Fibers contribute towards reducing the bleeding in fresh concrete and renders concrete more impermeable in the hardened stage. Contribution of certain percentage of fibers in concrete towards flexural strength is smaller compared to the strength given by the rebars. Most importantly fiber restricts the growth of crack under load thereby arresting ultimate cracking. Nonmetallic fibers like alkali resistant glass fiber and synthetic fibers provide resistance against chemicals.
Reinforcing capacity of fiber is based on length of fiber, diameter of fiber, the percentage of fiber and condition of mixing, orientation of fibers and aspect ratio. Aspect ratio is ratio of length of fiber to its diameter which plays an important role in the process of reinforcement.
Generally, the fibers used to reinforce concrete can be characterised as discontinuous, discrete fibers with length less than 50mm and diameter no more than 500mm. The actual purpose of incorporating fibers in the concrete matrix was the development of a composite with improved strength, both compressive and tensile. By analysing the results of the earliest developments in this field it can be observed that neither the compressive nor the tensile strength were increased by any appreciable amount.
The actual benefits of fiber reinforcement were difficult to highlight by the researchers at that time. Later on, during the modern development of FRC in late 1970’s and early 1980’s, when the testing equipment and analysis procedures became more quantitative and better qualitatively the concept of energy absorption (or fracture toughness) was introduced. This concept enabled the toughness measurement of materials. It was then that the major advantage of FRC was discovered and it was not other than the outstanding property of absorbing large amounts of energy compared to Ordinary Portland Cement Concrete. Even today, after more than three decades of research in this field it can be said that the principal benefit of FRC is the high fracture toughness. However, further research with different types of fibers and admixtures targets the development of a composite with increased tensile and compressive strengths, besides the fracture toughness. These FRC composites are now known as the high performance fiber reinforced concrete (HPFRC). The production of a cement based material having high tensile and compressive strengths, remarkable energy absorption capacity and which will be homogeneous and isotropic (almost similar to cast iron) is no longer an utopia any more. The incessant research in the field of FRC has led to the production of HPFRC, which shows a combination of amazing properties compared to other cementitious composites.
Fibers contribute towards reducing the bleeding in fresh concrete and renders concrete more impermeable in the hardened stage. Contribution of certain percentage of fibers in concrete towards flexural strength is smaller compared to the strength given by the rebars. Most importantly fiber restricts the growth of crack under load thereby arresting ultimate cracking. Nonmetallic fibers like alkali resistant glass fiber and synthetic fibers provide resistance against chemicals. Reinforcing capacity of fiber is based on length of fiber, diameter of fiber, the percentage of fiber and condition of mixing, orientation of fibers and aspect ratio. Aspect ratio is ratio of length of fiber to its diameter which plays an important role in the process of reinforcement.
No comments:
Post a Comment