Fibre Reinforced Concrete

Fiber Reinforced Concrete Trade Name : Wirand Concrete

What is a Fiber…? Small piece of reinforcing material

possessing certain characteristic properties. Can be circular or flat. Parameter used to describe fiber – “Aspect ratio”. Aspect ratio is ratio of its length to its diameter. Typical aspect ratio for fibers ranges from 30 to 150.

What is Fiber Reinforced Concrete (FRC)? Fiber reinforced concrete (FRC) is concrete

containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers. Within these different fibers that character of fiber reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation and densities.

History of FRC…  The concept of using fibers as reinforcement is not new.

Fibers have been used as reinforcement since ancient times.  Historically, horsehair was used in mortar and straw in mud bricks.  In the early 1900s, asbestos fibers were used in concrete, and in the 1950s the concept of composite materials came into being.  There was a need to find a replacement for the asbestos used in concrete and other building materials due to the health risks associated with the substance were discovered.  By the 1960s, steel, glass (GFRC), and synthetic fibers such as polypropylene fibers were used in concrete, and research into new fiber reinforced concretes continues today.

Fibers used… Although every type of fiber has been tried out in cement and concrete, not all of them can be effectively and economically used. Each fiber has some characteristic properties and limitations. Fibers used areqSteel fibers qPolypropylene, nylons qAsbestos, Coir qGlass qCarbon q q 

Steel Fiber Reinforced Concrete… Most commonly used fiber. Round fiber of diameter 0.25 to 0.75mm. Enhances flexural, impact and fatigue

strength of concrete. Used for-overlays of roads, airfield pavements, bridge decks. Thin shells and plates have also been constructed using stell fibers.

Polypropylene/Nylon Fiber Reinforced Concrete…

Suitable to increase impact strength of

concrete. Possess high tensile strength but their low modulus of elasticity and higher elongation do not contribute to the flexural strength.

Asbestos Fiber Reinforced Concrete…

Mineral fiber, most successful of all as it

can be mixed with portland cement. Tensile strength of asbestos varies between 560 to 980 N/mm2. Asbestos cement paste has considerably higher flexural strength than portland cement paste. For unimportant concrete work, organic fibers like coir, jute and canesplits are also used.

Glass Fiber Reinforced Concrete…

Recent introduction. Very high tensile strength 1020 to 4080

N/mm2. Alkali resistant glass fiber has been developed. Shows comparable improvement in durability to conventional E-glass fiber.

Carbon Fiber Reinforced Concrete…

Posses very high tensile strength 2110 to

2815 N/mm2 and Young’s modulus. Cement composite consisting of carbon fibers show very high modulus of elasticity and flexural strength. Used for cladding, panels and shells.

Factors affecting properties of Fiber Reinforced Concrete… Transfer of stress between matrix and

fiber. Type of fiber. Fiber geometry. Fiber content. Orientation and distribution of fibers Mixing and compaction technique of concrete. Size and shape of aggregates.

Relative Fiber Matrix Stiffness Modulus of elasticity of matrix must be much lower

than that of fiber for efficient stress transfer. Nylon and propylene fiber impart greater degree of toughness and resistance to impact. Steel, glass and carbon impart strength and stiffness to the composite. Interfacial bonds also determine the degree of stress transfer. Bonds can be improved by larger area of contact, improving frictional properties and degree of gripping and by treating steel fibers with sodium hydroxide or acetone.

Volume Of Fiber Strength largely depends upon the quantity of

fibers used. Tensile strength and toughness of the composite linearly increase with increase in volume of fibers. Higher percentage of fibers is likely to cause segregation and harshness of concrete and mortar.

Aspect Ratio Of Fiber One of the important factor affecting the

properties and behavior of composite. Increase in aspect ration upto 75, increase the ultimate strength of concrete linearly. Beyond 75 relative strength and toughness is reduced.

Orientation Of Fibers One of the major difference in conventional

reinforcement and fiber reinforcement. Specimens with 0.5% volume of fiber were tested and it showed that when fibers were aligned parallel to the load applied, more tensile strength toughness was seen as compared to randomly distributed and perpendicular fibers.

Workability and Compaction of Concrete… Use of steel fibers decrease the

workability. External vibration fails to compact the concrete. Poor workability is also result of non uniform distribution of fibers. Fiber volume at which this situation is reached depends on the length and diameter of fiber used. Workability and compaction standard can be improved with help of water reducing admixture.

