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Superb Stewardship

Burbank, California, may be the famous studio location for The Tonight Show with Johnny Carson, but the EcoCampus at Burbank Water and Power (BWP) broadcasts its own show worthy of a different fame. The project debuted as the only industrial category selectee among 150 national and international projects for the Sustainable Sites pilot program in 2012. BWP and its design partner, AHBE Landscape Architects in Los Angeles transformed an aging power plant site into a regenerative green campus with aspirations toward net-zero water use.

“Being good stewards, doing the work of service, our landscape is reflective of those values we have here,” said BWP Conservation Manager Joe Flores. BWP offers regular tours of its EcoCampus to educate visitors about several stormwater management technologies there which include permeable pavers and concrete planks. At the heart of the campus, Centennial Courtyard features 4 x 16 x 3 1/8 in. thick planks in a multi-colored array of pewter, amber, caramel, mocha and charcoal. While larger and longer paving units continue growing in popularity, this three-year-old project represents early pioneering with planks.

Contemporary Cool

Two distinct trends have emerged over the past few years including a shift from warm earth-tone colors to cooler shades of gray, and growing use of larger paver units, slabs and planks. AHBE designers wanted a modern, linear appearance for the courtyard, and once BWP saw samples of the planks from an ICPI member manufacturer, BWP fell in love with them. The decision was also influenced by the salvaged and repurposed structures BWP chose to retain from the original site. Though initially the plan was to remove everything, BWP envisioned a transformation rather than a complete demolition. Old generator pads became seating areas; utility tunnels became infiltration chambers; equipment plinths became garden sculptures; and a two-story steel skeleton substation became a trellis for a shade canopy. Multicolored planks provided the desired complement. “If we just poured concrete [for the courtyard], it wouldn’t be very visually interesting,” said Mr. Flores. “The pavers add a material richness you want in that kind of environment,” he added.

As Above, So Below

From the outset, BWP wanted to develop a green campus with sustainable stormwater detention and filtration technologies. The Centennial Courtyard planks sloped to drain stormwater into a phytoextraction canal. Formerly a tunnel that carried power cables from the power plant to the electrical substation, the six-foot deep tunnel floor was perforated and then backfilled with select soils and plants that filter stormwater runoff as it permeates down into aquifers. At each side of the canal, fountains of recycled water are circulated by solar-powered pumps.

A green street development spanning three city blocks along Lake Street includes an 8 ft wide permeable paver sidewalk and filtration planter bump-outs collecting and infiltrating water into concrete bioretention cells with trees. “With permeable pavers, you’re able to do stormwater capture and then direct the water to encourage trees and plants to grow roots downward, which is healthy for the landscape, and also alleviates problems of roots uplifting sidewalks,” Mr. Flores explained.

The visual qualities of the landscape are noteworthy, but what lies beneath—a campus-wide water filtration system—is truly remarkable. Five water filtration technologies were used: infiltration, flow-through, detention, tree root cells, and stormwater capture. According to BWP, this was the first time this number of sustainable landscape technologies were integrated into a single industrial site.

Watch a video about sustainable green infrastructure projects at Burbank Water and Power.

Pixilation and Progeny

Three types of pavers were used for the courtyard and green street, according to AHBE Landscape Architects Principal Evan Mather, ASLA, RLA. “We used plank pavers for the courtyard, rectangular pavers where we didn’t want to infiltrate, for example, next to buildings, and permeable pavers where we wanted to infiltrate,” said Mr. Mather. “The overall look of the campus doesn’t present scored concrete; it’s more about the individual pixilation of the paver materials.”

Regarding maintenance, Mr. Flores said, “It’s not as much as you might think. We don’t have to do much other than blowing [leaves and debris] and cleaning up the occasional spill.” Because the pavers are multicolored, a few spots here and there aren’t nearly as noticeable as they would be on a continuous white concrete surface, Mr. Flores said.

Congruent Values

The close collaboration among the project owners, landscape designers and the paver manufacturer resulted in a creative synergy where each drove the others toward greater excellence. “They were a fantastic partner,” Mr. Mather said of BWP. AHBE has been a leader in sustainable design for 30 years, Mr. Mather said, but an industrial power plant might be the last place one would think of when it comes to sustainability. With all its green merits, the BWP EcoCampus really is for the people. Human utilization of the campus and courtyard space drove the design from the outset according to Mr. Flores. “Using the space in this way creates a healthy work environment…because it’s congruent with the values of people who want to work here.”

To anyone mulling over a similar redevelopment project, Mr. Flores offers this advice: “Consider not just the physical elements but the human and cultural aspects that define the values of your organization. How can you express that through the use of your physical space?” Addressing these human aspects resurrected this site with support from carefully selected and placed concrete paving units.

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Cyclone Sighting

Since the 1990s, municipalities and private property owners constructed millions of square feet of pervious concrete (PC), porous asphalt (PA) and permeable interlocking concrete pavements (PICP) in parking lots, alleys and streets. The number one question is about maintenance. The next questions typically are how often should the surface be cleaned and with what equipment?

All permeable pavements require regular surface cleaning to remove embedded sediment and to maintain surface infiltration. Regenerative air machines used for routine cleaning are effective in removing loose sediment and debris. Low surface infiltration into highly clogged pavements with tracked-in or settled sediments can be raised with a true vacuum machine. Equipment availability, costs, personnel time or outsourcing costs for surface cleaning suggests a need for a single machine that provides routine maintenance cleaning, as well as restoration of clogged surfaces when maintenance is neglected.

The diesel-powered Cyclone CY5500 carries approximately 1,200 liters (300 gal) of water.

The diesel-powered Cyclone CY5500 carries approximately 1,200 liters (300 gal) of water.

A machine that might qualify for this role is the Cyclone CY5500. Originally developed to clean tire rubber from runways, this machine was tried in June 2015 on porous asphalt (PA), pervious concrete (PC), and permeable interlocking concrete pavement (PICP) in a residential neighborhood in Northwest Washington, DC. All of the permeable pavements were installed by the District of Columbia Department of Transportation (DDOT) as part of a combined sewer overflow mitigation program.

