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Flower-like, hierarchically nanostructured α-MoO3 was successfully synthesized via a one-step, template-free solvothermal route. Morphological characterization demonstrated that the nanostructures were hierarchically assembled by overlapping single-crystalline nanobelts with exposed (010) facets. These nanobelts, with a width of 40–60 nm and a thickness of 20–30 nm, grew radially from the core of the α-MoO3 flower. The growth mechanism of the α-MoO3 flower was speculated to be through oriented self-attachment of the nanobelts. The gas sensor based on α-MoO3 flowers showed an excellent sensing performance towards triethylamine (TEA) in terms of a high response (931.2) and excellent selectivity towards 10 ppm TEA. Especially, the detection limit was down to 0.001 ppm at a working temperature of 170 °C. The surface status of the α-MoO3 flowers before and after exposure to TEA at 170 °C was investigated by XPS. The probable oxidization product of TEA was analyzed by GC-MS. The MoO3 sensing mechanism could be interpreted as the transformation of triethylamine to vinylamine through two catalytic oxidation processes: the reactions with chemisorbed oxygen, and with lattice oxygen. The possibility relating to an enhanced gas sensing response of the three-dimensional (3D) flower-like α-MoO3 was discussed. [ABSTRACT FROM AUTHOR]

3D network-like, hierarchically structured, porous nanowall NiO arrays were grown in situ on ceramic tubes by a facile but environmentally friendly hydrothermal reaction with a subsequent calcination process. The arrays were constructed of the interconnected porous nanosheets, which were further assembled with abundant nanoparticles. The gas-sensing properties of such porous nanowall NiO array film sensors were investigated with eight inorganic and organic gases. The H2S-sensing performance was observed to be in a large dynamic range (1 ppb to 100 ppm) and the lowest detection limit was 1 ppb at 92 °C compared with other reported oxide-based sensors. The sensor exhibited not only high sensitivity, good selectivity and reproducibility to H2S with resistance to humidity at a low temperature of 92 °C and room temperature, but also good linear relationship under concentration ranges of ppm level (1–100 ppm) and ppb level (1 ppb to 1 ppm). The excellent sensing performance of this array film sensor to H2S could be ascribed to the porous structures in the unique nanowall arrays with a large specific surface area, which benefit H2S molecules to adsorb/desorb onto/from the array surface as well as the electron transfer. The formation of NiO arrays and their possible H2S-sensing mechanism are discussed in detail. [ABSTRACT FROM AUTHOR]

• For the first time, the hierarchical α-Fe 2 O 3 /α-MoO 3 hollow spheres were prepared by one-step solvothermal route under acidic condition. • First exploration of the ANI gas-sensing performance for the sensor based on hierarchical α-Fe 2 O 3 /α-MoO 3 hollow spheres. • First confirmation of the possible oxidative product of ANI through GC–MS technique. • α-Fe 2 O 3 /α-MoO 3 hollow spheres exhibited higher sensing response, lower detection limit and faster recovery speed at 217 °C. The sensing materials consist of more than one metal oxides species may endow the gas sensors with superior sensing abilities. MoO 3 , an acidic oxide, its precursors are usually produced in acidic solution via hydrothermal/solvothermal method and their hierarchical structures would dissolve and collapse under alkaline circumstance, hampering the functionalization of MoO 3 by other conventional metal oxides which stably exist in basic solution. In this paper, a binary metal oxide, denoted as hierarchical heterostructured α-Fe 2 O 3 /α-MoO 3 hollow spheres were fabricated via a simple one-step solvothermal process. The 4.55 at% α-Fe 2 O 3 -decorated α-MoO 3 sensor exhibits remarkable sensing performance for aniline (ANI) with high sensitivity and selectivity at 217 °C. In particular, it shows higher response (32.5) to 30 ppm ANI compared to pristine α-Fe 2 O 3 (2.1) and α-MoO 3 (3.2) sensors, respectively, along with fast response time (3.6 s). Besides, the detection limit to ANI is further decreased from 1 ppm for the pristine α-MoO 3 sensor to 0.01 ppm. Possible oxidation product of ANI was confirmed through GC–MS technique for the first time. The gas sensing mechanism of α-Fe 2 O 3 /α-MoO 3 to ANI is speculated as the oxidation of ANI to azobenzene by chemisorbed oxygen. The possibility relating to the superior reducing gas-sensing properties of α-Fe 2 O 3 -decorated α-MoO 3 to ANI was demonstrated. This work provides a logical strategy to design metal oxide composites for high performance gas sensor. [ABSTRACT FROM AUTHOR]

• Using [C 12 mim][PF 6 ] as morphology template to assistantly synthesize monodispersed hollow α-Fe 2 O 3 ellipsoids with highly porous shell. • The sensing performance of α-Fe 2 O 3 hollow ellipsoids to n-butanol is significantly improved by proper amount of [C 12 mim][PF 6 ]-loading. • The sensor has a high response, short recovery time and good stability to n-butanol at 217 °C. • XPS analysis explains the good sensing performance of hollow α-Fe 2 O 3 ellipsoids to n-butanol. Monodisperse α-Fe 2 O 3 hollow ellipsoids have been assistantly fabricated via small amount of [C 12 mim][PF 6 ] (IL) addition from a simple one-pot method based on hydrothermal treatment of FeCl 3 ·6H 2 O, followed by calcination at various temperatures. The phase and microstructure of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption techniques. Further studies reveal that both calcination temperature and the amounts of IL have a strong effect on the structures. The well known Ostwald ripening process is responsible for the transformation from solid ellipsoids to hollow ellipsoids. The gas sensors based on the as-synthesized hollow α-Fe 2 O 3 ellipsoids calcined at 300 °C exhibited not only high response, short recovery time and good stability to 100 ppm n-butanol at 217 °C, but also low detection limit (0.1 ppm) compared with those under higher calcination temperature and the products obtained without ILs-addition. IL-loading α-Fe 2 O 3 hollow ellipsoids could be a promising candidate for highly sensitive n-butanol gas sensors. [ABSTRACT FROM AUTHOR]

• Develop a novel unwelded, unbolted, UHPFRC grouted connection for prefabricated columns. • Examine the load transfer mechanism of the grouted connection experimentally and numerically. • Examine the ultimate resistance and deformation behavior of the grouted connection. • Evaluate and recommend analytical models to predict ultimate resistance of grouted connection. This study develops a novel unwelded, unbolted, ultrahigh-performance fibre-reinforced concrete (UHPFRC) grouted connection for prefabricated square tubular composite columns. Herein, eight full-scale columns with UHPFRC grouted connections are tested to investigate their ultimate tensile and compressive resistance. The test results show that the novel connections exhibit good tensile and compressive resistance and structural stiffness. The primary failure modes are punching shear of the end plate, welding fracture at the inner tube, tube yielding and local buckling of the steel tube. The test specimens are simulated using finite element (FE) analysis in ABAQUS. The experimental and simulated results are in good agreement, indicating that the FE simulations can capture the observed failure modes and ultimate tensile and compressive resistance. Thereafter, existing analytical design formulas are evaluated to assess their suitability to predict the compressive and tensile resistance of prefabricated tubes with/without the novel grouted connections. A good agreement between the formula predictions and the test results are observed. These analytical formulas have the potential to be used in the design of the novel unwelded, unbolted, UHPFRC grouted connections for prefabricated steel, reinforced concrete and steel–concrete composite columns. [ABSTRACT FROM AUTHOR]

