Compressive Toughness Research Articles

Effects of aggregates and fibers on the strength and permeability of concrete exposed to low vacuum environment

The performance and regulation of concrete in low vacuum environments are receiving increasing attention. This study investigates the effects of aggregates and fibers on the strength and permeability of concrete in a low vacuum environment, using varying gradients of sand ratios (37.5 %, 40 %, and 42 %) and aggregate-to-binder ratios (3.27, 3.92, and 4.14). Three types of non-metallic fibers are utilized: polyethylene (PE), polyvinyl alcohol (PVA), and glass fibers. Evaluations focus on concrete strength, mass loss, gas permeability, capillary water absorption, and porosity. Results indicate that higher sand and aggregate-to-binder ratios enhance both flexural and compressive strength. Fiber incorporation improves flexural and compressive toughness, with PE fibers showing the most significant toughening effect. The low vacuum environment increases the strength of the concrete but reduces its axial compression toughness ratio and increases brittleness, while fiber incorporation helps improve the compression toughness of the concrete. Higher sand and aggregate-to-binder ratios reduce mass loss and accelerate drying equilibrium, while fibers increase mass loss and prolong drying equilibrium, with PVA fibers causing greater mass loss. The pattern of concrete mass loss can be explained by the tortuosity of the moisture diffusion path. Additionally, low vacuum significantly increases the gas permeability of concrete. Enhancing the sand and aggregate-to-binder ratios reduces permeability both before and after low vacuum treatment. Although fibers increase the gas permeability, they help mitigate this increase under low vacuum condition. Capillary water absorption tests reveal that concrete under low vacuum condition has a significantly higher water absorption rate compared to air-drying condition. Increasing sand and aggregate-to-binder ratios reduces water absorption and capillary water content, whereas fibers have the opposite effect. Porosity tests show that moisture migration in a low vacuum environment is mainly related to permeable porosity, while total porosity is more closely related to compressive strength.

A lignin-based controlled/sustained release hydrogel by integrating mechanical strengthening and bioactivities of lignin

The favorable antioxidant and antimicrobial activities of lignin have been shown to promote wound healing. However, the accumulation of lignin in high concentrations in the body brings about varying degrees of biotoxicity. Herein, a controlled/sustained release polyvinyl alcohol/chitosan/sulfonated lignin hydrogel (PVA-CS-L) integrated mechanical strengthening and bioactivities of lignin was developed. The lignin-induced non-covalent bond network (van der Waals force, hydrogen and electrostatic interactions) promoted energy dissipation when the hydrogel was subjected to stretching and compression. This endowed the PVA-CS-L hydrogel with improved tensile (∼36 kPa) and compressive strength (∼900 kPa), as well as compressive toughness (∼9.0 MJ/m3), which were superior to the polyvinyl alcohol/chitosan hydrogel (PVA-CS) (31 kPa, 680 kPa, and 7.5 MJ/m3, respectively). The construction of electrostatic interaction could not only slow down the sudden release of lignin but also make the hydrogel exhibit a good pH-sensitive behavior of controlled-release lignin. Also, the developed hydrogel had good biocompatibility and the released lignin had reactive oxygen species scavenging as well as inhibitory activity against Staphylococcus aureus. Finally, preliminary evaluation of drug delivery reveals that the presence of lignin enabled the hydrogel to exhibit longer-lasting controlled/sustained epigallocatechin gallate release properties. Such lignin-based controlled/sustained release hydrogel that integrates the molecular structure and biological difunctional features of lignin gives new insight into cost-effective, easy-to-operate manufacturing of load-bearing and bioactive materials.

Experimental Study on the Mechanical Properties of Steel Fiber Ferronickel Slag Powder Concrete

