•Available detection techniques for steel corrosion degree or damage are provided.•Passive “prevention solutions” and active “therapy solutions” are offered to alleviate corrosion.•Joint ...implementation of structural strengthening and corrosion protection is promising.
Performance deterioration of existing reinforced concrete (RC) structures due to corrosion of inside steel reinforcement has been a worldwide issue for long, in particular for RC structures in aggressive environments. Although extensive research on steel corrosion has been carried out over past decades, it is still a challenging problem in civil engineering. Starting from a brief introduction on corrosion mechanism of steel in concrete, this paper presents a comprehensive review on corrosion detection techniques and protection methods for existing RC structures where corrosion has already occurred. Direct detection methods based on electrochemical and physical principles related to the steel corrosion process, and indirect methods based on measurement of corrosion-induced damages in reinforced concrete are critically reviewed, with the basic working mechanism and state of the art of each method given. According to protecting mechanism, corrosion protection methods are categorized into “prevention solutions” and “therapy solutions”, with the former including high-performance fiber-reinforced cementitious composite (HPFRCC) overlay, anti-corrosion coating and corrosion inhibitor while the latter including cathodic protection (CP) and electrochemical chloride extraction (ECE). Among them, HPFRCC overlay is regarded as effective in corrosion prevention due to its high durability although it is mainly used for strengthening because of its excellent mechanical properties, while carbon fiber reinforced polymer (CFRP) can be acted as both strengthening material and anode in CP and ECE. The dual functions of these materials make them very promising in protecting corrosion-damaged RC structures. The paper aims to not only provide useful information to researchers working on detection and protection of steel corrosion, but also shed lights on the advanced strengthening strategies for corrosion-damaged structures.
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•A novel green corrosion inhibitor was prepared from the waste PAL.•The PAL extract was conformed as an efficient mixed type corrosion inhibitor.•QM/MD simulations based on UPLC-MS ...supported the donor–acceptor adsorption and inhibition mechanism for PAL extract.•XPS provided the formation evidence of the carbonaceous/nitrogenous film on steel surface.
In this study, an environmentally friendly corrosion inhibitor was prepared from waste Platanus acerifolia leaves (PAL) for reducing the chloride-induced reinforcement corrosion. Four extraction methods were employed in the preparation work. The inhibiting performances of the four types of PAL extracts and two benchmark inhibitors were studied by various electrochemical measures. After that, the optimal group was obtained (extract #4, prepared by an ultrasonic-assisted alkali-pretreated ethyl extraction method) and analyzed with ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) to determine its main chemical constituents. The inhibition/adsorption mechanism was analyzed via X-ray photoelectron spectroscopy (XPS) as well as the quantum mechanics and molecular dynamics simulations. According to the results of electrochemical experiments, the PAL extract is an excellent mixed type inhibitor that restrains both the cathodic and anodic reactions. UPLC-MS results provided the existence evidence of more than ten kinds of flavonoids or oligopeptides in the PAL extract. XPS and simulation results indicated that these flavonoids/oligopeptides exerted their inhibition effect by generating a nitrogen-carbon film on the steel substrate via the donor–acceptor interactions of reactive sites.
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To examine the effects of elevated temperature on recycled aggregate concrete as well as recycled aggregate
concrete beams made using new and reused steel reinforcement, four concrete mixes with ...different recycled aggregate
replacement ratios (0%, 25%, 50%, 75%) and two types of steel reinforcement (new steel and reused steel reinforcement)
were used to cast the beams. Twenty- four cubes and twenty-four beams were tested using a compressive strength test and
four-point load test, half of them made with new steel reinforcement and the other half using reused-steel steel reinforcement.
Twenty-two beams were subjected to an elevated temperature of (400) °C for (3) hours, while two beams were kept as control
beams. While half of the cubes were subjected to an elevated temperature of (400) °C for (3) hours and the others were tested
at normal room temperature. It was observed that replacing natural aggregate with recycled aggregate by (25%, 50% &75%)
decreased the compressive strength by (8.04%, 16.39%, and 27.9%) respectively without being subjected to elevated
temperature and by (4.07%, 20.36%, and 33.31%) respectively after been subjected to elevated temperature. New steel
reinforcement beams made of (25%, 50%, and 75%) recycled aggregate had lower ultimate strength by (3.75%, 10.12%, and
27.08%) respectively compared to fully natural aggregate new steel reinforcing beams all subjected to elevated temperature.