This paper develops a novel rubberized ultra-lightweight high ductility cement composite (RULCC) with added rubber powder and low content PE fiber (0.7%), and investigates the dynamic compressive response and failure mechanism of the RULCC both experimentally and analytically. The test program examines the dynamic compressive stress-strain relationship of the RULCC through Split Hopkinson Pressure Bar (SHPB) impact tests. The results show that the rubber powder aggregates have significant effect on the compressive strength, stress-strain relations and failure mechanism of the RULCC. A volume replacement of fine aggregates with 5%, 10% and 20% rubber power results in a reduction in static compressive strength by 29.5%, 47.7% and 60.3%, respectively. The RULCC with a low fiber content of 0.7% in volume exhibits a 3% direct tensile strain, and a 4–5% tensile strain can still be achieved after 10% rubber powder is added to the RULCC, showing a high ductility of the material. The SHPB impact test shows that the compressive strength increases with strain rate. An empirical model, taking into account of the replacement ratio of the rubber powder aggregates in the RULCC, is developed in this paper to evaluate the Dynamic Increasing Factor (DIF). The experimental and analytical studies are essential to better understand the fundamental dynamic behavior of the RULCC for its further applications in engineering applications, such as protective structures, etc. [ABSTRACT FROM AUTHOR]

Hierarchical, heterogeneous CuO/NiO nanowall arrays were in situ grown on ceramic tubes by hydrothermal reaction with subsequent calcination. Functionalization of CuO endowed the CuO/NiO sensor with enhanced H 2 S sensing performance. Typically, the 2.84 at% CuO decorated NiO sensors exhibited higher sensing response, better selectivity, lower detection limit and faster recovery speed at 133 °C in comparison with the pristine NiO ones. • Preparation of the novel hierarchical CuO/NiO nanowall arrays film sensor by one-step hydrothermal route without any surfactant or template. • First in situ deposition of the CuO/NiO nanowall arrays on ceramic tubes to form H2S gas sensor. • CuO/NiO nanowall arrays exhibited higher sensing response, better selectivity,lower detection limit and faster recovery speed at 133 °C. Hierarchical and heterogeneous CuO/NiO nanowall arrays were in situ grown on ceramic tubes via a facile template-free hydrothermal route, and then were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. The resultant composites exhibit network-like CuO/NiO array structures constructed by interconnected porous nanosheets, in which the decoration of CuO nanoparticles in NiO nanowall arrays was confirmed by XRD, XPS and TEM analyses. The 2.84 at % CuO decorated NiO sensor exhibits excellent sensing properties at 133 °C. The response to 5 ppm H 2 S attains 36.9, which increases as high as 5.6 times compared to the NiO one. The detection limit to H 2 S is further decreased from 1 ppb for the pure NiO sensor to 0.5 ppb. The CuO/NiO sensor shows a wide linear range from 50 to 1000 ppb, good repeatability, selectivity and long-term stability, which is expected to be a candidate for ppb-level H 2 S detection in real and complex environment of industrial production. Furthermore, the dominant H 2 S sensing mechanism is discussed from the view of the homo- and hierarchical architecture of the CuO/NiO arrays as well as the chemical and electronic sensitization effects of CuO decoration. [ABSTRACT FROM AUTHOR]

• X-ray microcomputer tomography was used to monitor the corrosion product development of the RC element. • The distribution of rust products in the plane and space was investigated under different corrosion rates. • The Effect of external confinement on corrosion products distribution was discussed. • The bond performance of corroded RC element was found to relate the "hollow volume" that can be defined using X-ray μCT. Rebar corrosion destroys the bond interface between concrete and the original rebar and, thus, affects their collaborative performance. External confinement, such as a concrete cover or fiber reinforced polymer (FRP) jackets, is a promising method to solve this problem since both can improve the bond properties between corroded rebars and concrete. However, existing tests results have shown the expected bond performance between rebars and its external concrete surroundings to be unstable for corrosion condition, and much of the bond strength data of corroded specimens is highly discrete. Traditional test methods such as cutting specimen are difficult to explain the instability of bonding phenomenon since it likely to destroy the rebar's bonding interface during processing the specimen. In this study, X-ray microcomputed tomography (X-ray μCT), a new type of non-destructive testing method, was adopted to scan the inside of the corroded specimens and perform a three-dimensional reconstruction enabling a complete understanding of corrosion development. This paper also presents a thorough research analysis that focuses on the effects of variation in corrosion rates as well as the thickness of the concrete cover and FRP layers on the distribution of rust products and the volume change of rust products on the bond interface. Test results indicate that the distribution of corrosion products in 2D/3D is directly related to the location of cracks in the concrete cover, and increasing confinement (concrete cover thickness, FRP layer number) leads to a more uniform distribution of corrosion products. In addition, by using X-ray μCT, the "hollow volume," defined as the volume between the surface of the uncorroded steel bar and the inside of the concrete cover, could be accurately obtained. Most importantly, this hollow volume was found to be the main factor affecting the bond performance of corroded reinforced concrete. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the performance of H-type end anchorage on the flexural strengthening of Fiber Reinforced Polymer (FRP) plated reinforced concrete (RC) beams. The H-type end anchorage (EA) consists of an anchorage section, a connection section and a deformation section. In the experimental study, the H-type EA was installed at the ends of FRP plate, and the FRP-plated RC beams were subjected to four-point bending load. The strengthening mechanism of H-type end anchorage mainly depends on the width of its deformation part, which further determines the overall axial stiffness of the end anchorage. The effect of H-type end anchorage on the flexural performance was evaluated in terms of critical loads, failure mode, deflection, ductility and strain behavior of various materials, all showing great improvement as compared to the FRP-plated RC beams without end anchorage. H-type end anchorage was found to be activated after certain thresholds of load was reached, and the elongation became excessive after its yielding. Finally, an analytical model was proposed and verified by the experimental results to estimate the ultimate load and failure mode of the EA-strengthened RC beams. [ABSTRACT FROM AUTHOR]

Highlights • Effects of the mechanical properties of end anchorage on the bond behavior are investigated. • An analytical model is derived to predict the bond performance. • A design method of end anchored FRP strengthened concrete structures is proposed. Abstract This study presents a new design method of end anchored (EA) fiber reinforced polymers (FRP) strengthened concrete structures. A previously developed analytical model is modified to predict the performance of EA-strengthened concrete structures under direct pullout loading. The typical performance is composed of five stages, where excessive deformation occurs in the end anchorage during the last two stages. The ultimate loads under different failure modes are obtained, showing that low axial stiffness of the end anchorage results in low increase in the ultimate load and premature debonding failure (before ductility is developed in the end anchorage), whereas high axial stiffness significantly increases the ultimate load and yields brittle failure such as FRP rupture. Effects on the bond performance due to various axial stiffness and strength of the end anchorage are investigated in a sensitivity study. To achieve good ultimate load and ductility, critical strength and axial stiffness of end anchorage is derived. Finally, a design method is proposed for the EA-strengthened concrete structures. [ABSTRACT FROM AUTHOR]

