بررسی تأثیر افزایش دما بر روی بتن های حاوی فنر فلزی بازیافتی و مقایسه با الیاف های رایج

Although concrete is the most widely used construction material, its deficiency in shrinkage and low tensile resistance is undeniable. However, the aforementioned defects can be partially modified by addition of fibers. On the other hand, possibility of adding waste materials in concrete has provided a new ground for use of recycled concrete aggregates in the construction industry. In this study, a constant combination of recyclable coarse and fine concrete aggregates was used to replace the corresponding aggregates at 50% substitution percentage. Moreover, in order to investigate the effects of fibers on mechanical and durability properties of recycled aggregate concrete, the amounts of 0.5%, 1%, and 1.5% steel fibers (ST) and 0.05%, 0.1% and 0.15% polypropylene (PP) fibers by volumes were used individually and in hybrid forms. Compressive strength, tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption, toughness, elastic modulus and shrinkage of samples were investigated. The results of mechanical properties showed that PP fibers reduced the compressive strength while positive impact of steel fibers was evident both in single and hybrid forms. Tensile and flexural strength of samples were improved and the energy absorption of samples containing fibers increased substantially before and after crack presence. Growth in toughness especially in hybrid fiber-reinforced specimens retarded the propagation of cracks. Modulus of elasticity was decreased by the addition of PP fibers while the contrary trend was observed with the addition of steel fibers. PP fibers decreased the ultrasonic pulse velocity slightly and had undesirable effect on water absorption. However, steel fiber caused negligible decline in UPV and a small impact on water absorption. Steel fibers reduce the drying shrinkage by up to 35% when was applied solely. Using fibers also resulted in increasing the ductility of samples in failure. In addition, mechanical properties changes were also evaluated by statistical analysis of MATLAB software and smoothing spline interpolation on compressive, flexural, and indirect tensile strength. Using shell interpolation, the optimization process in areas without laboratory results led to determining optimal theoretical points in a two-parameter system including steel fibers and polypropylene.

In this study, high strength concrete of 75 MPa compressive strength was investigated. The experimental program was designed to study the effect of fibers and hybrid fibers (steel and polypropylene fibers) on the fresh (workability and wet density) and hardened properties (compressive strength, splitting strength, flexural strength and dry density) of high strength concrete. Results show that decreases in slump flow of all concrete mixtures containing steel, polypropylene and hybrid fibers compared with control mix (0% fiber). Hybrid high strength concrete with steel and polypropylene fibers showed superior compressive, splitting, flexural strengths over the others concrete without or with single fibers content. The test results indicate that the maximum increase in compressive and flexural strengths are obtains with the hybridization ratio (70%steel + 30% polypropylene) and were equal to 14.54% and 23.34% respectively, compared with the control mix. While, the maximum increase in splitting tensile strength with (100% steel fiber + 0 polypropylene) is 21.19%. KEYWORDS: High strength concrete, Fibers, Hybrid fibers high strength concrete, Mechanical properties.

Adding fibers improves concrete performance in respect of strength and plasticity. There are numerous fibers for use in concrete that have different mechanical properties, and their combination in concrete changes its behavior. So, to investigate the behavior of the fiber reinforced concrete, an in vitro study was conducted on concrete with different fiber compositions including different ratios of steel, polypropylene and glass fibers with the volume of 1%. Two forms of fibers including singlestranded and aggregated fibers have been used for testing, and the specimens were tested for compressive strength and dividable tensile strength (splitting tensile) to determine the optimal ratio of the composition of fibers in the concrete reinforced by hybrid fibers. The results show that the concrete with a composition of steel fibers has a better performance than other compounds. In addition, by adding glass and propylene fibers to the composition of steel fibers, the strength of the samples is reduced. Also, if using the combination of fibers is required, the use of a combination of glass fibers with steel fibers will provide a better compressive strength and tensile strength than the combination of steel fibers with propylene.