The use of ferronickel slag powder (FNSP) as a cementitious additional material has been supported by numerous reports. FNSP concrete has the same shortcomings as ordinary concrete, including low hardness. In this study, in order to make FNSP concrete more durable, end-hooked type steel fibers were incorporated. To understand how various elements affect the mechanical properties of steel fibers, an experiment was carried out on the mechanical properties of steel FNSP concrete (SFNSPC). FNSP’s principal ingredients, with a particle size distribution ranging from 0.5 to 100 μm and a sheet-like powder shape, are CaO, SiO2, Al2O3, MgO, and others, according to tests conducted on the material’s microstructure and composition. Then, eighteen mix proportions were developed, comprising six distinct FNSP replacement rate types and three distinct steel fiber content types. Crucial metrics were evaluated and analyzed, including the relationship among the toughness, tensile strength, and compressive strength as well as slump, splitting tensile strength, compressive strength, and uniaxial compressive stress–strain curve of SFNSPC. The results showed that the slump of SFNSPC under different FNSP replacement rates decreased with increasing steel fiber volume. Steel fibers have a small but positive effect on SFNSPC’s compressive strength; nonetheless, as FNSP replacement rates increased, SFNSPC’s slump gradually decreased, though not by much. These results show that FNSP is a viable alternative cementitious material in terms of strength. Specifically, the splitting tensile strength of SFNSPC improves with an increase in steel fiber content, and the pace at which SFNSPC strength drops with an increase in the FNSP replacement rate. With varying mix proportions, the stress–strain curve trend of SFNSPC remains mostly constant, and steel fibers improve the compressive toughness of SFNSPC. After adding 0.5% and 1.0% steel fibers, the toughness index of concrete with different FNSP replacement rates increased by 8–30% and 12–43%, respectively.

Tissue-adhesive, stretchable and compressible physical double-crosslinked microgel-integrated hydrogels for dynamic wound care

Integrated wound care through sequentially promoting hemostasis, sealing, and healing holds great promise in clinical practice. However, it remains challenging for regular bioadhesives to achieve integrated care of dynamic wounds due to the difficulties in adapting to dynamic mechanical and wet wound environments. Herein, we reported a type of dehydrated, physical double crosslinked microgels (DPDMs) which were capable of in situ forming highly stretchable, compressible and tissue-adhesive hydrogels for integrated care of dynamic wounds. The DPDMs were designed by the rational integration of the reversible crosslinks and double crosslinks into micronized gels. The reversible physical crosslinks enabled the DPDMs to integrate together, and the double crosslinked characteristics further strengthen the formed macroscopical networks (DPDM-Gels). We demonstrated that the DPDM-Gels simultaneously possess outstanding tensile (∼940 kJ/m3) and compressive (∼270 kJ/m3) toughness, commercial bioadhesives-comparable tissue-adhesive strength, together with stable performance under hundreds of deformations. In vivo results further revealed that the DPDM-Gels could effectively stop bleeding in various bleeding models, even in an actual dynamic environment, and enable the integrated care of dynamic skin wounds. On the basis of the remarkable mechanical and appropriate adhesive properties, together with impressive integrated care capacities, the DPDM-Gels may provide a new approach for the smart care of dynamic wounds. Statement of significanceIntegrated care of dynamic wounds holds great significance in clinical practice. However, the dynamic and wet wound environments pose great challenges for existing hydrogels to achieve it. This work developed robust adhesive hydrogels for integrated care of dynamic wounds by designing dehydrated, physical double crosslinked microgels (DPDMs). The reversible and double crosslinks enabled DPDMs to integrate into macroscopic hydrogels with high mechanical properties, appropriate adhesive strength and stable performance under hundreds of external deformations. Upon application at the injury site, DPDM-Gels efficiently stopped bleeding, even in an actual dynamic environment and showed effectiveness in integrated care of dynamic wounds. With the fascinating properties, DPDMs may become an effective tool for smart wound care.

Effect of steel fiber content on failure strength and toughness of UHPC-CA at low temperature: An experimental investigation

As a potential and sustainable construction material, ultra-high performance concrete containing coarse aggregate (UHPC-CA) finds promising applications in engineering constructions, particularly in severe cold regions. This study conducts an experimental study to investigate the influence of fiber content (ranging from 0.0 % to 3.0 %) on the uniaxial compression and splitting-tension failures of UHPC-CA across a temperature range of −90 °C∼20 °C. Through microstructure analysis, the underlying mechanisms and quantitative analysis behind the low-temperature enhancement effect and fiber reinforcement effect on the nominal strength and toughness of UHPC-CA were elucidated. The test results show that as the temperature drops from 20 °C to −90 °C, nominal strengths of UHPC-CA monotonically increase (with a maximum increase 88.1 % for splitting-tension strength while 72.6 % for compressive strength), but the compressive toughness reduces with a maximum decrease 54.6 %. Additionally, the incorporation of steel fibers can enhance the nominal strengths and compressive toughness, exhibiting the fiber reinforcement and toughening effects. Compared to the UHPC matrix, all the increases for nominal strengths and compressive toughness of UHPC-CA with 2.0 % steel fibers at room temperature are higher than those at low temperatures, demonstrating that the decreasing temperature can weaken the fiber reinforcement and toughening effects, which may attribute to fact that the formation of microcracks (due to the expansion of phase change of pore ice) in the surface between steel fiber and UHPC matrix at low temperatures, as observed in the microscopic test. However, as the fiber content exceeds 2.0 %, the splitting-tension strength decreases, thereby it is recommended that the optimal steel fiber content is around 2.0 % for UHPC-CA at low temperatures. Finally, considering the quantitative effects of steel fiber characteristics and temperature, the empirical prediction models for cryogenic nominal strengths were proposed and verified, which can well predict compressive and splitting-tension strengths of UHPC-CA with various steel fiber contents at low temperatures. This study can provide an experimental data reference for the safety design of UHPC structures and contribute to promoting the application of UHPC-CA in the engineering construction of cold regions.

