How “green” is your pavement network? Dragos Andrei, Ph.D., P.E., M.ASCE Associate Professor, Civil Engineering Department California State Polytechnic University Pomona, California id you ever wonder how to build a sustainable pavement? Well, it is very simple: make it out of recyclable materials, use renewable energy to build it (no harmful emissions please), and make it last forever, so that there is no need for maintenance, rehabilitation and traffic closures. Can’t do? I agree; we are far from building the perfect road. And we don’t have only one road to worry about, we have entire pavement networks that are aged, aging, and in need of costly maintenance and rehabilitation.
So what can be done? Reduce, reuse, and recycle. You must have heard this many times. But when it comes to pavement maintenance and rehabilitation this translates into reclaiming the aged and deteriorated pavement materials and recycling them into renewed materials. This article provides basic information for those interested in integrating recycling and reclaiming strategies in their pavement management systems (PMS). It is the pavement management system/program that produces maintenance and rehabilitation recommendations for the entire pavement network over a number of years. The ins and outs of pavement management as well as how recycling and reclaiming can be included in PMS are the main topics of this article. In addition, agencies are encouraged to raise the bar and require that maintenance and rehabilitation recommendations always include several alternatives of which at least one specifically addresses sustainability, be it in the form of reclaiming, recycling, reduc104
ing energy consumption, harmful emissions and/or traffic disruptions.
Pavement Management: Under the Hood Agencies develop multi-year capital improvement plans by using pavement management systems (PMS). These are in fact complex decision systems that allow agencies to spend their resources in the most efficient manner. In general, most efficient means to maintain or improve the overall condition of the entire pavement network within the constraints of limited financial resources. The main components of a PMS are: • Database of pavement condition: the entire pavement network is divided into smaller sections which have consistent condition and characteristics (such as traffic, surface materials, time of construction, etc.) • Performance prediction models: these models are used to predict the rate of pavement deterioration in the next five to seven years. The pavement condition index (PCI) is used most often as a measure of pavement condition. The solid red line in Figure 1 (page 108) represents the decrease in pavement condition with time, deterioration caused by the combined effects of traffic loading and the elements, such as changes in temperature and moisture conditions. The curve shows that without maintenance and rehabilitation, virtually all pavements are expected to fail after a certain
period of performance. Hence the “Do Nothing” label. Note that different models are used for different categories of pavements; for example asphalt concrete surfaced residential streets and Portland Cement concrete arterials will deteriorate at different rates and will be assigned different performance curves. • M&R strategies: these are the maintenance and rehabilitation strategies used by an agency to maintain the pavement network. Several key aspects need to be known about the M&R strategies included in PMS: •
Immediate effect in pavement condition
Long-term effect in pavement condition (or life extension)
The effect of M&R is graphically illustrated in Figure 1. An immediate increase in PCI will be followed by deterioration under traffic which can happen at a faster or slower rate, depending on the M&R strategy used and the condition of the pavement at the time of M&R. The effect, as shown in Figure 1, is an extension in the service life of the pavement structure. • Annual budget: funds available every year to be invested in the maintenance and rehabilitation activities. Unfortunately, many local agencies in the United States have only about 10% of