Today, concrete is regarded as one of the main materials in the construction industry, but besides its advantages, it is brittle and fragile and its tensile strength is lower than compressive strength. Due to the development of science and technology, the use of metal, polymer, glass and natural fibers in the construction industry is considered as an effective step in eliminating the poor tensile strength of ordinary concrete. Thus, in this research, the effect of steel and macro synthetic fibers on the behavioral model of concrete and mechanical properties (compressive and tensile strength, modulus of elasticity) and durability (electrical resistance, water permeability of concrete) have been investigated. Hence, in this research, 10 mixing designs with three different types of fibers, including steel, macro synthetic, polyolefin, and polypropylene fibers with 0.5, 1, 1.5 vol% were tested, and the results show that the steel fibers have no considerable effect on the compressive strength at a percentage higher than 0.5 and significantly increase the tensile strength and reduce the electrical resistance. The macro synthetic fibers of polyolefin and polypropylene have insignificant effect on compressive strength and even reduced compressive strength at high percentages and have a positive effect on tensile strength, electrical resistance, and water permeability, and the fibers can be used to increase the area under the stress-strain curve.

In fruit trees damage of frost and freezing is depended to time of chillhng and tree phonological stage. Almond (Prunus amygdalus B. (and apricot (P. armeniaca L.) cultivars are usually the first fruit trees to bloom and susceptible to damaging frosts in the early spring. A study was conducted on different types of almond and apricot cultivars in order to investigation the main factors related to frosting, irregular of productivity and low crop load of trees for 10 years. Six almond cultivars; Sahand, A200, Shkoofeh (very late bloom), Touno, Super nova (late bloom and self- compatibility), Managa (early bloom) and 6 apricot cultivars; Canino, Royal, Telton (self- compatibility), Ordbad, Nasiri and Asgarabad (self- Incompatibility) were evaluated for aspects of some biological and physiological characteristics that related to frost tolerance and fruit set. The results of 10 years evaluation showed that some cultivars despite were resistant to spring frost and usually their crop load was optimum. In addition of freezing damage, other factors like; undesirable climatic conditions in flowering time, direct or indirect influence on bearing and fruit set. Touno and Super nova as self compatibility and late blooming almond cultivars, Canino, Royal and Tilton as self- compatibility apricot cultivars were tolerant to cool and unfavorable climatic conditions in early spring. Therefore, they usually had higher and regular productivity. This differences were related to some phonological and physiological characteristics like; time of flowering, interior components of flower buds, time of niter and period of dormancy, temperature reaction of flower buds, effective pollination period, self – compatibility, frost resistance of pistils and flowers.

This study investigates the behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with hybrid macro-micro steel and macro steel-polypropylene (PP) fibers. Compression, direct and indirect tension tests were carried out on cubic and cylindrical, dogbone and prismatic specimens, respectively. Three types of macro steel fibers, i.e., round crimped (RC), crimped (C), and hooked (H) were combined with micro steel (MS) and PP fibers in overall ratios of 2% by volume. Additionally, numerical analyses were performed to validate the test results. Parameters studied included, fracture energy, tensile strength, compressive strength, flexural strength, and residual strength. Tests showed that replacing PP fibers with MS significantly improves all parameters particularly flexural strength (17.38 MPa compared to 37.71 MPa). Additionally, the adopted numerical approach successfully captured the flexural load-deflection response of experimental beams. Lastly, the proposed regression model for the flexural load-deflection curve compared very well with experimental results, as evidenced by its coefficient of correlation (R2) of over 0.90.

Aims: In this study, the mechanical characterization of no-fines concrete solutions is addressed experimentally, with the purpose of possibly increasing their strength by using silica fume and embedded fibers (steel and nylon fibers) as possible efficient reinforcement. Background: Due to competition between developed and advanced countries, the contemporary construction sector is currently experiencing a shortage of fundamental building materials. In this regard, no-fines concrete is becoming increasingly popular, and it has been proven in the literature that it can offer some advantages as an economic and lightweight solution compared to conventional concrete. However, experiments and investigations are still needed to investigate the potential mechanical advantages for its efficient use in buildings, given that the major limitation compared to normal concrete is represented by limited strength. Objective: The primary objective of the present study is to assess the mechanical strength of no-fines concrete samples in which steel fibers, nylon fibers, and partial cement replacement with silica fume are used. For this purpose, no-fines concrete specimens are produced with fixed mix proportions of 1:6 cement-aggregate (c-a) ratio, various coarse aggregate gradations ((20-10) mm and (10-5) mm), and fixed w/c ratio (0.42). Methods: The experiments are carried out on cubes, cylinders and prisms of concrete samples with various aggregate solutions. The nominal length of both types of fibers is fixed at 20 mm. Steel fibers with 1 mm in diameter and nylon fibers with 0.3 mm, 0.4 mm, 0.5 mm, or 0.6 mm diameters, respectively, are taken into account to explore their effects on compressive strength, split tensile strength, and flexural strength. Results: The presented experimental results showed various mechanical advantages, such as increased compressive, splitting tensile and flexural strength parameters, for most of the examined samples. Nylon fibers, in particular, proved to significantly increase compressive, splitting tensile, and flexural strength values, compared to normal concrete, with additional benefits compared to steel fibers (for the examined arrangements and configurations). Conclusion: Overall, the examined compositions and mixtures of silica fume-based no-fines concrete samples encourage further investigations for the optimization of these solutions. In this regard, in addition to mechanical capacities, further key parameters (such as weight, cost, impact on concrete microstructure, etc.) will be taken into account.

