Understanding Aggregate Size for Stronger Concrete

The size of coarse-grated aggregates is a key factor in determining the strength of concrete. Generally, smaller coarse-grated aggregates are used for stronger concrete, with 20mm aggregates meeting the threshold for strong concrete and 40mm aggregates for normal strength concrete. Fine aggregates are used to fill the voids of coarse-grained aggregates, so the smaller the coarse-grained aggregates, the finer the fine aggregates should be. This increases the workability of concrete. To illustrate how maximum density curves are determined, Table 1 shows the associated calculations for a maximum aggregate size of 19.0 mm.

This refers to a gradation that contains only a small percentage of aggregated particles in the small range. It's important to note that the size of the aggregates is the size that most parts pass through a sieve of that size, not all, so there is no need to be too demanding. For base and subbase aggregates where permeability is important for drainage and frost resistance, many agencies will specify a maximum percentage by weight passing for this sieve. The digital image analysis method has the potential to estimate the characteristics, i.e., the size and shape of aggregates quickly and accurately. This method can measure other characteristics of particles besides size, such as shape.

It also provides a common reference for gradations, even if it is not the “best gradation of aggregates”. When selecting aggregate size for concrete, it's important to consider what strength you're looking for. If you're looking for medium strength concrete, 40mm aggregates are best; if you're looking for high strength, 20mm is best. The maximum density line appears as a straight line from zero to the maximum aggregate size for the mixture being considered (the exact location of this line is somewhat debatable).

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