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Mechanical Properties and Microstructure of Ultra-High-Performance Concrete Containing Recycled Aggregates Co-Modified with Steel Fibres and Nanosilica after Exposure to Elevated Temperatures

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SSRN 2023年

作者： Sun, Hang Luo, Liang Yuan, Huan Li, Xi Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Transportation and Science Engineering Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

This study explores the mechanical properties and microstructure of ultra-high-performance concrete with recycled aggregates (UHPC-RA) enhanced by nanosilica (NS) and steel fibers (SF) at elevated temperatures. Thirty-six mixtures, varying in RA replacement rates, SF, and NS content, were prepared and tested for compressive strength, splitting tensile strength, and elastic modulus. Microstructural analyses included SEM morphology, XRD composition, pore size distribution, thermal conductivity, and elemental distribution studies. Results show temperature-induced changes, including SF oxidation and spalling, causing brittle failures due to weakened cementitious matrix and ITZ bonding. Moisture evaporation and hydration product decomposition lead to mass loss. Compressive strength initially increases and then decreases with rising temperatures, while overall splitting tensile strength decreases. Deterioration in UHPC-RA's microstructure is main reason for macroscopic mechanical property degradation. Linear relationships between compressive and splitting tensile strength were established. SEM and XRD confirmed that NS particles contribute to the conversion of CH to C-S-H gels. © 2023, The Authors. All rights reserved.

关键词： Steel fibers

Influence of Mix Proportioning Parameters and Curing Regimes on the Properties of Ultra-High Strength Alkali-Activated Concrete

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SSRN 2023年

作者： He, Haiyu Zhang, Rong Song, Yuhuan Zhi, Xudong Fan, Feng Key Lab of Structures Dynamic Behaviour and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China

This study investigates the influence of mix proportioning parameters and curing regimes on the material properties of alkali-activated binder-based ultra-high strength concrete (AAB-UHSC). The effects of five groups of mix proportioning parameters (i.e., fly ash replacement ratio, silica fume replacement ratio, alkali to binder ratio, water glass modulus, and steel fiber content) and three curing regimes(i.e., ambient curing, standard curing, and hybrid curing) on the workability, compressive strength, flexural strength and microstructure development of AAB-UHSC were systematically evaluated. The results indicated that increasing the steel fiber and silica fume dosage negatively affected the flowability of freshly mixed AAB-UHSC. There existed an optimal alkali-to-binder ratio and water glass modulus in terms of flowability, compressive strength, and flexural strength, but the fly ash replacement ratio had a complex effect on the material performance of the AAB-UHSC. The microstructures of the specimens cured in hybrid curing regimes were denser, and fewer cracks were observed, which resulted in higher strength compared to specimens cured under ambient curing and standard curing conditions. The three types of curing regimes adopted barely alter the phases and molecular bonds of hydration products based on the XRD and FTIR results. In addition, the correlations between the compressive strength of the AAB-UHSC obtained under ambient curing conditions, standard curing conditions, and obtained under hybrid curing and standard curing conditions were analyzed, and the fitted results had higher correlation coefficients (R2). © 2023, The Authors. All rights reserved.

关键词： Compressive strength

Enhancing Ultrasonic Flaw Detection by a Nonconvex Sparse Regularization Approach

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SSRN 2023年

作者： Wu, Biao Zhou, Wensong College of Civil Engineering Nanjing Tech University Nanjing211816 China Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education School of Civil Engineering Harbin Institute of Technology Harbin150090 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China

Ultrasonic testing has been an important tool for the detection of hidden defects in materials yet its effectiveness is usually compromised by the noise originated from both the testing system and the material being evaluated. Motivated by the prior knowledge that only a small number of defects or reflectors exist within the tested material thus the measured signal can be viewed as a linear combination of a few echoes, a novel signal processing method is proposed in this study where a nonconvex sparse regularization method based on lp-norm (0 © 2023, The Authors. All rights reserved.

