Toughness Index Research Articles

The prevalence of common mental health problems and associated psychosocial issues in elite swimmers

Abstract: Introduction: The mental health of elite athletes has been recognised as of great importance. There have been relatively few studies examining the prevalence of mental health problems in swimmers. None have commented on the range of psychosocial problems associated with mental ill-health. The aim of this study was to identify the prevalence of common mental health problems and psychosocial problems in elite swimmers. Methods: The study was conducted on a national swimming squad competing at the international level. All athletes (n=55) were invited to participate. The response rate was 63.3% (n=36). The study was cross-sectional in design. Data was collected using a battery of psychometric tests yielding information on distress (The Distress Screener), anxiety and depression (PHQ-9, K10), sleep disturbance (PROMIS scale), alcohol consumption (AUDIT-C), smoking behaviour, adverse nutrition behaviour, career satisfaction (Career Satisfaction Scale) and mental toughness (Mental Toughness Index). Results: The prevalence of depression was 14% (n=5). Six percent (n=2) reported suicidal ideation in the last 2 weeks. Fourteen percent met criteria for distress. There were positive correlations between depression and sleep disturbance ( r=.343, p<.05), between anxiety/depression and distress ( r=.380, p<.05), and between depression and distress ( r=.531, p<.01). Career dissatisfaction was identified in 46% of participants and was inversely correlated with mental toughness ( r=.485, p<.01). Low mental toughness and adverse alcohol use were identified in 37% and 23% of participants, respectively. Conclusions: Elite swimmers experience common mental illnesses and associated psychosocial problems. There is a relationship between career dissatisfaction and low mental toughness. Sport governing bodies should assess their own athlete populations and implement programmes to support mental health.

Matrix Tailoring for Polyvinyl Alcohol (PVA) Fiber-Reinforced Ductile Cementitious Composites

The main concern for the limited practical applications of strain-hardening cementitious composite, especially in China, is the high cost of imported materials, mainly polyvinyl alcohol fibers. This study uses local ingredients to develop strain-hardening cementitious composite reinforced with non-oil-coated Chinese polyvinyl alcohol fiber. The cementitious matrix consisting of cement, fly ash, viscosity-modifying agent, and silica fume was prepared, and the matrix tailoring was performed to achieve improved mechanical performance. The prepared composites were evaluated by rheology, three-point bending, and tensile characterizations. It is found that with the given local ingredients and matrix modification, the toughness index value of 100 ( I40) according to the American Society for Testing and Materials can be achieved. Besides, the tensile results showed the improvement of 45% and 60% for first-cracking strength and peak tensile strength values, respectively. The effects of matrix modification are also analyzed statistically using the analysis of variance for the mechanical properties of the cementitious composite. The post hoc statistical analysis using the Tukey–Kramer honestly significant difference illustrated the optimum cementitious mix from the experimental data. The presented results of cost-effective strain-hardening cementitious composite are expected to promote the practical applications of strain-hardening cementitious composite in China.

Experimental investigation of raw steel fibers derived from waste tires for sustainable concrete

The increasing pollution burden is a significant hurdle in achieving the United Nations’ goals for a sustainable society. Various methods are used to handle pollution, including recycling waste into new products and using waste to improve other materials’ properties. In this respect, the trend of using waste materials, especially waste fibers, in the construction industry to improve the strength and durability of concrete is also receiving attention. Currently, most countries use raw steel fibers from waste tires (RSFs) to enhance the properties of cement composites. Using RSFs in construction materials can help decrease pollution and produce low-cost sustainable materials. Therefore, it is essential to explore the suitability of RSFs for enhancing the properties of cement composites. This study aims to explore the suitability of RSFs for durable and sustainable cement composites. The study’s specific aim is to evaluate the efficiency of locally available RSFs of Bratislava, Slovakia, for improving local concrete durability and strength properties. For this purpose, the concrete C20/24 of Cemix Bratislava is used. 0.30% to 0.75% of RSFs are added in raw form by volume fraction of the concrete. A statistical analysis of 1057 RSFs is performed to determine the frequencies of their dimensions. The workability of the concrete is measured by using the slump test. The concrete’s hardened properties, including compressive strength (CS), split tensile strength (SS), flexure strength (FS), and modulus of elasticity (EM), are evaluated. In addition, water absorption (WA) and linear shrinkage (LS) are also determined. All tests are performed following the ASTM standards except the test for EM. The precrack and postcrack energy absorption and toughness index are also reported for each strength property. The maximum enhancement of 20% and 16% is noted in CS and SS for RSF-incorporated concrete. At the same time, the FS did not improve. The WA increased, and LS decreased for RSFRCs compared to PC. Therefore, it can be concluded that raw steel fibers from discarded tires have the potential to be used for producing sustainable and durable concrete.

