Specifications for Dense Graded Bituminous Mixes
2009 Edition

Introduction to IRC 111 - Essential Formulas, Tables & Guidelines

1. Calculation of Maximum Theoretical Specific Gravity (Gmm) - ASTM D2041

Used for determining air voids and compaction objectives:

Formula (Vacuum Bowl Method)	Explanation
	A = dry mass of sample (g) <br> D = combined mass of lid, bowl, and water (g) <br> E = combined mass of lid, bowl, sample, and water (g)

2. Marshall Compaction Procedure

• Target Air Voids: 7.0 ± 0.5%
• Compaction: Adjust number of blows per side (initial ~10 blows)
• Specimens: Six total, divided into two groups for dry and conditioned testing

3. Indirect Tensile Strength (ITS) Calculation

Tensile strength (St) in kPa is computed as:

[ St = \frac{2000 \times P}{t \times d} ]

• P: Maximum load applied (N)
• t: Thickness of specimen (mm)
• d: Diameter of specimen (mm)

4. Tensile Strength Ratio (TSR) Formula

[ TSR = \frac{S_2}{S_1} ]

• (S_1): Average tensile strength of dry specimens (kPa)
• (S_2): Average tensile strength of conditioned specimens (kPa)

5. Summary of Mix Requirements (Table 8)

Scope of IRC 111 for Dense Graded Bituminous Mixtures

Important Highlights from Clause 2.2:

• Dense graded bituminous mixes comprise mineral aggregates blended with bituminous binders.
• These mixes are produced in hot mix plants and laid using mechanical pavers.
• Primarily used for binder and wearing courses on highway pavements.
• The binder course is the intermediate layer between base and wearing courses.

Types of Dense Graded Bituminous Mixes (Based on Table 1):

Aggregate Gradation and Bitumen Content (Excerpt from Table 7):

• Nominal maximum aggregate sizes differ per mix: DBM (37.5 mm), SDBC (13.2 mm), BC (19 mm).
• Bitumen content typically ranges between 4% and 5.4% depending on the mix.

Summary Diagram (Mermaid.js):

graph TD
    A[Dense Graded Bituminous Mixes] --> B(DBM)
    A --> C(SDBC)
    A --> D(BC)
    B --> E[Base/Binder Course]
    C --> F[Wearing Course]
    D --> G[Wearing Course]
    E --> H[Layer Thickness: 50-100 mm]
    F --> I[Layer Thickness: 25-40 mm]
    G --> J[Layer Thickness: 25/40/50 mm]

This section assists in selecting appropriate mix types, layer thicknesses, and layers count in highway pavement design as per IRC 111.

Material Requirements as per IRC 111

1. Fine Aggregates (Clause 3.3.1)

• Must pass through 2.36 mm sieve and be retained on 0.075 mm sieve.
• Natural sand is prohibited in binder and wearing courses; permitted up to 50% in base courses.
• Aggregates should be clean, hard, durable, dry, and free from dust or harmful substances.
• Sand Equivalent value should be minimum 50 (IS: 2720 Part 37).
• Plasticity Index must not exceed 4 for particles passing 0.425 mm sieve (IS: 2720 Part 5).

2. Coarse Aggregate Characteristics (Refer Table 5)

3. Maximum Specific Gravity (Gmm) Calculation (Clause 24.2.2010)

• Bowl Method Formula:

[ G_{mm} = \frac{A}{D + A - E} ]

• Flask Method Formula:

[ G_{mm} = \frac{A}{D + A - E} ]

Where:

• (A) = Dry mass of sample (g)
• (D) = Mass of lid and container with water (g)
• (E) = Mass of lid, container, sample with water (g)

Key Points in Mix Design According to IRC 111

1. Fines to Bitumen Ratio (Clause 3.5.4)

• Ratio of fines to bitumen by weight of total mix should be between 0.6 and 1.2 for all mixes listed in Table 7.

2. Job Mix Formula (JMF) Details (Clauses 4.3 & 4.3.1)

The JMF should specify:

• Material Information:
  • Source and origin of all constituent materials.
  • Proportions of each material.
• Binder Details:
  • Type and percentage of binder by total mix weight.
• Aggregates:
  • Percentages of coarse aggregate, fine aggregate, and mineral filler (including filler).
  • Precise percentage passing each sieve size for the combined gradation.
  • Individual grading curves and proportions for each aggregate size fraction.
• Batching Information:
  • Weights of each aggregate type and bitumen per batch (for batch plants).
• Test Data:
  • Aggregate physical properties results.
• Mixing and Compaction Temperatures:
  • Specified temperatures for mixing and compacting.

3. Aggregates Blending (Clause 4.3.1)

• Blending of multiple aggregate sizes is carried out by weight to meet the target gradation.
• Laboratory mix design defines gradation percentages per sieve size.
• These blending proportions are critical for field production.

