LECTURE - 1

LIGHT WEIGHT CONSTRUCTION MATERIALSTHE NORTHCAP UNIVERSITY, GURGAON1

UNIT-1LECTURE - 4

Brig. S.K. Sharma (Retd.) Pro Vice Chancellor and Professor Department of Civil Engineering, The Northcap University, Gurgaon

INDEXTHE NORTHCAP UNIVERSITY, GURGAON2FIBRE REINFORCED CONCRETESLURRY INFILTRATED FIBER CONCRETES (SIFCON)SLURRY INFILTRATED MAT CONCRETE (SIMCON)USES OF SIMCONPROPERTIES OF SIMCONSIFCON VS SIMCON

FIBRE REINFROCED CONCRETETHE NORTHCAP UNIVERSITY, GURGAON3The presence of microcracks at the mortar-aggregate interface is responsible for the inherent weakness of pain concrete. The weakness can be removed by inclusion of fibers in the mix. The fibers help to transfer loads at the internal microcracks. Such a concrete is called fiber-reinforced concrete. Thus, the fiber-reinforced concrete is a composite material essentially consisting of conventional concrete or mortar reinforced by fine fibers.

Video: YouTube Fiber Reinforced Concrete, 06:25

THE NORTHCAP UNIVERSITY, GURGAON4The addition of small, closely spaced and uniformly dispersed fibres to concrete would act as crack arrester and substantially improve its static and dynamic properties. This type of concrete is known as Fibre Reinforced Concrete.Fibre reinforced concrete can be defined as a composite material consisting of mixtures of cement mortar or concrete and discontinuous, discrete, uniformly dispersed suitable fibres. Continuous meshes, woven fabrics and long wires or rods are not considered to be discrete fibres.

DISCRETE FIBER REINFORCED CONCRETE THE NORTHCAP UNIVERSITY, GURGAON5As brought out above, in this system, the concrete is reinforced by the random dispersal of short, discontinuous and discrete fine fibers of specific geometry. The fibers can be imagined as an aggregate with an extreme deviation in shape from the rounded smooth aggregate. The fibers interlock and entangle around aggregate particles and considerably reduce the workability, while the mix becomes more cohesive and less prone to segregation.

THE NORTHCAP UNIVERSITY, GURGAON6The fibers suitable for reinforcing the concrete have been produced from steel, glass and organic polymers. Naturally occurring asbestos fibers and vegetable fibers, such as jute, are also used for reinforcement. Fibers are available in different sizes and shapes.They can be classified into two basic categories: Those having a higher elastic modulus than concrete matrix called hard intrusion. Those with lower elastic modulus called soft intrusion.

DISCRETE FIBER REINFORCED CONCRETE (CONTINUED..) THE NORTHCAP UNIVERSITY, GURGAON7In contrast to reinforcing bars in reinforced concrete which are continuous and carefully placed in the structure to optimize their performance, the fibers are dis-continuous and are generally randomly distributed throughout the concrete matrix. As result the reinforcing performance of steel fibers, for example, is inferior to that of reinforcing bars.

THE NORTHCAP UNIVERSITY, GURGAON8In addition, the fibers are likely to be considerably more expensive than the conventional steel rods. Thus, fiber-reinforced concrete is not likely to replace conventional reinforced concrete. However, the addition of fibers in the brittle cement and concrete matrices can offer a convenient, practical and economical method of overcoming their inherent deficiencies of poor tensile and impact strengths, and enhances many of the structural properties of the basic materials such as fracture toughness.

DISCRETE FIBER REINFORCED CONCRETE (CONTINUED..) THE NORTHCAP UNIVERSITY, GURGAON9Essentially, fibers act as crack arrestor restricting the development of cracks and thus transforming an inherently brittle matrix, i.e., Portland cement with its low tensile and impact resistances, into a strong composite with superior crack resistance, improved ductility and distinctive post-cracking behavior prior to failure. Uses: Steel fibers are probably the best suited for structural applications. Due to superior properties like increased tensile and bending strengths, improved ductility, resistance to cracking high impact strength and toughness, spalling resistance, and high energy in hydraulic structures, airfield and highways pavements bridge decks, heavy duty floors and tunnel linings.

SLURRY INFILTRATED FIBER CONCRETES (SIFCON)THE NORTHCAP UNIVERSITY, GURGAON10In general, the superior toughness and energy absorption properties of FRC in comparison to conventional concrete improve, as volume fraction of fibers increases. Techniques for achieving high fiber volumes include the strategy of pre-placing dry fibers in the framework and infiltrating the bed of fibers with a cementing slurry. This composite is called slurry infiltrated fiber concrete(SIFCON).

