Standard Specifications and Code of Practice for Design and Construction of Surface Dressing

IRC 110: Introduction - Key Formulas, Tables & Specifications

Voids in Surface Dressing Construction (Clause 2.1)

• Voids % at stages:
  • Just laid aggregates: 50%
  • After rolling: 30%
  • After traffic: 20%

Aggregate Quantity (Single-coat Surface Dressing)

[ Q_a = \frac{ALD \times 1000}{100 \times (100 - V)} ]

• (Q_a) = quantity of aggregates (m³/m²)
• (ALD) = Average Least Dimension of aggregates (mm)
• (V) = voids % (use 20% after traffic)

Add 10% for aggregate loss (whip off).

Bitumen Quantity (kg/m²)

[ Q_b = \frac{75 \times 20 \times ALD}{100 \times 1000} ]

• Bitumen occupies 75% of 20% void thickness.

ALD Determination (Clause A.2.2)

• Use nomograph (Fig. A3) based on:
  • Median size (50% passing sieve)
  • Flakiness Index
• ALD = function of median size & flakiness index.

Factors Affecting Design (Weighting Factors)

Sum factors to adjust binder and aggregate rates.

Approximate Application Rates (Tables 5a & 5b)

IRC 110: Scope - Key Formulas, Tables & Specifications for Surface Dressing

Voids in Surface Dressing (Clause A.2.1)

• Voids at stages:

  • Just laid aggregates: 50%
  • After rolling: 30%
  • After traffic: 20%

• Aggregate quantity (m³/m²) for single-coat:

  [ \text{Aggregate quantity} = \frac{ALD \times (1 - \text{voids after rolling})}{1000} ]

• Aggregate quantity with 10% loss allowance:

  [ \text{Corrected aggregate} = \text{Aggregate quantity} \times 1.1 ]

• Bitumen quantity (kg/m²) for single-coat:

  [ \text{Bitumen quantity} = 0.75 \times 0.20 \times ALD \times 10 ]

ALD (Average Least Dimension) Determination (Clause A.2.2)

• Use nomograph (Fig. A3) based on median size and flakiness index.
• Median size = sieve size where 50% passes.
• ALD accounts for shape (flakiness).

Weighting Factors for Design (Traffic, Surface, Climate, Aggregates)

Sum factors to get overall weighting factor.

Design Steps Summary:

1. Select nominal aggregate size (Table 3).
2. Select binder type.
3. Determine ALD.
4. Sum weighting factors.
5. Use Fig. A4 chart to find binder and aggregate application rates.
6. Adjust for traffic slope and binder type.

Approximate Application Rates (Tables 5(a) & 5(b))

IRC 110 - Definitions & Key Formulas for Surface Dressing

Voids at stages of Surface Dressing:

• Just laid aggregates: 50% voids
• After rolling: 30% voids
• After traffic operation: 20% voids

Aggregate Quantity (single coat) per m²:

[ Q_a = \frac{ALD \times 10}{1000} \quad \text{(m³/m²)} ]

• ALD = Average Least Dimension of aggregates (mm)

Corrected for 10% loss (whip off):

[ Q_{a,corrected} = Q_a \times 1.1 ]

Bitumen Quantity (kg/m²) for single coat:

[ Q_b = 0.75 \times 0.20 \times ALD \times 1000 ]

• Bitumen occupies 75% of 20% voids after traffic

Determination of ALD:

• Use median aggregate size (50% passing sieve size)
• Use flakiness index
• Use nomograph (Fig. A3) to find ALD from median size and flakiness index

Weighting Factors for Design:

Sum factors to get overall weighting factor for design.