Abstract Premature debonding failure of fiber-reinforced polymer (FRP) laminate is a primary reason for an accelerated onset of low working stress in the FRP of reinforced concrete (RC) structures strengthened with externally bonded (EB) FRP. Hybrid-bonded (HB) FRP can effectively prevent the debonding failure of FRP, leading to a significant enhancement in the ultimate strength of the HB-FRP system. The HB-FRP method mainly relies on external positive pressure provided by the anchoring device to improve the interfacial bond strength. Therefore, the magnitude of the positive pressure determines the strengthening effect of the anchoring system. This paper first optimizes the existing HB mechanical anchoring device. The positive pressure exerted on the FRP was adjusted by varying the torque to the anchoring device. The optimized anchoring device was used to study the bond behavior of the FRP-to-concrete interface under different torques. The test results showed that the debonding stress could be regulated by adjusting the torque, leading to a change in failure mode of the FRP-concrete interface. With the increase of torque, the utilization rate of FRP and ductility increased. When the torque was higher than a certain threshold, the FRP ruptured, after which, the continuously applied torque had no significant effect on the FRP-concrete interfacial bond behavior. Based on the experimental results, an ultimate bond strength model of the FRP-to-concrete interface under different torques was developed. Compared to the experimental results, the model showed satisfactory accuracy. [ABSTRACT FROM AUTHOR]

This study presents the results of the flexural behaviour of hybrid large-rupture-strain (LRS) FRP-concrete-steel double-skin tubular (DST) beams with eccentric encased steel tube. The unique design of these beams demonstrates excellent ductile potential, with a flexural ductility index greater than eight. The variation in eccentricity of the encased tube is found to be the key factor controlling the ductility index parameter. The hybrid beams were found to exhibit ductile flexural failures, with the fracture of the FRP laminate at the bottom being considered the precursor to ultimate failure. Non-linear finite element models and a simplified theoretical approach are developed, and good agreements are achieved when compared to the experimental data. The calibrated numerical model is used to perform parametric studies on the variation in the size of the inner tubes. The results revealed that the flexural resistance, in terms of load and moment, increases at a near-linear trend with the increase in tube diameters. However, an opposite trend was observed for the ductility of the beams. [Display omitted] • The flexural behaviour of the hybrid DST beams is examined. • The flexural performance is significantly enhanced by the eccentric design. • The eccentricity is the primary factor for the ductility index. • A design-oriented simplified approach is developed and verified. • A non-linear FEM is developed and calibrated to perform parametric studies. [ABSTRACT FROM AUTHOR]

• A low-cost high-performance hybrid fiber ECC is designed and evaluated. • A systematic analysis including macroscopic and microscopic mechanical properties is performed. • The optimal design of HF-ECC is performed by pseudo-strain-hardening indices and multi-criteria evaluation. Engineered cementitious composites (ECC) is a fiber reinforced high-performance cementitious material with an ultra-high tensile strain capacity (above 3%) and excellent durability. However, such excellent strain capacity far exceeds some engineering requirements and is usually not fully utilized. Meanwhile, its high cost limits it application only in local engineering. In this study, a low-cost high-performance hybrid fiber ECC (HF-ECC) with both polypropylene (PP) fiber and polyethylene (PE) fiber was manufactured. Both macroscopic and microscopic mechanism analyses were conducted to investigate the effect of fiber characteristics and proportions on the performance of HF-ECC. The results show that the ultimate tensile strain of HF-ECC can reach 5% even the volume fraction of PP and PE fibers account for 1%, respectively. Its fiber cost is 43.8% lower than that of pure PE-ECC, which reduces the corresponding total cost by 27.5%. This paper presents an in-depth investigation of the characteristics of HF-ECC, direct tension, compression, fiber-bridging, pore structure, fiber distribution, and fiber dispersion. Finally, the optimal design of the HF-ECC is conducted through pseudo-strain-hardening indices and multi-criteria evaluation. [ABSTRACT FROM AUTHOR]

The architecture of PO43− modified 2D TiO2 nanosheets was constructed by ionic liquids (ILs)-assisted hydrothermal method. The nanosheet structure can be regulated by the addition of different amount of ionic liquid. Using the composite nanosheets a chemoresistive gas sensor was prepared for trimethylamine (TMA) detection. Most reported TMA sensors need to be operated at a relatively high operating temperature, but in this paper, the as-synthesized PO43−-modified 2D TiO2/Ti2O(PO4)2 nanosheet sensor has high response (S = 87.46), short response time (14.6 s), and good reproducibility to 100 ppm TMA gas, when the temperature is 170 °C. In contrast to the single-phase TiO2 sensor, the gas-sensing property of the composite one is obviously enhanced. Moreover, its response shows excellent linear relationship with TMA concentration from 0.2 to 500 ppm, and a detection limit of 0.2 ppm. The TMA detection mechanism was investigated by analyzing the changes of the surface adsorption oxygen content by XPS and gaseous products using gas chromatography after the sensor was in contact with TMA. [ABSTRACT FROM AUTHOR]

The bonding between CFRP (Carbon Fiber Reinforced Polymer) laminate and steel plays a key role in the strengthening effects of CFRPs on a steel structure. In this paper, the toughness of the adhesives and the bonding thickness were investigated on the CFRP-steel bond performance using a single lap shear test. The properties of the adhesives, brittle (linear elastic) or tough (nonlinear elastic, lower modulus, higher elongation), led to apparent differences in the ultimate load, stiffness, the shape of the bond-slip curve, and the stress distribution of the CFRP-steel bond. For the tough adhesive, an increase of the bonding thickness from 0.5 mm to 1.5 mm improves the fracture energy but reduces the interface stiffness. On the contrary, for the brittle adhesive, the effects of the bonding thickness are negligible. According to the test and literature results, key parameters of the bond-slip models of the tough adhesive and brittle adhesive in the case of the delamination of CFRP laminate were determined. • The type of adhesive has a significant effect on the interfacial adhesion. • The effects of the bond thickness are dependent on the adhesive types. • Two new bond-slip models are proposed and verified. [ABSTRACT FROM AUTHOR]

