Method of Test for Toughness of Natural Building Stones
1969 Edition

The standard does not explicitly define the exact dimensions or form of toughness test specimens within the provided sections. However, customary practice and related IS codes suggest using standardized notched specimens such as Charpy or Izod types. Typical dimensions include approximately 55 mm in length, 10 mm in width and thickness, with a V-shaped notch at a 45° angle and 2 mm depth. Additionally, any seams, fissures, or defects must be documented as they influence toughness outcomes. Toughness is quantified by the height of the pendulum blow causing failure, and when planes of structural weakness exist, both individual and average toughness from three specimens are reported. For detailed specimen dimensions, refer to standards like IS 1757 or ASTM E23.

To obtain representative samples as per the guidelines, inspect the quarry face or natural deposit for variations in strata, color, and texture. From quarry ledges, select separate unweathered stone samples weighing at least 25 kg from all distinctly different strata, excluding any blasted or damaged pieces. For field stones and boulders, conduct a thorough survey of the deposit, classify stone types and conditions, and collect separate samples for each identified class. When noticeable variability in quality exists, multiple samples covering the range should be taken. This approach ensures that the samples accurately represent the average stone quality for testing.

The impact testing apparatus must be a pendulum-type machine capable of delivering consistent impact energy. The cylindrical specimen is securely positioned on an anvil without lateral constraints, with its top surface center aligned tangentially to the spherical end of the plunger. The hammer is released in free fall starting at 1 cm for the initial blow, increasing by 1 cm increments for subsequent blows until specimen failure occurs. The toughness is then recorded as the height of the blow at which failure happens, ensuring repeatable and accurate toughness measurements.

Toughness is assessed by testing three specimens per set using the specified toughness testing machine. If a plane of structural weakness is visible, toughness values for each specimen and the average for the set must be reported separately, noting the orientation related to the weakness. When no such weakness is observed, individual and average toughness values are still reported. Reports should clearly specify whether the specimens had any structural flaws and include all relevant observations to ensure accurate representation of the stone's durability.

Specimens with apparent structural weakness planes should be prepared and tested in two orientations: one set drilled perpendicular to the weakness plane and another set parallel to it. Toughness tests are then performed on both sets independently. The individual and average toughness values for each orientation are recorded and reported distinctly, alongside any observations of seams, fissures, or anomalies that might affect results. This method captures the anisotropic toughness characteristics of the stone, providing a realistic evaluation relative to the structural weaknesses.