Methods for Sampling of Aggregates for Concrete
1986 Edition

The standard recommends sampling aggregates while they are in motion for accuracy, ideally during loading or unloading. At the conveyor discharge point, increments should be collected at regular intervals using a container that captures the entire falling stream without overflow. If sampling at discharge is impractical, increments should be taken directly from the moving belt at the center, left, and right sections, utilizing a scoop to gather fine particles. This approach ensures that the sample accurately represents the material on the conveyor.

To obtain representative samples from stockpiles, it is advised to use mechanical equipment to form a small, well-mixed sampling pile by combining material from different levels and locations. If such equipment is unavailable, increments should be taken equally from the upper, middle, and lower thirds of the pile's volume. Prior to sampling, remove the outer segregated layer, which typically contains coarser particles. A vertical board should be placed above the sampling point to prevent segregation during sampling. These measures reduce bias and ensure the sample reflects the overall pile quality.

The minimum gross sample weight depends on the maximum nominal size of the aggregate, with values specified in a detailed table. For example, fine aggregates with nominal sizes up to 4.75 mm require a minimum gross sample weight of 10 kg, while coarse aggregates vary from 10 kg to 175 kg depending on size. Each gross sample must consist of at least 10 increments, with each increment weighing at least 1 kg. The increments should be evenly taken across the sampling area using suitable scoops to guarantee representativeness and efficiency.

The coning and quartering process entails thoroughly mixing the gross sample, then forming a cone-shaped pile by consistently dropping scoops at the same spot. The cone is flattened by pressing its top with a smooth surface. The flattened pile is then divided into four equal parts by drawing two perpendicular lines intersecting at the center. Two diagonally opposite quarters are discarded, and the remaining two are combined. This procedure is repeated until the sample size matches the laboratory requirements. For fine or all-in aggregates, slightly damp material improves accuracy, ensuring the test sample remains representative.

Samples must be packed individually using airtight and moisture-resistant containers or bags to prevent contamination and loss of fine particles. Coarse aggregates require secure containers or bags, while fine and all-in aggregates should be stored in tight containers or closely woven bags. Each package should be clearly labeled with sample identification, origin, material type, and any handling instructions. Prior to packing, the sample should be reduced appropriately using methods like coning and quartering to ensure representativeness and maintain sample integrity during transportation.