Methods of sampling hydraulic cement
1986 Edition

IS 3535 advises sampling hydraulic cement preferably while it is in motion, such as during conveyor transport or loading/unloading. For silos with cement depth up to 2 meters, a slotted tube sampler measuring about 1.5 to 1.8 meters long and 35 mm in diameter with telescopic brass tubes is used. For depths exceeding 2 meters, a sampling pipe with an air jet is recommended to collect samples from various depths. Sampling increments should be taken uniformly across the sub-lot, with one increment for every 10 tonnes or fraction thereof, each increment weighing at least 2 kilograms. Sampling operations may be conducted in multiple stages to accumulate sufficient material for testing, ensuring representative and standardized sample collection.

According to IS 3535 clauses, increments must be immediately placed into moisture-tight and airtight containers to prevent moisture absorption and aeration. When using cans, they should be completely filled and sealed right after sampling. Alternatively, moisture-resistant multi-layer paper or plastic bags can be employed, provided they are strong enough to resist damage and can be sealed promptly to exclude excess air. Each container or bag must be clearly labeled with relevant sub-lot identification to maintain traceability. These precautions preserve sample integrity during storage.

The cement lot should be segmented into sub-lots based on its total weight in accordance with Table 2 of IS 3535. For bulk storage, sub-lots are marked across the pile surface, while for ship holds, the quantity is divided into sub-lots proportionate to the weight. In the case of wagons and bags, the lot is split into nearly equal groups by number. The number of sub-lots increases with lot size, ensuring each sub-lot is roughly equal in weight or count. This systematic subdivision facilitates representative sampling and effective quality control throughout the entire lot.

IS 3535 specifies sampling frequencies during different manufacturing stages. For clinker, hourly samples are taken from kiln output and aggregated into daily composites. During cement grinding, setting time samples are collected every hour with daily composites formed, while fineness samples are taken every alternate hour, also combined daily. Chemical composition and other properties typically require weekly composite samples. These schedules ensure continuous monitoring, enabling detection and correction of quality variations in the production process.

The standard prescribes thoroughly mixing the gross sample, breaking up lumps, and removing foreign materials before passing the material through an 850-micron IS sieve. Hardened lumps or contaminants that don't break apart are discarded. Subsequently, mechanical reduction is performed using sample splitters or riffle samplers designed to maintain randomness and representativeness. This process continues until the laboratory sample weighs approximately 11 kilograms, providing a manageable and accurate sample for testing.