Two Worlds Together

In 2010, the Transportation and Development Institute (T&DI) of the American Society of Civil Engineers (ASCE) hosted the first national Green Streets and Highways conference. This came from a need for stormwater managers to learn more about the world of road managers and vice versa. Stormwater managers realize that roads cover about 25% of urban areas, generating significant property damage from water pollution, minor flooding and combined sewer overflows in older cities. Not surprisingly, road managers view stormwater as a lower priority compared to road user safety and efficiency. Also, road agencies generally are larger than stormwater agencies at every level of government, and that typically translates into greater financial, technical and political clout.

Most road agencies view permeable pavement as suitable for car parking lots and alleys with occasional applications in low-volume residential streets. Such projects are at the margins of road agency priorities and their budgets, and many of these applications lie in the private sector. Permeable pavements have yet to be embraced by road agencies because they are seen as new and untried under regular truck or bus traffic. This is where more structural testing and evaluation of hybrid pavements may allow for more passes from higher-weight vehicles. This can place permeable pavement more in the mainstream of the road manager’s world.

Along these lines, moving permeable pavements more into mainstream acceptance and use by road managers will require several components. As noted, first and foremost is accelerated, full-scale load testing to validate the ability to withstand truck traffic. Such testing must result in structural design methods and easy-to-use, reliable thickness charts. While there has been some full-scale load testing for pervious concrete and porous asphalt, a recent full-scale load study by UC Davis on PICP resulted in design charts. This magazine issue includes a summary of the UC Davis work, cost savings implications for designers and where the charts will be used.

The second component is specifications. Cities and county road agencies often rely on, adopt and adapt construction specifications developed by state departments of transportation (DOT). Even provisionally issued specifications by a state DOT tells local road agencies that a particular technology such as permeable pavement has been vetted by knowledgeable experts. There are currently two DOTs that have published PICP specifications; Caltrans and Washington, DC. ICPI assisted in developing these. We hope to do more of this.

The third component is training. There are two sides to the training coin: one is for contractors that results in certification of competent, experienced individuals; the other is inspection training for road agency personnel. ICPI has seen fast growth in PICP classes for contractors and in those receiving a PICP Specialist Designation. This credential is becoming a requirement in local and state agency specifications. To help address this need, an inspection presentation is now available for ICPI members to present to stormwater and road agency personnel.

The fourth component is maintenance/management procedures and costs. A critical maintenance aspect for permeable pavements is regular surface cleaning with vacuum equipment. Permeable pavement will be more readily embraced by state DOTs and especially by local road agencies when existing street cleaning equipment can be used for cleaning. Regularly maintained PICP performs for decades. However, many installations don’t see regular cleaning that results in restoration of the surface infiltration with powerful vacuum equipment and perhaps water. ICPI has funded maintenance research in the past. This includes work by North Carolina State University and the Toronto and Region Conservation Authority. ICPI and its sister organization, the ICPI Foundation for Education and Research, are reviewing more research options for the near future.

This issue’s cover story features another realm where the two worlds of stormwater and pavement are usually close together, and that’s on military bases. These mostly self-contained environments are of such a scale that one person or a small group of people down the hall from each other manage pavements and drainage. There are a growing number of them using interlocking and permeable interlocking concrete pavements. The cover story provides an example of integrating the two worlds of pavement and drainage management from a need to solve flooding problems and pavement rehabilitation.

As industry, academia and governments address the four requirements for permeable pavement that lead to it becoming mainstream road infrastructure, the two managerial worlds will work more closely together. One resource that can support this process is ASCE publishing a new book called Permeable Pavements.


HNA 2015 Call for Entries

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You can’t win if you don’t enter: 2014 HNA Award winners received substantial exposure of their creations and companies.

Residential and commercial contractors of segmental paving and wall systems are encouraged to enter the Hardscape North America Awards contest. The contest offers contractors significant exposure to their finest projects. Past winners have been featured in this magazine as well as Hardscape, Concrete Products, Concrete International, Landscape and Irrigation, Landscape Architect and Specifier News, and Concrete Masonry Designs. The post-HNA press release announcing the 2014 winners received more than 59,000 headline impressions on Google and Yahoo! news feeds.