The sites included PC in two nearby on-street parking lanes. One was cast-in-place PC and the other was a precast PC panel, among several. These two areas received contributing run-on from the impervious center lane of the street. The PA and PICP were situated in alleys, with some or little run-on from impervious surfaces and instead received sediment from adjacent vegetated areas. All of the permeable pavements were subject to leaves and debris from a mature urban forest canopy. None of the pavements were older than a year in service.

 

The diesel-powered Cyclone CY5500 is an off-road vehicle smaller than the truck-size equipment. This machine carries approximately 1,200 liters (300 gal) of water, much of which is drawn back into the machine, filtered and re-used.

The Cyclone machine relies on water applied under pressure in a circular motion within a surrounding chamber in close contact with the permeable pavement surface. The water pressure can be varied by the operator from 1,200 psi (8 MPa) to 4,350 psi (30 MPa). Water is blasted against the pavement surface and the speed of the rotating head applying the water provides some suction (hence the cyclone name) to pull most of the water back into the machine for reuse. The machine manufacturer claims cleaning rates as high as approximately 10,000 sf (935 m²) per hour on most permeable pavements.

Prior to conducting cleaning, ASTM C1701 Standard Test Method for Infiltration Rate of In Place Pervious Concrete and C1781 Standard Test Method for Surface Infiltration Rate of Permeable Unit Pavement Systems was applied to each surface. The former test method is applicable to PC (and PA). Both test methods produce comparable results. This is illustrated in Figures 2 through 5.

The pre-wetting initial infiltration test measurement was conducted to determine the extent of clogging. All of the pavements were clogged with little or no infiltration within the ring. Then, the four areas were cleaned in the following order: cast-in-place PC, PICP, PA, then the precast PC panel. The Cyclone machine passed twice over the same area of permeable pavement almost immediately after the initial infiltration testing (called pre-wetting). Figure 6 shows the Cyclone machine making a typical pass of about 30 ft (10 m) in length on an alley.

Figure 6

Figure 6: The Cyclone machine cleans a PICP alley.

After the second pass, the ASTM test ring was applied to the pavement surface and an additional (approximate) 8 lbs (5 kg) of water was applied (the surface infiltration rate was calculated per the ASTM standards). Both ASTM standards use the same surface infiltration calculation. If the surface infiltration rate was under 250 mm/hr (100 in./hour) the Cyclone machine made an additional two passes, the ring reapplied in the same location and an additional approximate 8 lbs (5 kg) of water applied into the ring. The table provides a summary of the surface infiltration test results.

The table indicates increased infiltration rates after the first two passes on the PC, PICP and PA. Infiltration rates doubled for the PC and PA but could be considered low. There was little if any change in the infiltration rate of the precast PC panel after the first two passes. The second two passes yielded better results with PC infiltration rate doubling again and the PA almost reaching the same level. The precast panel saw a substantial increase as well, from <20 in./hr (<508 mm/hr) to 130 in./hr (3,302 mm/hr) after the second round of two passes.

Figure 7

Figure 7: PICP after two passes of the Cyclone machine. Note aggregate and sediment removed resulting in open joints and a permeable surface.

The most notable observation is that the PICP only required two passes of the Cyclone machine rather than four to increase the infiltration rate from 20 in./hr (<508 mm/hr) to 327 in./hr (8,306 mm/hr). The joint widths in the PICP were narrow, approximately ¼ in. (6 mm) wide and many of the small aggregates were pulled out with the sediment after the first two passes. Some of the stones were left on the surface of the pavers after the second pass and these could be swept back into the joints. See Figure 7. Additional aggregate should be supplied given these results.

In this experiment, the Cyclone machine was assigned to clean highly clogged pavements. It can be set on a lower pressure setting to clean a less clogged condition, i.e., remove loose material from the pavement surface. In the case of this brief demonstration however, the PICP surrendering sediment with the jointing aggregate to the Cyclone machine explains the resulting high infiltration rate after two passes rather than four passes, as conducted on the other surfaces. This demonstrates the ability of clogged PICP to experience restored infiltration rates as compared to monolithic surfaces, even when heavily clogged.

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Why Aren’t All Streets like This?

The morning after an overnight rainstorm, Tom Sweet, AECOM senior engineer, walks two blocks from the Downtown Berkeley BART station and puts on his yellow safety vest to inspect the Allston Way permeable paver street he helped design. “How’s the ride?” he asks a passing skateboarder, who gives a thumb’s up in response. Local residents approach from the adjacent park, ask if he’s involved with the new street and tell him how beautiful it is. When he explains the street can also infiltrate stormwater, filter pollutants, reduce runoff to San Francisco Bay and improve the health of the park’s trees, they ask, “Why aren’t all streets like this?”

Facing an aging infrastructure as are many cities today, the City of Berkeley sought a durable alternative to its existing asphalt road surfaces in need of replacement. Situated on a hill that slopes down to San Francisco Bay, mitigating stormwater runoff also ranked highly among its priorities. A public works commission began extensive research into green infrastructure redevelopment options and called in David Hein, P. Eng., Vice President of Transportation with Applied Research Associates, Inc. (ARA).

“The City had wanted to do this for a long time,” said Mr. Hein, referring to the City Council’s desire to construct a green roadway using a permeable paver system as a demonstration project. A 40-year life-cycle cost analysis showed permeable interlocking concrete pavement to be almost the same cost (less than 2% difference) as an impermeable flexible pavement. However, the analysis did not take into account the benefits from permeable pavements such as reducing stormwater runoff volume, peak flows and pollutant loads. If these cost factors were taken into account in the LCCA, the permeable pavement would have the lowest total present worth cost, according to Mr. Hein.

Suitability Evaluation

With numerous sites proposed by the City for the PICP demonstration street, an evaluation matrix created by ARA for this project determined the best choice. The suitability design matrix identifies key factors that may influence design and effectiveness for a specific project, categorizes those factors as primary or secondary considerations and assigns weighted values on a scale of 0-100. If the score totals less than 65, the project is not considered a good candidate for permeable pavement. Scores between 65 and 75 are worthy of consideration, but scores over 75 indicate a well-suited site. A section of Allston Way received a high evaluation with a score of 81.

