NCC 2019 Volume Two
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Part 3.2.3 Concrete and reinforcing
3.2.3.1 Concrete
Concrete must comply with the following:
(a)
Concrete must be manufactured to comply with AS 3600; and—
(i)
have a strength at 28 days of not less than 20 MPa (denoted as N20 grade); and
(ii)
have a 20 mm maximum nominal aggregate size; and
(iii)
have a nominal 100 mm slump.
(b)
Water must not be added to the mix to increase the slump to a value in excess of that specified.
(c)
Concrete must be placed, compacted and cured in accordance with good building practice.
State and Territory Variations
State and Territory Variations
In South Australia after 3.2.3.1(c) insert SA 3.2.3.1(d), (e), (f) and (g) as follows:
(d)
Concrete in slabs must be adequately compacted, and slab surfaces, including edges, moist cured for 7 days.
(e)
After vertical surfaces are stripped of formwork, slab edges must be finished prior to curing.
(f)
Loading of concrete slabs with stacked materials or building plant must not occur for a minimum of 7 days after pouring although construction of wall frames and setting out brickwork may be undertaken during this period.
(g)
Concrete must not be poured if the air temperature on site exceeds 32ºC unless written instructions from a professional engineer are followed.
Explanatory information:
Explanatory information:
- Complete discharge of the concrete from the truck should be made within one and a half hours of initial mixing with water unless a suitable retarder has been specified.
- Compacting concrete by vibration removes air pockets and works the concrete thoroughly around reinforcement, service penetrations etc. and into corners of formwork to increase durability and resistance to termite infestation and salt damp attack. Care should be taken not to over-vibrate. The finishing and curing of slab edges provides an improved edge finish which is resistant to edge dampness.
- Care should be taken when using chemical curing methods, because some products may not be compatible with adhesives used to fix surface finishes to the slab.
3.2.3.2 Steel reinforcement
(a)
Materials used for reinforcing steel must comply with AS 2870 and be—
(i)
welded wire reinforcing fabric; or
(ii)
trench mesh; or
(iii)
steel reinforcing bars.
(b)
Steel reinforcing bars may be substituted for trench mesh in accordance with Table 3.2.3.2.
Explanatory information:
Explanatory information:
Reinforcement types referenced in this Part are described as follows:
- Square mesh is designated in terms of the diameter of each bar and the spacing of consecutive bars. For example, SL62 consists of 6 mm bar at 200 mm spacings.
- Trench mesh is designated in terms of the number of longitudinal bars and the diameter of each bar. For example, 3-L11TM consists of 3 longitudinal bars each of which are 11 mm in diameter.
- Reinforcing bars are designated in terms of the number of bars and the diameter of each bar. For example, 6-N12 consists of 6 bars each of which are 12 mm in diameter.
(c)
Minimum laps for reinforcement as shown in Table 3.2.3.1 and Figure 3.2.3.1 must be provided where reinforcing is used.
Table 3.2.3.1 Minimum lap for reinforcement
|
Reinforcement |
Minimum splice |
Minimum Lap at “T” intersections |
Minimum Lap at “L” intersections |
|
Steel reinforcing bars |
500 mm |
Full width across the junction |
One outer bar must be bent and continue 500 mm (min) around corner |
|
Trench mesh |
500 mm |
Full width across the junction |
Full width across the junction |
|
Square and Rectangular Mesh |
The two outermost transverse wires of one sheet must overlap the two outermost transverse wires of the other |
Not applicable |
Not applicable |
Figure 3.2.3.1
Table 3.2.3.2 Alternative mesh/reinforcing bar sizes
|
Trench mesh (TM) |
Area — mm 2 |
Reinforcing bar alternative |
Trench mesh alternative |
|
2–L8TM |
91 |
2-N10 or 1-N12 |
Not applicable |
|
3–L8TM |
136 |
2-N10 or 2-N12 |
Not applicable |
|
4–L8TM |
182 |
2–N12 |
2–L11TM |
|
5–L8TM |
227 |
2–N12 |
3–L11TM |
|
2–L11TM |
180 |
1-N16 or 2-N12 |
2x2-L8TM |
|
3–L11TM |
270 |
3–N12 |
2x3-L8TM |
|
4–L11TM |
360 |
2-N16 |
2x4-L8TM |
|
2–L12TM |
222 |
2–N12 |
3–L11TM |
|
3–L12TM |
333 |
3-N12 |
4–L11TM |
|
4–L12TM |
444 |
4-N12 |
5–L11TM |
Notes to Table 3.2.3.2 :
1.
Where necessary 2 layers of mesh may be used.
2.
L11TM and L12TM may be replaced by RL1118 and RL1218 mesh respectively.
3.
L11TM may be replaced by two layers of L8TM.
(d)
Footings and slabs-on-ground must have concrete cover between the outermost edge of the reinforcement (including ligatures, tie wire etc.) and the surface of the concrete of not less than the following:
(i)
40 mm to unprotected ground.
(ii)
30 mm to a membrane in contact with the ground.
(iii)
20 mm to an internal surface.
(iv)
40 mm to external exposure.
(e)
Reinforcement must be cleaned of loose rust, mud, paints and oils immediately prior to the concrete pour.
Explanatory information:
Explanatory information:
In order to obtain a good bond between concrete and reinforcement, the reinforcement should be free of contamination by mud, paint, oils, etc. It is not necessary for the reinforcement to be completely free of rust. Some rusting is beneficial in promoting a good bond as it roughens the surface of the steel. Loose rust, however, must be removed from the reinforcement.
(f)
Reinforcement must be placed as follows:
(i)
All reinforcement must be firmly fixed in place to prevent it moving during concreting operations.
(ii)
Reinforcement must be supported off the ground or the forms by bar chairs made from wire, concrete or plastic.
(iii)
When using wire chairs the minimum concrete cover (see 3.2.3.2(d)) to the uncoated portion of the chair must be obtained.
(iv)
Wire chairs on soft ground or plastic membrane must be placed on flat bases.
(v)
Bar chairs must be spaced at not more than 800 mm centres for steel fabric.
Explanatory information:
Explanatory information:
Reinforcement is designed to be in a particular place so as to add strength or to control cracking of the concrete. A displacement from its intended location could make a significant difference to the life or serviceability of the structure.
Supports for fabric reinforcement are provided to prevent the fabric distorting when workers walk on top of it to place the concrete and maintain the correct concrete cover to the fabric.