Tailoring Mechanical Reliability in Transparent ZnO-Zincone Thin-Film Electrodes with Organic Interlayer Interfaces and Thickness.

To address the inherent brittleness of conventional transparent conductive oxides, researchers have focused on enhancing their flexibility. This is achieved by incorporating organic films to construct organic-inorganic hybrid layer-by-layer nanostructures, where the interlayer thickness and interface play pivotal roles in determining the properties. These factors are contingent on the type of material, processing conditions, and specific application requirements, making it essential to select the appropriate conditions. In this study, ZnO-zincone nanolaminate thin films were fabricated using atomic layer deposition and molecular layer deposition in various structural configurations. Transmission electron microscopy, X-ray diffraction, and scanning electron microscopy were used to conduct a thorough analysis of the thin-film growth and structural transformations resulting from the deposition conditions. Furthermore, the influence of structural differences at the interfaces on the mechanical properties of the films was investigated by employing both tensile and compression-bending fatigue tests. This comprehensive examination reveals noteworthy variations in the mechanical responses of the films. Thin films characterized by internal porosity and an intermixed amorphous structure demonstrated enhanced compressive toughness, whereas rigid organic layers improved flexibility. These findings offer valuable insights into the development of flexible, transparent multilayer films.

Effects of Steel Fiber Content on Compressive Properties and Constitutive Relation of Ultra-High Performance Shotcrete (UHPSC)

Shotcrete is widely used in civil engineering as a supporting structure. In this paper, the compressive behavior of ultra-high-performance shotcrete (UHPSC) with different steel fiber content by volume (0, 0.5%, 0.75%, 1%, 1.25%, 1.5%) was investigated. The results showed that the failure pattern of UHPSC was changed from brittle failure to ductile failure with the increase in steel fiber content. The compressive strength, peak strain and compressive toughness of UHPSC increased with the increase in steel fiber content, but the elastic modulus and Poisson’s ratio did not change significantly. With content of 1.5% steel fibers, its axial compressive strength, peak strain and compressive strain energy were 122.7 MPa, 3749 με and 0.269 MPa, respectively, increased by 14%, 23.5% and 55.5% compared with those without steel fiber. The peak strain and compressive toughness were higher than that of ultra-high-performance concrete (UHPC), while the elastic modulus of UHPSC was lower than that of UHPC. Based on the experimental data, the relationship between compressive strength, peak strain, compressive toughness and the change in the characteristic value of steel fiber content (λf) were revealed. The uniaxial compressive constitutive model of UHPSC with different steel fiber content was established and reflected the change rule of the shape parameter of α (constitutive model ascending section) and β (constitutive model descending section) with λf. The experimental results were in good agreement with the model calculation results, which can provide theoretical support for the structural design of UHPSC.

