Diese Präsentation wurde erfolgreich gemeldet.
Wir verwenden Ihre LinkedIn Profilangaben und Informationen zu Ihren Aktivitäten, um Anzeigen zu personalisieren und Ihnen relevantere Inhalte anzuzeigen. Sie können Ihre Anzeigeneinstellungen jederzeit ändern.

fibre reinforced concrete

15.806 Aufrufe

Veröffentlicht am

It gives a brief introduction on fibre reinforced concrete

Veröffentlicht in: Ingenieurwesen
  • Hello! Get Your Professional Job-Winning Resume Here - Check our website! https://vk.cc/818RFv
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier
  • Hello! Get Your Professional Job-Winning Resume Here - Check our website! https://vk.cc/818RFv
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier

fibre reinforced concrete

  2. 2. What is Fibre? • Fibre is a small piece of reinforcing material which increases structural integrity. Why Fibre ? Concrete: • Weak in tension • Brittle
  3. 3. What is fibre reinforced concrete • FRC is a Portland cement reinforced with more or less randomly distributed fibres .
  4. 4. Types of fibres 1. Steel fibre:
  5. 5. 2. Glass fibre:
  6. 6. • Asbestos fibre:
  7. 7. • Polypropylene fibre:
  8. 8. • Carbon fibre:
  9. 9. • Aramid fibre:
  10. 10. Source: Santa Kumar
  11. 11. Factors effecting the properties of FRC 1. Volume of fibres: • low volume fraction (less then 1%): Used in slabs and pavement that have large exposed surface leading to shrinkage cracking • Moderate volume fraction(between 1 and 2%): Used in construction method such as shotcrete • High volume fraction(greater then 2%): Used in making high performance FRC
  12. 12. 2. Aspect ratio of fibre: = fibre length/fibre diameter Source: M.S Shetty
  13. 13. 3. Orientation of fibres: • Aligned in the direction of load • Aligned in the direction perpendicular to load • Randomly distribution of fibers
  14. 14. 4. Relative fibre matrix: • Fibre should be significantly stiffer than matrix • Low modulus of fibres imparts more energy absorption while high modulus of fibres imparts strength and stiffness. • Low modulus fibres e.g. nylon, polypropylene • High modulus of elasticity e.g. steel, glass and carbon fibres.
  15. 15. 5. Workability and compaction of concrete: • Usage of steel fibres , higher aspect ratio and non-uniform distribution of fibres will reduce workability • Prolonged external vibration fails to compact the concrete • These properties can be improved by increasing water/cement ratio or by using water reducing admixtures
  16. 16. 6.Size of coarse aggregate: • Restricted to 10mm • Friction between fibres and between fibres and aggregates controls orientation and distribution. 7. Mixing: • Mixing of FRC needs careful precautions to avoid balling effect and segregation • Increase in aspect ratio, volume percentage and size of coarse aggregate will increase the difficulties.
  17. 17. Developments in FRC 1.High fibre volume micro fibre system: • length – 3mm • Diameter – 25 microns • Specific surface > 200 cm2/gram • Mixing of FRC needs careful conditions to avoid balling effect • Sand particles of size not exceeding 1mm • Low sand to cement ratio. • Requires large dosage of super plasticizers • Omni mixer is used for mixing
  18. 18. Omni mixer used in high volume FRC
  19. 19. 2. Slurry infiltrated fibre concrete(SIFCON): • Invented by lankard in 1979 • Pre-placing the dry fibres and cement slurry is infiltrated. • Volume of fibres can be increased to 20% • increase in flexural capacity and toughness. • used in blast resistant structures • better suited for three dimensional application such as zones of reinforcing bars anchorages
  20. 20. 3. Slurry infiltrated mat concrete (SIMCON): • Infiltrating continuous steel fibre mats with a specially designed cement based slurry. • Mats are made up of stainless steel. • Fibre volume is less than that required for SIFCON, but same flexural strength and energy absorption. • Aspect ratio exceeding 500 can be used. • Since mat is predefined configuration, handling is minimized and balling effect is reduced
  21. 21. • Cracks are small and discontinuous and possibility of water seepage is low . • Concrete slurry uses very little water to pack the mat very tight some of the cement remains unhydrated.
  22. 22. Applications of SFRC • Highway and airfield pavements
  23. 23. • Hydraulic structures
  24. 24. • Fibre shotcrete
  25. 25. • Precast applications
  26. 26. • Structural applications
  27. 27. Behaviour of SFRC in Tension • Effect of incorporating fibres – delay and control tensile cracking • Fibres (ductile) + matrix (brittle) composite (ductile) • Sharing of tensile load (most predominant feature of FRC)  until the matrix cracks ( fibre & matrix)  once matrix cracks (fibres)  this mechanism gives rise to favourable dynamic properties 1. Energy absorption 2. Fracture toughness
  28. 28. • Mangat reference (1976) “ The effect of fibres in a cementitious material is principally to cause relief of tensile stress at the crack tip and prevent unstable crack propagation”
  29. 29.  Kelly (1970) • Investigated the mechanism of pull-out. • Load-elongation curve of fibres in tension depends on volume fraction of fibres. • Response in tension (based on FRC or SIFCON) stage1: before cracking the composite elastic- (elastic stage) stage2: after cracking –fibres tend to pull out – sudden change in load elongation curve. - if maximum post cracking stress › cracking stress – (multiple cracking stage) stage 3: beyond the peak point - failure and/or pull out of fibres across single critical crack. • Note : the post cracking strength increases with increase in bond strength, aspect ratio and volume fraction of fibres.
