Concrete Footings, Slabs, Columns & Beams

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Copyright: Quasar Management Services Pty Ltd
Concrete Footings, Slabs, Columns & Beams
Copyright: Quasar Management Services Pty Ltd
Features of Concrete in Structures Set out below are some of the principal considerations for reinforced concrete
slabs-on-ground, footings and concrete superstructures.
Concrete is a mixture of portland cement, sand, stone (called aggregate) and
water, which sets hard. It may include various other components which
provide colour, increase strength, accelerate hardening, retard hardening,
improve fluidity, lighten the structure and many other functions.
•Concrete is strong in compression, but weak in tension.
i.e. It may crack when pulled apart, but not when squeezed together.
Tensile strength is provided to concrete structures by the incorporation
of steel reinforcement.
•Concrete shrinks and thus cracks. The inclusion of steel reinforcement
(at close centres) will restrict the width of cracks that for in concrete as it
shrinks.
•Steel reinforcement rusts, expands and spalls the concrete if it is placed
too close to the concrete surface or if the concrete does not include
sufficient cement to protect the steel.
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General Behaviour of Concrete Structures When a concrete slab is suspended, it will bend under the action of its self weight and any
imposed gravity loads. This will cause cracks to form at the top of the slab over supports and at
the bottom of the slab at the centre of the span. It is at these locations the main tensile
reinforcement is placed.
Note: There is other reinforcement placed in concrete slabs and beams to control shrinkage
cracking, support the main reinforcement and to control diagonal shear cracking near supports.
Bottom face
reinforcement
at centre span
Bottom face
reinforcement
at centre span
Top face
reinforcement
at support
Top face
reinforcement
at support
Top face
reinforcement
at support
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Basic Concrete Specification
Concrete for House Construction in Rural Villages
Concrete shall comply with the Drawings, Building Regulations and relevant
Standard
(AS
2870).
Unless stated otherwise, properties shall be not less than:
Characteristic compressive strength of
20
MPa
Maximum aggregate size of 20 mm
Of sufficient slump to facilitate the nominates means of placement
The following site-mix concrete is deemed suitable for footings, slab-on-ground
and columns.
•1 part portland cement
•2 parts clean sand
•4 parts crushed stone or gravel
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Basic 20 MPa Concrete Specification For 1 cubic metre of 20 MPa concrete, the mix should consist of:
•8 bags (40 kg each) of GP or GB portland cement
Cement is also available in 20 kg bags, in which case 16 would be required.
•0.5 m3
of sand
Sand should be clean sharp sand, NOT brickiessand or plasters sand.
•1.0 m3
of 20 mm coarse aggregate
Aggregate should be clean 20 mm river gravel, crushed aggregate or similar.
•220 –230 litres of water
Less water should be used if the sand and aggregate are damp.
Set out below are the typical quantities for lesser volumes of 20 MPa concrete mix.
Source: Cement Concrete & Aggregates Australia
Grade 20 ConcreteVolume of Concrete (m
3)
Mix 1 cement : 2 sand : 4 gravel
(by volume)
0.20.40.60.81.0
Cement (Number of 40Kg bags)23578
Sand (m3)0.10.20.30.40.5
Gravel [20mm Coarse Aggregate] (
m3)0.20.40.60.81.0
Water (litres)50-6070-80140-150180-200220-230
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Basic 25 MPa Concrete SpecificationFor 1 cubic metre of 25 MPa concrete, the mix should consist of:
•9 bags (40 kg each) of GP or GB portland cement
Cement is also available in 20 kg bags, in which case 18 would be required.
•0.5 m3
of sand
Sand should be concreting sand or sometimes refined to be sharp sand NOT brickies
sand or plasters sand. Care in adding water is the key to a successful mix
•0.8 m3
of 20 mm coarse aggregate
It is important that concrete be made from clean 20 mm crushed aggregate , river
gravel or similar
•200 –220 litres of water
Less water should be used if the sand and aggregate are damp
Set out below are the typical quantities for a 25 MPa concrete mix.
Source: Cement Concrete & Aggregates Australia
Grade 25 ConcreteVolume of Concrete (m
3)
0.20.40.60.81
Cement (40Kg bags)24689
Sand (m3)0.10.20.30.40.5
20mm Coarse Aggregate (m
3)0.20.40.50.70.8
Water (litre)50-6070-80140-150180-200200-220
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Masonry Veneer and Cavity Construction Reactive clay foundations under a building may swell to form a dome or shrink form a dish.
In both cases, the concrete footings or beams & slabs will bend, placing stresses on the
superstructure.
