Relevant Degree Programs
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - May 2021)
Concrete structures are severely susceptible to degradation as a result of mechanical or environmental processes. In most cases, retrofit is the only available option because reconstruction of the deteriorated structure is neither a feasible nor financially practical option. The overall performance of a repaired structure is highly dependent on the properties of its interface, which is the weakest part of the system. Fiber reinforced concrete (FRC) is a recognized repair material, however, there are still some knowledge gaps including lack of comprehensive understanding of the synergistic effects of fiber addition and surface preparation on composite structure, long-term behavior and durability of interfaces, and lack of standard design equations for concrete-FRC interfaces. In this study, synergistic effects of different fibers at various volume ratios and surface preparation on failure mechanism, bond strength, and crack growth resistance of concrete-FRC interfaces is investigated under Mode-I loading regime. Based on experimental data, design equations are proposed for concrete-FRC interfaces under Mode-I. These models address tensile strength and crack growth resistance of concrete-FRC interfaces encompassing various variables including surface preparation, type of repair material, and ductility of substrate and repair layers. Furthermore, the micromechanical properties of concrete-FRC interfaces are studied and the impact of fiber addition and curing condition on microhardness, porosity, durability, and water absorption of composite structures is assessed using micro-indentation, scanning electron microscopy (SEM), and micro-computed x-ray tomography (CT-scanning) techniques. Results indicate that there is a strong relationship between surface treatment, fiber content, and composite mechanical behavior. Fiber addition and improved surface treatment enhance response of composite systems in Mode-I. Semi-empirical models exhibit saturating trend between mechanical response improvement and surface preparation/fiber content. Moreover, micromechanical results indicate effectiveness of fibers in mitigating pre-loading and shrinkage damages. In conclusion, FRC can be considered as a promising repair material for repair of deteriorated concrete structures. It can effectively mitigate pre-loading damages as well as mitigating failure under tensile stresses leading to improved mechanical performance and durability of repaired systems. Suggestive models can be employed for numerical simulations and can be used by practitioners for design purposes and to predict composite response of repaired structures.
Master's Student Supervision (2010 - 2020)
A significant portion of concrete infrastructure in North America is deteriorating and will require repair or rehabilitation action in the near future. An effective repair can be jeopardized by a bond which is unable to withstand the subjected loading and durability conditions. Fatigue loads are a cause of structural concrete deterioration and cracking with respect to service load conditions such as vehicular traffic as well as high amplitude loading events such as earthquakes and storms. Currently the response of cementitious repair interfaces tested under fatigue loading is not comprehensively examined in existing literature. In this study, the modified slant shear cylinder test with different bond plane inclinations was used to experimentally determine the bond strength of composite substrate-repair specimens subjected to monotonic and fatigue loading protocols. The effect of both roughened and near-smooth interfacial profiles is considered, as well as the use of steel fiber reinforcement in the repair material. The associated bond parameters are derived from experimental test results using previously identified predictive models and failure envelopes for concrete interfaces. 2D Digital Image Correlation (DIC) is additionally used to examine strain distributions on the surface of slant shear specimens prior to failure. A discussion on the degradation of the adhesive bonding mechanism is presented and the resulting implications on bond strength and bond parameters are examined. The interfacial bond investigation is complemented with a discussion on the limitations of the employed predictive models as well as a review of relevant code provisions and research guidelines pertaining to interfacial shear bond subject to cyclic and fatigue loads.
Recycling waste materials as replacement for natural resources in building products could help in lowering the environmental impact of the construction industry, provided that their application and processing is properly engineered. Wood waste is one of the chief construction wastes in Canada and many other countries worldwide. In this study, a novel bio-composite panel made with recycled wood chips is presented and assessed.The bio-composite binder was a natural hydrated lime with addition of metakaolin. The inclusion of various additives such as sodium hydroxide, recycled wood ash, and magnesium-rich powder recycled from the cutting waste in the production of magnesium oxide boards, was also explored. The effects of different binder compositions and proportions on the microstructure of the binder, its compatibility with the wood chips, and the engineering properties of the final bio-composite product were investigated. Finally, the effect of different curing conditions is considered, including accelerated carbonation by CO₂ incubation.Following ASTM specifications, 3 replicates of 550 x 550 x 70 mm panels for each bio-composite formulation and curing condition were cast. Specimens were cut from the panel to test the mechanical and thermal properties. Extent of carbonation within the panel was analyzed by standard colouring observation after addition of phenolphthalein and compared with control specimens cured without CO₂ incubation. These analyses were supported by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) of the binders and the bio-composite to monitor the various reactions occurring in the binder, including hydraulic and pozzolanic reactions, carbonation and additional reactions.An optimised binder composition of lime and metakaolin was successfully designed based on the strength data obtained on binder pastes. The bio-composite produced by combining wood chipsand the optimised binder possessed good mechanical and thermal properties. While it met the minimum requirements of compressive strength and thermal conductivity as specified by ASTM standards, future work will need to focus on improvement of the flexural behavior. It was also found that carbonation curing of specimens helped in rapid strength gain and improvement of the matrix. Further, microstructure analysis of the bio-composite helped identify and characterise the reaction products that enhanced its properties.