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The use of pozzolans is very necessary and inseparable for the sustainable development and better performance of the concrete industry. In the production of concrete, the combination of iron powder, fly ash, metakaolin and limestone powder under the name of fracking is used as materials and substitutes for cement in different percentages. The compressive strength of this concrete is higher than normal concrete. This type of concrete is a very new concrete that few tests have been done on it in the world, so there is not lot of information available about it. According to the studies, the most important features of this concrete are the use of iron waste, reduction of air and environmental pollution, cost savings and higher compressive strength than ordinary concrete. In this research, in order to protect the environment and reduce environmental pollution, fracking has been used as a relative substitute for cement. After obtaining the appropriate proportions, the frac mixture with percentages of 0, 3, 6, and 9 was considered as a substitute for cement. There were 8 tests in this research, 4 tests of the first category were carried out with the mentioned percentages of frac and 0% of steel fibers, but in the 4 tests of the second category, the volume of 1% of steel fibers was considered in the mixture. In this research, a total of 16 concrete samples were made, of which 8 of the first batch were used for pre-heating tests and 8 of the second batch were used to collect the results and performance of the concrete after heating. took After making the concrete samples and performing the necessary processes, the concrete samples were molded and placed on the vibrating table in order to make them denser and prevent voids in the concrete. After vibrating for a sufficient time, the samples were placed in the open space for 24 hours and then placed in the water basin for the processing process. A group of samples was taken out of the pond after 7 days to perform compressive and tensile strength tests (at the age of 7 days, due to the freshness of the concrete, exposure to high heat was not done) . After 28 days, the second batch was removed from the water and prepared for testing. The tests performed on these samples include compressive strength before and after heating, bending strength before and after heating, ultrasonic before and after heating, and water absorption before and after high heat. To test the performance of the samples after heating, the samples were placed in the furnace at a temperature of 450 degrees Celsius for 60 minutes (one hour) and after one hour, the samples were removed from the furnace and The samples were cooled at a temperature of 24 degrees Celsius. After the cooling of the samples, the tests were conducted on the samples, and the results indicated that the increase in the amount of frac leads to a 16% increase in the compressive strength before heating and improving its mechanical properties compared to ordinary concrete.

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Shotcrete, a pneumatically sprayed concrete mixture, has gained significant popularity in the construction industry due to its versatility and adaptability. However, the demand for high-strength shotcrete has intensified, driven by advancements in equipment and admixtures. Fiber-reinforced high-strength shotcrete (FRHSS) offers enhanced quality, adhesion, and construction speed, making it ideal for stabilizing excavations and slopes, strengthening masonry and concrete structures, and reinforcing underground structures. Additionally, the increased strength allows for reduced section dimensions, leading to more economical designs.

This research investigates the effects of aggregate gradation and admixtures, including micro silica, superplasticizer, accelerator, and micro recycled steel fibers (MRSFs), on the strength and performance of FRHSS. The study employs wet-mix and dry-mix shotcrete methods, examining the properties through laboratory and field experiments.

The results demonstrate that achieving high-strength shotcrete is more feasible with the wet-mix method. Fiber-reinforced wet-mix shotcrete attained a 28-day compressive strength of 987 kg/cm², representing an 80% and 77% increase in compressive strength and energy absorption, respectively, compared to conventional fiber-reinforced wet-mix shotcrete. Furthermore, fracture toughness tests revealed that MRSFs effectively prevent microcrack propagation and control deformations. FRHSS incorporating MRSFs exhibited a 28% and 97% increase in compressive strength and energy absorption, respectively, compared to the corresponding mix without fibers.
 

