In today’s sustainable design environment there are a lot of ways you can “green” your facility. Often overlooked, however, are opportunities outside your facility. In a process called sustainable development, economic, environmental and social policy areas are evaluated to create the most optimal development plan. Think for a minute about conventional concrete used for parking lots, streets, driveways, etc. where runoff flows over the solid flat surface into a drain or gutter and into a stream, river or lake. Now consider pervious concrete as a beneficial sustainable design alternative to reduce runoff volumes, enhance stormwater quality, and reduce permitting headaches when developing a site.
For those unfamiliar with the product, the main difference between conventional concrete and pervious concrete is that pervious concrete possesses a void structure that allows stormwater to permeate, rather than flow across its surface. Its use has become very popular throughout the Southern and Western United States for its ability to recharge groundwater and local aquifers, reduce pollutant concentrations in storm runoff, and reduce the possibilities of flooding in urban areas. By introducing this alternative into an effective Low-Impact Development plan, a sustainable development project can be successfully created.
Water Efficiency // Small changes can reap great rewards in water use reduction.
Office buildings with a 50/50 ratio of men and women can reduce their water consumption by 20% by simply replacing the standard 2.2 gallon per minute aerators on the hand sinks with water saving 0.5 gallon per minute aerators. Material cost would be less than $20 per faucet.
That same office building could also replace the ladies’ water closets with dual flush models (1.6 GPF for solids and 0.8 to 1.1 GPF for liquids) and increase the savings to over 30%. Building with a larger percentage of females would reap even greater savings in both water and sewer costs. That’s right, we pay to bring it in, THEN we have to pay again for it to leave our buildings.
Rainwater harvesting or grey water reuse for irrigation or use in flushing fixtures can reduce water use in those fixtures and/or irrigation by up to 100%!
Pervious concrete is created with carefully controlled amounts of water and cementitious materials to create a thick paste that forms around the aggregate particles. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drain quickly, on the order of 500 in. per hour.
While some research suggests pervious concrete is not suitable for all conventional uses, there is proven research available that pervious concrete is actually a strong and highly durable material, making it very structurally sound for its intended applications. Parking areas properly designed and constructed will last 20-40 years with little or no maintenance and can achieve strengths in excess of 3000 psi, according to the National Ready Mix Concrete Association (NRMCA). For this reason, pervious concrete has proven to be more than just an environmentally responsible alternative, but a quality paving surface as well. Not to mention cost-saving benefits (more on that later).
Using pervious concrete can minimize the difficulty of meeting site permitting requirements in several ways: 1.) stormwater runoff reduction, 2.) stormwater treatment, 3.) zoning credits, and 4.) tree protection. The implementation of pervious concrete has allowed permitting for these uses to remarkably improve.
Due to pervious concrete’s large void ratio—nearly 15-30 percent—rain and snow are able to immediately flow through the pores and crevasses. With conventional concrete, however, this runoff must be collected and then transported away from the site via an additional conveyance system. With increased volumes and increased discharge amounts comes increased operational and maintenance costs for the local taxpayer, and many times for the developer as well through stormwater impact fees on impervious outdoor areas. For this reason, pervious concrete can be a very advantageous component of a site development when attempting to reduce stormwater runoff, recharge groundwater, support sustainable construction, provide a solution for construction that is sensitive to environmental concerns, and help owners comply with EPA stormwater regulations.
Most pervious concrete applications can be designed where the rock base under the pavement will detain the designed storm event and reduce or entirely prevent runoff from the paved area. In addition, pervious concrete allows for natural water filtration through its rock base and underlying subgrade, providing for safe and natural stormwater treatment. This can result in a remarkably efficient and cost-saving solution for any project’s stormwater worries, taking pressure off infrastructure and taxpayer maintenance dollars. A developer may also receive credit for reducing onsite stormwater treatment volume.
Zoning credits gained by using pervious concrete are by far the most desirable benefit for any cost-conscience engineering firm or developer. Pervious pavement can meet new city zoning regulations requiring groundwater recharging and protecting the health of the natural environment.
Creative uses for pervious concrete include tree protection. This simple yet effective application can save a developer substantial money in tree removal and replacement while promoting the reduction of urban heat island effect on a site. Additionally, in many cities and counties, a developer may not remove a tree (or trees) without replacing it with an equal diametric amount of trees, and sometimes twice as much. For example, if a 40 in. diameter pine tree is removed for a new development in its place, the developer may have to replace it with 80 inches of new trees. This can create a significant expense for the development’s budget. However, if pervious concrete were to be used, the project could potentially retain the existing trees and implement them into the landscaping plan for the site.