The aggregates used in the production of concrete are inert granular materials such as gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates. The aggregates may be natural, manufactured, or recycled.
In this article, we discuss the geometrical requirement of the aggregates such as size, grading, shape, shell content, fine content, and quality used in the production of concrete as per the European Standards (EN - 12620).
1. Aggregate Size
The aggregates sizes shall be designated as d/D using a pair of sieves sizes selected from the basic sieve or the basic set plus set 1 or set 3, as shown in table 1. The aggregate sizes shall have D/d not less than 1,4.
In any condition, a combination of sizes from set 1 and 2 is not permissible.
Table 1: Sieve sizes for specifying aggregate sizes.
2. Aggregate Grading
The grading of aggregates shall be carried out in accordance with EN 933-1, which shall comply with the requirements given in the tables below.
1. Coarse Aggregate
The coarse aggregate shall adhere to the grading requirement specified in Table 2 appropriate to their size designation d/D and selected categories.
Table 2: Grading requirement for coarse aggregate.
For graded coarse aggregates where,
a) D > 11,2 mm and D/d > 2; or
b) D < or = 11,2 mm and D/d > 4,
The following additional requirements shall apply for the percentage passing the mid-size sieve;
1) all grading shall comply with the overall limits given in Table 3,
2) the producer shall document and, on request, declare the typical grading passing the mid-size sieve and tolerance selected from the categories in Table 3
Table 3: Overall limit and tolerances for coarse aggregate grading at mid-size sieves.
For single size coarse aggregates where,
a) D > 11,2 mm and D/d <or= 2; or
b) D <or= 11,2 mm and D/d <or= 4,
there shall be no requirement additional to those specified in Table 2.
2. Fine Aggregate
The fine aggregates shall comply with the general grading requirement specified in Table 2 above appropriate to their upper sieve size D.
The following additional requirements shall be applied to control the variability of the fine aggregate.
Typical grading is expressed as the percentage by mass of aggregate passing through the sieve sizes specified in Table 4.
Table 4: Tolerance on producer's declared typical grading for general use fine aggregates.
3. Natural Graded 0/8 mm Aggregate
The natural graded 0/8 mm aggregate shall comply with the general grading requirement specified in Table 2.
The following additional requirement shall be applied to control the variability of natural graded0/8 mm aggregate.
1) The producer shall document and, on request, declare the typical grading for each aggregate produced;
2) Grading shall comply with the tolerance given in Table 5,
Table 5: Tolerance on producer's declared typical grading for natural graded 0/8 mm aggregate.
4. All-in Aggregate
All-in aggregate shall be supplied as a mixture of coarse and fine aggregate with D <or= 45 mm and d=0 and shall comply with the general grading requirements for the category selected from Table 2.
All-in aggregates shall also comply with the requirements for the percentage passing the two intermediate sieves specified in Table 6 appropriate to their aggregate size.
Table 6: Grading requirement for all-in aggregates.
5. Filler Aggregate
The grading of filler aggregate determined in accordance with EN 933-10 shall conform to the limits specified in Table 7.
Table 7: Grading requirement for filler aggregate.
6. Special use Aggregate
The special aggregate gradings are required for a particular end use of the concrete; special grading envelopes shall be defined using the R 20 series of sieves specified in ISO 565:1990 and incorporating the appropriate sieves from 0,063 mm; 0,125 mm; 0,250 mm; 0,500 mm; 1 mm; 2 mm; 4 mm; 8 mm; 16 mm; 31,5 mm and 63 mm.
The required shape of coarse aggregates shall be determined in terms of the flakiness index, as specified in EN 933-3. The flakiness index shall be the reference test for the determination of the shape of coarse aggregates.
The flakiness index shall be declared in accordance with the relevant category specified in Table 8, according to the particular application or end-use.
Table 8: Categories for maximum values of flakiness index.
Where required, the shape Index determined in accordance with EN 933-4, shall be declared in accordance with the relevant category specified in Table 9 according to the particular application or end-use.
Table 9: Categories for maximum values of shape index.
4. Shell Content of Coarse Aggregate
The shell content of coarse aggregate is determined in accordance with EN 933-7 shall be declared in accordance with the relevant category specified in Table 10-
Table 10: Category for maximum value of shell content of coarse aggregate.
5. Fines Content
The fines content of the aggregate is determined in accordance with EN 933-1 shall be declared in accordance with the relevant category specified in Table 11. The fines content of filler aggregate shall comply with the requirements of Table 7.
Table 11: Categories for maximum values of fines content
6. Fines Quantity
The harmfulness of the fines in the fine aggregate, including filler aggregate, shall be assessed in accordance with Annex D of EN 12620.
The properties of concrete such as workability, durability, strength, weight, and, shrinkage are governed by the properties (composition, shape, and size) of aggregate used in the concrete.
Generally, aggregate passing the sieve of 20mm and retaining the sieve of 12.5mm is preferred for the production of concrete.