This paper reports a comparative experimental study on the mechanical properties of concrete containing different types of fibres: polyvinyl alcohol (PVA), polypropylene (PP) and steel fibres. Compression and three-point bending tests are performed on both plain concrete and each type of fibre-reinforced concrete (FRC). The experimental results show that the presence of fibres has less of an effect on the FRC's compressive strength. The tensile strength is commonly increased by the addition of fibres, but an appropriate fibre content of PVA or PP fibres should be selected. PVA and PP fibres decrease the concrete's elastic modulus, but steel fibres increase the modulus due to the steel's higher Young's modulus. The FRC containing PVA shows brittle characteristics, but the FRC containing steel or PP fibres have load-deflection curves with flattened descending paths. Flexural behaviour of the concrete is improved by addition of steel or PP fibres, but not by PVA fibres, and the concrete's fracture toughness is increased by the addition of steel fibres.

Earthen masonry is generally brittle, weak and poor in damage resilience. There is historic evidence that natural fibers such as straw and horsehair have been used to reinforce earthen masonry to prevent desiccation cracks and improve tensile strength. However, fibers have also been known to negatively affect mechanical properties such as compressive strength (an important quality control parameter for load bearing masonry) by creating voids and lowering density. This paper reports on findings of a study directed at investigating the feasibility of avoiding such problems in compressed and stabilized earth blocks through optimizing the fiber length when using soil from Newberry, Florida. Standard polypropylene fibers were selected for the study. The two different lengths of fibers studied were 54 mm and 27 mm. The test results showed a general improvement in compressive strength of the fiber reinforced matrices compared to the unreinforced ones. While an improvement in modulus of rupture (MOR) was observed for matrices reinforced with 54 mm fibers, results varied for the other fiber-reinforced matrices. An improvement in post-initial crack behavior was observed for all fiber-reinforced matrices compared to the unreinforced ones. The 54 mm fibers yielded the best results based on the influence on MOR, compressive strength, and deformability compared to the other matrices. INTRODUCTION Earth has been used as a construction material since early civilization. Adobe, molded earth, wattle and daub, and cob are all forms of earthen construction that have been in existence for centuries. Globally, about a third of the human population resides in earthen shelters. In developing countries, the number is estimated to be as high as 50% (Minke, 2009).The use of locally available materials is highly encouraged by proponents of the green building movement. It is generally accepted that earthen masonry is a green material considering that at it uses indigenous soils 661 Construction Research Congress 2014 ©ASCE 2014

It is known from the literature that there are relatively few studies on the engineering properties of ultra-high performance concrete (UHPC) in early age. In fact, in order to ensure the safety of UHPC during construction and sufficient durability and long-term performance, it is necessary to explore the early behavior of UHPC. The test parameters (test control factors) investigated included the percentage of cement replaced by silica fume (SF), the percentage of cement replaced by ultrafine silica powder (SFP), the amount of steel fiber (volume percent), and the amount of polypropylene fiber (volume percentage). The engineering properties of UHPC in the fresh mixing stage and at the age of 7 days were investigated. These properties include freshly mixed properties (slump, slump flow, and unit weight) and hardened mechanical properties (compressive strength, elastic modulus, flexural strength, and splitting tensile strength). Moreover, the effects of the experimental factors on the performance of the tested UHPC were evaluated by range analysis and variance analysis. The experiment results showed that the compressive strength of the C8 mix at the age of 7 days was highest of 111.5 MPa, and the compressive strength of the C1 mix at the age of 28 days was the highest of 128.1 MPa. In addition, the 28-day compressive strength in each experimental group increased by 13%-34% compared to the 7-day compressive strength. In terms of hardened mechanical properties, the performance of each experimental group was superior to that of the control group (without fiber and without additional binder materials), with considerable improvement, and the experimental group did not produce explosive or brittle damage after the test. Further, the flexural test process found that all test specimens exhibited deflection-hardening behavior, resulting in continued to increase carrying capacity after the first crack.

