The technical side of aggregate quality often materializes under a single laboratory heading. Granulometry, i.e. grain size distribution, is the fundamental parameter that determines which mixture, which layer and which application an aggregate is suitable for. From the concrete plant chief to the asphalt laboratory engineer, from the landscape applicator to the infrastructure contractor, all stakeholders approach the same material with different questions, but their common reference is the sieve analysis results. In our three generations of supply accumulation, while delivering calcite and dolomite aggregate originating from Saraylar (Marmara Island) to different sectors, we prepare the sieve analysis report of each batch as part of the shipping document. In this article, we share the laboratory steps of sieve analysis, the approach of the TS EN 933-1 standard, grain class definitions, and ideal gradation curves for concrete and asphalt mixtures.
Sieve analysis, despite its simple appearance, requires disciplined laboratory practice. TS EN 933-1, i.e. the method applied in Turkey and compatible with the European EN 933-1 standard, describes the wet and dry sieving steps to determine the grain distribution of the aggregate. Before the test, the sample is representatively prepared by the cone quartering method, dried in an oven at 110 degrees until constant weight is reached. The sample mass is determined according to the grain size class, with at least 5 kilograms of sample used for an aggregate with a 32 mm upper limit. The dried sample is first washed under water on a 0.063 mm sieve, this step ensures the separation of very fine particles from the main mass. After washing, the sample is dried again and sieved mechanically or manually on the standard sieve set.
The standard sieve set is determined according to the class of aggregate. The sieve series commonly used for concrete and asphalt aggregates includes openings of 63, 31.5, 16, 8, 4, 2, 1, 0.5, 0.25, 0.125 and 0.063 mm. In some applications, intermediate openings such as 22.4 and 11.2 mm are also added. After sieving, the mass remaining on each sieve is weighed on a precision scale, proportioned to the initial sample mass and cumulative passing percentages are calculated. The results are plotted on a semi-logarithmic graph, with the sieve opening on the horizontal axis in logarithmic scale and the passing percentage on the vertical axis in linear scale. The resulting curve is the granulometry fingerprint of the aggregate.
Aggregate grain class definitions are shown according to the EN norm as lower limit slash upper limit. The 4/8 millimeter class refers to the grain range with a lower limit of 4 mm and an upper limit of 8 mm. The 8/16 millimeter and 16/32 millimeter classes are defined with the same logic. Within the tolerance framework specified in the standard, the presence of certain proportions of grains below the lower limit and above the upper limit is permitted, with the large majority of the main mass remaining within limits. The EN 12620 standard determines the suitability criteria for the use of these classes as concrete aggregate. The EN 13043 standard offers a parallel framework for asphalt mixtures.
