Good Crack Resistance Research Articles

Corrosion-resistant titanium-based electrodes synergistically stabilized with polymer for hydrogen evolution reaction

The economic and reasonable design of highly stable and corrosion-resistant electrodes is fundamental to achieving the industrial-scale hydrogen productions via water electrolysis, but electrodes’ premature failures are often caused by corrosion and stress damage. Therefore, these challenges are successfully solved by utilizing conductive and crack-resistant polyaniline “stabilizer” with a mild chemical plating process to construct the catalytic electrode on a titanium substrate (15 %PANI-NiB@Ti) in the present work. The 15 %PANI-NiB@Ti catalytic electrodes have been in continuous operation for 350 h at the current density of 200 mA cm−2 with the high efficiency of 98.4 % in a 323.15 K environment. With the high economy and universality, the catalytic electrodes have good catalytic performance and reliability in the extreme industrial environments, such as high temperature, air, and high current density. Except for the above advantages, the 15 %PANI-NiB@Ti catalytic electrodes also have good cracking resistance, which provides a novel and feasible approach to the industrial application of transition metal catalytic electrodes.

Compressive Bearing Capacity and Ductility of Slurry-Infiltrated Fiber Concrete Blocks with Two-Dimensional Distributed Steel Fibers

Slurry-infiltrated fiber concrete (SIFCON) has excellent potential for application as a new material with good crack resistance, impact resistance, and seismic performance. In this paper, SIFCON blocks were cast in a single pour using the custom-made two-dimensional directional steel fiber placement device, followed by compressive testing. Based on the test results, the effects of fly ash substitution rate, steel fiber aspect ratio, and steel fiber volume fraction on the compressive bearing capacity and ductility of SIFCON blocks were investigated. The results indicate that the custom-made device in this paper effectively achieves the directional placement of steel fibers, offering a cost-effective solution that optimizes the construction process. Regarding the test results, it was observed that the compressive bearing capacity of SIFCON blocks decreases linearly with increasing fly ash substitution rate, while the addition of fly ash improves the ductility of the blocks. Notably, a 31% decrease in bearing capacity was noted when the fly ash substitution rate increases from 0% to 40%, whereas the ductility ratio increased by 99% for the same substitution rate range. Furthermore, the results revealed a positive correlation between the bearing capacity and ductility of SIFCON blocks with higher steel fiber aspect ratios and volume fractions. Specifically, the bearing capacity increased by 19% and 33% with steel fiber aspect ratio increments from 33 to 70 and volume fraction increases from 10% to 14%, respectively. Additionally, the ductility ratio of the test blocks increased by 104% when the aspect ratio of the steel fibers increased from 33 to 70, and by 37% when the volume fraction of steel fibers rose from 10% to 14%.

Hybrid Effect of Basalt and Polyacrylonitrile Fibers on Physico-Mechanical Properties of Tailing Mortar

In this study, 50% iron ore tailings (IOTs) were used to prepare the cemented mortar at low economic costs and with great environmental benefits. Basalt fiber (BF) and polyacrylonitrile fiber (PANF) were added to the tailing mortar to improve the comprehensive performance of tailing mortars, including BF (0~0.5%), PANF (0~0.05%) and the combination of them. The results show that the addition of BF and PANF can significantly improve the ultrasonic velocity, uniaxial compressive strength (UCS), split-tensile strength (STS), flexural strength (FS) and toughness of the tailing mortar. A novel finding is that the enhancement of hybrid fibers is much better than single fiber, and the best hybrid fiber combination is B0.25P0.05 (0.25 wt% BF and 0.05 wt% PANF), because this combination not only causes the most considerable increase in strength but also possesses great cost-effectiveness. Compared to the B0P0 group without fibers, the maximum increments of B0.25P0.05 in UCS, STS and FS are 45.74%, 52.33% and 15.65%, respectively. It is evidenced that the improvement in STS is the largest because the fibers have good cracking resistance and bridging effect in the tailing mortar. The scanning electron microscope (SEM) further confirms that too many hybrid fibers will agglomerate and produce more voids, which is harmful to the development of the internal structure. Beyond B0.25P0.05, the hydration products are also reduced due to the decrease in nucleation sites, observed by combining X-ray diffraction (XRD) tests. Therefore, it is suggested that the hybrid fibers containing 0.25% BF and 0.05% PANF should be used in this tailing mortar.