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Fire can not only lead to many human and financial losses, but also can cause structures to collapse and destroy them. For this reason, it is necessary and inevitable to protect buildings against fire and conduct more research in the field of better understanding the effects of combining different materials with each other and obtaining materials with greater resistance to fire. Concrete and concrete structures are always used by construction engineers due to their resistance, availability and resilience against fire. Ordinary concrete loses its strength at high temperatures, and the use of unreinforced concrete is not very useful due to its brittleness and weakness in tensile strength. In concrete, the tensile strength is lower than its compressive strength, and for this reason, researchers are trying to increase the resistance to fire and heating by improving the tensile strength of concrete. Reinforcing concrete with rebar is always a solution to increase the tensile strength in concrete parts, one of the most important weaknesses of using rebar in concrete is that the reinforcements form a small part of the concrete cross-section and actually cause the concrete to be inhomogeneous. In this research, double-bent steel fibers have been used to overcome the mentioned weakness and reinforce the concrete. It should be noted that concrete containing steel fibers has favorable compressive and tensile strength due to the high tensile strength of steel fibers. In order to achieve this goal and achieve fiber concrete that has good fire resistance, we defined seven different mixing plans with different percentages of steel fibers and lubricants. Concrete samples were produced using double-bent steel fibers in amounts of 0.5, 1, and 1.2 percent by volume of concrete and superlubricant in 0.5, 1, and 1.3 percent by weight of cement, and then in Cubic molds with dimensions of 10x10x10 cm and cylindrical ones were sampled as standard, and after setting the cement, the 28-day-old concrete samples, after heating and placing inside the electric heater with different temperatures, were divided into two The method of gradual cooling with ambient air and fog spraying (water spraying) is similar to what firefighters do when extinguishing a fire, after measuring the amount of weight loss of the heated samples, the weight loss values ​​were presented in the form of a diagram, then the samples were subjected to tests Compressive strength, tensile strength (Brazilian test) and ultrasonic wave speed (ultrasonic test) were placed, and the results and data of each of them for each mixing design were presented in the form of a diagram after examination and classification, so that the effect of high heat on Concrete containing steel fibers and super-lubricant should be determined. The results clearly showed the improvement of the tensile strength in three volume percentages of fibers by 14.6, 16.8 and 64.5%, respectively, compared to concrete without fibers, and also the compressive strength of concrete after bearing the heat of 250 degrees Celsius and cooling to the fogging method had 44.5, 31.6, and 9.3 percent, respectively, and in the gradual air cooling method, the compressive strength was 43.3, 44.9, and 50 percent, respectively.


 

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The porosity of electrospun nanofibers web is a significant parameter affecting various areas of nanofibers applications. Thus, at first, the effect of most effective parameters, the concentration of polymer solution and flow rate, on the diameter of polyvinyl alcohol nanofibers, as a dissolving component, were investigated. Afterward, the hybrid web of polyamide 6/polyvinyl alcohol (PA/P) was prepared via a two-sided dual-nozzles electrospinning method. The morphology, diameter, pore size of nanofibers web and the effect of dissolving constituent were studied based on images of the scanning electron microscope. To measuring the porosity of nanofibrous webs, three practical and straightforward methods that have been proposed in the literature were utilized. It was observed that when one component was dissolved, the diameter of the resultant web was decreased, and the porosity has been reduced to about 70% based on the best selected method of porosity. Additionally, the average pore size of electrospun PA6 webs has been decreased about 30-58% relative to the original hybrid webs.

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Research subject:
As a low price biomass, rice husk is able to accumulate a large amount of silica in its texture. The process for extracting this silica is greener than the conventional ones. The present research addresses the effects of the different process parameters on amorphous silica extraction from rice husk through a precipitation method.
Research approach
In the extraction process, first the rice husk was burned in the open air and then turned into white ash in an electric furnace. This ash was converted into sodium silicate solution using NaOH, and finally the silica was precipitated from this solution by sulfuric acid. The effect of solid to solvent ratio, the duration of the alkaline dissolution step as well as the pH and temperature of acid precipitation step have been investigated. Moreover, a special application of the amorphous silica in rubber industry was also investigated.
Main results
The results showed that a low solid to solvent ratio at the alkaline dissolution stage as well as an acidic pH along with a high precipitation temperature are required to obtain the highest production efficiency and to obtain high purity amorphous silica. The purity and chemistry of obtained silica were quite similar to commercial sample in the rubber industry; however, the surface area and pore volume of obtained silica was less than the commercial one. It was also found that prolonging the alkali dissolution step slightly increases the production efficiency. The obtained silica exhibited very close performance to the commercial sample, in the rubber-to-fiber adhesion system (RFS). This indicates the high ability of precipitated silica to be replaced by commercial types, which are mainly produced by more cost-effective and less biocompatible processes.