Size Of Coarse Aggregates Maximum size of aggregates should be

restricted to 10 mm. Fibers also act as aggregate. The interparticle friction and between fibers and between fibers and aggregates controls the orientation and distribution of fibers which affect the properties of composite. Friction reducing admixtures and admixtures improving the cohesiveness can significantly improve the mix.

Mixing qMixing is important to avoid balling of aggregates, segregation and to obtain uniform composite. qIncrease in aspect ration, volume percentage, size and quantity of aggregates intensify the balling tendencies. qA steel fiber content in excess of 2% by volume and an aspect ratio of more than 100 are difficult to mix. qAddition of fibers before addition of water is important to get uniform dispersion of fibers in concrete mix.

Typical Proportions For FRC… Ingredients

Proportions

Cement content 325 to 550 kg/m3 W/C Ratio

0.4 to 0.6

Sand/Total aggregates

50-100%

Max aggregate 10 mm size Air content

6-9%

Fiber Content: Fiber

Percentage

Steel

1% for 78Kg/m3

Glass

1% for 25Kg/m3

Nylon

1% for 11Kg/m3

Advantages Of FRC

Over Conventionally Reinforced Concrete… Increased static and dynamic tensile strength. Energy absorbing characteristics and better

fatigue strength. Uniform dispersion of fibers throughout the concrete provides isotropic properties.

Applications… Overlays of air-fields. Road pavements. Industrial flooring. Bridge decks. Canal lining. Explosive resistant structure. Refractory lining. Fabrications of precast products like pipes,

boats, beams, staircase steps, wall panels, roof panels, manhole covers etc. Manufacture of prefabricated formwork moulds of “U” shape for casting lintels and small beams.

Manhole cover

Precast canal lining

Bridge decks

Road pavement

Applications…

Applications…

Fire place made out of GFRC

Air field runway

Current development in FRC:qHigh fibre volume micro-fibre system. qSlurry infiltrated fibre concrete(SIFCON). qCompact reinforced composites. q q

High fibre volume microfibre system:qCan replace asbestos fibre. qImproves toughness and impact strength. qThese properties make it attractive for thin precast products such as roofing sheets ,cladding panels. qCement composites are useful for repair & rehabilitation works. q

Slurry infiltrated fibre concrete:qSIFCON was invented by Lankard in 1979. qSteel fibre bed is prepared and cement slurry is infiltrated. qMicro-fibre contents up to about 20% by volume can be achieved. qIncrease in both flexural load carrying capacity and toughness. qHigh compressive strength is achieved. qUsed for blast resistant structures & burglar proof safe vaults.

Compact reinforced composites(CRC):qConsist of an extremely strong ,dense cement matrix. qExtremely expensive. qExhibits flexural strength up to 260Mpa & compressive strength of about 200Mpa. qAs strong as structural steel. qCan be moulded and fabricated at site. q

Polymer concrete :qConcrete is porous due to air voids ,water voids. qImpregnation of monomer & subsequent polymerization is the latest technique adapted to reduce porosity and improves strength.

q q q q q

Types: qPolymer impregnated concrete(PIC). qPolymer cement concrete(PCC). qPolymer concrete(PC). qPolymer impregnated & surface coated polymer concrete.

Polymer impregnated concrete: Precast conventional concrete ,cured & dried in oven. Polymerization carried out by using radiation ,application of heat or by chemical initiation. Monomers used are methylmethacrylate ,styrene ,acrylonitrile ,t-butyl styrene. Amount of monomer loading depends on quantity of water and air that has occupied the total void space. Monomer loading time can be reduced by application of pressure.

Polymer cement concrete:Made by mixing cement ,aggregates ,water &

monomer. Monomers used in PCC are polyster-styrene ,epoxystyrene ,furans ,vinylidene chloride. A superior PCC made by furfuryl alcohol aniline hydrochloride in the wet mix is claimed to be specially dense ,non-shrinking ,high corrosion resistance ,low permeability & high resistance to vibrations and axial extension.  

Polymer concrete:Aggregate bound with a polymer binder. Minimizes void volume in the aggregate mass. Strength obtained is 140 Mpa with a short

curing period. The graded aggregates are prepacked & vibrated in mould. Tend to be brittle & it is reported that dispersion of fibre reinforcement would improve the toughness & tensile strength of material.