C-TiO 2 nanoparticles were prepared by using a facile template-free solvothermal method, in which the C was induced directly from the raw material itself. The C-TiO 2 sensor showed excellent gas-sensing performance to alcohol at the optimal working temperature of 170 °C. Especially, the response increased with the carbon chain lengths increasing from C1 to C5. The XPS, GC, GC–MS techniques and theoretical calculations were carried out to explore the gas-sensing mechanism of C-TiO 2 to n-pentanol, which was speculated as the first oxidization to aldehyde and further decomposition into carbon dioxide and water. • C-TiO 2 nanoparticles were prepared by a template-free solvothermal method, where the C was induced directly from the raw material itself. • The sensor based on C-TiO 2 showed excellent gas-sensing performance to different carbon chains (C1 to C5) alcohols. • The sensor based on C-TiO 2 nanoparticles exhibits excellent n-pentanol gas-sensing properties at low operating temperature. • The possible n-pentanol sensing mechanism is proposed on the basis of theoretical calculations, XPS, GC and GC-MS. C-TiO 2 nanoparticles with the diameter of 30 ± 8 nm were prepared by using a facile template-free solvothermal method, in which the C was induced directly from the raw material itself. The sensor based on C-TiO 2 showed excellent gas-sensing performance to alcohols at the optimal working temperature of 170 °C. Especially, the response increased with the carbon chain lengths increasing from C1 to C5. The response to 100 ppm n-pentanol was 11.12, which was 5.4 times higher than that of the pure anatase TiO 2. Besides, the theoretical calculations, XPS, GC and GC–MS techniques were carried out to explore the gas-sensing mechanism of C-TiO 2 to n-pentanol. The n-pentanol was speculated oxidization to aldehyde and decomposition into carbon dioxide and water eventually. [ABSTRACT FROM AUTHOR]

A large number of salt caverns by solution mining are abandoned widely. After reasonable reformation, some of these caverns are expected to store energies, such as petroleum, natural gas, and compressed air energy. Different from other countries, salt formations of China are mainly bedded with lower thickness. In order to improve the mining efficiency of bedded salt formations, solution mining with double-well convection is widely adopted, which brings more horizontal caverns with larger dimensions and also larger roofs. When these horizontal caverns are transformed into underground energy storage, the layered roofs are easily suffered from unbalanced deformation and failure, and then become the channels of oil or gas leakage. Therefore, a series of theoretical analysis and numerical simulation were carried out to reveal the failure mechanism and stability of the bedded roof, and then some meaningful conclusions are acquired. Firstly, in the overlying strata, the argillaceous anhydrite layer is the key roof in the selection of the abandoned horizontal cavern for energy storage. Secondly, according to plate theory, the invalid of the bedded key roof needs to be treated into failure and instability respectively. Thirdly, the analysis on the vertical and horizontal stress in the key roof shows that it does experience a second type of instability. Finally, in order to maintain the stability of bedded key roof, the main influence factors require careful and comprehensive consideration, including the length of the long side, the thickness of the protective salt layer, and the internal pressure. [ABSTRACT FROM AUTHOR]

Developing green materials for infrastructure construction is of vital importance for sustainable development. Limestone calcined clay cement (LC3) is an appropriate alternative for the reduction of CO 2 emissions and resource consumption in the cement industry. Recycled concrete aggregate (RCA), seawater and sea sand are potentially advantageous from a sustainability perspective, especially in coastal regions. Fiber-reinforced polymer (FRP) bars with excellent corrosion resistance are ideal alternative materials for steel bars in a corrosive environment. In this paper, a new type of green concrete structure incorporating LC3, seawater, sea sand, RCA, and FRP bars was investigated, and the performance was assessed to verify the considerable sustainable advantages while considering life cycle cost and environmental impacts. The results showed that the proposed LC3 concrete exhibited lower environmental impacts: compared with traditional concrete, and the CO 2 and energy consumption of LC3 concrete were reduced by 32%–41.7% and 23.3%–28%, respectively. Although the initial cost was higher for LC3 and CFRP bars, this disadvantage could be offset by their longer service life and lower maintenance costs during their life cycle. Compared with traditional RC structures, the total cost, CO 2 and energy consumption in the life cycle were reduced by 39%, 30.5%–65.4%, and 18.5%–58.9% for the LC3 concrete structure, respectively. In contrast to the life cycle cost, the LC3 replacement ratio had a negative effect on the environmental indices for the LC3 concrete and structure. Considering the promising advantages in economy and environmental impact, the proposed LC3 concrete and structure provides an effective approach for the sustainable development of the construction industry. • A type of green concrete structure incorporating LC3, seawater, sea sand, RCA, and FRP bars. • LC3 concrete exhibits lower environmental impacts, decreased as the LC3 replacement ratio increases. • LC3 concrete structure shows excellent environmental and economic advantages. [ABSTRACT FROM AUTHOR]

Hollow NiO microspheres were prepared using one-step hydrothermal method assisted by geminal dicationic ionic liquid (DIL) 1, 2-bis (N-dodecylimidazolyl) ethane bromide ([C 12 -2-C 12 mim][Br 2 ]). The structures of the prepared microspheres can be controlled by adjusting the concentration of ionic liquid and reaction temperature. Furthermore, the amount of ionic liquid residue in these microspheres can also be controlled by changing the calcination temperature. Among them, the NiO hollow microspheres prepared by calcining the precursor at 600 °C (Ni1–600) in air display the most excellent gas sensing performance, including high response (35.6–100 ppm H 2 S) and low working temperature (50 °C). The excellent gas sensing performance of the Ni1–600 is attributed to the ionic liquid residue with appropriate content, which enhances the interaction between the analyte and the sensing material. The strong interaction effectively increases the sensitivity and reduces the working temperature of the sensor. The NiO hollow microspheres are expected to be a promising candidate material for the highly sensitive H 2 S gas sensor at near room temperature. [Display omitted] • Using [C 12 -2-C 12 mim][Br 2 ]-assisted synthesis of hollow NiO microspheres. • Excellent gas sensing performance induced by [C 12 -2-C 12 mim][Br 2 ] residue. • The NiO microspheres have high response and selectivity to H 2 S at 50 °C. • XPS and GC–MS explain the sensing performance of hollow NiO microspheres to H 2 S. [ABSTRACT FROM AUTHOR]

• The increase of FA content improved SAAM's capacity to bind chloride. • CaAl-LDH was the most effective in reducing the content of free Cl-. • Chloride binding capacity of MgAl-LDH was compromised by less strength loss. The chloride binding mechanism of alkali-activated materials (AAM) under various granulated blast furnace slag (GBFS)/fly ash (FA) ratios is investigated in this work. Two types of layered double hydroxides (LDH), i.e., MgAl-LDH and CaAl-LDH, and active magnesium oxide (MgO) were added to reduce the concentration of free chloride in AAM. The results demonstrate that the ratio of GBFS to FA has non-negligible influence on the AAM's ability to bind chloride. The content of bound chloride increased by 3.78%-17.42% as the FA content in seawater-based alkali-activated materials (SAAM) raised. The chloride binding forms of SAAM were mainly chemical binding by the hydrated calcium aluminate (AFm) phase and physical adsorption by calcium (alumino) silicate hydration (C-(A)-S-H) gels when the FA dosage is less than 20% in SAAM. When the FA mass ratio in SAAM was larger than 20%, the chloride binding form of SAAM was mainly the physical adsorption by calcium (sodium) alumino-silicate hydrate ((C, N)-A-S-H) gels. Among the three additive materials, CaAl-LDH was the most effective in reducing the free chlorine content by 11.34%. While for MgAl-LDH, the chloride binding capacity was compromised by the less strength loss. In this work, seawater was used as the mixing water to introduce chloride ions, the results of which could provide a reference for the application of seawater in future projects. [ABSTRACT FROM AUTHOR]

