The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Jianhe Xie - One of the best experts on this subject based on the ideXlab platform.
-
Experimental study on rehabilitation of corrosion-damaged reinforced Concrete beams with carbon fiber reinforced polymer
Construction and Building Materials, 2013Co-Authors: Jianhe XieAbstract:Abstract The repair and rehabilitation of reinforced Concrete (RC) structures in coastal areas is a challenging engineering problem. In order to retrofit the degraded RC structures, numerous studies have been devoted to the method of non-corroded RC components retrofitted with carbon fiber reinforced polymer (CFRP). There is, however, less research available on corroded, patched and CFRP-repaired RC specimens. The purpose of this paper is to investigate rehabilitation of corrosion-damaged RC beams with CFRP, which focus on the effectiveness of CFRP-repaired methods and the effects of CFRP amount on flexural behavior of the beams. In this study, a modified retrofit method based on Substrate repairs was developed, which is bonding CFRP after replacing V-notch of Substrate Concrete with polymer mortar. To compare the modified method with two common retrofit methods, which are respectively bonding directly CFRP and bonding CFRP after replacing damaged Concrete, four-point bending experiments were conducted on a series of corrosion-damaged RC beams with CFRP. Important factors were considered in the experimental study, including the number of CFRP layers and corrosion level denoted by the mass loss rate of tensile steel. There were totally 32 RC beams (250 mm × 150 mm × 1400 mm) constructed in these experiments, 27 of which were corroded by an accelerated aging approach. The results show that the modified retrofit method could provide better load carrying capacity for the beams having more than 15% mass loss of tensile steel. In addition, to improve the short-term performance, the simple method of directly bonding CFRP was suitable for the beams having less than 15% mass loss of tensile steel. It is noted that bonded CFRP could not work for the damaged beams which undertaken more than 50% mass loss of tensile steel. In particular, it is indicated that by optimizing the amount of CFRP, it is possible to balance strength recovery with control of failure mode.
Reza Kohani Khoshkbijari - One of the best experts on this subject based on the ideXlab platform.
-
determination and prediction of bonding strength of polymer modified Concrete pmc as the repair overlay on the conventional Concrete Substrate
Ksce Journal of Civil Engineering, 2019Co-Authors: Ali Sadrmomtazi, Reza Kohani KhoshkbijariAbstract:In order to achieve a durable repair overlay, high bonding strength to Substrate Concrete and having the least amount of cracks in overlay are the main issues. Polymer Modified Concrete (PMC) consists of Portland cement Concrete with a polymer modifier. Its advantages are proper bonding strength to Substrate Concrete, high tensile and flexural strength and low amount of shrinkage and permeability which makes it a suitable material for repair overlays. In this paper, 24 mix designs of polymer modified Concrete as the repair overlay containing two different types of modifier polymers (Styrene Butadiene Resin (SBR)-based and Acrylic-based polymers) with different replacement percentages and various amounts of silica fume was considered to investigate the effect of type and amount of polymers and also properties of the mentioned overlays on their bonding strength to the Substrate Concrete. Two different methods for bonding assessment had been used and compared with each other. In both polymer modifiers, maximum bonding occurred in presence of polymer with 20% of cement weight. SBR-based PMC showed stronger bonding than other type of modified Concrete. According to the results, with aid of linear regression analysis and Fuzzy Logic method the bonding strengths are predicted with acceptable accuracy.
-
An Investigation on In-situ Strength and Bonding Strength of Polymer Modified Concretes (PMC) as Repair Overlays on Conventional Concrete Substrate
Journal of Rehabilitation in Civil Engineering, 2017Co-Authors: Ali Sadrmomtazi, Reza Kohani KhoshkbijariAbstract:Polymer modified Concrete (PMC) consists of Portland cement Concrete with a polymer modifier. Its advantages are proper bonding strength to Substrate Concrete, high tensile and flexural strength and low amount of shrinkage and permeability. Using PMC overlays can be considered as a method for preservation of damaged Concrete structures due to their suitable performance and durability. In this research, 24 mix designs of polymer modified Concrete as the repair overlay containing two different types of modifier polymers (Styrene butadiene rubber (SBR)-based and Acrylic-based polymers) with different replacement percentages and various amounts of silica fume was considered to investigate the effect of type and amount of polymers and also presence of silica fume. The in-situ strengths are obtained by the Pull-off Method in different conditions of presence of cores and without cores on cubic samples and without cores on repair overlays. The bonding strength of repair overlays to the Substrate is also assessed and a formula is presented for prediction of bonding strength and in-situ strength by consideration mechanical properties.In both polymer modifiers, maximum bonding occurred in the presence of polymer with 20% of cement weight. SBR-based PMC showed stronger bonding compared to the Acrylic-based PMC.
Atorod Azizinamini - One of the best experts on this subject based on the ideXlab platform.