关键词： Defects

The Micro–Mechanical Mechanism of Multiple Cracking behavior Induced by Interface Strengthening for Ultra–High–Performance Concrete

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SSRN 2023年

作者： Du, Junjie Xiao, Huigang Zhang, Fengling Liu, Min Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China School of Civil Engineering Shandong University 17923 Jingshi Road Jinan250061 China

The multiple cracking behavior of ultra–high–performance concrete （UHPC） is strongly dependent on the bridging of cracks by fibers and the spatial strength distribution of matrix. A good match between fiber bridging properties and matrix tensile strength can significantly improve the utilization of fibers and matrix. In this study, a micromechanics based theoretical model is proposed, which can match the matrix tensile strength with the fiber–matrix interface bonding strength. The spatial strength distribution of the matrix and the stress transfer between the fiber and the matrix is considered in the model. Bridge stresses, additional stresses, stress transfer distances, and pulley forces at the crack face for various crack openings are derived. Dense multiple cracks were observed in the UHPC tensile samples at a common condition ( ) designing based on the calculation results. The applicability of the model is validated by comparing the simulation results and the experimental results in previous investigations at the same paraments ( ). With the proposed model, the mechanism of fiber–matrix interface enhancement contributing to the multiple cracking behavior can be understood. The results of this study could provide fundamental insights for the design of UHPC for various ductility and strength requirements. © 2023, The Authors. All rights reserved.

关键词： Fibers

A Two-Stage Mitigation Method for Optical Turbulence-Induced Errors in Vision-Based Structural Displacement Measurement

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SSRN 2024年

作者： Zhang, Xiulin Zhou, Wensong Chen, Xize Wang, Yonghuan Wu, Qi Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China Central Research Institute of Building and Construction Co. Ltd MCC Group Beijing100088 China

Vision-based structural displacement measurement techniques have been widely applied. However, the visual sensors used for remote monitoring of structures in high-temperature weather are easily affected by optical turbulence, which introduces errors in displacement measurement. Therefore, this paper proposes a two-stage optical turbulence-induced error alleviation method. In the first stage, the steerable pyramid method is used to decompose the monitoring video, and the phase of each position is independently temporal filtered at different spatial scales and directions to reconstruct the video. To further reduce errors with spatial randomness, a feature point matching method considering the weighted distance is used to track the displacement of multiple measurement points on the target structure in the reconstructed video, and the results are spatially filtered in the second stage. The effectiveness of the proposed method was verified through static and dynamic target experiments using a heater to simulate optical turbulence in the laboratory. © 2024, The Authors. All rights reserved.

关键词： Errors

A 4D Digital Recovery of the Morphological Evolvement During Pitting Corrosion in Austenitic Grain structure

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SSRN 2023年

作者： Wang, Mingzhi Yang, Xu Wang, Zhenbo Wang, Wei School of Civil Engineering Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology Harbin150090 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China FAW GROUP Changchun130011 China

Pitting corrosion is one fatal phenomenon in metallic material deterioration. A comprehensive understanding of mesoscale corrosion morphology aids the material design for macroscale resilience. This paper presents a confluence between numerical grain structure reconstruction and multiphase corrosion kinetics. A cellular automaton algorithm is proposed to digitally recover the austenite grain structure through nucleation. Image-based input technique is adopted to perform a grain size distribution comparison between digital and practical austenite grain mesostructure. The morphological evolvement during a nanoscale Lattice Boltzmann corrosion is quantitatively characterized by surface area and surface roundness factor. Single pitting results show that the heterogeneous phase distribution contributed up to 7% of the surface roughness of a single pit in the designed environment. The surface roughness development of single pit corrosion is independent of the damage depth under the designed environment. A damage depth threshold exists to trigger the verticle corrosion pit development towards non-spherical morphology. Multiple pitting results show that grain boundary percolation is crucial to maintain mesostructure integrity. This work suggests that manufactured metallic material with high grain boundary resistivity provides a mesoscale skeleton, providing structural resistance in an environment with anti-corrosion requirement. © 2023, The Authors. All rights reserved.

