Abstract
Three kinds of nano-concrete, i.e., 2.0% nano-SiO
2
doped, 2.0% nano-CaCO
3
doped and 1.0% nano-SiO
2
-1.0% nano-CaCO
3
co-doped concretes (NS, NC, NSC) were prepared for a study on static ...property and dynamic property under different strain rates (50–130 s
−1
) using HYY series hydraulic servo test system and Φ100 mm split Hopkinson pressure bar test system, and a comparison with plain concrete (PC) as well. The results have shown that under static load, as compared with PC, NC has both strength and elastic modulus increased obviously, while NS has strength decreased and elastic modulus increased, and under dynamic load, there is an obvious strain rate effect for the dynamic compressive strength, impact toughness, energy dissipation and impact failure mode of concrete. Under the same strain rate, the dynamic compressive strength, peak strain, impact toughness and energy dissipation of NC are significantly increased, while its dynamic elastic modulus is decreased. Compared with PC, NS has dynamic compressive strength, peak strain, impact toughness and energy dissipation decreased, and dynamic elastic modulus increased, NC has static and dynamic mechanical properties improved, NS has static and dynamic mechanical properties weakened, and NSC is between PC and NC in static and dynamic mechanical properties, but generally improved. Doped with nano-CaCO
3
, NC has compactness improved, weak areas reduced, and pore size distribution optimized, while doped with nano-SiO
2
, NS has obvious internal weak areas, with pore structure degraded.
Adding short steel fibers into slag-based geopolymer mortar and concrete is an effective method to enhance their mechanical properties. The fracture properties of steel fiber-reinforced slag-based ...geopolymer concrete/mortar (SGC/SGM) and unreinforced control samples were compared through three-point bending (TPB) tests. The influences of steel fiber volume contents (1.0%, 1.5% and 2.0%) on the fracture properties of SGC and SGM were studied. Load-midspan deflection (
) curves and load-crack mouth opening displacement (
-CMOD) curves of the tested beams were recorded. The compressive and splitting tensile strengths were also tested. The fracture energy, flexural strength parameters, and fracture toughness of steel fiber-reinforced SGC and SGM were calculated and analyzed. The softening curves of steel fiber-reinforced SGC and SGM were determined using inverse analysis. The experimental results show that the splitting tensile strength, fracture energy, and fracture toughness are significantly enhanced with fiber incorporation. A strong correlation between the equivalent and residual flexural strengths is also observed. In addition, the trilinear strain-softening curves obtained by inverse analysis predict well of the load-displacement curves recorded from TPB tests.
Steel rebar buckling is an important failure mode in reinforced concrete (RC) columns. Fiber-reinforced polymer (FRP) composites provide an effective mean that can restrain or delay longitudinal ...rebar buckling. To accurately predict the strength and ductility of FRP-strengthened rectangular RC columns, it is necessary to accurately evaluate the interactions between FRP confinement and steel reinforcement buckling behavior at as any loading levels as possible. This paper proposed a composite beam model and a tension-bending beam model to evaluate the lateral support stiffness of FRP-wrapped concrete cover on steel reinforcement in the corner regions and flat sides of rectangular columns. Then, the whole stress-strain curves for reinforcing bar buckling behavior considering the lateral support of FRP jackets can be obtained and validated with the existing test database. For FRP-strengthened rectangular RC columns under monotonic axial compression, the overall load-bearing capacity of RC columns can be determined by summarizing axial loads sustained by FRP-confined corresponding plain concrete (PC) columns and the load contribution of steel rebars considering FRP lateral support. The accuracy of the proposed method is demonstrated by comparing theoretical predictions with test results. This calculation method can accurately predict the strength and ductility of FRP-wrapped rectangular columns within a 20% variation margin, which provides a reliable basis for the design of concrete structures.
•A composite beam model and a tension-bending beam model are developed to evaluate the spring stiffness.•A method is established to predict the overall behavior of FRP-confined rectangular RC columns considering bar buckling.•The factors affecting rebar buckling and the performance of FRP-confined rectangular RC columns are analyzed.
