02-10-2012, 04:40 PM
TO COMPARE FLEXURAL STRENGTH OF STEEL AND POLYPROPYLENE FIBER REINFORCED CONCRETE
TO COMPARE FLEXURAL.pdf (Size: 699.08 KB / Downloads: 132)
INTRODUCTION
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(hand mixing). Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers. Within these different fibers, characteristic of fiber-reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation and density .Since plain concrete is weak in tension and brittle, to increase the load bearing capacity of concrete in tension, fibers are added, also they are used in concrete to control cracking due to both plastic shrinkage and drying shrinkage and increasing tensile strength.. To determine flexural strength, direct test is difficult so SPLIT TEST on cylinder specimen and FLEXURAL TEST on beam (indirect test) are performed. Though none of them gives exact tensile strength of concrete but split test results are considered more accurate.
RELEVANCE OF THE PROJECT WORK :
Steel fibre reinforced concrete and polypropylene fibre reinforced concrete are in minimal use in india as much of work has to be done in this field.
Polypropylene fibres and steel fibres are easily available and cost effective thus can be used excessively.
Steel and polypropylene fiber not only increase tensile strength but also its ductility, durability, improve impact resistance and decreases repairing requirement thus they can replace plain cement concrete in future infrastructures.
Incerease in tensile strength of concrete reduces steel reinforcement cost thus using fibre reinforced concrete can make structure cost effective.
METHODOLOGY Polypropylene Fibre:
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles (e.g., ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. Steel fibres: Steel fibre is one of the most commonly used fibre. Generally, round fibres are used. The diameter may vary from 0.25 to 0.75 mm. The steel fibre is likely to get rusted and lose some of its strengths. But investigations have shown that the rusting of the fibres takes place only at the surface. Use of steel fibre makes significant improvements in flexural, impact and fatigue strength of concrete, It has been extensively used in various types of structures, particularly for overlays of roads, airfield pavements and bridge decks. Thin shells and plates have also been constructed using steel fibres.
OBSERVATIONS :
We have conducted the Flexure test and Split tensile strength test on concrete specimens. For Flexure test, 3 beams and for Split tensile test, 3 cylinders were casted. 0.5%, 0.75% and 1.0% fibre by volume is used to prepare fibre reinforced concrete of steel and polypropylene fibres both. After 28 days of curing under water, specimens were tested and results obtained are tabulated below.
RESULTS AND DISCUSSION: FLEXURAL TEST:
As per the observed data, the flexural strength of steel fibre reinforced concrete is 7.5% to 21% more than that of polypropylene fibre reinforced concrete with dosage of 0.5% to 1.0 % (by volume) of fibres .The enhancement in flexural strength is achieved due to the improvement in mechanical bond between the cement paste and fibre. As amount of steel fibre increases in mix, it greatly helps to reduce widening of crack more effectively as it has better abrasion, aspect ratio , more tensile strength , elasticity, better packing and bonding than polypropylene fibre, thus resulting in increase in flexural strength.
CONCLUSION :
It is found that when fibre reinforced concrete is used, fibres mixed in concrete lock the cracks and gives relatively higher value of modulus of rupture. When values given by steel and polypropylene fibre reinforced concrete are considered, steel fibres are found effective.
In hand mixing process, steel fibres are easier to mix than polypropylene fibres. Before mixing polypropylene fibres are needed to be wet then only these can be mixed. Steel fibres can be directly added to the mix.
On the other hand polypropylene fibres are cheap and durable. Effect of changes of environmental conditions on polypropylene fibre are negligible but steel fibres can catch rust after certain period.
Polypropylene fibre can be preferred to steel fibre as they cost much less than steel fibres to obtain same strength , also they slightly increase self weight of the structure thus more reinforcement bars can be provided in order to increase strength.
Highly recommended for economical structures in places like INDIA where economic factor and durability are major issues.