关键词： Surface roughness

Tensile Resistance of Novel Interlocked Angle Connectors Used in Steel-Concrete-Steel Sandwich structures

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SSRN 2022年

作者： Zhou, Zhaohui Wang, Yonghui Zhai, Ximei Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China

This paper reports a new interlocked angle connector (IAC) for steel-concrete-steel sandwich structures, and the tensile behaviors of the IACs was also studied in detail by performing the tensile test. There were 14 specimens with different parameters being designed, including embedded depth of IACs, thicknesses of steel sheet, steel angle and bottom plate, side length of steel angle, diameter of steel tube and interlocking bolt. The failure modes and tensile resistances of the proposed IACs were obtained, and three failure modes were identified, including concrete breakout failure, tensile fracture failure of the steel angle and concrete direct shear failure. The main parameters affecting tensile resistance of the IACs were also discussed and analyzed. In addition, analytical models were proposed for predicting the ten¬sile resistances of IACs and their accuracies were also verified via comparing the pre¬dicted values with test results. Finally, the tensile resistances of IACs were compared with those of J-hook connectors, and improved tensile resistance could be observed for the proposed IACs. © 2022, The Authors. All rights reserved.

关键词： Tensile testing

Experimental Study of the Wake of Multi-Rotor Turbine

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SSRN 2022年

作者： Xiong, Xue-Lu Laima, Shujin Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control Ministry of Education Harbin Institute of Technology Harbin150090 China

This paper describes a comparative experimental study of the wake of a multi-rotor turbine and a single-rotor turbine. The wake merge process in the multi-rotor wake is analyzed from various perspectives. A jet-like gap flow region and a momentum redistribution region are found in the region before and after the full merge of the individual rotor wakes, respectively. Compared to the single-rotor wake, the fully merged multi-rotor wake is found to have a slower recovery rate and a lower turbulent kinetic energy. Furthermore, two sources are found for the peak frequency in the multi-rotor wake which results in different peak frequencies at different locations. One of the two sources is the rotor wake meandering with the meandering frequency maintain the same throughout the wake, and another one corresponds to the dynamic of the shear layer in the gap region with its peak frequency decrease in the streamwise direction. The yawed multi-rotor wake is found to be similar to the non-yawed case except for the wake deflection of the yawed case. And the deflection is more pronounced in the yawed multi-rotor wake than in the yawed single-rotor wake which indicates a higher yaw efficiency for the multi-rotor turbine. © 2022, The Authors. All rights reserved.

关键词： Wakes

Sensitivity Analysis on Effective Parameters for Snow-Melting Performance on Automatically Snow-Melting Fabric Roof And Application on Practical structure

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SSRN 2022年

作者： Zou, Jialin Sun, Xiaoying Liu, Qing Key Lab of Structures Dynamic Behavior Control of China Ministry of Education Harbin Institute of Technology Harbin150090 China Key lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China

In recent decades, numerous membrane structures have been built in the cold region of china. Nevertheless, collapse caused by uneven snow distribution and snow sliding from the edge of roofs occur frequently. This collapse threatens the people’s lives and property. In order to prevent collapse of membrane structure, the automatically snow-melting fabric roof based on electrical-thermal system is presented in this study. Automatically snow-melting fabric roof based on electrical-thermal systems are environmental friendly and clean for eliminating snow that has accumulated on fabric roof. The main task in design the automatically snow-melting fabric roof is determining heating feasibility. A thermal simulation method for the snow melting process is described. This numerical method can predict surface temperature, snow-free area ratio and the coefficient of variation for temperature when climatic condition and heating wire layout parameters are provided. The model is validated experimentally and the influence analysis between the inputs( the heating wire power and spacing, wind velocity, solar radiation, ambient temperature and snow thickness) and the outputs of snow-melting performance are found by thermal simulation. Finally, the three layout scheme of heating wire have been proposed based on snow distribution of four prevailing wind direction and have been applied to ensure that snow-melting fabric roof based on electrical-thermal system studied are feasible to control thickness of snow layers in practical membrane structure. © 2022, The Authors. All rights reserved.

关键词： Snow