Rockport, Ind., is a small, quiet city surrounded by beautiful foliage and gently rolling hills. To mirror that attractiveness, it is important to the city and its residents to have aesthetically pleasing roads. State Road 70 (between U.S. 231 and State Road 66 outside of town), which is about 10 minutes away from the city of Rockport, recently had some minor rutting and asphalt deterioration problems. As material, fuel and labor prices have continued to rise, the need for cost-effective road maintenance also has increased. So, the state decided to use microsurfacing on an 8.5-mile stretch of the two-lane state road. A microsurface layer over the top of the existing asphalt not only fixed those problems, but also improved skid resistance, increased the road’s wear life and provided a better aesthetic look.
Strawser Inc., a pavement preservation contractor based in Columbus, Ohio, won the bid to microsurface that stretch of road. The company is enjoying a recent upward turn toward pavement preservation. It also seems that the rest of the state is paying attention. During the six-day job near Rockport, more than 20 state and county representatives came to see the job and analyze if it could be a cost-effective alternative for them.
“With asphalt prices being so high, states don’t have the money to do as much hot mix,” said Chauncey Nance, director of field operations for Strawser. “This year, we’ll do about 8,000-10,000 tons of microsurfacing in Indiana, which is as much as I can remember doing in one year. It’s good to see preservation becoming something that the states really want to focus on, because it can truly benefit a state’s budget and the overall appearance of its roads.”
The Rockport job required 131,000 sq yd of microsurfacing to be laid over the two-lane road with a continuous microsurfacing paver. The material mix consisted of 2,036 tons of Type A (comparable to Type II) aggregate, 58,026 gal of asphalt emulsion, 427 bags of cement and about 10% water to lay a ½-in.-thick layer using two coats over the entire project. To determine the mix, Strawser worked with its asphalt emulsion supplier, which performed a full-mix design consisting of all of the ingredients. The supplier tested it thoroughly to make sure it would hold up to the standards expected by the state and then sent it off to them for approval. In doing so, the mix was made specifically to fit the road and surrounding environment to ensure a longer wear life. Once the mix was approved, the continuous paver was calibrated and set with material ratios according to the mix design.
To apply the mix, Strawser used a Bergkamp Inc. M1 full-size continuous microsurfacing paver, variable-width spreader box and five mobile support units. The variable-width spreader box was connected to the back of the paver, using four augers to maintain the mix and evenly distribute it across the pavement. The box can expand and contract while paving to adjust to varying pavement widths. The mobile support units held and transported aggregate, asphalt emulsion and water to the continuous paver as it moved down the road.
Each morning the paving crew started at its staging area, located approximately 10 minutes from the paving site. The staging area housed all of the materials that were used on the job. The continuous paver and mobile support units were filled with the necessary materials and then commuted to the paving site. The crew blocked off a 1- to 2-mile area, removed the pavement markers and cleaned the road using a street sweeper. Then they applied a tack coat made of three parts water and one part asphalt emulsion, which was put down on the road to better adhere the microsurface to the existing asphalt. The tack dried for about 30 minutes, and then the continuous paver applied the first coat of the new microsurfacing layer. The mobile support units, located in different spots farther down the road, slowly backed up to the continuous paver one at a time as it was paving to refill the material compartments as needed. Continuous paving eliminated the number of construction joints—or small bumps—left in the road, increased worker efficiency and left a nice-looking smooth surface.
Seconds and thirds
Most of the job required two coats of microsurfacing to equal 32 lb/sq yd of material for a ½-in.-thick layer. The first coat, called the “scratch coat,” consisted of 14 lb/sq yd of material and acted as a leveling surface to fix the minor rutting. The No. 1 objective with this coat was to get the road level and provide a solid base for the second coat to adhere to. A stiff rubber strike-off, connected to the back of the spreader box, was used to level the surface without wiping out the ruts.
During the scratch-coat process, only one lane of traffic was blocked off, so traffic could drive on the other lane while the road was being preserved. Because microsurfacing sets so quickly, the road crew never had to shut down the entire road, so there was only a short delay for motorists. After finishing with the scratch coat, the crew waited about 30 minutes and then re-opened it to traffic and blocked off the other side so a scratch coat could be placed on it as well.
After laying the scratch coat on both sides, the crew went back to work on the second coat. The surface coat consisted of 18 lb/sq yd of material. The purpose of this coat was to provide a skid-resistant and aesthetically pleasing finish. The stiff rubber strike-off on the spreader box was replaced with a more flexible and smooth rubber strike-off to provide the final finish.
Like most projects, this one presented an obstacle to overcome. Strawser assessed the road before doing the project, but there was more significant deterioration to about 7,500 sq yd of the road than originally thought. That section had more traffic and a higher volume of large trucks than the other parts, causing more deterioration and minor delamination that required a third microsurfacing coat. Strawser put down 46 lb/sq yd of material in that 7,500-sq-yd area. The first two coats consisted of 14 lb/sq yd each, and the third coat required 18 lb/sq yd.
Preserving a trend
Strawser started in the pavement preservation business in 1977 and works in Indiana, Michigan, Ohio, Tennessee and Kentucky with multiple preservation methods. Other than microsurfacing, Strawser also provides slurry seal, crack seal and chip seal.
“We’ve definitely seen an increase in the popularity of pavement preservation over the last few years,” said Nance. “Like all of our preventive maintenance methods, microsurfacing is more cost-effective for the budgeted dollars if the road doesn’t have major structural damage. A microsurfacing job can cost approximately 65% less than a new hot-mix overlay, so putting a pavement preservation program into place can free up a lot of money to fix more roads. I like to equate it to a house that needs new windows. You would replace the windows, not build a new house. Then use that money to buy other things.”
Though microsurfacing is not a replacement for an asphalt overlay, it can be used to extend the overall life of the pavement and delay the need for asphalt overlays or major reconstruction. Untreated roads are adequate for many years of use. However, the longer they go untreated, the more they deteriorate under the surface. Microsurfacing leaves a new skid-resistant surface that is free of cracking and raveling and protects against weathering. Oxidation, loss of oils and loss of matrix also are minimized. The waterproof surface prevents further deterioration, provides an appearance that is appealing and can increase property values.
“Microsurfacing technology is relatively inexpensive when compared with other methods to remediate these types of problems,” said Bill Cooper, Bergkamp’s director of sales and marketing. “And if applied as part of a comprehensive pavement maintenance program, it will result in extended service life with lower costs and improved safety. The right contractor, applying the right treatment to the right road, can make all the difference when determining where to spend limited dollars on transportation infrastructure maintenance.”
A few weeks after the job was completed, Nance went back over the surface with members from the Indiana DOT. They drove on it and examined it for all of the qualities mentioned before. Final inspection showed that they passed all requirements. To insure the job, Strawser provides a two-year warranty on the finish. The warranty protects against any premature wear or delamination, meaning Strawser would come out and fix that part of the road if there were any kind of a problem.
“We have the utmost confidence in this process and can easily provide a warranty to back it,” said Nance.