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ICPI encourages contractors to take advantage of this opportunity for company and project exposure and promotion. The contest recognizes only the highest quality projects, exemplars of craftsmanship and design using concrete pavers and paving slabs, clay pavers and segmental retaining walls. Award winners will be announced at the HNA 2015 Awards Reception on Thurs., Oct. 22, 2015, at the Kentucky Exposition Center in Louisville, KY.

Visit Questions can be directed to ICPI at 703-657-6900 or to


Inspection of PICP Systems

With the rapid growth of permeable interlocking concrete pavements (PICP), there is a pressing need for increased awareness and improved execution of inspections during construction. The greatest needs often emerge in two areas: 1) pre-construction coordination among project owners/manager, designers, product suppliers, testing labs, the contractor and subcontractors; and 2) compaction inspection for PICP system stability and long–term performance.

To better address these and other needs, ICPI released a one-hour PowerPoint presentation on PICP inspection for project inspectors. The presentation also informs designers, job superintendents, crews and product suppliers about inspection aspects common to most PICP projects.

The program is approved for one hour of ASLA and AIA continuing education credit and is also eligible for earning one professional development hour. For ICPI certified installers, this program also earns one hour of continuing education for maintaining certification. For a presentation, contact an ICPI manufacturing member with a request. To find those nearby, visit the home page of and use the “Find a local…” search engine. ICPI members providing the presentation must be ICPI-approved continuing education program presenters.


Lifetime Achievement

ICPI recently recognized industry leaders Chris Ross and David Bender for a life of significant contributions to the segmental concrete pavement industry.

The ICPI Lifetime Achievement Award recognizes life-long, high-impact contributions to the industry through knowledge, technical innovation, and advocacy. The award emphasizes innovation, dedication of the recipient to safety and well-being of employees, demonstrated leadership, and/or outstanding contribution to the industry from volunteer service to ICPI which promotes growth and advancement of the association and/or industry. The award recognizes noteworthy public service activities at the local, regional, state, national or international levels that bring honor to the industry or to ICPI.

ICPI Chairman David Pitre noted, “Both Chris and David helped lay the groundwork for which our association and industry operates. Without them, our industry would not be where it is today.”


Chris Ross served as ICPI’s Chairman-elect in 1998 and 1999, and then as ICPI Chairman in 1999 and 2000. With his oversight, he supported the transition of ICPI from a small association management company to Bostrom Corp. who helped grow ICPI from a $700,000 budget in 1998 to more than $2 million in 2007. Under Mr. Ross’ chairmanship, ICPI laid some foundations that their board and committees rely on today. Some of these include the ICPI policy manual, policies on financial reserves, development of the certification courses, and regional meetings. The ICPI Foundation was created while he was chair.

Several groundbreaking projects were supplied by Mr. Ross, including Massey Coal Terminal in Newport News, VA (now owned by Shell). This project led to another landmark project, the Port of Baltimore. The Baltimore project set a successful example among port engineers and engineering consultants, and helped open other U.S. ports to using concrete pavers.


In 1980, Mr. Bender moved from Canada to Texas and established Pavestone Company, now one of the largest paver manufacturing companies in North America. Seven years later he returned to Canada to establish Pavestone Plus (later renamed Navastone) where he worked for the next 20 years. In 1986, Mr. Bender penned a very passionate letter to the National Concrete Masonry Association (NCMA) detailing how pavers are different [than other pavements] and persuaded the need for the industry to support and market pavers accordingly. Long before its inception, his efforts helped lay the groundwork for the creation of ICPI in 1993.

Mr. Bender continued his passion for growing the industry. His company is a charter member of ICPI. Soon after its establishment, Mr. Bender led the association serving as chairman from 1995-1997. He is attributed with several leadership accomplishments that helped shape the association and industry. One of these was the development of the ICPI Certification Program, which today has had more than 25,000 participants. Mr. Bender also directed several marketing efforts to help overcome other barriers to paver sales success. These included the development of the product certification program, a multi-national public relations campaign, municipal products slideshow and a video on mechanical installation.