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According to the novel achievements, nanotopography and steric geometry of the microenvironment around the cells have a drastic role on their fates. Hence, fabrication of biocompatible nanostructures as the scaffolds for the cell culture and in the next step, accurate determination of their physical and geometrical characteristics is widely considered. Despite of broad utilization of Atomic Force Microscopy to investigate topological traits of sophisticated nanopatterns; its capability to characterize electrospun nanofibers has not been studied inquiringly. In the present research, chitosan nanofibers which were successfully electrospun at the optimized conditions were then evaluated using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) respectively. The results suggested that recruitment of both of these techniques have their own advantages and disadvantages. As the first noticeable issue, while the sample preparation and scanning procedure in SEM imaging may disrupt native structure of fibers, probing the sample by AFM doesn't need any pre-imaging treatment. The main application of SEM in analysis of nanofibrillar structures is the rapid survey of nanofibers shape, orientation, diameter and consistency. In the other side, three dimensional imaging by AFM makes it possible to determine whole surface roughness, roughness along fibers and woven tissue thickness. Furthermore, regarding some technical advices, AFM can be used to estimate nanofibers average diameter as well as SEM.

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Aims: Nylon or polyamide is one of the most used and most important polymers used in the plastic and fiber industries of the world. For this reason, its use is less sensitive to the properties of its very poor biodegradability. Therefore, the aim of the present study was the biodegradability modification of synthetic polyamide 6 (pa6) fibers via in-situ melt blending with recycled poly (lactic) acid plastic food container flakes (r-PLA) during the melt spinning process.
Materials & Methods: In this experimental study, polyamide chips 6 in textile industry and Poly (Lactic) Acid Plastic Disposable Container Flakes were used. The weight loss, mechanical properties, and surface morphology variations of pure and modified fiber samples after soil burial test were analyzed for comprehensive biodegradability study of the modified fiber samples. Data were analyzed by One-Way Analysis of Variance.
Findings: The mechanical tests performed on Norris fiber showed successful production of blend fibers with the percentages of 5, 10, 20, 30, and 40 of the components of r-PLA and A 50% r-PLA fiber sample did not have acceptable mechanical properties. The changes of PA6/r-PLA blended fibers with a significant increase in r-PLA component in the PA6 substrate were significant.
Conclusion: The blend modified of PA6 and Poly (Lactic) recycled samples, with a composition containing from 5% to 40% of the dispersed recycled poly-lactic acid fraction have successfully melt spinning capability. By increasing the percentage of recycled poly lactic acid in the blended fibers, the mechanical properties show improvement in samples of 5% and 10% by weight and show reduction in higher percentages. Iincreasing the biodegradability of modified PA 6 fibers with increasing the r-PLA content is obviously confirmed.

