CONSTRUCTION TECHNOLOGY

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• CONSTRUCTION TECHNOLOGY
• maintenance

CEM 417
SOURCES FROM slide MOHD AMIZAN MOHAMD MOHD
FADZIL ARSHAD SITI RASHIDAH MOHD NASIR FKA, UiTM
Shah Alam.
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WEEK 8

• Temporary Works

1. Formwork
2. Shoring Scaffolding
3. Trench support system
4. Underpinning

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WEEK 8

• Temporary Works

1. Formwork
2. Shoring Scaffolding
3. Trench support system
4. Underpinning

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WEEK 8
LEARNING OUTCOME

• At the end of week 8 lectures, student will be
  able to
• Identify the functions of formworks. (CO1 CO3)
• Explain the requirements of a good formwork.
  (CO3)
• Identify the suitable materials and their
  advantages/disadvantages for formworks. (CO3 CO4)

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FORMWORK
Is a mould or box into which wet concrete can be
poured and compacted so that it will flow and
finally set to the inner profile of the box or
mould.
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FORMWORK

• Purpose to contain freshly placed and compacted
  concrete until it has gained enough strength to
  be self-supporting
• to produce a concrete member of the required
  shape and size
• to produce the desired finish to the concrete
• May be describe as a mould or box

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General design of formwork

1. sufficiently rigid to prevent undue deflection
   during the placing of the concrete
2. Sufficient strength to carry the working load and
   the weight or pressure of the wet concrete and to
   withstand incidental loading and vibration of the
   concrete
3. Set to line and level within the specified
   tolerance and include any camber (bend) which may
   be required

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General design of formwork

• 4. joints should be sufficiently tight to
  prevent loss of mortar from the concrete
• 5. size of panels or units should permit easy
  handling
• 6. design should permit and orderly and simple
  method of erection and striking
• 7. Arrangement of panels should be such that
  they are not trapped during striking and it
  should be possible to strike side from beams
  without disturbing the soffit formwork

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General formwork requirement

• Should be strong enough to support the load of
  wet concrete which is generally considered to be
  approximately 2400 kg/m3
• It must not be able to deflect under load which
  would include the loading of wet concrete, self
  weight and any superimposed loads such as
  operatives and barrow runs over the formwork
• 3. It must be accurately set out.
• Concrete being a fluid when placed, it will take
  up the shape of the formwork which must therefore
  be of the correct shape, size and in the right
  position

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General formwork requirement

• 4. It must have grout-tight joints.
• Grout leakage can cause honey-combing of the
  surface or produce fins which have to be removed.
  
• The making good of defective concrete surfaces is
  both time consuming and costly.
• Grout leakage can be prevented by using sheet
  materials and sealing the joints with flexible
  foamed polyurethane strip or by using a special
  self adhesive tape

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• A worker on the project greases the joints
  between Boards to ensure they are grout-tight.

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Extension pipe bridges with the formwork
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Material for formwork

• Main requirements-
• Hardness
• Permeability
• Surface texture
• Formwork facing material-
• Timber
• Plywood
• Steel
• Concrete
• Glass-reinforced plastic
• Hardboard
• Expanded polystyrene

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Formwork linings

• To obtain smooth patterned or textured for
  surfaces
• Inside of form can be lined with various
  materials such as oil-tempered hardboard, moulded
  rubber, moulded PVC and glass fibre reinforced
  polyester

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Timber formwork

• Basic standard qualities-
• Reasonable price and availability
• Should not be so soft
• Should be easily worked by hand or machine and
  nailed easily
• Should be stiff to avoid deflection
• Should be stable when exposed to sun or rain
• Should reduce defects
• Not suitable for green timber
• Moisture content not less than 20

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Advantages of timber formwork

• More economic
• Easy to handle and formed into required shape
• Maximum re-use
• Easy to fix insert

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Disadvantages of timber formwork

• Not enough strength as compared to steel formwork
  to carry large pressure.
• Excessive shrinkage due to temperature changes.
• Leakage through joints and apertures.
• Easily damage during fixing and dismantling of
  formwork.
• The pattern of grain, knots, bad flaws will leave
  imprint to the face of concrete.

