In the world of construction, there are numerous methods that can be used when planning out your project. When deciding which materials or method shall be used in the construction of pavement, there too are various methods of which you can choose from. It has been determined that traditional materials or impervious paving surfaces such as concrete, asphalt, pavers, and stone defy green building principals by creating excess storm water run-off and adding to the heat island effect. These impervious surfaces are also known to increase the required capacity of municipal stormwater systems, allowing harmful pollutants to run into waterways. Conversely, the term “permeable” is defined as a material or membrane which allows liquids or gases to pass through it. Likewise, the term “permeable paver”, an alternate paving system, mimics the way natural land absorbs water. Porous pavers and pervious concrete are all permeable pavers who adhere to the green building principals. These pavers are recognized for their ability to reduce surface runoff, and trap suspended solids which therefore filters pollutants from stormwater. Although they both identify as porous pavers, the terms “porous pavement” and “pervious concrete” are distinguishable. While Pervious concrete is defined as a mixture of uniform aggregate, water, and Portland cement, porous pavers are designed to present openings between and within the pavers which can be filled with vegetation or aggregate. Despite their differences, beneath the surface, both types require a similar compacted stone aggregate layering process to create a “reservoir” or accept stormwater before the percolation of water into the subgrade. Prior to design and installation, the specific physical and aesthetic qualities that each of these systems possesses should be considered.
Porous pavement is accredited for their ability to provide the same advantages as traditional concrete pavers while also having more sustainable and visually appealing characteristics. These high-quality pavers have exceptional durability and are able to tolerate heavy loads, offer low maintenance, and their flexibility make for easy repairs. Due to their extremely eco-friendly and affordability for low traffic, low-speed roads, porous pavers are ideal for parking lots, driveways, and pedestrian walkways. Opposed to their rigid cousins (impermeable surfaces), porous pavers can properly manage surface water that may pollute and cause dangerous flooding and erosion to fragile ecosystems. Its design offers a significant reduction of these risks and the need for man-made irrigation systems for watering vegetation by allowing the water to permeate the earth and constitute a natural cleaning and renewal process. Porous pavers allow the ground cover to be planted and can provide emergency vehicle access and landscaping at the same time as controlled runoff. Typically, traditional impermeable pavers such as asphalt aid to the heat island effect which can affect local communities and ecosystems greatly. By installing a porous paving system, an owner can help combat this effect rather than releasing it into the air and increasing temperatures. Porous systems can also improve elements of landscaping and includes financial benefits due to its quick and easy removal for underground repairs, its ability to maximize land use, and because it can be laid in remote areas without normal construction plants. Similarly, the chemical makeup of pervious concrete creates a very porous medium which allows water to directly convey in large volumes to underlying soils. Akin to porous pavers, pervious concrete may too reduce the amount of untreated runoff which may discharge into storm sewers, aid in the reduction of the heat island effect, and mitigate pollutants that can harm and contaminate watersheds and ecosystems. Pervious concretes eliminate hydrocarbon pollution more than traditional pavements (asphalt) may emit from their sealers, and the infrastructures financially benefit the developer by eliminating costly curb and gutter installations, time-consuming stormwater detention vaults, and piping systems, and reclaims those lots consumed by ponds and vaults. Collectively, both pervious and porous systems provide a higher albedo and eliminate the need for expensive collection and detention systems.
Typically, permeable concrete holds a load-bearing capacity of between 259,000 to 345,600 pounds per square foot depending on soils. High permeable soils such as sand have the best ability to carry loads, which therefore allows the pavement to become stronger and more stable when wet. As a result, the expected lifespan is can range from 15-20 years with proper siting, installment, design, and maintenance. Porous paving systems with flexible plastic grids range in performance. The Geoblock Porous Pavement system which consists of a series 20” x 40” x 2, interlocking, high strength blocks has the total load bearing capacity of 130,000 pounds per square foot (lbs./ ft2), while the Netpave 50 holds a load-bearing capacity of only 27,870 lbs./ ft2. Due to an accumulation of fine partials or organic growth, a reduction in perviousness can occur over time. For the reason being, by some manufacturers, it is recommended on an approximate 4-year cycle, that the surface is cleaned with commercial street sweeping and or vacuuming equipment. Maintenance of these systems also includes trimming/mowing, irrigation, fertilization, and seeding of the vegetation. Lastly, minor grid replacement should be conducted 10 years after installation.
When selecting the perfect paving system for a project, elements such as climate should firstly be taken into consideration. In most regions, pervious concrete can be applied. However, the practice has its challenges when introduced to colder climates. Its design prevents washout from adjacent soiled areas to drain onto the pervious concrete surface. Consequently, with regard to the sand and salt being applied for the removal of snow and ice, care should be taken as the sand may become wedged into the surface of the material. This occurrence can cause damage which may prevent water from passing through the system. Additionally, infiltrating runoff below the surface can possibly cause frost to heave. However, design modifications can reduce this risk by providing an adequate base layer. Despite this difficulty, evidence suggests that snow may actually clear more quickly on pervious surfaces than it would on impervious surfaces, which in turn reduces the need for snow plowing. Contrary to conventional impervious systems, snow is more likely to drain through the pervious concrete rather than ponding and refreezing, which minimizes the need to apply deicing materials to the surface. To stay clear of these potentially irreversible events, it is essential to quickly vacuum, rather than plow up any snow/ice treatment that is applied to pervious pavers. Moreover, the California Coastal Commission suggests that “Winter abrasives should not be applied to the pavement surface. Deicing salts should not be applied near groundwater drinking supplies, but environmentally- benign deicers are permissible. Snow- plow blades must be raised ~1” to protect the surface.”
The application of porous paving systems is increasing rapidly in northern cold climate areas. While traditional pavements may crack and allow infiltration during the winter season, porous pavers are more resistant to frost heave due to its design which breaks any capillary connection to groundwater. Porous systems may, however, require more salt during the first application as the resulting melted liquid infiltrates into the surface. Luckily, days afterward, much of the salt applied remains on the surface, reducing the need for application during the winter months. For porous systems, existing equipment can be used for snow removal, but it is recommended that skid plates/rollers are adjusted so that plow blades are 1” above the surface. If these infrastructures are incorrectly managed or not managed at all, during the winter, then the purpose of the sustainable method will be defeated, and pollutants will run off the surface.