Experimental study on Corn Straw Fiber (CSF) toughening EPS concrete

The natural Corn Straw Fiber (CSF), it has the advantages of light weight, high strength, good toughness and renewable, can delay the cracking and improve the toughness of cement-based materials. The effects of different mass fractions of CSF and Expanded-Polystyrene (EPS) particles on the compressive strength, flexural strength, splitting tensile strength and their failure modes, load-displacement curves and toughness of EPS concrete were analyzed by full factorial experimental design method. The compressive toughness index (I0, I1) and fracture energy (Gf) were defined to evaluate the effect of CSF on toughening EPS concrete. The results show that the addition of CSF can improve the compressive strength, flexural strength and cracking toughness of EPS concrete to a certain extent. The maximum compressive strength occurred in the E1F3 specimen with a CSF content of 3 % in Group I, which was 1.12 MPa, and the improvement rate was also the highest among the four groups, reaching 69.7 %. The compressive toughness index I1 also reached its maximum in the E1F3 specimen; The maximum flexural strength occurred in the E3F4 specimen with a 4 % CSF content in Group III, which was 0.885Mpa, with the highest improvement rate of 127.38 %. The maximum fracture energy Gf reached 0.827 in the E3F4 specimen. However, another additive, EPS particles, did not significantly improve the physical and mechanical properties of concrete. According to the SEM images and toughening mechanism analysis, it was discovered that tight adhesion between EPS particles and CSF with cement matrix, and the failure mode of CSF was tensile fracture, which could maximize the effect of CSF high tensile toughness. On the basis of mechanical properties and toughening effect, the relationship formulas between variable factors and strength, toughness index were fitted, and the optimal content of EPS and CSF were determined to be 1.3 % and 3 %, respectively.

Experimental investigation on axial compressive and splitting tensile behaviour of reinforced concrete with a low content of hybrid steel fibres

This study intends to explore how the hybrid steel fibre reinforcement with a low content affects the mechanical characteristics of concrete. The axial compression properties of hybrid steel fibre-reinforced concrete (HSRC) were systematically investigated regarding stress-strain curves, failure modes, elastic modulus, and toughness. The crack propagation and fracture process of HSRC were analyzed based on the cumulative crack width and horizontal strain field. The results showed that the micro-straight steel fibre (mSF) demonstrated a more pronounced influence on post-peak stress retention in the axial compression test, whereas macro hooked-end steel fibre (MHF) positively affected the peak strain enhancement. The average peak stress of the HSRC increased by 8.6 % higher than that of H40 and 16.4 % higher than that of S40. It is noteworthy that the mixing of steel fibres at a low fibre content was detrimental to the compressive toughness. The splitting tensile test showed a transitional stage before the HSRC reached its peak load, during which the load steadily increased and crack propagation slowly occurred. Moreover, the digital image correlation (DIC) measurement results suggested that mSF can enhance the internal quality of concrete. The study contributes to a deep understanding of the synergistic reinforcement mechanism and the fracture processes in HSRC.

Degradable, anti-swelling, high-strength cellulosic hydrogels via salting-out and ionic coordination

Cellulosic hydrogels are widely used in various applications, as they are natural raw materials and have excellent degradability. However, their poor mechanical properties restrict their practical application. This study presents a facile approach for fabricating cellulosic hydrogels with high strength by synergistically utilizing salting-out and ionic coordination, thereby inducing the collapse and aggregation of cellulose chains to form a cross-linked network structure. Cellulosic hydrogels are prepared by soaking cellulose in an Al2(SO4)3 solution, which is both strong (compressive strength of up to 16.99 MPa) and tough (compressive toughness of up to 2.86 MJ/m3). The prepared cellulosic hydrogels exhibit resistance to swelling in different solutions and good biodegradability in soil. The cellulosic hydrogels are incorporated into strain sensors for human-motion monitoring by introducing AgNWs. Thus, the study offers a promising, simple, and scalable approach for preparing strong, degradable, and anti-swelling hydrogels using common biomass resources with considerable potential for various applications.

Enhancing fire resistance in geopolymer concrete containing crumb rubber with graphene nanoplatelets

Geopolymer concrete (GPC) has a tendency to spall and lose its strength at high temperatures, rendering it brittle. This research incorporates graphene nanoplatelets (GNPs) to enhance the fire resistance of GPC. A comprehensive experimental framework, comprising 20 distinct mix designs, was developed. Crumb rubber (CR) was substituted for natural sand in the mixture proportions, ranging from 10% to 30% by volume, while GNPs were incorporated in quantities ranging from 0.1% to 0.4% by weight of fly ash. The objective of this study is to assess the mechanical properties of these mixtures after exposure to 30, 60, and 90 min of ISO 834 standard fire. The properties of GPC were analyzed both before and after exposure to fire. The attributes and properties investigated include spalling, mass loss, stress-strain behavior under compression, compressive strength, compressive toughness, modulus of elasticity, and porosity. Furthermore, the study examined the interfacial interaction between the aggregates and the geopolymer matrix, as well as microstructural and morphological changes due to fire exposure, utilizing field emission scanning electron microscopy (FESEM). The results indicated that GNPs significantly mitigated the loss of post-fire compressive strengths of GPC. The Response Surface Methodology (RSM) was employed to develop statistical models and optimize the mixture proportions of CR and GNPs, aiming to maximize the compressive strength and the modulus of elasticity while minimizing the mass loss of GPC after exposure to fire. The optimization outcomes suggested that a mixture containing 10% CR and 0.3% GNPs represented the optimal composition for enhancing the fire resistance of GNP modified rubberized GPC.

