What is the Optimal Aggregate Size for the Strongest Concrete?

The shape and size of aggregate used in concrete can have a significant impact on the strength of the final product. Generally, smaller aggregates will produce the strongest concrete. However, other characteristics such as surface texture, mineralogy, and levelness can also affect the strength of concrete. Recycled concrete is a viable source of aggregate and can be used in granular subbases, soil cement, and new concrete.

The ideal aggregate particles should have a cubicle or spherical shape and the correct mineral composition. Flat, elongated particles should be limited to 15 percent or less. Aggregates should be handled and stored to minimize segregation and degradation and prevent contamination. Aggregate categories include gravel, sand, recycled concrete, slag, topsoil, ballast, type 1 MOT, and geosynthetic aggregates.

ASTM C 33 provides classification requirements for coarse-grained and fine aggregates. Leveling limits and maximum aggregate size are specified to affect the amount of aggregate used, cement and water requirements, workability, pumpability, and concrete durability. The ancient river sediment has been reworked by the action of the sea to leave clean and well-classified aggregates. The stone is mined, crushed and ground to produce a variety of aggregate sizes that conform to “coarse-grained” and “fine” specifications.

With the same cement content and consistency, concrete mixes containing larger aggregate particles require less mixing water than those containing smaller aggregates. Specifying leveling limits and maximum aggregate size is important for workability and cost.

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