Lately Steel fibers are now being used to enhance mechanical properties of all type of concrete and extensively used in UHPC. The product use is further being explored in a wider area and the research is on. This blog provides a general view of the SFRC
Fiber Reinforced Concrete
A Brief History
Fibber Reinforced Concrete
Fibbers in Concrete
Steel Fibber Types
Effects of Fibbers in Concrete
Developments in SFRC
Applications of SFRC
Fiber vs. Fibre
There is no difference in meaning between fiber and fibre. Fiber is the preferred spelling in American English, and fibre is preferred in all the other main varieties of English
Steel Fiber reinforced concrete (SFRC) is now being used is stabilizing the surfaces in underground works and on hydro power projects, Road infrastructure works and in repair and maintenance of concrete structures. Lately Steel fibers are now being used to enhance mechanical properties of all type of concrete and extensively used in UHPC. The product use is further being explored in a wider area and the research is on. This blog provides a general view of the SFRC
NSC Normal Strength Concrete
HSC High Strength Concrete
SCC Self Compacting Concrete
UHPC Ultra High-Performance Concrete (Ultra High-performance Fiber
RCC Reinforced Cement Concrete
FRC Fiber Reinforced concrete
SFRC Steel Fiber Reinforced Concrete
ASTM American Society for Testing and Materials
ECC Engineered Cementitious Composite
Fibers are being used for about last 30 years, to resist the shrinkage and temperature stresses created in concrete, which is quasi ductile and weak in tension.
Out of glass, poly fibers and steel fibers, the steel fibers are most successful to resist such stresses in concrete and helpful in providing ductility and durability to concrete .
A fiber is a particle having more length in comparison to its thickness. The length to thickness ratio is called aspect ratio. The fibers may be continuous and discontinuous. Discontinuous fibers can be dispersed randomly in comparison to non-discontinuous fibers.
The properties of fibers specially the tensile strength, when used in a composite, enhances the behavior of the composites. Fiber reinforced concrete is a composite.
The composite has two parts:
– the matrix and
– the reinforcement,
Matrix may be concrete (NSC- HSC-SCC-UHPC), plastic or other materials
Reinforcement (as in RCC) may include natural and manufactured fibers (steel, glass, synthetic) that provide tensile strength and other properties.
Fibers are in use in construction works since long. Mud Phuska (mud + straw) was used in mud plasters, mud bricks and mud layers laid in floors and roofs of houses. Mud is composed of loam, silt, mud, straw (cow dung also) and water. The Mud Phuska , so prepared was molded in forms of the sizes of bricks and on drying, these bricks were used in construction of wall like structures in houses. The formed such bricks were stamped also by the manufactures.
Mud mortar with fibers was used as binder for mud bricks and in plastering and flooring. The tensile stresses in the structure so produced, were countered, and controlled by the resistive force of the straw. In underdeveloped and developing countries, use of mud with straw is still in practice.
This concept was later introduced in other binding materials such as concrete, which is widely used material for construction with low tensile strength. Plain Concrete has several constituents and is called composite. Other additions to plain concrete are rebars and fibers. Reinforced concrete with steel reinforcement is commonly in use everywhere , but to improvise the ductility and tensile strength of concrete , fibers are used in it. Use of fibers reduces temperature and shrinkage stresses and also reduces the tension steel requirement sometimes. These fibers may be made of steel, glass, or polymeric synthetic fibers or even natural fibers.
Fiber-reinforced concrete (FRC)
FRC is a composite that contains fibrous material as discussed above. The workability and hardened properties of the concrete gets better. The characteristics of FRC depends on the type of material of fibers, strength, shape and size of the fibers and their dispersion in the matrix.
This blog shall cover the Steel Fiber Reinforced Concrete (SFRC). Thin artificial fibers have less impurities (good quality output in manufacturing process as compared to other thick structural members) and are stronger and are preferred in construction. The natural fibers exist in purest form in varying properties.
Fibers in Concrete
Fibers in concrete do not act in uncracked concrete. At the start of crack development process, when crack develops, the tensile stress of the fibers is used to stop cracking. So, the fibers provide post cracking strength or residual strength. The residual strength of the fibers depends on physical properties (such as shape, length, thickness) and chemical properties ( such as types of material ) and the dispersion of the fibers in the concrete or concrete composite.
The post cracking behavior of FRC is assessed and applied to design application for ground rested slabs or for structures subjected to bending.
(Reference ASTM C 1609/1609 M-Flexural test)
The designer should suggest the specifications after laboratory testing and suggest the type of fibers and its physical and chemical properties and the flexural test and compressive strength values to be achieved. Quality control on mix operation is important to have proper dispersion of the fibers in concrete mass.
The steel fibers conforming to ASTM C 1116/ 1116 M (Type 1) and as per manufacturer’s instructions may be used.
The polymeric fibers may be used as per manufacturer’s recommendation but conforming to ASTM C 1116/1119M (Type 3)
Furthermore, information can be obtained by the following standards:
EN 14889-1:2006 Fibers for Concrete. Steel Fibers. Definitions, specifications & conformity
EN 14889-2:2006 Fibers for Concrete. Polymer Fibers. Definitions, specifications & conformity
EN 14845-1:2007 Test methods for fibers in concrete
ASTM A820-06 Standard Specification for fibers in Fiber Reinforced Concrete
ASTM C1018-07 Standard test methods for flexural toughness & first crack strength
Steel Fibre Types
The types of steel fibres are defined by ASTM A8201 91
(1 PSI= 0.0069 MPa)
Type I: cold-drawn wire; [145,000 psi (1000 MPa) to 445,000psi (3070MPa)]; round wires with deformed ends and in varying diameter
Type II; cut sheet (rectangular or square shapes with dimples- depressions)
Type III: melt-extracted
Type IV: mill cut
Type V: modified cold-drawn wire