However, there were a number of initial concerns expressed about the project. The cycling and skateboarding communities weren’t sold on a segmental road surface for the heavily trafficked bike route of Allston Way. City engineers had concerns about the utilities below the street and the depth of excavation required for a properly installed PICP system as well as the suitability of Berkeley’s clay soil for infiltration. City arborists made specific requests for care and caution in excavation around tree roots. And a small time window for construction to coincide with the adjacent high school’s summer break added another challenge. To address these concerns and requirements, the initial design underwent some innovative refinement.

Refined Design

“We had a fairly deep section proposed,” explained Mr. Sweet. “Over the course of the design, as a cost-benefit, we looked into making the section thinner from a pragmatic approach.” And that’s when flexible HDPE cellular confinement for the aggregate base entered the picture. From an initially proposed depth of 41 in., the addition of an 8 in. cellular confinement layer provided enough structural stability and strength to reduce excavation to 29 in. It shaved a full foot off the excavation depth requirement, thus saving time, reducing the cost of off-haul as well as emissions and minimizing risk to the underlying utilities.

A few more innovations addressed concerns about clay soil infiltration and the street’s nearly 3% longitudinal slope. Eleven check dams were specified, but the flexible design permitted non-uniform placement at the most logical locations, i.e., where the sections had been excavated to full depth and around the existing utilities. “We didn’t want all the water to go to one end and oversaturate the subsoils, so we were very careful in the detailing to segregate the water,” Mr. Sweet said.

Additionally, the underdrain was raised up 6 in. from the subbase to take advantage of some detention and infiltration over clay soil. “It’s an opportunity that most projects miss,” explained Mr. Sweet. “A lot of folks in the profession say, ‘It’s clay soil, we can’t infiltrate.’ In fact, you can infiltrate, you just need to be more careful with how you do it and where you do it.” The sizes of the openings in the underdrain were carefully considered. “We wanted to recover but we didn’t want it to act as a conveyance,” said Mr. Sweet. The underdrains buffer the rate of flow leaving each check dam. Though the water level might reach the holes in the perforated pipe, limiting the number and the opening size allows water to go higher. Designed for a 48-hour drawdown, the underdrain system is a water recovery mechanism, not an instantaneous outflow. “Personally, I am very excited about this system. I think it’s almost the highlight of the project,” said Mr. Sweet.

Breaking New Ground

Construction of the project took place during the summer of 2014. The curb-to-curb pavement surface area totaled 29,145 sf (2,700 m²). Don Irby, P.E., Associate Civil Engineer with the City of Berkeley Public Works Department, managed the construction from beginning to end. This was Mr. Irby’s first permeable paver project. “We had to close the road for almost three months because it’s just not really economical to do this type of installation in sections,” Mr. Irby said. “That played into our location selection because we had to look at driveway access. There are a lot of things you need to take into account when you site one of these projects.”

Ghilotti Construction Co. managed the road closure as the general contractor for the project and handled the careful excavation around utilities and tree roots.

European Paving Designs Inc. (EPD), an ICPI-certified installer, installed the pavers. “As soon as we saw the tight spec for this project, we were really motivated to get the job,” said EPD CEO Randy Hays. “[The specification] referenced ICPI’s PICP manual. We knew we had the expertise and experience to make it successful.”

With a seven-man crew working in two phases, the blend of reddish orange-and-charcoal pavers was installed in a herringbone pattern before installing pavers for striping. “That seems to work the best,” Mr. Hays said. “It allows for some give and take with the location of the stripes, so if we have to shift it an inch for alignment, as long as there are no small pieces, that’s the right way to do it.” Yellow-pigmented pavers provided contrast with the darker pavers, all supplied by Pavestone Company. The EPD crew laid out the pavers for the stripes, cut the sections out from the installed field and then inserted the yellow pavers. Mr. Hays said his foremen recall people first seeing the completed installation while they were doing cleanup work. “They were looking down as they crossed the street and said, ‘Wow, that’s unique.’”

Manuals for Labor

As part of their involvement on the project, ARA created two manuals for use by the City of Berkeley. One established a maintenance plan and the other specific maintenance procedures. Mr. Hein explained, “Ultimately, the purpose of ICPI is to provide guidance to people on the use of paver products. If you handle them, here’s how you do it right. I think the Utility Cut Manual and the Maintenance Guidelines are very important.” Each manual’s appendix includes ICPI Tech Spec 6 — Reinstatement of Interlocking Concrete Pavements.

Results Exceed Expectations

In the year and a half since the Allston Way project’s completion, it has been routinely and closely monitored. “The system has exceeded expectations with regard to stormwater management,” said Mr. Irby. “The infiltration rate that we’re seeing is better than we had estimated.” He added, “We haven’t published the data yet, but what we’ve gathered to date does show that the pollutant levels have been reduced.”

“The most recent storm we monitored was 1.75 in. over 19 hours, a fairly large storm for California,” said Mr. Sweet. “And we attenuated 94% of the runoff. We did readings off the discharge pipe and it really shows the benefit of spreading the water out and letting it infiltrate at a comfortable rate, to the extent that it can.”

Additionally, the City Forestry Department is monitoring the health of trees in the adjacent park to see if there is noticeable improvement. The trees are photographed on a regular basis for analysis, but this study will require a good deal of time before results become apparent.

“There was a lot of concern about the roughness of the surface from the cycling community, but I haven’t heard a word from them since it was installed,” said Mr. Irby. “And we see hundreds of bikes on the street every day, and skateboarders too. It’s an incredibly smooth surface.” That smooth surface is due to EPD’s expert installation of the ADA-compliant pavers specified, which feature a quarter-inch joint and interlocking spacer bars. In fact, the permeable paver surface is likely safer for cyclists to traverse in wet conditions because it prevents standing water from collecting of the pavement surface. “The coefficient of friction for a permeable paver surface is better than most asphalt roads,” Mr. Irby explained. “There are lots of benefits that people aren’t really aware of.”

The Intangibles

“The arc of this project was very gratifying,” Mr. Sweet said. Given the initial concerns expressed by the City and the community, “Everyone landed in the same place saying, ‘Wow, this project is worthwhile, it’s interesting, it’s the right thing, and it turned out great.’”

