Phased Construction of Asphalt Pavements
by Joe Heintz, P.E., on May 21, 2019
Phased construction has become a common practice in recent years – particularly in residential developments. In order to build a roadway to gain site access as quickly as possible, contractors initially place the aggregate component of the pavement and an asphalt binder layer. Once the overall site construction has been completed, the remaining asphalt is placed, ensuring a pleasant, clean finish to the road. This technique is particularly useful when local trenches are required for the installation of utility pipes and cables.
Pavement distress in the form of cracking at the surface of the asphalt is common on roads within housing subdivisions. In many cases, these cracks start to appear within a very short period of time following construction – sometimes in as little as one or two years.
Once the cracking starts to develop, the pavement’s deterioration will accelerate very quickly. Pavement distress such as the “alligator" cracking shown in third photo below is characteristic of a deep-seated problem within the pavement structure. In other words, a standard surface rehabilitation program will not be sufficient to overcome the problem and instead, the current owner of the road will face an expensive replacement of the road’s foundation layers.
Cause of Premature Pavement Failure
Consider the three pavement sections below. Based on the American Association of State Highway and Transportation Officials (AASHTO) design method for flexible pavements, the allowable trafficking levels obtained for these pavement sections are shown in ESALs above Figures 1 through 3.
As you can see in this typical example, leaving off the 1.5 inches of asphalt surfacing during a phased construction procedure results in an 80% reduction in the trafficking capacity of the pavement. For subdivision roads however, the majority of heavy traffic is experienced during the construction of the surrounding housing and the road itself.
It is not surprising then, that when the asphalt surface layer is installed at the end of phased construction, the rest of the road is approaching the end of its design life. The placement of the surface layer results in some additional trafficking capacity, but after a year or two, the road will start to show surface distress – indicative of structural integrity problems associated with the lower layers.
The performance benefits associated with the inclusion of Tensar Geogrids within the aggregate base have been demonstrated and quantified through extensive research and project monitoring for more than 20 years. In this specific application, it can be demonstrated that the loss in trafficking capacity, resulting from the absence of the asphalt surface layer during the critical phased construction period, is more than compensated for by the inclusion of a layer of Tensar TriAx Geogrid within the pavement section.
The bottom line — the long-term performance of the road is better than it was intended to be in the original pavement design, while the risk of early failure is dramatically reduced.
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