Frequently Asked Pavement Questions
Q. What is the normal method used to resurface a roadway?
Hot mix asphalt (often referred to as HMA) is a mixture of various sizes of aggregate which is bound together with asphaltic cement. HMA is placed with a paving machine which contains electronic and manual controls that can put it at the proper grades and depths. TDOT’s most commonly utilized HMA mix, referred to as “411D” due to its designation in section 411 of TDOT’s Standard Specifications, can cost anywhere from $60,000 to $90,000 per lane mile (1 lane, 1 mile long) depending on location and whether existing asphalt needs to be milled (removed) first.
Q. Why does TDOT use pavement preservation methods?
When properly utilized, pavement preservation methods extend the roadway life at what is often a fraction of the cost. A thorough analysis of any roadway’s condition (pavement age, traffic volume, surface deficiencies, etc.) indicates when application of a preservation treatment would be the most cost effective means of protecting the initial investment. Typically, it is practical to expect that the further a pavement is permitted to deteriorate, the more expensive it will be to repair. When long life cycles are considered (i.e. 40+ years) overall costs are significantly reduced when pavement preservation programs are implemented.
Q. What are the types of pavement preservation?
Most treatments available for use on TDOT roadways are described within the Departmental Standard Operating Guidelines (SOG) for Resurfacing. Examples include but are not limited to traditional hot mix overlays, mill and replace treatments, thin lift asphalts, crack sealing, fog sealing, longitudinal joint stabilization, and microsurface. Lower impact treatments which have a lower cost but a higher return on investment are generally considered “pavement preservation treatments”. One example would be microsurface, which at approximately $21,000 per lane mile costs approximately 34% as much as atraditional 1-1/4” asphalt overlay (~$62,000 per lane mile) but lasts 58% as long (7 years expected life with a microsurface vs 12 years with overlay).
Q. Does TDOT recycle any of the material generated from “milling” projects, aka when old asphalt is removed before paving?
TDOT does have a program for recycling/reusing old asphalt millings into new asphalt mixtures. This re-used material, known as “Recycled Asphalt Pavement” (RAP) is permitted in new TDOT mixtures at rates up to 35% by mass. Limits for RAP are maintained by TDOT’s Materials and Tests Division such that excessive amounts of RAP do not permit asphalt mixtures which fail to quickly and need to be repaired too early. In recent years, the Department has also evaluated in-place recycling methods such as Hot In-Place recycling, where 100% of the material on the road way is recycled in place using infrared heat and material additives. These techniques utilize 100% of recycled materials and minimize the need for hauling material to and from projects.