Strategies to improve the impact resistance of self-compacting concrete (SCC) after freeze-thaw cycles

Three strategies including rubber particles, steel fibers and asphalt-coated coarse aggregate (ACCA) were introduced to improve the impact resistance of self-compacting concrete (SCC) after freeze-thaw cycles. The impact compression properties of SCC after 200 freeze-thaw cycles were investigated using a 75-mm split Hopkinson pressure bar (SHPB). The fineness modulus of residue (Mr) and impact toughness index (ITi) were defined to evaluate the impact-resistance performances of SCC. Results show that dynamic properties of SCC including peak stress, peak strain, Mr and ITi show remarkable strain rate effect. The decrease scale of Mr for SCC with modifying materials is considerably lower than that of the control group, indicating a less damage degree caused by freeze-thaw cycles. The ITi of SCC is greatly improved by three types of modifying materials, and the efficiency of improvement is ordered as: SCC-SF > SCC-ACCA > SCC-R. The average ITi decrease rate of SCC-R, SCC-SF and SCC-ACCA in all strain-rate range is 3.3%, 2.0% and 1.3%, respectively, which is much lower than that of SCC0 (7.8%), indicating a reduced impact toughness loss caused by freeze-thaw cycles. The enhancement of impact resistance for SCC with three types of modifying materials is highly related to their crack propagation effect during the impact compression process.

Thermal failure of diamond tools indicated by diamond degradation: Damage evaluation and property prediction on small image datasets

High temperature induced diamond degradation often leads to the failure of diamond tools. In this work, diamond samples holding different degrees of thermal damage were prepared by heating and sintering. The influence of diamond particle size and processing temperature was investigated through mechanical testing and micromorphology observation, meanwhile, a dataset containing 2870 SEM images showing diamonds with different degrees of degradation was constructed. By modification of VGG16 network, classification models and regression models were developed for thermal damage evaluation and sample property prediction. Training strategies including transfer learning and data augmentation were implemented and verified essential on the small dataset, where drop-out showed no positive effects. Two classification models (3-class and 65-class) were constructed and trained for damage evaluation. Visualized damage feature maps exported from Grad-CAM revealed the influential mechanism of thermal damage on diamonds, which proved the effectiveness of the classification models as well. Under the optimized training strategies, regression models were built for sample property prediction. The models towards toughness index, bending strength loss, relative density and Rockwell hardness were examined. Comparing the output results with real property values in test sets, the first two models matched well, and the latter two showed the opposite. It verified the validity of the regression models for property prediction as they were all established based on diamond damage image datasets. The loss in bending strength loss prediction model was smaller than that of toughness index, indicating bending strength easier to be shorten than impact toughness for diamond/metal composites suffering thermal impacts.

Association of self-efficacy and mental toughness with sport performance in Brazilian futsal athletes.

Self-efficacy is considered a component of mental toughness, but there are few studies investigating the relationship of sport self-efficacy with mental toughness in performance athletes, especially in team sports. The objective was to examine the impact of sport self-efficacy mediated by mental toughness on the sport performance of Brazilian futsal athletes. The sample was composed of five adult male teams participating in the National Futsal League 2020, totaling 77 athletes. As instruments, we used: athlete identification sheet, Perceived Self-Efficacy Scale in Sports (PSES), Mental Toughness Index (MTI) questionnaire and the performance data from the National Futsal League 2020 (NFL). The data were analyzed using the Kolmogorov-Smirnov test, Mann-Whitney "U" test, Spearman's correlation, network analysis (LASSO), with the indicators of centrality: strength, proximity and degree of intermediation (p < 0.05). The results showed that the investigated sample presented high levels of Perceived Self-Efficacy Scale in Sports (PSES) (Md = 4.66) and mental toughness (MT) (Md = 6.44). PSES presented a positive relationship with the number of wins, and negative relationships with the number of red cards and wrong passes (r = -0.08). MT indirectly influenced these variables through its connection with PSES (r = 0.30). The best ranked teams presented higher amounts of goals for, fouls, shots on goal, tackles, assists, and wins. The time of practice revealed an inverse relationship with the number of defeats, while age was positively related to the number of wrong passes (r = 0.09). The centrality indicators showed that the number of games stood out as the most central variable in the network, due to its degree of strength, proximity and intermediation. Moreover, the high degree of proximity and intermediation of the tackles made presented a connection with the number of assists (γ = 0.25; n = 77). We can conclude that sport self-efficacy and mental toughness are intervening factors in the sport performance of Brazilian futsal athletes.