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Abstract: Chloride penetration resistance of concrete is considered a key parameter affecting durability of structures exposed to marine environments. Chloride diffusivity of concrete can be determined by immersion or ponding tests. However such tests are time consuming and costly. These facts have lead researches to develop accelerated tests such as the rapid chloride penetration test RCPT (ASTM C1202). In the RCPT test, the electrical charge passing during six hours through a 50 mm concrete disc, under potential difference of 60 volts is measured. A main concern expressed for the RCPT test has been the rise in temperature of concrete specimens which results in a reduction in concrete resistivity. The other criticism towards the RCPT test is the role of ions other than chloride ion, particularly the (OH)^- ion in conductance of electrical charge. It has therefore been suggested that some complementary cementitous materials can cause a reduction in the electrical charge passed, by reducing the concentration of (OH)^- ions in pore solution. Another quick method for measuring chloride resistance of concrete is the Rapid Chloride Migration test RCMT (AASHTO TP64). This test is in general similar to the RCPT method. However for avoiding the heating of specimen, the applied voltage is adjusted in accordance with the initially passed charge. Also in the RCMT test, for avoiding the influence of other charge carrying ions, the actual chloride ion penetration into the specimen is determined. A further method proposed for appraisal of chloride resistance of concrete, is determination of electrical resistance. For avoidance of heating of concrete specimens, electrical conductivity measurements are carried out for short durations. This research was carried out with the aim of comparing the results of various quick methods for determination of chloride resistance of concretes containing various supplementary cementitous materials. In the experimental study the control mix had a water cement ratio of 0.38 and cement content of 420 Kg/m³. Mixes containing various amounts of supplementary cementitous materials including silica fume, fine fly ash, pumice, fly ash and slag were studied. For the RCPT test, the temperature effect resulted in considerable overestimation in the effect of using of supplementary cementitous materials in improving chloride resistance of concrete. Temperature rise did not occur during the RCMT test, and this test therefore does not suffer  In the case of optimum fiber value, the obtained results from laboratory tests have shown a reduction in compressive strength and value of ultrasonic test around 8.7% and 2.5% respectively. Moreover it has shown an increase in tensile strength, flexural strength, electrical resistance and value of VB test about 33%, 10%,11% and 51% respectively. Consequently utilizing such fibers in sleeper concrete could be suggested for practical applications.

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In this paper, the effect of processing temperature on the elastic and viscoelastic properties including storage modulus, loss modulus and damping value of PVC/plain weave fiberglass composites laminates was investigated. For this, composite samples with [0/90]10 lay ups were produced in three different temperatures including 160 ᵒC, 200 ᵒC and 230 ᵒC using film stacking procedure. Firstly, the flexural strength and modulus of the samples were measured using three points bending test according to ASTM D790-07 standard. Then, viscoelastic properties of the samples were measured in the temperature range of 25 ᵒC up to 220 ᵒC using Dynamic Mechanical Thermal Analysis (DMTA) and the effect of temperature on the viscoelastic properties was studied. Also, the effect of fiber/ matrix impregnation quality on the thermal and dynamic properties of the samples was evaluated using optical microscope images. It was concluded that the temperature of 230 ᵒC is proper to achieve high quality impregnation, according to both DMTA and three points bending test. Also, it was seen that increase of processing temperature up to 230 ᵒC increases the storage modulus; however, processing temperature doesn’t affect the glass transition temperature of the samples.

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Adding particles and fibers to the adhesive layer is a method suggested to improve the stress distribution and to increase the strength and toughness of adhesive joints. In this paper, the effects of adding the metal fibers and also the reduction of fiber horizontal distance on distribution of peel stress and shear stress toward longitudinal and transverse directions were studied using finite element analysis. The obtained results showed that the reduction of the horizontal distance between the metal fibers in the longitudinal direction improves the distribution of the peel stress and shear stress and leads to a significant reduction in their maximum values in the joint length with respect to the non-reinforced adhesive. Meanwhile, reduction of the horizontal distance between the metal fibers in the transverse direction first degrades the peel stress and then improves it. Despite the trend observed for the peel stress with the transverse direction, the distribution of the shear stress with reduction of the horizontal distance between the metal fibers becomes more uniform and the maximum values of shear stress regularly decreases in the joint length due to considerable load sharing of the metal fibers in the adhesive layer. In addition to the analyses carried out on the distribution of stress in the joints length, the distribution of peel stress and shear stress were also investigated in joint width, which was indicative of a significant effect of the metal fibers in the transverse configuration.

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In the case of presence of deep micro-cracks within the composite structures, they must be replaced. The self-healing phenomenon which is inspired from the biological systems such as vascular networks in plants or capillary networks in animals, is an appropriate strategy to control the defects and micro-cracks. In the present research, by taking accounts the advantages of self-healing concept, an attempt has been made to control the micro-cracks and damages which were created in composite structures. To do so, series of micro glass tubes were employed to provide a self-healing system. These micro-tubes were filled with epoxy resin/anhydride hardener as a healing agent. When the structure is subjected to loading conditions, some damages or micro-cracks are created. In this situation, the micro glass tubes will rupture and the healing agent flows in the damage area, leading to the elimination of the defects over a time span. The aim of this study is to find out the appropriate self-healing material volume fraction and healing time to obtain an efficient healing. For this purpose, glass micro-tubes containing various healing agent loadings of 0.75, 1.65 and 2.5 vol.% were incorporated in epoxy-carbon fibers composites and the tensile behavior of the specimens were assessed during different time span from defect creation. The highest tensile strength recovery of 89% was observed for the specimen with 1.65 vol.% healing agent. Also the results show presence of micro tube decrease the fracture strain and over the time span fracture strain recovered.