Essential Reading

Sponsored by the Low Impact Development Committee of the Urban Water Resources Research Council of ASCE’s Environmental and Water Resources Institute, Permeable Pavements presents a comprehensive, 260-page resource on design, construction and maintenance of permeable pavement systems. This e-book and printed edition represent a significantly updated compilation since Bruce Ferguson, FASLA, wrote Porous Pavements in 2005. ASCE’s book is richly illustrated with photos, diagrams and tables.

Permeable Pavements synthesizes diverse materials and practices using this technology with the help of academics, industry, civil and environmental engineers and scientists. The book benefits from these viewpoints with 17 authors plus 13 contributors and reviewers.

The book’s three primary editors, Bethany Eisenberg, LEED AP, Kelly Collins, PE and David R. Smith provided the structure, fact-checking, graphics and a consistent narrative style. The result is a book that can be used on almost every project.

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The book presents an overview of design considerations common to all permeable pavement systems in the first chapter. Detailed design, construction, use and performance information follow in separate chapters on porous asphalt, pervious concrete, permeable interlocking concrete pavement, grid pavements and some recent proprietary products. Additional chapters summarize maintenance considerations, hydrologic design approaches, essential components for specification writing and key areas for additional research. The book’s extensive use of fact sheets and checklists can be instrumental in design, construction and maintenance by stormwater agencies, designers, contractors and project owners. Appendices also include a fact sheet clarifying information on common concerns, as well as tables summarizing water quality treatment performance and costs.

The downloadable e-book and soft cover print version each retail for $120 ($90 for ASCE members). Visit the “publications” section at to order the book.


Basic Draining

Arriving at the base operations building at Peterson Air Force Base in Colorado, civil engineer Fred Brooks, P.E., LEED AP, is still struck by the beauty of an intricate compass design. It’s created with multi-colored concrete pavers, arranged in a huge circle. But he’s equally thrilled by the pavers in the parking lot. “Everyone loves these pavers,” says Mr. Brooks, U.S. Air Force Environmental Element Chief, 21st Civil Engineering Squadron. “We may have started these projects on this base as a way to handle stormwater, but they’ve done much more than that. They’ve shown how attractive and welcoming a base can look.”

Peterson AFB first started considering pavers to help meet the stormwater runoff requirements established in the 2007 Energy Independence and Security Act. Section 438 mandates all federal facilities manage runoff from 95 percent of all storms. Meeting this requirement often requires permeable pavements.

In Colorado, storms can come up suddenly with short-term deluges, causing flooding. Mr. Brooks says airfields quickly became submerged and buildings flood as well. Even without Section 438’s mandate, Mr. Brooks knew something had to change. After attending a seminar in Spokane, WA, and hearing about permeable pavers, he experienced a light-bulb moment. “This was the answer we needed,” he says. “I just had to get everyone else to see the light, too.”

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Mr. Brooks began by dividing the base into drainage catchments, focusing on the most problematic sections first. For example, one particular street with a catchment area of 35 acres included several older buildings that drained into the street. Flooding was a frequent concern, but a detention pond was deemed unfeasible and a complete sewer replacement would have been costly.

Mr. Brooks knew getting buy-in from others on base was crucial for such a significant project. Thus, he had the road to McDonald’s replaced with pavers. “Almost everyone on our base uses that road,” he says with a laugh. “I’m not sure if that’s good or not, but it’s the way it is. By paving that road first, I was able to expose people to the value of pavers, aesthetically and functionally.”

He also addressed weight load concerns by calling a special meeting (see sidebar) and composing a presentation about short-term versus long-term costs to assure base decision-makers that pavers were worth the investment. For instance, he noted that maintenance crews repainted road stripes nearly every year. By utilizing pavers as the striping instead, repainting costs would be eliminated.

In his presentation, Mr. Brooks emphasized how easily utilities could be accessed, as well as the advantages of more efficient road repair. He also discussed the aesthetic appeal of pavers. “Ultimately, we want people who are working here to be happy, and everyone feels better when they’re at a place that looks nice,” says Mr. Brooks.


After managing and shaping perceptions about cost and concerns about weight, Mr. Brooks was able to embark on a multi-stage project that involved several roads and parking lots, as well as the compass design for the entrance to the base operations building. The pavers, produced by an ICPI member, feature a minimal chamfer and smooth surface. This made them more suitable for pedestrian areas and wheelchair access and thus the design complied with the Americans with Disabilities Act design guidelines.