Experimental study on axial compression behavior of square pultruded GFRP tubular stub column

To investigate the influence of aspect ratio and width-to-thickness ratio on the axial compression behavior of square pultruded glass fiber-reinforced polymer (GFRP) tubular stub columns, axial compression tests were conducted on 12 GFRP tubular columns. The mechanical properties of the GFRP tubular columns, including load-bearing capacity, initial stiffness, compressive toughness, and ductility coefficient, were analyzed. The test results reveal that all GFRP tubular columns exhibit crushing failure, with specific failure modes, including mid-section fracture and longitudinal tearing along the corners of the columns. The load-bearing capacity is negatively correlated with the aspect ratio and width-to-thickness ratio. The initial stiffness negatively correlates with the aspect ratio, and the compressive toughness negatively correlates with the width-to-thickness ratio. The Hashin damage criteria for the C3D8R solid element was developed by utilizing the explicit finite element subroutine ABAQUS-VUMAT to analyze the axial compression behavior of GFRP tubular columns. Through parameter analysis, the relationship between the load-bearing capacity and fiber orientation was obtained, and an empirical equation for predicting the load-bearing capacity of the GFRP tubular column was proposed.

Influence of hybrid steel-polyacrylonitrile fibers on the mechanical toughness and freeze-thaw resistance of sulfoaluminate cement composites

Sulfoaluminate cement (SAC), an environmentally friendly low-carbon cement, is commonly applied for rapid repair and construction. However, limited studies were conducted to elevate the performance of SAC-based materials by using the hybrid fiber modification, especially the durability. This study investigated the mechanical behaviors and freeze-thaw (F-T) resistance of SAC-based materials with hybrid steel-polyacrylonitrile (PAN) fibers, as well as their enhancement mechanism characterized using X-ray computed-tomography (CT) and scanning electron microscope. The results showed that incorporating hybrid fibers remarkably increased the flexural and compressive toughness of mortars, with steel fibers contributing the most critically. The fiber hybridization also significantly enhanced the F-T resistance of mortars, with PAN fiber being the main contributor. Specifically, the use of hybrid fibers caused a 61.0% improvement in the relative dynamic elastic modulus of mortars after 300 F-T cycles. CT scanning demonstrated that incorporating PAN fibers reduced the porosity of mortars and restrained the initiation and propagation of microcracks, while uniformly and randomly distributed steel fibers interspersed between macrocracks. Morphology observation illustrated that PAN fiber addition was conducive to enhance the anchoring force of steel fiber. Accordingly, the hybrid steel-PAN fibers contributed to suppress cracking at different scales and achieved a positive hybrid effect. At last, the results of this work provide a promising design solution for SAC-based composites to achieve better toughness and frost resistance.

Experimental investigation of the compressive and shear behaviours of grouted and hollow masonry constructed with PVA fibre-reinforced mortar and grout

Polyvinyl alcohol (PVA) fibres are ultra-high-performance fibres that can be used to reinforce cementitious composites. This study experimentally investigated the compression and shear behaviours of grouted and hollow masonry constructed with fibre-reinforced mortar (FRM) used for the joints and/or PVA fibre-reinforced grout (FRG). In this regard, the effect of increasing the fibre content of 6 mm PVA fibres in the FRM on the behaviour of masonry was investigated. Moreover, the effect of changing the fibre length (8 mm and 13 mm PVA fibres) and the fibre content of 13 mm PVA fibres in the FRG on the behaviour of masonry was investigated. This was accomplished by constructing and testing 31 masonry prisms and 29 masonry assemblages. The behaviour of PVA-reinforced masonry was evaluated based on compressive strength, shear strength, modulus of elasticity, modulus of rigidity, compressive strain at peak compressive stress, shear strain at peak shear stress, compression ductility index and compression toughness. In addition, the compression and shear stress-strain curves, failure modes and crack propagation of PVA-reinforced masonry were compared with unreinforced masonry. It was concluded that using PVA fibres in the grout minimized the masonry face shell spalling, and most of the post-peak deterioration appeared in the form of masonry cracks and less face shell spalling compared with unreinforced masonry. In addition, using PVA-FRM only or PVA-FRM with PVA-FRG could increase the compressive strength of grouted masonry. In contrast, using PVA-FRM did not change the compressive strength of hollow masonry. Furthermore, all grouted assemblages with PVA-FRM and PVA-FRG (except for assemblages with 13 mm PVA-FRG with a fibre content of 0.10% by weight of grout) have similar average shear strength compared with unreinforced assemblages. Finally, As the fibre content of 6 mm PVA fibres in the FRM of hollow assemblages increased, the shear strength and the modulus of rigidity decreased. This study highlights the improvements and drawbacks of using PVA Fibres in mortar and grout on the compressive and shear performances of hollow and grouted masonry.