Shear bearing capacity calculation of low-rise SFRC shear wall with CFST columns based on simplified softened strut and tie model

In the paper, an innovative shear wall, which is referred to as steel fiber reinforced concrete (SFRC) shear wall with concrete filled steel tube (CFST) columns, is introduced, based on the high bearing capacity and large stiffness of concrete filled steel tube column (CFSTC) and good cracking resistance and strong toughness of steel fiber reinforced concrete. The loading mechanism of steel fiber reinforced concrete shear wall (SFRCSW) with concrete filled steel tube columns is analyzed, and shear bearing capacity calculation method. A simplified model of the steel fiber reinforced concrete shear wall web softening tension bar is proposed, concrete and distributed web reinforcement to the shear bearing capacity of steel fiber reinforced concrete shear wall web is identified. Furthermore, a new algorithm to obtain the shear bearing capacity of steel fiber reinforced concrete shear wall with concrete filled steel tube columns is established, and then it is validated by using the test results of steel fiber reinforced concrete shear wall with concrete filled steel tube columns under low-cycle repeated loading. The results showed that all tested shear wall specimens exhibited obvious shear failure characteristics and a typical diagonal cracking pattern after test. The steel fibers obviously improved the crack forms of the steel fiber reinforced concrete shear wall web and the seismic behavior of steel fiber reinforced concrete shear wall with concrete filled steel tube columns. In addition, the proposed calculation method is scientific and accurate to analyze and predict the shear bearing capacity of low-rise steel fiber reinforced concrete shear wall with concrete filled steel tube columns.

Flexural behavior of BMSC beam exposed to the harsh environment

Basic magnesium sulfate cement concrete (BMSC) was invented in 2013, which has many merits: excellent mechanical performance, good toughness and good crack resistance. But the mechanical performance of BMSC beams laid in the harsh weather for a long time is not known. The mechanical properties of six corroded reinforced BMSC beams were studied for applying this new concrete to practical engineering. It can be found that there is no rust crack before loading test. The bearing capacity of corroded reinforced BMSC beam laid in the harsh environment for two years, especially in the weather of long-term freeze-thaw cycles and acid rain, degraded by 11.9 % and the bending rigidity degraded by 17.0 %. Based on the attenuation of steel corrosion and deterioration of BMSC after the harsh exposure, the model of bearing capacity and cracking load of the corrosion-damaged BMSC beam is proposed. This paper is helpful to the application of BMSC members in the area of harsh environments.

Experimental study on fatigue behavior of UHPC joint in negative moment region of π-shaped steel–concrete composite beams

To improve the crack resistance of concrete bridge decks in the negative moment region of π-shaped steel–concrete composite beam, a novel ultra-high performance concrete (UHPC) joint was first proposed. Based on an actual bridge, a 1:2 scale model was then designed as the specimen. A fatigue test was conducted to investigate the variation of its structural properties during fatigue loading, and a static test was performed to evaluate its residual bearing capacity. The test results show that the new UHPC joint has good crack resistance under fatigue loading and can meet the engineering requirements. The stiffness of the specimen significantly decreases after 3 million fatigue cycles. However, without significant fatigue damage on the surface of specimen, plenty of stiffness is reserved. It is found that there is no significant slip between the concrete deck and steel girder, and between the UHPC and normal concrete in the static test after fatigue, indicating that the studs inside the π-shaped steel–concrete composite beam are arranged reasonably and the interaction of the overall structure is reliable. Furthermore, the ultimate bearing capacity of the specimen decreased by only 9.4% from its design value after being subjected to 3 million fatigue cycles. It is revealed that the application of UHPC in the composite beam effectively improves its crack resistance, resulting in a smaller reduction in bearing capacity. This paper can provide theoretical foundation for the preparation and application of the π-shaped steel–concrete composite beams with UHPC joints.

