Lesley Sneed

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.

Experimental Analysis of the Bond Behavior of Glass, Carbon, and Steel FRCM Composites

In recent decades, the construction industry has witnessed a rapid growth of interest in strengthening and retrofitting of existing reinforced concrete (RC) and masonry structures. Fiber reinforced polymer (FRP) composites have gained great popularity, and several studies are now available in the literature on their use in strengthening and retrofit applications. Promising newly-developed composite materials are represented by the so-called fiber reinforced cementitious matrix (FRCM) composites. FRCM composites are comprised of high strength fibers embedded within a cementitious matrix that is responsible for the stress transfer between the existing structure and the strengthening material. FRCM composites are still in their infancy, and very limited results are available in the literature on RC and masonry strengthening applications. This study presents an experimental campaign conducted on different FRCM composites comprised of glass, carbon, or steel fibers embedded within two different cementitious matrices and applied to concrete prisms. The single-lap direct-shear test was used to study the stress-transfer mechanism between the FRCM composite and the concrete substrate. Two different composite bonded lengths were investigated. Debonding occurred at the matrix-fiber interface for some of the composites tested and at the concrete-matrix interface for others. This work contributes to the study of the bond behavior of FRCM composites, which represents a key issue for the effectiveness of FRCM composite strengthening.

Torsional Repair of Severely Damaged Column Using Carbon Fiber-Reinforced Polymer

Although a limited number of studies have been conducted on the use of externally bonded composites for torsional retrofit or strengthening of reinforced concrete (RC) members, very few are available on torsional repair. This paper evaluates a method for repairing severely damaged RC columns subjected to torsional moment using externally bonded carbon fiber reinforced polymer (CFRP) composites. A half-scale RC column that was previously tested to failure under constant axial load and cyclic torsional moment was repaired with externally bonded CFRP using a rapid methodology. CFRP sheets with fibers oriented in both the transverse and longitudinal directions were applied to restore the strength and ductility of the damaged column to its original condition. This study demonstrates that this method can be used to restore the torsional performance of severely damaged RC columns. Contributions of the transverse and longitudinal CFRP sheets to the torsional resistance are evaluated, and repair design for torsional moment using this method is discussed.

Seismic repair of reinforced concrete bridge columns: review of research findings

AbstractRepair has become a viable option for restoring the use of earthquake-damaged RC elements, even those that have been severely damaged. To select and design an appropriate repair system for damaged RC bridge columns, it is important that results from previous studies are known. This paper presents a comprehensive summary and review of techniques to repair earthquake-damaged RC bridge columns, as well as numerical methods for analyzing the response of repaired columns. Repair of columns with and without fractured longitudinal reinforcing bars is discussed. Studies are reviewed in terms of the apparent damage, repair technique, and performance of the repair. Advantages and disadvantages associated with each repair technique are discussed.

An Evaluation of Anchorage Systems for Fiber-Reinforced Polymer (FRP) Laminates Bonded to Reinforced Concrete Elements

Many studies have shown that fiber-reinforced polymer (FRP) laminates are an effective alternative for structural retrofit and repair of insufficiently reinforced concrete members; however, achieving the full tensile capacity of the externally bonded FRP is often very difficult. This is especially true when FRP is used on elements where there is inadequate length to develop the full tensile strength of the FRP laminate, leading to premature debonding failure. Anchorage systems attempt to mechanically restrain the FRP or improve the FRP-to-concrete bond, thus reducing the length required to develop its full design strength. Many types of anchorage systems have been tested by different investigators, but mixed and inconclusive results have been presented. Additionally, no evidence exists to show that one particular type of anchorage system is completely effective in developing the full tensile strength of FRP. The lack of conclusive results is exacerbated by the absence of a consistent testing procedure for evaluating anchorage strength and a system for categorizing the purpose of the anchorage system, despite the current design guides recommendation that anchorage testing should precede the strengthening of a structure with FRP. An overview of previously tested anchorage systems is presented along with applicable testing procedures from existing literature. The limitations of each anchorage system are mentioned with respect to specific structural strengthening applications. The existing anchorages are then categorized according to their specific application to FRP anchorage, and the applicability of testing procedures to each anchorage category is discussed. Finally, the need for systematic testing is discussed and potential research topics are explored.

Three-Dimensional Numerical Modeling of Single-Lap Direct Shear Tests of FRCM-Concrete Joints Using a Cohesive Damaged Contact Approach

AbstractThe bond behavior of fiber-reinforced cementitious matrix (FRCM) composites applied as externally bonded reinforcement is the most critical concern in this type of application. FRCM–concret...

Experimental Investigation of Glass and Carbon FRCM Composite Materials Applied onto Concrete Supports

In recent decades the growing need for strengthening and retrofitting existing structures has led to the development of innovative strengthening materials. Fibre reinforced composites have been shown to be an effective strengthening solution for flexural and shear strengthening and for confinement of axially/eccentrically loaded elements. Fibre Reinforced Cementitious Matrix (FRCM) composites, comprised of high-strength fibres and an inorganic matrix, are a newly-developed type of composite that has better resistance to high temperature and compatibility with the substrate than traditional fibre reinforced polymer (FRP) composites. This paper investigates the behaviour of FRCM composites comprised of a glass or carbon fibre net tested using single-lap direct-shear tests. Observations regarding the load response and failure mode of FRCM-concrete joints with different geometrical and mechanical characteristics are provided.

Confinement of Clay Masonry Columns with SRG

In this study, the behavior of clay masonry columns confined by steel reinforced grout (SRG) composite with a natural hydraulic lime mortar is investigated. An experimental study was carried out to understand the behavior of masonry prisms with a square cross-section confined by SRG composite jackets subjected to a monotonic concentric compressive load. Test parameters considered in this study are the density of steel fibers and column corner radius. The effectiveness of the confinement is studied in terms of load-bearing capacity with respect to unconfined columns.

Manufacturing and evaluation of polyurethane composite structural insulated panels

Composite materials are increasingly used in applications of civil infrastructure and building materials. The new generations of two-part thermoset polyurethane resin systems are desirable materials for infrastructure applications. This is due to high impact resistance, superior mechanical properties, and reduced volatile organic compounds when compared to the conventionally used resin systems such as vinyl ester and polyester. Glass fiber-reinforced two-part polyurethane composites and low-density polyurethane foam are used to design and manufacture composite structural insulation panels using vacuum assisted resin transfer molding process for temporary housing applications. Using these types of composite panels in building construction will result in cost-efficient, high-performance products due to inherent advantages in design flexibility. Use of core-filled composite structures offers additional benefits such as high strength, stiffness, lower structural weight, ease of installation and structure replacement, and higher buckling resistance than the conventional panels. Energy efficiency is known to be inherently better with the core-filled composite panel than in a metallic material. The panels can be designed to resist the required loads, and the study aims to evaluate the ability of lab scale tests and models to predict part quality in full-scale parts. Furthermore, it discusses the manufacturing challenges. Flexural tests and energy consumption evaluations were performed on these structural components. Finite element simulation results were used to validate the flexural experiment findings.