Posts Tagged: Greenbuild

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 »

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 »