Lesson 7/Learning Event 2
Learning Event 2
REPAIRS FOR SURFACE FAILURES
The principal cause of surface failure is subgrade or base failure. Surface failures are also
caused by disintegration, and instability of the surface course. Types of surface failures are
described below.
TYPES OF SURFACE FAILURES
Disintegration
Disintegration means the decomposition of the surface. Under this heading, there are several
possible causes that are listed below:
Hardening of asphalt films
Insufficient asphalt
Stripping of binder
Instability
An unstable wearing surface is incapable of withstanding deformation under the impact of
traffic. Some of the causes for instability and their effects are listed below:
Excess asphalt (binder) will cause bleeding
Smooth or rounded aggregate will cause low friction
Too soft an asphalt
Low density (lack of proper compaction)
Uncured prime or tack coats will soften lower portion of pavement
Too much prime or tack will cause instability
Dirt between pavement and base will cause a slippage plane
Lack of bond between layers will move under traffic
FAILURE EFFECTS
The following conditions may occur from either foundation or surface failures.:
Potholes (chuckholes) caused by lack of binder (asphalt), poor drainage, or excess
openings in the mix, and structural weakness.
Longitudinal or transverse cracking caused by subgrade shrinkage, or by swelling and
heaving in the soils.
Ravelling in a pavement caused by insufficient asphalt (binder), burning of binder
material or aggregate.
Bleeding surface caused by excess asphalt content.
Alligator cracks caused by lack of support.
REPAIR METHODS
Next, and the most important, are repair methods required to correct deficiencies in the surface.
Patching requires skill and close supervision. The
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