“I’m happy I got to be a part of this project,” Mr. Irby said. “I have coworkers who go out of their way just to walk by that street because it’s really nice to look at.”

“The City of Berkeley is really committed to the environmental aspects of construction,” Mr. Hays said. “Sustainability in the construction industry, especially with regard to water conservation, is very important. Building streets that actually return water to an underground system is a pretty cool thing.”

As for the question “Why aren’t all streets like this?” That answer may just be a matter of time.

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Cool by the Poolside

A Familiar Start: Compaction

Pools made with a flexible liner or fiberglass require much excavation and soil backfill against them. This soil is almost impossible to compact adequately because there is a high risk of compaction equipment damaging the pool wall, the metal “knee” wall/wing wall supports, and/or pipes. Pools made with gunite concrete or poured concrete can have walls of sufficient thickness and support where backfill soil against them can be compacted. However, the soil directly against the wall will be difficult to compact, again because of the risk of damage to a plate compactor or to the pool wall. Therefore, settlement can occur here as well.

Some paver installation contractors claim that installing and compacting the soil backfill and aggregate base can reduce the risk of settlement. That may be true assuming that maximum density is achieved for both materials during compaction. However, the places compaction equipment cannot reach will be at risk of settlement. If a contractor uses a compacted aggregate base, then a warranty should be included in the price to cover the cost of returning to the site a few years later to inspect and lift settled paver areas. Given unpredictable future costs and hassles for the contractor (not to mention the owner), it’s better to complete a job that doesn’t include a return visit.

To avoid returning for paid (or worse still, unpaid) callbacks due to settlement issues, use a 4 in. (100 mm) thick concrete pad as a base. Placing a 2 in. (50 mm) thick layer of free-draining compacted aggregate such as ASTM No. 57 stone under the base enables water to drain from below. Figure 2 illustrates this material placed over a compacted, crushed stone base. The concrete base surface should slope at least 1.5% to allow water to drain.

A key aspect of all pool surfaces is no settlement or undulations that present walking or tripping hazards, or slipping hazards from birdbaths. By providing a rigid, sloped foundation, a concrete deck under the concrete pavers helps maintain safety. This should be the first priority and result of all pool projects.

Wear an Apron or the Full Dress?

When a concrete base is used, should it be built as an apron covering only areas of settlement-prone compacted soil and aggregate base around the pool perimeter? Or should it extend as a full dress under the entire area of the concrete pavers? A dress is preferred. The problem with apron construction is differential settlement of the soil and base next to the concrete base under the concrete pavers will almost always occur regardless of diligent soil and base compaction. Slideshow images show installation and a completed concrete full dress surrounding the entire pool area, as well as installed coping attached to the concrete base structure. In this case, the coping is not resting on the pool wall.

Overlays on Existing Concrete Decks

Installing concrete pool decks with an overlay of concrete pavers is less expensive than removing and replacing the entire concrete deck. To qualify for an overlay on an existing concrete deck, the concrete should not be heaving or faulted, as this often indicates severe settlement of the soil beneath or expansive clay soils. In these cases, subsurface drains can remove excess water from the soil. Expansive soils can be stabilized with lime. Both should be done after demolishing the concrete deck and before pouring a new one. The advice of a professional civil engineer familiar with the local soils should be obtained in such situations.

Cracks in the existing concrete base can be filled with a cement-based patch to prevent migration of bedding sand into them. The junction of the concrete slab with the pool wall should be sealed with a neoprene or urethane sealant (often applied with a caulking gun). This keeps water from getting behind the pool wall and saturating the base and soil.

There is a growing trend toward using paving slabs, generally 12 x 12 in. (300 x 300 mm) or larger. Sometimes these are mixed with smaller units. All units should be at least 2 inches thick. They require a thin, coarse (drainable) bedding sand layer, typically no thicker than ¾ in. (20 mm), screeded smooth, ready to receive the paving slabs (or pavers).

Slabs and pavers should be compacted with a plate compactor with rollers on the bottom to reduce the risk of cracking slabs. Joints are then filled with sand, and sealer is applied. Prior to placing and screeding the bedding sand, 12 in. (300 mm) wide geotextile strips should be applied over concrete deck joints, placed and turned up at joints against structures, and placed along coping to prevent bedding sand loss.

Prior to applying the pavers, all area drains must be raised to the new finished elevation of the installed pavers. Holes must be drilled into the vertical drain pipe directly above the concrete deck. This drains excess water from under the pavers. The holes should be covered with geotextile to prevent ingress of sand.

Many overlays use thin, tile-like concrete pavers placed directly over a concrete deck. Thin pavers typically range between 1 to 1½ in. (25 and 40 mm) thick and are generally about 4 in. (100 mm) wide by 8 in. (200 mm) long. Unlike sand-set slabs or pavers, concrete pavers are directly applied to the existing concrete deck without bedding sand after cracks are patched. Edge pavers are secured with a polymer adhesive or mortar (in non-freezing areas).

Fine sand is swept and washed into the joints until they are full. Using thin pavers as new construction of course avoids bedding sand as well. In new or rehabilitative projects, washing sand in the joints enables it to flow under the pavers so no rocking or clicking of pavers occurs when walked upon.

After the surface is completely dry (usually in 24 hours), it receives sealer to hold the sand in the joints and reduce water ingress. The sealer is typically reapplied every three to five years to maintain the sand in the joints and protect the surface. Even with this maintenance cycle, overall costs are well lower than replacing the entire concrete deck. Sealers also greatly reduce the risk of mold and bacteria, thereby addressing concerns of health officials regarding public pools.

Advantages of Pavers

Tie-downs for pool covers can be installed below the pavers with high-strength grout-filled sleeves. Tie-down caps should be even with the paver surface. Should pipe or wiring repairs be needed, concrete pavers can be removed and reinstated with no ugly patches. The units resist chlorine and bromine, as well as freeze and thaw cycles. Concrete pavers offer a slip-resistant surface even when sealed. Salt-water pools can attack concrete surfaces, so be sure they are thoroughly sealed.

