Specification for Semi-Dense Bituminous Concrete
1987 Edition

Overview of Semi-Dense Bituminous Concrete Specifications

• Coverage: This document focuses on design, materials, and construction guidelines for bituminous surfacing.
• Design Objectives: Emphasizes durability, cost-effectiveness, and resistance to climatic conditions.
• Material Classification: Defines grading categories with detailed sieve analysis requirements.

Aggregate Sieve Passing Percentages

• Grading 1 corresponds to coarser aggregates; Grading 3 to finer.
• Proper aggregate grading is vital for workability and strength.

Refer to clauses 3 through 7 for detailed mix design and construction procedures.

Scope of Semi-Dense Bituminous Concrete Usage

This section defines the limits and applicability of the code, primarily addressing flexible pavement design and construction incorporating bituminous macadam and concrete layers.

Highlights:

• Applicable to flexible road pavements utilizing bitumen-based materials.
• Encompasses material selection, design methodology, construction processes, and quality assurance.
• Intended for highways and other roads subjected to different traffic intensities.
• Specifies detailed aggregate grading norms for bituminous mixtures.

Aggregate Grading Table (Excerpt)

Design Overview

• Mix design is governed by the job mix formula (Clause 5).
• Construction and testing protocols ensure pavement longevity and performance.

This scope standardizes pavement design to enhance safety and durability on Indian roadways.

flowchart TD
    S[Scope: Flexible Pavements] --> M[Materials]
    S --> D[Design Parameters]
    S --> C[Construction Methods]
    S --> Q[Quality Assurance]

Design Guidelines Using the Marshall Method

Essential parameters for bituminous mix design include:

• Stability tests confirm adequate strength.
• Flow values indicate flexibility of the mix.
• Voids in mix control air content for durability.
• VMA ensures sufficient binder coating around aggregates.
• Binder percentage is optimized to meet these criteria.

This framework ensures a balanced mix providing durability and performance.

flowchart TD
    A[Select Aggregates] --> B[Determine Binder Percentage]
    B --> C[Prepare Marshall Samples]
    C --> D[Apply 50 Compaction Blows per End]
    D --> E[Measure Stability & Flow]
    E --> F{Meets Specs?}
    F -- Yes --> G[Finalize Mix]
    F -- No --> B

Material Requirements & Tables

1. Aggregate Gradation (TABLE 4)

2. Coarse Aggregate Criteria (TABLE 3)

• Water absorption may reach 2% under special cases.

3. Fine Aggregate & Filler

• Fine aggregate must pass the 2.8 mm sieve and be retained on 90 µm sieve, comprising clean, durable materials.
• Filler should be inert, pass through 710 µm sieve, with at least 90% passing 180 µm and 70% passing 90 µm sieves, examples include stone dust and cement.

Job Mix Formula Essentials

Defines proportions of coarse and fine aggregates, filler, and bitumen necessary to achieve semi-dense bituminous concrete with desired properties.

1. Design Parameters (Marshall Method)

2. Aggregate Requirements

• Coarse aggregates are crushed, angular, clean, and free from harmful substances.
• Fine aggregates pass 2.8 mm sieve but retained on 90 µm sieve.
• Filler is inert and meets specified gradation.

3. Coarse Aggregate Physical Properties

4. Calculation of Job Mix

• Aggregate blending by weight or volume to achieve target gradation.
• Optimum bitumen content determined from laboratory tests.
• Verify that the mix fulfills Marshall criteria.
• Use representative samples matching construction materials.

5. Formula Summary

[ \text{Job Mix Formula} = \text{Coarse Aggregate} + \text{Fine Aggregate} + \text{Filler} + \text{Optimum Bitumen}]

Construction Guidelines

1. Base Layer Preparation

• Ensure the base is firm, clean, and free from dust.
• Repair any potholes or depressions with premixed materials and compact thoroughly.

2. Material Specifications

• Coarse aggregates must be crushed, angular, clean, and retained on 2.8 mm sieve.

• Limits include:

  • Aggregate Impact Value ≤ 30%
  • Los Angeles Abrasion ≤ 40%
  • Flakiness Index ≤ 30%
  • Stripping Value ≤ 25%
  • Water Absorption ≤ 1% (up to 2% in exceptions)
  • Soundness: Sodium sulphate loss ≤ 12%, Magnesium sulphate loss ≤ 18%

• Fine aggregates pass 2.8 mm sieve and retain on 90 µm, clean and durable.

• Filler must be inert, passing 710 µm sieve, with 90% passing 180 µm and 70% passing 90 µm sieves.

3. Job Mix Formula Application

• Blend aggregates accurately by weight or volume to meet gradation.
• Use the optimum bitumen content from lab determinations.
• Match construction material characteristics to lab samples.

4. Aggregate Gradation Examples

Quality Assurance Procedures

• Aggregate Gradation: Regular sieve analysis at cold feed end to maintain mix gradation.
• Physical Properties: Test aggregates every 50-100 m³ or as specified.
• Bitumen Testing: Verify penetration and softening point per IS standards; maintain temperature between 150-177°C and viscosity 150-300 cSt.
• Temperature Control: Aggregate temperature should not exceed 163°C (±10°C); temperature difference between aggregate and bitumen ≤ 14°C.
• Mix Sampling: Collect samples per 100 tonnes or daily.
• Tests on Mix: Conduct Marshall stability, flow, voids, density, bitumen content, and aggregate gradation after extraction.

Permissible Deviations from Job Mix Formula

• Use on-site laboratory to monitor all stages.
• Achieve uniform compaction with a minimum field density of 98% laboratory density.
• Rolling sequence: edges to center; on superelevated stretches, from lower to upper edge.
• Keep roller wheels moist without oil or water contamination.

flowchart TD
    S[Sample Aggregates] --> G[Check Gradation]
    G -->|Within Limits| P[Proceed]
    G -->|Out of Limits| A[Adjust Mix]
    P --> B[Sample Bitumen]
    B --> T[Test Penetration & Softening Point]
    T -->|Pass| M[Mix Production]
    T -->|Fail| C[Adjust Binder]

Guidelines on Weather and Seasonal Constraints

• Mix Temperature during Laying:
  • Maximum allowed: 160°C
  • Minimum allowed: 120°C
• Rolling Temperature Window:
  • Conduct rolling between 80°C and 160°C to prevent surface defects.
  • Complete rolling before mix temperature drops below 80°C.
• Thickness Measurement: Use penetration depth of hot steel scale correlated with production data.
• Field Density Testing: Perform at least one test per 500 m²; target density ≥ 98% of lab density.

Aggregate Physical Limits (TABLE 3)

Temperature & Rolling Timing Illustration

gantt
title Mix Temperature & Rolling Schedule
dateFormat  HH:mm
axisFormat  HH:mm
section Temperature (°C)
Mix Laying (120-160°C) :active, laying, 12:00, 4h
Rolling Window (80-160°C) :rolling, after laying, 3h
Rolling Completion before <80°C :milestone, finish, after rolling, 0h

• Ideal weather is dry with moderate temperatures to ensure proper compaction and bonding.