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 58-10 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 INDEX, 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.
Paver Thickness – How to Select the Right Paver
Paver shape and thickness must be selected based on the application. Most planks and slabs are not suitable for vehicular applications. Concrete segmental units not meeting ICPI or CSA definitions of a concrete paver should be evaluated based on Traffic Loading Index criteria. The project pavement engineer should confirm that the product can meet expected performance for vehicular loading conditions.
HOW THICK SHOULD A PAVER BASE BE?
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.
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.
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.
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.
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.
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.