Basic Paver Guidelines
Basic paver installation requires some thought. This article provides methods and tips to consider.
Before you start your base installation you need to confirm the elevations/grades on your project. As noted in section 1, it is best to have the elevations marked on the grade stakes that are already established. Most contractors in the industry will use a transit or a laser level to establish their elevations/grades. However, some contractors may rely on a string line and a line level for setting their elevations/grades. The elevations that you mark should indicate your finished gravel base elevation as well as your bedding sand elevation, and finished paver elevation. Remember to incorporate the slope/positive pitch for drainage as well. Most slopes/positive pitch should fall in the minimum range of 1% – 1.5%. ( Example: your vertical drop in a 10 foot run would be between 1″ – 1.5″ ). In addition, make sure that your slope/pitch is flowing away from any structures. It can be to your benefit to attach a string line from one grade stake to another to help maintain your elevations.
Base Materials And Modified Base Materials
Aggregate base materials typically used by municipalities, cities, states or provinces for flexible asphalt pavements are acceptable for interlocking concrete pavers. Base aggregates should contain various particle sizes to allow for proper drainage and compaction. Most aggregate suppliers should be able to provide you with the proper sieve sizes on the granular base materials being used on your project.
Modified base materials should be anticipated when environmental conditions, traffic loads and severe sub grade conditions exist. Your granular base materials can be fortified with other materials such as cement or asphalt to ensure an overall stronger pavement base. Cement or asphalt mixed in small quantities with your granular base will stiffen after installation. In general, modified base materials are used for commercial and industrial applications.
Factors For Base Thickness
Proper installation of the granular base is generally the most neglected step in the pavement installation. The granular base is the foundation for the whole paving installation. Without a properly installed and compacted gravel base the project will most likely fail over time.
In general, the base thickness is determined by traffic loads, drainage, moisture, soil type, sub grade soil strength and climate.
Pavement usage is typically grouped into 4 categories.
- Pedestrian (sidewalks and patios)
- Residential (driveways)
- Commercial (municipal parking lots and streets)
- Industrial (loading docks, ports, container terminals, bus terminals, airport stand applications)
The base aggregate requirements for each of the above pavement applications are listed below. It is important to note that you should never install frozen base material, nor should base material be installed over a frozen soil sub grade. If you do, it can result in pavement failure in the future.
Pedestrian – sidewalks, patios and pedestrian areas should have a minimum base thickness of 4 in over well drained soils. In northern climates with numerous freeze/thaw cycles the minimum base thickness for pedestrian applications should be 6 in.
Residential – driveways should have a minimum base thickness of 6 in over well drained soils. In northern climates with numerous freeze/thaw cycles the minimum base thickness for residential driveways should be 9 in.
Commercial– municipal parking lots and streets should have a minimum base thickness of 6 in over well drained soils. In northern climates with numerous freeze/thaw cycles the minimum base thickness can range from 9 in – 12 in. A civil engineer can determine the appropriate base thickness needed on your project as well.
Industrial – in industrial and heavy duty applications it is best to consult or hire a qualified civil engineer that is familiar with the local soils and traffic conditions so they can determine the appropriate base thickness.
Base Design And Installation Factors
Drainage And Frost Action
It is very important to drain all moisture away from the granular base course. It is best to install any channel drains, catch basins or any type of drainage appurtenances prior to installing your granular base. Always make sure that you have properly graded the site before installing the granular base.
In most areas in north America, you will encounter frost penetration into the pavement application. The frost action must be taken into consideration when designing your paver project.
Frost action is generally characterized by the following:
Pavers are heaving due to the expansion of water in the granular base material during freezing.
Material strength is reduced due to the thawing of the frozen granular base material.
It is also best to have a basic understanding of frost susceptible soils. Soils that have slight frost severity are generally soils that contain gravel, sands and clays. Soils that have a greater frost severity are soils that contain a fair amount of silt, sandy silts, fine silts and also lean clays. So depending on your region, you need to take into consideration the soils with which you will be working and the frost action that may occur with your soils.
If the depth of frost penetration does not go below the anticipated granular base thickness then there is no need to alter the base design. But when the frost penetration does go below the anticipated granular base thickness, the base design should be altered.
Base Installation And Compaction
When installing your aggregate base material, the material should always be spread and compacted in 3 in lifts. Example: if your project requires 6 in of compacted granular base, then you would have two equal lifts at 3 in. If you project requires 9 in of compacted granular base, then you would have 3 equal lifts at 3 in. Each lift of aggregate should be compacted completely. The overall compaction of the aggregate base should be compacted to a minimum of 95% proctor density as determined by astm 1557, while the highest of compaction (100%) is preferred.
As noted in section 2.3, frozen aggregate or completely saturated material should never be installed. If the aggregate material is completely dry, then adding a sprinkle of water will promote effective compaction.
Just like compaction on the soil sub grade, adequate compaction of the aggregate base material is critical to minimizing any settling to the brick paver application. Aggregate base compaction should always be done with either a vibratory roller or a large plate compactor. Small plate compactors are not recommended because they will not achieve true base material densities. The base course should be compacted with a compactor that can deliver a minimum of 5000 lbs. Density measurements of the compacted base can be made with a nuclear density gauge or other methods that are approved by local and state transportation departments. Nuclear density tests are usually done on commercial and industrial projects. The final compacted base course thickness should be uniform and not vary more than +3/4 in ( 19 mm ) or – ½ in ( 13 mm ). Variations in elevations should not exceed 3/8 in ( 10 mm ) over a 10 ft run. The finished surface of the compacted aggregate base course should be uniform and smooth. Any variations that you have in the elevations can be adjusted with a choke course. A choke course is a fine material (such as screens ) that can be spread out and compacted into the surface of the base course which will help adjust your final base elevations. The compacted base course should not allow bedding sand to migrate into it. If you anticipate this happening in certain areas, a choke course can be applied and compacted. Note: bedding sand should never be used to fill in any larger variations in the base course.
Final Base Inspection
With your aggregate base course installed and compacted, it is best to do a final inspection of the base course itself before you start to install your bedding sand. The base course should be inspected in all areas that might allow the migration of bedding sand. Such locations can be curbs, catch basins and utility structures. These areas should be covered with a geo textile fabric to prevent the migration of bedding sand.
It is critical that all the grades/elevations have been checked and the base material thoroughly compacted. Any significant variations in the base course should be repaired prior to the installation of the bedding sand. Failure to fix any variations will show in the future as pavement surfaces will ultimately tend to show the characteristics of the base course below.