This study compares high strength rubberized concrete (HSRC) with steel fibre (SF) doses of zero, two-thirds, five percent, and one percent per cubic inch. The microstructure was also examined when Portland cement substituted with ground granulated blast furnace slag (GGBS) at weight percentages of 0%, 10%, and 20% per cubic inch. Adding elastomeric chemicals to a cementitious matrix improves building parts' physical qualities, durability, and climatic resistance. It will also soften HSRC, preventing shrinkage and foundation movement. Several specimens were heated to 150°C , 300 °C, 450 °C, and 600 °C for an hour. As rubber content increases, fire-tested goods at a certain depth cool. The ideal amounts of shredded tire rubber determined in the material using machinery-related, destructive, and non-destructive testing that included workability, comfort, and strength. The effect of GGBS and SF on the material's composition at extremely high temperatures using XRD and SEM. The results show that combining rubberized components like GGBS and SF with 4% rubber reduces CO2 emissions without decreasing strength. This combination can also improve the physical properties and durability of high-performance concrete at high temperatures. The tested rubberized concrete with GGBS components (0% to 20%) and SF volume percentages (1% to 5%) at 25°C, 150°C, 300°C, 450°C, and 600°C. Samples' compressive strength dropped between 25 and 600 degrees Celsius, except at 150 degrees Celsius, when 20% GGBS and various amounts of SF had a higher compressive strength than room temperature samples. M10S1 also has the lowest GWP-impact normalized energy ratio and M20S1-M10S1 mixes are eco-friendly also a potential replacement for a conventional concrete.

Over the decades, there has been a significant increase in the use of fibres in concrete for improving its properties such as tensile strength and ductility. The fibre concrete is also used in retrofitting existing concrete structures. Among many different types of fibres available today, glass fibre is a recent introduction in the field of concrete technology. Glass fibre has the advantages of having higher tensile strength and fire resistant properties, thus reducing the loss of damage during fire accident of concrete structures. In this investigation glass fibres of 450 mm length are added to the concrete by volume fraction of up to 1% to determine its strength and fire resistant characteristics. Comparison of the strength and fire-resistance performance of conventional concrete and glass fibre concrete was made. The paper presents the details of the experimental investigations and the conclusions drawn there from. Generally, concrete is strong in compression and weak in tension. Concrete is brittle and will crack with the application of increasing tensile force. Once concrete cracks it can no longer carry tensile loads. In order to make concrete capable of carrying tension at strains greater than those at which cracking initiates, it is necessary to increase the tensile strength. To increase the tensile and flexural strength, fibres are added in concrete. The addition of fibres to concrete will result in a composite material that has properties different from those of un-reinforced concrete. The extent of this variation depends not only on the type of fibres, but also on the fibre dosage. The incorporation of fibres into a brittle concrete can have the effect of controlling the growth and propagation of micro cracks as the tensile strain in the concrete increases. Care is needed in using fibre as additive in concrete. The use of fibres in concrete has increased with the development of fast-track construction. In fact, nearly 65 per cent of the fibres produced worldwide is currently used in concrete. It offers increasing toughness and ductility, tighter crack control and improved load-carrying capacity. Different types of fibres are available in the market for reinforcing concrete and they are: steel, glass, acrylic, aramid, carbon, nylon, polyester, polyethylene, polypropylene, etc. Besides, natural fibres like sisal, wood cellulose, banana, jute, etc., have also been used. From the above mentioned fibres, glass fibre is more advantageous on the basis of strength and fire resistant characteristics. It has been recognized that adding small, closely spaced and uniformly dispersed fibres to concrete serves to arrest cracks and improve its properties under static and dynamic loading. Round steel fibre is the most common variety in use for improving the tensile, flexural, impact and fatigue strength of concrete. The ductility and toughness of concrete are also improved with the addition of this fibres. Steel fibre have been used in various types of structures such as earthquake resistant structures, road overlays, airfield pavements and bridge decks. Alkali resistant glass fibre reinforcement is a relatively new addition to the family of fibres that impart high tensile strength, high stiffness, high chemical resistance and considerable durability to FRC (Fibre Reinforced Concrete). Adding polyesters fibre to concrete pavements resulted in the developments of the micro shrinkage cracks induced during hydration. These fibres improve the flexural strength and energy absorption of concrete . Glass fibres are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fibre makes good thermal insulation, with a thermal conductivity of order of 0.05 w/(mk). The strength of the glass fibre is usually tested and reported for virgin or pristine fibres those which have just been manufactured. The freshest and thinnest fibers are more ductile. The more the surface is scratched, the less the resulting tenacity. Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber. Humidity is an important factor in the tensile strength. Moisture is easily absorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity. Glass fibres improve the strength of the material by increasing the force required for deformation and improve the toughness by increasing the energy required for

