Papers by Keyword: Bond Strength

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Authors: Sung Yong Choi, Young Hwan Park, Woo Tai Jung
Abstract: Fiber Reinforced Concrete (FRC) is a representative strengthening method adopted to improve the sudden brittle failure of concrete under tension and dynamic loadings and to control the generation and propagation of cracks occurring during the curing process. The strengthening performance provided by the fiber is sensitively influenced by the physical properties of the fiber itself as well as by its volume ratio but is also varying according to the difference in the bond performance at the interface between the fiber and concrete. Even if the fiber exhibits outstanding physical performance, if the bond performance does not reach similar level, the fiber will not be able to develop fully its performance. Currently, the methods improving the fiber bond performance are essentially focusing on the improvement of the mechanical bond performance by changing the longitudinal shape of the fiber such as the application of crimped and hooked fibers. A very few methods intend to improve the bond performance by increasing the bond area of the fiber itself. Therefore, this study increases the surface area of the fiber by changing its section while preserving its volume during the fabrication process, conducts tests on the bond performance between the cement paste and the fiber with changed surface area, and examines the changes in the bond performance according to the increase of the surface area.
1440
Authors: Wen Jun Qu, Kun Wang, Yan Xiong
Abstract: During the electrochemical realkalisation treatment for carbonated concrete, the bond strength between rebar and concrete was changed duo to the physical and chemical action. The pull-out test was used to study the effect of current density on the bond strength between rebar and concrete. The realkalisated products of the concrete were studied using X-ray diffraction (XRD). Test results show that after electrochemical realkalisation treatment (ERT), the bond strength of reinforced concrete increases; The current density has the significant effect on the bond strength; The amount of sodium silicate of the concrete is changed after ERT, Due to the increment of the sodium silicate that can increase the bond strength between the concrete and the rebar, it makes for the increase of the bond strength.
1185
Authors: Sandro Botas, Rosário Veiga, Ana Luísa Velosa
Abstract: This article deals with some of preliminary tests to study the adherence mechanism of lime mortars to late XIXth Century tiles. The bond between them is mainly physical. A water absorption by capillary test and a suction test were performed to study the parameters of mortar penetration in tiles porosity. The old tiles seem to have a higher porosity than new ones. Some of the new specimens can be used to simulate the old tiles in future tests without applying partially destructive tests to historical objects.
403
Authors: Myung Hyun Lee, Won Seon Seo, Jong Ho Kang, H.Y. Choi, Y.K. Kim, H.B. Yim, Kyung Sik Oh, Deuk Yong Lee, J.Y. Choi, Nam Sik Oh
Abstract: Adhesion characteristics of base-coated single crystal brackets for orthodontics were investigated to evaluate the feasibility for the ceramic bracket applications. Sapphire single crystal ingot were machined, abraded and spray-coated with slurries containing 50 wt% of flux and 40µm, 80µm and 150µm of granules. Maximum adhesion to the base surface of the brackets was observed when the size of granule in the slurries was 80µm. It may be due to higher bonding area of adhesive to granule and to base as a result of interlocking structure which has moderate thickness and uniform distribution of granules. The one-way analysis of variance indicated that there were not significant differences in bond strength measurements between the once and twice coating condition in 80µm and 150µm granule groups. But ARI values exhibited large differences between once and twice coating groups and showed different median or ranges. Adhesive remnant of adhesive resin was minimized when the slurry of 80µm granule was coated once. Reduction in adhesive remnant is likely due to the higher bonding of adhesive resin to granules. No teeth and bracket damages were found in any teeth de-bonded by shear force. The base-coated brackets with higher strength (12.9 MPa) and no adhesive remnant were newly proposed for the orthodontics applications.
137
Authors: Jee Sang Kim, Jong Ho Park
Abstract: Researches on Ultra High Performance Concrete (UHPC) have been conducted worldwide owing to its outstanding durability and strength performances compared to normal concrete. This paper experimentally investigates the bond properties of reinforcements embedded in UHPC using direct pull-out tests. The specimens were prepared for various compressive strength levels of 120, 150, and 180MPa, diameters of reinforcements of 13, 16, 19, 22 and 25mm, cover to bar diameter ratios and bonded lengths. The influences of each test variable on bond properties are examined and may be a useful data for design and analysis of UHPC structures.
