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. In contracts, construction, or purchase, the term “maximum aggregate size” refers to the smallest screen that 100% of your aggregate can pass through. The digital image analysis method has the potential to estimate characteristics such as size and shape of aggregates quickly and accurately. 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.
Some PCC mix designs use aggregates with gradual separation to provide more economical mixing, since less sand can be used for a given workability. Integral aggregate is an aggregate that contains a proportion of material of all sizes from a well, crushing plant, or river bed. The selection of the methodology for measuring characteristics such as size and shape of the aggregate depends on parameters such as accuracy, reliability of the method, time required to analyze the sample, human efforts required, measurement of other characteristics besides size, robustness of test equipment, initial cost of equipment, maintenance and operating costs. Aggregates are a broad category of materials such as sand, gravel, crushed stone, slag and recycled concrete. It refers to a gradation that contains only a small percentage of aggregated particles in the small range.
For medium strength concrete, 40mm aggregates are best and for high strength concrete 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). Only 15-34% of the aggregates in zone 1 will pass through a 0.6 mm screen; 35-59% in zone 2; 60-79% in zone 3; and 80-100% in zone 4.The shape of your aggregates is important to workability of concrete, quantity you want to place and strength you want to make.