Specification for Bitumen Mastic Wearing Courses (First Revision)
2013 Edition

Per IRC 107, the temperature for mixing and cooking bitumen mastic should be between 170°C and 200°C, with bitumen addition typically between 170°C and 180°C. The overall cooking duration is a minimum of 3 hours without exceeding 200°C. When laying, the temperature must be maintained at approximately 170°C, not surpassing 200°C. Additionally, laying should be avoided on damp surfaces or when ambient temperatures in the shade fall below 15°C to ensure proper adhesion and workability.

According to IRC 107, the base surface must be shaped and leveled to the specified grade and camber. Irregular or undulating surfaces should be repaired by sealing cracks, patching potholes, and applying a corrective bituminous layer such as bituminous concrete or dense bituminous macadam. The surface must be thoroughly cleaned and dry; if moisture is present, drying with a blow lamp is necessary. Binder-rich areas must be scraped and repaired before application. Angle irons of 25 or 50 mm thickness should be installed to contain the mastic. For concrete surfaces, a tack coat of VG 10 bitumen is applied as per IRC:16, with heating to prevent blistering. Bridge decks require additional checks and repairs to joints, drainage, and cracks prior to surfacing.

IRC 107 specifies that bitumen mastic should be composed of mineral fillers (commonly limestone dust), fine aggregates, and coarse aggregates added last, all bound with industrial grade VG 30 bitumen. The manufacturing process involves sequential heating and mixing: initially heating filler with half the bitumen at 170-200°C for about one hour, then adding fine aggregates and the remaining bitumen with continued mixing, followed by incorporation of coarse aggregates. For anti-skid surfaces, precoated hard stone chips sized between 9.5 mm and 13.2 mm are spread at approximately 0.05 m³ per 10 m², coated with 2-3% VG 30 bitumen, protruding 3-4 mm above the surface, with a flakiness index below 25% to enhance skid resistance.

Joint treatment per IRC 107 involves warming the existing bitumen mastic by applying excess hot mastic, followed by trimming the joint flush with the surface. The vertical face of the joint should ideally be shaped into a 'Y' profile to facilitate penetration. The joint face is then coated with VG 30 grade bitumen, after which base mastic blocks—free from coarse aggregates—are applied. These blocks are softened using blow lamps and finished flush with the surface by toweling. It is crucial that the molten mastic penetrates to the bottom of the joint for strong bonding. All joints should be constructed at the 'green' stage, shortly after laying, to avoid oxidation and ensure good adhesion.

Yes, IRC 107 outlines several precautions for bridge deck applications. The deck must be inspected and any deficiencies in camber, crossfall, expansion joints, and drainage spouts corrected. Loose expansion joint components should be secured, and cracked or damaged concrete repaired or replaced. The surface needs thorough cleaning and drying; wet surfaces require drying with a blow lamp. Crack sealing and patching of potholes, along with corrective bituminous courses, are necessary for irregular surfaces. A tack coat of VG 10 bitumen should be applied following IRC:16 guidelines, with the surface heated to prevent blistering. During laying, angle irons (25-50 mm) must be used to contain the mastic, which should be maintained at 170°C. Any bubbles that form must be punctured immediately to ensure a durable surface.