323
Authors: Jee Sang Kim, Sang Hyun Lee, Jung Wook Choi
Abstract: Epoxy coated reinforcements have been used extensively in bridge decks and substructures to protect against corrosion brought on by de-icing salts or marine environments. They need longer development lengths because of poor bond to concrete and special treatments on sites due to vulnerability of damage during transportation, storage and bending process. A new method of pre-heating of reinforcement before coating process using an IGBT(Insulated Gate Bipolar Transistor) control was applied to improve the bond of epoxy coating to reinforcements. In this paper, the bond-slip properties of newly developed epoxy coated bars are investigated and compared to those of black bars. The direct pull out test according to EN Standard was used with varying the diameters of reinforcements. The experimental results show that the new process is very efficient in increasing bond capacity of epoxy coated bars to concrete comparing those of traditional ones.
241
Authors: Jee Sang Kim, Jongho Park
Abstract: Geopolymer concrete is an emerging construction material that uses a by-product material such as fly ash to completely replace the ordinary Portland cement. This material is being studied extensively and shows promise as a greener substitute for ordinary Portland cement. This paper evaluates the bond strength and development length of reinforcements embedded in geopolymer concrete with reinforcing steel using pull-out tests. The test according to EN 10080 was carried out on 27 specimens for three kinds of geopolymer concrete of 20, 30 and 40 MPa compressive strength and 10, 16 and 35 mm diameter reinforcing bars. The tests show that the bond strengths in geopolymer concrete were decreased as the diameter of reinforcement increased as in ordinary concrete and the values were greater than those in ordinary concrete. Also, the bond-slip curves were obtained which have similar shape with those of ordinary concrete. The equation for the determination of development length based on this experiment was proposed.
441
Authors: Seung Jo Lee, Jung Min Park
Abstract: This paper deals with structural behavior of highly intelligent reinforced concrete (hereinafter, HIRC) beams actuated by embedded shape memory alloy wires through an extensive experimental program. The experiments were conducted under the monotonic loading condition. Based on the structural experiments involving HIRC, load-temperature deflection curve, ductility-effective depth, recovery, crack patterns, and failure mode comparison were made for investigative purposes. The results of the experiments confirmed that the ductility, recovery rates, and other properties of the HIRC specimens reinforced with SMA, wire mesh, fiber, and admixtures were superior to those of the unreinforced RCBs. The experimental results indicate that a good recovery rate in the HIRC beams could be obtained when the SMA wires were heated. Accordingly, the SMA wires could be potentially used for structural self-rehabilitation capability and deformation monitoring in architecture and civil structures.
423
Authors: Bo Liu, Li Huang, Dong Yang Li
Abstract: Based on the local deformation theory, we study the mechanics behavior of anchorage interface of full-length bonded rock bolt by using a mathematics model (tri-linear model). With pull-out load increasing, the changing process of anchorage interface of full-length bonded bolt is divided into three stages in this paper: elastic stage, plastic softening stage and crack slipping stage. It is found that in the state of elastic, axis force decreases rapidly with bolt depth increasing, and when pull-out load is greater than elastic ultimate load, attenuation degree will slow for the occurring of interface plastic softening and crack slipping in the top of bolt. The result indicates that the continuous change of axis force with bolt depth reflects that the bolt interface bond strength changes with the increase of pulling load.
3254
Authors: Jaya Nepal, Hua Peng Chen, Amir M. Alan
Abstract: The bond between concrete and steel is the critical element of reinforced concrete (RC) structures, which directly affects their load carrying capacity and serviceability. Hence the evaluation of bond strength degradation is an essential parameter to predict the residual strength of RC structures affected by reinforcement corrosion. Existing research studies in this field mainly focus on numerical and experimental investigations. Few attempts have been made using analytical approach but there is still a need of reliable model which considers the critical mechanical factors affecting the bond strength of corroded RC structures. This paper presents a simple and realistic analytical model of bond strength degradation by using fracture mechanics combining the action of adhesion, confining pressure and corrosion pressure at steel concrete interface. Finally, the results obtained from the proposed model are examined with published experimental data. The study demonstrates that the proposed analytical model agrees with the experimental data of existing investigations.
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