THE NORTHCAP UNIVERSITY, GURGAON11SIFCON was first developed in 1979 by Lankard Materials Laboratory, Columbus, Ohio, USA, by incorporating large amounts of steel fibers in steel fiber reinforced cement-based composites.SIFCON is similar to fiber reinforced concrete in that lends significant tensile properties to the composite matrix. The fiber volume fraction, Vf (volumetric percent of fibers), of traditional fiber reinforced concrete is limited by the ability to effectively mix the fibers into the fresh concrete. This limits the fiber volume Vf to between 1% and 2%, depending upon the type of fiber used and the required workability of the mix. On the other hand, SIFCON specimens are produced with Vr between 5% and 30%. The fiber volume depends upon the fiber type, i.e. length and diameter, and the vibration effort utilized to fill the form. Smaller or shorter fibers will pack denser than longer fibers, and higher fiber volumes can be achieved with added vibration time.

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Placement of Steel fibers in a moldThe first step in the preparation of SIFCON

THE NORTHCAP UNIVERSITY, GURGAON13Attention should be paid to the orientation of fibers. If fibers are aligned along the diameter of the cylinder (Core) a much higher compressive strength can be expected compared to a cylinder in which fibers are aligned along the axis of the cylinder. Actually, it is reported that specimens with fibers perpendicular to loading axis may exhibit twice the strength of specimens with fibers placed parallel to load direction, Cylinders shown in the figure are cored vertically and horizontally from a slab with horizontally placed steel fibers.

Fiber orientation and edge effect in a molded SIFCON cylinder specimenOrientation of fiber in cored SIFCON as influenced by the coring direction with respect to fiber placement directionTHE NORTHCAP UNIVERSITY, GURGAON14

SLURRY INFILTRATED MAT CONCRETE (SIMCON)THE NORTHCAP UNIVERSITY, GURGAON15Recently, another form of slurry infiltrated fiber composite called slurry infiltrated mat concrete (SIMCON) has been developed. SIMCON is a new generation of high performance fiber reinforced concrete (HPFRC) made by infiltrating continuous steel fiber-mats with a specially designed cement-based slurry. Thus, instead of reinforcing concrete with steel bars, it is reinforced with sheets of stainless steel fibers injected with a mixture of cement, aggregates and water, called slurry. Uses: Fiber mats (available in rolls) are shaped and wrapped around existing columns and beams and injected with concrete slurry for repairing or strengthening existing structures. The mats are made of recycled stainless steel fibers.

USES OF SIMCONTHE NORTHCAP UNIVERSITY, GURGAON16SIMCON can be used in new construction or to reinforce existing structures. In conventional concrete reinforcement is designed to fail before the concrete and at failure large slabs chunks of concrete break apart from the reinforcement and fall from the structure.In SIMCON at failure, the mass of fibers and concrete does not collapse. Instead of large chunks breaking and falling from a structure, the material crumbles into small harmless flakes which pose little danger to people or property below. This controlled form of failure is a key advantage of SIMCON.

PROPERTIES OF SIMCONTHE NORTHCAP UNIVERSITY, GURGAON17The advantage of steel fiber mats over a large volume of discrete fibers is that the mat with predecided configuration provides inherent strength and can utilize fibers with much higher aspect ratios. The fiber volume is less than half that required for slurry infiltrated fiber concrete (SIFCON), while achieving similar flexural strength and energy absorption capacity. Since the mat is already in a pre-formed shape, handling problems are minimized and balling does not become a factor.The superior performance of the SIMCON over SIFCON is related to the bonding of the mat fibers in the composite concrete. In SIFCON, the relatively short embedment lengths of 25 mm fiber, results in fiber pullout as the primary failure mode. In the SIMCON composites, the failure mode comprises multiple cracks and ultimate failure occurs through fiber breakage in the high tensile stress zones of one or more of the crack planes. In the mat reinforced composites, the yield strength of the steel is fully utilized.

SIFCON vs SIMCONTHE NORTHCAP UNIVERSITY, GURGAON18SIMCON is also easier to handle and construct than with SIFCON. SIMCON is also better suited for applications where one dimension is much smaller than the remaining two, such as bridge deck overlays. On the other hand, SIFCON is better suited for three-dimensional applications, such as zones of reinforcing bar anchorage or of beam column joint.

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Thank you