Christian Carloni

Role of the Matrix Layers in the Stress-Transfer Mechanism of FRCM Composites Bonded to a Concrete Substrate

AbstractFiber-reinforced cementitious matrix (FRCM) composites represent a newly developed promising technique for strengthening RC structures. The FRCM composites are comprised of high-strength fibers applied to the concrete substrate through an inorganic cementitious matrix. In this work, single-lap direct-shear tests were carried out on FRCM strips, comprised of one layer of fiber net embedded within two layers of matrix, bonded to a concrete block. The weakness of FRCM-concrete joints was observed to be the debonding at the matrix-fiber interface. The experimental results indicated that the role of each matrix layer is different. The stress-transfer mechanism between the fiber filaments and the matrix layers on either side of the fiber net was studied by means of a fracture mechanics approach, and three models of the interfacial cohesive material law were proposed for each matrix-fiber interface.

FRP-Masonry Debonding: Numerical and Experimental Study of the Role of Mortar Joints

Fiber-reinforced polymers (FRP) composites are used as supplementary reinforcement to increase the in-plane shear capacity or to provide out-of-plane load-carrying capability of masonry walls and to modify the collapse mechanism in arches and vaults. In these applications, the efficiency of load transfer is limited by the debonding of FRP from the masonry substrate. In this paper, the debonding mechanism of FRP-masonry is experimentally studied. Experimental procedures and test specimens are designed to investigate the progressive debonding of FRP from brick and mortar substrates and relate it to the response obtained from the FRP-masonry interface. Surface displacements during debonding are obtained using digital image correlation. A one-dimensional numerical model is developed for predicting the fracture behavior along the FRP-masonry interface using the cohesive fracture parameters from the brick and mortar interfaces obtained from the computed strains.

Confinement of masonry columns with PBO FRCM composites

The overarching goal of this work is to provide a fundamental understanding of the behavior of solid brick masonry columns confined with fiber reinforced cementitious matrix (FRCM) composites. FRCM is a newly-developed type of composite material comprised of a cementitious inorganic matrix (binder) and embedded fibers that are usually bundled to improve the bond between the matrix and the fibers. Compression tests were carried out to investigate the influence of the FRCM confinement and the brick patterns on the load-carrying capacity of the confined columns. Compression tests were conducted on brick masonry columns with different brick configurations. Digital image correlation measurements on the surface of the composite and on the surface of the brick for the control specimens were attempted in order to understand the role of the mortar joints and the arch effect across the section of the columns due to the confinement. The experimental results indicate that FRCM composites can effectively increase the load-carrying capacity of brick masonry columns and the failure mode could be different from the one observed for masonry columns confined with fiber-reinforced polymer (FRP) composites.

Application of fracture mechanics to debonding of FRP from RC members

During the last two decades, externally bonded uni-directional fiber-reinforced polymer (FRP) composites have been widely used for strengthening, repairing, and rehabilitation of reinforced concrete (RC) structural members. The bond characteristics contribute to the effectiveness of the stress transfer achieved between the FRP composite and the concrete substrate. Debonding of the FRP composite reinforcement is the most critical concern in this type of application. Under monotonic and fatigue loading conditions, FRP-concrete shear debonding has been idealized as a Mode-II fracture problem along the bi-material interface. A cohesive material law is used to describe the interfacial stress transfer at the macroscopic level. The area under the entire curve represents the fracture energy and is related to the load-carrying capacity of the interface. In this paper, previous experimental results and literature are discussed to show how the fracture energy can be considered a true fracture parameter. In addition, a simplistic one dimensional numerical analysis of the direct shear test is presented with the intent of pointing out the effect of the fracture parameters related to the cohesive material law on the load carrying capacity. The results are instrumental to discuss the strain limits provided in the ACI 440.2R-08 document.

Analyzing bond characteristics between composites and quasi-brittle substrates in the repair of bridges and other concrete structures

Abstract: During the last two decades, externally bonded fiber-reinforced polymer (FRP) composites have been widely used for strengthening, repairing, and rehabilitating reinforced concrete (RC) structural members. The bond characteristics contribute to the effectiveness of the stress transfer achieved between the FRP composite and the concrete substrate. Debonding of the FRP composite reinforcement is the most critical concern in this type of application. Under monotonic and fatigue-loading conditions, FRP–concrete shear debonding has been idealized as a Mode-II fracture problem along the bi-material interface. A cohesive material law is used to describe the interfacial stress transfer at the macroscopic level. The area under the entire curve represents the fracture energy, and is related to the load-carrying capacity of the interface. In this chapter, previous experimental results published by the author are discussed to show how the fracture energy can be considered a true fracture parameter. The results are instrumental in discussing the strain limits provided in international codes and guidelines. Future research needed and newly developed composites are introduced at the end of the chapter.

Debonding between FRP and Underlying Masonry: First Results of a 3D Finite Element Model

Experimental and numerical results show that the predominant failure mode of FRP strengthened masonry structures is the interfacial debonding, which occurs prior to reaching the compressive strength of the substrate and/or the tensile strength of the FRP composite. In this paper, a three-dimensional numerical model is developed to simulate the experimental response of direct shear test of FRP-masonry joints and. A damage model is adopted for both mortar and bricks characterized by a different behavior in tension and compression.