MODULE 1-2 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) HMA Surface 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

Traffic Subgrade Soil MaterialsC&M Variation Environment M&R PAVEMENTPERFORMANCE 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 Wheel Load Rutting Mechanism

Subgrade Soil Subbase Base HMA Surface Wheel Load Fatigue Cracking Mechanism

Location Along HMA Surface Contraction HMA Friction on Underside of HMA Surface Tensile Stress Crack or Cold Joint Crack or Cold Joint Surface Tensile Strength Thermal Cracking Mechanism

200+ mm HMA Surface Oxidation Penetration Surface-Initiated Crack Interface Between Lifts Top-Down Cracking Mechanism

Separation of asphalt binder from aggregate Stripping Mechanism

Subbase Course HMA Overlay Subgrade Soil PCC Slab Underlying Joint Tension Shear Wheel Load 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 Principles of Pavement Design. Second Edition. John Wiley & Sons, New York, NY. American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures, American Association of State Highway and Transportation Officials, Washington, DC.