  30. 30. • In the curve OA – debonding of fibre • In case of short fibres – debonding occurs at max load • Debondind energy per unit area = (area of OAB under the stress-strain curve)/(surface area of fibre) • The additional energy dissipation of fibre concrete results from debonding energy as well. Source: santakumar
  31. 31. Source: M.S Shetty
  32. 32. Behaviour of FRC in Compression • Increase in compressive strength of FRC is marginal and ranges from 0% to 20%. • However, post cracking compressive stress-strain response changes substantially. • Change is due to Increase in strain at peak load & ductility beyond ultimate load – higher toughness • Higher toughness – prevents sudden & catastrophic failures (especially in case of EQ & blast type of loads)
  33. 33. •Toughness = total area (A1+A2) / area A1 Source: M.S Shetty
  34. 34. Behaviour of FRC in Flexure • There are 3 stages of response in flexure stage1: process zone - more or less linear response up to elastic limit. - transfer stress from matrix to the fibres by interfacial shear - imposed stress is shared between matrix and fibre until first crack. stage2: pseudo-plastic zone - it is the non-linear portion between the elastic point and max load capacity point. - stress in matrix is progressively transferred to the fibres. - fibres pull-out from the matrix (non-linear load-deflection) - results in multiple cracking
  35. 35. stage3: stress free zone - descending portion following peak strength until strain limit. - load-deflection curve represents ability of the fibre composite to absorb large amounts of energy before failure. - fibres are completely pulled-out • Flexural strength of fibre composite is fc = ultimate strength of fibre composite fm = max strength of plain matrix (concrete) C and D are constants determined experimentally for plain concrete C=1 and D=0 for FRC ultimate strength C=0.95,D=4.95 for FRC first cracking strength C= 0.85, D= 4.95
  36. 36. Source: M.S Shetty
  37. 37. Crack Arresting • Crack resistance is lower than the ultimate stress • Once cracking is subjected to coupling impact of increased loads, material ageing, structure fatigue – increase microcracks • Microcracks – upward shifting of N-A, tension area of concrete is lost – decrease of structural rigidity – deterioration of structural durability. • Propogation of micropcracks – emergency situation • Fracture mechanics – stress singularities at crack tips • Stress intensity factor › critical stress intensity factor of FRC – Propagation of cracks - functional obsoleteness & structural failure
  38. 38. Bridging action of steel fibres
  39. 39. CASE STUDY • Research program is funded by National Basic Research Program of china • Published in 15 may 2013 in JESTR
  40. 40. Case study to arrest cracks Crack arresting and strengthening
  41. 41. • Supposing unilateral crack under pure bending • Stress concentration factor of edge crack is more than central penetrated crack under same loading – unstable propagation • HFRP is bonded to the surface – resists stress concentration of crack at crack tip– edge crack in to internal eccentric crack • From the super position principle where, are stress intensity factors at crack tip A, the rebar and the HFRP sheet. • HFRP – one layer of unidirectional CFRP sheet (300 g/m^2) & one layer of unidirectional GFRP sheet (600 g/m^2) adhered to the bottom by epoxy
  42. 42. Tensile strength is increased by 171% & fracture elongation is increased by 70%
  43. 43. 2 no. of specimens, 8mm dia bars, 3% of nylon (tensile- 6 Mpa)
  45. 45. STRESS INTENSITY FACTOR VS CRACK HEIGHT WITH HFRP •HFRP increases ductility separately by 36% and 106%
  46. 46. Mix Design Procedure • Corresponding to required 28-day field flexural strength of SFRC – design strength of laboratory mix is determined. • For known geometry, stipulated volume fraction- w/c ratio is selected between 0.45 and 0.60 • Depending on max size of agg. & fibre concentration – cement paste content is determined by mass • Ratio of FA to CA varies from 1:1 to 1:3, ratio of 1:1.5 is a good start for volume % of fibre up to 1.5 and length of fibre up to 40mm.
  47. 47. • From w/c ratio & paste content – cement & water content • Fibre content is obtained by taking density of fibres as 7850 kg/m^3 • Total quantity of agg. Is determined as wt. of agg. = wt. of FRC – ( wt. of water, cement & fibre) • Quantities of FA &CA are determined by ratio of FA:CA= 1:1.5 • Trial mix is checked for workability by appropriate test.
  48. 48. Applications in India and abroad • More than 400 tones of Shakti man Steel Fibers have been used recently in the construction of a road overlay for a project at Mathura (UP).
  49. 49. • A 3.9 km long district heating tunnel, carrying heating pipelines from a power plant on the island Amager into the center of Copenhagen, is lined with SFC segments without any conventional steel bar reinforcement.
  50. 50. • Steel fibers are used without rebars to carry flexural loads is a parking garage at Heathrow Airport. It is a structure with 10 cm thick slab.
  51. 51. Conclusions • The total energy absorbed in fiber i.e., area under the load-deflection curve is at least 10 to 40 times higher for fiber-reinforced concrete than that of plain concrete. • Addition of fiber to conventionally reinforced beams increased the fatigue life and decreased the crack width under fatigue loading. • At elevated temperature SFRC have more strength both in compression and tension. • Cost savings of 10% - 30% over conventional concrete flooring systems.