Tentative Specification for Built-Up Spray Grout

IRC 47 introduces Built-up Spray Grout (BSG) as an alternative to conventional water bound macadam, suitable for base or binder courses but not as wearing courses. BSG consists of two compacted layers of crushed coarse aggregates with bituminous binder applied after each layer, finished with key aggregates, total thickness not exceeding 75 mm (Clause 1 Introduction). The binder can be straight-run bitumen (IS:73), road tar (IS:215), or approved cutback, with grades selected per climate (Clause 4.1). Aggregates must be clean, strong, durable, and cubical, meeting physical requirements in Table 1 below (Clause 4.2.2). Grading of coarse and key aggregates is specified in Table 2 (Clause 4.2.3). Construction requires dry, clean base preparation and binder application rates per Table 3 (Clause 5.3).

Sources: Clause 1 Introduction, Clause 4.1, Clause 4.2.2, Clause 4.2.3, Clause 5.3

The scope of IRC 47 covers the tentative specifications for built-up spray grout used in road construction. Key points include:

• Construction should not proceed if atmospheric temperature in shade is below 16°C or during damp, foggy, rainy, or dusty conditions (Clause 5.1).
• The base course must be prepared to a uniform grade and section, free of depressions, pot-holes, and thoroughly compacted (Clause 5.3).
• The surface must be dry and cleaned thoroughly by sweeping, brushing, and blowing to remove dust and foreign matter.
• For old black top surfaces, cleaning must remove sand, dirt, and loose matter.
• For stabilized soil or porous aggregates, a bituminous primer per IRC:16-1965 must be applied and cured before construction.
• Binder application rates for tack coat are specified in Table 3, applied uniformly and heated to the correct temperature.

The relevant table for binder quantity per 10 m² is:

This ensures proper adhesion and surface preparation for spray grout application.

Sources: Clause 5.1, Clause 5.3, Table 3 in Clause 2.36

Key materials specifications from IRC 47 for built-up spray grout are as follows:

• Binder Types (Clause 4.1.1):

  • Straight-run bitumen per IS:73 (grades 80/100, 60/70, 30/40)
  • Road tar per IS:215 (grades R.T.4 or R.T.5)
  • Approved cutback bitumen

• Aggregates (Clause 4.2):

  • Must be crushed stone, slag, gravel, or similar, clean and durable.
  • Physical requirements (Table 1):

• Grading of Aggregates (Table 2):

These materials ensure durability and bonding in built-up spray grout base or binder courses but are not for wearing courses. The binder grade depends on climate (Clause 4.1.2).

Sources: Clause 4.1.1, Clause 4.1.2, Clause 4.2.1, Clause 4.2.2, Clause 4.2.3, Table 1, Table 2

Key specifications for aggregates in built-up spray grout per IRC 47 Clause 4.2 are as follows:

• Aggregates must be crushed stone, slag, gravel, or similar, clean, strong, durable, cubical, and free from deleterious materials (Clause 4.2.1).

• Physical requirements for coarse and key aggregates are given in Table 1:

• Grading of aggregates per Table 2 (percent passing by IS sieve sizes):

These ensure durability and proper bonding in spray grout construction. For detailed construction steps and binder application rates, see Clauses 5.5 to 5.11.

Sources: Clause 4.2.1, Clause 4.2.2, Table 1, Clause 4.2.3, Table 2

The binder for built-up spray grout in IRC 47 shall be one of the following as per Clause 4.1.1:

• Straight-run bitumen of suitable penetration grade complying with IS: 73 (e.g., 80/100, 60/70, or 30/40 grades)
• Road tar of suitable grade conforming to IS: 215 (e.g., R.T. 4 or R.T. 5)
• An approved cutback bitumen

The binder grades depend on climatic conditions as per Clause 4.1.2.

For application, the binder is heated to the appropriate temperature and applied uniformly to the base at rates specified in Table 3 (Clause 5.3):

This binder is applied after each compacted coarse aggregate layer to bond the layers, finishing with key aggregates on top, with total thickness not exceeding 75 mm (Clause 5.10).

Sources: Clause 4.1.1, Clause 4.1.2, Clause 5.3, Clause 5.10

Key construction specifications for built-up spray grout per IRC 47 include:

• Weather and Seasonal Limitations: Construction shall not proceed if atmospheric temperature in shade is below 16℃, or if pavement is damp, foggy, rainy, or dusty (Clause 5.1).

• Preparation of Base: The base must be uniformly graded, dry, and thoroughly cleaned by sweeping and brushing. For stabilized soil or porous aggregates, apply a bituminous primer as per IRC:16-1965 and cure before construction (Clause 5.3).

