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Great Expectations

Building systems and pavement systems must become institutionalized before they are fully embraced by designers, owners, and users. We’re not talking about the institutionalization of people into wards of the state, but rather, how building technologies become normal and expected in a society. In order for building systems to achieve that level of expectation in a culture, the institutionalization process begins with the manufacturing industry of that particular building or pavement system.

Components of the Process:

  • Standard product specifications (i.e., ASTM/CSA), design and construction criteria
  • Research to expand applications and define limits—this can be materials testing or testing the performance of systems and assemblies
  • Construction training for qualified labor
  • University education for young and emerging design professionals
  • Manufacturing quality control and quality assurance certification
  • Marketing via advertising, public relations, brochures, trade shows, continuing education presentations, and websites to communicate system features, advantages and benefits

 

Most of the pavement owned by public agencies and private corporations is asphalt or concrete. Institutionalization of these pavements began about a century ago and continues today. We expect these pavements in our culture. They are in our mental as well as our physical landscape. We’d like to see similar expectations develop for segmental concrete pavement here in North America. Segmental concrete pavement is already expected and used extensively in many other countries, such as the Netherlands and Germany.

As pavement owners, federal, provincial, state and local governments annually invest billions of dollars in construction, ownership, and maintenance. Industry and academia conduct research and train young designers as investment momentum builds. This process is a key characteristic of a mature and fully institutionalized pavement technology, where pavement owners take over the reigns from industry to see through the final stage of institutionalization.

Permeable pavement is experiencing this transition now, thanks to tougher stormwater runoff regulations. Since the late 1990s, pervious concrete, porous asphalt, and permeable interlocking concrete pavement (PICP) have seen millions invested in university research, construction, and performance evaluations. The industries representing these pavements started the process, and some stormwater agencies are continuing it.

Though much polluted runoff comes directly from roads, transportation agencies have been slower to accept permeable pavement as the norm for low-speed pavements. That’s because permeable pavement must follow the same institutionalization path as conventional pavement types, and transportation agency gatekeepers demand it. Their path is more technically demanding than that required for acceptance by stormwater management agencies because of concerns about structural support, safety, and durability, among others.

The additional research required to address these concerns leads to transportation agency ownership of the institutionalization process.

When a sufficient number of transportation agencies embrace permeable pavement, their energy and funding will accelerate the institutionalization process. We are already seeing small signs of this in the works. Federal and state regulatory forces gathering behind the scenes are pushing transportation agencies from vague interest into needing permeable pavements. When that happens, agency ownership of the institutionalization advances. This eventually leads to our society expecting permeable pavement—and that is a great expectation.

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PICP Fire Truck Demo

It’s a rainy day in Louisville, so the pavement surfaces are already saturated. The nearby asphalt pavement is pooling rain water on the surface, while the newly installed permeable interlocking concrete pavement shows no surface water pooling. To show how permeable pavers aid in water runoff, 1,800 gallons of water was sprayed on the surface by the Louisville Fire Department. The water infiltrated the surface almost immediately. Learn more about Permeable Interlocking Concrete Pavement at www.permeablepavement.org.

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PIWP?

To maintain its original character, one of only two remaining segmental wood-paved areas in Chicago saw restoration of its original construction. Dating from 1909 and located in the city’s Gold Coast neighborhood along Lake Michigan, the alley is enshrined on the National Register of Historic Places and designated a City of Chicago Historic Preservation Landmark. While not officially one of Chicago Department of Transportation’s 100-plus green alleys designed to reduce stormwater runoff, the alley has some sustainable aspects without official certification from the Forest Stewardship Council.

It took 10 years for the CDOT and the community to undertake the venture, says Michael Lev, vice president of TranSystems, the major consultant for the project. “The traditional thing to do would be to cut everything out and put in a concrete alley, but the community felt strongly that concrete was not the right solution,” Lev says. Instead, CDOT decided to replace the original wood pavers with new ones. The construction team vetted various wood species for the new blocks, first considering used railroad ties but finally deciding on black locust wood due to its durability, density, resistance to insects and rotting, visual appeal and lack of odor.