Mechanical properties of high-performance concrete by replacing cement with quaternary cementitious material with lignin as an additive material

The performance of the preponderance of materials can be described by characteristics dependent on their mechanical properties. These parameters can include strength, strain, and stiffness. Strength or stiffness alone is insufficient to characterize fiber-reinforced concrete’s behavior. This study investigates and analyses the mechanical properties of High-performance fiber-reinforced concrete developed with Lignin and brass-coated micro steel fiber. Cementitious elements such as Ground Granulated Blast-furnace Slag, Metakaolin, Alcoofine-1203 and Granite powder are used in conjunction with cement to create High-Performance Concrete. It was found that a mix ratio of 1:1.17:2.20 yielded an M60-grade of concrete using water-to-cement proportion of 0.32. Brass-coated micro steel fibers were used, and the flexural toughness was measured according to ASTM C1018. The toughness index of the structural member was calculated, together with its equivalent flexural Strength, with the application of three-point loading. These results suggest that the brass coating on the mild steel fiber significantly impacts the flexural toughness characteristics of the three-point bending beam specimen. When increasing the percentage of brass-coated micro steel fiber ranging from 0.5% to 2%, the flexural toughness parameters progressively enhance. It is found that 1.5% of fiber depicts the maximum Strength and toughness.

Experimental Study on Mechanical Properties of Basalt Fiber Concrete after Cryogenic Freeze-Thaw Cycles.

Basalt fiber (BF) has received much attention in recent years for engineering practice and scientific research related to basalt fiber reinforced concrete (BFRC) due to its advantageous mechanical properties and cost-effectiveness. By researching its performance characteristics after cryogenic freeze-thaw cycles, the advantages of BFRC's mechanical properties can be further exploited in order to expand its application scope. The effects of the fiber volume fraction, temperature gradient, and number of freeze-thaw cycles on the compressive strength, toughness index, splitting tensile strength, flexural strength, etc., of BFRC were investigated. Additionally, the damage mechanism of BFRC after freeze-thaw cycles was analyzed via scanning electron microscopy (SEM). The results show that the compressive strength of BFRC reaches its peak value when the fraction reaches 0.1% under the conditions of freezing and thawing cycles from room temperature to -80 °C. When the fraction of BFRC is 0.1%, and the maximum reduction is 17.1%, the splitting tensile strength decreased most sharply when the fraction was 0.1%, and the decrease amplitude was 40.9%, and the flexural strength decreased most acutely when the fraction was 0.3%, and the maximum decrease was 44.62%. The addition of basalt fibers can reduce the damage to the microstructure of concrete and improve its plastic degradation characteristics to a certain extent. With a decrease in the minimum temperature of the cryogenic freeze-thaw cycle, the optimal fiber content for compressive strength increases. Nevertheless, the splitting tensile strength and flexural strength of BFRC is improved as the fiber content increases under the cryogenic freeze-thaw environment.

