Aggregate is the particulate material
that provides structure to concrete, such as sand, gravel, and crushed stone.
Choosing the appropriate aggregate for the concrete mixtures is extremely
important to the performance of the concrete. Aggregate can occupy up to 75%
volume of the concrete. There are also more recent types of concrete, such as Confoam by Conco, that use only fine aggregate to create lightweight concrete.
That means that the choice of aggregate greatly affects the strength, weight,
cost, and other properties of the concrete.
The main categories of aggregate are
mined aggregate, smelting slag waste, and recycled concrete. Mined aggregate is
what is most commonly thought of when referring to aggregate. Slag refers to
the by-product remaining after the desired metals are extracted from raw ore.
Recycled concrete, also known as crushed waste concrete, is created using
conventional stone crushing equipment on concrete, after which concrete rebar must be removed and
then the resulting aggregate is washed and graded.
Size of aggregate
The American
Society for Testing and Materials (ASTM) publishes the standard classification
for sizes of aggregate for different construction uses. Finer aggregate is
generally made from sand or crushed stone and is 0.2 inches or less. On the
other side of the spectrum, coarse aggregate is usually between 0.375 and 1.5
inches in size. Aggregate particles get sorted with wire-mesh sieves comprised
of square openings the size specified by ASTM and others. Generally both coarse
and fine aggregates are combined in the concrete mix to control workability,
pumpability, and shrinkage.
Choosing the right aggregate
Aggregate must conform to stringent standards to perform to design specifications. This includes not only
the size but also the cleanliness and hardness of the aggregate. If clay or
other fine materials are on the surface of aggregate it can impact how the
cement paste bonds with each particle. Additionally, the moisture content of
the aggregate must be considered when creating the mixture to ensure that the
right amount of water remains after the aggregate absorbs water. Also,
considering the abrasion and skid resistance of the aggregate is essential for
surfaces that will be subject to wear, such a floors and pavements where harder
aggregate must be used.
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. Please contact us for more information about our full
range of premium Portland area concrete services including shotcrete.
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