A recent change to AS 1379, the Australian Standard for the specification and supply of concrete, has set a default slump for concrete used in residential slabs and footings. This means that concrete will now be supplied at a default slump of 100mm in cases where the customer has not specified a slump.
The change to the Standard is an initiative of industry association, Cement Concrete and Aggregates Australia (CCAA), aimed at improving the consistency and quality of concrete used in residential slabs and footings.
When concrete is supplied to site at a slump of 80mm, the concrete placer often asks the driver to add water in order to make the concrete easier to place and compact. However concrete that is not designed for higher slumps can often result in a loss of strength in the concrete, as well as problems such as cracking and dusting, when uncontrolled water is added on site.
Understandably, the concrete supplier cannot take responsibility for concrete when this happens.
The change to the Standard is aimed at encouraging house builders and concrete placers to nominate a concrete slump that is suitable for the intended placing method (for example chute, pump) as well as where the concrete is to be placed (thin sections, congested reinforcing. This, in turn, will reduce the likelihood of complaints and expensive call-backs for house-builders.
CCAA and their member companies in the premixed concrete industry have launched an information campaign - comprising a DVD, posters and brochures - to alert the housing industry to the change.