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The fiber metal laminate composites a new generation of hybrid composites that have high strength to weight ratio. Good mechanical properties combining the properties of metals and fiber composites, led to the widespread use of composites in the industry, especially the aviation industry find. Add shape memory alloy to fiber metal laminate composite, due to super elasticity properties of alloy, makes the alloy formed during the impact hysteresis loop, will attract a lot of energy and impact properties of the fiber metal laminate composites increased. In this study, effects of different strains of nickel-titanium shape memory alloy wire high temperature, experimental in this type of composites against low speed impact using the impact falling, investigated. In metal part of fiber metal laminate composites, 2024-T3 aluminum alloy sheet and in composite part of glass fibers and epoxy resin is used. 6 wires with the pre strains 1, 2 and 3% in order to wrapping in the fibers metal laminate composites, was used. Increase the impact resistance of such composites by increasing pre strain as well as the energy absorbed by the shape memory alloy when impact, the results of this research was.

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Over the course of time into the 21th century, concrete has been known as one of the most high usage materials in the construction industry. As a consequence, trying to produce light concrete is an active and developing area within the new field of construction science. This technology consists of lowering the whole weight of structure by using new bulding techniques, new materials and optimizing ways of manufacture. Lowering the weight not only economizes on the expenses, time and energy but also decreases the damages of earthquakes. Furthermore, it keeps the constructions safe and minimizes the damages resulting from the overweight of the structure during different waves of shocks and aftershocks. In spite of considerable amount of compressive strength, low tensility strength and relatively high fragility of the concrete, there are limitations in using it in some parts which are partially or fully under forces of tention in different parts of structures. This fundamental defect of concrete in practice can be eliminated by reinforcing it through using steel tabs in the direction of traction forces. Having in mind that the armature just constitues a small part of the whole cross section of the structure, it will not be correct to conceive of the cross section of concrete as an isotropic and homogeneous surface. In recent decades, in order to come up with the isotopic condition and decrease the fragility, weakness and retrogression of concrete new techniques and trends of applying slender fibers running through the internal section of the bulk of concrete has become prevalent and common practice. The concrete containing nano materials compared with the normal concrete affected by nono chemical materials with cement particles and clcium hydroxide crystals which exist in cement, has a severe effect on the performance of concrete composites while such mixtures come into each others’ contact.
In this study,we examined the effect of Nano-silica and polypropylene fibres on mechanical properties and durability of normal and light weight concretes. In the design of light weight concrete, lecalight weight aggregates were used. More than 384 cubic and cylindrical samples were made based on ASTM standards and compressive strenght, indirect tensile strength, ultrasonic and electrical resistance experiments were done.
The results of the experiments showed considerable increase in mechanical characteristics and durability of normal and light weight concretes. Nano-silica contributes to the proper spread of the fibers. Compressive strength, indirect tensile strength, and the dynamic elasticity module of the ordinary concrete were higher than those of the light weight concrete, while the electrical resistance of the light weight concrete was higher compared to the corresponding samples.
Compressive strength and indirect tensile strength increased to 71 and 55 percent in normal concrete and to 43 and 47 percent in light weight concrete respectively. Considerable increase in electrical resistance indicates high durability of these kinds of concretes. Of course, economic considerations of using nano-silica and polypropylene fibers require special attention. Finally, the right amount of utilization of the polypropylene fibers and nano silica were determined in order to achieve normal concrete and light weight concrete with optimal properties.