In this paper, according to the national standard and testing methods,the direct tension strength,splitting tensile strength and cubic compressive strength test were carried out for 8 different groups of hybrid fiber (containing steel fiber, macro-polypropylene fiber and dura fiber) reinforced HPC specimens.The results showed that when the volume proportion of ternary hybrid fiber was less than 1%, there was not obvious influence for the concrete compressive strength, but the splitting tensile strength increased by 26% ~ 69%; the ratio between splitting tensile strength and compressive strength for HFRC increased to 1/12~1/9. When added 0.7% steel fiber, 0.19% macro-polypropylene fiber and 0.11% dura fiber, the confounding effect was the best. Based on the advantages and disadvantages of tensile splitting strength and direct tensile strength test and the results of tests, the concept of equivalent tensile strength and calculative formula was put forward .

Addition of steel fibres to concrete is known to have a significant positive influence on the mechanical properties of concrete. Micro polypropylene (PP) fibres are added to concrete to improve its performance under thermal loads such as in case of fire by preventing the phenomena of explosive spalling. An optimum mixture of steel and micro PP fibres added to concrete may be utilized to enhance both the mechanical and thermal behaviour of concrete. In this work, systematic investigations were carried out to study the influence of elevated temperature on the mechanical properties and physical properties of high strength concrete without and with fibres. Three different mixtures for high strength concrete were used, namely normal concrete without fibres, Steel fibre reinforced concrete and Hybrid fibre reinforced concrete having a blend of hooked end steel fibres and micro PP fibres. The specimens were tested in ambient conditions as well as after exposure to a pre-defined elevated temperature and cooling down to room temperature. For all investigated concrete mixtures the thermal degradation of following properties were investigated: compressive strength, tensile splitting strength, bending strength, fracture energy and static modulus of elasticity. This paper summarizes the findings of the tests performed.

Exterior walls in buildings are exposed to various forms of thermal loads, which depend on the positions of walls. Therefore, one of the efficient methods for improving the energy competence of buildings is improving the thermal properties of insulation plaster mortar. In this study, lightweight fine aggregate (LWFA) and micro rubber ash (MRA) from recycled tires were used as partial replacements for sand. The flow ability, unit weight, compressive strength, tensile strength, thermal conductivity (K-value), drying shrinkage and microstructure scan of lightweight rubberized mortar (LWRM) were investigated. Ten mixtures of LWRM were prepared as follows: traditional cement mortar (control mixture); three mixes with different percentages of LWFA (25%, 50% and 75%); three mixes with different percentages of MRA (2.5%, 5% and 7.5%); and three mixes consisting both types with determined ratios (25% LWFA+5% MRA, 50% LWFA+5% MRA and 75% LWFA+5% MRA). The flow ability of the mortars was 22+-2 cm, and LWRM contained LWFA and MRA. The compressive and tensile strength decreased by approximately 64% and 57%, respectively, when 75% LWFA was used compared with those when the control mix was used. The compressive and tensile strength decreased when 5% MRA was used. By contrast, mixes with determined ratios of LWFA and MRA affected reduced unit weight, K-value and dry shrinkage.