The base of the alley was another issue. “We thought it was pretty unusual to have poured a concrete base under a wood paver street at that time,” Lev says. Although using the existing base reduced costs and construction waste, he says, it also presented drainage complications. “We actually had to create a permeable paver design, but there was this solid concrete base underneath,” Lev says. “We ended up detailing a pattern of weep holes, which the contractor drilled into the base, to allow water to percolate through the bedding sand and the sand in between the pavers, through some filter fabric, and then through the weep holes,” he says. Obviously, open-graded, highly permeable jointing and bedding aggregates used in today’s permeable interlocking concrete pavements aren’t compatible with wood pavers. While sand isn’t as permeable as open-graded aggregates, the passage of any water through sand joints and bedding certainly contributes a bit to stormwater runoff reduction.

Most importantly, the renovated alley retained its cultural value. The renovation of the century-old alley further confirms Chicago as the birthplace of green alleys before naming them as such. As a testament to the alley’s history and durability, a small portion of its west end remains paved with the original 1909 paver blocks. The project won the 2012 American Public Works Association Project of the Year Historical Preservation category award for projects less than $5 million. A glance back to the past suggests that permeable interlocking concrete pavement assumed a role begun by permeable interlocking wood pavement alleys.

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HNA 2012 Awards

Brown Hall, Colorado School of Mines

• Project Location: Golden, CO

Square Feet of Project: 35,000

Contractor: Rocky Mountain Hardscapes, LLP

PRODUCT MANUFACTURER: Pavestone Company

With the construction of Brown Hall, the intent of the design created a beautiful and compelling pedestrian environment in newly vacated streets in the heart of the Colorado School of Mines campus. This solution also accommodated emergency and service vehicle loads and avoided exceeding historic off-site storm flows, while meeting the campus maintenance requirements for a long-lasting, durable pavement surface. The pavement profile captures water on slopes in places which exceeded 8%. This required site specific detailing, including subsurface check dams and subdrains, since the typical design is for under 5% slopes. The pavement system was designed for partial and full infiltration and in places adjacent to the building a liner was included at the bottom of the profile to protect the building foundation from surface water infiltration. An electric snowmelt system was incorporated into the paver design at building entrances. Paver colors were selected to meet the solar reflectance values allowing the project to achieve the LEED credit SSc7.1 – Heat Island Effect/Non-roof. Other LEED credits toward which the paver system contributed were: Stormwater Management Quantity Control Credit 6.1; Stormwater Management Quality Control Credit 6.2; Regional Materials Credit 5. In order to maintain continuity, designer and contractor collaborated on careful detailing of edge conditions around utility manholes and valve covers to accommodate the paver geometry and layout. Specific layout rules helped the contractor minimize redos and avoid a poor result. Team commitment meant spending time in the field to review the paver installation layout to ensure a quality installation and realize the design intent in a non-modular world. While the goal was LEED Silver, with the contribution of a permeable paver system, Brown Hall achieved LEED Gold certification.

 

Lake Forest Country Club

Project Location: Hudson, OH

Square Feet of Project: 3,000

Contractor: Rock Bottom Lawn & Landscaping

PRODUCT MANUFACTURER: Belgard; Unilock

This project consisted of creating an outdoor event venue accommodating all types of gatherings from weddings to informal lunches. The design creates a functional meeting space that highlights and utilizes the picturesque lakefront setting. While the lake served as a beautiful backdrop to the project, it also created challenges in planning and construction. Excess water and slope down to the lake were resolved by engineered retaining walls and extensive drainage under the patio. A professionally diverse staff planned every aspect of the project, including the water feature, the custom bar and grill, and the carefully selected landscaping. To help reduce the scale of the 3,000 sf (279 m2) patio, it was constructed over a grid pattern, accentuated by key vertical elements such as the fireplace, bar, grill and water feature. An inlay of deep red creates the grid that draws your eye down straight lines toward these focal points. Sinuous walls provide a contrast to the rectilinear pavers. A swimming pool, water slides and lounging deck were completed by a separate contractor. The canopy system requested by the association was uniquely designed to conform to the project layout.

 

DARTMOUTH CROSSING SIDEWALKS

Project Location: Dartmouth, NS

Square Feet of Project: 132,000

Contractor: Cornerstone Interlocking Brick Ltd.