The design of buildings with
conventional masonry veneer and cavity
masonry walls involves:
•Increasing the stiffness of the
footings or beams & slabs
•Incorporating articulation joints
in the masonry walls to “break
up” the structure, thus pre-
empting the formation of any
cracks.
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Crack Formation in Masonry House Walls As the foundations shrink or swell and the concrete
footings (or beam & slab) respond, the following can occur.
Unreinforced Masonry Walls
•Unreinforced masonry walls of weak masonry may
form multiple small cracks.
•If unreinforced masonry walls have relatively high
strength, they will remain intact for small movements,
but will eventually crack. Most likely, this will be a
single large crack, the most undesirable outcome.
Reinforced Masonry Walls Connected to Concrete Slab
•Single leaf reinforced hollow concrete masonry
superstructures built integrally with the concrete
footings, incorporating steel starter bars, vertical
“wide spaced” reinforcement and a continuous
horizontal bond beam are capable of cantilevering and
spanning large distances without cracking.
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Problem of Excessive Water in Concrete Broadly speaking, excess water in fresh concrete
leads to high shrinkage, cracking and loss of
strength; while too little water in fresh concrete
restricts its flow and makes it hard to compact.
The problems associated with excessive water are
as discussed in the following slides.
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Problem of Excessive Water in Concrete
.
Reference: Beware of excess water, Cement
Concrete & Aggregates Australia, March 2006:
Strength–The strength of the concrete, and hence it’s
ability to support loads, can be severely diminished by
too much water in the mix.
Cracking–As water evaporates from concrete during
the hardening process, there is a tendency for “early-
age cracking” and “drying shrinkage cracking”. The
width and extent of cracks will increase as the amount
of water is increased.
Delamination–If concrete is too wet when finished, it
could dry and shrink at the surface, which remaining
moist underneath, causing delamination to occur.
Abrasion / Surface Dusting -Excessive moisture in
concrete can lead to reduced abrasion resistance of the
surface, leading to ‘dusting’ and possibly to exposure of
the coarse aggregate
Durability–Concrete with excess water will be more
prone to penetration by water and salts , and may
exhibit increased risk of reinforcement corrosion and
spalling of the surface (concrete cancer).
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Source: Ryan, W.G. & Samarin,
A.,
Australian Concrete Technology,
Longman Cheshire, 1992
Problem of Excessive Water in Concrete Water / Cementitious Content
If water is added to concrete after it leaves the
batching plant, the amount of cement (and fly ash,
if used) stays the same, but the amount o f water
increases. Thus the ratio of water to cementitious
content drops.
This graph demonstrates how the strength of
concrete drops significantly as the water to
cementitious content increases.
Water to cementitious content in the range 0.45 to
0.80 is usual for conventional concrete, with 0.6
being common.
If just 25 litres of water is added to a cubic metre
of fresh concrete, the water to cemetitious content
would increase by approximately 17 % and the
compressive strength would drop by
approximately 20 %.
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Problem of Excessive Water in Concrete Specifying Slump
One means of controlling the proportion of water in
freshly mixed concrete is to specify an upper limit for
“slump”.
Historically, the choice of permissible slump was the
prerogative of the Engineer, and specifications of 80 mm
and 100 mm were common.
The Ryan & Samarinrecommendation for reinforced
footings is 50 mm to 100 mm, while the recommended
slump for pavements and slabs is 50 mm to 80 mm.
A value of 100 mm is now reflected in BCA Volume 2
Clause 3.2.3.1 (a) (iii).
Source: Ryan, W.G. & Samarin, A.,
Australian Concrete Technology,
Longman Cheshire, 1992
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Problem of Excessive Water in Concrete Slump Test
The fluidity of fresh concrete may be
measured by the slump test.
Concrete slump is determined by moulding
fresh concrete in a 300 mm high steel cone.
The mould is then removed and the fresh
concrete will settle. The slump (the distance
down from the top of the cone) can be
measured.
The slump test gives an indication of the
quantity of water in the fresh concrete,
although slump is also influenced by the
grading of the fine and coarse aggregate, the
shape of the aggregate and the quantity of
cement.
Foot plates
300
100
100
Handles
1.5 mm thick
galvanized sheet steel
cone
Slump
De-moulded
slumped
concrete
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Source: Readymix -The Effect of Excess Water in Concrete
http://www.readymix.com.au/Toolbox/DIY/excessWater.shtml
Similar information is available in:
Beware of excess water, Cement Concrete & Aggregates Australia, March 2006:
From this chart, it is clear that:
•If no other adjustments to a mix are made,
25% increase in slump from 80 mm to 100
mm could result in a reduction in strength
of approximately1.5 MPa (approximately
7.5% in 20 MPa concrete)
•If no other adjustments to a mix are made,
50% increase in slump from 80 mm to 120
mm could result in a reduction in strength
of approximately 25%.