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PLYWOOD

• Strong and light
• Supplied in sheets - 1.2m wide
• Standard length 2.4m, 2.7m or 3.m
• Thickness from 3mm to 19mm
• Thickness for lining or curved work 16 mm or
  less

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plywood formwork
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ADVANTAGES OF PLYWOOD FORMWORK

• Large panel
• Leakproof
• Large level surface
• No casting or cupping of surface smooth surface
• Can be nailed to edges without splitting
• High resistance to impact loads
• Available in several thickness

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Disadvantages of plywood formwork

• Grain pattern on concrete face
• Less durable
• More expensive compared to timber

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Metal formwork - STEEL

• Based on manufacturer pattern
• Double uses compare to timber, i.e. 30 or 40 uses
• Produce smooth, variable colour concrete surface

ADVANTAGES
DISADVANTAGES

• Limited to the shape of the structure.
• Standard steel unit are too heavy and difficult
  to handle.

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Metal formwork

• ALUMINIUM
• Selection of type and grade is important
• Based on environment
• Due to degradation and corrosion when subjected
  to marine environments
• Need special release agent

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PLASTIC

• rigid form when form is not suitable using
  timber or steel (thermo-formed)
• flexible form for lining material for mould
  faces
• Provide high quality surface finish
• Disadvantages impermeable and need special
  release agent

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GLASS FIBRE REINFORCED PLASTIC (GRP)

• Strong and light weight
• Use to produce a high quality surface finish, eg.
  Sculpture profile and repetition
• Comprises of polyester resin reinforced with
  glass fiber
• Thickness varies from 5 to 16 mm
• Can be used more than 100 times if handle with
  care
• Disadvantages similar with plastic formwork

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SURFACE TREATMENT

• Types of release agent to avoid defects
• Neat oil with or without surfactant
• Mould cream emulsion
• Chemical release agent
• Wax
• Barrier paint
• Water phased emulsion

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DEFECTS

• Two types of common defects-
• Blow holes
• small holes less than 15mm in diameter
• - Caused by trapped air between the formwork and
  concrete face
• Uneven color
• Caused by irregular absorption of water from the
  wet concrete by the formwork material

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Common failures of formwork

• Dimensional inaccuracy
• Lifting of single faced forms
• Inadequate of props
• Loss of material ties or props incorrectly
  spaced
• Surface blemishes

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Types of formwork

• Foundation
• Column
• Beam
• Slab
• Wall
• Climbing
• Sliding
• Permanent
• System
• Table

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75 mm high kicker
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skydeck slab formwork
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Concrete formwork and column steel reinforcing
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Formwork
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STRIKING OF FORMWORK

• The period before striking is depend on-
• Concrete used
• Weather and exposure of the site
• Any subsequent treatment to be given to the
  concrete
• The method of curing and other factors

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Concrete treatment
Stops Freeze/ Thaw Damage Fills voids and capillaries restricting moisture travel from both below and above the slab. Waterproofs concrete completely.
Improves Overall Strength, Density and Hardness By filling the internal and surface cavities with an insoluble gel, the sealer increases the density of the mix and strengthens the total structure. Additionally the compound protects the encapsulated re-enforcing steel from corrosion and future destruction.
Reduces Maintenance Costs for Aged Concrete High traffic surfaces resist abrasion damage longer. Top-coated materials retain their bonding properties for a greater length of time. Migration of corrosive salts are reduced. Life of flooring adhesives are greatly prolonged
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STRIKING OF FORMWORK

• Only when concrete is strong enough and able to
  carry imposed load
• Soffit forms to beam and slabs must be left in
  place longer than the side forms
• Should be with care and slowly to avoid damage
  and shock load on the partly hardened concrete

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Duration for f/work removing
location Surface or air temperature of concrete Surface or air temperature of concrete
16C 17C
Vertical f/work 12 hrs 18 hrs
Slab soffit (props left under) 4 days 6 days
Removal of props 10 days 15 days
Beam soffit (props left under) 10 days 15 days
Removal of props 14 days 21 days
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Curing

• Means controlling the moisture content and the
  temperature of the concrete after placing
• Important to develop concrete strength
• Excessive evaporation may cause multiple surface
  cracks wind cracking or plastic cracking
• Should start immediately after the removal of
  f/work
• Most effective method of curing cover with
  water proof sheets (building paper, polythene,
  damp sand, damp sawdust or wet cloth)

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General equipments

• Standard adjustable steel prop
• Consist of two tubular section
• One with 150mm square base and other with slides
  in it
• Fitted with square or beam type head (braced
  plate 350 mm long) to give a stable support

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General equipments

• Adjustable hanging bracket
• Used to hang a ledger from a beam or wall
• Some need to be used with folding wedges to
  enable the forms to be set and released
• Adjustable steel column/beam clamp
• Pins engaging holes through the bracket and
  horizontal beam
• Fine adjustment by screw clamp

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General equipments