Mn/DOT demonstrated a porous pavement vacuuming process using equipment owned and operated by Reliakor, a Minnesota based Company at MnROAD on November 4, 2009. Pervious concrete test cells 85 and 89 and porous asphalt cells 86 and 88 were vacuumed. Representatives from Mn/DOT Metro District, Mn/DOT Research, Mn/DOT Tech Support, Mn/DOT Maintenance Research, the City of Minneapolis, DNR, and Reliakor Services Inc were in attendance.
The test cells were approximately one year old at the time of the demonstration and were in good condition. The pervious concrete test cells had no surface raveling or joint distress and very few fine cracks. The porous asphalt test cells had isolated areas of surface raveling and light rutting. The voids in the pervious concrete and porous asphalt test cells appeared to be clean and free of debris. It is important to note that the brush on the vacuum was not used. The brush could pack debris further into the voids and increase clogging in the pervious/porous pavements.
The lack of porous asphalt pavement durability research in the seasonally diverse Minnesota climate preceded this research project. The purpose was to study the durability, maintenance requirements, hydrologic benefits, and environmental considerations of a porous asphalt roadway in a cold climate.
This research led to Report 2012-12, " Porous Asphalt Pavement Performance in Cold Regions"
With the construction of four new test cells in 2008, the Minnesota Department of Transportation (Mn/DOT) now has six unique pervious pavement test sections at the MnROAD test facility. Recorded temperatures in the pervious pavements and subgrades were compared to impervious Portland Cement Concrete (PCC) test sections over the same time interval. It was found that the subgrade in pervious PCC and Hot Mix Asphalt (HMA) was up to 4 °C warmer in the winter than impervious PCC pavements. The frost depth in an impervious PCC pavement was found to be 45.7 cm deeper than in a pervious PCC pavement of similar thickness. One pervious pavement test cell experienced 60% less freezing cycles over a three year interval than impervious PCC pavements of similar thickness. The air trapped in the pavement voids was suspected to be the main reason for the reduced number of freeze-thaw cycles by creating an insulating effect. In another pervious pavement, entrapped air within the base material may also insulate the pavement from the subgrade.