• Bituminous Binder Application: Binder heated to specified temperature and applied uniformly at rates given in the table below, preferably by sprayer, just before spreading coarse aggregates (Clause 5.3).

• Aggregate Requirements: Aggregates must be clean, strong, durable, and cubical. Physical properties and grading are specified in Tables 1 and 2 (Clause 4.2).

• Construction Layers: Two-layer composite construction with compacted crushed coarse aggregates and bituminous binder after each layer, total thickness not exceeding 75 mm. Not recommended for wearing course (Clause 5.10).

These ensure proper bonding, durability, and performance of the built-up spray grout base or binder course.

Sources: Clause 5.1, Clause 5.3, Clause 5.10, Table 5. CONSTRUCTION | Clause 2.36, Table 1 and Table 2 | Clause 4.2

For preparation of the base in built-up spray grout construction as per IRC 47 Clause 5.3, the underlying course must be shaped and conditioned to a uniform grade and section. Any depressions or potholes should be properly filled and compacted well in advance. The surface must be dry and thoroughly cleaned by sweeping, brushing, and blowing to remove all dust and foreign matter. For old blacktop surfaces, ensure they are clean and dry. For stabilized soil or porous aggregates, apply a suitable bituminous primer as per IRC:16-1965 and allow curing before construction. The binder should be heated to the specified temperature and applied uniformly at rates given in the table below, preferably by sprayer, just before spreading coarse aggregates.

This ensures proper bonding and a uniform base for subsequent layers. The surface preparation and binder application are critical for durability and performance of the built-up spray grout base course.

Sources: Clause 5.3

For spreading and compacting the first layer of coarse aggregates in built-up spray grout construction as per IRC 47:

• Spreading (Clause 5.5.1): Coarse aggregates shall be spread and hand packed at a rate of 0.5 m³ per 10 m² to a uniform depth, maintaining alignment and profile using a camber template.

• Rolling (Clause 5.5.2): Compaction is done with a 3-wheel power roller (8-10 tonnes) or equivalent vibratory roller, starting from edges towards center, ensuring surface variation does not exceed 12 mm from camber template or 3 m straight edge.

• Rolling must stop before voids close to prevent bitumen penetration issues.

• Binder Application (Clause 5.6): After rolling, apply binder heated to suitable temperature at 12.5 to 15.0 kg per 10 m² uniformly with mechanical sprayers. Aggregates must be surface dry before application.

• Key Specifications Table for Binder Quantity on Base (Clause 2.36):

These steps ensure uniform spreading, proper compaction, and adequate binder application for the first layer.

Sources: Clause 5.5.1, Clause 5.5.2, Clause 5.6, Clause 2.36

The first application of binder in built-up spray grout construction per IRC 47 involves applying heated binder uniformly over the compacted first layer of coarse aggregates. As per Clause 5.6 and 12.5, the binder quantity should be between 12.5 kg to 15.0 kg per 10 m² of road surface. The binder must be heated to the appropriate temperature for its type and grade and applied preferably with mechanical sprayers. Before application, the coarse aggregates must be surface dry to full depth. The binder types allowed include straight-run bitumen (IS: 73), road tar (IS: 215), or approved cutbacks, with grades selected based on climatic conditions (e.g., bitumen 80/100, 60/70, 30/40 or road tar R.T.4, R.T.5) as per Clause 4.1.1 and 4.1.2.

Additionally, the binder application rate for tack coat on base varies by base type (Clause 5.3):

This ensures proper bonding before spreading the next aggregate layer. The process is critical for achieving a durable, bonded base or binder course but not suitable as a wearing course.

Sources: Clause 5.6, Clause 12.5, Clause 4.1.1, Clause 4.1.2, Clause 5.3

For spreading and compacting the second layer of coarse aggregates in built-up spray grout construction as per IRC 47:

• Immediately after applying the binder on the first layer (12.5 to 15.0 kg per 10 m²), coarse aggregates shall be spread at the rate of 0.5 m³ per 10 m² uniformly and compacted similarly to the first layer (Clause 5.7).

• The spreading must be true to alignment and profile, using a camber template for uniformity (Clause 5.5.1).

• Rolling should be done with a 8 to 10 tonne three-wheel power roller or equivalent vibratory roller, starting from edges towards the center, overlapping by one third width, and on superelevated portions from lower to upper edge (Clause 5.5.2).

• Surface irregularities exceeding 12 mm must be corrected, and rolling should stop before voids close to prevent binder penetration issues (Clause 5.5.2).

• After compacting the second layer, a second binder application of 12.5 to 15.0 kg per 10 m² is applied (Clause 5.8).