Study on the deformation and cracking characteristics of bamboo fiber reinforced concrete anti-slide pile considering the aspect ratio, fiber dosage and its coupling effect with rebars

In order to avoid cracks in anti-slide piles and thus causing brittle damage, incorporating fibers in anti-slide piles to improve their ductility is an effective way to enhance the crack resistance. Bamboo fiber, as a low carbon fiber material, has good crack resistance and toughening effect, and can be used as a new concrete reinforcement material to enhance the crack resistance of anti-slide piles. In this paper, the load–displacement relationship, deformation and cracking characteristics of 28 bamboo fiber-reinforced concrete anti-slide piles are studied considering the aspect ratio, fiber dosage and its coupling effect with rebars. The main conclusions of the study are as follows: (1) The bamboo fiber used in the anti-slide pile can play the role of crack resistance. The plain anti-slide pile produces one main tension crack and full-section fracture failure, while the anti-slide pile with the coupling effect of bamboo fiber and rebars suffers from diagonal section instability failure with one main diagonal tension crack and several secondary cracks. (2) The anti-slide pile with 1% volume ratio of bamboo fiber can achieve better flexural and crack resistance. The optimal dosage for bamboo fiber with rebars is further reduced, which is 0.5% (3) The optimal aspect ratio of bamboo fiber is between 16.7 and 23.3, which can improve the flexural performance of anti-slide piles, but the aspect ratio of bamboo fiber fails to essentially change the failure mode of anti-slide piles. Fiber dosage has a significant effect on the cracking failure mode of anti-slip piles. The rapid development of microcracks in anti-slide piles can be restrained more effectively by the uniform distribution of bamboo fibers with appropriately small aspect ratio and volume ratio.

Anti-cracking concrete properties based on the synergistic expansion effect of internal curing agents

This paper designed 7 groups of C40 crack resistant concrete mix and conducted experimental research on working properties, mechanical properties, deformation properties and crack resistance, with monolithic laminated wallboard technology. The test results find that: the shrinkage compensated concrete with curing agent in light sand shows that the curing agent in light sand gives full play to the synergistic expansion effect. While significantly improving the design strength of concrete, it effectively controls the crack generation in the solidification process of concrete specimens, which has good crack resistance and durability. From the aspect of concrete mix design, this study provides an effective solution to control the cracks of cast-in-place concrete structures in the process of application of assembled monolithic laminated wallboard technology.

Shear behaviours of steel-HSFRC welded stud and perfobond rib connectors under static push-out experiments

In this study, high-strength fibre-reinforced concrete (HSFRC) was introduced into steel–concrete composite girders owing to its high strength, good cracking, and impact resistance. Sixteen push-out specimens were tested to study the shear behaviours of the welded stud and perfobond rib connectors used in steel-HSFRC composite girders. The failure modes, load–slip curves, and shear behaviours of the push-out specimens were analysed and compared. The experimental results indicate that the shear capacity and stiffness of these two types of connectors are improved when they are used in steel-HSFRC composite girders, whereas the ductility of the welded stud and one-hole perfobond rib connectors decreases. The stud diameter has a significant effect on the shear behaviour of welded studs, unlike the stud length. The shear capacity of perfobond rib connectors increases with an increase in the perforating rebar diameter and hole number. The initial stiffness and ductility of perfobond rib connectors were larger than those of welded stud connectors with similar shear capacities. Finally, shear capacity prediction equations for welded studs and perfobond rib connectors embedded in HSFRC are proposed and verified to have good accuracy and applicability.

Evaluating the Effects of Polyphosphoric Acid (PPA) on the Anti-Ultraviolet Aging Properties of SBR-Modified Asphalt.

