Until several decades ago, concrete primarily
contained portland cement, aggregate and water.
This allowed the coarse aggregate to dictate the water content, and the amount
of water in the concrete to determine the slump. Concrete with a lower slump value contained
less water and resulted in a better quality of concrete. Today much of the concrete we produce is a
blend of not only cement and aggregate but admixtures, fibers and polymers. This means the aggregate is not the only thing
that influences the amount of water added.
Now other factors are considered to determine the proper consistency.
So what is slump? It is defined as the measure of the
consistency of a specific batch of fresh concrete. To determine the slump, a simple test is done
that measures the amount of water added to the mix. The test is done using an Abrams slump cone,
which is a bottomless, 12” high circular cone with a base 8” in diameter and a top
4” in diameter.
The cone is placed on a level,
impermeable surface and filled in three stages with equal amounts of
concrete. Each layer is tamped down
using a special rod to make sure the concrete is compacted and leveled off with
the top of the cone. The cone is then carefully removed and the concrete is
left to settle or “slump.” Placing the
cone alongside the pile of concrete, the height of the concrete is compared to
the top of the slump cone and measured to the nearest 5mm. Wikipedia states, “The slumped concrete takes
various shapes, and according to the profile of slumped concrete, the slump is
termed as true slump, shear slump or collapse slump.”
A true slump is where the concrete
simply subsides but generally maintains its shape, whereas in a shear slump,
the top portion of the concrete shears off.
A collapse slump generally means the mix is too wet, or it may be a case
of a high workability mix that needs to have a flow test done rather than a
slump test.
Conco is a leading supplier of
concrete services for the Western United States. We have built our reputation by
offering superior concrete formwork, reinforcing, place and finish, shotcrete
and other ancillary services that benefit from our vast experience. The Conco Companies have four regional
offices to serve California, Oregon, Washington, Nevada and Colorado.
Source: concrete.org.uk/fingertips_nuggets.asp?cmd=display&id=559
en.wikipedia.org/wiki/Concrete_slump_test
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