IRC 48-1972 provides tentative specifications for bituminous surface dressing using precoated aggregates, detailing materials, application methods, and quality requirements for single or double coat treatments on road surfaces. It is intended for engineers and contractors involved in road construction and maintenance, focusing on achieving durable, well-adhered surface layers through precoating techniques that improve aggregate-binder bonding and surface performance.
Overview
IRC 48-1972 provides tentative specifications for bituminous surface dressing using precoated aggregates, detailing materials, application methods, and quality requirements for single or double coat treatments on road surfaces. It is intended for engineers and contractors involved in road construction and maintenance, focusing on achieving durable, well-adhered surface layers through precoating techniques that improve aggregate-binder bonding and surface performance.
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The Introduction section of IRC 48 outlines key material specifications and aggregate requirements for road construction. As per the provided tables, the physical properties of aggregates must meet limits such as a maximum abrasion value of 35%, impact value of 30%, flakiness index of 25%, stripping value of 25%, and water absorption not exceeding 1% (except slag). For slag, soundness loss is limited to 12% and bulk density must be at least 1120 kg/m³ (Table 4.2). Additionally, aggregate sizes for different construction coats are specified: the first coat uses 13.2 mm nominal size aggregates passing 22.4 mm sieve and retained on 11.2 mm sieve, while the second renewal coat uses 11.2 mm nominal size aggregates passing 13.2 mm sieve and retained on 6.7 mm sieve. These ensure proper material quality and gradation for durable pavement layers.
Sources: Table 4.2. Cover Material
The scope of IRC 48 includes specifications for cover material and aggregates used in bituminous surface treatments. Key details include:
Physical requirements for aggregates are specified in Table 1, including:
These ensure durability and suitability of aggregates for surface treatments as per IRC 48.
Sources: TABLE: 4.2. Cover Material, 4.2.2. Physical requirements, 4.2.3. Size
As per IRC 48 Clause 4.2, the cover material for road construction shall consist of crushed stone, crushed slag, crushed gravel (shingle), or other crushed aggregates that are clean, strong, durable, and fairly cubical, free from disintegrated pieces, salts, alkalis, vegetable matter, dust, and coatings. If crushed gravel is not economically available, rounded gravel or water-borne shingle may be used. The nominal size of aggregates for cover material is specified as follows:
| Type of Construction | Nominal Size of Aggregates | Sieve Designation of Aggregates |
|---|---|---|
| First coat or | 13.2 mm | Passing through 22.4 mm sieve and retained on 11.2 mm sieve. |
| Second renewal coat | 11.2 mm | Passing through 13.2 mm sieve and retained on 6.7 mm sieve. |
Physical requirements for aggregates include:
These tests correspond to IS 2386 (Parts I, III, IV, V) and IS 6241 standards.
Sources: Clause 4.2, Table 4.2 Cover Material, Table 1 Physical requirements
According to IRC 48, the binder used in surface dressing shall be one of the following: straight-run bitumen 80/100, road tar grade RT-3/RT-4, or approved cutbacks, with the grade selected based on climate conditions (Clause 4.1). For application, the binder must be heated to an appropriate temperature and sprayed uniformly using mechanical sprayers. The application rates are:
First coat:
Priming coat:
After binder application, rolling with a 6 to 8 tonne smooth wheeled roller should be done starting from edges towards the center, overlapping at least one-third of the previous pass, embedding aggregates firmly without crushing (Clause 5.4.3). For renewal coats, the second binder application should be immediate or soon after the first, especially when using road tar (Clause 5.5).
Sources: Clause 4.1, Clause 5.4.1, Clause 5.4.3, Clause 5.5, Clause 9.4
For construction under IRC 48, key specifications for cover material and aggregates are as follows:
Cover Material Sizes (Table 4.2):
Physical Requirements of Aggregates (Table 1):
| Property | Max/Min Value | Test Method |
|---|---|---|
| Abrasion value (Los Angeles machine) | Max 35% | IS:2386 (Part IV) |
| Aggregate impact value | Max 30% | IS:2386 (Part IV) |
| Flakiness index | Max 25% | IS:2386 (Part I) |
| Stripping value | Max 25% | IS:6241 |
| Water absorption (except slag) | Max 1% | IS:2386 (Part III) |
| Soundness (slag only, sodium sulphate 5 cycles) | Max 12% | IS:2386 (Part V) |
| Unit weight/bulk density (slag only) | Min 1120 kg/m³ | IS:2386 (Part III) |
Aggregate size depends on coat type as per Table 2 (not fully shown).
These ensure durability and proper bonding in pavement construction as per IRC 48 guidelines.
