Steel fiber concrete flooring can provide superior resistance to minimize cracks in hardened concrete, as well as maximum resistance to withstand heavy loads, either dynamic or static. If you decide to use steel fiber concrete flooring, you can select to use a ‘joint-less floor’. Joint-less floors are floors that have minimal joints, providing spaces without joints as large as 40 or 50-meter span wide.
Steel fiber dosage will vary greatly upon the project intended use, and the types of mesh being replaced. Common dosages are in the range between 20-30kg/m3 to 40-50kg/m3 for joint-less floors. Trowelling concrete will help to embed steel fibers into the concrete surface producing a better-finished product. Steel fibers will enhance the crack resistance of the concrete, and they can also be used to replace or supplement structural reinforcement. It only can be done through a structural engineer and with proper guidance.
How and When the Fiber is Added
Typically the fibers are added at the batch plant, just after all concrete aggregates are being mixed. Some people would request to have the fiber added at the job site, but then the QA/QC should have more control on how much fiber is added. The steel fiber manufacturer can provide guidance on how to mix and the amount needed to obtain the desired results. Be aware that if you add too much fiber, it might show up at the surface when finishing the concrete so be cautious about the amounts being mixed.
Costs of Steel Fiber Concrete Flooring
In general, and depending on the type of steel fiber used, it can add between $6 to $10 per cubic yard on top of the ready-mix concrete cost. This cost is based on the assumption that you are using 1.5 pounds per cubic yard of concrete.
How Workability is Affected
If you opt-in to add fiber to your concrete mix, be aware that there will be some changes in the way you manage this concrete. First of all, the slump will be affected, and it is recommended to add a superplasticizer to enhance the slump and make the concrete a little more fluid. Not all steel fiber can be used as a substitute for steel reinforcement, so make sure that your structural engineer has reviewed and analyzed the loads before proceeding.
Where to Use Steel Fiber Concrete Floors
Typical applications for steel fiber concrete flooring can be found on parking lots, playgrounds, airport runways, taxiways, maintenance hangars, access roads, and workshops. This method is also widely used for port pavements, container storage and handling areas, bulk storage warehouses, and military warehouses. Steel fiber reinforced concrete is commonly used in tunnel construction, as it provides additional flexural strength, reduces shrinkage cracking and reduces permeability.
Steel Fiber Reinforced Concrete (SFRC)
Steel fiber reinforced concrete is a composite material having fibers as the additional ingredients, dispersed uniformly at random in small percentages, i.e. between 0.3% and 2.5% by volume in plain concrete. SFRC products are manufactured by adding steel fibers to the ingredients of concrete in the mixer and by transferring the green concrete into moulds. The product is then compacted and cured by the conventional methods. Segregation or balling is one of the problems encountered during mixing and compacting SFRC. This should be avoided for uniform distribution of fibers. The energy required for mixing, conveying, placing and finishing of SFRC is slightly higher. Use of pan mixer and fiber dispenser to assist in better mixing and to reduce the formation of fiber balls is essential. Additional fines and limiting maximum size of aggregates to 20mm occasionally, cement contents of 350 kg to 550 kg per cubic meter are normally needed.Steel fibers are added to concrete to improve the structural properties, particularly tensile and flexural strength. The extent of improvement in the mechanical properties achieved with SFRC over those of plain concrete depends on several factors, such as shape, size, volume, percentage and distribution of fibers. Plain, straight and round fibers were found to develop very weak bond and hence low flexural strength. For a given shape of fibers, flexural strength of SFRC was found to increase with aspect ratio (ratio of length to equivalent diameter). Even though higher ratios of fibers gave increased flexural strength, workability of green SFRC was found to be adversely affected with increasing aspect ratios. Hence aspect ratio is generally limited to an optimum value to achieve good workability and strength. Grey suggested that aspect ratio of less than 60 are best from the point of handling and mixing of fibers, but an aspect ratio of about 100 is desirable from strength point of view. Schwarz however suggested aspect ratio between 50 and 70 is more practicable value for ready mix concrete. In most of the field applications tried out to date, the size of the fibers varies between 0.25 mm and 1.00mm in diameter and from 12mm to 60mm in length, and the fiber content ranged from 0.3 to 2.5 percent by volume. Higher contests of fiber up to 10% have also been experimented. Addition of steel fibers up to 5% by volume increased the flexural strength to about 2.5 times that of plain concrete. As explained above, mixing steel fibers considerably improves the structural properties of concrete, particularly tensile and flexural strength. Ductility and post cracking strength, resistance to fatigue, spalling and wear and tear of SFRC are higher than in the case of conventional reinforced concrete. SFRC is therefore found to be a versatile material for the manufacture of wide varieties of precast products such as manhole covers, slab elements for bridge decks, highways, runways, and tunnel linings, machine foundation blocks, door and window frames, piles, coal storage bunkers, grain storage bins, stair cases and break waters. Technology for this manufacture of SFRC light, medium and heavy duty manholes covers has been developed in India by Structural Engineering Research Centre, Chennai. Field experiments with two percent of fiber content indicated that SFRC runway slabs could be about one half the thickness of plain concrete slabs for the same wheel load coverage. Cement Research Institute of India (CRI) also demonstrated the use of SFRC in one of the jet bays at Delhi airport.