Besides their unmatched beauty compared to other deck surfaces, colored concrete pavers reduce the glare often associated with cast-in-place concrete pool decks. Almost every paver pool deck in warm climates consist of beige, coral, or buff colors that reduce glare from the sun. Because the units have joints, each unit has some opportunity to release heat faster than a cast-in-place concrete deck. Therefore, the units can be cooler underfoot than other surfaces. So a paver surface feels as well as looks cool.

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Research Raises the Barrier

A common barrier to using permeable pavements over clay soils is their lack of infiltration. A recent study released by North Carolina State University demonstrated that permeable interlocking concrete pavement (PICP) is an effective tool to improve stormwater runoff hydrology and water quality, even when sited over very low infiltration soils. Located at a city park in Durham, NC, this project researched PICP efficacy over nearly impermeable soils (approximately 0.01 in./hr or 0.254 mm/hr) from March 2014 through April 2015. Four parking stalls (540 ft² or 50 m²) were retrofitted with PICP with a very small contributing impervious area. PICP design followed design guidelines outlined in Chapter 18 of the North Carolina Department of Environment and Natural Resources (NCDENR) BMP manual.

Results through 13 months of monitoring indicated 22% volume reduction via subgrade infiltration and evaporation. Inter-event infiltration of water within the 6 in. (150 mm) thick subbase created storage to capture over 70% of the runoff volume from storm events less than 0.30 inches, and peak flows were significantly reduced by a median of 84%. The site exhibited exceptional pollutant removal efficiency with influent and effluent pollutant concentrations significantly reduced for total suspended solids (99%), total nitrogen (68%), and total phosphorous (96%). The median effluent concentrations of total nitrogen (0.52 mg/L) and total phosphorous (0.02 mg/L) were below “excellent” ambient water quality thresholds for the North Carolina Piedmont Region. The median total suspended solids effluent concentration was also very low (6.99 mg/L). Nitrogen and phosphorous are nutrients that can accelerate algae growth and damage to waterways. Many pollutants are carried with suspended solids, so their concentrations are an indirect indicator of water quality. Obviously, any reduction in runoff volumes translates to reduced pollutant loads into waterways.

Additional sampling of the various nitrogen forms at 12, 36, 60, and 84 hours post-rainfall was conducted to better understand mechanisms of nitrogen removal in permeable pavement. Results from one storm event indicated denitrification is likely occurring in the open-graded aggregate reservoir within the pavement. For the events monitored, significant reductions in average concentrations for copper (79%), lead (92%) and zinc (88%) were also observed. Typically shed by vehicles, metals in high concentrations can severely damage aquatic ecosystems.

Cumulative loading reduction for the catchment was excellent with loading removal efficiencies of 98%, 73% and 95% for total suspended solids, total nitrogen, and total phosphorous respectively. These results show permeable pavements built over low-infiltration clay soils provide considerable improvement of water quality and moderate hydrologic volume reduction benefits.

Monitored data was also used to calibrate DRAINMOD, a widely-accepted agricultural drainage model, to predict the cumulative and event-by-event hydrologic performance of the study site. DRAINMOD accurately predicted runoff volumes from the impervious drainage area with very high correlations between modeled and actual inflows to the site. Good agreement between predicted and measured drainage was also observed. Cumulative predicted drainage volume was within 6% of what was measured during the monitoring period. These results indicate DRAINMOD can be applied to predict the water balance of permeable pavements built over low-infiltration clay soils on a long-term, continuous basis. To receive a copy of the 46-page report written by Alessandra Smolek, Ph.D. student and Professor Bill Hunt, email requests to the editor at dsmith@icpi.org.

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Form Follows Function

Returning and new site visitors alike will find a refined and inviting homepage at ICPI.org. Contractors, designers, and homeowners are now able to access the specific information they need simply by clicking on the corresponding portal. A “Members Only” portal rounds out the quartet of initial entry points for exploration. More importantly, the new ICPI.org website also features a new search-by-proximity function for users to quickly find the resources and service providers closest to their location.

Ultimately, the new website design resulted from understanding the need to get ICPI members and the general public access to ICPI’s technical resources in an easier and more visually appealing manner. In such a visual industry, ICPI drew upon the stellar work of its members to showcase a range of design possibilities—new and sustainable—with easier access. Given the depth and breadth of information ICPI provides, the Institute structured the site by curating information specific to the needs of a particular site visitor— contractor, designer, or homeowner— rather than require the visitor to search through much of the available information as the old site required.

Another noteworthy change is the Paving Systems link in the green home-page navigation bar. Here, visitors can learn about the benefits, installation and maintenance requirements of concrete pavers, permeable pavers, paving slabs and grids. The Idea Gallery of old has been reimagined and renamed Project Profiles and provides more imagery and more information about each project. The familiar Resource Library tab is retained from the old site due to its usefulness for quick searches. Education & Certification remains a top-level category for visitors to access this important information. Events and Newsroom complete the offerings of the homepage navigation bar.

Not only does the new site include more photos, they are given more prominence to bring projects to life on screen. Also featured are designs for do-it-yourself ideas. Information on best practices gives guidance on homeowner topics such as how to choose the right contractor. For design professionals and contractors, Tech Specs provide a wealth of information to help design, specify, construct and maintain a project.

For Contractors

The contractor portal explains the benefits of being an ICPI contractor member. Contractors can enter and view featured projects, easily access info on how to become certified, learn how to sign up for courses, access archived webinars for self-guided education, and read tips on installation and maintenance. The contractor portal features:

  • Awards
  • Benefits
  • Certification
  • Education
  • FAQ
  • Installation
  • Maintenance
  • Resources

For Designers

The designer portal features guide specs, detail drawings, design manuals, technical papers, and more for those experienced with segmental pavement design as well as for those new to it. The designer portal features:

  • Guide Specifications
  • Detail Drawings
  • Design Manuals and Software
  • Project Profiles
  • FAQ
  • Technical Papers

For Homeowners

The homeowner portal provides information on different pavement types, design ideas, an overview of the basic considerations when selecting a contractor, and also DIY information and guidance. The homeowner portal features:

  • Pavement Types
  • Design Ideas
  • Installation Basics
  • DIY
  • Selecting a Contractor
  • Maintenance
  • Resources
  • FAQ

For Members Only

A broad and robust suite of opportunities await ICPI members through this portal. Tools to manage one’s profile and preferences, view upcoming events, a bookmark feature to collect articles, and access to the Member Directory are but a sample of the many benefits the new website offers. Additional resources include: minutes from past meetings and agendas for those upcoming; guidance for marketing one’s business; information on government relations; chapter resources; and information on promotions, incentive programs, how to sponsor an ICPI course for contractors, or become an instructor.