Approximate Application Rates:

Notes:

• For two-coat dressing, second

Key Formulas & Tables for Materials in IRC 110 (Surface Dressing)

1. Voids in Surface Dressing Layers (Clause 2.1, Fig. A1)

• Immediately after spreading aggregates: 50% voids
• After rolling/compaction: 30% voids
• After traffic operation: 20% voids

2. Aggregate Quantity (m³/m²) for Single-Coat Surface Dressing:

[ \text{Aggregate quantity} = \frac{ALD \times 1000}{(100 - \text{voids %}) \times 100} ]

• ALD = Average Least Dimension of aggregates (mm)

Adjust for 10% loss due to traffic whip-off: [ \text{Corrected aggregate quantity} = \text{Aggregate quantity} \times 1.10 ]

3. Bitumen Quantity (kg/m²) for Single-Coat Surface Dressing:

[ \text{Bitumen quantity} = 0.75 \times 0.20 \times ALD \times 10 ]

• Bitumen occupies 75% of 20% void thickness after traffic.

4. Nomograph for ALD (Clause A.2.2)

• ALD depends on median size and flakiness index of aggregates.
• Use Fig. A3 nomograph to find ALD by joining median size and flakiness index.

5. Factors Affecting Design (Overall Weighting Factor)

Sum factors from:

• Traffic volume (e.g., Medium-heavy = -1)
• Existing surface condition (e.g., Very rich bituminous = -3)
• Climate (e.g., Tropical = +1)
• Aggregate type (e.g., Flaky = -2)

6. Approximate Application Rates (Tables 5(a) & 5(b))

IRC 110: Surface Dressing Construction Method - Key Formulas, Tables & Specifications

1. Voids & Aggregate Quantity (Clause 2.1)

• Aggregate volume per m² (single coat):

  [ \text{Aggregate volume} = \frac{ALD \times (100 - 20)}{100 \times 1000} \quad \text{m}^3/\text{m}^2 ]

• Adjust for 10% loss due to whip-off:

  [ \text{Required aggregate} = \text{Aggregate volume} \times 1.1 ]

• Bitumen quantity per m²:

  [ \text{Bitumen} = 0.75 \times 20 \times ALD \quad \text{(kg/m}^2) ]

2. ALD (Average Least Dimension) Determination (Clause A.2.2)

• Use nomograph (Fig. A3) based on median size & flakiness index.
• Median size = sieve size at 50% passing.
• ALD accounts for shape & size of aggregates.

3. Design Factors for Binder & Aggregate Rates

Sum factors → Use Fig. A4 (design chart) to find binder & aggregate rates.

4. Approximate Application Rates (Tables 5(a), 5(b))

IRC 110 Appendix: Key Formulas, Tables & Specifications for Surface Dressing

1. Voids in Surface Dressing Construction (Fig. A1)

• Immediately after spreading aggregates: 50% voids
• After rolling/compaction: 30% voids
• After traffic operation: 20% voids

2. Aggregate Quantity (m³/m²) for Single-coat Surface Dressing:

[ \text{Aggregate quantity} = \frac{ALD \times 100 \times 1000}{(100 - 20) \times 100} ]

• ALD: Average Least Dimension of aggregates (mm)
• Add 10% for traffic whip-off loss.

3. Bitumen Quantity (kg/m²) for Single-coat Surface Dressing:

[ \text{Bitumen quantity} = 0.75 \times 0.20 \times ALD \times 1000 ]

• Bitumen occupies 75% of the 20% void space after traffic.

4. Determination of ALD (Average Least Dimension)

• Use the nomograph (Fig. A3) relating:
  • Median aggregate size (50% passing sieve)
  • Flakiness index
• ALD is found by drawing a line between these two values.

5. Weighting Factors for Design (Sum factors from):

• Sum these factors to get overall weighting factor.

6. Design Binder & Aggregate Application Rates

• Use Fig. A4 chart with ALD and weighting factor.
• Adjust binder rate for:
  • Slow traffic/climbing grade (-10%)
  • Fast traffic/downgrade (+10-20%)
• Adjust binder for type:
  • Penetration grade: -10%
  • Emulsion: Multiply by ( Z = \frac{\text{Bitumen content of emulsion (%)}}{90} )