On the other hand, reused-steel reinforcement beams had lower ultimate strength by (14.25%, 34.76%, and 40.89%)
respectively compared to natural aggregate reused-steel reinforcing beams all subjected to elevated temperature
Past earthquakes revealed that the brittle nature of unreinforced masonry (URM) structural walls often leads to extensive cacking and shear damage, which can seriously affect the structural integrity ...and thus compromise the safety of the entire building. Hence, finding an effective seismic retrofitting solution that can increase the safety of existing masonry building stock is of great importance. This paper explores the potential of alternative seismic retrofitting solutions for URM masonry walls - near-surface mounted austenitic stainless-steel helical bars. Being cold rolled from a plain round wire and subsequently tensioned through a free-twisting process, such a reinforcement can not only offer high durability, but also superior mechanical and bond properties, as well as effective redistribution of loads through the retrofitted masonry. In addition, the relatively high flexibility of the bars allows them to be mounted continuously along the joints of the wall, leaving the aesthetic of the retrofitted masonry intact. A total of nine single-leaf clay brick walls were tested under cyclic displacement reversals to examine the seismic performance of the reinforcement in terms of increasing in-plane shear capacity and ductility. Test specimens comprised cantilever walls with various retrofitting patterns, including flexural and shear helical reinforcements installed in the mortar joints or into the vertical slots cut into the masonry. The results showed considerable improvements in the ductility and energy dissipation of the walls after the retrofitting. For most of the retrofitted walls the value of q factors exceeded 4.0, which is greater than the typical q factors for reinforced masonry, thus indicating that large increases in ductility were achieved. The paper highlights the potential of helical stainless-steel bars as a seismic retrofitting reinforcement capable of preserving the structural integrity of masonry structures at increasing displacement demands without affecting the aesthetic of the surface of the walls.
•Helical reinforcement for URM offered desirable balance between flexibility, strength, and bond.•URM walls retrofitted with helical bars showed improved ductility and energy dissipation.•Novel retrofitting patterns utilising “wiggled” vertical bars were investigated.•Retrofitting with helical bars allows for preserving natural aesthetics of masonry.
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In a quest to ensure sustainability of the future generation, various research attempts are focusing on the use of alternative materials for construction. In this study, bamboo strips were used as ...reinforcement in a concrete that was made with supplementary cementitious materials and partial replacement of river sand with manufactured sand (m-sand). Cement was partially replaced by 25% of combination of admixtures such as fly ash and Ground Granulated Blast Furnace Slag (GGBS). In alignment with standard requirements, concrete samples such as cubes, cylinders and beams were produced and tested at stipulated periods. Micro scale analysis was performed on the bamboo using SEM and FTIR, and its tensile strength was also determined. The results of the micro scale and tensile strength tests revealed that bamboo is a strong and ductile material. The study showed that a combination of fly ash, GGBS and m-sand used as alternative materials in concrete improves the compressive and split tensile strengths. Under flexural loading, performance of bamboo reinforced concrete (BRC) made with alternative materials (fly ash, GGBS, and m-sand) was significantly low compared to BRC containing conventional materials. In addition, BRC made with conventional materials developed more flexural strength than the SRC, with a variation representing 6.5% strength gain.
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We present a uniaxial phenomenological model to accurately predict the complex hysteretic behavior of bolted steel reinforced elastomeric bearings and unbonded fiber reinforced elastomeric bearings. ...The proposed model is based on a set of only five parameters, directly associated with the graphical properties of the hysteresis loop, leads to the solution of an algebraic equation for the evaluation of the isolator restoring force, requires only one history variable, and can be easily implemented in a computer program. The proposed model is validated by means of experimental tests and numerical simulations. In particular, the results predicted analytically are compared with some experimental results selected from the literature. Furthermore, numerical accuracy and computational efficiency of the model are assessed by performing nonlinear time history analyses on a single degree of freedom mechanical system and comparing the results with those associated with a modified version of the celebrated Bouc-Wen model.
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•Reinforcement approaches for digital construction are summarised.•3D-printing of steel reinforcement based on gas-metal arc welding is described.•3D-printed steel bars’ mechanical performance is ...shown to be similar to that of conventional bars.•Printed steel bars’ failure is shown to be ductile, on both the micro- and macro-levels.•Printed steel bars’ bond to printable, fine-grained concrete is shown to be satisfactory.