PRODUCT MANUFACTURER: Permacon

The Dartmouth Crossing is a large retail development in Dartmouth, Nova Scotia. Among the typical big box stores are numerous upscale boutiques. When the architects and developers wanted to give these ‘lifestyle’ stores an inviting and appealing feel, they turned to 132,000 sf (12,263 m2) concrete paver sidewalks. Three challenges separated this project from other jobs. The first challenge was the complexity of the circular patterns and accent layouts. The cobblestone look was achieved by nesting half circles with a fan pattern between them. The amount of cutting involved was substantial as none of the factory-supplied circle kits were designed for this method of installation. The second challenge was the different thickness of the banding and soldier coursing.  At 80 mm thick (as compared to 60 mm for the field), the banding pavers and border details had to be graded, laid, and cut before repeating the same process for the thinner field pavers. The third challenge was a tight timeline. Although the work was spread over three years (2007-09), there was always pressure to complete paving for individual stores for grand openings. The unit paving was always left until the very end for over 50 store openings. The pictures for this entry were taken August 2012, four years after installation. The installation has performed flawlessly and looks great with the “main street” storefront designs.

 

Glen cove ferry terminal

Project Location: Glen Cove, NY

Square Feet of Project: 9,000

Contractor: KJB Industries, Inc.

PRODUCT MANUFACTURER: Nicolock
Paving StonesAs part of the waterfront revitalization in the City of Glen Cove, NY, a terminal dock was added for a ferry to take passengers from Glen Cove into New York City. The site was a contaminated superfund site and this clean up was a major part of the contract. The project consisted of a concrete bulkhead more than 600 ft (183 m) along the waterfront from which floating docks extend for ferries to unload passengers. The ramps from the dock to the top of the bulkhead are handicap accessible. Between the bulkhead and the parking lot, a landscaped, paver walkway and seating area was constructed. The walkway and parking area has area lighting for night use.

 

virginia street residence

Project Location: Omaha, NE

Square Feet of Project: 2,500

Contractor: Paver Designs

PRODUCT MANUFACTURER: Belgard

This two-stage project included a front patio area finished for a family wedding, and a driveway added after the wedding. The driveway was excavated to a depth of 16-18 in. (400-450 mm) and the patio is 12 in. (300 mm) deep. Crushed recycled concrete was used for the base with one inch of bedding sand. After the Mega-Arbel Stone pavers were placed, another inch (25 mm) of base was added for the Dublin Cobble paver areas. Holland stone pavers are usually used for the inlays. Three round seats were built next to the water feature and pebble designs were created in the center of each. Columns for the freestanding wall were designed with recessed areas for lights and for use as planters. Three-by-six inch (75 x 150 mm) Dublin cobble pavers were cut in half for the triple border in the narrower areas of the patio. The front paver entrance is gently ramped with no step for handicapped accessibility. The most difficult stage of this project was drawing over 20 diverse designs over the winter months and then making a final selection. Using the basement floor as a drawing board, the “Y” shaped designs were drawn on Masonite at appropriate angles and distances so that the mirrored pairs nearly touched, and a template was made from this. After laying the field of pavers, the mosaic areas were marked with the template. These pavers were cut out one at a time. All of the colored Holland stone pavers were cut into thirds, and then angles were cut to follow curves. The template was moved and traced 12 times; each triple-row design took eight hours to complete, an approximate total time of 96 hours just for the mosaic patterns. Many additional hours were spent cutting and installing the fish and triple borders. Pavers in the mosaic, as well as the koi and borders, were coated with Techniseal NuLOOK. These colors are rich and bright, well worth the extra effort. Techniseal Color Boost matte finish was applied to the Mega-Arbel Stone on the driveway. No finish was applied on the Dublin Cobble Pavers.

 

LOPEZ OUTDOOR LIVING

Project Location: Williamsburg, VA

Square Feet of Project: 3,500

Contractor: Mid Atlantic Enterprise, Inc.

PRODUCT MANUFACTURER: Hanson Hardscapes & Rediscapes

The main objective for this project was to turn a disabled American veteran’s unused, hilly backyard into a complete outdoor living destination. This meant creating a functional place for the client’s needs while being an exciting place for his young family to play and entertain. A major challenge in this project was altering the terrain to suit the design plan. The entire backyard had to be clear cut and over 3,000 cubic yards (2,300 m2) of earth removed. Poor drainage was corrected before installing the hardscape. To accommodate the elevation changes of the property and to support an ADA compliant ramp, two walls were constructed using Rediscapes Wall Block. One wall serves as a freestanding retaining wall specially constructed on a large concrete footer and reinforced with rebar and concrete. Everything was custom built including a new deck and pergola to blend the home and hardscape. This included a fully functional outdoor kitchen, a gunite pool and spa large enough to accommodate the client’s ever-growing family, two fire bowls and a fire pit to add the “wow” factor. In addition, a shed was built to complement the home while providing much needed storage space. A full landscape was installed, which included five 25 ft Magnolia trees to provide instant privacy in place of the overgrown woody area. To provide safety at night, the project was completed with strategically placed landscape lighting.