This chart shows that as increasing
quantities of water are added, there
is a resulting loss of strength.
Problem of Excessive Water in Concrete Slump
The problem is best indicated by the loss in
concrete strength, resulting from excess water.
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Problem of Excessive Water in Concrete Site Practices
Often concrete with an initial slump of 80 mm will
stiffen rapidly, particularly in hot or windy
conditions.
Concretors will request that “water be added” to
the mixer trucks.
The addition is most often done, despite BCA
Volume 2 Clause 3.2.3.1 (b), which states,
“Water must not be added to the mix to increase
the slump to a value in excess of that specified”.
The consequence of refusal is the risk of
uncompacted and poorly finished concrete.
Because the water addition is made on site, there
is very little control, and the resulting concrete
most often has more water than necessary, with a
resulting unpredictable increase in the risk of
shrinkage, cracking and low strength.
Provided that no water is added on site, concrete
may be specified with a 100 mm slump.
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Concrete Problems & Solutions Footing Reinforcement
A common footing design is
1000 x 1000 x 500 with 10 mm
diameter reinforcement.
In some cases the reinforcement
diameter is too small and the
dimensions of bent bars are incorrect.
The diameter, dimensions
and position of
reinforcement should be
inspected before placing
concrete.
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Concrete Problems & Solutions Pad Footings
Do not put too much reinforcement
in the footings and ground beams.
It is just a waste of money.
Footings and ground
beamsshould have
enough, but not too
much reinforcement
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Concrete Problems & Solutions Thickness and Reinforcement in Concrete Slabs-on-Ground
Often concrete slabs-on-ground are
only 50 mm thick and do not
contain any steel reinforcement.
This can lead to cracking and
moisture penetration.
The thickness of slabs-on-ground
(that are bigger than 3.0 m x 3.0 m)
should be at least 70 mm thick with
at least SL42 steel reinforcement
mesh (3.8 diameter at 200 mm
centres) over compacted fill. If the
thickness is increased, so should the
reinforcement be increased.
Australia
The thickness of slabs-on-ground
should be 100 mm thick with at
least SL72 steel reinforcement over
compacted fill.
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Concrete Problems & Solutions Formwork
Edge forms for suspended concrete slabs are
often difficult to secure and keep straight.
When permanent steel sheet formwork is used,
preformed metal edge forms can also be
screwed to the sheeting by short metal straps.
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Concrete Problems & Solutions Reinforcement Cover
Steel reinforcement must be surrounded with sufficient thickness of well compacted concrete to
prevent corrosion of the steel and spalling of the concrete, commonly known as “concrete cancer”.
Suspended concrete roof
corrosion (India)
Concrete lintel reinforcement
corrosion (India)
Concrete wall corrosion
(Australia)
The lapping of welded fabric reinforcement in the top
face of a slab will significantly increase the thickness of
reinforcement and reduce the cover.
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Concrete Problems & Solutions Reinforcement Congestion
Congestion of reinforcement within beams,
columns and the like reduces the cover and
leads to difficulties in compacting the
concrete around the reinforcement. This can
cause both corrosion and loss of bond
between reinforcement and concrete.
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Concrete Problems & Solutions Vibration
The strength of concrete members (footings, slabs, beams,
and columns) is dependent on the density of the concrete.
Concrete density can be maximized by adequate mechanical
vibration.
Mechanical vibration is recommended for all concrete
members. Although AS 2870 does not make mechanical
vibration of residential footings and slab-on-ground
construction mandatory, it is strongly recommended.
Photo: Wacker
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Concrete Problems & Solutions Concrete Finishing
Mechanical trowelling is used to produce a fine surface.
However, if the concrete has not achieved sufficient
hardness, the mechanical trowel (helicopter) may “dig
into” the surface.
Excessive trowelling will lead to a concentration of bleed
water at the surface and eventual dusting and/or
abrasion of the surface.
Photo: Wacker
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Concrete Problems & Solutions Curing
Contractors often neglect the correct curing of slabs, resulting in excessive cracking and/or
dusting and abrasion. It may be expedient for the Builder to assume responsibility for applying
and maintaining the curing system.
Sprayed curing compounds require less attention than moistening and covering the slab for an
extended period. Curing compounds should comply with AS 3799 and shall be hydrocarbon,
solvent-based acrylic, water-based acrylic or wax-based acrylic. However, wax-based
compounds should not be used in areas requiring the subsequent application of curing
adhesives.
