Why Make Pavements Porous?
Over the past 50 years development has increased and spread into areas that were once considered to be rural, drastically increasing the amount of impervious surfaces. The resulting increase in storm water has contributed to the bulk of the non-point source pollution affecting our environment and surface water quality. The detrimental affects extend past simple water quality issues and into the storm water runoff peak flows typically discharging to a surface water body. In some cases, erosion due to these specific discharge points transports large amounts of sediment into our rivers and streams. This directly affects the ecosystem of our streams and river banks. The current stormwater controls needed to buffer the affects of development can be costly and take up precious land that may be otherwise preserved for the natural habitat. Using a best management practice such as pervious pavements can help eliminate some of these problems.
If a pervious surface is properly designed and constructed, the impacts due to urbanization to the surrounding environment can be minimized. Utilizing pervious surfaces will ultimately enhance the ecosystem and human welfare. Prior to starting a pavement design and layout, pervious concrete and other porous surfaces should be considered as a possible BMP. If selected, a proper structural design should be done prior to ensure the pavement will continue to perform throughout the specified design life.
This type of pavement is also known as “no fines” concrete due to the aggregate gradation consisting of narrowly graded coarse aggregate, cement, water, admixtures, and, in some cases, fibers. Carefully controlled quantities of water and cement are used to create a paste that forms a thick coating around aggregate particles without flowing off during mixing and placing. Using just enough paste to coat the particles maintains a system of interconnected voids on between 8% to 35% depending on materials and intended application. Typically, when specified for a finished pavement surface, the interconnected void ratio will range from 8% to 17%. If the pavement is used as a drainable subbase, then the void ratio typically ranges from 17% to 35%. For parking areas and/or low volume roads, pervious concrete compressive strengths range from 3000 to 4000 PSI. If this material is used as a subbase for concrete or other finished pavement surfaces, compressive strengths typically are specified at 800 psi or less. This helps eliminate temperature shrinkage cracks that form in concrete during the curing process.
Environmental (LEED) Benefits
Pervious concrete provides several added benefits to the environment as recognized by the Leadership in Energy and Environmental Design (LEED). A summary of these benefits include the following:
Reducing the impact of the urban heat island effect. Light colored construction materials adsorb less solar heat than dark colored construction materials. This results in the direct reduction of urban heat that escalates other environmental problems such as air pollution and human welfare.
Reducing the noise pollution impacts with increased development. A pervious surface reduces the traffic noise at the source, particularly the noise from tires. A pervious surface both absorbs sound energy and allows some of the around the tires to be pressed into the voids dissipating air pressure before any noise is generated.
Reducing the impacts of stormwater runoff. Pervious surfaces allow water to infiltrate into the underlying soils instead of running off directly into storm drains and other treatment systems. This helps eliminate the amount of concentrated pollutants that typically is associated with the first flush of a particular rain event. These pollutants are now transported through the pavements matrix into the underlying soils where microbial degradation of hydrocarbon contaminants is enhanced with the addition of moisture and air from above.
Pervious Concrete “Paver Method”
Pervious Concrete “Paver Method” is a quality constructed durable concrete pavement surface placed with a high density paver, which helps eliminate many of the historical pitfalls associated with pervious pavement.
Some of the advantages of utilizing a high- density paver include:
- Increasing the longevity of the mix by achieving 90%+ compaction through the paver
- Increasing production speed by allowing the placement of a 10” lift at 30 foot widths with production ranging from 600 to 1200 cubic yards of material placed per day
- No finishing is required behind the paver
- No forms are required to meet specific grade requirements
- Low water to cement ratio which increases strength and durability
- No chemical admixtures needed if mixed in a pug-mill close to paving operations
- Zero slump mix is preferred when using a high density paver eliminating problems during placement with inconsistent mixes.
A.G. Peltz Group, LLC has been placing pervious concrete successfully with high density pavers for over 25 years across the United States. This pavement has been placed in areas such as Denver, Colorado; Lincoln, Nebraska; New York, Texas, and as far south as Tampa, Florida.
Tampa Bay Florida Airport “Budget Lot”
Pervious was selected for use by Budget due to rainfall issues at their car parking lot in Tampa. Due to frequency and energy associated with rainfall in the area, storm water runoff and associated flooding was a significant problem. Budget was looking for a long- term solution that would provide adequate drainage without compromising durability. “Paver Method” Pervious filled this niche.
Some project photos of the Tampa Bay project follow:
KCS Railway – Kendleton, TX
Pervious Concrete was utilized by the KCS Railway as a value engineering option at their Kendleton, TX intermodal facility in June of 2009. The layout for this facility included a packer pad and chassis parking area that is approximately 4500 feet long and 260 feet wide. Drainage at the site was installed utilizing a series of manholes at 300 foot centers. Due to the existing topography and operational concerns, the slopes between the manholes were minimal (.25%-.5%); consequently, the facility owners were concerned that the heavy rainfall events typical of the area would result in pooling water on the site. The end result could be increased maintenance cost as the pavement would prematurely deteriorate.
AG Peltz, LLC personnel approached KCS about developing a solution to the potential drainage issue. Instead of adjusting cross slope or adding expensive trench drains, AGP determined that they could add a Pervious Concrete strip which would allow water to pass directly into the under drain system instead of pooling on the pavement. AGP installed a 16 foot wide pervious strip utilizing high density pavers in June of 2009.
Pervious pavements are utilized as a finished pavement surface for light to medium duty pavements in areas where other storm water runoff controls are impractical or not cost effective. Pervious Concrete “Paver Method” is a quality constructed durable concrete pavement surface placed with a high density paver, which helps ensure that a durable pervious concrete pavement with adequate strength can be constructed in a timely manner.
If you believe that your company or facility might benefit from utilizing this innovative pavement alternative, please contact us for both design and construction assistance.
Dan Vipperman, P.E.
A.G. Peltz Group, LLC