Papers by Keyword: Bond

Abstract: The ecological thinking and the development of new materials foreground the composite structures made of FRP (fiber reinforced polymers) and concrete. Before the use in real concrete structures, the material characteristics and composite action with concrete need numerical, analytical, and experimental evaluation. The key to developing the composite action of an FRP reinforcement in concrete is a sufficient bond between the reinforcement and concrete. The GFRP (Glass Fiber Reinforced Polymer) bars as the most common and affordable alternative to steel bars are used in this study to investigate the bond with concrete on the analytical model. The finite element model simulates the beam-bond test of GFRP and steel bars to concrete. The effect of bar diameter and type of reinforcement on the bond behavior are analyzed. Finally, the results obtained from the analytical model are compared with the experimental results from the literature.

Abstract: Masonry existing buildings are subjected to significant structural damages when seismic events occur. Over the last decades, innovative techniques like composite materials based on inorganic mortar (FRCM – Fiber Reinforced Cementitious Matrices) have emerged as attractive solutions for the strengthening of civil structures. FRCM shows better compatibility with masonry substrates with respect to Fiber Reinforced Polymers. The effectiveness of FRCM reinforcement systems relies on the composite-substrate bond behavior which is affected by many parameters, leading to different failure mechanisms. Although numerous studies investigate the FRCM-substrate bond, few attentions have been paid to the study of fiber grid-matrix interface behavior. In this study, the preliminary results of a wider experimental campaign aimed at investigating the interface behavior between fiber and mortar accounting for the contribution of transversal grid wires are presented. Different typologies of fiber and mortar were tested and the results are compared and discussed.

Abstract: The strengthening and retrofitting of existing masonry built heritage has become an increasingly important issue in the last decades. Among the innovative solutions developed by the construction industry, the application of externally bonded fabric-reinforced cementitious matrix (FRCM) composites attracted a great interest, proving to be an easy, effective, and cost-efficient strengthening/retrofitting technique. FRCM composites were shown to be particularly suitable for applications on masonry due to the good compatibility between the composite inorganic matrix and the masonry substrate, which also promotes their durability.A crucial point for the effectiveness of externally bonded FRCM is the bond within the composite strip and between the composite and substrate. Indeed, composite debonding is the commonly observed failure mode. In order to improve the bond with the substrate, connectors (anchors) can be used to improve the bond capacity of the FRCM composite.In this paper, the mechanical and bond properties of a glass fiber reinforced polymer (GFRP) anchor spike, designed for FRCM strengthening, are investigated. First, tensile tests are performed to determine the elastic modulus and tensile strength of the anchor. Then, the anchor-masonry bond behavior is experimentally investigated using pull-out tests. Three different masonry substrates, namely a solid clay brick masonry, a tuff block masonry, and a stone masonry were adopted in the pull-out tests. The results show the influence of the substrate type on the anchor-masonry bond capacity and failure mode observed.

Abstract: Fiber-reinforced cementitious matrix (FRCM) composites have been increasingly adopted as externally bonded reinforcement (EBR) of existing concrete and masonry members. Being debonding at the matrix-fiber interface one of the most frequent failure mechanisms of externally bonded FRCM, the matrix-fiber bond behavior represents a fundamental aspect for the effectiveness of the external reinforcement. A cohesive material law (CML) that describes the interface where debonding occurs can be used to model the bond behavior observed. In this paper, a rigid-trilinear CML is used to solve the differential equation that governs the bond problem at the matrix-fiber interface of an FRCM composite. The CML adopted has peculiar characteristics that entail for a finite length of the bond stress transfer zone (BSTZ). Furthermore, it allows for a simple and accurate analytical solution of the bond problem. The analytical solution obtained is compared with the results of an experimental campaign comprising single-lap direct shear tests of a polyparaphenylene benzobisoxazole (PBO) FRCM composite specifically designed for masonry substrates. Different calibrations of the rigid-trilinear CML are proposed, also considering the matrix-fiber free end slip.

Abstract: The paper proposes an approach to assessing the grinding wheel wear, which includes the wear of grains and pulling them out of the bond, based on fatigue failure under cyclic loads caused by cutting forces, with a period of the order of microseconds. This approach is implemented on the basis of stress life calculation in the ANSYS Fatigue module using loading data obtained from the numerical simulation of grain-workpiece interaction. The simulation results allows to obtain the grain wear area, the level of bond fatigue fracture and the possibility of self-sharpening of the grinding wheel for a given grain size and operation conditions.