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Concrete Problems & Solutions Recesses in Concrete Slabs
In order to achieve falls in tiled floors in bathrooms and the like, it is preferable to recess the
concrete slabs, otherwise there will be a lip at the tiled edge. This recess may be formed after
the concrete has been screeded level. The corner position of recesses can be marked by fixing
temporary vertical reinforcing bars to the fabric. Such bars should not puncture the
membrane.
For large tiled areas, the slab should provide for uniform falls to wastes and associated
pipework. If there is likely to be difficulty in achieving such uniform falls, it may be advisable
to allow for a 40 to 50 mm screed laid subsequently by the tilerin accordance with AS 3958.1
Appendix A.. The thickness of the screed (if required), tile bedding and tiles should be shown on
the structural concrete details, to ensure that the finished levels are appropriate.
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Concrete Problems & Solutions Control Joints
Control joints in concrete structures should be of a material and detail such that they can
accommodate the movement that is expected.
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Concrete Problems & Solutions Termite Barriers
Care must be taken to ensure that any termite barrier can be properly located on the
finished concrete structure.
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Concrete Problems & Solutions Limits on Crack Widths
AS 2870 Residential slabs and footings
defines the following limiting crack widths.
To prevent termite penetration,
AS 3661.1-2000 Termite management
Part 1 New building workplaces a
limit of 1 mm on the permissible
width of cracks.
Source: AS 2870
Source: AS 3661.1
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Concrete Problems & Solutions Cracking Due to Excessive Retardant
Overdosing premixed concrete with retardant will cause excessive cracking and surface
defects consistent with the extremely slow hardening.
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Specifications
This module provides typical specifications,
summarised from the Electronic Blueprint.
More comprehensive editable building
specifications may be downloaded from:
www.electronicblueprint.com
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Scope
This section covers the construction of the following concrete members for residential
applications:
•Concrete footings
•Concrete ground beams
•Concrete slab-on-ground
•Concrete piers.
Other specifications cover:
•Concrete residential pavements and driveways
•Concrete that is incidental to drainage e.g. precast pits and thrust blocks,
•Concrete that is incidental to segmental paving and landscaping such as edging, and precast
concrete pavers,
•Concrete in retaining walls, such as footings and precast concrete blocks,
•Superstructures, comprising suspended beams, slabs, columns and stairs,
•Moisture and Tree Root Shields
•Masonry Fire Protection
•Termite protection systems for concrete slab-on-ground construction.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Relevant Standards
•AS 3600 Concrete Structures
•AS 3610 Formwork for concrete
•AS 3660.1 Termite management –New Building work
•AS 3660.2 Termite management –In and around existing buildings and structures –
Guidelines
•AS 3660.3 Termite management –Assessment criteria for termite management systems
•AS 1379 Specification and supply of concrete
•AS 1478.2 Chemical admixtures for concrete, mortar and grout
•AS 2870 Residential slabs and footings -Construction
•AS 3799 Liquid membrane-forming curing compounds for concrete
•AS 4200.1 Pliable building membranes and underlays-Materials
•AS/NZS 4671 Steel reinforcing materials
•AS 2159 Rules for the design and installation of piling (SAA Piling Code)
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Definitions
Site Classifications (based on AS 2870)
Class A –Most sand and rock sites with little or no ground movement from moisture
changes
Class S –Slightly reactive clay sites with only slight ground movement from moisture
changes
Class M –Moderately reactive clay or silt sites, which can experience moderate ground
movement from moisture changes
Class H –Highly reactive clay sites, which can experience high ground movement from
moisture changes
Class E –Extremely reactive sites, which can experience extreme ground movement from
moisture changes
Class P –Filled sites including soft or unstable foundation, soils, such as soft clay or silt or
loose sands, landslip, mine subsidence, collapsing soils, soils subject to erosion, reactive sites
subject to abnormal moisture conditions or sites which cannot be classified otherwise.
Note:
For deep-seated movements, typical of dry climates and corresponding to a design depth of
suction change equal to or greater than 3 metres, the classification Classes M, H and E shall be
modified to M-D, H-D or E-D.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Sand Bedding
A bedding sand layer 50 to 100 mm in thickness shall be placed over the compacted soil base to
the level of the underside of the slab.
Sand bedding shall comply with the relevant Standard (AS 2758.1).
Unless stated otherwise, sand shall be clean, free from salts, vegetable matter and impurities,
and with the following grading:
SievePercent Passing
4.75 mm90 to 100
2.36 mm60 to 100
1.18 mm30 to 85
0.600 mm 15 to 60
0.300 mm 5 to 30
0.150 mm 0 to 15
0.075 mm 0 to 10
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Vapour Barrier
Vapour barriers shall be placed over the bedding sand layer.
Adhesive tape shall be fixed around pipe penetrations.