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Paving the Way: Power Walk

I magine a world in which your footsteps create the energy to power streetlights. This world exists, and you live in it.

U.K.-based Pavegen Systems has created slabs that convert kinetic energy from human footsteps into renewable electricity that can power streetlights, electric signs, outdoor lighting, advertisements and more. Surplus electricity generated by human footfall is stored in a battery within the slab itself and can be used to charge various low power devices, such as cell phones.

When stepped on, the flexible rubber surface of each Pavegen tile depresses ever so slightly, and the technology inside the slab converts this energy to electricity. To engage pedestrians in this renewable energy process, 5 percent of the electricity generated is used to light up the slab—a friendly reminder that technology is at work below the surface.

These Pavegen slabs are durable, built to withstand the outdoor elements and, of course, heavy foot traffic. The green surface layer is made of 97 percent recycled vehicle tires, and the remainder of the tile is made up of 60 percent recycled materials. By installing this technology in areas that pedestrians frequent—train and bus stations, busy sidewalks, crosswalks, shopping malls, school hallways and dance clubs—we will be able to harness the potential of the human footstep as an energy source.

Simon Langton Grammar School for Boys in the UK first installed Pavegen slabs in its corridors in 2010. By September 2012, Pavegen slabs are slated to become part of the terrain at the Westfield Stratford City Shopping Centre in London, one of the largest urban shopping centers in Europe.

As more spaces around the globe take advantage of renewable energy technology and products like those created by Pavegen, we are provided with an extraordinary opportunity— to reduce our carbon footprint with our actual footsteps.

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Alleys Go Green with PicP

Green alleys, using permeable interlocking concrete pavement (PICP), require careful consideration during the design stages. Start with the end in mind, specifically calculating the amount of water that needs to be managed and where it is draining.

The first steps of the project are calculating runoff volumes from adjacent pavements and buildings, as well as timing how quickly water moves from roofs to the alley and into storm sewers.

In downtowns and highly urbanized areas, alley sewers receive roof runoff from downspouts and adjacent pavements. Green alleys provide a means to slow this flow, and in some cases, infiltrate a portion of the water into the soil subgrade. Slowing the flow can be done with berms and/or constricted outflow pipes that pool into catch basins before draining into the larger sewer system.

slow the flow

Berms are often required to slow flows when the subgrade slope exceeds 3 percent. Berms can consist of concrete, soil left in place, or lateral trenches dug across the width of the alley. The simplest berms consist of an open-graded base wrapped with two layers of geotextile, sitting atop the soil subgrade. Regardless of the material, the height of each berm depends on how much water needs to be detained and infiltrated (if soils are cooperative). Modeling flow is characterized by small ponds flowing one into the next. The outflow from one to the next can be via sheet flow, a knotch, or through a pipe (or pipes) penetrating the berms and aligning with the slope (i.e., oriented longitudinally).

Roof downspouts should drain water into the PICP base instead of its surface if there is an abundance of adjacent impervious surfaces. This reduces the risk of downspouts draining across impervious pavement and mobilizing sediment into the PICP openings. In addition, downspouts joining PICP base will flow longer in winter. In suburban settings, water from downspouts can run across vegetated areas, allowing for infiltration. Estimating the amount of runoff from the vegetated areas should assume the worst-case scenario for saturated soil infiltration rates.

modeling extremes

Depending on the geographic region, there could be extreme storms and rainfall depths that cannot be drained by the alley. When designing a green alley in these areas, the conditions that create flooding need to be modeled (i.e., the worst-case flooding scenario, including the depth and duration of standing water). If surface or subsurface bypass pipes or overland passages drain water from extreme rainfalls, all the better. If not, then the alley should be designed to minimize adjacent property damage in the event of deluge and flooding.

In downtowns and highly urbanized areas, alleys run next to building foundations. The foundations or sides of the alley will require covering by an impermeable liner to prevent water from infiltrating building foundations and basements, especially if the alley is designed as a detention/infiltration facility. This can be accomplished with restricted outflow pipes or perforated pipes along the soil subgrade that hold water until it deepens and then flows out of elevated drainpipes. In other instances where soil infiltration is negligible, there may be perforated drain pipes at the bottom of the alley that remove water almost immediately, which might obviate the need for liners against foundations.

