GUNITING

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GUNITING
by Noor Asyikin Sepiai
EDIT BY CKIEN
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INTRODUCTION
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• What is guniting ?
• Guniting is a mixture of cement,sand and water
  projected pneumatically at high velocity from a
  suitable nozzle onto the slope surface to produce
  a dense homogeneous protective layer.
• gunite is a trade name for dry gunned
  concrete.
• it means spray applied concrete. .
• Commonly used as facing for steep nailed sloped.
• Used dry mix with water cement ratio of 0.45 to
  0.5
• Cement content not less than 350 kg/m³
• The maximum aggregate size shall be less than
  10mm.

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• Function ?
• Gunite is applied to the excavated slope surfaces
  at locations shown on the drawings or at
  locations directed by engineers.
• Using guniting, concrete can be applied on
  irregular, vertical and overhead surfaces. This
  application is used commonly to protect slopes
  from erosion, as well as structures of large
  areas or uneven surfaces
• Gunite is extremely strong, dense, and highly
  resistant to weathering and many forms of
  chemical attack. Gunite can be successfully
  applied to any desired thickness with uniform
  quality throughout.

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Common gunite application

• swimming pool construction
• Refractory Installation
• Rockscaping
• Concrete Repair / Rehabilitation of Concrete and
  Masonry structures (bridges, walls, columns,
  beams, slabs, sewers)
• Backfill (sand gravel)
• Civil Infrastructure Projects
• Channels, Piers, Sea Walls
• Mines
• Tunnel Lining
• Slope Stabilization
• Retaining Fire Walls
• Concrete Pipe
• Fireproofing for steel structures
• Ditches

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• Quality finish
• Distance of spraying should be about 0.6m to 1.5m
  from treatment surface.
• Angle of spraying should as far as possible
  berpendicular to treatment surface.
• Formed in successively from top down without gaps
  or slumps.
• freshly gunite surface should be protected from
  rain or strong sunlight
• Wet slope surface should be allowed to dry by
  covering with tarpaulin for a few days before
  guniting to ensure good bonding between gunite
  slope surface.

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WORK SPECIFICATION
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• This works spec covers technical requirements for
  gunite mix,machine plant, surface preparation,
  method of operation, quality control works
  acceptance criteria.
• Dry process
• mixture of cement, aggregate and sand
  weighted / volume batched, throughly mixed dry
  and fed into a purpose-made machine where the
  mixture is suitably pressured, metered into a
  dry air stream and conveyed through hoses / piped
  to a nozzle before which water is introduced to
  hydrate the mix and is projected without
  interuption onto slope surfaces

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MATERIAL
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• Cement
• Cement shall be OPC and comply with the
  requirements of M.S. 522
• Sand / Aggregate
• Sand or aggregate shall be clean and durable, and
  free from clay or organic matters and other
  impurities.
• Sand and aggregate shall be not more than 10mm
  and shall comply with requirement om M.S 29 and
  M.S 30.
• Grading limits
• 10mm sieve ------ 100 passing
• 5.0mm sieve ------ 90-100 passing
• 2.36mm sieve ------ 75-100 passing
• 1.18mm sieve ------ 55-90 passing
• 600µm sieve ------ 35-59 passing
• 300µm sieve ------ 8- 30 passsing
• 150µm sieve ------ 0-10 passing

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• c) Water
• Clean
• Free from harmful matter.
• If test are required, they shall be in accordance
  with the requirements of M.S 28
• d) Reinforcement
• Unless, otherwise stated in the drawings steel
  fabric reinforcement shall be hard-drawn steel
  wire reinforcing fabric with wire diameter of
  6.0mm pitch of 200mm in the direction (BRC A6)
  and comply with requirements of M.S 145

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• e) Mix
• Gunite shall has minimum cement content of 35kg
  per cubic meter and with water/cement ratio of
  not exceeding 0.5 by mass.
• Mix proportion
• shall be designed by contractor to achieve
  minimum grade 30 or the specified grade of
  strength and shall be approaved by engineer
  before commencement of works
• Mix dry aggregate cement
• which are not applied on slope surface within
  30 minutes after mixing shall be discharges
• Admixture
• added at 3-5 by weight of cement to speed
  the setting rate of cement, when directed by
  engineer.
• All constituents shall be uniformly dispersed
  throughout mix. Mixing by hand is not allowed.

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QUALIFICATION OF OPERATORS
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• Contractor shall certify or provide documentary
  evidence to the engineer on the satisfactory
  performances and experience of the intended
  foreman, nozzle man and delivery equipment
  operators for the guniting work.
• Guniting operators shall gunite preconstruction
  panels for the Engineers assesment on skill and
  competence before acceptance of employment for
  guniting works.

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PLANT AND EQUIPMENTS
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• Before commencement of work, it shall be submit
  to engineer for approval the type, make and
  number of plant and equipment to be used.
• Drawing shown the proposed plant and works
  arrangement with brief description about the
  equipment, the method of operation and mix
  proportion, ect shall be included in the method
  statement as specified in clause 12(a)

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PRECONSTRUCTION TEST PANELS
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• Propose
• - To assess the quality of guniting(density,
  uniformity, strength, etc)
• - To assess works output rate to ensure the
  resources for guniting works are satisfactory
  with respect to skill quality
• Preconstruction testing
• - using plant identification
• - shall be undertaken in such time before
  commencemnet of the works to allow approval by
  the engineer.
• Trial mixes
• - each mix design shall be carried out by
  contractor.
• - for each mix design, 3 number test panels of
  minimum size 750mm x 750mm x 100mm thick shall be
  sprayed from each position required in the works
  (down-hand,vertical,overhead position) with layer
  thickness appropriate to that position.
• - panel mould shall be formed from 20mm thick
  plywood adequately braced and held rigidly in
  position.
• - Test panel min size 750mm x 750mm x 100 mm
  thick shall be sprayed from each position
  required in the works.

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INTERFACE PREPARATIONS
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• Earth or natural surfaces other than rock shall
  be compacted, trimmed and graded before guniting.
• Earth surface shall be maintained or equilibrium
  moisture (not too wet or to dry before guniting).
• Gunite shall not be applied on surface with loose
  or soft or wet materials. Wet surface (after
  rainfall) shall be covered by tarpauline for at
  least 2 days or until the surface moisture has
  moisture content within natural moisture content
  3 or as directed by engineers.
• Rock surfaces shall be cleaned free from loose
  materials, mud of foreign matters.
• Flow of water interferes with application of
  gunite or cause leaching of cement, the following
  water shall be directed by appropriate drainage
  channels to convenient locations where plugging
  can be carried out.
• Reinforcement shall be cleaned and free from
  loose mild scale, loose rust, oil or other
  coating prior to the application of gunite.

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Guniting for swimming pool
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Guniting for Retaining wall
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Guniting for drainage
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References

• Books workshop specification For Geotechnical
  works
• http//www.monolithic.com/construction/shotcrete_g
  unite/
• http//www.google.com.my/url?saXstart0oidefin
  eqhttp//www.needhamre-roofing.com/Glossary.htm
• http//www.google.com.my/url?saXstart7oidefin
  eqhttp//www.parpool-spa.com/Page/Help/Water_Che
  mistry_Terms.html
• http//www.reedpumps.com/gunite.htm
• http//www.reedpumps.com/gunitepool.htm

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THANK YOU