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15 pages, 7843 KiB

Open AccessArticle

Experimental Study on Dynamic Characteristics of Damaged Post-Tensioning Concrete Sleepers Using Impact Hammer

by Jung-Youl Choi, Tae-Hyung Shin, Sun-Hee Kim and Jee-Seung Chung

Materials 2024, 17(7), 1581; https://doi.org/10.3390/ma17071581 - 29 Mar 2024

Viewed by 734

Abstract

Concrete sleepers in operation are commonly damaged by various internal and external factors, such as poor materials, manufacturing defects, poor construction, environmental factors, and repeated loads and driving characteristics of trains; these factors affect the vibration response, mode shape, and natural frequency of [...] Read more.

Concrete sleepers in operation are commonly damaged by various internal and external factors, such as poor materials, manufacturing defects, poor construction, environmental factors, and repeated loads and driving characteristics of trains; these factors affect the vibration response, mode shape, and natural frequency of damaged concrete sleepers. However, current standards in South Korea require only a subjective visual inspection of concrete sleepers to determine the damage degree and necessity of repair or replacement. In this study, an impact hammer test was performed on concrete sleepers installed on the operating lines of urban railroads to assess the field applicability of the modal test method, with the results indicating that the natural frequency due to concrete sleeper damage was lower than that of the undamaged state. Furthermore, the discrepancy between the simulated and measured natural frequencies of the undamaged concrete sleeper was approximately 1.87%, validating the numerical analysis result. The natural frequency of the damaged concrete sleepers was lower than that of the undamaged concrete sleeper, and cracks in both the concrete sleeper core and the rail seat had the lowest natural frequency among all the damage categories. Therefore, the damage degrees of concrete sleepers can be quantitatively estimated using measured natural-frequency values. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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27 pages, 88912 KiB

Open AccessArticle

A Detailed Numerical Model for a New Composite Slim-Floor Slab System

by Sławomir Dudziak and Paweł M. Lewiński

Materials 2024, 17(7), 1464; https://doi.org/10.3390/ma17071464 - 22 Mar 2024

Viewed by 1466

Abstract

The paper concerns the numerical modelling of a new slim-floor system with innovative steel–concrete composite beams called “hybrid beams”. Hybrid beams consist of a high-strength TT inverted cross-section steel profile and a concrete core made of high-performance concrete and are jointed with prestressed [...] Read more.

The paper concerns the numerical modelling of a new slim-floor system with innovative steel–concrete composite beams called “hybrid beams”. Hybrid beams consist of a high-strength TT inverted cross-section steel profile and a concrete core made of high-performance concrete and are jointed with prestressed hollow core slabs by infill concrete and tie reinforcement. Such systems are gaining popularity since they allow the integration of the main structural members within the ceiling depth, shorten the execution time, and reduce the use of concrete and steel. A three-dimensional finite element model is proposed with all parts of the system taken into account and detailed geometry reproduction. Advanced constitutive models are adopted for steel and concrete. Special attention is paid to the proper characterisation of interfaces. The new approach to calibration of damaged elastic traction–separation constitutive model for cohesive elements is applied to concrete-to-concrete contact zones. The model is validated with outcomes of experimental field tests and analytical calculations. A satisfactory agreement between different assessment methods is obtained. The model can be used in the development phase of a new construction system, for instance, to plan further experimental campaigns or to calibrate simplified design formulas. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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18 pages, 2749 KiB

Open AccessArticle

Macroscopic and Microscopic Investigation of Gypsum Slag Cement-Stabilized Recycled Aggregate Base Layers

by Changdong Zhou, Pengcheng Shi, Hao Huang and Junan Shen

Materials 2024, 17(6), 1450; https://doi.org/10.3390/ma17061450 - 21 Mar 2024

Viewed by 1040

Abstract

The purpose of this study is to investigate the macro and micro properties of stabilized recycled aggregate base layers using gypsum slag cement (GSC) and compare them with ordinary Portland cement (OPC). To achieve this, four levels of recycled aggregate content (0%, 50%, [...] Read more.