Sources: TABLE: 4.2. Cover Material, 4.2.2. Physical requirements, Table 1
For Surface Finish in IRC 48, the key specifications relate to the nominal size and sieve designation of aggregates used in bituminous surface dressing. According to the provided table, for the first coat or second renewal coat, the nominal aggregate sizes and sieve designations are:
| Type of Construction | Nominal Size of Aggregates | Sieve Designation of Aggregates |
|---|---|---|
| First coat or | 13.2 mm | Passing through 22.4 mm sieve and retained on 11.2 mm sieve. |
| Second renewal coat | 11.2 mm | Passing through 13.2 mm sieve and retained on 6.7 mm sieve. |
These specifications ensure proper aggregate gradation for surface dressing. No explicit formulas are provided in the context for surface finish, but adherence to these aggregate sizes is critical for quality and durability of the surface layer.
Sources: TABLE: 4.2. Cover Material
As per IRC 48 Clause 5.7, the specifications for opening to traffic after surface dressing are:
Additional key points from Clause 5.4 and 5.5 include:
Surface evenness tolerances (Table 3) for surface dressing are:
| Type of base | Longitudinal profile (max undulation) | Cross profile (max variation) |
|---|---|---|
| WBM, penetration macadam, built-up spray grout | 12 mm | 8 mm |
| Bituminous macadam | 10 mm | 6 mm |
These ensure proper surface quality before opening to traffic.
Sources: Clause 5.7, Clause 5.4.1, Clause 5.4.3, Clause 5.5, Table 3
Frequently Asked
As per IRC 48, the aggregates suitable for precoating are crushed stone, crushed slag, crushed gravel (shingle), or other crushed aggregates that are clean, strong, durable, and fairly cubical, free from disintegrated pieces, salt, alkali, vegetable matter, dust, and adherent coatings. If crushed gravel is not available at reasonable cost, rounded gravel (shingle) or water-borne shingle may be used. The aggregates must be precoated with 0.75 to 1 percent of their weight of binder and allowed to cure for at least one week to become non-sticky for easy broadcasting (Clause 4.2.1 and 4.2.4). The nominal size of aggregates depends on the coat type: for the first coat, 13.2 mm aggregates passing through 22.4 mm sieve and retained on 11.2 mm sieve; for the second renewal coat, 11.2 mm aggregates passing through 13.2 mm sieve and retained on 6.7 mm sieve (Table 4.2).
Sources: Clause 4.2.1, Clause 4.2.4, Table 4.2
The recommended binders for different climate conditions as per IRC 48 are:
The choice depends on the climate, with these binders selected to suit temperature and weather variations to ensure proper adhesion and durability (Clause 4.1). Application rates vary by binder type and are specified to ensure uniform coverage (Clauses 9.4 and 17.5).
Sources: Clause 4.1, Clause 9.4, Clause 17.5
Precoated aggregates shall be prepared by first ensuring they are free of dust or fine particles and preheated to 60°C (except for cutbacks like RC-3). They are then precoated with 0.75 to 1 percent of their weight of binder, which is heated to its application temperature. The aggregate and binder must be thoroughly mixed in an approved mixer until all aggregates are uniformly coated. As per Clause 4.2.4, the precoated aggregates must be allowed to cure for at least one week so they become non-sticky and can be easily broadcast like normal aggregates. They can also be stored for a few months if required before application.
Sources: Clause 4.2.4
The specified application rates for binders and aggregates as per IRC 48 are as follows:
For binder application (Clause 9.4):
For binder application (Clause 17.5):
For precoating aggregates (Clause 4.2.4):
Aggregates should be screened to pass 13.2 mm sieve and retained on 6.7 mm sieve (Clause 13.2). The precoated aggregates must cure for at least one week before use.
These rates ensure uniform coverage and proper embedment of aggregates in the binder for surface dressing works.
Sources: Clause 9.4, Clause 17.5, Clause 4.2.4, Clause 13.2
As per IRC 48, surface dressing should preferably be carried out when the atmospheric temperature in shade is 16°C or above (Clause 5.1). Bituminous material shall not be applied when the surface or cover material is damp, or during foggy, rainy weather, or dust storms. For traffic control (Clause 5.2), the treated road length equal to a day's work shall be closed, with suitable diversions constructed. Adequate barriers, flags, traffic signs, and red warning lights must be provided for safety. All diversions should be watered to prevent dust from contaminating the cleaned or painted surface. When cutback bitumen is used, the surface must remain closed to traffic until sufficiently cured, with barricades and watchmen posted to control traffic (Clause 5.7).
Sources: Clause 5.1, Clause 5.2, Clause 5.7
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