Precipitation is the main component of global water cycle. At present, satellite quantitative precipitation estimates (QPEs) are widely applied in the scientific community. However, the evaluations ...of satellite QPEs have some limitations in terms of the deficiency in observation, evaluation methodology, the selection of time windows for evaluation and short periods for evaluation. The objective of this work is to make some improvements by evaluating the spatio-temporal pattern of the long-terms Climate Hazard Group InfraRed Precipitation Satellite’s (CHIRPS’s) QPEs over mainland China. In this study, we compared the daily precipitation estimates from CHIRPS with 2480 rain gauges across China and gridded observation using several statistical metrics in the long-term period of 1981–2014. The results show that there is significant difference between point evaluation and grid evaluation for CHIRPS. CHIRPS has better performance for a large amount of precipitation than it does for arid and semi-arid land. The change in good performance zones has strong relationship with monsoon’s movement. Therefore, CHIRPS performs better in river basins of southern China and exhibits poor performance in river basins in northwestern and northern China. Moreover, CHIRPS exhibits better in warm season than in Winter, owing to its limited ability to detect snowfall. Nevertheless, CHIRPS is moderately sensitive to the precipitation from typhoon weather systems. The limitations for CHIRPS result from the Tropical Rainfall Measuring Mission (TRMM) 3B42 estimates’ accuracy and valid spatial coverage.
The development of highly active, eco-friendly, and structurely fine-tunable organic luminophores is currently desirable for electrochemiluminescence (ECL). Tetraphenylethene (TPE) derivatives are ...the most representative aggregation-induced emission characteristic (AIEgens). In contrast, their aggregation-induced ECLs have not been detail studied. Herein, we report the bright cathodic aggregated state ECL of TPE derivatives by a coreactant approach. In this system, the substituents profoundly affect ECL emissions by changing the relative intensities of R and B band intensity ratios in their UV–vis spectra as well as the HOMO and LUMO energies. It was discovered that electron-withdrawing nitro-substituted TPE-(NO2)4 with a smaller LUMO/HOMO band gap and stronger R band featured the strongest ECL emissions and became the best luminophore for the highly efficient detection of iodide (I–) in the aqueous phase. This work not only reveals the influence of R and B bands in TPE derivative UV–vis spectra on their optical properties but also constructs a novel aggregation-induced ECL sensing.
By chemical precipitation of Au nanoparticles on the ZnO nanorods, the heterostructures were successfully obtained. The structures were investigated by several methods and it was revealed that with ...the increase of the Au precursor, the size of Au nanoparticles was increased and the interaction between Au nanoparticle and ZnO nanorod was also confirmed. The performance of the photodegradation of
p
-nitrophenol suggested that the activity was related with the amount of Au nanoparticles in Au/ZnO heterostructure to a great extent. It was suggested that by taking advantage of the one dimension ZnO nanorods with the effect of aspect ratio and surface defects as well as the local surface plasma resonance adsorption of Au nanoparticles, the heterostructures demonstrated an ideal activity under visible light for the disposal of low concentration of organic pollutants, suggesting a potential application in environmental remediation.
By taking advantage of one dimension ZnO nanorod with the effect of aspect ratio and surface defects as well as the local surface plasma resonance adsorption of Au nanoparticles, the Au nanoparticles/ZnO nanorods heterostructures were synthesized and demonstrated an ideal activity under visible light for the degradation of low concentration of organic pollutants.
Highlights
The Au nanoparticle/ZnO nanorod was synthesized.
A large increase of photoactivity was observed due to the synergistic effect of Au.
The Au/ZnO demonstrated a potential application in environmental remediation.
•The seismic behaviour of LRS FRP-wrapped non-ductile RC columns was experimentally investigated.•The advantage of LRS FRP-wrapped RC columns in seismic retrofit was demonstrated.•The influence of ...FRP confinement stiffness on seismic performance was studied.•The accuracy of cyclic compression model model of LRS FRP-strengthened concrete was verified.
