Properties of Asphalt Concrete Notes

Properties of Asphalt Concrete

Learning Outcomes

  • Familiarize the properties of asphalt concrete.
  • Identify the factors affecting the properties of asphalt concrete.

Asphalt Concrete

  • Asphalt concrete is an artificial building material.
  • It is obtained by mixing binder, filler, and aggregates.
  • Asphalt is a dark brown to black cementitious material.
  • It can be solid, semi-solid, or liquid.

Kinds of Manufactured Asphalt

Asphalt Cement
  • Refined to meet specifications for paving, industrial, and special purposes.
  • Uses:
    • Item 303 - Bituminous Seal Coat
    • Bituminous Surface Treatment
    • Bituminous Penetration Macadam Pavement
    • Bituminous Concrete Surface Course (Hot-laid)
Liquid Asphalt
  • Asphalt cement liquified by blending with petroleum solvents (diluents).
  • Usually a minimum of 55% of asphalt cement.
  • Classifications:
    • Rapid Curing (RC) Asphalt
    • Medium-Curing (MC) Asphalt
    • Slow-Curing (SC) Asphalt
Asphalt Emulsion
  • An emulsion of asphalt cement and water (usually 60% asphalt and 40% water).
  • Contains a small amount of emulsifying agent (1-2% emulsifier).
  • Classifications:
    • Anionic Emulsified Asphalt (-)
    • Cationic Emulsified Asphalt (+)
    • Blown or Oxidized Asphalt
Bituminous Mix
  • Mixture of asphalt (5-8%), aggregate (92%-95%), and additive (not more than 2%).

Use of Asphalt

  1. Binder to Asphalt concrete
  2. Waterproofing material
  3. Joint and crack filler
  4. Prime coat
  5. Tack coat
  6. Seal coat
  7. Undersealing (PCCP)
  8. Pipe coating
  9. Surface treatment
  10. Roofing

Types of Road Pavement

  • Flexible pavement
  • Rigid pavement

Asphalt for Road Pavement

Advantages
  • More economical
  • Ease of construction
  • Good comfort to drivers
Disadvantages
  • High maintenance cost

Properties of Asphalt

  1. Stability
  2. Durability
  3. Impermeability
  4. Workability
  5. Flexibility
  6. Fatigue Resistance
  7. Skid Resistance
Stability
  • The ability of asphalt concrete to resist deformation, rutting, or displacement under applied loads, especially at high temperatures.
  • Ensures the pavement can carry traffic loads without excessive distortion.
  • Factors Affecting Stability:
    • Aggregate interlock and gradation (aggregate characteristics)
    • Asphalt binder viscosity and grade (cohesion)
    • Compaction (degree of densification)
    • Air void content
    • Load magnitude and frequency
    • Mix temperature during laying and compaction
  • Reference: DPWH Blue Book Section 900, ASTM D6927 (Marshall Stability Test)
Durability
  • The ability of asphalt concrete to resist weathering, aging, and the damaging effects of water, oxidation, and traffic over time.
  • Durable asphalt maintains strength and flexibility throughout its service life.
  • Factors Affecting Durability:
    • Asphalt binder quality and type
    • Aggregate absorption and hardness
    • Air void content (too high or too low reduces durability)
    • Mix design (balanced asphalt content and gradation)
    • Proper compaction (to minimize permeability)
    • Environmental conditions (temperature cycles, rainfall, UV exposure)
  • Reference: DPWH Blue Book Section 900, ASTM D2872 (RTFO aging test)
Impermeability
  • The property of asphalt concrete that resists the penetration of water or air into the pavement structure.
  • Protects the base and subgrade layers from weakening and failure.
  • Factors Affecting Impermeability:
    • Air void content (lower voids increase impermeability)
    • Degree of compaction
    • Aggregate gradation (well-graded mixes reduce voids)
    • Asphalt content (adequate binder coats and seals aggregates)
    • Construction practices (proper joint sealing and surface finish)
  • Reference: DPWH Blue Book Section 900, AASHTO T166 (Density Test by Core Method)
Workability
  • Describes the ease with which a paving mixture can be placed and compacted.
  • Workability can be improved by changing mix design parameters, aggregate source, and/or gradation.
Flexibility
  • The ability of an asphalt pavement to adjust to gradual settlements and movements in the sub-grade without cracking.
  • An open-graded mix with high binder content is generally more flexible than a dense-graded, low binder content mix
Fatigue Resistance
  • The pavement's resistance to repeated bending under wheel loads (traffic).
Skid Resistance
  • The ability of an asphalt surface to minimize skidding or slipping of vehicle tires, particularly when wet.
  • For good skid resistance, tire tread must be able to maintain contact with the aggregate particles instead of riding on a film of water on the pavement surface (hydroplaning).
  • Typically measured in the field at 40 mi/hr with a standard tread tire under controlled wetting of the pavement surface.
  • Rough-textured aggregate (Open-graded mixture) 3/8 in – ½ in (10-13 mm) maximum size.

Quality Control Measures

  1. Selection of materials
  2. Design of mixture
  3. Aggregate production control
  4. Asphalt mix production control
  5. Sampling and testing of mixture
  6. Construction control
  7. Foundation control
  8. Drainage control

Defects on Bituminous Material

  1. SURFACE DEFECT – smooth surface, streaking
  2. CRACKS – edge cracks, shrinkage cracks, longitudinal cracks
  3. DEFORMATION – slippage, rutting, corrugation, shoving, settlements
  4. DISINTEGRATION – stripping, loss of aggregates, edge breakings

Laboratory Tests for Asphalt Mixture

  1. ASTM D1074-09 Standard test method for Compressive Strength of Bituminous Mixtures
  2. ASTM D6925-15 Standard Test Method for Preparation and Determination of the Relative Density of Asphalt Mix Specimens by Means of the Superpave Gyratory Compactor