Posts Categorized: Porous Pavements

The Integration of Pervious & Impervious Pavements to Address Green Infrastructure Needs

Written by: Samantha Justice, P.E. Green infrastructure incentive programs have become commonplace for new construction and redevelopment regulations. Five of the most common incentives include: Development incentives such as expedited permitting, decreased fees, zoning upgrades and stormwater requirement reductions. Grants Rebates and installation financing Awards and recognition programs Stormwater fee discounts A subset of green infrastructure, stormwater management usually includes the consideration of pervious and porous pavements. Traditional asphalt and concrete parking lot surfaces create significant stormwater runoff, and in many municipalities, cannot be used in expansion or new build situations. When the paved area is constructed completely with a porous pavement, stormwater concerns are greatly reduced. Depending upon the choice, pavements that return rainwater to the aquifer not only nearly eliminate stormwater runoff – they also reduce sheet flow and point load erosion problems at the pavement edges, and reduce need for additional stormwater infrastructure to convey the water away from the area. Porous pavement systems can be directly integrated with asphalt and concrete surfaces to reduce such failures and reduce or eliminate the need for stormwater conveyance channels, pipes, and swales. As a result, downstream stormwater pipe systems see less silt and less water which requires less maintenance… Read more »

Porous Pavements Myth Busters: Cost

Written By: William G Handlos, P.E. Does a porous pavement solution cost more? Porous pavements actually are less expensive to install than impervious concrete or asphalt when total project costs are considered. When evaluating parking lot construction costs for porous vs. impervious alternatives, the following cost “buckets” must be considered. Traditional pavements such as bituminous asphalt or Portland cement concrete enjoy low cost and ubiquitous installation contractors. This may lead one to think that choosing a porous pavement would lead to higher overall project costs… But that is a myth.   Most everything else about traditional parking lot construction is far more expensive than the porous pavement alternative. Traditional hard-surface pavements require inlet structures, castings and covers for inlets and manholes, underground pipe, outfall structures, and detention ponds. Costs & Maintenance of Stormwater Ponds Detention ponds have three major cost drivers. Land costs to locate a pond can vary wildly depending upon commercial real estate values, but it is not unusual for land to be upwards of $250,000/acre even in small markets. But the impact of the land utilized for detention ponds doesn’t end there. There is the lost opportunity cost for the unrealized rental or income value lost when… Read more »

Porous Pavements Myth Busters: Snow Removal

Written By: Samantha Justice, P.E. What You Need to Know About Removing Snow from Porous Pavements Vehicle and pedestrian use on porous pavements don’t stop because it’s winter. Roads need to be plowed, parking lots need to be cleared, and walking paths need to be snow and ice-free for safe use. This is true for all surface types: concrete, asphalt, and porous pavements—however, it is a common misconception that snow removal is more challenging with porous pavement systems. Myth Busted: Snow removal on a Porous Pavement System (PPS) is easy! Get the answers below to the frequently asked questions about removing snow from plastic, modular type porous pavers.   Can I Apply Salt to Porous Pavements? Applying salt or ice melt chemicals to gravel-filled PPS surfaces encourages snow and ice to melt, the same as it would on a concrete road. Most porous paver units are made with High Density Polyethylene (HDPE), a strong plastic that has a high resistance to environmental factors and is chemically inert. Cold temperatures and freezing and melting snow or ice will not cause damage or deformation to the paver material. Most importantly, HDPE is chemically stable, so it will not react to applied deicers,… Read more »

Porous Pavements Myth Buster: Clogging

Written By: Bill Handlos, P.E. All Porous Pavements Do Not Clog Well-designed porous pavement systems resist clogging While it is important to design porous pavement systems (PPS) to resist the effects of silt, grit, sand and other fine material that can slow or stop infiltration of water – It is a common myth that all porous pavement systems eventually clog. On the contrary, a good PPS system design, simple but effective site design and careful construction inspection and field guidance can all but eliminate the clogging threat. System design do’s and don’ts. Cross-sections will vary according to the porous pavement systems selected, but there are some common concepts that need to be followed for successful, long-lasting percolation.     Never place filter fabric immediately below the porous pavement surface. Whether using pervious concrete, porous asphalt, polyethylene injection molded paving block (such as GEOBLOCK vegetated or GEOPAVE non-vegetated PPS) or concrete paving stone, your cross-section should allow free flow from the paving layer to the base and storage layers. The last thing you want is to trap water in your pavement layer. Surprisingly, at least one aggregate PPS manufacturer sells their product with a filter fabric attached to the bottom of… Read more »