Better Experience, Faster Access

The redesigned ICPI.org website offers a better user experience and faster access to the infor-mation visitors are seeking while simultaneously presenting imagery in its proper prominence, front and center. The homeowner portal in par-ticular broadens the appeal and value of ICPI to the general public with the goal of heightening brand awareness. And the Member’s Only portal increases accessibility and usefulness for those who support the continued work of the Institute.

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A Magnificent Mile

Located in between mountains and Roadside America off Exit 441 of Interstate 5 at Westley, California, Howard Road handles much heavy truck traffic to and from “The 5.” Faced with worn asphalt pavement in need of replacement, the Stanislaus Public Works Director, Matt Machado, PE, LS, accepted the challenge of designing a long-term, economical pavement solution for the road using interlocking concrete pavement. This resulted in the largest publicly owned stretch of concrete pavers in California, about one mile (1.6 km) long.

Built over a weak soil subgrade (R-value < 5 or California Bearing Ratio < 2%) and to a Caltrans Traffic Index of 11, or just over 5 million 18,000 lb. (80 kN) lifetime equivalent single axle loads (ESALs), the design required 14 in. (350 mm) thick Caltrans Class 2 road base over a biaxial geogrid. The Class 2 base supports one inch (25 mm) of coarse bedding sand and 170,000 sf (15,794 m²) of 3 1/8 inch (80 mm) thick, machine-installed concrete pavers placed in a herringbone pattern.

Example of worn asphalt ready for replacement along Howard Road in Westley, CA.

Example of worn asphalt ready for replacement along Howard Road in Westley, CA.

Stanislaus County received six bids from $4.50 to $6.00/sf ($48 to $64/m²) to install the concrete pavers and bedding sand. Completed in fall 2014, the pavers were manufactured by Basalite Concrete Products in Dixon, CA, and machine installed by Earth Shelter Developers from Lodi, CA. Both are Interlocking Concrete Pavement Institute (ICPI) members. With Roadside America businesses like Denny’s, Chevron, McDonald’s and Joe’s Travel Plaza open 24 hours along Howard Road (speed limit 35 mph), an extensive traffic control plan required the contractor to maintain drive lanes to accommodate truck traffic during construction.

Previous Paver Experience

Mr. Machado used interlocking concrete pavement while working in a previous position as city engineer for Ripon, CA (pop. ~15,000), a farm community in San Joaquin County. Mr. Machado developed interlocking concrete pavement as a roadway standard adopted by City Council for new roads and for some pavement rehabilitations. With the new design standard in place, developers and the City constructed more than 1.3 million sf (120,774 m²) of roads between 2005 and 2008.

Main Street in historic downtown Ripon features 50,000 sf (4,645 m2) of interlocking concrete pavement.

Main Street in historic downtown Ripon features 50,000 sf (4,645 m²) of interlocking concrete pavement.

The Ripon City Council approved interlocking concrete pavement when comparing the cost of expanding the city asphalt road network by developers and then forecasting insufficient future funds for periodic grinding and resurfacing. While the additional initial developer costs for concrete pavers were transferred to the homebuyers, the increase was marginal compared to the full price of single-family homes.

The Life-cycle Selling Point

After finding success in Ripon with lighter-load street applications (and conservative structural design assumptions), interlocking concrete pavement presented a durable pavement rehabilitation alternative for heavily trafficked Howard Road. A benefit of interlocking concrete pavements is not requiring periodic resurfacing. For Ripon’s residential streets, life-cycle costs were studied over a generous 100-year period resulting in concrete pavers having about 75% lower life-cycle costs than asphalt. Maintenance costs for concrete pavers for the same period were approximately 20% the cost of asphalt. Heavier trafficked streets such as Howard Road with interlocking concrete pavement often have even lower life-cycle costs because resurfacing costs for asphalt roads increase under such traffic.

Machine-assisted installation of interlocking concrete pavement in Westley, CA.

Machine-assisted installation of interlocking concrete pavement in Westley, CA.

According to Mr. Machado, “This (Howard Road) project was built to show the structural value of concrete pavers and their economic value for heavy truck traffic.”  Interlocking concrete pavements offer high compressive strength concrete with the flexibility of asphalt pavement. Research in the United States and overseas demonstrates that the pavers in a herringbone pattern progressively stiffen or interlock while receiving traffic loads. The resulting stiffness of the paver and bedding layers, or their resilient modulus, is equivalent to the same thickness of asphalt. In some cases, their stiffness well exceeds asphalt during hot summers as experienced in Westley, CA, where asphalt weakens under temperatures typically around 100 deg. F (38 deg. C).

In other words, the 3 1/8 in. (80 mm) thick pavers and 1 in. (25 mm) bedding sand have an AASHTO layer coefficient (an expression of stiffness) equivalent to the same thickness of asphalt. This is demonstrated in ASCE/ANSI 58-10: Structural Design of Interlocking Concrete Pavement for Municipal Streets and Roadways published by the American Society of Civil Engineers as well as in Tech Spec 4: Structural Design of Interlocking Concrete Pavements from ICPI. Pending successful performance with some years under its belt, Howard Road might mean a design standard for Stanislaus County in the future.

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HNA 2015 Project Awards

The HNA Hardscape Project Awards recognize outstanding hardscape projects by contractors building residential walkways, patios, driveways, commercial plazas, parking lots and streets.

In its eighth year, the awards program received 75 entries. Fourteen winners and seven honorable mentions received recognition at an awards ceremony on Oct. 22, 2015, at the Kentucky Exposition Center in Louisville, Kentucky. Entries were judged on project intent, design, quality of construction and craftsmanship, compatibility with related construction materials and systems, construction innovation, detailing and overall design excellence.

