Methods of sampling of clay building bricks
1978 Edition

IS 5454 (1978) defines recommended procedures for sampling clay bricks to ensure representative and unbiased testing. The primary approaches include random sampling—selecting bricks arbitrarily across the batch to avoid bias—and composite sampling, which combines subsamples from various parts of the lot into a single test sample. Generally, a minimum of around 150 bricks should be extracted from a batch for testing. The lot is defined as bricks produced under consistent conditions within a specific timeframe. Sampling should encompass different layers and positions within the stack, avoiding damaged bricks. These methods guarantee the sample accurately reflects the batch quality for strength, dimension, and durability testing.

For visual and dimensional inspections, the lot should be split into at least 10 segments or transport units. From each segment, an approximately equal quantity of bricks is drawn at regular intervals. The exact sample size depends on the batch size, as detailed in Table 1 of the standard. Visual inspection sample sizes correspond to specific columns in the table, as do dimensional inspection sample sizes—both for individual bricks and groups of 20 bricks. When dimensions are specified for groups, bricks are organized accordingly and tested group-wise. The sampling quantities increase with batch size, ensuring thorough inspection coverage.

According to Clause 5.2.3 and Table 2, permissible defect limits vary based on batch size. For efflorescence defects, no defective bricks are allowed in smaller batches (2,001 to 35,000 bricks), while one defective is allowed in larger batches up to 50,000. Regarding warpage, zero defects are permitted in smaller samples, with allowances rising to two defective bricks in the largest samples. For batches with 2,000 bricks or fewer, defect limits and sample sizes are determined by agreement. These limits help maintain strict quality control by capping defective bricks in each batch.

Conformity for physical attributes like compressive strength is evaluated by randomly selecting bricks from a batch that has passed visual and dimensional checks. The bricks undergo standardized compressive strength tests, and the average strength is computed. If individual test values exceed the upper class limit, that limit is used for averaging. No single brick should have less than 80% of the specified minimum average strength. The batch is accepted if the average meets or surpasses the minimum required strength. This method ensures uniform reliability of bricks for structural applications.

This standard covers sampling and conformity requirements for solid, hollow, and perforated clay bricks but does not prescribe separate testing procedures for each type explicitly. The same testing methods apply across all types; however, sample sizes and acceptance thresholds may differ according to relevant referenced material specs. Physical tests such as compressive strength, breaking load, and transverse strength are carried out uniformly. Sampling reflects the brick type primarily through variations in quantities and permissible limits, ensuring consistent quality control irrespective of brick design.