Designing the Pavement System

Interlocking Concrete Pavers

The Science Behind the Structural Design


Interlocking concrete pavement systems, including permeable interlocking concrete pavement (PICP), are versatile and durable pavement systems which can be used for a variety of pedestrian and vehicular applications. The success of any pavement is dependent on proper design, construction, and maintenance.

What is the standard for paver sizes?


The ASCE has published paver dimension standards for both ICP and PICP. ASCE 58-16 is the latest edition of the ICP standard for structural design, and ASCE 68-18 is the recently published standard for PICP for both structural and hydrologic design.

Designers can utilize these ASCE design standards to calculate the minimum pavement section to withstand the damage of repetitive dynamic loading from traffic over the pavement's lifespan based on the native soil's bearing capacity. Equivalent single axle loads (ESALs) are used to determine the pavement damage done by each vehicle type compared to the damage caused by an 18,000-pound axle load. For example, passenger cars have a vehicle load factor of 0.0004 (it takes 2,500 cars to equal one ESAL) while a fully loaded fire truck can be as many as 10 ESALs.

How to Select the Right Paver Thickness


Once the traffic loading is calculated, paver thickness and aspect ratio must be selected to maximize performance and durability according to ACSE standards. The heavier the expected traffic, the thicker the paver needs to be to prevent rotation. Key factors for design of both ICPs and PICPs are subgrade strength, thickness of the base materials, paver thickness, paver aspect ratio, and laying pattern.

Is the Concrete Segmental Product a Paver, Slab or Plank?


Paver dimensions, shape, and thickness must be selected based on the application. Most long planks and large slabs are not suitable for vehicular applications. Concrete paver dimensions should be evaluated based on a variety of site-specific conditions. The project pavement engineer should confirm that the product can meet expected performance for vehicular loading conditions.
Chart of paver, slab, and plank dimensions and applications.
NOTE: Reference the Canadian Standards Association A231.1 and A231.2 for unit concrete definitions applicable in Canada.
Chart of sample aspect ratios for interlocking concrete paver design.
Sample Aspect & Plan Ratios

Paver Application Recommendations


The following chart contains general recommendations for both interlocking and permeable systems including minimum concrete paver thickness and maximum aspect ratio for several traffic types and uses. While this chart provides general recommendations. Rather than learning how to measure for pavers on the fly, a pavement design professional should confirm that the product selected meets local standards and site-specific traffic and use conditions.
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 vehicular 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, and therefore need vehicular-traffic-rated pavers. 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.