The purpose of this study is to investigate the macro and micro properties of stabilized recycled aggregate base layers using gypsum slag cement (GSC) and compare them with ordinary Portland cement (OPC). To achieve this, four levels of recycled aggregate content (0%, 50%, 60%, 70%) and three levels of binder materials (3.5%, 4.5%, 5.5%) were designed, where the binding materials included OPC and GSC. When GSC is used as the binding material with 0% recycled content, two scenarios for the ratio of slag to activator are considered: 4:1 and 4:2. For recycled content of 50%, 60%, and 70%, only the 4:1 ratio is considered. The macro-mechanical properties of the composite material were studied through compaction tests, unconfined compressive strength tests, and indirect tensile strength tests. Microscopic properties were investigated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Macroscopic test results indicate that, at an equal binder content, GSC exhibits a higher moisture content and maximum dry density compared to OPC. Moreover, the unconfined compressive strength and indirect tensile strength of GSC are higher than those of OPC. Microscopic test results reveal that the hydration products of both binding materials are essentially similar; however, under identical curing conditions, the hydration products of GSC are more abundant than those of OPC. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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23 pages, 4621 KiB

Open AccessArticle

Tensile Load-Bearing Behaviour of Concrete Components Reinforced with Flax Fibre Textiles

by Marcus Ricker, Sebastian Kuhn, Tânia Feiri, Katrin Zecherle, Jan Binde and Jana Winkelmann

Materials 2024, 17(6), 1313; https://doi.org/10.3390/ma17061313 - 12 Mar 2024

Cited by 2 | Viewed by 1070

Abstract

In recent years, the use of natural flax fibres as a reinforcement in composite building structures has witnessed a growing interest amongst research communities due to their green, economical, and capable mechanical properties. Most of the previous investigations on the load-bearing behaviour of [...] Read more.

In recent years, the use of natural flax fibres as a reinforcement in composite building structures has witnessed a growing interest amongst research communities due to their green, economical, and capable mechanical properties. Most of the previous investigations on the load-bearing behaviour of concrete components reinforced with natural flax fibres include inorganic impregnations (or even no impregnation) and exclude the use of textile fabrics. Also, the mechanical behaviour of textiles made of natural flax fibres produced as leno fabrics remains to be investigated. In this paper, the results of tensile tests on concrete components reinforced with bio-based impregnated leno fabrics are presented. For comparison, multilayer non-impregnated and impregnated textiles were considered. The results demonstrated that reinforced textiles yielded an increase in the failure loads compared to the concrete cross-sections without reinforcement. The stress-strain diagrams showed that the curves can be divided into three sections, which are typical for reinforced tensile test specimens. For the impregnated textiles, a narrowly distributed crack pattern was observed. The results showed that impregnated textiles tend to support higher failure stresses with less strains than non-impregnated textiles. Moreover, an increase in the reinforcement ratio alongside larger opening widths of the warp yarns enables higher failure loads. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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21 pages, 8843 KiB

Open AccessFeature PaperArticle

Optimized Building Envelope: Lightweight Concrete with Integrated Steel Framework

by Timo Haller, Nancy Beuntner and Karl-Christian Thienel

Materials 2024, 17(6), 1278; https://doi.org/10.3390/ma17061278 - 10 Mar 2024

Viewed by 1144

Abstract

This study presents a novel construction method for prefabricated wall elements by integrating a framework made of thin-walled sheet steel profiles into an optimized thermally insulating lightweight aggregate concrete (LAC) building envelope. The load-bearing function of the framework is provided by cold-formed Sigma-profiles, [...] Read more.

This study presents a novel construction method for prefabricated wall elements by integrating a framework made of thin-walled sheet steel profiles into an optimized thermally insulating lightweight aggregate concrete (LAC) building envelope. The load-bearing function of the framework is provided by cold-formed Sigma-profiles, which are spot-welded to non-load-bearing U-profiles at the vertical ends. The LAC shapes the wall and stabilizes the thin-walled steel profiles against buckling, but has no further load-bearing function, thus allowing the reduction of its necessary compressive strength and subsequently minimizing its density. As a result, the LAC exhibits strength and density values well beyond existing standards, providing highly competitive thermal conductivity values that meet today’s energy requirements without the need for additional insulation materials. Tailored composite specimens verify the stabilization of load-bearing sheet steel profiles by the LAC, which not only prevents buckling but also increases the load-bearing capacity of the overall system. The feasibility of this approach is validated by the production of two prototypes, each comprising a full-sized wall, in two different precast plants using distinct process technologies. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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15 pages, 8283 KiB

