Slump is the measure of the
consistency in a specific batch of fresh concrete. A slump test accesses the consistency of the fresh
concrete, and to ensure that the correct amount of water has been added to the
mix.
To conduct the test, an Abrams slump cone is used, a bottomless, 12” high circular cone with an 8” in diameter base and a 4” in diameter top. 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.”
The slump cone is placed alongside the
pile of concrete in order to measure the height of the concrete in comparison
to the top of the cone. Measurements are
taken 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.”
If the concrete simply subsides but
generally maintains its shape, it is considered to be a true slump. In the case of a shear slump, the top portion
of the concrete shears off. If the test
results in a “collapse slump”, it typically indicates the mix is too wet; or it
may be a high workability mix that needs to have a flow test done rather than a
slump test.
Up until just a few decades ago,
concrete was made from portland cement, aggregate and water. In this type of concrete mix, the coarse
aggregate dictated the water content, and 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 and other factors have to be
considered to determine the proper consistency of the concrete.
At The Conco Companies, we are one of
the leading concrete contractors in the Western U.S. and offer a wide range of
quality services and products. Our
experience includes providing services for commercial, educational, parking and
other construction development as well as public works projects. We serve California, Washington State,
Oregon, Colorado and Nevada.
Sources: concrete.org.uk/fingertips_nuggets.asp?cmd=display&id=559
en.wikipedia.org/wiki/Concrete_slump_test
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