Novel flower-like ZnO nanomaterials were synthesized by a simple solvothermal method without using any template and surfactant combined with subsequent calcination. The resultant ZnO flowers displayed a hierarchical structure with diameters of 1.4–1.6 µm, consisting of overlapped nanorods grew radially from the center of the ZnO flowers. The gas sensors based on such ZnO flowers were highly sensitive to H 2 S gas in terms of a high response (157.3) and excellent selectivity towards 100 ppm H 2 S at the low operating temperature of 92 °C, accompanied with the detection limit of 0.05 ppm. The superior gas-sensing capabilities might benefit from the porous hierarchical architecture, which could facilitate the rapid adsorption of gas molecules and enhance the consequent charge transfer. Furthermore, the surface state of the ZnO flowers before and after exposure to H 2 S gas at 92 °C were investigated through the XPS technique and a possible H 2 S sensing mechanism over ZnO was proposed. [Display omitted] Flower-like ZnO hierarchical nanostructures were synthesized via a solvothermal method without using any template and surfactant. The gas sensors based on such ZnO flowers were highly sensitive to H 2 S gas in terms of high response and excellent selectivity at the low working temperature of 92 °C. A possible H 2 S sensing mechanism over ZnO was proposed. • Flower-like ZnO hierarchical structures were synthesized by a simple solvothermal method. • H 2 S-sensing mechanism for ZnO was deduced as two combined reactions of H 2 S with ZnO. • The sensors based on the ZnO flowers realize a low working temperature detection of H 2 S. [ABSTRACT FROM AUTHOR]

Impressed current cathodic protection (ICCP) has been proven to be an effective technique to inhibit steel corrosion. Based on the ICCP method, a hybrid reinforced concrete (RC) structural system of carbon fiber reinforced polymer (CFRP) bars/steel bars was proposed, in which CFRP bars are used as the reinforcement material and anode material simultaneously. The bond performance of the steel bar-concrete interface with ICCP was studied here. The effects of the ICCP current density and the pre-corrosion ratio on bond performance were considered through a series of experiments, including the accelerated corrosion test, the ICCP test, the linear polarization test, and the pull-out test. Experimental bond strengths were also compared with values predicted by existing models. The results showed that cathodic protection with the CFRP bar as the anode material was effective, and further steel corrosion was inhibited significantly, leading to an improvement in the corroded steel bar-concrete bond performance. In addition, the bond strength decreased gradually as the ICCP current density and the pre-corrosion ratio increased. A significant discrepancy existed between the experimental bond strength and the predicted value, indicating that the bond performance varied with the paths to achieve the same corrosion state. [ABSTRACT FROM AUTHOR]

[Display omitted] • Usage of the ionic liquid [Bmim][BF 4 ] as the fluorine source and morphology modifier. • The synthesis of (0 0 1) and (1 0 1) facets of TiO 2 co-exposed nanocubes by a simple one-step hydrothermal method. • The TiO 2 nanocubes to acetone gas at 170 °C, the detection limit is 30 ppb and the response time is only 2.2 s. Early and painless detection of type-I diabetic patients by detecting acetone concentration in their exhaled breath would be a rapid and effective means. TiO 2 materials with exposed active (0 0 1) facet were synthesized mostly with HF as raw material, and the particle size was relatively large. In this work, (0 0 1) and (1 0 1) facets co-doped TiO 2 nanocubes with particle size < 50 nm were successfully prepared by a simple one-step hydrothermal process assisted by the ionic liquid ([Bmim][BF 4 ]) as the fluorine source and morphology modifier. Due to the exposure of the active (0 0 1) facets, the sensor exhibited good gas response to acetone gas at a low operating working temperature (OWT) of 170 °C with a detection limit as low as 30 ppb and a response time of only 2.2 s for 100 ppm acetone gas, and also relatively excellent selectivity, reproducibility, moisture resistance and long-term stability. It is worthy to point that, the changes of acetone concentration were compared in exhaled gas from healthy people and type-I diabetic patients, and the responses to exhaled gas of type-I diabetic patients were also tracked at different time in the same day. This provides significant convenience for early and painless diagnosis of type-I diabetic patients. [ABSTRACT FROM AUTHOR]

Flax fiber reinforced polymer (FRP) is an emerging low-carbon alternative to steel. This paper proposes a novel method to streamline and optimize the production of closed type flax FRP. The material properties of flax FRP were greatly improved due to the reliable bonding provided by optimum amount of epoxy resin. The optimized flax FRP stirrups were then used as shear reinforcement in thirteen reinforced concrete (RC) beams, which were subjected to three-point bending until failure. To further improve the performance of flax FRP stirrups in RC beams, the effects due to partial bonding, width and layer of flax FRP stirrups were investigated. The partial bonding of flax FRP significantly increased the effective strain of flax FRP and the resultant shear capacity. Increasing the width or layer of FFRP stirrups minimally improved the shear capacity. The environmental impact intensity of steel, fully and partially bonded flax FRP stirrups were evaluated using life cycle assessment (LCA). The optimized flax FRP stirrups decreased environmental impact intensity by minimizing the negative impacts of epoxy. As compared to the steel stirrups, the partially bonded flax FRP stirrups decreased the environmental impact intensity in most categories by 50–100%. [ABSTRACT FROM AUTHOR]

• The mechanical behavior of pre-damaged concrete strengthened with the highest rupture strain at present is addressed. • The performance of some existing strength and strain models for confined damaged concrete is evaluated. • A continuous integrable and derivable model was validated. The lateral confinement of fiber-reinforced polymer (FRP) has a significant impact on the deformability, strength, and energy dissipation of core concrete, especially for damaged concrete. To address the performance of damaged concrete strengthened with the large rupture strain of FRP (LRS-FRP), the effects of damage degree, confinement stiffness, and loading rate were analyzed. Results show that the strain efficiency factor of LRS-FRP made of recycled polyethylene terephthalate (PET) can be stabilized at a high value of 0.87 even with a high damage degree when used for strengthening cylinders, which is larger than other FRP (BFRP and CFRP) and agrees with PET confined undamaged concrete reported in existing papers. The test results indicated that the increased initial damage degree result in a slight decrease in ultimate strain and ultimate strength. The loading rates will improve the initial compressive strength of core concrete, this result in the increase of the reflection point stress of LRS-FRP confined concrete from the elastic stage to the enhancement stage. But, the tangent modulus of the enhancement stage is hardly affected by loading rates even though the core concrete is under different initial damage conditions. One strength model with good performance after evaluation and a continuous integrable and derivable model are incorporated into this new work, which predicts the performance of damaged concrete strengthening with LRS-FRP. [ABSTRACT FROM AUTHOR]

