Fiber reinforced concrete consists of Portland cement, aggregate and fibers. There are different types of fibers used in concrete like synthetic fibers, glass fibers, natural fibers and steel fibers. As per the type of fiber induced in concrete its characteristics change. These fibers in concrete are distributed randomly so as to fill the cracks of the structure. These fibers are normally mixed in concrete so as to avoid and minimize the plastic shrink cracking and drying shrink cracking. When these fibers are used in concrete it reduces the permeability and lowers the flow of water.
The main purpose of these fibers reinforced concrete is to increase the concrete toughness so that it can withstand a considerable amount of stress during the post-cracking stage.
Advantages and Disadvantages of fibers in concrete:
· Saves time and money by reducing slab thickness which in turn saves concrete and placement costs. Saves on joint forming costs and maintenance by wider joint spacing. Increases the speed of construction due to simpler joints and error free steel fabric positioning. So, as a result it reduces material and labor costs.
· Fibers reinforced concrete results in durable concrete with high and fatigue flexural strength, spalling, improved abrasion and impact resistance.
· If proper proportions of steel fibers are not used, then there are chances of the steel fibers coming out of the concrete which in turn would affect the finishing of the slab.
· Strict control of concrete wastage should be monitored. As wastage of concrete will ultimately result in wastage of fibers that are induced in it.
Mix Preparation and applications
Steel fiber reinforced concrete has fibers distributed uniformly at random in percentage ranging from 0.3 % to 2.5 %. The steel fibers are added to the ingredients of concrete in the mixer and are then transferred into moulds. The product is then compressed and alleviated by conventional methods.
Use of pan mixer and fiber dispenser is recommended so that it can help better to mix and reduce the formation of fiber balls. Steel fibers are included in the concrete to increase the flexural and tensile strength. The steel fiber with a better aspect ratio is considered to be superior. It is suggested by scholarly people like gray and Schwarz that aspect ratio between 50 and 70 is more desirable from strength point of view.
Steel fiber reinforced concrete is therefore found to be a more versatile material for manufacturing and repairing precast products like slab elements for bridge decks, runways and highways, machine foundation blocks, tunnel linings, coal storage bunkers and many more.