Monthly Archives: February 2019

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 »