Alleys often have utility poles that should not be surrounded with open-graded base. The utility poles should be moved or the open-graded base should be directed around them. They should be treated as structures; therefore, impermeable liners should be placed several feet away from their perimeter. Another option may be encasing the underground portion of the poles in concrete. Consultation with an engineer from the company that owns the poles is essential. The depth of the poles and distance of undisturbed soil around each should be discussed.

Alleys may have some distance between the back of the buildings and the alley surface. This space can be lawn, a separate garage or outbuilding, or gravel or dirt parking spaces. To reduce the risk of sedimentation and clogging, consider paving these surfaces with permeables as well. PICP alleys require curbs, which occasionally can be sloped to block or divert water and sediment flows from adjacent parking spaces away from the permeable surface.

Alley maintenance is almost non-existent in many cities because surface cleaning, snow removal and deicing are not budgeted. All permeable pavements for green alleys will require regular surface vacuuming. Because some sewer authorities have installed green alleys, they have assumed surface cleaning, especially if the city doesn’t maintain alleys. Surface cleaning is essential, because incidental litter from trash, leaves and grass clippings can accumulate on alley surfaces. For whomever maintains the alleys within a city, green alleys should be included in computerized pavement or sewer management systems.

transforming character

Underground utilities generally are not an issue, as long as they consist of waterproof piping and are deep enough to survive compaction of stone base materials over them without damage. Keep in mind that some utility lines are encased in open-graded stone, and that stone can be a pathway for water if adjacent to a permeable pavement base. In such cases, the flow of water onto the stone around a pipe exposed at the side of a permeable pavement excavation will need to be stopped with low-strength concrete fill.

When alleys go green with PICP, they can be paved with light colored paving units, which can enhance night lighting and help reduce urban temperatures. Alleys in older cities are often made of stones or bricks, and PICP can take on the appearance of either surface, thereby preserving and reinforcing the paving tradition and design context of these older cities.

The transformation from an unsightly alley in a backyard to a clean, well-kept space may increase private property values and earn money for the city in the form of higher property taxes. And for cities with combined sewers, green alleys are another effective tool in the green roads/green infrastructure toolbox that can reduce combined sewer overflows with stormwater detention and infiltration.

Combined sewers or not, green alleys can increase a neighborhood’s character and provide much-needed public spaces in dense urban areas.

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Rethinking A Lot

One of the standing jokes about shoppers is their urge to park as close to the store as possible, even if this requires driving around the lot for a few extra minutes looking for that premium parking space. Once the car is parked, the parking lot is merely an ‘in-between’ space to get through as quickly as possible to reach one’s destination.

A recent book, Rethinking A Lot – The Design and Culture of Parking by Eran Ben-Joseph, tells us what we already know about supersized, mostly vacant parking lots: They erode urban visual, environmental and social quality. A shocking statistic, however, is Ben-Joseph’s estimate of the total area of parking in the U.S. at 500 million spaces.That’s about 3,590 square miles (929,805 ha)—an area slightly larger than Puerto Rico.

Ben-Joseph redeems parking lots used for community or social functions, such as farmers’ markets, tailgating and traveling carnivals. He recognizes that parking lots present significant opportunities for combining social spaces and economic gain. Parking lots with environmental benefits, such as permeable surfaces, receive recognition as well. Installing solar panels and parking cars under them might make sense as solar cell costs decrease. Imagine a garage structure built from solar panels paid for by the very electricity that is generated and sold back to the power company.

From the industry perspective, a parking pavement area more or less the size of Puerto Rico will need to be replaced in the next 50 years. With tightening stormwater regulations, some lots will be retrofitted with permeable pavement. Even if a modest 3 percent of this massive parking area is converted to permeable interlocking concrete pavement (PICP), that’s two square miles or 55.7 million sf (518 ha) per year of PICP. We are rethinking a lot.

Speaking of rethinking, you’ve probably noticed the new look and feel to this magazine. You are holding the first of the next generation. The name change from Interlocking Concrete Pavement Magazine to Interlock Design includes layout and content enhancements. We continue to present quality information on commercial and municipal interlocking pavement projects for design professionals, contractors and project owners. Advertising will soon include outstanding products from paver manufacturers and allied concrete product producers. We invite readers to send successful projects to feature in future issues. From our first publication in February 1994, to this new one, and those to come, we aim to present you with many new ideas and reasons to rethink a lot.

