Tommaso D’Antino

Investigation of Bond Behavior of PBO Fiber-Reinforced Cementitious Matrix Composite-Concrete Interface

This paper presents the results of an experimental study conducted to understand the behavior and stress-transfer mechanism of fiber-reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net embedded within two layers of polymer-modified cement-based mortar. Single-lap shear tests were conducted on specimens with composite strips bonded to concrete prisms. Parameters that varied were bonded length and width of composite. Additionally, the external coating layer of matrix was omitted on a limited number of specimens to examine the interfacial behavior between fibers and matrix and the role of the matrix in the stress transfer. Strain measurements along the composite bonded length were used to investigate the stress-transfer mechanism. Results suggest that the effective bond length of this composite is within the range of 250 to 330 mm (10 to 13 in.). Unlike with fiber-reinforced polymer (FRP) composites, no width effect was observed in terms of the maximum load. Finally, the stress-transfer mechanism at the matrix-fiber interfaces on either side of the fiber net was found to be unequal.

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.

Fiber Reinforced Composites with Cementitious (Inorganic) Matrix

Fibre reinforced composite systems are increasingly used in civil engineering infrastructure applications for strengthening and rehabilitation of reinforced concrete (RC) structures. Composite materials represent a sustainable alternative to new construction because they allow for an extension of the original service life and therefore prevent demolition of existing structures. Promising newly-developed types of matrix that potentially represent a valid, sustainable, and durable alternative to epoxy, employed in fibre-reinforced polymer (FRP) composites, are the so-called inorganic matrices. Within the broad category of inorganic matrices, cement-based mortars have raised some interest in recent years. This chapter intends to highlight the potentials of this new category of fibre-reinforced composites as a viable alternative to traditional FRP systems. The latest advancements in this field and the new challenges that researchers will face in the future are presented and discussed.

Bond Between EBR FRP and Concrete

This chapter provides an overview of the debonding process between the FRP reinforcement and the concrete substrate. The main aspects of the debonding phenomenon are described and discussed, showing also mechanical interpretation of different processes. Experimental techniques to study the bond behavior between FRP and concrete are also described and corresponding available experimental results are shown to compare performances of different set-ups. Finally, an extensive description of the existing bond capacity predicting models is reported, together with the main international Codes provisions, allowing the designer for operating in common practice.

Performance of Different Types of FRCM Composites Applied to a Concrete Substrate

This research aimed to investigate the performance of fiber reinforced cementitious matrix (FRCM) composites employed as externally applied strengthening system for reinforced concrete members. The results of an experimental campaign conducted on FRCM composites applied to a concrete substrate are shown and discussed. The composites were comprised of different types of fibers, namely carbon, glass, steel, and basalt fibers, and different types of cementitious matrix. Single-lap direct-shear tests were performed to study the behavior of the different composites. Specimens with different bonded lengths were tested to investigate the stress-transfer mechanism and to investigate the existence of an effective bond length. Comparisons between the peak loads obtained with the direct-shear tests and the tensile strength of the fibers, which provide an indication of the exploitation of the fibers, were carried out.

Confinement of RC Elements by Means of EBR FRP Systems

This chapter reviews the issues of confinement in plain and reinforced concrete under concentric compression and summarizes the state of the art regarding the available confinement models for strength and stress-strain behaviour of encased confined concrete, and the corresponding magnitude of dependable strain capacity. The mechanisms of confinement failure, the evolution of Poissons’ effects under low and high confinement, and the ensuing material compaction at high confining pressures (plastification) are discussed. The effects of stress concentrations near corners, the effectiveness of layers and influence of adhesive, other scale effects and the influence of specimen morphology on mechanical behaviour are also outlined. Next, the chapter concentrates on the effects of embedded reinforcement both longitudinal and transverse. Confinement effectiveness in the presence of combined flexure and shear (in plastic hinge regions), local effects due to rotation capacity increase, and effects of FRP confinement on overall member behaviour are discussed. Shape effects that occur in hollow or oblong sections are also considered. Furthermore, the chapter gives an outline regarding the characteristics of the international database of tests for confinement, and its calibration with the database of the available confinement models including those included in the design standards (ACI, CNR and EC8-III).

Shear Strengthening of RC Elements by Means of EBR FRP Systems

In this chapter, a thorough review of some typical models adopted to represent the effect of EBR FRP systems on the shear capacity of RC elements is carried out, by comparing their advantages, their accuracy and also by highlighting their possible weaknesses. Then, more light is shed upon the so-called “variable angle strut model”, commonly adopted in RC structures, but whose application in the FRP field raises some concerns. Along the same line, the formulations provided by current Codes for the evaluation of the shear capacity of FRP-RC elements are widely discussed and proved to overestimate the actual shear capacity. Having assessed some of the shortcomings of such models, an alternative approach is proposed. The final outcome is a revised model for EBR FRP shear-strengthening that accounts for the actual contribution of steel stirrups and FRP strips/sheets to the shear capacity, while at the same time checking the stress in concrete.