Axial compressive behavior of ultra‐high performance concrete‐filled double skin high‐strength steel tubular short columns

AbstractIn this paper, seven ultra‐high performance concrete (UHPC)‐filled double skin high‐strength steel tubular (UHPCFDST) columns and four UHPC filled high‐strength steel tubular (UHPCFST) columns axial compression tests were carried out. The effects of hollow ratio, width‐to‐thickness ratio of the outer steel tube, and cross‐section combination form on the axial compression performance of UHPCFDST were studied, and the failure mode, axial load–strain curve, and strain response were discussed. The results showed that the high‐strength steel tube had good compatibility with UHPC, and all specimens finally had serious buckling deformation. The peak load of UHPCFDST specimens decreased with the increase of the hollow ratio, the ductility and toughness were improved. The width‐to‐thickness ratio of the outer steel tube had the most significant effect on the axial compression performance of the specimens. With the increase of the width‐to‐thickness of the outer steel tube, the ductility of the specimens tended to increase, and the toughness index first increased and then decreased. Finally, a unified calculation model for the ultimate compressive capacity of UHPCFDST and UHPCFST specimens was proposed, and the predicted value was in good agreement with the experimental value.

Mechanical behavior and microscopic mechanism of fiber reinforced coarse aggregate cemented backfill

Backfills have traditionally served as artificial stope roofs during the mining of cemented undercut-and-fill, which still has many problems, such as weak tensile strength, brittleness, poor ductility, etc. To improve the stability of the backfill, fluidity tests, mechanical tests, and microscopic characteristics tests were conducted on fiber-reinforced coarse aggregate cemented backfill (FCCB) with different polypropylene fiber (PPF) contents and curing times based on the existing filling parameters of Longshou mine in China. The results showed that the slump and expansion of FCCB slurry presented a slight linear decrease with an increase in PPF content, and the slurry satisfied the requirement of self-flow transport. Additionally, the uniaxial compressive strength (UCS) and splitting tensile strength (STS) of FCCB showed growth to a different extent. When the PPF content was 0.10 %, the enhancement effect was optimal. However, the backfill deteriorated as the content was more than 0.10 %. Moreover, the effects of a single 15 mm PPF on UCS and STS were better than that of hybrid fibers with different scales. The peak strain and the compressive and splitting toughness index (Ti) of FCCB increased at different degrees with an increase in PPF content, which was significantly higher than that of the backfill without fiber. After adding PPF, the backfill appeared characteristic of a crack but not broken. Furthermore, the hydration products, including CSH gel, Ca(OH)2 (CH), and ettringite (AFt), increased and became thicker with curing time, the compactness of the interfacial transition zone (ITZ) increased, the pores decreased, and the adhesion of PPF and cement stone increased, enhancing the microscopic mechanical properties of FCCB. This study would improve the safety of mining and have high application value.

Performance analysis of cost‐effective hybrid polypropylene‐steel engineered cementitious composites and prediction based on artificial neural network

AbstractEngineered Cementitious Composites (ECCs) is a high‐performance fiber‐reinforced cementitious composite renowned for their excellent tensile strain hardening behavior. Among the reinforcing fibers, PolyVinyl Alcohol (PVA) featuring sufficient tensile strength but the fiber's cost is relatively high. Hence, this research has attempted to obtain strain‐hardening ECC by locally available fibers. Hybridization of Recron 3s PolyPropylene (PP) fibers and hooked‐ended steel fibers (SFs) were chosen to improve the strain hardening behavior. According to the compressive test and direct tensile test results, mixes developed with 1.7% PP and 0.3% SF displayed better strain corresponding to ultimate load due to the better dispersion of the fibers. Toughness indices and residual strength factor were also estimated using ASTM C 1018 standards. Based on the observations, slabs contains 1.9% PP along with 0.1% SF has a significant impact on toughness indices and residual strength factor. However, the fracture energy increases by increasing the equivalent steel reinforcing indices from 20 to 55. Finally, the cost of the composites has been compared by frequently used PVA‐ECCs from the literature. It could be concluded that the cost could be reduced by around 75% by using the currently used hybrid ECC rather than PVA‐ECC. This study also presents the prediction of mechanical properties of hybrid ECC based on the artificial neural network. In conclusion, feedforward neural networks using a backpropagation algorithm and two processing layers demonstrated adequate ability to predict the mechanical properties of hybrid ECCs.

