Sieve analysis, or gradation testing, is a method used to determine the particle size distribution of granular materials, such as crushed rock, sand, clay, granite, etc. Sieve analysis is used in civil engineering because the distribution of different grain sizes can affect the engineering properties of aggregates.  The size distribution is critical to the way the material performs in use. Aggregates are used as a stable foundation with predictable, uniform properties.  In other words, aggregate helps prevent differential settling under a road or building (uneven or unequal settling, which can cause structural damage).  Aggregate can also be used as an extender that binds with cement or asphalt to form concrete.  In this case, the aggregate adds strength to the overall composite material.

Having a sieve analysis performed is important when analyzing materials because their particle size distribution can affect the strength of the concrete, the time it takes to harden, the solubility of the mixture, and other factors.  Sieve analysis helps to determine compliance with design and production requirements for the project it is being used in.

So, how is a sieve analysis done? Like the name implies, it utilizes a series of sieves with progressively finer screening material.  Prior to testing, the sieves must be cleaned with a wire brush to ensure that nothing remains from previous samples. The desired sieves are then placed in what is called a sieve nest. The nest of ASTM-specified sieves is placed on a mechanical shaker, with the sieve with the largest openings at the top and the sieve with the smallest openings at the bottom. The mechanical shaker agitates the nest, moving the aggregate progressively down through the sieves. The smallest pieces fall to the bottom, and the largest stay in the upper sieves, separated by particle size. When the sorting is complete, the mass weight of each sample size increment is measured and recorded, and a grain size distribution curve graph can be created.  The data obtained is used to classify the aggregate into categories such as fine or course, and can identify soil types like gravel, sand, or silt.  Well-graded soil will result in a gentle curve; poorly graded soil will produce a straighter or more irregular curve, indicating less variation in particle size.

Gradation testing is an important quality control and quality acceptance tool performed in Encorus Group’s accredited Civil Materials Testing Lab. Let Encorus Group help you with your aggregate testing! Call or email our Civil Materials Testing Manager Jeremy Lake at 716.592.3980 ext. 133 or [email protected].