This paper presents experimental studies and numerical simulations of circular reinforced concrete (RC) columns wrapped with Polyethylene Naphthalate fiber reinforced polymer (PEN FRP, a kind of large-rupture-strain FRP) and conventional CFRP. A total of seven columns were designed and fabricated, including a control column, three columns strengthened with CFRP, and three columns strengthened with PEN FRP. All columns were subjected to cyclic lateral load and a constant high axial load. The effectiveness of PEN FRP strengthening was systematically analyzed and discussed regarding the failure mode, displacement ductility, lateral cyclic load–displacement curve, stiffness degradation and energy dissipation capacity. The test results indicated that the control column exhibited inferior ductility and peak lateral strength, while FRP-strengthened columns possess better energy dissipation capacity and ductility. Further study found that PEN FRP was preferred to CFRP with similar tensile stiffness in seismic strengthening. Finally, based on the cyclic compression model of LRS FRP-strengthened concrete, the improved tensile model of FRP-strengthened concrete, and the cyclic stress–strain model of reinforcing steel, numerical simulations for seismic performance were carried out in OpenSees. It was found that the numerical simulation results of all FRP-strengthened RC columns were in excellent agreement with the test results. To better understand the effect of FRP confinement stiffness on the seismic performance of circular columns, parametric analysis was performed. Results showed that the numerical simulations need to consider the buckling of longitudinal reinforcement for accurately predicting the seismic behavior of FRP-strengthened columns of lower confinement stiffness.
Zinc oxide (ZnO) and cobalt (Co)-ZnO nanocomposites were first reacted with 2-Methylimidazole to synthesize the zeolitic imidazole frameworks as precursors. After calcination in nitrogen, the ZnO/N-C ...and Co/ZnO/N-C composites were received, respectively. The structure and composition of the samples at different stages were characterized in order to illustrate the transformation process. Finally, the ZnO/N-C and Co/ZnO/N-C composites were employed as catalysts for the hydrogenation of
p
-nitrophenol by sodium borohydride. The catalytic results suggested that the Co/ZnO/N-C composite with a proper amount of metallic cobalt, better dispersion, small size, and synergetic effect of N doping on carbon displayed a much more efficient catalytic ability for the reduction of
p
-nitrophenol in comparison with the ZnO/N-C composite as well as the Co/N-C composite synthesized by ZIF-67. The present work would provide further insight into the design of metal-carbon-based materials from the corresponded metal-organic frameworks derived from the relevant metal oxides and development of their applications from the aspect of interface and colloid chemistry.
•A modified concrete damaged plasticity model is proposed considering the deformation and mechanical characteristics of LRS FRP-confined concrete.•The 3D finite element analysis of longitudinal ...reinforcement buckling in LRS FRP-confined RC columns is realized.•The effect of longitudinal reinforcement buckling on member is illustrated by the FEA results.•The factors affecting the buckling of longitudinal reinforcement are studied, and an empirical formula for determining the failure of members by the buckling of longitudinal reinforcement is proposed.
Large rupture strain (LRS) FRPs have great potential to be used for seismic retrofit of RC columns because of its high rupture strain (i.e., > 5%) that provides better confinement effects. However, in FRP-confined RC columns, the longitudinal reinforcements may buckle before the LRS FRP rupture, especially in the case of large stirrup spacing. This study aims to present a 3D finite element (FE) model for simulating the buckling effect of longitudinal reinforcements in LRS FRP-confined RC columns. A modified concrete damaged plasticity model (CDPM) is proposed to consider the deformation and mechanical characteristics of LRS FRP-confined concrete. Removal of failed concrete elements is considered to facilitate the buckling of longitudinal reinforcements in LRS FRP-confined RC columns. The FE analysis accuracy was verified by comparisons with test results. The factors affecting the buckling of longitudinal reinforcements were discussed through an extensive parametric study. Empirical formulas for the stress and strain values at which the longitudinal reinforcement starts to soften were developed. An empirical formula for the ultimate axial strain of LRS FRP-confined RC columns determined by longitudinal reinforcement buckling was also obtained by regression analysis.
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