Method of test for determination of true specific gravity of natural building stones
1974 Edition

The standard requires selecting a representative sample either from quarried material or natural rock that reflects the average grade and is sufficient for all necessary specimens. Initially, a 0.5 kg portion is taken, washed thoroughly to remove dust or coatings, dried, and crushed to particles not exceeding 3 mm. This crushed material is then mixed well and reduced to a 50 g test sample, which is ground in an agate mortar until passing through a 150-micron IS sieve. Magnetic particles introduced during processing must be removed using a magnet to ensure purity.

Drying is conducted in an oven maintained between 105°C and 110°C until the specimen attains a constant weight, ensuring all moisture is eliminated. After drying, samples are cooled in a desiccator to prevent moisture reabsorption before weighing. This process is vital for accuracy, as residual moisture would affect weight measurements and consequently the calculated specific gravity, potentially compromising the consistency and reliability of test results.

The method specifies using a 50 ml specific gravity bottle fitted with a capillary tube stopper. An analytical balance with suitable precision is required for weighing the bottle empty, with stone powder, with powder plus distilled water, and with distilled water alone. Distilled water at laboratory temperature is used to fill the bottle for volume determination. This setup ensures precise measurements necessary for calculating the true specific gravity.

Following crushing and grinding to pass through a 150-micron sieve, any magnetic contaminants introduced are removed by passing the sample near a magnet. This step prevents iron or other magnetic particles, possibly derived from steel tools, from skewing test results, thus maintaining sample integrity for accurate determination of specific gravity.

The true specific gravity is computed using the weights of the empty bottle with stopper (W1), the bottle plus stopper plus powder (W2), the bottle plus stopper plus powder plus distilled water filling the bottle (W3), and the bottle plus stopper plus distilled water (W4). The formula applied is G = (W2 - W1) / [(W4 - W1) - (W3 - W2)]. The room temperature during testing must be recorded, and the final result rounded following IS 2:1960 rounding rules. The report should include the specific gravity value, test temperature, sample identification, date of sampling, stone type, and any relevant observations or deviations.