Porous Pavements Myth Buster: Winter Durability

Written By: Bill Handlos, P.E. Properly designed porous pavement systems do not get damaged by the dynamics of freeze thaw cycles. For decades, civil engineering roadway designers have been trained to use positive drainage, crack sealing, and sealcoating to keep the area under pavement dry. The prevailing mentality was to use well-graded, tightly compacted base under impervious concrete or asphalt wearing surfaces. When water gets between the well-graded base and the impervious surface—frost conditions would lift pavements, weaken base structure, create potholes and in general, wreak havoc with the life of the pavement.    So, it is not surprising that age-old tenets related to moisture, seepage and freeze-thaw cycles get mistakenly applied to porous pavement systems. What makes well-designed porous pavement cross-sections so resistant to the power of freezing and expanding water? The answer is space. Poorly-graded crushed aggregate offers up to 40% void ratio which gives water a place to move, a place to expand into upon freezing, and a network of pathways to drain. High void ratio systems allow the Earth’s natural warmth to move up from below the frost line into and through the open-air system just as water and ice-melt moves down and through the system…. Read more »

Porous Pavements Myth Buster: Winter Maintenance

Written By: Bill Handlos, P.E. Winter Maintenance for Porous & Pervious Pavements Porous pavement systems are a great way to reduce the amount of stormwater runoff on your site, and incorporate Low Impact Development (LID) practices. One of the simplest ways of creating a porous pavement area is to confine unbound aggregate in a rigid paving unit such as the GEOPAVE® Aggregate Porous Paver. The GEOPAVE system is similar to pervious concrete and porous asphalt solutions, but is usually both less expensive and easier to install. Porous Pavements Are Difficult to Maintain in Winter Weather Conditions.   NOT TRUE! The GEOPAVE Aggregate Porous Paver system is easy to maintain, and requires no special equipment. GEOPAVE parking lots or low volume roadways can be maintained in much the same way as a regular concrete or asphalt surface. An unbound aggregate system has many maintenance benefits over other porous pavement systems. Look at the table below and you’ll see how the GEOPAVE system beats pervious concrete and porous asphalt every time.     (Click Chart to Zoom)   The GEOPAVE rigid porous pavement system is comparable to standard paving materials, and a cut above other porous pavement systems. GEOPAVE systems have all of… Read more »

Why would you put nails in an aggregate porous pavement?

Written By: Bill Handlos, PE Every one of them. Each and every one of the spikes required to anchor this “invisible” product has pushed up. If consistency is the hallmark of excellence, then the maker of the gravel pavers that comes on a roll—“nailed” it. Take a look at what mother nature does, after each winter, to 8 inch spikes that were intended to hold down the ultra lightweight gravel paving product. For those of you who are blessed to live in an area where there is not frost each winter, let me explain. Whether you get 12 inches or 3 feet of frost, the frozen ground pushes up rocks, pipes, fence posts, garden lanterns and, yes, 8 inch nails. As a result, the parking area constructed in Wisconsin, whose specifications call for the use of spikes that are intended to stop the material from moving under the rotational torque loading of pneumatic tires (or for you non-engineers, tires) — well, that parking lot has just become the local tire repair center’s best friend. Tires do not like nails. Tires especially do not like nails that are sticking out by about an inch firmly held in place waiting to attack… Read more »

Impervious Gravel vs. Porous Aggregate Paving Systems

Written by William G. Handlos, P.E. For two decades, I held the position of City Engineer and frequently had to explain to disbelieving homeowners, developers and elected officials – that gravel driveways and parking lots were not porous.  I would explain that for purposes of stormwater runoff, such gravel pavements must be treated exactly as we would concrete and asphaltic pavements.  They often bristled at the idea that gravel did not percolate water and were upset to find that their gravel driveway, lots and roadways were assumed to shed 100% of rainwater. So it is with more than a dose of irony that I now have found myself in the position of regularly explaining to local and state officials that aggregate pavements are not necessarily impervious.  Stakeholders are so accustomed to repeating the impervious gravel mantra…that they forget to notice that porous aggregate is not the same thing as gravel.  I think it is best to start with a primer on the vernacular. A “good” gravel (Image 1) should have 40 to 70% stone, well-graded from 1/4” to 2-1/2” diameter; 20 to 50% sand; and 10% +/- fines. It should resist abrasion, shed water and be capable of being compacted. A… Read more »