The ultraviolet (UV) aging of asphalt is an important factor affecting the long-term performance of asphalt pavement, especially in high altitude cold regions. The current studies have reported that styrene butadiene rubber-modified asphalt (SBRMA) has a good cracking resistance at low temperatures. In addition, polyphosphoric acid (PPA) is an effective modifier that can enhance the anti-UV aging properties of asphalt. However, the understanding of the improvement mechanism of PPA on the anti-aging of SBRMA remains unclear. Therefore, this study aimed to evaluate the effect of PPA on the UV aging resistance of SBRMA. The rheological properties of PEN90 asphalt(90#A), SBRMA, and PPA/SBR modified (PPA/SBR-MA) before and after UV aging were evaluated by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The molecular weight and chemical structure of 90#A, SBRMA, and PPA/SBR-MA were determined by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), and the interaction and modification mechanism of the modifiers were analyzed. The rheological analysis shows that the high and low temperature performances of SBRMA are improved by adding PPA, and PPA also significantly reduces the sensitivity of SBRMA to UV aging. The microscopic test results show that PPA has a complex chemical reaction with SBRMA, which results in changes in its molecular structure. This condition enhances SBRMA with a more stable dispersion system, inhibits the degradation of the polymer macromolecules of the SBR modifier, and slows down the aging process of base asphalt. In general, PPA can significantly improve the anti-UV aging performance of SBRMA. The Pearson correlations between the aging indexes of the macro and micro properties are also significant. In summary, PPA/SBRMA material is more suitable for high altitude cold regions than SBRMA, which provides a reference for selecting and designing asphalt pavement materials in high altitude cold regions.

Frost Resistance and Shrinkage Characteristics of Soil Stabilized by Carbide Slag and Coal Gangue Powder

With the increase of expressway construction in seasonal frozen soil region, the freeze-thaw problem of subgrade soil has attracted more and more attention. In addition, the comprehensive utilization of industrial solid waste has become an important measure to build a resource-saving and environment-friendly society. In order to improve the frost resistance of subgrade soil and realize the resource utilization of industrial solid waste, carbide slag (CS) and coal gangue powder (CG) were applied to the subgrade soil. The unconfined compressive strength (UCS) test, freeze-thaw cycle test, dry shrinkage test, temperature shrinkage test and scanning electron microscope (SEM) test were carried out on CS-CG stabilized soil with a ratio of CS:CG = 70:30 and dosages of 5%, 10% and 15%. The freeze-thaw cycle degradation model of CS-CG stabilized soil was constructed to show the freeze-thaw deterioration mechanism after the mechanical properties, pore structure, and durability characteristics of the stabilized soil were examined. The results showed that the CS-CG stabilized soil had good frost resistance. After 6 freeze-thaw cycles, the UCS at 7d and 28 d was 2.86 MPa and 3.79 MPa, respectively, which were 22.6% and 35.5% lower than in samples that underwent no freeze-thaw action. The CS-CG stabilized soil had good crack resistance, slightly better dry shrinkage strain than lime stabilized soil, and excellent temperature shrinkage performance. With the increase of CS-CG dosage, the hydration products increased continuously. After freeze-thaw cycles, however, large pores and cracks gradually appeared in the stabilized soil, which led to an increase of porosity and pore diameter, and a decrease of pore abundance. Due to the influence of hydration degree, the porosity change at 7 d was less than that at 28 d. There was a f(n)/f0=βexp−λΔh relationship between UCS residual ratio and porosity variation of the CS-CG stabilized soil, and it had a good correlation. The CS-CG stabilized soil had good frost resistance and shrinkage characteristics, and could replace traditional cementitious materials such as Portland cement (PC) and lime for subgrade soil improvement in regions with seasonal frozen soil. Future research needs to focus on the performance regulation of CS-CG stabilized soil, which can make it more widely used.

Strong, Tough, and Adhesive Polyampholyte/Natural Fiber Composite Hydrogels.