Partially impregnated & surface coated concrete:Significant increase in strength of original

concrete. Polymerisation can be done by thermal catalytic method. Depth of monomer penetration depend upon pore structure of hardened & dry concrete ,duration of soaking & viscosity of monomer. Excellent penetration can be achieved by ponding the monomer on concrete surface.

Properties of PIC:Tensile strength:-



q Impregnated concrete is observed to be 3.9 times that of the control specimen using radiation process of polymerization.

  FLEXURAL STRENGTH:PIC with polymer loading of 5.6% MMA shows flexural strength 18.8 Mpa as compared to 5.2Mpa of the control specimen. q

Stress-strain relationship:-



 Has linear stress-strain relationship to failure.  Very little departure from linearity up to 90% of

ultimate strength.  No abrupt change at the proportional limit.

Compressive strength:-



Using MMA as monomer & with polymer loading of

6.4% ,144 Mpa strength is obtained using radiation technique & 130 Mpa using thermal catalytic process. Higher strengths are obtained with MMA impregnated sample than with polyster styrene.

Creep:-



 After typical initial movement during load application

,these concretes expand under sustained compression.  Creep deformation generally stabilises after 2-3 months. 

Shrinkage:-



 Occurs through two stages i.e. initial drying & through

polymerisation.  Several times greater than the normal drying shrinkage.  Shrinkage is less for higher modulus of elasticity.

Water absorption:-



Maximum reduction of 95% in water absorption has been

observed with concrete containing 5.9% polymer loading.

Co-efficient of thermal expansion:-



PIC has higher co-efficient of thermal expansion than

conventional concrete. Radiation polymerised concrete has co-efficient of thermal expansion of 5.63 *10-6 and styrene impregnated specimens have shown a value of 5.1*10-6

Resistance to abrasion:-



PIC shows appreciable improvement in resistance to

abrasion. 5.5% MMA impregnated concrete has been found to be 50 to 80% more resistant to abrasion than the control speciman.

Wear & skid resistance:-



 On actual wear track test ,the treated surfaces

show excellent skid resistance than the unimpregnated surfaces.  The wear after 50,000 simulated vehicular passes has been less than 0.025 cm.

Fracture of PIC:-



 Impregnation improves the strength of mortar

matrix & also the strength of paste-aggregate interface by elimination of cracks.  Brittle nature of PIC presents a severe design limitation.  Fracture mode of PIC can be altered by incorporating a small quantity of fibres in the matrix.  Fibres serve to inhibit crack propogation through the mortar by acting as crack arrestors.

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Applications of PIC:Prefabricated structural elements:-



For solving problems of urban housing storage

,maintaining quality ,economy & speed ;prefabricated techniques of construction are used. Can be used in high rise building due to easy handling and erection.

Prestressed concrete:-



PIC provides high compressive strength of 100-140

Mpa ,hence useful for larger spans and heavier loads. Low creep properties of PIC make it good material for prestressed concrete.

Marine works:-



PIC possessing high surface hardness ,very low

permeability & greatly increased resistance to chemical attack ,is a suitable material for marine works.

Desalination plants:-



Material used in construction of flash distillation vessels in

desalination of water has to withstand corrosive effects of distilled water ,brine and vapour at temp. of 143 C. It is seen that there is a saving in construction of cost over that of conventional concrete by the use of PIC.

Nuclear power plants:-



Nuclear container vessels are required to withstand high

temp. & provide shield against radiations. PIC having high permeability ,durability and strength are thus used.

Sewage disposal works:-



Concrete sewer pipes deteriorate due to attack of

effluents. Concrete structures are subjected to attack from corrosive gases in sludge digestion tanks. PIC due to its high sulphate and acid resistance is suitable for such works.

Water proofing of structures:-



Seepage and leakage of water through bathroom slabs

has not been fully overcome by conventional water proofing methods. Use of polymer impregnated mortar provides better water proofing,

Industrial applications:

 Concrete has been used for floor in tanneries .chemical

factories ,dairy farms and in similar situations for withstanding the chemical attack ,but performance is unsatisfactory.  PIC provides a permanent solution for durable flooring in such situations.

Impregnation of ferrocement products:-



Ferrocement construction techniques are extensively

used in manufacture of boats ,fishing trawlers ,domestic water tanks ,grain storage tanks ,manhole cove ,etc. Ferrocement products are generally thin & as such are liable to corrode. Application of polymer impregnated techniques should improve the functional efficiency of ferrocement products.

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