Designing the Pavement System

Interlocking Concrete Pavers

Science Behind Pavement Analysis & Design


Interlocking concrete pavement systems have been proven to be a durable and effective alternative, even in vehicular applications; but, as with any proper concrete pavement design, construction and maintenance procedures are required. ASCE 58-16 was created by the ASCE/T&DI Structural Design of Interlocking Concrete Pavement Standards Committee to provide guidelines for interlocking concrete paver design and developing appropriate pavement structures for various Traffic Load Index and subgrade conditions.

This standard guideline was developed based on the 1993 AASHTO Guide for Design of Pavement Structures, which calculates the thickness of a road cross section required to withstand the traffic load index for the given lifespan based on the native soils bearing capacity. ESALs (Equivalent Single Axle Loads) express the equivalent damage created by each type of vehicle as compared to an 18,000-pound axle load. For example, passenger cars have a Vehicle Load Factor (VLF) of 0.0004 (it would take 2,500 cars to create the same damage as one ESAL) while full fire trucks range from 0.21 to 6.87.

In terms of selecting an acceptable paver for the given traffic load, both the paver thickness and aspect ratio have to be considered. The heavier the expected traffic, the thicker the paver needs to be to prevent it from flipping (rotating) out of place. Controlling the aspect ratio, which is the longest length divided by the thickness, helps to prevent the flexural loads expected from the given traffic type from exceeding the limitations of the concrete.

How to Select the Right Paver Thickness


Paver shape and thickness must be selected based on the application. Most long planks and large slabs are not suitable for vehicular applications. Concrete segmental units should be evaluated based on site-specific conditions. The project pavement engineer should confirm that the product can meet expected performance for vehicular loading conditions.

HOW THICK SHOULD A PAVER BASE BE?


Chart of paver, slab, and plank dimensions and applications.
NOTE: There is currently no industry-recognized definition of a plank paver. Canadian Standards Association have slightly different criteria for pavers and slabs. There are criteria including dimensional tolerances and physical testing requirements. There is currently no industry-recognized definition of plank (linear product). Oldcastle recommends a plan ratio of less than or equal to 4:1 for vehicular applications.
Chart of sample aspect ratios for interlocking concrete paver design.
Sample Aspect & Plan Ratios

The Design Standard


The following are the recommended minimum paver thickness and aspect ratio based on Traffic Load Index, which is an Oldcastle-developed guideline for designing flexible segmental paving structures based on paver thickness, peripheral friction based on unit shape, and expected load conditions as a selection criteria for vehicular applications. These guidelines are based on sand bedding set over dense graded aggregate.
Interlocking concrete paver walkway in a commercial plaza.

Commercial Pedestrian


There are no restrictions for use in pedestrian only areas.
However, in areas that will be subject to maintenance or
emergency vehicles, a 2 3/8” (60mm) thick unit should have an
aspect ratio less than or equal to 4:1, and 80 mm less than or
equal to 5:1. Planks and slabs can be used if properly designed
by a pavement engineer.

Interlocking concrete paver parking lot with spaces for trees.

Facility & Business Parking


Facility and business parking are primarily used by cars, but will be subject to occasional service or delivery truck traffic. In these areas, the minimum recommended paver thickness is 3 1/8” (80mm), and the units should have an aspect ratio less than or equal to 4:1. Planks and slabs should not be used in parking applications unless properly designed and engineered.
Interlocking concrete paver roadway with solid yellow lines in the center, using pavers with a thickness of 4”, aspect ratio of 3:1.

Commercial & Residential Roads


Commercial and residential roads, like subdivision roads,
are primarily used by cars, delivery trucks and occasional
heavy transports. In these areas, the minimum recommended
paver thickness is 3 1/8” (80mm), and the units should have an aspect ratio less than or equal to 3:1. Planks and slabs should not be used for roadway applications. A 45 or 90-degree herringbone paver pattern or L-shaped product is recommended for all vehicular roadway pavements.
School bus pickup roadway using interlocking concrete pavers, thickness of 4”, aspect ratio of 3:1.

Minor Collector & Bus Parking


Minor collectors or bus parking lots have an increased number of
heavy vehicles driving over the surface on any given day. In these areas, the minimum recommended paver thickness is 4” (100mm), and the units should have an aspect ratio less than or equal to 3:1. Planks and slabs should not be used in heavy vehicular applications. A 45 or 90-degree herringbone paver pattern or L-shaped product should be used for all vehicular roadway pavements.