Hydrogels with high mechanical strength, good crack resistance, and good adhesion are highly desirable in various areas, such as soft electronics and wound dressing. Yet, these properties are usually mutually exclusive, so achieving such hydrogels is difficult. Herein, we fabricate a series of strong, tough, and adhesive composite hydrogels from polyampholyte (PA) gel reinforced by nonwoven cellulose-based fiber fabric (CF) via a simple composite strategy. In this strategy, CF could form a good interface with the relatively tough PA gel matrix, providing high load-bearing capability and good crack resistance for the composite gels. The relatively soft, sticky PA gel matrix could also provide a large effective contact area to achieve good adhesion. The effect of CF content on the mechanical and adhesion properties of composite gels is systematically studied. The optimized composite gel possesses 35.2 MPa of Young's modulus, 4.3 MPa of tensile strength, 8.1 kJ m-2 of tearing energy, 943 kPa of self-adhesive strength, and 1.4 kJ m-2 of self-adhesive energy, which is 22.1, 2.3, 1.8, 6.0, and 4.2 times those of the gel matrix, respectively. The samples could also form good adhesion to diverse substrates. This work opens a simple route for fabricating strong, tough, and adhesive hydrogels.

Influence of Surfacing Fe-Based Alloy Layers on Wire Arc Additive Manufactured Ni-Based Superalloys Material on Its Microstructure and Wear Properties.

Wire arc additively manufactured (WAAM) Ni-based materials have good properties but are costly and hard to cut, leading to difficulties in machining after welding and wasting the materials. To overcome these shortcomings, this work proposes a method of surfacing Fe-based alloy layers on WAAM Ni-based material. The effect of this method on the microstructure and wear properties of WAAM Ni-based materials is discussed. In this work, a Fe-based alloy (JX103) was welded as the last layers of the WAAM Ni-based superalloy (JX201) material. The hardness, microstructure, and wear behavior of the material with different residual Fe-based materials were tested and analyzed. Our results indicate that the surface hardness was smoothly increased from HV350 to HV400 by overlaying Fe-based alloy layers. Microstructure analysis shows that γ-Fe gradually disappears, and the carbide form changes from WAAM Ni-based superalloys to Fe-based alloys. In the fusion boundary, the occurrence of cellular dendritic growth, a type -Ⅱ boundary, and low dilution indicate good crack resistance and good connection performance between these two materials. The wear test showed that the wear resistance of JX201 was decreased by changing the last layer to JX103. However, as the residual thickness of JX103 decreased, the influence gradually reduced. Meanwhile, the wear mechanism changed from severe abrasive and adhesive wear to light abrasive wear. When the thickness is less than 0.5 mm, the wear weight per minute is at the same level as the sample without JX103.

Dynamic stress–strain relationship of steel fiber-reinforced rubber self-compacting concrete

Rubber has good elastic properties; however, its incorporation reduces the strength of concrete. Due to the high elasticity of rubber and the good crack resistance of steel fibers, the mixing of steel fibers and rubber can effectively improve the impact toughness index of concrete with sufficient strength. An impact test of steel fiber-reinforced rubber self-compacting concrete (SRSCC) was carried out using a split Hopkinson pressure bar (SHPB) in the present work, in which the strain rate ranges from 65.3 s−1 to 137.6 s−1 and steel fibers with four volume fractions of 0%, 0.5%, 1.0% and 2.0% and rubber contents with four volume fractions of 0%, 10%, 20% and 30% are considered. Experimental results revealed that, (i) the dynamic compressive strength, toughness index, stress impact factor (DIF-σ) as well as strain impact factor (DIF-ε) of SRSCC increase obviously with the increase of strain rate; (ii) with the increase of rubber content, the dynamic compressive strength decreases and the toughness index increases. When the rubber content reached 30%, the dynamic compressive strength decreased by 40–50% and the toughness index increased by 20–30%; (iii) the DIF-σ increases first and then decreases slightly with the increase of rubber content, which reaches the maximum value when the rubber content is 20%. What’s more, the effect of rubber content on DIF-σ at high strain rate is more obvious; (iv) the steel fiber content shows strengthening effects on the dynamic compressive strength and toughness index and almost has no effects on the DIF-σ and DIF-ε of SRSCC. Finally, the dynamic stress–strain relationship of SRSCC was proposed.

