Evaluation of the microstructural, mechanical, and durability performance of novel surface-treated fibers in cementitious composites
| dc.contributor.author | Viradiya, Jaykumar | |
| dc.contributor.supervisor | Gupta, Rishi | |
| dc.date.accessioned | 2026-01-26T22:02:46Z | |
| dc.date.available | 2026-01-26T22:02:46Z | |
| dc.date.issued | 2026 | |
| dc.degree.department | Department of Civil Engineering | |
| dc.degree.level | Doctor of Philosophy PhD | |
| dc.description.abstract | With growing concerns about the aging and deteriorating infrastructure across Canada and globally, there is an increasing need for durable, high-performance construction materials that can withstand harsh environmental stressors. According to the 2024 report of the US federal highway administration (FHWA), freeze–thaw (F-T) damage is among the leading causes of premature distress in pavements, bridges, and other critical infrastructure components, particularly in northern regions [1]. Annual repair and rehabilitation expenditures due to environmentally induced degradation are estimated to exceed $20 billion USD in North America alone, with F-T cycling representing a major contributing factor [2]. Similarly, the 2019 Canadian Infrastructure Report Card indicates that over 40% of municipal concrete infrastructure is in fair to poor condition, mainly due to deterioration related to environmental exposure [3]. This underscores the pressing need for durable and effective solutions that can extend the service life of the infrastructure while minimizing maintenance interventions. Fiber-reinforced cementitious composite (FRCC) has emerged as a sustainable and practical solution due to its ability to improve crack control, post-crack ductility, and energy absorption in cementitious systems. Various types of fibers have been incorporated into FRCC, including steel, glass, carbon, basalt, and synthetic polymers such as polypropylene (PP). Steel fibers provide high tensile strength and stiffness, still they are susceptible to corrosion and increase both cost and density. Glass fibers are brittle and prone to alkali degradation in cementitious environments unless specially treated (e.g., alkali-resistant glass), which increases their cost and processing complexity. Carbon fibers offer excellent mechanical properties and chemical resistance, but are prohibitively expensive for most large-scale civil applications. In contrast, PP fibers offer a favorable balance of chemical stability, corrosion resistance, flexibility, low density, and costeffectiveness. However, the smooth and hydrophobic nature of PP fibers leads to weak interfacial bonding with the cement matrix, limiting stress transfer efficiency and mechanical performance. Optimizing this interfacial bond is key to enhancing both the mechanical efficiency and environmental resilience of the PP-FRCC, especially under cyclic temperature variations. Many researchers have studied a range of surface treatment techniques, such as cold plasma, chemical etching, flame treatment, surface mechanical pitting, and silica treatment via the solgel method, to address the persistent challenge of poor fiber–matrix interfacial bonding in FRCC. Although these methods have shown varying degrees of success in enhancing adhesion, they often require controlled environments, specialized equipment, or complex procedures, limiting their scalability for field applications. In addition, most existing studies primarily focus on conventional mechanical performance, such as pull-out, compression, and flexural strength—with limited investigation into the microstructural characteristics of the fiber–matrix interface. Furthermore, to the best of the author’s knowledge, no prior studies have evaluated the F-T durability of surface-treated FRCC.This leaves a critical gap in understanding the combined microstructural, mechanical, and durability mechanisms that govern the long-term performance of such systems. To address these issues systematically, this dissertation is structured into five distinct phases. Phase I focuses on the development and evaluation of three novel surface treatments for PP fibers used in cementitious composites, utilizing silica-fume as the key functional coating material. These treatments include: (i) adhesive dry coating, (ii) adhesive wet coating, and (iii) non-adhesive heat coating. The effectiveness of each method was assessed using contact angle measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), microhardness testing, and mechanical tests including fiber pull-out, flexural strength, and compressive strength. The findings of Phase I revealed that the silica-fume on the surface of the PP fiber reacts with portlandite [calcium hydroxide (CH)], significantly improving the interfacial transition zone (ITZ), particularly within the first 40µm from the fiber edge. In pull-out tests, adhesive dry and adhesive wet coated fibers exhibited 96% and 31% higher total energy absorption, respectively, compared to untreated fibers. Non-adhesive heat treated fibers demonstrated the most significant enhancement, with an 857% increase in energy absorption, accompanied by fiber fracture, indicating superior bond strength and stress transfer. Flexural testing also showed that all treated fiber composites achieved nearly double post-crack energy absorption compared to their untreated counterparts at same fiber dosage. These preliminary results confirm that the proposed treatments effectively enhance the fiber-matrix interface and the overall mechanical performance of PP-FRCC, without requiring restrictive long processing conditions. Phase II builds on the findings of Phase I by applying the most feasible surface treatment, adhesive dry coating, to multi-filament PP fibers and evaluating their performance across three fiber dosages: .3%, 0.6%, and 0.9% by volume. The aim was to assess the influence of treated fibers with various dosages on both the mechanical and microstructural characteristics of fiber-reinforced cementitious mortar (FRCM) and fiber-reinforced concrete (FRC). The study involved compressive strength, uniaxial and split tensile strength, flexural strength, and single fiber pullout testing, complemented by SEM and EDX analyses of the fiber–matrix ITZ. Phase II results showed that treated fibers with adhesive dry coating method, improved composite performance in all dosages, with particularly notable gains in post-crack energy absorption, flexural strength retention, and fiber–matrix bonding. In mortar systems, post-crack flexural toughness increased by 44–164%, while in concrete, post-crack toughness