Open AccessArticle

Characterization of Flexural Behavior of Hybrid Concrete-Filled Fiber-Reinforced Plastic Piles

by Sun-Hee Kim

Materials 2024, 17(5), 1072; https://doi.org/10.3390/ma17051072 - 26 Feb 2024

Viewed by 735

Abstract

The reinforcing fibers in filament winding fiber-reinforced polymer (FFRP) are not arranged in the axial direction; thus, the members are vulnerable to bending and shear stresses. To address the limitations, this study evaluated FRP-concrete composite piles with reinforcing fiber arranged in circumferential directions. [...] Read more.

The reinforcing fibers in filament winding fiber-reinforced polymer (FFRP) are not arranged in the axial direction; thus, the members are vulnerable to bending and shear stresses. To address the limitations, this study evaluated FRP-concrete composite piles with reinforcing fiber arranged in circumferential directions. In particular, modular pultruded FRP (PFRP) members were fabricated with reinforcing fibers arranged in the axial and circumferential directions. The exterior of the fabricated PFRP members was reinforced with FFRP, and the flexural performance of these members was investigated through flexural strength tests. The results obtained from the flexural tests and flexural-stiffness prediction formula differed by approximately 0.72–1.36 times. A comparison between the results of the flexural test and flexural-strength prediction equation showed an error of approximately 1 to 10%. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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20 pages, 12636 KiB

Open AccessArticle

Equation of State of Autoclaved Aerated Concrete–Oedometric Testing

by Yuri S. Karinski, Vladimir R. Feldgun and David Z. Yankelevsky

Materials 2024, 17(4), 956; https://doi.org/10.3390/ma17040956 - 19 Feb 2024

Viewed by 896

Abstract

This paper aims at investigating the triaxial behavior of Autoclaved Aerated Concrete (AAC) under extremely high pressures, and experimentally determine Equation of State (EOS) for several different AAC densities. Oedometric tests were carried out using a home-made high-pressure triaxial apparatus, and pressures up [...] Read more.

This paper aims at investigating the triaxial behavior of Autoclaved Aerated Concrete (AAC) under extremely high pressures, and experimentally determine Equation of State (EOS) for several different AAC densities. Oedometric tests were carried out using a home-made high-pressure triaxial apparatus, and pressures up to ~500 MPa were applied. The complete pressure-bulk strain relationships were measured, and new findings and insights were obtained. The paper presents the testing set-up and the measurement system. The data processing method accounting for the AAC pronounced shortening during the ongoing test is described using a weighted functions procedure for the circumferential strains’ calculation, with which the confining pressure was determined. The boundary conditions effects on the test results were investigated, and a new technique for specimen insulation was suggested to ensure loading without friction and the prevention of local shear failure. The experimental EOS for different AAC densities were obtained. EOS curves for different specimens with the same density demonstrated good to very good repeatability of the EOS curves over the entire pressure range. Based on the tests results and the density’s span, three classes of AAC are proposed. A preliminary attempt to apply the newly obtained EOS curves has been carried out to examine the energy dissipation for three different dynamic load levels. Although this is a preliminary stage that is beyond the objective of this paper, early interesting results were observed where an optimal AAC density, for which the highest energy has been absorbed, was identified. This finding encourages inclusion of that preliminary study as a closure section. Numerical simulations of wave propagation through ACC layers of different densities, laid on rigid supporting slabs, was carried out. The minimum total impulse imparted to the rigid slab was found for the optimal AAC density that has been determined above. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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16 pages, 5090 KiB

Open AccessArticle

Annual Transmittance Behavior of Light-Transmitting Concrete with Optical Fiber Bundles

by Adithya Shenoy, Gopinatha Nayak, Adithya Tantri, Kiran Kumar Shetty and Mangeshkumar R. Shendkar

Materials 2023, 16(21), 7037; https://doi.org/10.3390/ma16217037 - 4 Nov 2023

Cited by 3 | Viewed by 1340

Abstract

This study characterizes the transmittance behavior of structural light-transmitting concrete under natural sunlight. The experimentation involves the use of a novel test setup and a detailed analysis considering the variation and dependence on time of day, month of the year and seasonal variations. [...] Read more.

