Maximum Size of Coarse Aggregate
The maximum size of coarse aggregate may be specified in the ‘Max. aggregate size’ field on the Laboratory Measurements Dialog or on a Mix Design Form, unless the results entered on a Trial Mix Dialog are being used in the mix design.
The maximum size of coarse aggregate is the largest sieve size, through which almost all the aggregate would pass.
The maximum size of the coarse aggregate is important because it affects the free water content and percentage of fine aggregate needed for a given level of workability.
Concrete made with sizes of coarse aggregate greater than 40 mm (1.5 in.) often has poor strength, probably because the aggregate has different stiffness and shrinkage properties to those of the cement paste. The strength of such concrete is difficult to predict and the DOE Method, used by Firstmix, does not cater for aggregates with a maximum size greater than 40mm (1.5 in.).
In practice the maximum size of aggregate is usually controlled by the requirements of concrete placement. It is usually impractical to place normal reinforced concrete with an aggregate size greater than 40mm.
ACI 211.1-91 (see References 23) suggests that the maximum aggregate size should not exceed:
If the Laboratory Measurements Dialog is used to specify the aggregate properties, Firstmix estimates the maximum size of the coarse aggregate from the sieve percentages.
If trial mix results are used in a mix design, Firstmix calculates a nominal maximum aggregate size, which according to the DOE Method would provide the measured workability for the free water content of the trial mix for concrete made with aggregate of the given angularity.
Range: 10 - 40 mm or 0.375 - 1.5 in.