Multiphase Characteristics of Carbon Fiber-Reinforced Cementitious Materials Under Static and Freeze-Thaw Cyclic Loading Conditions

Aging concrete infrastructure, particularly in colder climates like Canada, demands urgent 
\nmaintenance and renewal due to the severe temperature variations. These conditions lead to issues 
\nsuch as cracking, spalling, and overall deterioration. To ensure the longevity and functionality of 
\ninfrastructures, it is crucial to use durable and high-performance materials. Adding fibers to the 
\nconcrete mix can improve its toughness and resistance to cracking. Fiber-reinforced concrete (FRC) 
\ncan withstand higher tensile stresses and distribute loads more effectively, increasing the overall 
\ndurability.
\nAmong various types of fibers, carbon fibers (CFs) have gained significant popularity due to their 
\nunique ability to confer self-deicing properties to cementitious materials. This characteristic holds 
\nparticular importance in colder climates, where maintaining safe and accessible infrastructure, 
\nduring harsh winter conditions is paramount. Carbon fiber-reinforced concrete (CFRC) has various 
\nadvantages over normal concrete, including self-deicing, high strength, durability, and corrosion 
\nresistance. CFRC's self-deicing capability is achieved through the electrical conductivity of CFs, 
\nwhich allows an electric current to be applied to generate heat and melt ice or snow. This feature 
\nimproves safety by preventing icy surface conditions and lowers maintenance costs for snow 
\nremoval and deicing chemicals. CFRC is also highly durable and strong, making it suitable for 
\ninfrastructure and architectural construction. Additionally, its resistance to corrosion ensures long lasting performance and extends the lifespan of CFRC structures.
\nIntegrating self-deicing CF reinforcement within concrete bus pads offers a practical approach 
\nto leverage their inherent self-deicing property, resulting in heightened passenger safety and 
\nconvenience throughout the winter season. With CFs generating heat to melt accumulated ice and 
\nsnow, the bus pads retain a snow-free surface, thereby mitigating the potential for slips and 
\naccidents among passengers and pedestrians. This endeavor directly fosters a transit environment 
\nthat is safer and more accessible.
\nWhile numerous studies have studied self-deicing characteristics of CFRC in colder climates, a 
\nnotable research gap exists in examining how CFRC responds to the rigorous challenges of 
\nfreezing and thawing (FT) cycles. Despite the extensive exploration of CFRC's ability to melt ice 
\nand snow, the absence of investigations into its deterioration behavior under cyclic freezing and 
\nthawing conditions is a critical oversight. This dissertation aims to fill the existing knowledge gap 
\nand challenges related to the performance assessment of CFRC under cyclic freezing and thawing 
\nloading conditions, as well as introducing an optimized mix design for concrete suitable for colder 
\nclimates. The research methodology involves a comprehensive investigation that incorporates both 
\ndestructive and non-destructive testing techniques.
\nIt is clear that a multitude of pertinent factors, encompassing factors such as fiber and aggregate 
\ntype, fiber length, cement paste composition, and different admixture can have significant impacts
\non the performance of cementitious composites. Within the context of this dissertation, however, 
\nthe study has meticulously centered its investigative on carbon fiber's physical properties and its 
\nconcentration. In the pursuit of refining the mix design to attain optimal outcomes, the research 
\nengaged in an array of destructive analyses, including compressive strength tests, splitting tensile 
\nstrength tests, and flexural strength tests. These tests provide insights into the strength and 
\nstructural behavior of CFRC under FT conditions, allowing for an evaluation of its performance.
\nIn conjunction with conventional destructive tests, this research integrated non-destructive 
\ntesting (NDT) methodologies to appraise the structural integrity and quality of the CFRC specimens. 
\nEmploying advanced techniques including ultrasonic testing, rebound hammer analysis, and 
\nground-penetrating radar, a comprehensive evaluation was systematically conducted on CFRC 
\nsamples subjected to an extensive and rigorous regimen of 300 FT cycles. Throughout this 
\ndemanding exposure, the samples underwent the complete array of non-destructive assessments 
\nat regular 30-cycle intervals. This approach was undertaken to meticulously discern and analyze 
\nthe cumulative deteriorative effects that emanated from the repetitive FT cycles. These insights 
\nyielded a profound understanding of the durability performance of CFRC under the persistent 
\nchallenge of FT conditions.
