Data showed that all types of permeable pavement developed favorable conditions to allow surface infiltration during winter rain and melting events with subsurface temperatures remaining above freezing, even when air temperatures were well below freezing. However, PICP was shown to be less susceptible to the effects of freezing air temperatures compared to both pervious concrete (PC) and porous asphalt (PA).
The nature of PICP surface voids as well as the thermal mass of pavers may help insulate the aggregate reservoirs from surface temperature fluctuations much better than PC or PA.
A University of Toronto study in 2020 compared deicing operations impact on PICP compared to impervious asphalt surfaces. This research studied the winter safety benefits of permeable pavement and the use of deicing road salts that potentially harming waterways and biological systems.
The researchers found that PICP can attenuate and buffer the release of salt to the environment, and that PICP surfaces can be treated with lower application rates of road salts. The study confirmed the general view that PICP eliminates the potential black ice formation from standing water re-freezing.
Rather than use de-icing salts or sand, an alternative is to use the same ASTM #8 or #9 chip as used in the paver joints. Because permeable pavers are made with high quality concrete, snow can be plowed or shoveled without the need for special blades or equipment.
Sources: Danz, et. Al, Subsurface Temperature Properties for Three Types of Permeable Pavements in Cold Weather Climates and Implications for Deicer Reduction, 2021, US Geological Survey. | Drake, et. Al, De-Icing Operations for Permeable Interlocking Concrete Pavements, 2020,University of Toronto.
Mitigating Urban Heat Island
The "heat island" effect impacts urban areas that have systematically used up existing natural ground cover by replacing them with buildings, parking lots and paved streets. The resulting lack of parkland and trees results in higher overall temperatures in these microclimates. In turn, these temperatures place a higher demand on energy, produce more pollution and greenhouse gas emissions, and clearly create quality of life issues for all those living in such environments.
One strategy to mitigate the heat island effect is to use high reflectance, light-colored paving materials. Solar Reflectance (SR) or albedo, is the percentage of solar energy reflected by a surface. Most existing studies on cool pavements have focused on increasing the solar reflectance which can reduce pavement and even subsurface temperatures. The LEED rating systems require light colored pavers to have an initial SR of ≥ 0.33 for potential credit. Belgard Commercial has a large offering of colors that can contribute to heat island mitigation strategies.
Although using lighter colored reflective paver blocks does benefit Urban Heat Island, the increased pavement reflectance adversely affects human thermal comfort during hot periods due to an increase in the Mean Radiant Temperature contributed by the increased reflected radiation striking the human bodies. Using the PICP system as an evaporative system is a way of mitigating this impact. Water that is stored in the base is allowed to slowly evaporate through the pavers thereby cooling the paver surface. It is no different than how our bodies cool off by perspiring.
Studies at University of California-Davis found that keeping water near the surface of the pavement, through sprinkling water on the surface or injecting water into the pavement to keep the water level near the surface, will increase the evaporation rate and consequently produces a better evaporative cooling effect. “Stored water in the base of pavement allows water to slowly evaporate through, thereby cooling the paver surface”
Source: Li, Hui "Evaluation of Cool Pavement Strategies for Heat Island Mitigation", University of California-Dave, 2012. BENEFITS PERMEABLE INTERLOCKING CONCRETE PAVENTS
Paving Around Trees
The ability of air and water to be able to move through the PICP to new or existing vegetation is key to their survival and growth. By adding load bearing tree soils that support the weight of pavement and vehicles but still provides space for tree roots to flourish, the pavement can extend right up to the border of the tree pit. This practice is not possible with conventional paving without the use of specialized structural supports (steel grates, concrete vaults).