Mr. Brooks designed two separate permeable pavement sections for Paine St. based on flow and infiltration conditions. The first included a drainage pipe at the subgrade level below an open-graded aggregate reservoir layer. During periods of heavy runoff from storms producing flash flooding, the aggregate storage layer provides a buffer to control the discharge rate from the drainage pipe. The other section, which doesn’t require a drainage pipe, allows Mr. Brooks to assess the system’s ability to handle direct infiltration into the sandy subgrade.

The first installation involved more than 18,000 sf (1,670 m2) of pavers in a herringbone pattern, followed by another installation of the same area. In the second project, which was also a roadway, a section of the street had a low point that often flooded after storms. Although extension of storm sewer lines would have resolved flooding, that was deemed too expensive. Permeable pavers eliminated the need for storm sewers and project to outlast asphalt by a considerable amount of time.

The next phase for the base operations building included 20,000 sf (1,860 m2) of permeable pavers for the parking bays and for the compass design. The effort was so notable that the contractor, ICPI member Rocky Mountain Hardscapes, won a Hardscape North America Award in 2011 for the project. From there, two more parking lots were installed in 2012 and 2013 with more than 56,000 sf (5,200 m2) of pavers.

The permeable pavements dramatically reduced, and in many cases eliminated, the need for detention ponds for managing stormwater and snowmelt. In fact, when Mr. Brooks leads tours of the facility, he often dumps a bottle of water on the pavers to demonstrate their infiltration efficiency. Since achieving LEED credits is also important for the base, the designers were able to qualify for stormwater credits by demonstrating better control of peak flows, erosion mitigation, and increased on-site infiltration. “It’s human nature to resist change, and to look at the cheapest option,” says Mr. Brooks. “But what these projects have shown is that you can implement change in a way that’s cost-effective and appealing on a number of levels.”


Peterson Air Force Base’s use of concrete pavers serves as an example to other military bases and federal facilities, especially with regard to meeting the requirements in the Energy Independence and Security Act. Like Peterson AFB, many will be searching for ways to handle runoff while implementing long-term solutions that are durable, cost-effective, and sustainable. This appears to be happening.

Mr. Brooks notes that since Peterson AFB installed the permeable pavement, the Air Force Academy installed pavers for a 58,000 sf (5,400 m2) parking lot attached to its medical clinic, and Fort Carson utilized pavers for a test pad for tanks.

Looking to the future, it’s likely that paver projects will continue at Peterson AFB, since Mr. Brooks has mandated it. He revised the base’s “facilities of excellence” plan that outlines requirements to contractors so that permeable pavers must be used on any parking lots and low-volume roads in the future. “I wanted to make sure that these efforts wouldn’t be lost when I move on,” he says. “The pavers have made such a difference on this base, and I want that to continue.”


The Smart Start Small

For those new to bituminous-set paving, there are additional variables that simply don’t exist for traditional sand-set paver installations. Knowing these variables and planning accordingly is essential for a successful and profitable installation. “There’s a lot more work to it, but the benefits make it worth the trouble, especially for commercial applications,” says Mike LaMonica, estimator and project manager for Syrstone.


Bituminous-set applications on a rigid concrete base have a proven track record of superior performance under heavy vehicular traffic, especially in urban settings, according to ICPI’s Tech Spec 20: “Construction of Bituminous-Sand Set Interlocking Concrete Pavement.” Though more expensive (typically 30-50% higher than sand-set pavers due to additional materials and labor), long-term performance justifies the cost when compared to sand-set installations under the same wheel loads. Interlocking concrete pavement crosswalks with bituminous setting beds on concrete bases have an estimated lifespan of 7.5 million 18,000 lb equivalent single axle loads or ESALs, according to ICPI’s Tech Spec 19.


1.) Base thickness and reinforcing varies with traffic, climate and subgrade conditions. 2.) Concrete base minimum 2% slope from centerline to curb. 3.) Do not provide weep holes to subgrade when water table is less than 2 ft. (0.6 m) from top of soil subgrade. Provide drain holes to catch basins.