\nThe synergistic integration of both destructive and non-destructive testing methodologies yields 
\na holistic and nuanced comprehension of CFRC performance in areas with colder climate such as 
\nCanada. This assimilated knowledge stands as a pivotal cornerstone for the formulation of an 
\nintricately optimized mix design, one fortified to effectively withstand the challenges imposed by 
\ncyclic FT cycles. The research outcomes have the potential to contribute to the advancement of 
\nCFRC technology, enabling its effective use in regions with colder climates and facilitating the 
\nconstruction of durable and resilient infrastructure in such areas.
\nThe dissertation is divided into three milestones, each with its own set of objectives and tasks, 
\nto systematically address the research questions and challenges related to CFRC.
\nMilestone 1 encompassed a comprehensive evaluation of mechanical properties and physical 
\nproperties in different carbon fiber types, emphasizing a comparative analysis on commonly used 
\nCFs. The research extended to a novel bitumen-based carbon fiber (BBCF) from Alberta, seeking 
\nto understand its microstructure and potential for market adaptability. Techniques such as scanning 
\nelectron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy, along with 
\nmechanical and electrical tests, were incorporated to assess the behavior of different types of CFs.
\nMilestone 1 also presented a novel method using a supplementary cementitious materials (SCM) 
\nfiber coating technology. This breakthrough improved the interfacial transition zone (ITZ) between 
\nfibers and the cement matrix, resulting in improved composite performance. The goal of this 
\nmilestone was to meticulously compare and establish correlations between the diverse properties 
\nexhibited by various fiber types. This systematic investigation attempted to identify the best fiber 
\nchoice for incorporation into cementitious materials, thereby improving the cementitious 
\ncomposite's overall performance.
\nMilestone 2 shifted the focus to investigating the mechanical and fracture behavior of carbon 
\nfiber-reinforced cementitious composite (CFRCC) and the interrelationship between materials 
\nproperties and mechanical performance. A systematic approach for Laboratory testing and 
\nstructural analysis has been presented in this milestone.
\nUniaxial tension tests were performed on dog bone-shaped Carbon Fiber Reinforced Mortar 
\n(CFRM) to analyze the behavior of samples subjected to axial tensile forces. Flexural characteristic 
\nof CFRC samples is key parameter that involves composite behavior under bending loads. While 
\nflexural testing often employs beams, it may not effectively represent the performance of fiber reinforced concrete due to considerable differences in cracking behavior of FRC with normal 
\nconcrete. This discrepancy is particularly noticeable in slab and pavement applications, owing to 
\nthe substantial variability in flexural behavior observed in Fiber-Reinforced Concrete (FRC) beams. 
\nAdditionally, the smaller fracture area resulting from a lower count of fibers further compounds this 
\ndistinction.
\nDuring this milestone, a thorough and comprehensive analysis was conducted, focusing on the 
\nflexural strength of both round panels and beams. The flexural failure observed in round panels 
\nclosely emulated the behavior seen in structural slabs, aligning with the principles of the yield line 
\ntheory. 
\nThe characterization of flexural behavior involved toughness indices and key flexural strength 
\nparameters, including bending strength and modulus of elasticity. This analysis process ultimately 
\nled to the identification of an optimal mix design. This finding underscores the significance of fiber 
\ncontent in influencing the overall behavior and performance of CFRC composites.
\nFurthermore, to compare the experimental results of CFRC beam and panel flexure behavior, 
\nan analysis of variance was conducted. This statistical examination unveiled a notable 41% 
\ndiscrepancy in flexural properties between the two distinct sample geometries. This observation highlights the importance of considering sample geometry when assessing the flexural behavior of 
\nCFRC materials.
\nMilestone 2 also involved a meticulous investigation into the FT behavior of the CFRC samples, 
\nevaluating their durability under the stress of 300 FT cycles. By studying the FT performance of the 
\nCFRC samples, the research aims to gain insights into the durability and resistance of CFRC to the 
\neffects of FT cycles, which can include cracking, spalling, and degradation. This information is 
\nvaluable for assessing the suitability and long-term performance of CFRC in colder climates, where 
\nFT cycles are a

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