Effect of incorporating recycled macro fibres on the properties of ultra-high-performance seawater sea-sand concrete

Ultra-high-performance concrete (UHPC) is an ideal material for constructing marine infrastructures, but faces obstacles such as limited local raw materials (i.e., freshwater and river-sand) and corrosion of steel reinforcement. Non-metallic reinforcement is preferable for reinforcing marine UHPC, especially when seawater and sea-sand are used to develop ultra-high-performance seawater sea-sand concrete (USSC). Recently, the authors' group proposed a cost-efficient UHPC reinforced with discrete macro fibres mechanically processed from waste glass fibre-reinforced polymer (GFRP) composites. This present study aimed to explore the potential application of incorporating macro fibres in USSC. A series of tests were conducted to investigate the fundamental properties of macro fibre reinforced USSC with the examined variables including the content (0 %, 2 %, 4 %, and 6 %) and lengths (30 mm and 60 mm) of macro fibres. Comparisons were made between USSC and UHPC with river-sand and freshwater (UTRC), which were both reinforced with macro fibres. The results revealed that incorporating macro fibres in USSC improved the compressive toughness index (CTI) and flexural toughness by up to 84.00 % and 40.15 times respectively, but decreased the workability and compressive strength by up to 42.22 % and 21.45 % respectively. The effect of incorporating macro fibres on the properties of USSC was more prominent than that of its counterpart of UTRC. A theoretical model was then developed for predicting the flexural toughness of various concrete with macro fibres based on the regression analysis on the available test results.

High-flowable and high-performance steel fiber reinforced concrete adapted by fly ash and silica fume

The incorporation of steel fibers in concrete imparts strain-hardening characteristics, significantly elevating the tensile toughness of the concrete mixture. However, this enhancement often comes at the expense of reduced workability and strength, posing challenges in achieving optimal densification in practical engineering applications. Moreover, the improvement of the performance of steel fiber-reinforced concrete (SFRC) hinges on the establishment of interfacial transition zone (ITZ) between steel fibers and the concrete paste. It has been established that the introduction of fly ash and silica fume to concrete mixtures can increase fluidity and strength. Consequently, this study investigates the impact of fly ash and silica fume on the performance enhancement and workability of SFRC mixtures, scrutinizing both macroscopic and microscopic aspects. Two sets of high-flowable steel fiber-reinforced concretes (HF-SFRC) incorporating silica fume or fly ash were prepared and subjected to testing. The assessment covered mechanical properties, including compressive strength, compressive toughness, and flexural toughness, along with the microstructure. The microstructure provides evidence that fly ash and silica fume reduced the voids in the concrete matrix to different degrees and that the fully hydrated dense matrix contributed to reinforcing the bond between steel fibers and the cement matrix. The synergistic effect among fly ash or silica fume, steel fibers, and cement in the mixture resulted in enhanced flowability and improved mechanical properties in HF-SFRC.