Bituminous setting beds on a rigid base have replaced mortar or sand-cement bedding materials in many pedestrian applications and in nearly all vehicular ones. Mortar-set pavers have not performed well under vehicular traffic and are susceptible to deterioration from freeze-thaw and exposure to deicing salts. Concrete bases are recommended in vehicular and pedestrian areas; asphalt bases should only be used in pedestrian areas.


There are two main variables with bituminous-set paver jobs that require upfront research and planning before putting a bid together. The first is availability of materials. Where is the nearest reputable asphalt batch plant that can produce a smaller quantity of the mix needed (7% asphalt to 93% concrete sand)? The plant will likely have a regional DOT-spec top mix or a performance-grade mix that is similar to ICPI guide specifications. Once a plant is located, the distance to the jobsite needs to be considered for determining trucking costs. For vehicular traffic installations, is traffic already present at the site that will require partial access? If so, the installation may need to be completed in phases which will require separate truckloads. Be sure to build the additional trucking costs of multiple deliveries into the estimate, as well as the minimum delivery load and the anticipated spoilage if the minimum is in excess of the needed quantity. These costs can add up and eat into profit margins quickly if not considered from the outset.

The second main variable is timing. “Everything with the bituminous setting bed is time-dependent,” Mr. LaMonica explains. The concrete or asphalt base is placed first and must cure. Next, an emulsified asphalt tack coat may be needed (recommended for vehicular applications, but typically not required for pedestrian applications) that will require curing time. Then, the bituminous setting bed is laid and must cure. On top of that, a neoprene-asphalt (neo-asphalt) adhesive must be applied that also requires curing. Planning around these downtimes is critical to efficiently manage labor hours. Ideally during curing downtimes, crews can work on cutting pavers or on another part of the installation that may be sand-set, or on housekeeping tasks to keep the jobsite clean and orderly. Typically, commercial jobs involve multiple other trades so keeping feet off of the installation-in-progress can be a challenge, but is very important given the messy nature of the materials. Vigilance is required and good communication will help prevent other crews from making a mess, especially if they are not familiar with the process and stages during which the surface should not receive foot traffic.


For those looking to enter the world of commercial projects by taking on a bituminous-set installation, Mr. LaMonica advises to start small, do your research and have the proper funds.

“I almost envy the residential installer who has the design eye to incorporate multiple hardscape components into his work,” Mr. LaMonica says. “The contractor has more control in the residential world because he can see the job through from beginning to end.”

The commercial world is so different, Mr. LaMonica says. A construction manager oversees the whole project, the paperwork and record keeping are a distraction, the profit margins are generally lower, payment is slower and design changes are often problematic to get approved and paid. “I tell the residential guy looking to do commercial, if you can’t afford to fund a job for 60, 90, or 120 days, you shouldn’t be in that world,” Mr. LaMonica says.

ICPI’s Commercial Paver Technician Installer Course covers bituminous-set paver installation. For more information, visit


The Results Are In

Two years in the making, the University of California Pavement Research Center in Davis recently released a report on full-scale load testing of permeable interlocking concrete pavement (PICP). The report proposes revised design charts that reduce the thickness of a subbase thickness chart published in ICPI’s 2011 manual, Permeable Interlocking Concrete Pavements. The revised charts from UC Davis provide more cost-effective thicknesses.

The subbase thickness in the 2011 ICPI manual are calculated using the flexible pavement design methodology in the 1993 Guide for Design with Pavement Structures by the American Association of State Highway and Transportation Officials (AASHTO). Well-known among pavement engineers, this book provides methods for calculating dense-graded base thicknesses under roads. The methods do not cover calculations for open-graded bases for permeable pavements. Conservative adjustments to AASHTO methodology were made to develop the 2011 design chart for open-graded materials.

The UC Davis research validates ICPI’s subbase thickness chart while refining it by considering the number of days per year a subbase sees standing water, i.e., 0, 10, 30, 60, 90, and 120 days. The resulting charts present thinner subbases at the lower end of this range of exposure to standing water when compared to the ICPI chart which assumes high exposures to saturated subgrades and subbases. Subbase thickness also depends on other factors such as the amount of soil support and anticipated wheel loads.

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The UC Davis Heavy Vehicle Simulator load tests PICP structures.