Summary Table for Fines to Bitumen Ratio

flowchart TD
    A[Lab Mix Design] --> B[Determine Sieve-Wise Proportions]
    B --> C[Calculate Weight-Based Blending Ratios]
    C --> D[Prepare Job Mix Formula]
    D --> E[Field Implementation]
    E --> F[Batch Mixing and Compaction]

This sequence ensures compliance with gradation and binder content for optimal durability and performance.

IRC 111 Guidance on Construction Procedures and Quality Assurance

Overview of Construction Operations (Clause 5)

• Emphasizes proper placement of dense graded bituminous layers in base, binder, and wearing courses.
• Critical to maintain temperature control, proper mixing, placing, and compaction techniques.

Quality Control Tests and Their Frequency (Table 13, Clause 6.4.1)

Important Notes:

• Temperature control during mixing and paving is essential for workability.
• Stability and voids tests confirm durability.
• Frequent sampling guarantees consistent quality and compaction.

flowchart TD
    A[Material Acquisition] --> B[Quality Testing]
    B --> C[Mix Design]
    C --> D[Mixing and Heating]
    D --> E[Placement and Spreading]
    E --> F[Compaction]
    F --> G[Quality Control Testing]
    G --> H[Final Approval]

This systematic approach aligns construction with IRC 111 requirements.

Control Measures for Dense Graded Bituminous Mixes as per IRC 111

Key Tests and Their Frequencies (Clause 6 & Table 13)

Allowable Deviations from Job Mix Formula (Table 9)

Moisture Susceptibility Test Method as per IRC 111

Specimen Preparation and Conditioning

• Compact six specimens using Marshall compactor targeting air voids of 7.0 ± 0.5% (adjust number of blows starting near 10 per side).
• Split specimens into two groups with approximately equal air void content:
  • Dry Group: Store at room temperature, then soak in water at 25°C for 2 hours before testing.
  • Conditioned Group: Vacuum saturate specimens, wrap in plastic with 10 ml water in sealed bags, freeze at -18 ± 3°C for at least 16 hours, thaw in 60 ± 1°C water bath for 24 hours, then soak at 25°C for 2 hours prior to testing.

Indirect Tensile Strength (ITS) Test

• Measure specimen thickness (t, mm).
• Apply diametral load at 50 mm/min using Marshall testing equipment.
• Calculate tensile strength (St) using:

[ St = \frac{2000 \times P}{t \times d} ]

Where:

• (P) = Maximum load (N)
• (t) = Specimen thickness (mm)
• (d) = Specimen diameter (mm)

Tensile Strength Ratio (TSR)

[ TSR = \frac{S_2}{S_1} ]

• (S_1): Mean ITS of dry specimens (kPa)
• (S_2): Mean ITS of conditioned specimens (kPa)
• A higher TSR indicates superior resistance to moisture damage.

ASTM D2041: Determination of Maximum Theoretical Specific Gravity (Gmm)

• Used to determine air void content and compaction targets.
• Involves vacuum saturation of loose mix submerged in water at 25°C.
• Calculation formula (vacuum bowl under water method):

[ G_{mm} = \frac{A}{A - (C - B)} ]

Where:

• (A) = Dry sample mass in air (g)
• (B) = Mass of bowl under water (g)
• (C) = Mass of bowl plus sample under water (g)

Equipment Summary

• Marshall compactor for specimen preparation.

Summary of ASTM D2041 Procedure as per IRC 111 Annex B

Objective:

• To determine the Theoretical Maximum Specific Gravity (Gmm) of loose bituminous mixtures at 25°C.
• This value is essential for calculating air voids, binder absorption, and compaction targets.

Required Equipment:

• Vacuum container (bowl or flask) with ~4000 ml capacity.
• Vacuum pump capable of achieving residual pressure ≤ 4.0 kPa.
• Precision balance with 0.1 g accuracy.
• Water bath maintained at 25 ± 1°C.
• Manometer or pressure gauge for monitoring vacuum.

Key Equations:

Method	Formula	Variables
Vacuum Bowl Under Water		A = dry sample mass (g) <br> B = bowl mass under water (g) <br> C = bowl + sample mass under water (g)
Bowl in Air Method		A = dry sample mass (g) <br> D = lid & bowl + water mass (g) <br> E = lid, bowl, sample + water mass (g)
Flask Method		A = dry sample mass (g) <br> D = flask & cover + water mass (g) <br> E = flask, cover, sample + water mass (g)

Procedure Summary:

• Weigh representative sample (1500-2500 g) and place in vacuum container.
• Add water at 25°C to cover sample completely.
• Apply vacuum to remove air bubbles (residual pressure ~3.7 kPa).
• Maintain vacuum with agitation for 15 ± 2 minutes.
• Weigh container plus sample submerged or in air as per selected method.
• Calculate Gmm using corresponding formula.

Application:

• Gmm values are used to evaluate volumetric properties and compaction requirements for bituminous mixes.