This study characterizes the transmittance behavior of structural light-transmitting concrete under natural sunlight. The experimentation involves the use of a novel test setup and a detailed analysis considering the variation and dependence on time of day, month of the year and seasonal variations. The test set consisted of 28 variations of fiber configurations, with two different diameters, spacing and bundling techniques used to increase the area of fibers while maintaining spacing to aid the placing of concrete without compromising on transmittance. The study provides a real-time observational understanding of the behavior of light-transmitting concrete, a result usually obtained by modelling and simulation. The statistical analysis helps in understanding the impact of various variables as well as their interrelationships, which can help in design optimization. Based on the behavior as well as the stipulations of standards, the applicability of the material to various structural applications has been identified. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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21 pages, 9058 KiB

Open AccessArticle

Experimental and Numerical Study of Concrete Fracture Behavior with Multiple Cracks Based on the Meso-Model

by Zhanliang Wang, Wei Zhang and Yiqun Huang

Materials 2023, 16(18), 6311; https://doi.org/10.3390/ma16186311 - 20 Sep 2023

Cited by 1 | Viewed by 1098

Abstract

In this paper, a series of experimental and numerical studies were carried out to investigate the effect of multiple cracks on concrete fracture behavior. Seven groups of double-crack concrete three-point bending (TPB) experiments with different crack lengths and different crack distances were carried [...] Read more.

In this paper, a series of experimental and numerical studies were carried out to investigate the effect of multiple cracks on concrete fracture behavior. Seven groups of double-crack concrete three-point bending (TPB) experiments with different crack lengths and different crack distances were carried out. The experimental results showed that the bearing capacity of double-crack specimens was slightly larger than the standard specimen with one central crack. Additionally, with an increase in the second crack length or with a crack distance reduction, the concrete’s bearing capacity increased correspondingly. Based on the experiments, a numerical meso-model was developed based on applying cohesive elements. The aggregate, mortar, interface transition zone (ITZ), and potential fracture surfaces were explicitly considered in the model. In particular, cohesive elements were used to characterize the mechanical behavior of the ITZ and potential fracture surfaces. A modified constitutive concrete model was developed by considering the potential fracture surfaces’ damage relation and friction effect. The accuracy of the developed meso-model was validated through a comparison between simulation and experiments. Based on meso-models, the influence of multiple cracks on the concrete bearing capacity was investigated by analyzing the energy evolution. The analysis results showed that the bearing capacity has a linear relation with the proportion of mode II energy consumption during the fracture process, which explains why specimens with multiple cracks have a slightly larger bearing capacity than the standard specimens. In summary, this study has found that in three-point bending fracture tests primarily characterized by mode I fractures, the presence of multiple cracks near the main crack slightly enhances the load-bearing capacity of the specimens. This is attributed to a slight increase in internal energy dissipation associated with the presence of these multiple cracks. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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30 pages, 10104 KiB

Open AccessArticle

An Innovative Absorption Propagation System Hollow Block Made of Concrete Modified with Styrene–Butadiene Rubber and Polyethylene Terephthalate Flakes to Reduce the Propagation of Mechanical Vibrations in Walls

by Maciej Major, Izabela Adamczyk and Jarosław Kalinowski

Materials 2023, 16(14), 5028; https://doi.org/10.3390/ma16145028 - 16 Jul 2023

Cited by 1 | Viewed by 2044

Abstract

This paper discusses an innovative APS hollow block wall with a frame made of concrete modified with recycled materials. The technical data of the hollow block, the percentages of the recycled materials, including SBR rubber granules and PET flakes in the modified concrete, [...] Read more.

