Bagged concrete mix is ideal for
small to medium sized jobs around the home or work place.
 Available
in 20 kg bags, bagged concrete mix is a blend of cement,
sand and aggregate. All the user must do is add water. It is well
suited for small to medium sized jobs such as floors, patios,
steps, setting fence posts or columns, barbeque foundations,
garden paths and edging, drains and gutters.
Allowing for waste you will need about 110 x 20kg
bags of concrete per cubic metre which makes it unsuitable as well
as uneconomical for larger jobs, although in situations where
access or cleaning up is difficult, for example high rise
buildings or environmentally sensitive areas convenience can
sometimes outweigh economics.
The table below shows some typical applications
where bagged concrete could be used and the number of 20kg bags
that would be required. The single carport example shows how
impracticable it would be to use bagged concrete for large jobs.
|
|
Length |
Width |
Depth |
Bags |
|
Two-bag volume |
900mm |
200mm |
100mm |
2 |
|
Post hole |
250mm |
250mm |
500mm |
4 |
|
Path |
900mm |
1m |
75mm |
8 |
|
Single carport |
6m |
3.5m |
100mm |
220+ |
For larger jobs ready mixed concrete delivered to your home is
a much better and cheaper option. Most companies will supply as
little as .3 cubic metres (mini load) and you only have to tell
the company what you need it for and they will mix the right
strength for your application.
Some typical quantities that you may need for common projects
are shown below.
|
|
Length |
Width |
Depth |
Amount m3 |
|
Brick footings |
per metre |
300mm |
300mm |
0.1 |
|
Shed slab |
2m |
2m |
100mm |
0.4 |
|
Single carport |
6m |
3.5m |
100mm |
2.1 |
When working out your concrete requirements you will be working
with area and volume. Below are a few hints on working with both.
AREA
Area is generally simple to calculate using basic arithmetic.
Just make sure you use the same units for all measurements.
Irregular areas with straight sides can be most easily worked out
by breaking them up into smaller rectangles and triangles. You can
then calculate the areas separately and add them all up to make
the total.
The easiest way to work out the area of a more complicated
layout is with a scale drawing, ruled off in metre or half-metre
squares. Simply total the squares, averaging out the part-squares,
or preferably counted as whole squares, leaving the excess as an
allowance for wastage.
VOLUME
Volume equates simply to (area) multiplied by (thickness).
Remembering that for things like drives, paths or other paved
areas, the horizontal dimensions will probably be worked out in
metres and the thickness in millimetres. Make sure decimal points
are in the right place. e.g. 75mm = 0.075metres. |
