The Midwest is no stranger to the use of interlocking concrete and permeable pavement solutions for many private, commercial, municipal and educational projects. In particular, municipalities with rivers that overflow seasonally and those receiving polluted stormwater are increasingly deploying permeable interlocking concrete pavements (PICP) for their projects and enjoying the benefits.
In St. Louis, the challenges of an aging combined sewer system and new stormwater requirements mandated in 2006 by the City’s Metropolitan Sewer District (MSD) led to the implementation of PICP in alleys, parking lots, sidewalks, trailheads and many other applications. Multiple projects including a series of green alleys constructed since the MSD mandate demonstrated concrete pavers as a trusted solution for many City initiatives, as well as for private projects. While often used to reduce stormwater pollution, the successful performance and aesthetic appeal of concrete pavers in projects across the city has led to their popularity and continued use.
Eco-Installation: Lewis and Clark Community College – National Great Rivers Research and Education Center
At the National Great Rivers Research and Education Center at Lewis and Clark Community College in East Alton, IL, it’s all about green. Established to lead research, education and outreach related to the interconnectedness of large rivers and their communities, being “green” was non-negotiable for the center’s construction. The first of two phases of construction began in 2008 with a field center to drive research and serve as a home base for educational programs.
The project secured a total of $6.8 million in construction funding with an additional $16.3 million designated by former Illinois Governor Pat Quinn. From the project’s inception, the goal was obtaining the highest Leadership in Energy and Environmental Design (LEED) certification. LEED credit-earning components for this project include: sustainable heating and cooling systems; a detention basin for stormwater quality control; plus permeable interlocking concrete pavement, as well as other pervious pavement systems.
The paver portion of the project includes a plaza, sidewalk and main access road totaling more than 25,000 sf of manually and machine-placed pavers, installed in less than one week’s time. Speed of installation was a factor in the project’s success because it quickly opened the roadway (unlike other pavement options that require downtime while curing), thus enabling multiple construction efforts to occur simultaneously.
“The facility is a showplace for green building that incorporates multiple types of green paving systems,” says Dave Godar, P.E. for Sheppard, Morgan & Schwaab, Inc. Material reuse was accomplished by using fly ash in the cast-in-place concrete and in the modified soil road base.
Also, the project had to consider the historic flood levels from the nearby Mississippi river. “We didn’t want permeable pavement where the flood level is, because it could clog,” Mr. Godar says.
The sidewalk portion of the project covers about 875 square yards; another 2,500 square yards makes up the roadway. The system uses 3-1/8 in. thick concrete pavers, 2 in. of bedding aggregate, 4 in. of open-graded aggregate base and 12 in. of larger aggregate subbase over filter fabric or geotextile.
“There are two schools of thought about using filter fabric,” Mr. Godar says. “Some say that over time the filter fabric can become clogged and prevent the rainwater from soaking into the ground. This site had sand material as the subgrade. We opted to go with filter fabric to prevent the underlying sand material from migrating up into the voids of the subbase aggregate, which could cause settlement of the pavers.”
To reduce labor costs, project design included machine installation for the interior pavers. “It was all kind of new,” Mr. Godar says of the plans created in 2009. “We hadn’t done anything like this before, although there were some examples out there.”
Funding for the project included some federal highway money, which meant all approvals had to go through the Illinois Department of Transportation (IDOT). Because many of the components were not standard and were not covered by IDOT specifications, some of the materials were considered experimental. The project took most of the 2010 construction season to complete. “The idea was for this to be a showplace,” Mr. Godar says. “It is open to the public, so if we had clients who wanted something similar, we could point them to the National Great Rivers Research and Education Center.”
Health Appeal: Ranken Jordan Pediatric Bridge Hospital
At Ranken Jordan Pediatric Bridge Hospital, about 15 miles northwest of St. Louis, permeable pavers satisfied the hospital’s stormwater requirements, providing an overall healthy feel to the campus. Coined a “bridge” hospital, the facility staff works to help children transition between hospital and home. With a history of expansion and growth, the hospital was built in 1941 as the Ranken-Jordan Home for Convalescent Crippled Children. In the 1960s, it expanded to accommodate more patients and staff, and in 2002, moved to a new 62,000 sf, 34-bed facility in Maryland Heights, MO. Several years later, the facility required more parking for patients and visitors.
When the organization first looked into expanding its parking capacity in 2009, stormwater requirements came into play immediately. The facility includes bio-retention basins and rain gardens. PICP met the MSD’s stormwater reduction requirements.