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In this research work, the self-healing behavior of epoxy matrix composite which reinforced by hollow glass fibers as self-healing container was investigated. For doing this, in first step, the hollow glass fibers were filled with the epoxy resin and hardener by creating a partial vacuum. Then, the filled hollow glass fibers with different percent of 1, 3 and 5 vol.% were embedded in the epoxy matrix. In the next step, by applying press, the destruction was created in these composites. Then, these destructed composites were healed at ambient temperature at different times of 2, 4, 7 and 14 days. Then, for accessing to the optimum healing time and percentage of hollow fibers in composite, the flexural test was applied in these composites. In the final step, the mechanical properties of composite with the optimum healing time and percentage of reinforcement were evaluated via tensile, flexural and impact exams. The obtained results show that the optimum percentage of hollow fibers and time for healing process are 3 vol.% and 7 days. Also, the healing efficiency of composite in optimum conditions (3 vol.% hollow fibers and 7 days healing time) at tensile, flexural and impact exams were approximately 77, 54 and 92 % respectively.

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In this work, effect of thermal cycling on the flexural properties of fiber-metal laminate (FML) has been evaluated. FML plates were composed by two aluminium 2024-T3 and a epoxy polymer-matrix composites ply formed by four layers of basalt fibers. For FML samples the thermal cycle times were about 6 min for temperature cycles from 25 °C to 115 °C. Flexural properties were evaluated on samples after 20, 35 and 55 thermal cycles, and compared to non-exposed samples. While the thermal cycling decreased the flexural strength of chemical treated FML (etched aluminium), increasing at first, and then decreasing after a while was observed in electrochemical treated FML (anodized aluminium). The flexural modulus of FML showed irregularly changes for both of FML with anodized aluminium and FML with etched aluminium. The energy absorption of FML with etched aluminium showed a sharp decline with increasing thermal cycling while the energy absorption of FML with anodized aluminium showed a Low and irregular changes. Evaluation optical microscope showed that the mechanism of failure for the FML with etched aluminium after thermal cycling changed from failure of FML to separation between layers of FML, while for the FML with anodized aluminium before and after thermal cycling it was failure of FML and it has not changed.

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In this study, the impact strength multi-layer slabs reinforced by steel and nylon fibers, as well as the combination of these two fibers under the influence high velocity projectile, was investigated. To achieve this goal, 30 slabs one layer and three layers with dimensions 40 *40 * 7.5 cm were reinforced by 1% of the fiber, 30 slabs made 10 different models , each with 3 models Sample was made. A non-fiber model, as a control sample, and other slabs all have a constant volume 1 percent fiber, the difference being in the type and composition the fibers in different layers the slabs. The slabs were made with Kalashnikov , PK Kalashnikov and Dragunov guns at a distance 50 meters tested. In the test the projectile's encounter, three parameters penetration depth, area the damaged front and rear area and the volume damaged area in the samples were calculated and compared. Based on the results obtained, steel fibers can increase the resistance concrete slabs against the impact the projectile and reduce the surface area and volume the damaged area and significantly reduce the penetration depth. Steel fibers at best reduced the penetration depth 64 % in the kalashinkov gun and reduced the area and volume the damaged area in the dragunov weapon by 88 % and 98 % respectively. Also, steel fibers can prevent crack expansion by increasing the bond strength, provided that the fibers the nylon have a much lower impact than steel fibers. the nylon fiber could reduce the penetration depth and demolition area the sample in kalashnikov weapon by 37 % and 59 %, respectively, and reduce the volume damaged area in the dragunov weapon by 84 %, respectively. In addition, in this research, 12 samples cubic pressure were placed on the side 10 cm, 12 cylindrical tensile samples 10 × 20 cm and 12 small flexion beams with dimensions 32 *8 *6 cm and tested. It was observed that steel and nylon fibers cannot have a significant effect on the compressive strength, As a result the addition one percent the steel fiber, nylon and a combination these, this increase is 7.7, 2.6 and 6.4 % , which can be neglected. but steel fibers can significantly increase the tensile and flexural strength the concrete. addition one percent the steel fiber could create a 2.5 – fold increase in tensile strengths and increase the resistance 2 - fold in bending specimens. This is the nylon fibers do not have a significant impact on the tensile and flexural strength. Adding one percent the nylon fibers in the tensile and flexural samples could increase the resistance these specimens by 16 % and 24 % respectively. It was observed in the bending test of beams that steel and nylon fibers can be bent by bending in the cracks to increase the shape the weld so that the change in the maximum area the beam with the addition one percent steel fiber from about 4 mm in the control sample increase to about 25 mm.

