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Frequently Asked Questions

Item No.: sf010
Q: What's is Steel Fibre Reinforced Concrete?(SFRC)

Steel fiber reinforced concrete is comprised of hydrolic cements containing fine and course aggregates and steel fiber. A superplasticizer is often used to enhance the mix workability. Steel fiber products are available in a variety of types and sizes from various manufacturers. The underlying principle however on all SFRC designs is to provide discontinuous reinforcement and effective crack control.

Q: How to compare with other steel fibres?
A: Steel fibres come in many shapes and sizes each with different performance levels. To make a true comparison between different products and ensure the correct selection is made, it is recommended that each potential supplier be asked to supply accredited test results for their products in accordance with one of the internationally recognized standards
Q: What is the difference between ASTM-A820 Type I and Type II steel fibers?
A: ASTM A820 is the standard specification for steel fibers to be used in concrete. Type I steel fiber is a cold-drawn wire and Type II is a cut sheet. The Type I steel fiber will have either a circular or semicircular cross-section. The Type II steel fiber will have a rectangular cross-section.
Q: How do Steel Fibers work?
A: Steel fibers reinforce in three dimensions throughout the entire matrix. They restrain micro-cracking and act as tiny reinforcing bars. The earlier a crack is intercepted and its' growth inhibited, the less chance it will develop into a major problem.
Q: What concrete properties Steel Fiber improve?
A: FLEXURAL STRENGTH: 1 1/2 to 3 times increase in first crack and flexural bending strength can be achieved over plain concrete using a 1" fiber. FATIGUE RESISTANCE: The fatigue strength of steel fiber concrete is 1 1/2 times that of conventional concrete. IMPACT RESISTANCE: Steel fibers greatly increase concrete's resistance to damage from heavy impact. SHRINKAGE: Steel fibers themselves do not affect the shrinkage rate but they do minimize and help eliminate shrinkage cracks. ABRASION RESISTANCE: Steel fibers offer a high degree of protection against abrasion and goughing along with any spalling being greatly reduced. PERMEABILITY: By effectively reducing the micro cracking SFRC will reduce the overall porosity of the matrix, making the concrete less permeable WHAT ABOUT CRACKING? Concrete has always been an unpredictable material and no methodology can entirely eliminate cracking. Using SFRC offers an extremely effective means of controlling cracks. This together with proper sub-base preparation, joints and curing are all essential to overall job performance.
Q: What is the difference between polypropylene and steel fibers?
A: PP fibers help control plastic shrinkage cracking which can occur in the very early stages of concrete drying. Steel fibers reinforce the concrete in its' hardened state, thereby improving its' strength and durability.
The major difference between steel and synthetics is their respective Youngs modulus and tensile yield strength. Steel fibers have a sufficient high modulus of elasticity and tensile strength to assume excess strain across a crack and hold it tightly.
Q: What is the function of polypropylene fibres ?
A: The main property of these fibres is to reduce the formation of shrinkage cracks in freshly poured concrete. After the concrete has hardened the fibres have little further effect on crack control or provide any form of reinforcement.
Q: How does SFRC lower costs over the installation life?
A: Depending on the quantity and complexity of reinforcement in traditional design, SFRC can offer substantial costs savings. The superior performance of steel fiber will often reduce maintenance over the installations life, thus reducing the project cost.
Q: What is the typical dosage rate?
A: SFRC dosage rates depend on the application of the concrete properties required. Typically 40 lb. to 100 lb. will satisfy most requirements. Lower dosages tend to be used when replacing conventional wire mesh. At higher concentrations SFRC will meet the most demanding requirements.
Q: Do steel fibers affect the slump of concrete?
A: Adding steel fibers, particularly at higher concentrations, will give rise to an apparent loss as measured by the slump test. It is recommended that a super plasticizer be added to increase the slump 1-2" greater than the final desired target slump.
Q: How are fibers added to the concrete?
A: Fibers can be added at the batch plant by depositing onto an aggregate conveyor. They can also be added to a transit mixer on site by use of a lightweight conveyer attached directly to the back of the vehicle.
Q: How do we finish SFRC slabs to eliminate fibers sticking out of the surface?
A: The answer is mechanical vibration on the surface of the slab. Today a vibrating screed, a roller screed, or a laser screed is used to consolidate the concrete while providing the surface elevation of the slab required by the engineers. The mechanical vibration of these screeds will embed the steel fibers within the plastic concrete.
Q: Do fibres ball during mixing ?
A: Fibre clumps and balls during mixing not only cause blockages and machine breakdowns but also effect output. Shwitcom recommends that a fibre doser be used when mixing.
Q: Can steel fibres be added at the ready mix plant ?
A: Yes , introduce steel fibres after all other ingredients are already in truck. Set the truck mixer on charging speed and add fibres at a rate not to exceed 100 pounds/minute. Mix for a min. of 40 revolutions at charging speed .
Q: Can steel fibres be added on site ?
A: Yes, gradually feed fibres in the mix via conveyor or OHSA approved scaffolding .
Q: Can steel fibre reinforced concrete be pumped ?
A: Yes, but expect a 1 to 3 inch slump loss through the hose depending on the steel fiber dose rate, ambient temperatures and hose length. A mid-range water reducing agent (MRWR) is commonly used to enhance workability and ease of flow through pump lines. High-range water reducers (HRWR) may be required in some cases. Typically, a 4 to in. Diameter hose is required.
Q: Are steel fibres compatible with curing compounds ?
A: Yes, common curing compounds produced by a host of major manufacturers including Master Builders, Grace, and Euclid are commonly used on SFRC floors
Q: Can abrasion resistant toppings and liquid sealants can be applied over steel fiber reinforced floors?
A: Yes, steel fibres are compatible with dry shake or spray-on toppings.
Q: How do I cut joints on my steel fibre reinforced concrete slab?
A: Both wet-cut and early entry saws are commonly used to form contraction joints. Cut the joints to 1/3 slab depth, if possible, per ACI 302.1R guidelines. Generally limit joint spacing to ACI and PCA recommendations for unreinforced concrete.
Q: How will steel fibres affect my flatness and level ratings?
A: Flatness and level are generally not affected at dosages up to 70 pounds per cubic yards
Q: Will steel fibers rust?
A: This question is the most frequently asked and is precipitated by the fact that rebars and wire mesh are known to rust/corrode. There are a number of factors that contribute to the rusting/corrosion of rebars and wire mesh. They include the concrete's permeability, oxygen and moisture and chloride ions. The total package then produces galvanic cells at the surface of the rebars and wire mesh. The rebar or wire mesh is the conduit for the electrical current flow. The reaction is called an electrochemical process and requires moisture.
The steel fibers are not connected and are protected by the high alkalinity of the concrete from rusting/corroding. Unlike rebar and wire mesh the steel fibers are micro reinforcing el ements within the concrete and do not possess the same mass and configuration of rebar and wire mesh. Thus the steel fibers within the concrete cross-section will not rust. Any steel fibers exposed at the surface of the concrete will rust, but only that portion of the fiber exposed.