This paper discusses an innovative APS hollow block wall with a frame made of concrete modified with recycled materials. The technical data of the hollow block, the percentages of the recycled materials, including SBR rubber granules and PET flakes in the modified concrete, and the composition of the concrete modified with this mixture of recycled additives, are presented. To demonstrate the effectiveness of the solution in reducing mechanical vibrations, the effect of the interaction of different frequencies of the mechanical wave on reducing these vibrations was evaluated for APS blocks and Alpha comparison blocks. The test was carried out on a developed test stand dedicated to dynamic measurements for sixteen frequencies in the range from 8 to 5000 Hz, forcing a sinusoidal course of vibrations. The results are presented graphically and show that the new type of APS hollow block wall was much more effective in reducing mechanical vibrations. This efficiency was in the range from 10 to 51% for 12 out of the tested 16 frequencies. For the frequencies of 8, 16, 128, and 2000 Hz, the values were obtained with a difference of 3.58% in favor of the APS hollow block. In addition, the study of the damping effectiveness of the APS hollow blocks, in relation to the vibrations generated by an M-400 impact mill, showed that the APS block wall had a higher damping efficiency of 16.87% compared to the Alpha hollow block for the signal reading on the floor next to the mill, and 18.68% for the signal reading on the mill body. The modified concrete used in the production of the APS hollow blocks enabled the effective use of two recycled materials, SBR rubber and polyethylene terephthalate, in the form of PET flakes. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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11 pages, 4800 KiB

Open AccessArticle

Evaluation of a Hydrophobic Coating Agent Based on Cellulose Nanofiber and Alkyl Ketone Dimer

by Nag-Seop Jang, Chi-Hoon Noh, Young-Hwan Kim, Hee-Jun Yang, Hyeon-Gi Lee and HongSeob Oh

Materials 2023, 16(12), 4216; https://doi.org/10.3390/ma16124216 - 7 Jun 2023

Cited by 2 | Viewed by 1573

Abstract

In this study, we report on the development and testing of hydrophobic coatings using cellulose fibers. The developed hydrophobic coating agent secured hydrophobic performance over 120°. In addition, a pencil hardness test, rapid chloride ion penetration test, and carbonation test were conducted, and [...] Read more.

In this study, we report on the development and testing of hydrophobic coatings using cellulose fibers. The developed hydrophobic coating agent secured hydrophobic performance over 120°. In addition, a pencil hardness test, rapid chloride ion penetration test, and carbonation test were conducted, and it was confirmed that concrete durability could be improved. We believe that this study will promote the research and development of hydrophobic coatings in the future. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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21 pages, 10018 KiB

Open AccessArticle

Numerical Analysis of Low-Velocity Impact Behaviour of Protective Concrete-Filled Steel Plates Composite Wall

by Hongmei Xiao, Peng Yu, Limeng Zhu, Chunwei Zhang and Po-Chien Hsiao

Materials 2023, 16(11), 4130; https://doi.org/10.3390/ma16114130 - 1 Jun 2023

Cited by 1 | Viewed by 1403

Abstract

In this research, a protective concrete-filled steel plate composite wall (PSC) is developed, consisting of a core concrete-filled bilateral steel plate composite shear wall and two lateral replaceable surface steel plates with energy-absorbing layers. The PSC wall is characterised by high in-plane seismic [...] Read more.

In this research, a protective concrete-filled steel plate composite wall (PSC) is developed, consisting of a core concrete-filled bilateral steel plate composite shear wall and two lateral replaceable surface steel plates with energy-absorbing layers. The PSC wall is characterised by high in-plane seismic performance as well as out-of-plane impact performance. Therefore, it could be employed primarily in high-rise constructions, civil defence initiatives, and buildings with stringent structural safety criteria. To investigate the out-of-plane low-velocity impact behaviour of the PSC wall, fine finite element models are validated and developed. Then, the influence of geometrical and dynamic loading parameters on its impact behaviour is investigated. The results show that the replaceable energy-absorbing layer could significantly decrease the out-of-plane displacement and plastic displacement of the PSC wall due to its large plastic deformation, which could absorb a significantly large amount of impact energy. Meanwhile, the PSC wall could maintain high in-plane seismic performance when subjected to impact load. The plastic yield-line theoretical model is proposed and utilised to predict the out-of-plane displacement of the PSC wall, and the calculated results agree very well with the simulated results. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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18 pages, 8990 KiB

