This lesson introduces and then tests the viewer on the variables that must be considered when using segmental pavements to support pedestrian and vehicular loads on municipal streets. According to the American Society of Civil Engineers (ASCE), the following four variables are critical to consider:
An ESAL is a standard unit that is used to measure the amount of damage vehicles inflict on a surface. 1 ESAL = the impact from a single 18,000-lb axle load. The damage to a pavement caused by one pass of a large tractor-trailer in exponentially greater than that caused by a two door sedan.
It takes roughly 20,000 passes of the sedan to cause the same amount of same amount of damage as one pass of a tractor-trailer. In these scenarios, the design ESALs will be predetermined. This is usually based on the expected traffic mix. Reference ASCE and ICPI Tech Spec 4 to calculate the appropriate ESAL rating to a design.
Aggregate bases stabilized with asphalt or cement are recommended under very heavy loads, and over weak or saturated soil subgrades. These are sometimes used when adequate aggregates are not available or when a stabilized base is more economical than unstabilized aggregate. Poor subgrade should be avoided if possible, but when it is necessary to build over weak soils there are several methods available to improve subgrade performance.
Soil characteristics play a major factor in the design of pavements. It is important to accurately assess the type of soil on a site. Soils are classified by the Unified Soils Classification method (ASTM D2487, 2006a). Soils that have a course grain and good drainage are generally stronger than fine grained soils with poor drainage. For example a gravel soil with good drainage is significantly stronger than a clay soil with poor drainage.
In order to develop the friction between neighboring units, the units within a paved surface must be restrained from drifting away from one another. This is accomplished through the use of edge restraints that keep the pavers in a contiguous arrangement. It is ideal to have all of the edges of a paved surface restrained as this will result in load transferring in more than a single direction.
The preparation of the base is the final element in the successful load carrying capacity of concrete pavers. Although this is not a visible “design” element it is an important general principle that must be considered during initial conceptual design phases. The previous two principles deal primarily with the surface layer which is the top layer of the five total. The remaining four exist below the surface of the pavers.
When it comes to permeable paver design, several factors go into making a functional system. One must size the system appropriately taking rainfall, infiltration rates, available area, void space, layer depth, and time all into consideration. This lesson will introduce you to all those critical factors in these three lesson components:
The Principle of Interlock:
Interlock is the inability of a paver to move independently from its neighbors. It is critical to the structural performance of interlocking concrete pavement. When considering design and construction, three types of interlock must be achieved: vertical, rotational, and horizontal interlock. These are illustrated in Figure 1.