“At the time it was fairly cutting edge,” says Ted Spaid, co-founding principal of SWT Design, based in St. Louis, which led design for the project. “The MSD had just started enacting water quality management regulations for the region.” Rather than using underground stormwater tanks and other solutions, the design team decided on PICP to meet the requirements.
The first of Mr. Spaid’s projects with PICP took place at SWT’s office as an early test run right when the pavers first became available. Having successfully worked with them, SWT decided to use them in the hospital project. The pavers were manually installed between September and October of 2009, but required some special design attention because the parking lot presented a challenge with its radial layout. The designers addressed this by taking advantage of the paver pattern. The contractor installed the entire parking lot in a herringbone pattern, which can accommodate radial layouts, and saw cut the edge pavers to fit the non-uniform shape.
Another unique design element used pavers in contrasting colors to designate parking stalls rather than paint lines on the pavement. “The installation itself was a month-long process,” Mr. Spaid says. But the outcome was several-fold, for the 20,980-sf installation. First, it satisfied required municipal green elements by draining to rain gardens to help with bio-filtration. And while there was additional expense due to the paving materials, the aesthetic appeal was a positive payback.
“Many clients are timid about wanting to spend the extra money on permeable pavers, but then they realize it delivers more than stormwater management. If you can turn stormwater management into a positive aesthetic attribute, it’s much nicer. There are multiple layers of savings by using the pavers correctly and strategically.”
For example, the parking lot design allowed for surface runoff to sheet-flow over the asphalt and infiltrate into the permeable pavers. Eventually, that water would go to a centrally located rain garden or bio-retention area, and would flow to a larger detention basin as needed to prevent downstream flooding.
“This design replaced the need for typical drainage structures and piping system that you would find throughout a parking lot,” Mr. Spaid says. “Based on a cost-benefit analysis, a traditional stormwater infrastructure design was comparable to the cost of the permeable paving system. Furthermore, the permeable pavers provided the required stormwater management to decrease the flow of runoff and help control sediment.”
The pavers and rain garden also decreased the size of the necessary detention basin and preserved land for future expansion. The project is maintained with annual vacuuming and regular cleaning. MSD requires an annual inspection report that includes dates of inspections and cleaning methodology. Additionally, the report must confirm that all stormwater structures are functioning and that watersheds have not been disrupted by pavement clogging or erosion. The report must demonstrate that all best management practices (BMPs) and landscapes are functioning as designed.
In a care setting, particularly one focused on children, the sub-story is aligning construction materials with quality and health, Mr. Spaid says. “It’s a healthy living story,” he says. “Here we are at a pediatric care facility and we want to show quality care for children. Through stormwater management and rain gardens, there’s a story to be told about water quality and creating an environment not only contributing to a healthy planet, but to human well-being and aesthetics.”
Trailhead Series: Great Rivers Greenways
Concrete pavers may be “green,” but they’re not often found in the woods. The Great Rivers Greenway (GRG) District is an exception. The network spans more than 100 miles of trails and greenways among 1,400 acres through St. Louis City, St. Louis County and St. Charles County that support hiking, biking, walking and other outdoor activities. Established in 2000, the GRG initiative set out to improve health, reduce pollution and stabilize communities, among its many goals.
That’s where PICP comes in. In 2006, the organization extended one of its trails, which involved installing two new trailheads. Given the stormwater restrictions then recently passed by the MSD, the Great Rivers Greenway project managers and designers crafted a proposal for PICP as the surface for the new sites. A handful of other trailheads and parking areas built in the following years also realized the benefits from PICP.
“We considered leaving it asphalt,” recalls Carey Bundy, project manager for GRG. “It would be cheaper on the front end,” she says, “but PICP would count toward water quality credits. We went with pavers mainly because if something did go wrong later, they are much easier to get into and work on.”
Because it spans the city and two counties, funding for GRG projects comes from various sources, including tax dollars and federal grants. GRG resources are used to build and improve the trail network and then projects are turned over to the municipalities for maintenance. Working with pavers required a lot of testing, partnerships on design elements and determining performance requirements that would satisfy the mission of the trails.
The installations were not easy. “The most challenging part is the location and site accessibility,” says Scott Rozier, president of St. Louis-based Rosch Company. “The trails go through the middle of the woods, or across old abandoned tracks, and it’s very challenging logistically to get the subbase installed and place everything where it needs to be.”
In spite of the challenges, GRG found that the PICP systems with additional green elements such as plantable walls and reclaimed water systems have performed well. So well in fact, more projects are in the design and planning stages as a result. “Initially, people said they wanted to go with the traditional route and didn’t want to try this new but different material,” Ms. Bundy says. “But it’s on the ground now in a lot of places. Getting a pilot installed so people can see what it is, that is very helpful.”