What Makes a Good Concrete Aggregate?

To achieve a high-quality concrete mix, the aggregates used must be clean, hard, and strong particles that are free from absorbed chemicals or coatings of clay and other fine materials that could cause deterioration. The aggregate is also essential for the strength, thermal and elastic properties, dimensional stability, and volume stability of concrete. Optimizing the grading based on aggregate availability and project requirements will result in cost-effective concrete with good workability and finishability. This article provides an overview of the most important factors to consider when selecting and dosing concrete aggregate. Recycled concrete is created by breaking, removing, and crushing existing concrete to a preferred size.

Aggregates are a broad category of materials such as sand, gravel, crushed stone, slag, and recycled concrete aggregate. Although cement and concrete are often used interchangeably, cement is actually an ingredient in concrete. If their absorption is not satisfied, these sponges steal water from the designated amount of mixing water, reducing concrete settling. The use of non-potable water or water of unknown purity can jeopardize the quality and workability of concrete. Excess sanding is also used when pumping concrete to allow better flow as well as when swaging concrete to allow finer details.

The absorption and surface moisture of aggregates are simple but critically important aspects of producing concrete that consistently achieves the specified or desired strength. Changes in gradation, maximum size, unit weight, and moisture content can alter the character and performance of the concrete mix. This development and hardening process continues for years, which means that concrete grows stronger as it ages. Note that removing sand from a mix transforms conventional concrete into a fineless mix, also known as permeable concrete (see Permeable Concrete Pavements).

Concrete aggregates

are produced to Australian standards (AS 275) or to more specific customer requirements.

Producing good quality, durable concrete containing a portion of recycled concrete aggregate often requires test concrete mixes and close control of the properties of old recycled concrete with mix adjustments made as needed. When selecting an aggregate for use in a concrete mix, it is important to consider its cleanliness, hardness, strength, absorption rate, surface moisture content, gradation, maximum size, unit weight, and moisture content. These factors will all affect the character and performance of the resulting mix. Additionally, it is important to ensure that non-potable water or water of unknown purity is not used in order to maintain the quality and workability of the mix. Finally, it is important to note that removing sand from a mix transforms conventional concrete into a fineless mix known as permeable concrete.