Methods of test for aggregates for concrete, Part 4: Mechanical properties
1963 Edition

Per IS 2386 Part 4, conducting the Aggregate Crushing Value (ACV) test requires the following apparatus: an open-ended steel cylinder 15 cm in diameter equipped with a plunger and base plate featuring machined and case-hardened surfaces with hardness above 650 VH; a straight metallic tamping rod of circular cross-section 16 mm in diameter and 45 to 60 cm length with a rounded end; a balance capable of weighing up to 3 kg with 1 g precision; a compression testing machine with a 40-tonne capacity and uniform loading to achieve maximum load within 10 minutes, optionally with spherical seating; a rigid cylindrical metal measure 11.5 cm in diameter and 18 cm in height; and IS standard sieves of sizes 12.5 mm, 10 mm, and 2.36 mm. This combination ensures accurate and consistent measurement of aggregate crushing resistance.

The abrasion resistance of coarse aggregates is determined by rotating the test sample along with an abrasive charge inside the Los Angeles machine. The procedure involves placing the sample and charges into the machine, rotating it between 20 and 33 revolutions per minute. For gradings A through D, 500 revolutions are completed, whereas for gradings E through G, 1000 revolutions are performed. The machine ensures uniform peripheral speed with abrasive impacts on the sample. After rotation, the material is discharged and sieved through a size coarser than the 1.70 mm IS sieve to separate fines, which are then screened on the 1.70 mm IS sieve. The percentage weight loss of the sample after abrasion quantifies the abrasion value. This method is preferred over the Deval machine for assessing abrasion resistance.

The polished stone value (PSV) test involves evaluating the resistance of roadstone to polishing under simulated traffic conditions, which reflects the skid resistance potential of the aggregate. Specimens are prepared by embedding 40 to 50 particles in sand-cement mortar, forming samples approximately 90.5 by 44.5 mm in size with a thickness of at least 12.5 mm, curved to a 400 mm radius. These specimens are mounted on a polishing machine wheel about 405 mm in diameter and subjected to accelerated polishing. After polishing, the coefficient of friction is measured using a friction tester, with tests repeated on at least two specimens. The mean friction value, expressed as a percentage, is reported as the PSV. This value is crucial in road construction since higher PSV indicates better resistance to polishing, contributing to safer road surfaces with improved skid resistance.

Sample preparation for mechanical testing per IS 2386 Part 4 requires selecting freshly quarried rock free from visible incipient cracks. If structural weakness planes exist, specimens should be oriented so some have these planes perpendicular to the specimen's cylindrical axis. Sample sizes depend on the test: approximately 8 x 4 x 4 cm cubes for grinding-only operations, and about 15 x 15 x 10 cm blocks for combined drilling, sawing, and grinding. For particle preparation, at least 3 kg of material passing the 10-mm IS sieve but retained on the 8-mm sieve should be used. Particles must be clean, free from dust, non-flaky, and not elongated. Care should be taken to avoid damage during preparation; cold water is used continuously during grinding, drilling, and sawing to prevent heating and microfractures, ensuring representative and undamaged samples.

According to IS 2386 Part 4, after achieving the prescribed maximum penetration during testing, the applied load must be released before removing and sieving the aggregate. The fines passing a 2.36 mm IS sieve should fall within the range of 7.5% to 12.5%; if not, the load must be adjusted and the test repeated to achieve this range. Measurement tolerances stipulate that no two test results on the same surface should differ by more than ±3%, and the average of 11 samples should not deviate by more than +1.5%. For friction coefficient calibration, the formula p = (W × X × Z × M) / (P × D) × 100 is employed, where variables represent parameters such as the weight of the swinging arm, distances, pointer length, normal load, and sliding distance. These controls ensure repeatability and accuracy of the measurements.