To address the problem of insufficient ductility of traditional Carbon Fibre-reinforced polymer (CFRP) strengthened marine structures and to enhance the application of CFRP in marine engineering, the present study develops novel prestressed CFRP-strengthened RC beams using H-type end anchors with ductility controllable devices. In this device, part of the reinforcement bars are replaced by CFRP, which is prestressed as the structural enhancement material. The CFRP sheet is connected with a tensioned screw, which is used to realize the function of early warning based on a large plastic deformation when the structure is overloaded. Thus, the ductility of the composite structure could be improved based on yielding of the screw rod rather than the fracture failure of the CFRP sheet compared to that with CFRP bonded. This study investigates the flexural static and impact performance of the representative large-scale RC beams strengthened by prestressed CFRP through four-point bending and drop-weight impact. The results show that the H-typed end anchor and raising the prestress level of CFRP not only improve the ultimate resistance and ductility, but also realize the overload warning function under static load. Accordingly, the design still shows advantages in energy consumption and impact resistance through drop-weight impact. An advanced 3D nonlinear finite element model is built to simulate well the multiple impact performance in terms of the failure modes, impact force and displacement history. This study provides a new approach to address design deficiencies with insufficient ductility behaviour while using CFRP as a strengthening material. This prestressing technology is able to utilize the material efficiency of high-strength CFRP and open a new path for CFRP applications in marine civil engineering. • Develop a novel prestressed CFRP strengthened RC beam using ductile fused anchor. • Perform flexural tests on novel prestressed CFRP strengthened RC beams. • Perform multi-impact tests on novel prestressed CFRP strengthened RC beams. • Provide a new FE simulation framework for multi-impact test. • Analyze the time-lag between impact force and midspan displacement. [ABSTRACT FROM AUTHOR]

• FRP strengthening methods without/with anchorage decreased ductility by 37.2% and 29.3%. • H-anchorage simultaneously increased the ductility and load capacity for RC beams. • Prestress loss of FRP was 3–10% in the first five to ten hours, and stopped increasing afterwards. • H-anchorage increased elastic flexural stiffness for specimen using low-strength concrete. • Excessive plastic deformation was developed in fuse, leading to ductile failure. • Proposed design method ensure the optimum load capacity and ductility. Most FRP strengthening methods increased load capacity at the cost of decreased ductility. A review of 551 specimens from 64 literatures shows that the ductility of FRP strengthened RC beams experienced an average decrease of ductility by 37.2%. To achieve balanced improvement of ductility and load capacity, a previously proposed H-anchorage is adopted to prestress FRP laminates and to strengthen reinforced concrete (RC) beams in flexure. A total of ten specimens were cast and tested under four-point bending, the test results are presented and discussed. The effects of concrete strength, bond scheme, and prestress level of FRP were investigated. The H-anchorage was found to improve the utilization of FRP in tension, achieve great increase of load capacity, and maintain satisfactory ductility. Partial bonding of prestressed FRP effectively improved the flexural performance within the elastic range, and the load capacity generally increased with increasing prestress level of FRP laminates. The increase of ductility was more prominent in the specimens using high-strength concrete than those using low-strength concrete. During the loading process, the deformed concrete section remained planar. Based on this observation, an analytical model is proposed to estimate the load capacity, reaching good agreement with the experimental results. Finally, a design method is proposed for optimizing the configuration of H-anchorage to ensure optimum performance in terms of load capacity and ductility. [ABSTRACT FROM AUTHOR]

• Numerical methods to simulate nonlinear behaviors of a novel H-type end anchored (EA)-FRP system are established. • Interface adjusting mechanisms of H-type EA-FRP system and its strengthening mechanisms on RC beams are investigated numerically. • Simplified design formulas for predicting the ultimate deformation of RC beams strengthened by H-type EA-FRP system are proposed. • Strain relaxation caused by interface slip is considered when calculating the ultimate deformation. A ductile end anchorage (EA) system for fiber-reinforced polymer (FRP) sheets using H-type anchors has been recently proposed to compensate for the loss of deformation capability of externally-bonded FRP strengthened reinforced concrete (RC) beams. The effectiveness of the novel anchorage system has been verified by existing experimental results, while there still lack of deep investigations on its strengthening mechanisms and quantitative evaluations of the deformation capability. Against this background, high-fidelity finite element (FE) models of FRP-plated concrete members and RC beams with H-type end anchors are developed using LS-DYNA in this paper. The most proper simulation approach is identified through comparing with the experimental results. Based on the validated FE model, the mechanical behaviors and strengthening mechanisms of the end anchorage system are investigated thoroughly. Extended parametric studies are conducted to study the influences of FRP thickness and the width of the anchorage deformation section on the strengthening effectiveness. Based on the findings in the numerical simulation, the strength model of EA-strengthened beams is improved, and an analytical model for predicting the ultimate deflection of EA-strengthened beams is established. [ABSTRACT FROM AUTHOR]

• Bond behaviors of FRP bars in ECC were investigated experimentally and numerically. • Splitting failure is prevented due to the post-crack resistance of ECC. • Effects of geometric structure of rebar surface on bond behavior were investigated. • A simplified bond failure model was established based on the pullout failure mode. The bond performance of engineered cementitious composites (ECCs) and fiber-reinforced polymer (FRP) bars was investigated via pullout tests. The experimental results indicated that increasing the ECC strength led to a proportional increase in the bond strength, and rebars with higher ribs exhibited higher bond strengths (by a maximum of 55%) than counterparts with lower ribs. A finite-element model of an ECC thick-walled cylinder was developed to examine the interfacial bond failure mechanism and was validated by experimental data. Experimental and simulation results indicated that owing to the excellent post-crack resistance of the ECC material, splitting failure at the rebar–ECC interface was prevented, and the shear resistance of ECC corbels between the rebar ribs significantly affected the bond failure. A simplified bond-strength model was then developed according to the pullout failure mode, and a new equation for the bond strength that accounts for the surface configuration of the rebar was derived. [ABSTRACT FROM AUTHOR]

Double skin tubular columns (DSTCs) filled by ultra-lightweight cement composites (ULCCs), as primary load-bearing elements, are a practical and reasonable structural asset in lightweight civil infrastructure. This DSTC-ULCC system combines the advantages of three materials, 1) outer fiber-reinforced polymer (FRP) 1–3 ply jackets, 2) filled ULCCs, and 3) inner steel tubes to achieve lightweight, high strength and superior ductility. This article presents an experimental study on the mechanical behavior of DSTCs with FRP and ULCCs under axial compressive loading. The experiment designed a total of 26 DSTCs that were all filled with ULCCs. The key parameters were the number of FRP layers and the inner steel tube properties, (i.e., thickness and diameter of the steel tube). The test results indicate that the properties of the inner steel tube not only influences the effective FRP rupture strain ratio but also the ultimate axial strain of confined ULCCs. This calls attention to the inward buckling behavior for larger void ratios; moreover, thinner steel tubes result in more axial deformation of ULCC-filled DSTCs. In addition, ULCCs showed a much lower elastic modulus compared with normal concrete, which helped cause the change of transition stress of ULCCs in DSTCs, and FRP confinement can effectively increase the elastic length of the stress–strain curves for ULCCs. The experimental results are subsequently compared with predictions from an FRP-confined ULCC model, which led to a new ultimate strain model proposed herein for ULCC-filled DSTCs. The comparison demonstrates that the model can provide reasonably accurate predictions of the stress–strain curves of ULCCs in hollow DSTCs. [ABSTRACT FROM AUTHOR]