This two-layer composite construction yields a thickness not exceeding 75 mm and is finished with key aggregates (Clause 5.10).

Sources: Clause 5.5.1, Clause 5.5.2, Clause 5.6, Clause 5.7, Clause 5.8, Clause 5.10

The second application of binder in built-up spray grout construction is applied after compacting the second layer of coarse aggregates. As per Clause 5.8, the binder quantity shall be 12.5 kg to 15.0 kg per 10 m². This binder is heated to the appropriate temperature and applied uniformly, preferably with mechanical sprayers. Following this, key aggregates are spread and compacted to form a uniform closed surface (Clause 5.9). The binder types suitable include straight-run bitumen (grades 80/100, 60/70, 30/40), road tar (RT4, RT5), or approved cutbacks (Clause 4.1.1 and 4.1.2). The binder application rate on different bases is given in the table below (Clause 5.3):

The process ensures bonding between layers and a durable base or binder course, but this construction is not suitable as a wearing course (Clause 5.10).

Sources: Clause 5.8, Clause 5.9, Clause 4.1.1, Clause 4.1.2, Clause 5.3

The application of key aggregate in built-up spray grout as per IRC 47 involves placing a top layer of key aggregates over two compacted layers of coarse aggregates bonded with bituminous binder, with a total thickness not exceeding 75 mm (Clause 5.10). The key aggregates must conform to grading and physical requirements to ensure durability and bonding. The binder used can be straight-run bitumen (grades 80/100, 60/70, 30/40), road tar (R.T. 4 or R.T. 5), or approved cutback (Clause 4.1.1 and 4.1.2). Key aggregates grading and physical properties are specified in Tables 1 and 2 below. The binder application rate depends on the base type (Table 3). The construction involves spreading, compacting coarse aggregates, applying binder, and finishing with key aggregates as per Clause 5.5 and 5.6.

Sources: Clause 5.10, Clause 4.1.1, Clause 4.1.2, Clause 4.2.1, Clause 4.2.2, Clause 4.2.3, Clause 5.5, Clause 5.6

For Surface Finish and Quality Control in built-up spray grout as per IRC 47 Clause 5.10 and related sections, key specifications include:

• Binder Types: Straight-run bitumen (IS:73), road tar (IS:215), or approved cutback; grades depend on climate (e.g., bitumen 80/100, 60/70, 30/40).

• Aggregate Requirements: Clean, strong, durable, cubical fragments free from impurities.

• Physical Properties of Aggregates:

• Aggregate Gradation (% Passing, IS:460):

• Construction: Two-layer compacted crushed aggregates with bituminous binder after each layer; total thickness ≤ 75 mm; not for wearing course.

These ensure proper surface finish and quality control for spray grout base or binder courses.

Sources: Clause 5.10, Table 1, Table 2

As per IRC 47 Clause 5.11, the built-up spray grout surface must have the wearing course applied before opening to traffic because it is an open-graded construction. However, in special cases, limited traffic may be allowed with vehicle speeds restricted to 16 km/h. The construction involves two layers of coarse aggregates compacted with bituminous binder applied after each layer at 12.5 to 15.0 kg per 10 m² (Clauses 5.6, 5.8). Key aggregates are then spread at 0.13 m³ per 10 m² and rolled to embed them fully (Clause 5.9). Surface evenness tolerances are: longitudinal profile variation max 12 mm over 3 m straight edge, max 30 undulations >10 mm per 300 m; cross profile variation max 8 mm checked with camber template (Clause 5.10).

Sources: Clause 5.11, Clause 5.6, Clause 5.8, Clause 5.9, Clause 5.10

As per IRC 47 Clause 5.1, built-up spray grout construction shall NOT be done when the atmospheric temperature in shade is below 16°C, or when the pavement is damp, foggy, rainy, or during dust storms. This ensures proper curing and bonding. The base surface must be dry and thoroughly cleaned before construction (Clause 5.3). For bituminous binder application, the binder shall be heated to the specified temperature and applied uniformly at rates given in Table 3 (Clause 5.3). The binder quantity for the first and second layers is 12.5 to 15.0 kg per 10 m² (Clause 12.5 and 5.8). Key aggregates are applied at 0.13 m³ per 10 m² immediately after the second binder application (Clause 5.9). The surface finish tolerances are: longitudinal profile variation max 12 mm over 3 m straight edge, and cross profile variation max 8 mm with camber template (Clause 5.10). Opening to traffic is allowed only after wearing course application or with speed restriction of 16 km/h (Clause 5.11).

Sources: Clause 5.1, Clause 5.3, Clause 12.5, Clause 5.8, Clause 5.9, Clause 5.10, Clause 5.11