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Moving Pavement

A few California developers and local agencies are already using PICP. Caltrans development of specs and a design guide should support increased PICP use.

The California Department of Transportation (Caltrans) is the first state transportation agency to develop a specification and design guide for permeable interlocking concrete pavement (PICP). Typically, state governments rely on their stormwater departments to develop such information. Stormwater departments reside within agencies that have “environment,” “water” or “conservation” in their titles. Examples include permeable pavement guidelines from the Virginia Department of Conservation and Recreation, North Carolina Department of

Environment and Natural Resources, and the Rhode Island Department of Environmental Management, to name a few.

plainly speaking

Caltrans has developed a draft specification for PICP and pervious concrete that will be released in the coming months. This was done with support by the Concrete Masonry Association of California and Nevada (CMACN), the California Nevada Cement Association (CNCA) and the Interlocking Concrete Pavement Institute. All permeable pavement specifications are written in the Caltrans “plain language” style and initially will be “non-standard special provision specs” used for non-highway facilities. This specification status allows for greater flexibility in modifying specs during construction. In addition, this status enables Caltrans to initiate permeable pavement projects and then return to the specifications a year or two later with revisions drawn from construction experience. Based on successful experience and further

technical review within Caltrans, the specifications eventually should be a permanent entry in the Caltrans book, Standard Specifications, periodically updated by the agency.

DRAFT CHANGES

The draft PICP specification uses the existing structure of Standard Specifications, placing PICP in Division V Surfacing and Pavements, Section 40 Concrete Pavements. PICP is situated in a subsection labeled 40-9 Permeable Interlocking Concrete Pavement. This section covers the concrete pavers, which must conform to ASTM C936, Standard Specification for Solid Concrete Interlocking Paving Units, as well as the permeable jointing and bedding stone. Jointing stone sizes conform to ASTM No. 8, 89 or 9 stone, and selection is based on the maximum joint width between pavers. Bedding stone is consistently No. 8 stone. Other changes to Caltrans specs include Section 26 Aggregate Bases, which introduces a new Class 4 base with gradation, cleanness and durability requirements per Caltrans California Test methods, as well as a minimum 30 percent void space. Changes were also made to Section 19 Earthwork to allow for lower compacted soil densities than that required for conventional pavement.

One requirement of the Caltrans PICP specification is that the job foreman holds a certificate of completion in the Interlocking Concrete Pavement Institute PICP Technician Course. This requirement includes qualified construction personnel on job sites. Also, Caltrans acceptance of the completed PICP includes surface infiltration testing using ASTM C1701, Standard Test Method for Infiltration Rate of In Place Pervious Concrete. The minimum construction acceptance infiltration rate is 100 in./hr (250 cm/hr). This infiltration rate can be consistently attained regardless of the percentage of paver open surface area or the jointing materials.

REDUCTION TREATMENT

All permeable pavement projects are subject to review and approval by the Caltrans Office of Stormwater Management-Design, and structural designs are reviewed and approved by Caltrans Pavements Program. The hydrologic design criteria require capturing 85 percent of all storms, also known as the water quality volume (WQV) capture depth. The emphasis is on treatment in managing stormwater across most of California rather than on volume reduction due to low rainfall. This WQV calculation method is well established within Caltrans and by the California Stormwater Quality Association. The most effective means of treatment—by reducing volumes—is accomplished with permeable pavement.

WIDER IMPLICATIONS

Storms with higher depths can be managed by the permeable pavement if required. The maximum infiltration time is 48 hours and the minimum acceptable soil infiltration rate is 0.01 in./hr (0.25 mm/hr). This minimum rate enables permeable pavements to be used in compacted soils, including some clay soils, resulting in about ½ in. (13 mm) of infiltrated water over 48 hours.

Caltrans structural design is essentially for cars and limited truck use on low-speed areas such as parking lots. The design approach is conservative and does not account for experience in other states with heavier loads/repetitions. The CMACN, CNCA and the ICPI Foundation for Education and Research are preparing to conduct PICP structural testing at the University of California Pavement Research Center in Davis, which will provide design charts to Caltrans for PICP base thicknesses. This study is slated to start before the end of 2012 and has wider implications on structural design for state and local agencies, as well as designers and industry outside California.

As with many states, numerous California city and county agencies reference state highway specifications for pavement materials and construction practices in their development standards. The inclusion of permeable pavements in Caltrans’ provisional specification sends a credible message to city and county engineering departments and further supports permeable pavement application beyond limited use expected by Caltrans.