MPC Research Reports
Report Details

Title:	Repairing Concrete Structures Using Near-Surface Mounted Composites with Inorganic Resins under Simulated Multi-hazard Damage
Authors:	Yail "Jimmy" Kim
University:	University of Colorado Denver
Publication Date:	Dec 2022
Report #:	MPC-22-490
Project #:	MPC-648
TRID #:	01870539
Keywords:	bonding, composite materials, compressive strength, concrete structures, fiber reinforced polymers, repairing, resins

Abstract

The first part of the study presents the time-dependent interfacial behavior of near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) strips bonded to a concrete substrate using inorganic resins. Four types of bonding agents (mortar, polyester-silica, ultra-high performance concrete (UHPC), and geopolymer) are tested to appraise the potential for NSM applications with a focus on rheological and mechanical performance during a curing period of 28 days. Unlike mortar and geopolymer resin cases, the rheological resistance of the polyester-silica and UHPC resins increases within 30 minutes owing to an evolved setting process. The hydration of mortar continues for up to 28 days of curing in line with assorted chemical reactions. The compressive strength of polyester-silica gradually ascends to 35 MPa (5,076 psi) at 28 days, while that of UHPC rapidly rises to 95.3 MPa (13,822 psi) at three days. Contrary to the stabilized interfacial capacity of the specimens with mortar and geopolymer after seven days, the capacity of the specimens with polyester-silica steadily develops until 28 days. Unlike the failure mode of other cases over time, a shift in the plane of failure is noticed for the mortar-bonded interface. The post-peak response and energy dissipation of the interface are controlled by the resin type and curing period. Analytical modeling quantifies the level of hazard and clarifies the functional equivalence of the interface with the inorganic resins against conventional organic epoxy resins.

The second part of the study discusses the feasibility and relevance of cementitious resins as a bonding agent for NSM CFRP strips. Contrary to conventional organic matrices, such inorganic resins offer promising performance when subjected to aggressive environments, especially under thermal distress. Three emerging resins are employed (polyester-silica, UHPC, and geopolymer) to strengthen reinforced concrete beams alongside NSM CFRP. After stochastically simulating various levels of pitting corrosion for a period of 100 years, the outcomes are represented in the beams by reducing the cross-sectional area of steel reinforcement before applying the rehabilitation system. The emphasis of experimental investigations lies in the workability of those resins and the flexural response of the retrofitted beams. Material-level testing reveals that the rheological properties of the resins are not related to their compressive strength. Regarding load-carrying capacity, the beams bonded with polyester-silica outperform the beams with other resins; however, UHPC enables stable degradation over the years. The interfacial characteristics of the resins dominate the mechanical interaction between the damaged internal reinforcing steel and CFRP, thereby altering the tendency of capacity drops, post-yield plateaus, and crack distributions. Through analytical modeling, the provisions of existing design guidelines are evaluated, and a modification factor is suggested to promote the cementitious resins for NSM CFRP.

How to Cite

Kim, Yail "Jimmy". Repairing Concrete Structures Using Near-Surface Mounted Composites with Inorganic Resins under Simulated Multi-hazard Damage, MPC-22-490. North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Mountain-Plains Consortium, 2022.