Open AccessArticle

Influence of Mechanical Screened Recycled Coarse Aggregates on Properties of Self-Compacting Concrete

by Waiching Tang, Mehrnoush Khavarian, Ali Yousefi, Bill Landenberger and Hongzhi Cui

Materials 2023, 16(4), 1483; https://doi.org/10.3390/ma16041483 - 10 Feb 2023

Cited by 7 | Viewed by 1821

Abstract

The use of recycled coarse aggregates (RA) in concrete is a sustainable alternative to non-renewable natural aggregate (NA) to fabricate concrete products using in concrete structures. However, the adhered mortar on the surface of RA would considerably impact the qualities of concrete products. [...] Read more.

The use of recycled coarse aggregates (RA) in concrete is a sustainable alternative to non-renewable natural aggregate (NA) to fabricate concrete products using in concrete structures. However, the adhered mortar on the surface of RA would considerably impact the qualities of concrete products. As a practical treatment procedure, mechanical screening can remove the adhered mortar. This research aims to study the influence of mechanical screening on the fundamental properties of RA and the resulting self-compacting concrete (SCC). The RA were mechanically screened up to four times, and their physical properties including particle size distribution, water absorption, and crushing value were investigated. The properties of RA-SCC including workability, density, compressive and tensile strengths, modulus of elasticity, and microstructure were also examined. The results demonstrated that screening reduced the water absorption of RA from 6.26% to 5.33% and consequently enhanced the workability of RA-SCC. Furthermore, it was shown that increasing the screening up to twice improved the mechanical properties of concrete. In particular, screening increased the compressive strength of concrete by 15–35% compared to the concrete with unscreened RA. Similar improvements were found in tensile strength as well as the elastic modulus results. The microstructure of screened RA-SCC was comparable to that of the control concrete, showing minimal porosity and cracks along the interfacial transition zone. In conclusion, once or twice screening is recommended to the recycling facility plant to remove adequate amount of adhered mortar and fines while preventing damages to the RA. Improving the quality of RA via mechanical screening is one of the promising approaches to increase their potential for use in concrete, thereby reducing extraction of natural resources and promoting a circular economy. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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Review

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34 pages, 11231 KiB

Open AccessReview

Effect of Steel Fibers on Tensile Properties of Ultra-High-Performance Concrete: A Review

by Wanghui Du, Feng Yu, Liangsheng Qiu, Yixuan Guo, Jialiang Wang and Baoguo Han

Materials 2024, 17(5), 1108; https://doi.org/10.3390/ma17051108 - 28 Feb 2024

Cited by 2 | Viewed by 2372

Abstract

Ultra-high-performance concrete (UHPC) is an advanced cement-based material with excellent mechanical properties and durability. However, with the improvement of UHPC’s compressive properties, its insufficient tensile properties have gradually attracted attention. This paper reviews the tensile properties of steel fibers in UHPC. The purpose [...] Read more.

Ultra-high-performance concrete (UHPC) is an advanced cement-based material with excellent mechanical properties and durability. However, with the improvement of UHPC’s compressive properties, its insufficient tensile properties have gradually attracted attention. This paper reviews the tensile properties of steel fibers in UHPC. The purpose is to summarize the existing research and to provide guidance for future research. The relevant papers were retrieved through three commonly used experimental methods for UHPC tensile properties (the direct tensile test, flexural test, and splitting test), and classified according to the content, length, type, and combination of the steel fibers. The results show that the direct tensile test can better reflect the true tensile strength of UHPC materials. The tensile properties of UHPC are not only related to the content, shape, length, and hybrids of the steel fibers, but also to the composition of the UHPC matrix, the orientation of the fibers, and the geometric dimensions of the specimen. The improvement of the tensile properties of the steel fiber combinations depends on the effectiveness of the synergy between the fibers. Additionally, digital image correlation (DIC) technology is mainly used for crack propagation in UHPC. The analysis of the post-crack phase of UHPC is facilitated. Theoretical models and empirical formulas for tensile properties can further deepen the understanding of UHPC tensile properties and provide suggestions for future research. Full article

(This article belongs to the Special Issue Concrete in Structural Engineering: Fabrication and Mechanical Behavior ‖)

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