Vapour barriers shall comply with the Drawings, Building Regulations and relevant Standard
(AS 4200). Unless stated otherwise, vapour barriers shall be not less than medium impact
resistance polyethylene vapour barrier 0.2 mm thick.
In areas of known salt damp, a damp-proofing membrane with high impact resistance is
required. Adhesive tape shall be PVC for normal applications, or polyethylene tape for fixing to
higher strength or thicker membranes.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Reinforcement for Concrete Slab on Ground and Footings
Reinforcement shall be placed in accordance with the drawings such that the following laps and
cover are achieved. Three N12 corner bars 2.0 metre long shall be placed at all re-entrant
corners.
ReinforcementMinimum Required Laps
Bars500 mm
Fabric2 cross wires overlapping
Trench mesh500 mm
Bar and Fabric Reinforcement
Reinforcement shall comply with AS 4671, AS 2870. Unless stated otherwise, properties shall be
not less than:
•Deformed bars -500 MPa, normal ductility (N)
•Square fabric, rectangular fabric and trench mesh -500 MPa, low (L) or normal (N)
ductility ribbed wires
•Fitments -500 MPa, low (L) or normal (N) ductility ribbed wires
•Round bar (e.g. R250 N10 for dowels) -250 MPa round.
Fibre Reinforcement
Fibre reinforcement used for enhancing toughness and impact resistance of concrete shall
comply with the relevant Standard (ASTM A820 Type 1 for steel fibres). Unless stated otherwise,
fibre reinforcement shall be polypropylene or steel fibres capable of being mixed uniformly
throughout the concrete.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Bar Chairs
Bar chairs shall be placed at one metre centres both ways. Bar chairs shall incorporate wide
bases and be placed on metal bases that do not puncture the vapour barrier.
Where fabric with 7 mm bars at 200 mm centres (SL72), or lighter, is used, the bar chair spacing
shall be reduced to 800 mm.
Bar chairs shall be placed to give the following clear cover.
•40 mm in concrete in contact with unprotected ground
•40 mm in concrete exposed externally
•30 mm to a sealed vapour barrier
•20 mm to the internal surface
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Concrete for slab on ground and footings
Concrete shall comply with AS 2870. Unless stated otherwise, properties shall be not less than:
•Characteristic compressive strength of 20 MPa (Strength grade N20)
•Maximum aggregate size of 20 mm
•Of sufficient slump to facilitate the nominates means of placement
•Subject to plant control testing.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Placing Concrete
Trenches and footing excavations shall be dewatered and cleaned prior to concrete placement so
that no softened or loosened material remains. All concrete shall be compacted by mechanical
immersion vibrator.
Notes
Formwork -Edge forms for suspended concrete slabs are often difficult to secure and keep
straight. When permanent steel sheet formwork is used, preformed metal edge forms may
also be screwed to the sheeting by short metal straps.
Reinforcement Cover -The lapping of welded fabric reinforcement in the top face of a slab
will significantly increase the thickness of reinforcement and reduce the cover. The slab
thickness shall be such as to provide both sufficient cover and sufficient effective depth.
Finishing Concrete
Concrete surfaces shall be finished as noted below unless specified otherwise.
•Floor slabs -Steel float.
•External paths, driveways and parking areas at less than 10% slope -Fine broomed steel
float.
•External paths, driveways and parking areas at greater than 10% slope -Coarse broomed
steel float.
•Vertical surfaces exposed in the completed building -Rubbed back to fill all voids and
provide smooth surface.
•Vertical surfaces not exposed in the completed building -Off form finish.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Recesses in Concrete Slabs
In order to achieve falls in tiled floors in bathrooms and the like, recess the concrete slabs to
avoid a lip at the tiled edge. This recess may be formed after the concrete has been screeded
level. The corner position of recesses may be marked by fixing temporary vertical reinforcing
bars to the fabric. Such bars should not puncture the membrane.
For large tiled areas, the slab should provide for uniform falls to wastes and associated
pipework. If there is likely to be difficulty in achieving such uniform falls, it allow for a 40 to 50
mm screed laid subsequently by the tiler. The thickness of the screed (if required), tile bedding
and tiles should be shown on the structural concrete details, to ensure that the finished levels are
appropriate.
Curing Concrete
All concrete shall be cured using a sprayed curing compound.
Wax-based compounds shall not be used in areas requiring the subsequent application of curing
adhesives.
Notes
1. The Builder shall;
Apply and maintain the curing system; or
Ensure that the Contractor correctly applies and maintains the curing system.
2. Sprayed emulsions require less attention than moistening and covering the slab.
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Specifications –Footing, Ground Beams, Slab-on-Ground, Piers
Formwork
Formwork shall comply with the relevant Standard (AS 3610).