Numerical Compressive Toughness of Steel Fiber-Based Reinforced Concrete with Various Densities

Numerical Compressive Toughness of Steel Fiber-Based Reinforced Concrete with Various Densities

Performance enhancement of recycled coarse aggregate concrete by incorporating with macro fibers processed from waste GFRP

Reprocessing into coarse aggregates of concrete is a sustainable solution for the disposal of construction and demolition (C&D) waste. The use of recycled coarse aggregates however leads to a degradation in the mechanical properties of the resulting concrete, which then limits the use of recycled aggregates concrete (RAC) in structural elements. The incorporation of discrete fibers shows to be effective in eliminating the mechanical degradation problem of RAC, and this paper has therefore proposed to use macro fibers recycled from waste glass fiber reinforced polymer (GFRP) to reinforce RAC, thus improving the robustness of using RAC in structural elements. The effect of incorporating macro fibers on the mechanical properties of RAC has been first examined through a series of compression and bending tests. The tensile constitutive law of concrete was then derived based on the load-deflection response of the beam specimens using an inverse analysis. The results revealed that the mechanical properties (e.g., compressive toughness, flexural strength, flexural toughness) of RAC can be significantly enhanced by adding macro fibers. For concrete with 50% recycled aggregate (RA), the increase of macro fibers (from 0% to 0.5%, 1%, and 1.5%) leads to the enhancement of flexural strength from 3.13 MPa to 3.54, 4.69, and 5.97 MPa, and the toughness (T150) from 1.4 J to 35.5, 59.2 and 77.6 J, respectively. Such enhancements in the mechanical properties of RAC demonstrate the feasibility of the proposed method.

Mechanical performance study of basalt-polyethylene fiber reinforced concrete under dynamic compressive loading

In order to enhance concrete's impact resistance, this study investigates the effects of single basalt fiber and basalt-polyethylene hybrid fiber on concrete through split Hopkinson pressure bar (SHPB) tests, emphasizing their significance in engineering applications. A comparative analysis of the failure modes, dynamic compressive strength, dynamic compressive toughness, and dynamic growth factor of specimens was conducted under different strain rates and polyethylene fiber volume fractions. The study considered concrete damage, strain rate effect, and the toughening effect of fibers, introducing the damage factor, and establishing a dynamic damage constitutive model for fiber-reinforced concrete. The results showed that basalt-polyethylene fiber reinforced concrete (BPFRC) exhibited better impact resistance and deformation capability. There were improvements observed in dynamic compressive strength, dynamic compressive toughness, and dynamic growth factor. The addition of basalt fiber (BF) and polyethylene fiber (PE) played a buffering role in inhibiting crack propagation and slowing down the damage process. The optimum PE volume fraction for dynamic compressive strength was 0.1% at a strain rate of 60 s−1, 0.15% at a strain rate of 95 s−1, and 0.05% at a strain rate of 120 s−1, all with a BF volume fraction of 0.25%. The optimum fiber volume fractions for dynamic compressive toughness and dynamic peak toughness were consistent, both at 0.25% BF and 0.1% PE. The established dynamic damage constitutive model for fiber-reinforced concrete can effectively describe the impact resistance performance of BPFRC, and the experimental curves fit well with the constitutive curves. Furthermore, it was observed that BF acted as macrofibers, bridging to restrain the post-hardening cracking of concrete, while PE acted as microfibers, inhibiting the propagation of plastic cracks, reducing internal defects in concrete, and enhancing the ductility and toughness of concrete. Consequently, BPFRC holds significant potential value in engineering applications.

Mechanical performance evaluation of steel fiber-reinforced concrete (FRC) based on multi-mechanical indicators from split hopkinson pressure bar (SHPB) test

Fiber-reinforced concrete (FRC) is a new composite material composed of various fibers and a cement matrix that has been widely used and developed in the construction engineering field. In this paper, split Hopkinson pressure bar (SHPB) tests are carried out with the aim of investigating the mechanical properties and failure characteristics of FRC containing different types and dosages of steel fibers. The main findings are as follows: At a fiber content of 0 %–3.5 %, the strength of FRC shows two trends: continuously increasing and then decreasing. The ductility of hooked-end steel fiber-reinforced concrete (HFRC) is better than that of hybrid steel fiber-reinforced concrete (HSFRC) and straight steel fiber-reinforced concrete (SFRC) under static loads, whereas the ductility of HSFRC is better than that of SFRC and HFRC under dynamic loads. Straight steel fibers (SF) are better than hooked-end steel fibers (HF) in improving tensile toughness but worse than HF in improving compressive toughness. In terms of the degree of failure, NFRC and HFRC were the most severely fragmented, whereas SFRC and HSFRC exhibited better integrity. Finally, based on the multi-mechanical indicators of the FRC, a comprehensive performance evaluation method and optimization suggestions for the FRC are proposed. This provides theoretical support for the application of FRC as seismic-resistant materials in reinforced structures (i.e., anti-slide piles, retaining walls, and beam structures) of rocky landslides in strong seismic areas, which have important engineering significance.