Experimental Study on Compressing and Insulation Performance of Recycled Fiber Concrete

In order to study and explore the related changes of crack resistance, compressive strength and thermal insulation performance of recycled fiber concrete blocks with polyester fiber as the main component. The test blocks were designed and manufactured in the laboratory, three kinds of concrete test blocks with different specifications were obtained after curing for 28 days. Through experiments, three kinds of test blocks with different specifications were tested for thermal insulation performance, crack resistance and compressive strength. With the help of the electronic universal testing machine controlled by microcomputer, relevant data are obtained. The results show that the fiber concrete with polyester fiber as the main component has good crack resistance and thermal insulation performance, which can prevent new cracks and delay the development of cracks in matrix materials to a certain extent. In addition, waste clothes are used as raw materials for research to solves the problems of cost and environmental pollution of traditional fiber concrete, and reduces the pollution of traditional waste clothes treatment. Waste fabric is also a form of waste of social resources. Therefore, rational utilization of this potential huge resource is the inevitable requirement of a conservation-oriented society and a low-carbon life, and the only way for sustainable development.

Numerical study on dynamic properties of rubberised concrete with different rubber contents

As a green environmentally-friendly material, rubberised concrete (RuC), which has the characteristics of low elastic modulus, large deformation capacity, high damping, good energy dissipation and good crack resistance, has attracted extensive attention and research in the civil engineering discipline. However, most of existing studies are based on experimental tests on RuC material properties, and there has been no numerical study based on meso-scale modelling of RuC yet. To more comprehensively investigate the RuC dynamic material properties without conducting intensive experimental tests, this study developed a high-fidelity meso-scale model considering coarse and fine aggregates and rubber crumbs to numerically investigate the mechanical properties of rubberised concrete under different strain rates. The meso-scale model was verified against both quasi-static compressive testing data and Split Hopkinson Pressure Bar (SHPB) dynamic testing data. Using the verified numerical model, the dynamic properties of rubberised concrete with various rubber content (0%–30%) under different strain rates were studied. The numerical results show that the developed meso-scale model can use to predict the static and dynamic properties of rubberised concrete with high accuracy. The dynamic compressive strength of the rubberised concrete increases with the increment of the strain rate, and the strain rate sensitivity increases with the rubber content ranging from 0 to 30%. Based on intensive numerical simulation data, empirical DIFs is used as a function of strain rate and rubber content to predict the dynamic strength of rubberised concrete.

Fracture features of calcium carbonate whisker-based composites under freezing and thawing cycles using semi-circular bend test

Calcium carbonate whiskers (CW) showed good cracking resistance at the microscale. In this research, four different CW volume fractions (1.0%, 1.5%, 2.0%, and 3.0%) were added into cement mortar. The purpose was to further investigate the fracture behavior by using a semi-circular bend test (SCB) of SCB-CW after different freezing and thawing cycles (0 cycles, 25 cycles, 50 cycles, 75 cycles, and 100 cycles). In addition, three analytical models of SCB-PM and SCB-CW were established to predict the stress-strain response after different freezing and thawing cycles. The experimental results showed that the lowest mass increment, electric flux, highest residual flexural strength, fracture toughness, and fracture energy after different freezing and thawing cycles were observed in SCB-CW3.0. It was observed from the experimental results that only model II completely satisfied its basic requirements and its parameter c was closely correlated with the number of freeze-thaw cycles and the CW volume fraction. Highlights Calcium carbonate whisker is added to enhance the fracture behavior of mortar. The different freezing and thawing cycles are considered. The results are obtained using semi-circular bend test and analytical models are established. The highest fracture parameters are observed in SCB-CW3.0 under different freezing and thawing cycles. The model II is suggested for predicting the experimental response of composites.

