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Aggregates 101: What are They and for What are they Used?

Wednesday March 3, 2021 comments Tags: aggregates, construction materials

 

Aggregate is essentially a fancy word for dirt. There are, however, many different types of aggregates and each type has a different purpose.

An aggregate is composed of one or more kinds of rock fragments to form one collection of material. Construction aggregate specifically includes types of aggregate from coarse, to medium-grained particle-material. The categories of aggregates include gravel, sand, recycled concrete, topsoil, ballast, and geosynthetic aggregates (synthetic products commonly used in civil engineering projects used to stabilise terrain). 

The many uses of aggregates can be organized into three categories:

  1. Load-Bearing Materials
  2. Filling Materials
  3. Infiltrating Materials

 

The most common use for aggregate materials is mixing concrete. Aggregates would be mixed with cement to bolster volume, increase stability, and reduce erosion of the finished product. Fine aggregate makes up the concrete that immediately comes to mind when we hear the term, i.e. grey sidewalk concrete. Examples of fine aggregates would be sand, crushed stone, and crushed slab screenings. For bigger and thicker concrete slabs, coarse aggregates like gravel, stone fragments, and slag would be used to form a super strong concrete. Often, a mixture of fine and coarse aggregates is used to further strengthen the material.

Another common use of aggregate materials is mixing mortar. Mortar is a building construction material used to bond stone, brick, tile, or concrete blocks into a structure. Aggregates are mixed with cement and water to form a viscous substance. Mortar is pliable enough to be spread with a trowel but strong enough to hold heavy building materials.

Roadways also utilize aggregates for stabilization. They help distribute the heavy load of vehicles to avoid cracking and facilitate ground water running off the road to keep drivers safe.

Believe it or not, the medium-sized rocks surrounding railroad tracks are also considered an aggregate! Loaded trains weigh upwards of a thousand pounds. In order to keep the railway ballasts from breaking, that weight must be properly distributed and guided into the ground. A coarse, tough aggregate such as crushed granite is used to support the rails and distribute the weight of the train. Using such large particles also ensures maximum drainage to avoid the dangers of standing water on the tracks.

Other uses of aggregates include, of course, any and all projects that call for filler materials. We encounter this type of aggregate on a daily basis! Baseball fields, public parks, golf bunkers, etc. all require fill dirt!