Lesson 7/Learning Event 1
Learning Event 1
REPAIRS FOR BASE AND SUBGRADE FAILURES
Bituminous surfaces, like most other surfaces, require frequent maintenance. It is seldom
possible to concentrate enough effort to prevent failures in bituminous surfaces; therefore, it is
essential for engineer officers and construction foremen to understand the principles, equipment,
and procedures required for adequate maintenance and repairs.
Bituminous surfaces are repaired or resurfaced with other bituminous materials, because of their
plastic and adhesive characteristics. The original pavement actually is improved when the new
material is properly placed. A bituminous surface is a flexible surface; therefore, it is directly
dependent upon its foundation (base course, subbase, subgrade, etc.) for its load carrying
capacity. Whenever a foundation failure occurs, that part of the wearing surface which lies
above the weakened area will also fail.
TYPES OF FOUNDATION FAILURES
The greatest single enemy of any pavement structure is moisture. Moisture saturation must be
prevented, as much as possible. The only positive approach to keeping the foundation dry is to
Frost action may be another cause of foundation failure. Water freezing in the bases, select
materials, or subbase will cause the formation of ice lenses and frost voids, and a resulting heave
in the bituminous surface.
Poor Soil and Construction
In the Theater of Operations time and equipment are not always available to properly select
construction materials and adequately place and compact the foundation. For this reason the
foundation is not adequate to withstand the pounding of military traffic.
A flexible pavement structure may be able to carry its design load indefinitely with never a
failure. However, if an extremely heavy load passes over the surface, it may fail. On both
military and civilian roads and airfields, load limits are usually set so that failures from
overloading will not occur.