Monday, May 01, 2017

What are crack repair techniques?

Crack Repair Techniques:
  1. Sealing with epoxies
  2. Routing and sealing
  3. Stitching
  4. External stressing
  5. Overlays
  6. Grouting
  7. Blanketing
  8. Autogenous healing
Sealing with epoxies :
  • Injection epoxy bonding compounds in high pressure in to cracks
PROCEDURE
Sealing with epoxies
Sealing with epoxies

  1. Drill into the cracks
  2. Flush out cracks by injecting water/ other solvents
  3. Dry the surface
  4. Epoxy injection in to holes
  5. Curing of epoxy
  6. Remove surface seal by grinding
Routing and Sealing
Routing and Sealing
Routing and Sealing

  • Simplest, most common, inexpensive method
  • For both fine and larger isolated cracks
  • This method involves enlarging the crack along its exposed face and sealing it with a suitable joint sealant
  • Most used for floors and pavements
  • Side effects-
    • Chemical attack
    • Corrosion of rebar
    • Swelling
Stitching
Stitching
Stitching

Stitching may be used when tensile strength must be reestablished across major cracks.


  • Stitching involves
    • drilling holes on both sides of the crack
    • grouting in U-shaped metal units with short legs called staples or stitching dogs


External Stress
  • The development of cracking is due to the tensile stress, thus can be arrested by suppressing this stress
  • Cracks can be closed by inducing a compression force to over come the tensile stresses
  • The compressive force is applied by
    • Pre- stressing wires or rods
    • Wedging- by opening the cracks and filling with expanding mortar, by jacking and grouting or by actual driving wedges.
Blanketing
  • Blanketing is similar to routing and sealing
  • used on a larger scale and is applicable for sealing active as well as dormant cracks.
  • Following are the types of blanketing joints
    • Type I
    • Type II
    • Type III
    • Type IV
      • Type I
      • The first type of blanket joints use elastic sealants
      • They return to their original shape, when not under an externally induced stress
      • A bond breaker should be used at the bottom of the chase, so that the sealant is free to deform.
      • Type II
      • use sealant materials that are known as mastic sealants
      • their details are similar to that of an elastic sealant, except that the bond breaker is omitted and the sealant is bonded to the bottom as well as to the sides of the chase.
      • Type III
      • It is a mortar plugged joint
      • A recess in the form of a trapezoid to accomodate the mortar plug is made
      • This recess is filled with mortar
      • Type IV
      • A water cripped bar is used
Overlays
  • Used to seal cracks
  • Used when large no of cracks, treating each crack is expensive
  • Active cracks- overlays done with materials which are extensible but not flexible. Eg: Polymeric membrane with top coat of tar
  • Dormant cracks- any type of overlays may be used
Eg: polymer modified Portalnd cement mortar or concrete, or by silica fume concrete
Grouting
  • Similar to epoxy injection
  • Epoxy not used where fire resistance and cold weather
  • Grouting is effective alternative
  • When the crack is straight line- drill out the length of crack- grout it to form a key
  • This method is effective in shopping water leaks.
Autogenous Healing
  • It is the natural process of crack repair that can occur in concrete in the presence of moisture
  • The repair is by a combination of mechanical blocking by particles carried into the crack with the water and the deposition of calcium carbonate from the cementitious material
  • Mechanism
  • Autogenous healing occur by the carbonation of calcium oxide and calcium hydroxide present in the cement by CO2 present in the air and water
The resulting CaCO3 and Ca(OH)2 crystals precipitate accumulate and grow through and out from cracks.



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