Combination – Commercial: Less than 20,000 SF

DeSoto AmphitheaterDeSoto Amphitheater

  • LOCATION: Millersburg, PA
  • INSTALLER: GoldGlo Landscapes LLC
  • SUPPLIER: E.P. Henry

This outdoor performing arts venue sits on a steep slope between Wiconisco Creek and the Ned Smith Center. The design needed to seat 250 guests, plus have room for tables and chairs on the paver dining terrace and deck. Existing soil under the walls, steps and patios was replaced with over 750 tons of gravel. The craftsmanship is visible in every detail, from the gentle curve of the seating to the installation of the engraved seat caps and pavers. The sod between the terraces serves as a permeable drainage system and helps cool the guests.

Combination – Commercial: More than 20,000 SF

Ithaca Commons Streetscape 2Ithaca Commons Streetscape

  • LOCATION: Ithaca, NY
  • INSTALLER: Syrstone, Inc.
  • SUPPLIER: Hanover Architectural Products

Ithaca Commons included over 67,000 sf of vehicular concrete pavers, with granite pavers and curbs. Hardscape challenges on this project included many grade changes leading to over 1,500 linear feet of drains while keeping the running pattern of the narrow plank-style paving visually true over two blocks. Another challenge was cutting thousands of linear feet of diagonal accent bands around manholes and other apprentices. Alternating color blends were used within each cell, framed with diagonal accent bands. Pavers were installed with polymeric jointing sand on an ASTM C33 sand bed over a reinforced concrete slab with weep holes.

Combination – Residential: Less than 4,000 SF

italian villa 4Italian Villa

  • LOCATION: Fort Collins, CO
  • INSTALLER: Lindgren Landscape
  • SUPPLIER: Belgard

The homeowners desired a warm, Italian-inspired outdoor living space. The existing landscape was an ocean of junipers and a concrete patio with little shade. The remodeling included shade structures, a kitchen, fireplace and bocce court. A 10-foot change in elevation presented a challenge in grading and safety, and is navigated by way of huge slab stairs meandering down the slope. A drainage system was designed to evacuate water from the sunken oyster shell-covered bocce court. Although plans and 3-D models were made to portray the project to the homeowners, on-site meetings and extensive communication were necessary throughout the project to explain the components and to make changes as desired.

Combination – Residential: More than 4,000 SF

Taunton Resort 5Taunton Resort

  • LOCATION: Minnetrista, MN
  • INSTALLER: Mom’s Landscaping & Design
  • SUPPLIER: Anchor Block Co.

The main focus of the design was the infinity pool, with the infinity edge facing the lake. A large lounging patio features light-colored travertine and a bluestone inlay. The bluestone was also carried into the overlook fire pit patio with 4-inch-wide planking. There is a water feature with plants to break up the hardscapes. A 6,000 sf driveway was installed in the front yard. One of the biggest challenges was the 23 feet of grade change from the walkout basement to the shoreline. Three curved ledgestone retaining walls were built to correct the grade. Bluestone steps with a charcoal paver walkway were installed down the hillside.

Concrete Paver – Commercial: Less than 15,000 SF

University of Nevada, Reno Wolfpack Logo Baseball ProjectUniversity of Nevada, Reno Wolfpack Logo Baseball Project

  • LOCATION: Reno, NV
  • INSTALLER: Hain Enterprises
  • SUPPLIER: Basalite Concrete Products

The material and labor for this UNR Wolfpack baseball stadium project were donated in appreciation of the university’s importance and contributions to the community. The intricate design contains some 2,400 sf of Basalite San Francisco Cobble in Positanocolor laid in an “I” pattern. The baseball was created with specially made white San Francisco Cobble rectangles. The wolf is done in the same paver, but in black. The teeth of the UNR mascot, Wolfie, were meticulously cut by hand and inset. The stitching of the baseball is in Chili Pepper Red Mission-style pavers, and arcs were cut into the pavement.

Concrete Paver – Commercial: More than 15,000 SF

MEGA Snake and Ladder Paver ProjectMEGA Snake and Ladder Paver Project

  • LOCATION: Abu Dhabi, U.A.E.
  • INSTALLER AND SUPPLIER: DUCON Industries FZCO

This project serves as the centerpiece of a play area for approximately 4,000 students at a primary school located in Abu Dhabi, U.A.E., and as the starting point to the possibilities of designing other enlarged board games carved in pavers. This project extends beyond the snake and ladder game to a general play area covered with stretched fabric that reflects the underlying theme of this paver installation. The boundaries of the paver design were pushed by the inclusion of numerous shapes and curves overlapping a cubical structure.

Concrete Paver – Permeable: Residential

r97VNJ83RCCTK7xSZW0P_firelane_3_res_02Firelane Road Residence

  • LOCATION: Menasha, WI
  • INSTALLER: Stumpf Creative Landscaping
  • SUPPLIER: County Materials Corp.

Only 90 feet from Lake Winnebago, this home had to comply with state regulations requiring permeable surfaces on paved areas of waterfront properties. Three sizes of permeable pavers were used in a 75/25 percent mix of a blended buff and solid cream color. The 4 in x 8 in size was used to create an eye-catching double border with dark brown sailor course on the inside, edged with a soldier course of the same cream color used in the drive. A matching walkway defines the entryway. Limestone boulders provide a decorative accent that helps transition the hardscape with the surrounding areas.

Concrete Paver – Residential: Less than 3,000 SF

The Hollywood DrivewayThe Hollywood Driveway

  • LOCATION: Los Angeles, CA
  • INSTALLER: Go Pavers
  • SUPPLIER: Olsen Pavingstones

The project involved installing a concrete paver driveway to a house located on a hillside. The delivery of materials to the project’s location at the top of the hill required the use of more manpower. A flat top textured paver design was installed in the driveway, giving the project a modern, contemporary look desired by the homeowners. The Timber Top design of the pavers used gave the appearance of wood flooring. Charcoal-colored pavers were chosen, best fitting the aesthetic of a driveway. The pattern used for the project was “Random Runner,” meaning the pavers are laid side-by-side in a linear pattern, which appears more than the actual total size of the installation at 2,450 sf.