In pavement design, the mix of anticipated wheel loads over the pavement’s life are combined and equalized into 18,000-lb axle loads called ESALs or equivalent single axle loads. This load unit provides a consistent measurement that also relates to pavement rutting. To give an idea of an ESAL, an over-the-road tractor-trailer typically exerts 3 or 4 ESALs with one pass over a pavement. The PICP loaded at UC Davis received over 2.5 million ESALs using a machine simulating truck wheel loads. Pictures of the Heavy Vehicle Simulator (HVS) are above, as well as a video of it running dual truck tires on the test track.

In pavement research, the best way to determine how many ESALs define pavement lifespan in years is to conduct full-scale accelerated load testing. In other words, a pavement is loaded with many wheel passes until it fails or is no longer considered useful. UC Davis pavement engineers conducted load testing with an HVS that accelerates loading, accomplishing 20 years of loading in just five and a half months. For PICP, failure is defined as excessive rutting, typically over 1 in. (25 mm). Interestingly, none of the concrete pavers cracked while the pavement was loaded with truck tires at the UC Davis testing facility while rutting to over 2 in. UC Davis design charts for subbase thicknesses use 1-in. rutting as the failure criteria.

The comprehensive UC Davis study began with a literature review that found little domestic research and a paucity from overseas. The study then load tested some local existing PICP projects with an 18,000-lb truck axle to better understand deflection under it and the pavement strength. The deflection data was used to estimate the stiffness (elastic modulus) of each pavement layer by conducting computer-based mechanistic analysis modeling that correlates modeled and measured stresses, surface deflections, and permanent strains (rutting) to pavement layer strengths. This data was also used to determine subbase thicknesses for full-scale testing at a 96-ft long PICP test track over which the HVS could run truck tires and loads.

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The PICP cross sections tested at UC Davis with the HVS machine.

The test track included three subbase thicknesses (approximately 18 in. or 450 mm, 27 in. or 650 mm and 37 in. or 950 mm) instrumented to provide data on stresses while loaded and rutting (see diagram below). The weak clay soil subgrade was compacted and non-woven geotextile was placed on the subgrade and sides of the excavation. Above the subbases was a 4-in. (100 mm) thick layer of ASTM No. 57 aggregate, 2 in. (50 mm) of No. 8 aggregate, 3 1/8-in. (80 mm) thick concrete pavers and permeable jointing aggregate. A concrete curb restrained the No. 57 aggregate, bedding and pavers. The figure below shows a cross section of the test track. The aggregates were granite quarried from the foothills of the Sierra Nevada Mountains.

The testing represents the first full-scale load testing on PICP in the western hemisphere and one of a few studies globally that examines the structural response of open-graded bases to wheel loads. The UC Davis design charts go to one million ESALs, the maximum loads also provided on the 2011 ICPI design chart. The revised charts will appear in an emerging ASCE national standard on PICP as well as in an updated edition of the ICPI PICP manual. Both are scheduled for release in 2016.

The project was funded by the ICPI Foundation for Education and Research, the Concrete Masonry Association of California and Nevada, the California Nevada Cement Association and the Interlocking Concrete Pavement Institute.


Weight and See

Engineers and architects often must emphasize that concrete pavers can handle the weight of large trucks, as well as heavy traffic. But on a military base, perceptions about weight can be even more acute. For example, when it comes to a 68-ton tank that repeatedly traverses one area, some assume that pavers won’t work. They believe it is a residential-only product for patios.

When considering pavers for Peterson Air Force Base, Fred Brooks also encountered hesitation from others about weight loads, especially on well-used roads. So, he invited all the base’s operations professionals to a meeting with one of the developers of permeable pavers. “A subject matter expert stood at the front of the room and everyone just threw questions at him,” says Mr. Brooks. “They were invited to ask whatever they wanted. Voicing concerns and receiving information about weight loads went a long way toward increasing assurance about the issue,” he notes.

Because the pavers can accept high loads, other military bases began noticing the success at Peterson AFB. Recently, Fort Carson in Colorado Springs constructed a permeable paver test pad for tanks in part due to the example set by Peterson AFB. The test pad easily accommodated the weight and turning forces from one of the heaviest battle tanks in service, the 68-ton M1A1 Abrams.

Photo Caption: A paver test pad at Fort Carson withstands the load of an M1A1 Abrams tank. (Credit: Continental Hardscape Systems, LLC)