Key Joint Form
Key joint forms shall comply with the Drawings, Building Regulations and relevant Standard
(AS 2870). Unless stated otherwise, key joint forms shall provide keys in 100, 150 or 200 mm
slabs, and shall include all required wedges and pegs. Where a control joint is to be constructed
with a flexible sealant, a polyethylene foam strip shall be inserted. Otherwise a PVC capping
strip shall be inserted. Unless stated otherwise, the colour shall be grey.
Stripping Formwork
Unless adverse weather or the use of retarders delays the hardening of concrete, the minimum
stripping time for formwork shall be 3 days.
Maintenance
The building owner is responsible for the building and site maintenance as detailed in the
CSIRO Pamphlet 10-19 Guide to Home Owners on Foundation Maintenance and Footing
Performance.
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Specifications –Concrete Superstructures
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Specifications –Concrete Superstructures
Scope
This section covers the construction of reinforced concrete superstructures, including beams,
columns, suspended slabs, stairs and walls.
Building Regulations and Standards
All materials and construction shall comply with the most recent version of:
the relevant parts of the Building Regulations:
•the Standards referred to therein;
•other Standards nominated in this specification; and
•other relevant Regulations.
Relevant Standards
•AS 3600 Concrete Structures
•AS 3610 Formwork for concrete
•AS 1379 Specification and supply of concrete
•AS 1478.2 Chemical admixtures for concrete, mortar and grout
•AS 3799 Liquid membrane-forming curing compounds for concrete
•AS/NZS 4671 Steel reinforcing materials
•AS 3850 Tilt-up concrete construction
•AS 1538 Cold formed steel structures code
•AS 1397 Steel sheet and strip
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Specifications –Concrete Superstructures
Reinforcement
Reinforcement shall be placed in accordance with the Drawings and the relevant Standard (AS
3600).
Unless specified otherwise on the drawings, structural laps shall be as follows:
N 12 bars 500 mm
N 16 bars 650 mm
N 20 bars 800 mm
N 24 bars1100 mm
Fabric 2 cross wires overlap
In slabs, bar chairs shall be placed at one metre centres both ways.
Unless specified otherwise in the Drawings or Standard, bar chairs shall provide cover not less
than the following:
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Specifications –Concrete Superstructures
Minimum Cover Requirements
for Standard Formwork and Compaction (mm)
Characteristic Compressive Strength of Reinforced
Concrete
Exposure
Classification
20 MPa25 MPa32 MPa40 MPa50 MPa
A12020202020
A2(50)30252020
B2(60)403025
B1(65)4535
C(70)50
Note:
These values may need to be increased to comply with the particular
Standard. The values in brackets apply when the exposure is to only one
surface.
Minimum Cover Requirements
for Rigid Formwork and Intense Compaction (mm)
Characteristic Compressive Strength of Reinforced
Concrete
Exposure
Classification
20 MPa25 MPa32 MPa40 MPa50 MPa
A11515151515
A2(35)20151515
B2(45)302520
B1(50)3525
C(55)40
Note:
These values may need to be increased to comply with the particular
Standard.
The values in brackets apply when the exposure is to only one surface.
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Specifications –Concrete Superstructures
In reinforced or prestressed concrete structrures:
Exposure Environment A1includes:
members in contact with the ground and protected by a damp-proof membrane,
residential footings in non-aggressive soils,
members in interior environments fully enclosed within a building except for a brief period of weather exposure during construction,
members in exterior environments above ground and further than 50 km from the coast, being non-industrial and arid climate
Exposure Environment A2 includes:
other members in non-aggressive soils
members in exterior environments above ground and further than 50 km from the coast, being non-industrial and temperate climate
Exposure Environment B1 includes:
members in interior environments in industrial buildings, being subject to repeated wetting and drying
members in exterior environments above ground and further than 50 km from the coast, being non-industrial and tropical climate
members in exterior environments above ground and further than 50 km from the coast, being industrial and any climate zone
members in exterior environments above ground and 1 km to 50 km from the coast, in any climate zone
members in fresh water
Exposure Environment B2 includes:
members in exterior environments above ground and up to 1 km from the coast (excluding tidal splash zones), in any climate zone
members permanently submerged in sea water
Exposure Environment C includes :
members tidal splash zones
Exposure Environment U includes:
members in aggressive soils
members in soft or running water
members in exposures other than those described above
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Specifications –Concrete Superstructures
Reinforcement
Reinforcement shall comply with the relevant Standard (AS 4671).