• We propose a novel lightweight CFRP-ULCC-steel sandwich composite for marine civil engineering application. • We examine the flexural resistance and deformation behavior of the lightweight sandwich composite members through bending test. • We develop a simplified method and fibre element approach to predict the flexural resistance of the composite members. • We recommend uniaxial concrete models to be used for prediction of flexural resistance. • We develop explicit design equations for RC, RR, CR, CC section considering different section classifications and material properties. This paper experimentally and analytically investigates the flexural behaviour of carbon fibre-reinforced polymer (CFRP)-ultralightweight cement composite (ULCC)-steel sandwich composite members filled with a novel ULCC. The flexural resistance and deformation behaviour of sandwich composite members manufactured with various section configurations, internal tube eccentricity and internal tube materials are compared. Four-point bending tests reveal that all of the composite members exhibit ductile flexural failures. The internal tube eccentricity and metal materials significantly affect the flexural resistance, whereas the internal tube configuration has a moderate effect. The composite members with circular internal tubes exhibit greater ductility and flexural resistance than those with rectangular tubes. Two analytical methods the simplified method and fibre element approach, which consider the section configurations, tube eccentricity and material properties based on the strain compatibility principle are developed to predict the composite members' flexural resistance. Moreover, two section classifications are presented. Typical confined concrete models and uniaxial concrete models are used for predicting flexural resistance. The derived models are verified against test results reported here and elsewhere; the confined concrete model provides unconservative flexural resistance predictions, whereas the uniaxial concrete model provides close, conservative predictions. A stepwise approach is proposed for designing lightweight CFRP-ULCC-steel sandwich composite members. [ABSTRACT FROM AUTHOR]

• Develop a novel double-layer steel-LHDCC-steel sandwich composite panel. • Report an experimental study on double-layer sandwich panels under punching loads. • Establish a punching cone model to illustrate the failure mechanisms. • Propose a new model considering the bond-slip effect to predict the ultimate resistance. This study develops a novel double-layer steel-lightweight high ductility cement composite (LHDCC)-steel sandwich composite panels with hybrid shear connectors. Two interventions are included compared to the traditional single-layer steel–concrete-steel panels: (1) material intervention: using ultra lightweight high ductility cement composite; and (2) structural intervention: using double layers to replace the single layer. The experimental program tests two full-scale single-layer sandwich panels and eight full-scale double-layer sandwich panels subjected to concentrated punching load. The specimens vary with different layer numbers, shear span-to-depth ratios, steel contribution ratios, types and spacing of shear connectors, and loading areas. The effects of these parameters on the load–displacement curve and failure mode of the composite sandwich panels are discussed in detail. Compared to the single-layer sandwich panels with comparable steel contribution ratio, the double-layer sandwich panels exhibit larger ultimate resistance and residual resistance. The punching cone model is established to illustrate the failure mechanisms of the double-layer sandwich panels, the failure sequence of which follows: (1) punching shear failure of concrete; (2) punching shear fracture of top plate; and (3) punching shear fracture of middle plate. Based on corresponding failure mechanisms, this study develops analytical models, taking into account of the above parameters, to evaluate the ultimate resistance of the composite panels. The developed models provide close predictions of each peak resistance of the single- and double- layer sandwich panels, which provides reference for the design of multilayer SCS composite panels. [ABSTRACT FROM AUTHOR]

• A new ICCP system was proposed with CFRP bar or SFCB as the anode material. • The electrochemical and mechanical performances of CFRP bar and SFCB was investigated. • CFRP bar and SFCB possess excellent electrical conductivity and low electrical resistance. • The mechanical properties of CFRP bar and SFCB deteriorate after polarization. • Dual-function of CFRP bar and SFCB can be achieved in ICCP syetem. Impressed current cathodic protection (ICCP) has been proved to be an effective method to inhibite steel corrosion. Combined with ICCP technique, a new system has been proposed in this paper with carbon fiber reinforced polymer (CFRP) as dual-functional material: auxiliary anode and partial reinforcement simultaneously. The electrochemical and mechanical performances of CFRP in the new ICCP system were investigated experimentally with two kinds of reinforcement bar: CFRP bar and steel-fiber composite bar (SFCB). First, the accelerated anodic polarization test and electrochemical impedance spectroscopy (EIS) measurement were carried out for CFRP bar and SFCB to verify the electrochemical performances. Then, the mechanical performance and underlying degradation mechanism were identified for CFRP bar and SFCB based on the uniaxial tensile test and scanning electron microscopy (SEM). Finally, the service life of CFRP bar and SFCB has been evaluated to confirm the fesibility of the proposed system in practical engineering. Results showed that CFRP bar and SFCB possess excellent electrical conductivity and low electrical resistance as the anode in ICCP system. Compared with SFCB, CFRP bar is more promising as an anode material with a stronger polarization resistance capability, an acceptable degradation of the mechanical property and a longer service life. With a current density of 20 mA/m2, the service life was evaluated as 62 years for CFRP bar while 7 years for SFCB. To improve the application of SFCB in ICCP system effectively, some modifications are necessary, such as replacing the inner steel bar with stainless steel bar or adding a protective layer between the steel bar and fiber layer. Furthermore, the proposed system shows great potential for marine RC structures and the comprehensive study of this system will be carried out in future work. [ABSTRACT FROM AUTHOR]

• Use large-rupture-strain FRP to retrofit corroded RC columns. • Ten double- and single-curvature RC columns tested under constant axial load together with horizontal cyclic loading. • Effects of corrosion level, axial load ratio and LRS-FRP thickness were clarified. Retrofitting reinforced concrete (RC) column by conventional fibre reinforced polymers (FRPs) can enhance the seismic performance to a limited level due to the small straining capacity and brittle failure of FRP. Existing findings have substantiated that the polyethylene terephthalate (PET) FRP with large rupture strain (LRS) (e.g., greater than 5%) are regarded as preferable to conventional FRP concerning enhancing the ductility of retrofitted RC columns. This paper experimentally evaluates the enhancement in seismic performance of corroded RC columns contributed by LRS-FRP strengthening based on testing of ten RC columns. The main test variables are the corrosion ratio of longitudinal reinforcement, axial force ratio, thickness of LRS-FRP and boundary condition. The seismic performance is systematically evaluated, including crack pattern, failure mode, lateral load resistance, hysteretic response, energy-dissipation capacity, stiffness degradation, ductility and strain responses of wrapped LRS-FRP. The results indicate that corrosion results in significant performance degradation in member strength and ductility. Notably, the failure mode of un-retrofitted corroded columns changes from typical flexural failure to shear-compression failure when the axial load ratio increases from 0.2 to 0.4, which case is prevented by LRS-FRP strengthening so that the retrofitted corroded column eventually experiences ductile flexural failure under larger axial load ratio. Moreover, LRS-FRP retrofitting remarkably improves the ductility and energy dissipation capacity of corroded RC columns compared with the un-retrofitted counterparts. [ABSTRACT FROM AUTHOR]

