Road paving operations, whether on major highways or small local routes, are a process that everyone on the roadway is an expert in. They can tell if the base was constructed properly because the road maintains its designed shape, and easily see and feel potholes created by drainage problems. Anyone behind the wheel can tell if the pavement was properly designed and installed by observing its longevity and, probably the most evident, by the ride quality.
After engineers have designed a paving job and set its specifications, it is up to the paving contractor to price and build the job properly. The measure of his or her work is generally in tons or square yards. There are many factors that combine for either of these calculations, but ultimately they must dictate how much the contractor will be paid. In search of larger profits, the two most abused factors are probably core depth and ridability. These two factors can be diametrically opposed if the contractor is not careful, and to a large extent, both of them are controlled by grade preparation. When the pavement base has been properly built it helps to control both, to the mutual advantage of the contractor and future travelers. Any attempt to fix a bad base with paving material is expensive and likely a short term band-aid.
Building a road today, in general, has evolved from a mass earthmoving job to a capacity increase or reconstruction job. In the case of reconstruction, the engineer is constrained by the previous work and its quality issues. Dealing with a roadbed ruined by years of soil and drainage issues, pavement instability and surface problems is very common. He rarely has the luxury of starting fresh and designing from the bottom up. He has to work with what’s there, warts and all, on a tight budget.
Much of the work strategy will be decided upon simply through technicians looking at the road. When deformation has occurred, soil borings and subsurface work can be necessary. Where surface spalling, cracking, rutting, raveling and joint failure occur, it is generally something that is dealt with by some form of pavement removal. None of these processes are free, of course, and only extend the days or weeks the job takes to complete.
Pavement milling has become the norm on the majority of reconstructed roads. When done properly, it can provide a recyclable material and correct the old rideability issues. To date, a ski of some sort is used to help regrade the base for new pavement. The problem here is that no real analysis of the existing surface was done other than deciding on areas and milling depths. No real plan has been made to measure against. You’re often recreating the same problems, mile after mile.
Mobile mapping using GNSS is a relatively new tool for the designer. Surface data can be collected without lane closure or survey crews working in traffic. That data can then be used to design a surface that is economical and has a satisfactory ride. The engineer can now integrate the visual with the three dimensional surface data. It is not only possible, but easy to generate a paving base that will give the pavement the two qualities that it needs: design thickness and smoothness. Finally, in bituminous pavement, highly accurate data also helps control density by providing a constant lift thickness. This allows the rollers to work at a constant pace without thin areas cooling and thick areas retaining too much heat. The compacting process is no longer hindered by variable depth and temperature, resulting in a much better roadway that will last for significantly longer.
So the surface that everyone is an expert in is ultimately controlled by something few people care to truly understand. Only when the materials underneath the paved surface are measured and built with the same highly accurate RTK-GPS data and machinery as the surface will the public will get what it wants: Longevity, stability and a good ride.