RIGID PAVEMENT BASICS

Rigid pavements are so named because the pavement structure deflects very little under loading due to the high modulus of elasticity of their surface course. A rigid pavement structure is typically composed of a PCC surface course built on top of either (1) the subgrade or (2) an underlying base course. Because of its relative rigidity, the pavement structure distributes loads over a wide area with only one, or at most two, structural layers

This section describes the typical rigid pavement structure consisting of: Surface course. This is the top layer, which consists of the PCC slab. Base course. This is the layer directly below the PCC layer and generally consists of aggregate or stabilized subgrade. Subbase course. This is the layer (or layers) under the base layer. A subbase is not always needed and therefore may often be omitted.

Basic Structural Elements :

The surface course (made of PCC) is the stiffest (as measured by resilient modulus) and provides the majority of strength. The underlying layers are orders of magnitude less stiff but still make important contributions to pavement strength as well as drainage and frost protection.

Surface Course

The surface course is the layer in contact with traffic loads and is made of PCC. It provides

characteristics such as friction (see Figure 2.21), smoothness, noise control and drainage. In addition, it serves as a waterproofing layer to the underlying base, subbase and subgrade. The surface course can vary in thickness but is usually between 150 mm (6 inches) (for light loading) and 300 mm (12 inches) (for heavy loads and high traffic).  shows a 300 mm (12 inch) surface course.

Base Course

The base course is immediately beneath the surface course. It provides (1) additional load distribution, (2) contributes to drainage and frost resistance, (3) uniform support to the pavement and (4) a stable platform for construction equipment (ACPA, 2001). Bases also help prevent subgrade soil movement due to slab pumping.

Subbase Course

The subbase course is the portion of the pavement structure between the base course and the

subgrade. It functions primarily as structural support but it can also:

1. Minimize the intrusion of fines from the subgrade into the pavement structure.
2. Improve drainage.
3. Minimize frost action damage.
4. Provide a working platform for construction

The subbase generally consists of lower quality materials than the base course but better than the

subgrade soils. Appropriate materials are aggregate and high quality structural fill. A subbase course is not always needed or used.

Joints

Joints are purposefully placed discontinuities in a rigid pavement surface course. The most common

types of pavement joints, defined by their function, are (AASHTO, 1993): contraction, expansion,

isolation and construction

Continous.....?