This paper presents a multi-objective assessment comparing the performance of natural fiber reinforced polymer (NFRP) and carbon fiber reinforced polymer (CFRP) in the flexural strengthening of RC beams. As NFRP laminates and concrete have similar elastic modulus, the NFRP-strengthened RC beams failed by FRP rupture, achieving higher ultimate loads and ductility than the CFRP-strengthened ones. Increasing NFRP reinforcement ratio and NFRP width significantly increased ultimate load and ductility. Narrow NFRP yielded higher strengthening efficiency than wide NFRP. Due to the large amount of impregnated epoxy resin, the cost advantage of natural fiber was greatly nullified and the total cost efficiency of NFRP laminates ranged between 60% and 160% that of CFRP laminates. Epoxy resin also increased the environmental impact of NFRP laminates, the NFRP and CFRP strengthening achieved similar environmental impact. Flax FRP generally yielded lower environmental impact than jute FRP. Prefabrication of NFRP laminates using vacuum infusion method is recommended to improve cost efficiency and lower environmental impact. Image 1 • Natural FRP achieved better flexural performance than the carbon FRP. • Increase of NFRP reinforced ratio leads to higher ultimate load and switches failure mode from NFRP rupture to IC-debonding. • Epoxy resin in NFRP laminates greatly increased the material costs. • Epoxy resin nullified the advantages of natural fibers in terms of environmental impacts. • Vacuum infusion can regain the NFRP's advantages in cost efficiency and environmental impacts. [ABSTRACT FROM AUTHOR]

To further improve the utilization rate of fly ash cenospheres (FAC) in cement-based systems, this paper introduced adopting nano-SiO 2 (NS) particles to develop a new high performance green lightweight engineered cementitious composites (HPGLW-ECC) incorporating FAC. The effects of NS at different dosages (0%, 1%, 2%, 3% and 4% by cement weight) on the mechanical properties and microstructure of lightweight ECC (LW-ECC) were investigated. High performance of NS treated LW-ECC was observed, e.g., the compressive strength, tensile stress and strain capacity at 28 d reached 56 MPa, 8 MPa and 10%, respectively. To understand the reaction mechanism, the thermal gravimetric analysis (TGA) and X-ray diffraction (XRD) analysis were conducted. Besides, the mercury intrusion porosimetry (MIP) analysis indicated that the NS particle effectively restrained the porosity and further refined the pore structure in LW-ECC mortar. The morphology observed by a scanning electronic microscope (SEM) uncovered that NS made the matrix denser and improved the interface transition zone (ITZ) between the FAC and the mortar. Image 1 • A new method is proposed to promote the application of fly ash cenospheres (FAC). • A new HPGLW-ECC is developed by adopting the enhancement effect provided by nano-SiO 2 (NS) particles. • Effects and mechanisms of NS on the microstructure and mechanical properties of HPGLW -ECC are investigated. • The optimized amount of NS addition is around 2% in term of enhancing the HPGLW-ECC. [ABSTRACT FROM AUTHOR]

The NFRP shows great advantages over synthetic FRP in terms of eco-friendliness, recyclability, cost per weight to resist tensile load and bio-degradability. In this study, the flexural performance of reinforced concrete beams strengthened with NFRP laminates is investigated. For the first time, this paper proves the advantages of NFRP over synthetic FRP in terms of strengthening effect and material cost. Two types of NFRP are selected for study: flax and jute. The mechanical properties of the NFRP laminates were first studied by standard coupon tests. A total of six reinforced concrete beams were externally bonded with NFRP laminates and tested under four-point bending. NFRP rupture and debonding were found to be the major failure modes of the strengthened specimen. The flexural performance was evaluated in terms of the load-deflection relationship, the load-strain relationship, the NFRP strain distribution, and the bond stress distribution. The test results showed that NFRP achieved strengthening effects similar to carbon FRP while its cost-efficiency was 20%–40% higher. The precision of current design codes to predict load-carrying capacity of NFRP-strengthened RC beam is evaluated, indicating further modifications to current design codes are needed for application to NFRP strengthening. [ABSTRACT FROM AUTHOR]

This study builds a large database from an extensive survey of existing single-lap shear tests on fiber-reinforced polymer (FRP)-concrete interfacial bonds, comprising 969 test results. Twenty shear-bond strength models published over the past 20 years have been collected and analyzed. These models take into account the effects of the concrete compressive strength, concrete width, FRP elastic modulus, FRP thickness, FRP width and FRP bond length on the ultimate bond strength of the FRP-concrete interface. This paper evaluates the predictive accuracy of the 20 collected models and finds that these models have limited accuracy. To accurately predict the bond strength of the FRP-concrete interface, this paper employs the back propagation neural networks (BPNN) method to train and test the database and builds an artificial neural networks (ANN) model that consists of weighted values, biases and transfer functions. The ANN model test conducts 84 training iterations and selects the optimal combination of input nodes. The accuracy of the developed ANN model is higher (i.e., lower predictive error) than that of the existing bond strength models in the literature. Furthermore, this paper develops an explicit user-friendly formula based on the trained ANN model. The proposed formula estimates and validates the 969 bond strength results, and the predictions using the explicit equation fit the test data very well with small error. As such, the formula can be easily applied during practical designs instead of the implicit processes in the ANN model. [ABSTRACT FROM AUTHOR]

• Production techniques of SFCB with round steel bar inner core were explored. • SFCBs with round bar inner core have comparable tensile performances with SFCBs with ribbed bar inner core. • The newly-developed SFCBs had bond strengths between round and ribbed rebars. A steel-FRP composite bar (SFCB) combines the advantages of both fiber-reinforced polymer (FRP) and steel rebars. This paper introduces production techniques of the newly-developed SFCB with a round steel bar inner core. Then, based on the factory-produced SFCB, the mechanical properties of SFCBs under tensile tests are evaluated, and the bonding performances of SFCBs in concrete are tested and analyzed. The experimental and analytical results indicate that the tensile performances of these new types of SFCBs with a round bar inner core compare favorably with those of SFCBs containing a ribbed bar inner core. The SFCBs had bond strengths between round and ribbed rebars, and the rebar diameter and surface treatment are key factors influencing the bond strength of SFCB-concrete interface. Besides, the bond-slip behavior of SFCB-concrete specimens can be predicted by improving the bonding models of FRP bars. [ABSTRACT FROM AUTHOR]