MODULE1-2

Introduction to HMA Pavements

Learning Objectives

• Describe the types of (HMA) pavements

• Identify the role of each pavement layer

• Discuss key issues related to pavement performance

• Describe HMA pavement response to traffic and environmental loading

• HMA

– with unbound (granular) base

– with bound (stabilized) base

– full-depth HMA

• Composite

– PCC/HMA

Types of HMA Pavements

Wearing Course

Binder Course

Base Course (Bound or Unbound)

Subbase Course (Usually Unbound)

HMASurface

Subgrade Soil

Course Terminology

• Asphalt cement

• Hot-mix asphalt (HMA)

• Structure:

Role of Pavement Layers

HMA Layer

Base Course

Subbase Course

Subgrade Soil

4 Roles:

Pavement Performance

• Functional Performance

– Providing users a safe and comfortable ride

• Structural Performance

– Ability to withstand traffic and environmental loadings

TrafficSubgrade

Soil

Materials C&MVariation

Environment

M&R

PAVEMENTPAVEMENTPERFORMANCEPERFORMANCE

Factors Affecting Pavement Performance

HMA Pavement Response

• Stresses, strains and deformations resulting from wheel loads

• Changes in material properties resulting from changes in the environment

Subgrade Soil

Subbase

Base

HMA Surface

WheelLoad

Rutting Mechanism

Subgrade Soil

Subbase

Base

HMA Surface

WheelLoad

Fatigue Cracking Mechanism

Location Along HMA Surface

ContractionHMA

Friction on Underside of HMA Surface

TensileStress

Crack orCold Joint

Crack orCold Joint

Surface

Tensile Strength

Thermal Cracking Mechanism

200+ mmHMA

Surface

Oxidation PenetrationSurface-Initiated Crack

Interface Between Lifts

Top-Down Cracking Mechanism

Separationof asphalt

binder from aggregate

Stripping Mechanism

Subbase Course

HMA Overlay

Subgrade Soil

PCC Slab Underlying Joint

TensionShear

WheelLoad

Reflection Crack Mechanism

• Frost heave

• Strength loss (due to moisture)

• Soil swelling

• Oxidation

Other Distress Mechanisms

Other Key Topics(covered in text)

• HMA Materials

– Asphalt binder

– Modified asphalts

– Asphalt rubber

– Mineral aggregate

• Superpave Binder Specification

Review• What are the different types of HMA

pavements?

• What is the role of each pavement layer?

• What is the difference between functional and structural performance?

• What are some of the important factors that affect pavement performance?

• What are some of the typical pavement distress mechanisms associated with HMA pavements?

Key References• Yoder, E. J. and M. W. Witczak. 1975.

Principles of Pavement Design. Second Edition. John Wiley & Sons, New York, NY.

• American Association of State Highway and Transportation Officials (AASHTO). 1993. Guide for Design of Pavement Structures, American Association of State Highway and Transportation Officials, Washington, DC.