Full Depth Asphalt Pavements for Private Driveways
In order to be a good investment, a residential driveway must be properly constructed. This information is designed as a general guide for private driveways. A driveway that is properly designed and constructed, will give many years of service with minimal maintenance. Such a driveway is simple and affordable to build.
Before construction begins buried utility lines in the vicinity of the driveway will be marked. This will include water and gas lines, telephone, electricity, cable, and any other utility service provided lines in the area. Homeowner-installed lines such as sprinkler systems, security systems, or power lines for a garage are not marked by the utility providers. It is necessary for the homeowner to locate and mark any private lines before any digging begins.
The sub-grade soil serves as a working platform to support construction equipment, as well as the foundation of the pavement. Because it will carry the loads transmitted to it from the pavement structure, it is important that the sub-grade be properly graded and compacted. After grading and compacting with a roller, the sub-grade will be tested to determine if it will support the loads that will be placed on it. This is done by driving a heavily laden truck over the sub-grade and noting the deflections. If a sub-grade area shows pronounced deflection, this shows that the area has not been sufficiently rolled or that the moisture content in of the sub-grade is too high. If additional compacting fails to correct the condition, the sub-grade may need to be removed and replaced by select materials.
Good drainage is important for pavement durability. It is desired to blend the surface of the pavement to the contour of the existing ground so that surface water will run away from the pavement in its natural course. In flat areas, the pavement should be crowned or sloped not less than 1/4th in. per ft. so all surface water will drain off. Where possible, roof drainage should be piped away from the surface of the pavement.
Primary consideration should be given to installing a driveway to the proper width. It should be no less than 8 ft., but 10 ft. is a more practical minimum width. If the driveway will be used for both pedestrians and automobiles, a 12 ft. width should be considered. It is generally desirable to preserve aesthetic objects such as trees and rocks. Driveways should conform to the terrain, to avoid large cuts in hilly areas. When possible, a curving driveway will be more attractive. A curved driveway needs to be increased in width on sharp curves.
Full depth asphalt pavements for residential driveways should be a minimum of 2.5 in. compacted thickness on a properly prepared sub-grade. This minimum is sufficient for many years of service when properly constructed. If there is a concern about foundation conditions or an exceptional number of heavy vehicles using the pavement, it may be desirable to increase the thickness.
Applying the Asphalt Mixture
The thick lift technique of placing lifts of 2.5 in. is in most instances satisfactory. However, if conditions necessitate thicknesses greater than 2.5 in. then the asphalt will be placed in two layers.
Weather conditions affect asphalt construction. For the best results, asphalt is not applied in wet or severe cold conditions. Regardless of the thickness of the course being placed, compaction is one of the most important elements to the proper performance of the pavement. That is why a properly prepared sub-grade against which to compact the pavement against. A steel wheeled tandem roller is used for this type of work.
It is not necessary to seal the surface of a newly constructed driveway in the first year. It is recommended to seal your driveway the year following installation. This will help the longevity of the pavement by blocking out harmful UV rays and chemicals, such as oil, solvents, and other harmful materials.
Definitions of Terms Used
Asphalt: A dark brown to black cementitous material. The predominating constituents are bitumens which occur in nature or are obtained in petroleum processing. In varying proportions, asphalt is a constituent of most crude petroleums.
Full Depth Asphalt Pavement: Pavement in which asphalt mixtures are used for all courses above the sub-grade or improved sub-grade.
Asphalt Concrete: A high quality thoroughly controlled hot mixture of asphalt cement and well-graded, high quality mineral aggregate.
Sub-Grade: The soil prepared to support a structure or a pavement system. It is the foundation for the pavement structure. The sub-grade soil is sometimes called “basement soil” or “foundation soil”.
Asphalt Base Course: A foundation course consisting of mineral aggregate, bound together with asphaltic material.
Asphalt Surface Course: The top course of an asphalt pavement, sometimes called the wearing course.