Asphalt Paving and Sealcoat  Blog

How Pavements Fail - Part 1

A variety of factors influence the life expectancy of parking lot and street pavements. Most of the Bay Area's streets and parking lots are constructed with an asphalt surface over a rock base. This type of construction is referred to as a "flexible pavement". The factors that contribute to failure for flexible pavements can generally be categorized in two
groups:

Loads:
Most arterial and collector pavement deterioration is associated with vehicle use or loads. Loads are the
vehicle forces exerted on the pavement by automobiles, trucks and buses. These forces create stress and
deformation within the pavement structure. Repeated loading creates fatigue and resulting distress in the
pavement. Excessive loading can lead to rapid deterioration of the pavement structure evidenced by cracking and distortion of the pavement surface. Damage caused by vehicles goes up exponentially with weight. A single large truck can cause as much damage as several thousand automobiles. Buses typically have an even larger load impact than heavy trucks due to the limited number of axles and tires they employ to distribute their weight.

Environmental Factors:
Surfaces that receive little use (such as local/residential streets) will eventually deteriorate due to environmental factors. Oxidation of the asphalt causes the binder to age and lose it capability to bind the asphalt. The pavement will then begin to deteriorate as evidenced by an asphalt structure that is crumbling and raveling. Other environmental factors such a frost heave and extreme heat also accelerate the deterioration of asphalt pavements.

Load and Environmental Factors Combined Result In Pavement Failure
As time passes, continual loading in the wheel paths causes the flexible pavement to wear out and lose its
flexibility. This causes the pavement to compress and stiffen forming ruts in the wheel paths. As wheel
loading continues, lack of flexibility in the pavement causes hairline longitudinal cracks to form. Continued
loading causes these cracks to grow in length, width, and depth. As the pavement surface wears due to studded tires and chains, it loses its ability to shed water. Water then collects in the ruts in the wheel paths and then in the longitudinal cracks. As the cracks deepen they eventually reach the aggregate base. Water then drains from the surface into the base. This water intrusion causes the base to soften. As the base softens, it can not support the pavement above it. Continual loading on the surface over a "mushy" base stresses the pavement beyond its ability to flex and the cracking grows into a patchwork of alligator
cracking. This additional cracking allows more water penetration. This pavement is now on its way to major
failure.

 

With all the rain, potholes, water penetration...it's a good time to start thinking about asphalt maintenance for 2009.