-
Chloride Penetration at Cold Joints of Structural Members with Dissimilar Concrete Incorporating UHPC
MDPI AG, 2019Co-Authors: Mahsa Farzad, Saiada Fuadi Fancy, Kingsley Lau, Atorod AzizinaminiAbstract:Ultra-high-performance Concrete (UHPC) has been introduced for reinforced Concrete structures due to its enhanced mechanical performance, including high compressive strength and tensile capacity. In certain applications, such as closure joints, connections, and Concrete repairs, reinforcing steel may be embedded in dissimilar Concrete elements partially incorporating UHPC. Superficially, UHPC can be considered to provide enhanced corrosion durability in marine environments due to its low permeability which would mitigate chloride-induced corrosion of rebar in the bulk material. However, the chloride intrusion through cold joints can be faster than that in bulk Concrete and may jeopardize the durability of structures. This research examines the possibility of enhanced chloride transport at the cold joint incorporating UHPC. The effectiveness of the bond on chloride penetration at the Concrete interface with various levels of moisture availability for the Substrate at the time of UHPC repair was examined. To this effect, the Substrate Concrete was conditioned to different moisture content including 0%, 75%, and 100% relative humidity, and soaked prior to UHPC repair Concrete casting. Chloride penetration was accelerated by an impressed current source and assessed by silver nitrate solution sprayed on the cold joint. Moreover, the tensile bond strength between Substrate Concrete and UHPC was measured using the splitting tensile test
-
Experimental and numerical study on bond strength between conventional Concrete and Ultra High-Performance Concrete (UHPC)
Engineering Structures, 2019Co-Authors: Mahsa Farzad, Mohamadreza Shafieifar, Atorod AzizinaminiAbstract:Abstract Ultra High-Performance Concrete (UHPC) has made progress in the bridge and building industry owing to its high strength, ductility, and durability. UHPC is a relatively expensive material and is mostly used in conjunction with conventional Concrete. Such composite structures should be designed considering the interaction of different Concrete layers. Generally, the simplest interaction model to simulate the complex behavior at the interface is ‘tie’ model, but simulation results may lead to an overestimation of load capacity. This study investigates a more realistic numerical approach comparing to tie interaction model, and its capability to predict the load capacity of structures where Substrate Concrete is joined to or repaired with an overlay Concrete. This modeling technique uses an interface plane between the Concrete layers. By calibrating the interface properties, designers can make a reliable prediction about the behavior of the composite structures. The numerical concept is evaluated when UHPC is employed as an overlay and normal strength Concrete as Substrate section. First, an experimental test program is performed on a series of composite specimens to characterize the bond performance between conventional Concrete layers as well as regular Concrete and UHPC. To validate the model, third-point loading beam, direct shear, and slant shear tests were performed. The numerical model is then used to evaluate the mechanism of force transfer at the interface between two materials. The results indicate that employing this modeling approach has the capability to provide a better estimation of the failure loads when compared to the tied model.
Chengwu Yang - One of the best experts on this subject based on the ideXlab platform.
-
bond performance between Substrate Concrete and repair mortar effect of carbon fibre and expansive agent
Construction and Building Materials, 2020Co-Authors: Shuo Feng, Huigang Xiao, Rongling Zhang, Chengwu YangAbstract:Abstract This study aims to investigate the impact of an expansive agent and carbon fibre in repair mortar (overlay) on the bond strength at different water-to-binder ratios (w/b). Measurements of the flexural and compressive strengths, drying shrinkage, and mercury intrusion porosimetry (MIP) were used to evaluate the properties of the overlays, and the compressive strength, drying shrinkage, and splitting tensile strength were adopted to evaluate the properties of Substrate. The exposure surface after splitting a cube into two halves was used as repair surface of Substrate. The bond strength was evaluated by a splitting tensile test, and backscattered electron images were acquired to observe micro-cracks of the repair bond. The experimental results indicated that the drying shrinkage of the repair mortar was reduced by the carbon fibre and expansive agent. The total porosity of the repair mortar was increased and the compressive strength was decreased by the expansive agent. Interface failure accompanied by partial Substrate failure and repair mortar failure accounted for 85.7% of bond failures. The incorporation of the expansive agent and carbon fibre in the repair mortar resulted in growth rates of 25.18% and 33.56%, respectively, for the splitting tensile bond strength at w/b of 0.30. This enhancement decreased as the w/b decreased. The repair effectiveness improved as the compressive strength ratio (repair mortar/Substrate Concrete) increased with a certain range (no more than 1.45). Therefore, the expansive agent and carbon fibre have the potential to improve the bond strength when the strengths of the Substrate and of the repair material are equivalent and the repair bond under splitting tensile stress.
Fin O'flaherty - One of the best experts on this subject based on the ideXlab platform.
-
Serviceability characteristics of flowing repairs to propped and unpropped bridge structures
Materials and Structures, 1999Co-Authors: Pal Mangat, Fin O'flahertyAbstract:The paper presents the results of a field investigation of repairs to Sutherland Street Bridge on B6080 in Sheffield, England. Flowing repair materials were used to apply large patch repairs to propped and unpropped columns of the bridge. Watertight shuttering was securely attached to the structure and flowing repair materials were either pumped or poured into the shuttering. The elastic modulus of the repair materials (Erm) used was greater than that of the Substrate Concrete (Esub).
-
Long-term performance of high-stiffness repairs in highway structures
Magazine of Concrete Research, 1999Co-Authors: Pal Mangat, Fin O'flahertyAbstract:This paper presents the results of field monitoring of repair patches in two reinforced Concrete highway bridges, Lawns Lane Bridge on the MI and Gunthorpe Bridge across the River Trent. The repairs were applied by spraying (guniting) repair materials to compression members of the bridges. The structural members were unpropped during repair and throughout the 60 week monitoring period. The strains in the repair patches were monitored with vibrating-wire gauges. Four different repair materials were investigated whose elastic modulus was greater than that of the Substrate Concrete (Erm > Esub). The results show that efficient repairs are achieved with Erm > Esub, the optimum relationship being Erm > 1·3Esub. This enables the repair material to shed a significant proportion of its shrinkage strain to the Substrate, thereby reducing restrained-shrinkage tension. It also enables the repair to attract externally applied load from the Substrate in the long term. The effect of creep and shrinkage on the performan...
