جستجوی مقالات مرتبط با کلیدواژه « polymer fibers » در نشریات گروه « عمران »

By adding fibers as well as additional materials in concrete, the properties of concrete can be increased in terms of durability, flexibility and tensile strength. Another use of artificial fibers to improve mechanical properties and reduce shrinkage of fresh and hardened concrete, increase energy absorption and resistance to impact and explosion can be mentioned. The use of fiber concrete has many advantages compared to the use of reinforced concrete, while it also has disadvantages, such as the lack of uniform distribution of fibers in the concrete matrix and the lack of proper adhesion between polymer fibers in cement mortar. Generally, fiber concrete is used in concrete parts due to smaller cracks and less width and more durability in case of uniform distribution of fibers. Research shows that fibers significantly increase the tensile strength, plasticity of mortar and concrete. In fact, after cracking, the fibers bridge between the crack plates and cause a significant increase in toughness and energy absorption capacity. Adding artificial fibers to concrete brings advantages such as reducing plastic grip cracks, reducing plastic drop cracks, increasing impact resistance and increasing resistance to crushing. In this research, the effect of different types of fibers with different volume percentages on the compressive, bending and tensile strength of the samples at different ages compared to the control sample has been measured by laboratory method. All kinds of samples have been tested to determine the resistance against surface explosions.

In recent years, the use of Roller–Compacted Concrete Pavement (RCCP) has developed in road pavement due to its great advantages. Adding fibers to RCC can improve some properties of the concrete, including flexural strength, fatigue resistance, crack growth rate, and shear transfer along cracks and joints. Many experiments have shown the advantages of using fiber-reinforced concrete in RCC, but more information is needed about their behavior in cold regions, and especially the exposure to Freeze-Thaw cycling. Investigation and comparing the effect of polymer fibers on the strength and durability of Roller-Compacted Concrete under Freeze-Thaw cycling are the main goal of the present article. Therefore, specimens with weight percentage of fiber equal to 1, 2.5, and 4% (by weight of cement) and fibers of to 5, 20 and 40 mm lengths are made. Durability test against a Freeze-Thaw cycling and compressive strength are measured on samples after 7, 28 and 90 days. Analysis of the results shows that the additive fiber increases the compressive strength of the RCC, but decreases its durability against the melting and freezing cycles. Therefore, the use of fibers on RCC in cold regions should be done due accuracy and attention.

A laboratory study was performed to determine the benefits of micro and macro fibers in roller-compacted concrete (RCC) for concrete pavements by measuring the RCCs mechanical and durability properties. To this aim three polymer fiber reinforced RCC mixtures with use of micro and macro polyolefin-based and polypropylene-based fibers in two volumetric content (1 and 2 kg/m3) were prepared and their mechanical properties including the compressive strength and flexural strengths (measured as modulus of rupture and toughness as energy dissipation and durability properties including salt scaling under freeze and thaw cycles and water permeability were evaluated. The results showed that, the macro fibers (as polyolefin-based fibers) could be efficiently enhanced the toughness in comparison with the micro fibers (polypropylene-based fibers). Moreover, the water permeability under pressure of both micro (polypropylene-based fibers) and macro fibers as (polyolefin-based fibers) reinforced concrete decreased up to 20% in comparison with the reference concrete. Furthermore, it was found that the application of micro fibers in comparison with macro fibers significantly improved the salt-scaling resistance of roller compacter concrete.

The improvement of compressive and tensile strength of concrete has a great importance in the construction industry. In this study, cubic samples constructed in a dimension of 150times150times150 mm containing different amounts of macro-synthetic (0.1 and 0.15 vol.%) and polymeric fibers (0.2, 0.3, and 0.35 vol.%) by means of seven mix designs. Compressive and splitting tests were performed using a universal testing machine. For each specimen, stress-strain and load-displacement behaviors, absorbing energy, ductility and crack patterns were investigated. In order to analyze the strain variations on the surface of the specimens digital image correlation (DIC) was applied. Moreover, finite element method (FEM) was conducted to evaluate the experimental results. The results of this study show that the presence of fibers in concrete has a significant effect on reducing size and number of cracks, and increases displacement compared to conventional concrete. In addition, displacement at the failure moment in tension and pressure for fiber contained concrete was more than the control specimen. According to the observations, addition of the fibers reduces compressive and tensile strength. However, it is so obvious from the results that by choosing the optimal amount, this reduction would be neglected in comparison with the positive effects of the fibers. Finally, the results indicate an acceptable agreement between the FEM and DIC evaluations. Therefore, considering the low cost and high speed of analysis with FEM and DIC methods, it is possible to combine these two methods as a useful tool to determine the surface characteristics of such specimens.

Rehabilitation (improvement) is a process and repairing method or modifying one structure in order to achieve the new operating conditions or increasing the useful life operation. In fact, in designing and implementation the retrofit, we are looking to achieve the new condition for concrete structure in terms of operating or loading. Retrofit operations can be necessity for design errors and problem causes, administrative problems and errors, changes in standards and regulations, increasing the useful life of the operation, changing the structure, increasing the classes and imposed load. Also, damaging in reinforced concrete columns can be cause the irreparable and strong damages. So, study the retrofitting the reinforced concrete columns by polymer fibers and with different layouts of polymer fibers. Improvements with polymer fibers and proper laboratory study have been used in order to validation exam for modeling. Then, proper retrofit layout of polymer fibers is discussed in Abaqus finite element software with simulation with several various models. After studying the hysteresis-bar curves transformation, load-displacement curve cover-transformation, ultimate load and the contribution of polymer fibers of models was found that samples those have polymer fibers have a greater ability to more loading bearing and also, have more absorb property and more energy amortization (82 percentage of increasing the capacity) than samples without fiber.

When the concrete loses its moisture, shrinkage and volume reduction is happen and eventually cracks create and deformations in the concrete are increased. If the reinforcement concrete member be bounde, strain caused by condensation cause cracking member and increases the deformation member with time. This phenomenon is due to the rapid evaporation of water in the concrete, occurs because of the wind and temperature rise. One of the main reasons for the decrease in strength and durability of concrete are cracks. In this study evaluated the effect of fibers by different volumes on reduce cracking that created by, shrinkage plastic on concrete slabs. Plastic shrinkage experiments in a greenhouse by using mold that was designed for this purpose. The parameters in this study are, the percentage of fiber volume to volume of concrete and concrete strength. Finally, the effect of polymer fibers on plastic shrinkage cracking of concrete was investigated and discussed.