If you have ever used the Park and Ride in Randolph (off I89 Exit 4) or parked your car in the College Street lot at Burlington’s waterfront, you may have noticed a coarser pavement texture under your tires. This unusual surface is pervious concrete – a paving material that allows water to flow through it and into underlying soils rather than running off its surface. This feature can protect nearby waterbodies from the damaging consequences of excess stormwater runoff.
Unfortunately, pervious concrete mixes tend to be more sensitive to harsh winter conditions – making them susceptible to breaking and clogging, as seen at both the Burlington and Randolph sites. Pervious concrete can become clogged when sand is applied in winter and can more easily break apart as water becomes trapped in the pore spaces and then expands when refrozen. Also, deicing salts can chemically react with the cement paste in the mix, weakening it and causing breakage and chipping. This can lead to self-clogging of the pavement and system failure. These maintenance practices are not recommended on pervious concrete, but researchers at the University of Vermont (UVM) have found that salt is readily tracked onto these surfaces by car tires and can cause damage at the tire dripline1.
Because sand and salt are a regular part of paved surface maintenance in Vermont, is pervious concrete appropriate given our winter realities?
There are three basic ingredients to pervious concrete: water, aggregate (stone pieces), and cement (paste that holds the aggregate together). Dr. Mandar Dewoolkar and his students are experimenting with different concrete mixes in a UVM lab to find a more durable blend for harsh winter conditions. The team evaluated the addition of sand, slag (a by-product from steel production), combination of slag plus silica fume (a by-product from smelting silicon metal), or fly ash (a by-product from coal combustion). Already, results are encouraging with all the mixes evaluated. The team has identified better durability to freeze-thaw cycles and salt application, while maintaining water movement through the material2,3.
As we develop land across our watersheds, having technological tools that soften our impact on natural infrastructure is critical. Pervious concrete in its initial form had some challenges, but through innovation and experimentation, we are seeing the potential of this material to enhance the sustainability of urbanized spaces.
- Suozzo MJ and Dewoolkar MM. 2012. Long-Term Field Monitoring and Evaluation of Maintenance Practices for Pervious Concrete Pavement in Vermont. Journal of the Transportation Research Board. 2292: 94 – 103.
- Anderson I and Dewoolkar MM. 2015. Laboratory Freezing-and-Thawing Durability of Fly Ash Pervious Concrete in a Simulated Field Environment. American Concrete Institute Materials Journal. 112(5): 603-612.
- Sevi AF, Walsh D, Anderson IA, Schmeckpeper ER, and Dewoolkar MM. 2016. Laboratory freeze-thaw durability of pervious concrete with respect to curing time and addition of sand, slag, silica fume, and saltguard. Vermont Agency of Transportation.