Unless stated otherwise, properties shall be not less than:
•Deformed bars -500 MPa, normal ductility (N)
•Square fabric, rectangular fabric and trench mesh -500 MPa, low (L) or normal (N)
ductility ribbed wires
•Fitments -500 MPa, low (L) or normal (N) ductility ribbed wires
•Round bar (e.g. R250 N10 for dowels) -250 MPa round
Bar Chairs
Bar chairs shall be placed at one metre centres both ways. Bar chairs shall incorporate wide
bases and be placed on metal bases that do not puncture the vapour barrier. Where fabric with 7
mm bars at 200 mm centres (SL72), or lighter, is used, the bar chair spacing shall be reduced to
800 mm. Bar chairs shall be placed to give the following clear cover.
•40 mm in concrete exposed externally
•20 mm to the internal surface
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Specifications –Concrete Superstructures
Concrete
Concrete shall comply with the relevant Standard (AS 3600).
The Drawings shall state the required strength and aggregate size for each member.
Unless stated otherwise, properties for low rise construction shall be not less than:
•Characteristic compressive strength of 32 MPa (Strength grade N32)
•Maximum aggregate size of 20 mm
•Of sufficient slump to facilitate the nominates means of placement
•Subject to plant control testing.
Curing Compounds
Curing compounds shall comply with the relevant Standard (or AS 3799).
Unless stated otherwise, curing compounds shall be hydrocarbon, solvent-based acrylic, water-
based acrylic or wax-based acrylic. Wax-based compounds shall not be used in areas requiring
the subsequent application of curing adhesives.
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Specifications –Concrete Superstructures
Placing Concrete
Trenches and footing excavations shall be dewatered and cleaned prior to concrete placement so
that no softened or loosened material remains.
All concrete shall be compacted by mechanical immersion vibrator.
Notes
Formwork -Edge forms for suspended concrete slabs are often difficult to secure and keep
straight. When permanent steel sheet formwork is used, preformed metal edge forms may
also be screwed to the sheeting by short metal straps.
Reinforcement Cover -The lapping of welded fabric reinforcement in the top face of a slab
will significantly increase the thickness of reinforcement and reduce the cover. The slab
thickness shall be such as to provide both sufficient cover and sufficient effective depth.
Finishing Concrete
Concrete surfaces shall be finished as noted below unless specified otherwise.
•Floor slabs -Steel float.
•Vertical surfaces exposed in the completed building -Rubbed back to fill all voids and
provide smooth surface.
•Vertical surfaces not exposed in the completed building -Off form finish.
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Specifications –Concrete Superstructures
Recesses in Concrete Slabs
In order to achieve falls in tiled floors in bathrooms and the like, recess the concrete slabs to
avoid a lip at the tiled edge. This recess may be formed after the concrete has been screeded
level. The corner position of recesses may be marked by fixing temporary vertical reinforcing
bars to the fabric. Such bars should not puncture the membrane.
For large tiled areas, the slab should provide for uniform falls to wastes and associated
pipework. If there is likely to be difficulty in achieving such uniform falls, it allow for a 40 to 50
mm screed laid subsequently by the tiler. The thickness of the screed (if required), tile bedding
and tiles should be shown on the structural concrete details, to ensure that the finished levels are
appropriate.
Curing Concrete
All concrete shall be cured using a sprayed curing compound.
Wax-based compounds shall not be used in areas requiring the subsequent application of curing
adhesives.
Notes
1. The Builder shall;
Apply and maintain the curing system; or
Ensure that the Contractor correctly applies and maintains the curing system.
2. Sprayed emulsions require less attention than moistening and covering the slab.
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Specifications –Concrete Superstructures
Permanent Formwork
Formwork shall comply with the relevant Standard (AS 1538, AS 1397).
Unless stated otherwise, permanent formwork shall be:
•Cold-rolled steel
•Manufactured from galvanised steel base material of thickness 0.75 mm, 0.90 mm or 1.00
mm (as nominated on the drawings)
•With 550 MPa yield strength
•With a galvanised coating not less 200 gm/m
2
(Z200).
Formwork
Formwork shall comply with the relevant Standard (AS 3610).
Stripping Formwork
Minimum stripping time for formwork shall be 14 days.
No masonry shall be constructed on slabs that are still supported by props.
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Sample Inspection Schedules
This sample inspection schedule defines a
minimum level of control that should be
exercised by a builder during construction.
It is not intended for use by licensed
tradesmen, installers or authority inspectors,
who would need to apply more rigorous
inspections.