Compressive Behavior of Interlocking Plastic Blocks Structural Elements Having Slenderness

Earthquakes are among of the most harmful and potentially fatal natural disasters. Masonry structures in seismic zones of urban and rural areas around the world pose a threat to human life. Housing that is both affordable and earthquake-resistant in earthquake-prone areas is currently in demand in developing countries. For affordable earthquake-resistant structures in earthquake-prone areas, numerous researchers have studied mortar-free interlocking structures. Plastic blocks are used in order to reduce the mass of the overall structure. To start with, structures under gravity are explored first because more than 95% of its design life, any structure has to withstand gravity. Prototypes of interlocking plastic-block columns, solid walls, and walls with an opening are considered for making the mortar-free structures. In this study, the effect of slenderness on the behavior of interlocking-plastic-block structural elements is investigated under compressive loading by a servo-hydraulic testing machine in the laboratory. The effect of slenderness on the behavior of one and two-block-wide structural elements was investigated in terms of the stress–strain curve, energy absorption, and toughness index under compressive loadings. Correlations between the compressive strength of interlocking-plastic-block structural elements with varying thicknesses were found. Scaled-down prototypes of interlocking-plastic-block structural elements having two-block wide depicted more resistance to compressive loads than one block wide structural elements. The correlations among the one and two block wide interlocking-plastic-block columns, single and double-block-wide solid walls, and single and double-block-width walls with an opening found in this analysis were Pdc = 2.2 Psc, Pdsw = 2.9 Pssw, and Pdwo = 3.5 Pswo. This study can be applied in the future to better understand the detailed behavior of interlocking plastic blocks.

Durability Performance of PVA Fiber Cement-Stabilized Macadam

To further improve the durability of cement-stabilized macadam and guarantee the use quality and sustainability of a semi-rigid base, the current study was carried out. With the help of a dry shrinkage test, temperature shrinkage test, freeze–thaw bending test, and fatigue test, the effect of incorporating PVA fiber on the deformation characteristics of cement-stabilized macadam was analyzed, and the changes in low-temperature residual toughness of the mixture before and after modification were compared. The low-temperature toughness of PVA fiber cement-stabilized macadam was evaluated with the help of the standard toughness evaluation method. The fatigue life prediction equation of PVA fiber cement-stabilized macadam was established based on the Weibull distribution. The results showed that PVA fiber can effectively improve the deformation characteristics, low-temperature toughness, and fatigue performance of cement-stabilized macadam. The low-temperature residual flexural tensile strength and low-temperature bearing capacity were increased by 10.3% and 55.3%, respectively. The residual toughness indices were increased by 58.6%, 88.1%, and 98.3% and the residual strength index was increased by more than 100%. The fatigue life was improved by 178~368% under different stress intensity ratios. The fatigue life values obeyed the two-parameter Weibull distribution, and the correlation between the fatigue life prediction equation and the measured data was significant. The fatigue life prediction error was between 0.03 and 4.9% under different stress intensity ratios.

Study on Bond Performance between Corroded Deformed Steel Bar and DS-ECC.

In order to study the bond performance between desert sands engineered cementitious composites (DS-ECC) and corrosion steel bars, seven groups of specimens were designed and manufactured. Through the center pull-out test, the effects of different types of desert sands, the rate of corrosion (0, 5, 10 and 15%), and the anchorage length of steel bars (5d and 8d) on the bonding properties of DS-ECC and corrosion steel bars were studied. Moreover, a de-rusting agent was used to remove the corrosion, and three groups of specimens were pulled out from the center of the de-rusted steel bars. The results showed that both Tengger DS-ECC and Mu Us DS-ECC have good bond properties with corrosion steel bars. The bond stress slip curves between DS-ECC and corrosion steel bars can be divided into four stages: the micro-slip, slip stage, failure stage and residual stage. The bond stress slip curves between DS-ECC and de-rusted steel bars can be divided into the micro-slip stage, failure stage and residual stage, and splitting and pulling-out failure occurs in DS-ECC specimens. The ultimate bond strength is the highest when the corrosion rate is 5%. The bond toughness index is positively correlated with the anchorage length of steel bars, and negatively correlated with the corrosion rate of steel bars. According to the test results, the bond-slip mathematical relationship is established.