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Reactive powder concrete (RPC) represents a new generation of cement-based materials composed of cement, reactive ultrafine powders, siliceous fine aggregates, super plasticizers and fibers. Due to its microstructural properties, this concrete demonstrates specific properties including high compressive and flexural strength, superb durability. Since this is a novel type of concrete, a single design code containing multiple experimental results of high quality, together with reliable stress-strain models for the nonlinear analysis of the structural members made of this concrete type is lacking. Although some experimental equations to predict the strength of the RPC members can be found in the literature, note that there are shortcomings in the information provided specifically regarding the RPC containing synthetic and hybrid fibers. Hence, in this study, ten different mix designs of RPC, containing steel fibers at the volume fractions of 1, 2, and 3%, polyvinyl alcohol fibers at the volume fractions of 0.25, 0.5, and 0.75%, together with hybridizations of the two fiber types at the total fiber volume fraction of 1% were prepared, and then tested to obtain accurate and applicable equations as well as the compressive stress-strain curve with the purpose of estimating the mechanical properties and better predicting the behavior of this type of concrete. Then, the effect of the type and volume fraction of fibers, together with curing regime on the properties of RPC including the compressive strength, strain at peak stress, modulus of elasticity, and the shape of stress-strain curve was investigated. The obtained results indicate that as the volume fraction of steel and polyvinyl alcohol fibers increases, the compressive strength and strain at peak stress of the RPC specimens decreases; a trend which is also observed as the volume fraction of synthetic fibers in the concrete mix containing hybrid fibers increases.. The trend which is observed for the strain at peak stress in the RPC is very close to that for its compressive strength. The secant and tangential modulus of elasticity values of the RPC also demonstrate trends similar to each other, and the tangential modulus of elasticity in all the specimens has values higher than the corresponding secant modulus of elasticity. The RPC containing high volume fractions of steel fibers shows high modulus of elasticity values, due to the crimped shape of fibers as well as the strong cohesion they provide in the concrete. Heat treatment has a positive effect on the compressive strength and strain at peak stress of the RPC specimens, due to the acceleration of the hydration process of cementitious materials at high temperatures as well as the formation of a dense matrix. By using the nonlinear regression analysis of the data, experimental equations were developed for the parameters affecting the stress-strain curve of RPC. Finally, based on the experimental parameters obtained for all the RPC specimens, a model was proposed to predict the compressive stress-strain curve. By comparing the proposed model with the experimental results of the stress-strain curve of RPC, it can be said that the proposed model is capable of predicting the experimental results with a very good accuracy.

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The statics of droplet hanging from the parallel fibers and the dynamics of droplet impact on the parallel fibers are investigated using high-speed imaging and volume of fluid numerical simulation. Experimental results show for the parallel fibers, the maximum volume of the droplet, which is able to hang statically from the fibers is measured to vary between 1.85 to 1.9 times of the one measured for a single fiber. The dynamics of droplet impact have been studied by varying the radius of the impacting droplet, the fibers radius, and the distance between the fibers. The threshold velocity of droplets by fibers has been obtained both experimentally and numerically with the fluid volume method. The results show that by increasing the impacting droplet radius and decreasing the fibers radius, the threshold velocity of droplet capture decreases. The maximum threshold velocity of droplet capture with parallel fibers varies in the range of 1.5 to 1.8 times of the threshold velocity of capture with a single fiber. The maximum threshold capture velocity of droplets occurs where the distance between fibers is in the range of 0.35 to 0.5 times of impacting droplet diameter. The threshold capture velocity on parallel fibers is also obtained analytically, using the energy balance method. The results of the analytical solution are in a fair agreement with experimental data and numerical simulation results.