Digital concrete construction has recently become the subject of very rapidly growing research activities all over the world. Various technologies involving 3D-printing with concrete have been developed, and the number of demonstration projects and practical applications has been increasing exponentially. Most of these approaches are focused on the placement of concrete, while the suggested solutions for incorporation of reinforcement are still rudimentary, and as such they lag behind the concepts for printing concrete. Since the use of (steel) reinforcement is mandatory in most structural applications, there is an urgent need to bring the technology of reinforcing 3D-printed structural elements forward. The article starts with a brief overview of the existing approaches in using reinforcement in digital concrete construction. Then the authors’ own research work is presented, namely a feasibility study on 3D-printing of steel reinforcement using gas-metal arc welding. A description of the newly developed 3D-printing process is followed by a demonstration of its feasibility in producing vertical steel reinforcement bars with and without extra ribs. The mechanical performance of the printed bars was investigated by means of uniaxial tension tests. The samples exhibited comparable mechanical properties to common steel reinforcement of the same diameter. The investigation of fracture surfaces confirmed a ductile mode of failure of the printed steel bars. Finally, the bond between printed steel bars and printable fine-grained concrete was tested by means of pull-out experiments. Here the overall performance could be rated as satisfactory, even though it could be improved by introducing extra ribs in the process of bar manufacturing.
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This paper describes a study of the corrosion behavior of Cr-modified steel reinforcement exposed at marine splash zone for a period of two years. The corrosion behavior was analyzed by the weight ...loss method, optical and electron microscopy, and X-ray photoelectron spectroscopy. The Cr-modified reinforcement exhibited high corrosion resistance in the actual marine environment. The protection mechanism of the Cr-modified reinforcement at the corrosion propagation stage was that Cr improved the protective quality and buffering ability of the rust layer against aggressive species, by increasing the Fe2+ and OH− content within the iron oxides and improving the compact degree of the rust layer.
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Sufficient bonding between Strain-Hardening Cementitious Composites (SHCC) and steel rebars is required to guarantee the stress transfer in structural applications. Although the bond between ...medium-strength SHCC and rebars has been extensively studied, the present understanding of this property for high-strength SHCC is very limited. Moreover, the previous pullout or bending test methods have some limitations. This study investigates the bond between deformed steel rebars and high-strength SHCC with a new direct tension approach, which is able to determine the fundamental interfacial stress versus displacement relation under pure tension. The effects of concrete block material and cover thickness, rebar diameter and embedment length, as well as confinement condition on the bond behavior were experimentally evaluated. The test results showed that high-strength SHCC can bond much better with deformed steel rebars than ordinary concrete and high-strength SHCC matrix (without fibers) due to the well-controlled splitting cracks, and that the geometry has certain influences on the bond strength. A simple but reasonably accurate finite element model for engineering applications was also proposed to analyze the bond behavior in structural components. In this model, all the non-linear behaviors were integrated into rebar/SHCC interfacial elements, so that the complicated steel surface geometry and/or the local splitting of concrete do not need to be explicitly modelled. Through a coupled experimental-numerical approach, the bond stress-displacement relationship was extracted from a small number of test results. The derived relationship was then employed for the prediction of additional test results, with good agreement achieved. With its general applicability demonstrated, the proposed numerical approach can facilitate the design of reinforced SHCC elements and structures.
•A new direct tension method was used to study the rebar/SHCC bond properties.•The effects of cover material and thickness, rebar diameter and embedment length, and confinement condition were evaluated.•A coupled experimental-numerical approach to extract the bond stress-displacement relationship from a few test results was proposed.•Integrating all non-linear behaviors into rebar/SHCC interfacial elements was proposed and found effective in numerical modeling.•SHCC can bond much better with deformed steel rebars than ordinary concrete and SHCC matrix (without fibers).
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•Presenting the tensile test results of naturally corroded steel bars.•Presenting the tensile test results of artificially corroded A706 deformed steel bars.•Examining the differences in the tensile ...behaviors between naturally and artificially corroded steel bars.
The tensile behaviors of corroded steel bars are important in the capacity evaluation of corroded reinforced concrete structures. However, information on the tensile behaviors of naturally corroded steel bars is scarce. Moreover, differences in tensile behaviors between steel bars from natural and artificial corrosion are not well-understood. In this study, tensile testing was conducted on corroded steel bars from a residential building exposed to natural chloride attack, and from A706 corroded steel bars obtained from artificial corrosion using the impressed-current method. Based on the test results, reduction factors were proposed to relate the tensile behaviors with the corrosion mass loss for both the naturally and artificially corroded bars. Moreover, reduction factors from previous studies for both naturally and artificially corroded steel bars were collected. Comparison of reduction factors from this study and previous studies has shown that reductions factors for bars naturally corroded by chloride attack are generally larger than those by carbonation corrosion. Moreover, it is more appropriate to use the impressed-current method on bars embedded in concrete than on bare bars to simulate natural corrosion caused by chloride attack. On the other hand, reduction factors from the impressed-current method on bare bars are generally closer to those from natural carbonation corrosion than bars embedded in concrete.
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