Prediction of mental strength from the satisfaction of basic needs in CABA and GBA esports players

Background: Esports are here to stay. Previous studies have shown that sports athletes have characteristics Esports are here to stay. Previous studies have shown that esports athletes have similar characteristics, such as satisfaction from competing, as those in traditional sports. However, being an area still growing, few studies have addressed them in Latin America. This study aimed to determine the relationship and predictors of mental toughness from the satisfaction of basic needs in amateur esports players from the Autonomous City of Buenos Aires and Greater Buenos Aires, Argentina. Methods: For this, a sample of 426 participants (85% male) was constituted, with a mean age of 22 years (SD = 3.67), who answered the Basic Needs Satisfaction in Sport Scale (BNSSS) and the Mental Toughness Index (MTI) questionnaire, as well as a sociodemographic questionnaire. Results: The results indicated a strong relationship between both variables, especially with the dimensions of competence satisfaction and perception of choice, also being the main predictors of mental strength. Conclusions: These results provide new empirical evidence for this area in formation, as well as different issues to be taken into account to develop mental strength and sporting success in esports.

The Mechanical Properties, Structural Stability and Thermal Conductivities of Y, Sc Doped AuIn2 by First−Principles Calculations

In this paper, based on density functional theory, the structural stability and mechanical properties of AuIn2 doped with RE (RE = Y, Sc) were investigated. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of the materials were calculated by Viogt−Reuss−Hill approximation. The calculation results show that Sc−SAu (trace of Au substituted by Sc in AuIn2), Y−SAu and Y−SIn have stable structure, and Y−SAu has obvious effect on the toughness indexes of AuIn2 alloy. Furthermore, based on Clarke and Cahill modes, the lattice thermal conductivity of the intermetallic compound was calculated and shows the same tendency with the Debye temperature and fast heat transfer rate in the direction of [110].

Low and intermediate temperatures fracture behavior of amorphous poly alpha olefin (APAO)-modified hot mix asphalt subjected to constant and variable temperatures

Low-temperature cracks (LTC) and intermediate-temperature cracks (ITC) are two important types of cracks in asphalt mixtures that cause damage to pavements and incur high maintenance costs on roads. On the other hand, temperature cycles, in addition to the traffic load on the asphalt mixtures, increase the possibility of structural failures. Therefore, it is necessary to study the solutions to deal with and control this type of cracking using appropriate methods. In this study, an attempt was made to evaluate the effect of amorphous poly alpha olefin (APAO) additive on the LTC and ITC behavior of Hot Mix Aspahlt (HMA) under loading conditions of modes I and II under constant temperature (CT) and variable temperature (VT) cycles. For this purpose, two geometries called symmetric specimen SCB (contains a vertical crack with an angle of 90°) and classical-modified specimen SCB-2 (contains an angled crack with an angle of 35°) were selected to simulate the loading conditions of mode I, as well as two geometries called modified specimen SCB-1 (contains a vertical crack with a 90-degree angle) and modified specimen SCB-2 (contains a vertical crack with a 90-degree angle) were selected to simulate mode II loading conditions. A total of four HMA mixtures were made, including one mixture without additives and three mixtures containing 3, 6, and 9 % APAO additives. Next, in order to simulate and match the road conditions with the laboratory samples, CT and VT conditions were applied to all samples. At temperatures of ± 15 °C, two fracture resistance indices called fracture toughness (KIC and KIIC) and fracture energy (GF) were studied to investigate the fracture behavior of HMA mixtures. Also, two other fracture indices, namely the Tensile Stiffness Index (TSI) and the Tensile Strength (TS), which represent the fracture behavior of the HMA mixture before the peak load, were evaluated. Finally, the flexibility of the mixtures was evaluated using brittleness indices such as the Flexibility Index (FI), Cracking Resistance Index (CRI), and Toughness Index (TI). The results showed that the fracture toughness and fracture energy of the HMA mixture containing 9 and 6 % APAO increased in mode I and II loading conditions under both CT and VT cycles compared to the base mixture. At temperatures of ± 15 °C, from the point of view of the fracture toughness index, the potential for creating angular cracks, and from the point of view of the fracture energy index, the full fracture potential of the mixture containing vertical cracks was higher (under CT and VT cycles). On the other hand, the reduction of the flexibility of the mixtures containing APAO percentages was concluded using FI, CRI, and TI indices. Also, the results showed that the addition of 3, 6, and 9 % of APAO additive to the HMA mixture increased the maximum preload indices, namely TSI and TS, and as a result, increased resistance to elastic deformation.

