bitumen mastic acid-resisting grade
1980 Edition

The bitumen employed in acid-resistant mastic must meet several physical criteria to ensure durability and chemical resistance. Typically, the softening point should be above 50°C to maintain stability under operational temperatures. Penetration values at 25°C usually range between 20 and 60 dmm, indicating suitable hardness. Additionally, ductility should be at least 10 cm to prevent cracking, and solubility in carbon disulfide must exceed 99% to confirm purity. The bitumen must also resist degradation when exposed to dilute acids, fulfilling its role as a protective flooring underlay in industrial environments.

Site preparation of bitumen mastic involves heating fine aggregates to temperatures between 170°C and 205°C, while bitumen is heated separately to 170°C–180°C. The heated bitumen is then added to the fine aggregates within a mechanically stirred mastic cooker. The mixture is cooked and agitated for approximately three hours, ensuring the temperature does not exceed 205°C to maintain material integrity. Depending on the layer thickness, coarse aggregates may be incorporated either during mastic production or added during remelting at the construction site. If the mastic is not immediately applied, it should be cast into blocks weighing about 25 kg for storage and transport.

To evaluate acid resistance, samples of bitumen mastic are prepared by mixing increments at temperatures ranging from 150°C to 250°C and formed into specimens at least 25 mm thick. These specimens are immersed in solutions of various acids with concentrations specified by the user. Observations are made for any visual changes such as surface cracks, discoloration, or softening, alongside measuring mass changes which should not exceed ±1%. Resistance is rated on a scale from Very Good to Very Poor based on these parameters. The results guide recommendations on the suitability of the mastic for exposure to particular acids and concentrations.

Sampling from bitumen mastic batches requires collecting five increments at evenly spaced intervals during the discharge process from the mastic cooker: beginning, quarter, half, three-quarter, and end points. Each increment must be at least 2 kg, and all increments are combined to form a representative composite sample, typically about 6 kg in total. Samples are then poured directly from the mixer into moulds with a minimum diameter or area of 100 mm and thickness of 25 mm, ensuring a float finish. Duplicate samples are prepared without remelting to preserve the sample’s integrity for laboratory analysis.

The standard specifies precise grading for fine aggregates, requiring 45-55% passing the 75-micron sieve (filler), 10-30% passing 212 micron but retained on 75 micron, 10-30% passing 600 micron but retained on 212 micron, and 5-20% passing 2.36 mm but retained on 600 micron, with no particles retained above 2.36 mm. Coarse aggregates must comply with IS 383-1970, be acid-resistant, and free of impurities. Their size and proportion depend on the mastic layer thickness, for example, no coarse aggregates for 10 mm layers, and increasing coarse aggregate content up to 95% retained on specified sieves for thicker layers. The overall coarse aggregate percentage by mass of total mastic ranges from 15-30% for 15 mm layers up to 30-45% for 25-30 mm layers. The bitumen content typically varies between 13-18%, combined with the fine and coarse aggregates to form the mastic.