increased by 41–128%, with flexure strength loss (compared to plain concrete) reduced by 35% for both FRCM and FRCM over untreated mixes. In mortar specimens, treated fibers reduced axial tensile and compressive strength losses by over 50% compared to untreated mixes, while in concrete, treated fibers similarly halved the strength reductions observed in compression tests. Microstructural analysis further confirmed that the silica coating promoted pozzolanic interaction with CH, resulting in a denser ITZ and enhanced bonding efficiency for this multi-filament PP fibers. Phase III builds on Phase II by extending the investigation of the F-T behavior of FRCC samples incorporating surface-treated PP fibers (using the proposed treatment) and by evaluating their durability under 300 F-T cycles. Although many studies have explored improving FRCC via surface-treatment methods, to the best of the author’s knowledge no reported work has examined the F-T behaviour of such treated FRCC at the composite level. By assessing the F-T performance of FRCC, this phase quantifies durability and resistance to cracking, spalling, material degradation, and residual flexural strength. These preliminary results provide a valuable basis for evaluating the suitability and long-term performance of FRCC made with the proposed surface-treated fibers, and are particularly important for cold climates where F-T cycling is a significant concern. Phase III revealed that surface-treated fiber mixes exhibited around 10% higher residual modulus of elasticity after 300 F-T cycles relative to untreated counterparts. Under flexural bending, the treated mixes exhibited ∼10% to ∼39% higher residual flexural strength retention and ∼26% to ∼ 78% higher residual post-crack toughness retention than the untreated mixes, across dosages up to Vf = 0.9%. Finally, correlation analysis between static and dynamic modulus of elasticity indicated that the ultrasonic pulse velocity (UPV) method is more reliable than the resonant frequency test (RFT) method for tracking stiffness changes under F-T. Phase IV focuses on the specialized application of FRC under operating temperatures of −18 ◦C and 80 ◦C, evaluating the performance of composites incorporating surface-treated PP fibers. At these extremes, the thermal-expansion mismatch between the cement matrix and hydrophobic, coated PP fibers can alter the fiber–matrix bond, which the surface treatment is designed to strengthen. Verifying that bond integrity and composite response at these extremes is a necessary check before claiming field durability. In this phase, compression, split-tension, fiber pull-out, and flexural bending tests were conducted to reveal the influence of these short-term targeted temperatures on the behavior of composites with both untreated and surface-treated PP-FRC. The primary objective was to assess the effect of these temperatures on the performance integrity of the proposed surface-treated fibers within the composite, particularly considering the significant thermal mismatch at the fiber–matrix interface introduced by the additional coating layers. This evaluation aimed to confirm the effectiveness of the surface treatment in enhancing fiber–matrix bonding and, in turn, its contribution to the overall composite performance beyond room-temperature applications. Phase IV results demonstrated that the proposed surface-treated fibers maintained their effectiveness in compression, split-tension, single-fiber pull-out, and flexural bending behavior of the composites under both −18 ◦C and 80 ◦C, comparable to their performance at room temperature. This confirms that the surface treatment enhances the fiber–matrix bond, thereby strengthening the ductile response of FRC and extending the applicability of these fibers beyond room-temperature conditions when compared to untreated counterparts. In Phase V, we introduce a modeling framework whose novelty lies in using our own surface-treated PP fiber pull-out data to drive flexural predictions of FRC at both room temperature and an elevated temperature of 80 ◦C. The framework adapts established cracked-section mechanics and fiber-bridging concepts, but calibrates the bond law with treatment-specific parameters measured in this study, thereby creating a transparent micro-to-macro link. It predicts peak load, residual strengths, and toughness at the standard deflection levels L/600 and L/150 in third-point bending per ASTM C1609 [4], and is validated at 23 ◦C (room temperature) as well as 80 ◦C (elevated temperature). This phase contributes a transferable, temperature-aware calibration workflow that links treatment-specific bond parameters from pull-out to member-scale flexural response. In practice, it enables rapid screening and design of dosage for surface treatments to meet peak, residual, and service-level deflection targets (L/600, L/150) per ASTM C1609 [4], when only basic matrix properties and fiber–matrix pull-out data are available. This thesis introduces novel, easy-to-apply surface treatments for hydrophobic synthetic fibers, primarily PP, to enhance interfacial bonding and densify the fiber–matrix interface in cementitious composites, thereby improving their overall performance. Unlike conventional surface-treatment methods that often require lengthy and complex processing, the approach proposed in this work is is rapid and simple, making it highly amenable to future in-line automation. The findings have significant potential to inform and guide future advancements in improving the overall performance FRCC by addressing poor fiber-matrix interface challenges . Moreover, this thesis establishes a foundation for integrating automated surface-treatment steps directly at the production stage through the prototyping strategies developed herein. | |
| dc.description.embargo | 2026-11-17 | |
| dc.description.scholarlevel | Graduate | |
| dc.identifier.uri | https://hdl.handle.net/1828/23074 | |
| dc.language | English | eng |
| dc.language.iso | en | |
| dc.rights | Available to the World Wide Web | |
| dc.subject | Surface treated fibers | |
| dc.subject | Silica-fume coating | |
| dc.subject | Supplementary cementitious material | |
| dc.subject | Polypropylene fibers | |
| dc.subject | Fiber surface modification | |
| dc.subject | Reinforced concrete durability | |
| dc.subject | SEM | |
| dc.subject | EDX/EDS | |
| dc.subject | Microstructural analyses | |
| dc.subject | ITZ modification | |
| dc.title | Evaluation of the microstructural, mechanical, and durability performance of novel surface-treated fibers in cementitious composites | |
| dc.type | Thesis |