Abstract: UHPC is a material which exhibits excellent mechanical properties and durability. Beside new structures it is also convenient for strengthening of existing structures. The paper investigates the possibilities of strengthening experimentally. A part of the experimental program is presented which is focused on bond of UHPC and existing concrete and on behaviour in bending. Acceptable bond may be achieved when the existing concrete is clean and reasonably rough. Structural elements are exposed to positive and negative bending moments. If UHPC overlay is applied, it works in compression and in tension. The experiments were therefore focused on verification of both alternatives (UHPC in compression and in tension). Finally, the conclusions from the experiments are drawn, which may be applied in practical design.

Abstract: This research studied the effect of eggshell powder as a partial replacement of cement on fresh and hardened properties of concrete. The cement was partially replaced with eggshell powder at these percentage 0%, 2.5 %, 5 %, 7.5% and 10%, (by weight of cement). The resulting concrete was compared for impact resistance, energy absorption, load-slip characteristics and ultimate bond strength. setting time (initial and final), slump, density and compressive strength also have been found. The obtaining results indicated the advantage of incorporation of eggshell powder in concrete. The concrete unit weight has not obviously affected by eggshell powder content. The 2.5% eggshell powder give the best results compared to reference mix.

Abstract: This paper compares the stress and strain behaviour of mechanical fasteners and elastic adhesive connections in timber façade applications. Two common designs with timber cladding are introduced. The traditional façade planks and multilayer large-format solid wood panels were selected. The resistance of a reference façade section with mechanical fasteners or adhesive bond to wind suction is determined according to the recommendations of European guideline ETAG 034. The pressure/suction chamber allowing hermetic closure was used. The sample deformation was measured at 15 locations, this also allowed to determine the elongation of the adhesive layer at break. The failure loads reached with the adhesive joint exceeded 20 kN/m² in both combinations of façade cladding. On the other hand, the sample with a large-format panel and mechanical fasteners showed the lowest failure load at 12 kN/m². The results confirmed that bonded joints are a suitable solution for large-format cladding, whereas an increase in the number of mechanical fasteners will be a more convenient solution for façade plank applications.

Abstract: The reinforcing steel embedded in concrete is generally protected against corrosion by the high alkalinity (pH = 12.5 to 13.5) of the concrete pore solution. The structural degradation of concrete structures due to reinforcement’s corrosion has an impact on the safety, serviceability and durability of the structure. The corrosion of reinforcements in the construction of a transport infrastructure (especially bridges), parking areas, etc., is primarily initiated by chlorides from de-icing salts. Glass fiber reinforcement polymer (GFRP) bars are suitable alternatives to steel bars in reinforced concrete applications. The bond between concrete and reinforcement is one of the basic requirements for the composite action of both materials. The transfer of forces between the steel reinforcement and the concrete is provided by the following mechanisms: adhesion, friction and mechanical interlocking. The bond between GFRP reinforcement and concrete is different and it is ensured by friction and mechanical interlocking of the rebar surface. The chemical bond does not originate between GFRP reinforcement and the surrounding concrete, so adhesion does not contribute to transfer of the bond forces. Some few test methods are used to determine the bond between GFRP reinforcement and concrete. The pull-out tests were used to determine the bond behavior between GFRP rebars and concrete. This paper describes the preparation, process, results and evaluation of the pull-out tests.

Abstract: In the present study, a series of pull-off tests is performed to determine the bonding properties of fiber reinforced polymer (FRP) composites applied to a brittle substrate. Pull-off test is simple, fast and cheap and it is generally employed to evaluate the bond strength between the composite and the substrate. It is a procedure that can be easily performed on-site for checking the quality of the reinforcement adhesion.A steel composite made of a unidirectional steel fabric embedded in an organic matrix (bi-component epoxy resin) was applied to the surface of fired-clay bricks. A shallow core perpendicular to the surface was realized in the test specimen, leaving the core attached to the brick. A steel dolly was glued to the external surface of the core using epoxy adhesive. A loading device was employed to apply the tensile force until failure. The effects of moisture presence on the substrate and shape of the cores on the pull-off strength were investigated.