Effect of Fiber Content on Mechanical Properties and Microstructural Characteristics of Alkali Resistant Glass Fiber Reinforced Concrete

Owing to its enhanced strength, ductility, and resistance to harsh environments, increasing research attention has been paid to alkali-resistant glass fiber reinforced concrete (ARGFRC). This paper presents experimental studies concerning the effects of fiber content on the mechanical properties and microstructural characteristics of ARGFRC. The amount of glass fiber was considered at levels of 0.0, 0.3, 0.5, 0.8, 1.0, 1.3, and 1.5% of the concrete volume. The compression, flexural, impact resistance, scanning electron microscopy, and energy dispersive spectroscopy tests were conducted. The flexural load-deflection curve, flexural strength, flexural toughness index, flexural fracture energy, postcracking stiffness, postpeak stiffness, and impact resistance energy absorption were obtained. Then the changing law affected by fiber content on these mechanical properties was further analyzed, and the corresponding equation was fitted. When fiber content was 1.5%, the flexural toughness index I5, I10, and I20 values were 4.0, 5.9, and 8.9, respectively, and increased by 3.0∼7.9 times. Glass fiber incorporation could increase the ductility and delay the brittle failure when the fiber content reached 0.8%. The largest postcracking stiffness was calculated at 36.174 kN/mm with a fiber content of 0.8%. The higher the fiber content, the larger the postpeak stiffness of the tested beams. Impact resistance test results demonstrated that the optimum fiber content was 1.3%. As the fiber content increased, the effect of the concrete grout on the fiber packaging decreased, according to the scanning electron microscopy analysis. The energy dispersive spectroscopy observation proved that adding a certain fiber content did not affect the concrete hydration reaction.

Strengthening and toughening behaviors and dynamic constitutive model of carbon-based hierarchical fiber modified concrete: Cross-scale synergistic effects of carbon nanotubes and carbon fiber

Considering the synergistic effects (filling, activating, bridging, anti-cracking, and interface-optimizing) of combined carbon fiber and carbon nanotubes, the strategy of using carbon nanotubes-carbon fiber cross-scale reinforcement (CNTs-CF) to enhance concrete was proposed. The strengthening and toughening behaviors of CNTs-CF modified concrete (CCMC) were experimentally investigated. The results showed that CCMC had good crushing resistance capacity, and the addition of an appropriate amount of CNTs-CF was conducive to alleviating the brittle failure characteristics of concrete materials. Compared with ordinary concrete, the static and dynamic strength properties and toughness indexes of CCMC were greatly improved. When the volume content of CNTs-CF in concrete was 0.3%, CCMC showed the most superior strengthening and toughening behaviors. The hierarchical assembly and synergistic effect of carbon fiber and carbon nanotubes realized the combination of high strength and high toughness of concrete materials. The proposed rate-dependent constitutive model with damage based on Weibull statistical theory in this study can be used to accurately predict the dynamic compressive stress-strain relationship curve of concrete under different fiber content and strain rate.

Behavior of ternary blended cementitious rubberized mixes reinforced with recycled tires steel fibers under different types of impact loads

This research primarily investigates the influence of incorporating steel fibers (recycled and manufactured) in Rubberized concrete (RuC) mixes on impact resistance. Impact resistance was comprehensively investigated for six steel fiber reinforced RuC (SFRRuC) mixes with a large volume of rubber, reaching a replacement of 40 % of fine and coarse aggregates. Besides mechanical properties, four different types of impact tests, including drop weight on concrete discs and prisms, rebound, and projectile impact, were performed. The impact results indicate that the incorporation of blended fibers in the RuC mixes substantially enhances the initial and failure impact energy of SFRRuC under drop weight tests on discs and prisms. The excellent impact performance was further confirmed by the results of the projectile impact test on concrete slabs, where the ejected mass as well as the crater sizes for the concrete slab containing 40 % rubber and steel fiber were the lowest, as the dual effect of rubber and steel fibers enhanced the ductility, toughness, and penetration resistance. Overall, the improved impact, flexural resistance and toughness index of SFRRuC compared to the plain concrete mix makes it a potential alternative and sustainable construction material for various applications including industrial floors and protective wall barriers in military structures.