Specification for Bituminous Concrete (Asphaltic Concrete) for Road Pavement (First Revision)

The Introduction of IRC 29 outlines key specifications for bituminous concrete mixes used in road construction. Key points include:

• Aggregate Requirements: Coarse aggregate must meet physical criteria such as maximum 30-40% Aggregate Impact Value, max 25% Los Angeles Abrasion or Flakiness Index, max 25% Stripping Value, and max 1% water absorption (exceptionally up to 2%) as per IS 2386 and IS 6241 (Clause 2.36).
• Aggregate Gradation: Three gradings are specified for different layer thicknesses (25 mm, 40 mm, 50 mm) with detailed sieve passing percentages given in Table 3.

• Mix Design: Binder content is fixed to meet mix requirements (Table 1, not shown). Job mix formula includes proportions of coarse aggregate, fine aggregate, filler, and binder, with permissible variations detailed in Table 4.

These form the foundational specifications for materials and mix design in IRC 29 (Introduction and Design Criteria sections).

Sources: Clause 1 Introduction, Clause 2.36, Table 2, Table 3, Table 4

The scope of IRC 29 covers the specifications and guidelines for bituminous concrete for road construction, including materials, mix design, construction, and quality control. Key points include:

• The work shall not be done in unsuitable weather (rain, fog, temperature below 10°C) as per Clause 6.1.
• Preparation of base must be to specified levels and free of dust before laying bituminous concrete (Clause 6.2).
• Tack coat application rates are specified in Table 5, e.g., 5.0 to 5.5 kg/10 m² for normal bituminous surfaces (Clause 6.3.4).
• Aggregate physical requirements and gradation are detailed in Tables 2 and 3, e.g., maximum 30-40% aggregate impact value, and grading ranges for different course thicknesses.
• Job mix formula requirements and permissible variations are given in Clauses 5.3 and 5.4, with Table 4 specifying allowable deviations.

These define the overall scope and technical framework for bituminous concrete works under IRC 29.

Sources: Clause 2, Clause 6.1, Clause 6.2, Clause 6.3.4, Table 5, Table 2, Table 3, Clause 5.3, Clause 5.4, Table 4

The key design criteria in IRC 29 include specifications for aggregates and mix design as follows:

• Coarse Aggregate Physical Requirements (Table 2):

  • Aggregate Impact Value: max 30-40%
  • Los Angeles Abrasion or Flakiness Index: max 25%
  • Stripping Value: max 25%
  • Water Absorption: max 1% (up to 2% in exceptional cases)
  • Soundness (Loss with sodium sulphate 5 cycles): max 12%
  • Soundness (Loss with magnesium sulphate 5 cycles): max 18%
  • Crushed slag requirements include unit weight ≥1120 kg/m³, max 20% glossy materials, sulphur content ≤2%, water absorption ≤10%, and max 6% flat/elongated pieces.

• Aggregate Gradation (Table 3): Specifies percent passing for different sieve sizes for three gradings based on layer thickness (25 mm, 40 mm, 50 mm). For example, for Grading 1 (25 mm thick course), 100% passes 13.2 mm sieve, 40-55% passes 2.36 mm sieve, and 6-9% passes 75 μm sieve.

• Mix Design: Binder content fixed to meet mix requirements (Table 1, not shown). Job mix formula includes proportions of coarse aggregate, fine aggregate, filler, and binder, based on laboratory design and must be approved by the Engineer.

• Permissible Variations (Table 4): Allowable deviations in aggregate gradation from the job mix formula for quality control.

These criteria ensure durability, strength, and proper gradation for bituminous concrete layers as per IRC 29 Section 3 and related tables.

Sources: Clause 3, Table 2, Table 3, Table 4

Key materials specifications from IRC 29 for bituminous concrete are as follows:

• Coarse Aggregate Requirements (Table 2):

  • Aggregate Impact Value: max 30-40%
  • Los Angeles Abrasion or Flakiness Index: max 25%
  • Stripping Value: max 25%
  • Water Absorption: max 1% (up to 2% in exceptional cases)
  • Soundness Loss (5 cycles): Sodium sulphate max 12%, Magnesium sulphate max 18%
  • Crushed slag must be air cooled blast furnace slag with unit weight ≥1120 kg/m³ and max 20% glossy materials.

• Fine Aggregate: Passing 2.36 mm sieve and retained on 75 µm sieve, clean, hard, durable, free from deleterious substances.

• Filler: Inert material passing 600 µm sieve, with at least 90% passing 150 µm and 70% passing 75 µm sieve.

• Aggregate Gradation (Table 3): Specifies % passing for different sieve sizes for three gradings based on layer thickness (25 mm, 40 mm, 50 mm).

• Tack Coat Application (Table 5): Bitumen quantity per 10 m² varies by surface type (5.0-7.5 kg).

These ensure quality and durability of bituminous concrete layers as per IRC 29 Clause 4 and 6.

