The cement used for the slurry is usually
Type 1 Portland Cement although other cements can be used.
If sand is specified in the mix design ideally it should be
fine with 2mm maximum size and 60 to 90% passing through a
600 micron sieve (8). Other ingredients such as Pulverized
Fuel Ash (PFA) can also be used. The water:cement ratio of
the slurry is usually between 0.5 and 0.6. If necessary more
water can be added to increased the workability. However it
is important not to use too little water in the slurry since
this can cause water to be drawn out of the foam.
The slurry can be made using a readymix
truck mixer. Firstly, the cement mortar slurry is made at
the batching plant, according to the mix design, by either
the DRY or WET method.
When using the DRY method the ingredients
are loaded, in their correct proportions, by ‘ribbon
feeding’, into the drum of a ready mix truck, where they are
For the WET method all the ingredients
are loaded into a high speed blade mixer and thoroughly
mixed, before being transferred to the readymix truck. The
WET method gives a better quality slurry.
The mortar slurry is then transported to
site, and the foam is added there, and not at the batching
Some batching plants are reluctant to
make mortar slurries, as they can stick to the insides of
the drum, making them hard to clean. However, this is not a
problem when making foamed concrete for several reasons:
more water is used in the slurry making
it less likely to stick
when the foam is added, the foamed
concrete is very fluid
the foam itself has a cleaning action.