Unit-1 Lecture-4 - Light Weight Construction Materials by Brig. S.K. Sharma

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UNIT-1LECTURE - 4

• LIGHT WEIGHT CONSTRUCTION MATERIALS

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

• FIBRE REINFORCED CONCRETE
• SLURRY INFILTRATED FIBER CONCRETES (SIFCON)
• SLURRY INFILTRATED MAT CONCRETE (SIMCON)
• USES OF SIMCON
• PROPERTIES OF SIMCON
• SIFCON VS SIMCON

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FIBRE REINFROCED CONCRETE

• The 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, 0625

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• The 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.

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DISCRETE FIBER REINFORCED CONCRETE

• As 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.

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• The 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.

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DISCRETE FIBER REINFORCED CONCRETE (CONTINUED..)

• In 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.

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• In 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.

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DISCRETE FIBER REINFORCED CONCRETE (CONTINUED..)

• Essentially, 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.

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SLURRY INFILTRATED FIBER CONCRETES (SIFCON)

• In 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).

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• SIFCON 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 mold The first
step in the preparation of SIFCON
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• Attention 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.

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Fiber orientation and edge effect in a molded
SIFCON cylinder specimen
Orientation of fiber in cored SIFCON as
influenced by the coring direction with respect
to fiber placement direction
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SLURRY INFILTRATED MAT CONCRETE (SIMCON)

• Recently, 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.

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USES OF SIMCON

• SIMCON 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.

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PROPERTIES OF SIMCON

• The 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.

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SIFCON vs SIMCON

• SIMCON 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