Influence of CaO-based expansive agent on chloride penetration resistance of marine concrete

CaO-based expansive agent (CEA) is a high performance expansive agent, which can well compensate for the shrinkage of concrete. However, due to micro-cracks caused by excessive expansion and poor chemical stability and gelling property of additional Ca(OH)2 (expansion product), durability of marine concrete may deteriorate. Therefore, the application of CEA in marine concrete is controversial. In this study, the autogenous deformation, compressive strength, and chloride penetration resistance of marine concretes containing various dosages of CEA were determined, and the influence mechanism of CEA on the chloride penetration resistance was further explored. The results showed that the addition of CEA increased the expansion deformation, chloride diffusion coefficient, and chloride penetration depth and decreased the compressive strength of marine concrete. In addition, as the dosage of CEA increased, porosity increased and chloride binding capacity decreased. Further discussion indicated that the addition of CEA increased the volume of large capillary pore with diameter between 400 and 5000 nm, and decreased the chloride binding capacity due to the increase in the SO3 content, both of which led to the decrease in chloride penetration resistance of marine concrete. However, when the dosage of CEA was not more than 6%, adding CEA can well compensate for the autogenous shrinkage and improve the crack resistance of marine concrete without a relatively small loss of compressive strength (≤8.7%). In addition, for the marine concretes containing CEA, the chloride diffusion coefficients were very small (<1 × 10-12 m2/s). Therefore, adding no more than 6% CEA, marine concrete had good crack resistance and chloride penetration resistance. Hopefully, the outcomes of this research can provide guidance for the application of CEA in marine concrete.

Tensile Behavior of Hybrid Fiber-Reinforced Ultra-High-Performance Concrete

Thirty dog bone-shaped specimens were tested to study the effects of steel fiber mixed with seven kinds of non-metallic fibers on the tensile properties of ultra-high-performance concrete (UHPC). Through experiments and micromorphological analysis, the effects of hybrid fibers on the compressive strength, tensile strength, peak strain, fracture energy, and characteristic length of UHPC were analyzed. The results showed that the hybrid fiber-reinforced UHPC showed good ductile failure characteristics, which reflected the good crack resistance and toughening effect of different fibers. The tensile stress–strain curves of UHPC with different hybrid fibers can be divided into two parts: ascending section and softening section, and the softening section was greatly affected by the type and content of fibers. Basalt fiber with a diameter of 0.02 mm had the most obvious strengthening effect on UHPC, and polyvinyl alcohol fiber with a diameter of 0.2 mm and length of 8 mm had the best toughening effect. The mixing of steel fiber and non-metallic fiber cannot only reduce the preparation cost but also improve the fracture energy and toughness of UHPC.

Highly Stretchable, Crack-Insensitive and Compressible Ceramic Aerogel.

Ceramic aerogels are attractive candidates for high-temperature thermal insulation, catalysis support, and ultrafiltration materials, but their practical applications are usually limited by brittleness. Recently, reversible compressibility has been realized in flexible nanostructures-based ceramic aerogels. However, these modified aerogels still show fast and brittle fracture under tension. Herein, we demonstrate achieving reversible stretch and crack insensitivity in a highly compressible ceramic aerogel through engineering its microstructure by using curly SiC-SiOx bicrystal nanowire as the building blocks. The aerogel exhibits large-strain reversible stretch (20%) and good resistance to high-speed tensile fatigue test. Even for a prenotched sample, a reversible stretch at 10% strain is achieved, indicating good crack resistance. The aerogel also displays reversible compressibility up to 80% strain, ultralow thermal conductivity of 28.4 mW m-1 K-1, and excellent thermal stability even at temperatures as high as 1200 °C in butane blow torch or as low as -196 °C in liquid nitrogen. Our findings show that the attractive tensile properties arise from the deformation, interaction, and reorientation of the curly nanowires which could reduce stress concentration and suppress crack initiation and growth during tension. This study not only expands the applicability of ceramic aerogels to conditions involving complex dynamic stress under extreme temperature conditions but also benefits the design of other highly stretchable and crack-resistant porous ceramic materials for various applications.