Monday, July 14, 2008

Road Maintenance Technologies - Road rehabilitation in Montgomery County Texas

Montgomery County has a visionary plan to maintain our roads in a financially constrained setting. Technology offers reduced costs and improved results, so the commissioner of precinct 3 is looking at technology to provide some major assistance to reach his goals. For road maintenance and construction, there are three technologies of importance:
  1. X-ray for analysis of the pavement
  2. Low temperature asphalt for the asphalt component of the surface mixture
  3. Porous Friction Course for the surface mixture that is laid on the road
These three technologies will provide solutions to reach these goals:
  • Predict surface cracking, holes and determine road thickness on county roads
  • Develop a rehabilitation program with planning, timing of application, and optimization of the replacement area in the road and/or the complete resurfacing of the road. In other words, be more proactive instead of reactive and be smarter in planning.
  • Better optimize cost vs benefit in the road rehabilitation program
There is a need to thoroughly understand the quality and subsurface issues of the roadbed. When water is embedded within the roadbed, we have a higher risk of road surface fracture. A cavity layer with water is where the asphalt surface is the weakest. Detecting that weakness gives us insight into structural deficiencies, which will eventually lead to road failure; so by knowing this, we can prepare plans to replace the problem areas even before the failure occurs. A health check of our roads is available using x-ray technology. This method also measures the thickness of the roadbed. Data on the road is collected in a van with an x-ray system mounted on the front of the van, directionally aimed at the road surface below it. X-ray data is collected into an on-board computer and subsequently processed with computer software. Traveling at the speed of traffic, the system in the van collects the data without impeding traffic movement. Then the data is analyzed and presented in layered graphics like a seismogram to those studying the road. Montgomery county is collecting this data now in our area to assess the condition of our roads.Click here for a more in-depth explanation of the technology. Typical Scan image

In this day of higher cost petroleum-based materials, we face inflated material costs for maintaining our roads. As asphalt prices rise, the selection of materials is even more important than it was a few years ago. In the past, repair of concrete roads required asphalt to be laid at 300+ degrees. The source of the asphalt in Montgomery County is in Conroe, so the asphalt must be loaded (at 350 degrees), transported, and coordinated with the preparation of the roadbed such that is stays above 300 degrees when it touches the roadbed at the project site. Sometimes the material must be turned away, because it is too cool to put down on the roadbed. Contracts are written to assume and include this waste. To combat this issue and lower county contractor costs, the low temperature asphalt method will be utilized by the precinct. This will facilitate a lower financial risk delivery to the work site, less time that the road area is closed, lowered contractor costs, and give the work crew a healthier environment to work. For those having deeper interest of this topic, a short description of other benefits of low temperature asphalt are found at this link.

A more descriptive review of this material and case studies are found at this link.

On Rayford Road, the county has been testing a different surface technology to improve safety and provide a more durable cost effective road surface. Porous Friction Course (PFC) is an asphalt mixture with a low bitumen content (high carbon molecules which are the residues of petroleum distillation), carefully designed to provide a fast lateral water exit from the roadbed and to have strong tensile properties. The difference between a standard asphalt surface and a PFC surface is incredible. In a rainstorm, the traditional surface will require that water exit the roadway by pushing the water off, typically as a spray which hinders a driver’s vision. Combined with water, traditional surfaces also act as water slides, slippery surfaces that are a road hazards. PFC on the other hand allows the water to escape the road horizontally through porous exits pushed by both gravity and tires. This has the added benefit of combating hydroplaning issues. PFC has been known to be a weaker tensile medium with normal additives, but today’s technology has been improved to compensate for that with stronger bonding elements. I saw a video on PFC technology, demonstrating its capability. Very impressive! The video showed a road with a traditional asphalt surface. Cars and trucks were lifting the water with the resultant spray producing a foggy mist above the roadway. After the new PFC surface was laid, almost the identical conditions produced a clear road with no evidence of standing water, just an apparently wet surface. The tires were not lifting the water into a mist above the road as before. So the next time you drive down Rayford Road in the rain, you should be able to notice the difference. PFC is also a sound inhibitor. The material, also due to its porous nature, absorbs more of the noise, presumably about 3 db, not significantly detectable. Under the surface of existing roadways, I was shown the water cavities that cannot be seen with the eye. With this material, any cavities should be dry, with all the water escaping to the sides of the roadway. A well designed porous surface will therefore maintain the integrity of the road as well as provide a means for water to escape. There is a downside however. This surface is hotter in the summer and darker than concrete at night. Headlights reflect off of concrete, illuminating the road much better than with asphalt. Try this link for more information on the PFC technology.

There is some debate in the journals on what is better, rock PFC or ARFC (Asphalt Rubber Friction Course technology). ARFC has very significant noise abatement properties along with its water exit properties. ARFC lowers road noise some 13 db while the rock PFC lowers the noise by about 3db, a very significant difference. Arizona is known for its quiet highways, because they are using ARFC. I am personally hopeful that ARFC will be deployed on our roads here in The Woodlands. Related short articles to be released soon:

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