UNIFIED FIBER-REINFORCED POLYMER COMPOSITE SOLUTIONS FOR ENHANCING THE STRUCTURAL DURABILITY OF AGING CIVIL INFRASTRUCTURE

Abstract

U.S. transportation assets continue to operate at or beyond design life under corrosion, chemical attack, and cyclic environmental loading, driving strength and serviceability deficiencies that demand constructible, design-checkable rehabilitation. This dissertation advances the structural use of fiber-reinforced polymer (FRP) and polymer-based systems through five coordinated studies that span material, interface, member, and system scales with direct relevance to design, detailing, and quality assurance.Project 1 quantifies the flexural behavior and failure mechanisms of RC beams strengthened with combined CFRP systems. Across five configurations—control, U-wrap only, NSM-CFRP bars only, NSM+full U-wrap, and NSM+shear U-wrap—the strengthened beams achieved substantial capacity gains: +19% (U-only), +83% (NSM), +99% (NSM+full U-wrap), and +105% (NSM+shear U-wrap). The combined systems promoted bar strain development, mitigated debonding, and shifted failures toward CFRP rupture when confinement was effective. Project 2 evaluates polymer-concrete (PC) overlays modified with multi-walled carbon nanotubes (MWCNTs) using direct tensile pull-off (ASTM C1583). On normal substrates, neat PC provided the most reliable adhesion; on sulfate-deteriorated substrates, a 0.5 wt.% COOH-functionalized MWCNT mix increased interface tensile capacity by ~15%, establishing substrate-conditioned material selection and dispersion guidance for bonded overlay design. Project 3 establishes grout-dependent composite action in GFRP slip-lined corrugated metal pipe (CMP) culverts via circumferential ring testing. Polymeric annular grout produced stiffness factors ≈7× those of cementitious grout for uncorroded rings (≈6.8× for corroded), elevating grout modulus and bond to first-order design variables for circumferential stiffness, load rating, and service-load deformation in trenchless rehabilitation. Project 4 isolates matrix/interface durability of CFRP under 0–250 freeze–thaw cycles using off-axis tensile coupons (ASTM D3039). Neat laminates lost strength, modulus, and ultimate strain; on the other hand, CNT-modified laminates largely retained their strength, stiffness, and strain capacity after 250 freeze–thaw cycles. The mix with 1.0 wt.% COOH-functionalized CNTs showed the smallest change in properties. CNT-modified laminates largely retained properties, with ~1.0 wt.% COOH and ~1.5 wt.% pristine mixes most resilient. SEM showed crack-bridging and improved fiber–matrix adhesion, informing durability factors for cold-region design. Project 5 investigates 3D-printed thermoplastic CFRP lattices (cage/flat) as internal reinforcement in PCC, UHPC, and PC beams. Four-point bending benchmarks demonstrate displacement-ductility enhancement with matrix-dependent differences between observed and predicted nominal moments; performance is sensitive to lattice placement (cover, floating/tilt) and junction quality, motivating installation checks and matrix-appropriate stress-block adjustments. Collectively, the dissertation contributes: (i) validated strength and failure data for combined NSM-and-wrap CFRP schemes enabling more ductile design checks; (ii) a chemically informed route to preserve overlay bond on sulfate-damaged substrates with functionalized CNTs; (iii) quantitative stiffness factors that elevate grout selection to a codifiable parameter for GFRP slip-lining; (iv) durability evidence that CNT nanomodification can stabilize off-axis CFRP properties under long-term freeze–thaw; and (v) structural-scale benchmarks for thermoplastic CFRP lattice reinforcement across cementitious and polymer matrices. Together, these results guide the design of durable composite rehabilitation systems against the key deterioration mechanisms.