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Construction Checklist
Builder:
Site:
Activity: Cast in-situ Concrete Piers
Item or Product Inspection RequiredAccept CriteriaHold
Witness
DateInspectorComment
Drawings & specificationsInspect controlled docsLatest issue on siteHold
Pier location
Check grid
Check hole position
+,-50mm
+,-50mm
Hold
Hold
Pier diameterCheck auger diameterAs specifiedHold
Founding materialVisual inspectionAs specifiedHold
Pier depth
Measure depth or
monitor volume
+,-20%Hold
Casing (if required)Measure diameter+ 20mm ,-10mm Hold
Reinforcement gradeSpot check markingsAs specifiedHold
Reinforcement diameterSpot check diameterAs specifiedHold
Reinforcement spacingSpot check+,-10%Hold
Reinforcement lapsSpot check+,-10%Hold
Reinforcement ligatures spacingSpot check+,-10%Hold
Concrete strengthSpot check docketsAs specifiedWitness
Copyright: Quasar Management Services Pty Ltd
Construction Checklist
Builder:
Site:
Activity: Concrete Footings, Ground Beams, Slab-On-Ground
Item or Product Inspection RequiredAccept CriteriaHold
Witness
DateInspectorComment
Drawings & specificationsInspect controlled docsLatest issue on siteHold
Footing widthSpot check+ 10%,-2%Hold
Footing lengthSpot check+ 10%,-2%Hold
Reinforcement coverCheck chair sizeAs specifiedHold
Edge formsCheck all edges+,-20 mmHold
Level on sand bedSpot check levels+ 10 mm, -30mmHold
Membrane and tapeSpot check tapingAs specifiedHold
Reinforcement gradeSpot check markingsAs specifiedHold
Reinforcement diameterSpot check diameterAs specifiedHold
Reinforcement spacingSpot check+,-10%Hold
Reinforcement lapsSpot check+,-10%Hold
Reinforcement ligature spacingSpot check+,-10%Hold
Plumbing roughed-inCheck all positions+,-50 mmHold
Concrete strengthDelivery docketsAs specifiedWitness
CuringSpot checkAs specifiedWitness
Copyright: Quasar Management Services Pty Ltd
Construction Checklist
Builder:
Site:
Activity: Concrete Superstructures
Item or Product Inspection RequiredAccept CriteriaHold
Witness
DateInspectorComment
Drawings & specificationsInspect controlled docsLatest issue on siteHold
Beam & column widthSpot check forms+ 10%,-2%Hold
Beam & column depthSpot check forms+ 10%,-2%Hold
Slab and stair depthSpot check forms+ 10%,-2%Hold
Reinforcement coverCheck chair sizeAs specifiedHold
Reinforcement gradeSpot check markingsAs specifiedHold
Reinforcement diameterSpot check diameterAs specifiedHold
Reinforcement spacingSpot check+,-10%Hold
Reinforcement lapsSpot check +,-10%Hold
Reinforcement ligature spacingSpot check+,-10%Hold
Plumbing & electrical roughed-inCheck all positions+,-50 mmHold
Concrete strengthDelivery docketsAs specifiedWitness
CuringSpot checkAs specifiedWitness
Copyright: Quasar Management Services Pty Ltd
Safety & Emergency Work Method Statements
All work shall be carried out in a safe manner,
minimizing risk of injury and fatality.
Work Method Statements, relevant to the particular
project, must be prepared in accordance with the
applicable legislation and regulations, for inclusion
as part of a site-specific Safety & Emergency Plan
and Job Safety Analysis.
Sample Work Method Statements for construction
activities are available in a Training Package,
“Site Safety” from www.electronicblueprint.com.
They are intended to demonstrate the principles
relevant to site safety for this form of construction.
However, they are not intended to be a complete list
of all requirements.
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Disclaimer&Copyright Disclaimer
This training package covers broad engineering principles and building practices, with
particular emphasis on affordable housing and associated village infrastructure in the Asia-
Pacific region. These broad principles and practices must be translated into specific
requirements for particular projects by professional architects, engineers or builders with the
requisite qualifications and experience. Associated sample specifications and drawings are
available in electronic format, with the express intention that architects, engineers and builders
will edit them to suit the particular requirements of specific projects. The design, construction
and costing of structures must be carried out by qualified and experienced architects, engineers
and builders, who must make themselves aware of any changes to the applicable standards,
building regulations and other relevant regulations. The authors, publishers and distributors of
these documents, specifications and associated drawings do not accept any responsibility for
incorrect, inappropriate or incomplete use of this information.
Copyright
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Allrightsarereserved.Permissionisgivenforindividualstousethismaterialinthe
preparationofdesigns,specificationandcontractsforindividualprojects.Permissionisalso
givenfornot-for-profitNongovernmentalOrganizationstousethismaterialinthepreparation
ofBuildingSkillsTrainingProgramsandforthedesign,specificationandconstructionof
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