Sources: Clause 2.36, Table 2, Table 3, Table 5, Clause 4, Clause 6

The key specifications and tables for Mix Design in IRC 29 are as follows:

• Physical Requirements of Coarse Aggregate (Table 2):

  • Aggregate Impact Value: max 30-40%
  • Los Angeles Abrasion or Flakiness Index: max 25%
  • Stripping Value: max 25%
  • Water Absorption: max 1% (up to 2% in exceptional cases)
  • Soundness Loss (Sodium Sulphate 5 cycles): max 12%
  • Soundness Loss (Magnesium Sulphate 5 cycles): max 18%

• Aggregate Gradation (Table 3): Specifies % passing for different sieve sizes for three gradings based on layer thickness (25 mm, 40 mm, 50 mm). For example, for Grading 1 (25 mm thick course): 100% passing 13.2 mm sieve, 40-55% passing 2.36 mm sieve, 6-9% passing 75 μm sieve.

• Job Mix Formula: Determined by blending aggregates and fixing optimum binder content using the Marshall method (Clause 5.3). It includes proportions of coarse aggregate, fine aggregate, filler, and binder.

• Permissible Variations (Table 4): Limits on variation in aggregate gradation from the job mix formula for quality control.

• Mix Preparation and Transport: Hot mix plant requirements, temperature control (binder 150°-177°C, aggregate 153°-163°C), thorough mixing, and transport in covered vehicles (Clause 6.4).

• Spreading and Compaction: Use of mechanical paver with screed, rolling sequence and roller types, achieving at least 98% density of Marshall specimen (Clause 6.5 and 6.6).

These details ensure the mix meets stability, performance, and durability criteria as per IRC 29.

Tables reproduced below:

Table 2. Physical Requirements of Coarse Aggregate

Table 3. Aggregate Gradation

Table 4. Permissible Variations from the Job Mix Formula (partial data available)

For full details, refer to IRC 29 Clause 5 and Tables 2, 3, and 4.

Sources: Clause 2.36, Table 2, Table 3, Clause 5.3, Table 4, Clause 6.4, Clause 6.5, Clause 6.6

Key construction specifications from IRC 29 Clause 6 include:

• Weather and Seasonal Limitations: Laying work shall not be done during rainy, foggy weather, dust storms, or when temperature is ≤10°C in shade (Clause 6.1).

• Base Preparation: The base must be shaped, cleaned, and conditioned to specified levels and crossfall. Profile correction or remedial measures are advised if the base is irregular or distressed (Clause 6.2).

• Tack Coat Application: A single coat of low viscosity bituminous binder (conforming to IS: 73, 217, 454, or 8887) is applied on a clean surface. Binder heating and spraying rates depend on surface type as per Table 5 below (Clauses 6.3.1 to 6.3.4).

TABLE 5. RATE OF APPLICATION OF TACK COAT

These ensure proper bonding and durability of bituminous layers during construction.

Sources: Clause 6.1, Clause 6.2, Clause 6.3.1, Clause 6.3.2, Clause 6.3.3, Clause 6.3.4, Table 5

As per IRC 29, Clause 7 (Opening to Traffic), traffic may be allowed only after the completion of the final rolling when the bituminous mix has cooled down to the surrounding temperature. This ensures the pavement has achieved adequate compaction and stability before being subjected to traffic loads. The key specification is that the mix must be fully compacted and cooled to ambient temperature before opening to traffic to prevent damage.

Additionally, Clause 6.6 details the rolling and compaction process, emphasizing that rolling should continue until a density of at least 98% of the laboratory Marshall specimen is achieved and roller marks are eliminated, ensuring pavement quality before opening.

No specific formula is given for opening time, but the cooling to ambient temperature is the controlling criterion.

Summary:

• Final rolling complete
• Mix cooled to surrounding temperature
• Density ≥ 98% of Marshall specimen (Clause 6.6.2)

This is critical to ensure durability and performance of the pavement under traffic loads.

Sources: Clause 7, Clause 6.6.2

Key controls for bituminous concrete construction per IRC 29 are summarized as follows:

• Aggregate Quality Controls: Coarse aggregate must meet physical requirements such as maximum 30-40% Aggregate Impact Value, max 25% Los Angeles Abrasion or Flakiness Index, max 25% Stripping Value, and max 1% water absorption (exceptionally up to 2%) as per IS 2386 and IS 6241 (Clause 2.36).

• Aggregate Gradation: Three gradings are specified for different layer thicknesses (25 mm, 40 mm, 50 mm) with detailed sieve passing percentages (Table 3).

• Job Mix Formula: Must be based on representative samples, specifying proportions of coarse aggregate, fine aggregate, filler, and binder content fixed by Marshall method (Clause 5.3).

• Permissible Variations: Table 4 defines allowable deviations in aggregate gradation from the job mix formula.

• Tack Coat Application: Bitumen quantity for tack coat varies by surface type, e.g., 5.0-5.5 kg/10 m² for normal bituminous surface (Table 5).

These controls ensure quality and durability of bituminous concrete layers.

Sources: Clause 2.36, Table 2, Table 3, Clause 5.3, Table 4, Table 5