Pavement Analysis and Design Definition Pavement – Pavement is the upper part of roadway, airport or parking area structure – It includes all layers resting on the original ground – It consists of all structural elements or layers, including shoulders

What is Design? – Conceived/developed plan for something to serve a specific function. What is a pavement design? – It is the process by which the structural components a road segment are determined taking into account the nature of the subgrade, density and traffic composition.

Functions of the Pavement – Reduce and distribute the traffic loading so as not to damage the subgrade – Provide vehicle access between two points under all-weather conditions – Provide safe, smooth and comfortable ride to road users without undue delays and excessive wear & tear – Meet environmental and aesthetics requirement – Limited noise and air pollution – Reasonable economy

Pavement Design Phases Highway design consists of three stages – Geometric design (route selection or alignment design) – Capacity design (number of lanes to meet traffic demand) – Structural design to withstand loads and environment Structural design consists of 3 steps – Selection of materials (types of pavement) – Proportioning of materials – Layer thickness design

Requirement of pavement structure 1. Sufficient thickness to spread loading to a pressure intensity tolerable by subgade 2. Sufficiently strong to carry imposed stress due to traffic load 3. Sufficient thickness to prevent the effect of frost susceptible subgade 4. Pavement material should be impervious to penetration of surface water which could weaken subgade and subsequently pavement 5. Pavement mat. shd be non-frost susceptible 6. Pavement surface shd. be skid resistant

Types of Pavement Failure Failure criteria Flexible Pavements Fatigue Cracking, Rutting, Thermal Cracking, Rigid Pavements Pumping or Erosion Others: Faulting, spalling, joint deterioration

Stresses and Strains in Asphalt Pavements

Stresses and Strains in Flexible Pavements Pavement response to applied wheel load – Stress & strain are produced in each layer – Pavement vertically deflects – Location and magnitude of responses determine type and extent of pavement deterioration and the rapidity of deterioration. – Determined using the theory of elasticity (Hook’s Law)

Pavement Responses Stresses, Strains, & Deflections Load-Related – Vertical – Shear – Tensile – Compression Non-Load-Related

Structural Response Models Help determine pavement responses as a function of applied load (traffic or environmental) Stress, Strain , Deflection

Responses are needed for two reasons: 1. Material characterization, and 2. Predicting pavement distress.

Tension Compression

Stresses and Strains Flexible Pavements Sources of Stress and Strain - Load related Vertical Stress and strain (rutting) Shear Stresses and strain Radial stresses and strain – Shrinkage stresses and strain (cracking) – Temperature-Induced Stresses and strains (cracking)