bond coefficient of 0.88 for determining the flexural capacity of beams with this type of reinforcement. The implications of variable bond for the behavior of concrete beams with glass fiber reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms is evaluated in chapter six. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded rebars, which are intended to represent sequential bond damage. Conforming to published literature, three shear-span-to-depth (av/d) ratios are considered: arch action (av/d < 2.0), beam action (3.5 ≤ av/d), and a transition from arch to beam actions (2.0 ≤ av/d < 3.5). When sufficient bond is provided for the element-level testing (over 75% of 5db, where db is the rebar diameter), the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the shear-span-to-depth ratio, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams and the slippage of the partially bonded rebars dominates their flexural stiffness. Compared with the case of beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of rebar stress is dependent upon the shear-span-to-depth ratios and, in terms of utilizing the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of rebar stresses with bond damage when subjected to arch and beam actions.33 0Item Restricted Investigating the durability and sustainability of materials used in Accelerated Bridge Construction (ABC)(Saudi Digital Library, 2023-11-13) Alyami, Ali; Thomas, PaulAccelerated bridge construction (ABC) is one of the advanced engineering techniques that is gaining popularity worldwide, presenting advantageous benefits to the modern in terms of minimizing traffic disruption, increasing safety, reducing construction costs, and shortening construction duration. However, current concrete materials are falling behind in meeting the future expectations and demands for sustainability and durability advancement in bridge engineering. Ultra-high-performance concrete (UHPC) is one of the promising concrete materials that present outstanding performance due to its superior mechanical and durability properties that will address various issues in bridge engineering, providing longer serviceability and enhanced durability in severe weather conditions. The high initial costs and carbon dioxide (CO2) emissions associated with the implementation of UHPC at the early construction stages present some concerns leading to limiting the widespread adoption of this product. This paper investigates the potential of UHPC versus other concrete materials, highlighting their durability and sustainability performance to seek its viability as cost-effective and green material option. The long-life cycle cost and environmental assessments show that UHPC has the potential to be one of the most durable and sustainable concrete materials due to the decreased costs associated with reduced concrete volume, maintenance frequency and CO2 footprint emissions over a long-time range.13 0Item Restricted Investigation Of Ultra-High Performance Concrete For Precast Decked Bulb-Tee Bridgegirder Connections(2023-05) Alkhalaf, Abdulsalam; Li, ChengyuIn recent decades, many state departments of transportation have chosen ultra-high performance concrete (UHPC) as a proper solution for several difficulties of the precast bridge system. The use of steel fiber reinforcement contributes significantly to the various advantages that UHPC material provides in comparison to conventional concrete. The fundamental goal of this research study is to develop and improve the transverse joint design (shear key) that provides satisfactory implementation in a connection area between two adjacent precast decked bulb-tee bridge girders using UHPC as a grout material. The design and building of fully simulated connected decks were completed to assess the strength and performance of this particular transverse joint using UHPC material under ultimate monotonic loading and cyclic loading (fatigue) as an experimental investigation. The focus of these experimental tests was on the bond between the precast concrete and UHPC material, cracking behavior under low stresses of cyclic loading, cracking and failure behavior under high stresses of cyclic loading, and monotonic ultimate loading behavior. Furthermore, a finite element analysis was performed for validation and clarification of the effect of the deck thickness on the connection joint's strength. Meanwhile, other studies, such as the interfacial bond strength between UHPC and conventional concrete and the bond behavior between the reinforcing rebars and the concrete, were executed to participate in investigating the performance and behavior of connection joints between the decks of bulb-tee bridge girders. These experiments and the subsequent analysis showed that the decked bulb-tee girder system using UHPC as grout material provided higher strength than the cast-in-place entire deck by approximately 44 percent in terms of the bending moment capacity. In this study, the particular transverse joint design and noncontact lap-splice of the connection joint exhibit acceptable behavior where the failure mode of all simulated decks was the conventional concrete crushing. The groove and intentionally roughened surfaces of the precast concrete members before casting the grout material (UHPC) show great improvement when they increase the bond strength compared to the smooth surface by approximately 73% and 77%, respectively. The form and content of this abstract are approved. I recommend its publication. Approved: Chengyu Li7 0