METHODS FOR SAMPLING
METHODS FOR SAMPLING OF AGGREGATES
Sampling is of equal importance as testing. Hence every precaution shall be taken to obtain samples which represent the true nature and condition of the material tested.
The terms associated with sampling process of aggregates are given below:
- Increment: The quantity of aggregate obtained by the sampling device at a time.
- Lot: The quantity of the material of the same class, nominal size, source inspected for testing is called a lot.
- Sub-lot: Before sampling, a lot is divided into a number of sub-lots of equal size.
- Unit sample: It is the quantity of aggregates collected at one point in sectional sampling or at one time from the conveyor.
- Gross sample: The unit samples or increments collected from sub-lots constitute gross sample.
- Laboratory sample: The gross sample is reduced using sample dividers or by quartering to obtain samples for laboratory testing.
- Aggregates: This includes crushed stone, crushed boulders, gravel, sand, industrial by- products or such inert materials.
- Coarse aggregates: Aggregates retained on 4.75 mm IS sieve.
- Fine aggregates: Aggregates passing 4.75 mm IS sieve is classified as fine aggregates. Fine aggregates may be natural sand, crushed hard stone (M-sand etc) or crushed natural gravel.
- All-in aggregates: A mixture of coarse and fine aggregates is termed as all-in aggregates.
- Road side production: It is the production of materials with a portable or semi-portable crushing, screening or washing plants established or re-opened in the vicinity of a work or project.
- Bank run sand: This includes previously worked pits or potential sources discovered through aerial photography or geo-physical exploration.
Sampling is required for the following purposes:
- Preliminary investigation for establishing asource of supply.
- Inspection of materials in shipments like truck, wagon, boat etc.
- Inspection of materials delivered at work site.
The general procedures to be followed in each of the above cases are briefly explained in this method. However, it is recommended to refer IS: 2430 for details.