Concrete Paver – Residential: More than 3,000 SF

Country Courtyard 3Country Courtyard

  • LOCATION: McCook, NE
  • INSTALLER: Grindstone Hardscapes
  • SUPPLIER: Belgard

The goal for this 4,560 sf patio, driveway and front entry was entertainment value with function for everyday life. The design was composed with three different pavers, using the same accent bands throughout. The front entry, driveway and fireplace all used a rustic Mega Arbel, while the sidewalks and main patio paved with the texture of Urbanas and Rustic Slabs. The 900 sf driveway leads past a small water feature and up to the front entry, or past a large waterfall to the backyard, which includes a fireplace, seating, outdoor kitchen, and lighting and heating features.

HONORABLE MENTIONS

 
Concrete Paver – Residential – Less than 3,000 sf

Spa Oasis 2

  • PROJECT: Spa Oasis
  • INSTALLER: GoldGlo Landscapes LLC

 

Concrete Paver – Commercial – Less than 15,000 sf

Lake Forest Country Club 3

  • PROJECT: Lake Forest Country Club
  • INSTALLER: Rock Bottom Lawn & Landscaping

 

Concrete Paver – Commercial – More than 15,000 sf

Westlake Shopping Center 5

  • PROJECT: Westlake Shopping Center
  • INSTALLER: Joos Lawnscapes Inc.

 

Combination – Residential – Less than 4,000 sf

Hassel Residence

  • PROJECT: Hassel Residence
  • INSTALLER: Paver Designs LLC

 

Combination – Residential – Less than 4,000 sf

Woodlands retreat 5

  • PROJECT: Woodland Retreat
  • INSTALLER: GoldGlo Landscapes LLC

 

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The Right Tool for the Job

One of the most important investments any contractor can make is in the right equipment. Efficient tools increase productivity, and this goes straight to the bottom line and to business success. The right tools with proper training help make crews safer by reducing injuries to backs, knees, fingers and elbows. Maintaining a healthy, efficient crew is essential to profitability.

“I have invested a lot of money and time into training my guys,” says Bill Gardocki, owner of Interstate Landscape Co. in New Hampshire. “I want them to be around on the crew for a long time.”

Mr. Gardocki, who has more than 40 years of experience in the hardscape industry, presented at Hardscape North America (HNA) in October with his son, Tom Gardocki, about the importance of investing in tools that promote health and maximize productivity. “The thing about tools is efficiency, speed and saving my guys’ backs, fingers and knees,” says Bill Gardocki.

During their HNA presentation, the Gardockis showcased and demoed some of the tools they have found to be the most beneficial for use on the job. They made a point to specifically not endorse any particular brand. The focus of their discussion informs the audience about the types of tools they rely upon as professionals.

PaverMARKERs

The Pave Edge paver marker lasts one month and doesn’t need sharpening.

Two new tools they’ve recently begun using are now among their favorites: One costs less than a dollar, the other around $12,000. The Paver Marker from Pave Tech saved their crews hours upon hours per week in labor, Bill Gardocki says, replacing the pencils, knives or whatever used previously to mark pavers for cutting. Just one marker will last a month and does not require sharpening.

The other new favorite tool of the Gardockis is called the Trimble System, an aftermarket package of sensors and a monitor that use GPS to provide precision accuracy for depth finding and can be installed on virtually any excavator. With a price around $12,000, this 2-D sensor system eliminates getting out of the cab of the excavator to measure while digging or grading, or having another crew member with a grade rod involved in these tasks.

The Trimble GCSFlex Grade Control System features body and boom sensors that can be retrofitted to most excavators. Using GPS, the system provides precise depth-finding information for the operator via an in-cab display monitor.

The Trimble GCSFlex Grade Control System features body and boom sensors that can be retrofitted to most excavators. Using GPS, the system provides precise depth-finding information for the operator via an in-cab display monitor.

Another key piece of equipment for safety and efficiency is the right-sized skid-steer loader. “I can’t tell you how many people buy undersized skid-steers because they say they can’t afford that extra $10,000 required to actually lift a full pallet of material,” says Tom Gardocki. “Instead, the crew has to unload three layers off of every pallet [before it can be moved]. You have to think about all the time it’s taking. You’re going to make up that $10,000 real quick.”

Many hardscape business owners initially opt for smaller pieces of equipment because they are lower in cost. However, this eventually costs more in the long run because of additional labor required. “You must have tools for efficiency. The average profit margin in this industry is 6 percent,” says Bill Gardocki. “One mistake on your job site, one breakdown on your job site, and that’s it. That’s your profit margin gone for that job.”

This problem is particularly pervasive when it comes to compaction, which is one of the most important things in pavement, explains Steve Jones, president of Pave Tech. “Compaction is one of those things you can’t start small; you have to start at a mid-range size because it is a time-consuming thing,” says Mr. Jones. “With a small compactor you can get the job done. It may take you two days, but with the right machine, it can get done in two hours.”

The Paver Pounder is a multi-bit utility tool with slide action that saves wear and tear on elbows and backs.

The Paver Pounder is a multi-bit utility tool with slide action that saves wear and tear on elbows and backs.

The Gardockis started using a plate compactor with a roller attachment about two years ago because 70 percent of their installations were paving slabs. They now use compactors with roller attachments on every single job.

When it comes to slabs, there are clamps and suction tools that prevent finger, back and knee injuries; make installation of slabs much easier; and also minimize cracking. According to Bill Gardocki, there is a steady growth in popularity of slab installations. This trend puts these tools high on the priority list.

Another favorite tool of the Gardockis is the Paver Pounder: a slide hammer that can use multiple attachments. With a breaker bit attached, this tool allows the installer, from a standing position, to crack a paver for removal rather than kneeling and whacking it with a hammer. This tool helps prevent tennis elbow, a painful condition that affects many while paving, as well as knee and back injuries.

Bottom line: To run a successful business, invest in tools that improve crew safety and boost productivity. “Compaction equipment: $12,000; small tools: $8,000; ancillary tools: $10,000. That’s $30,000, the price of your average pickup truck,” says Bill Gardocki. “Those are the tools that you need to be efficient in the hardscape industry.”

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Taking the Long View

When the city of North Bay, Ontario, explored the use of interlocking concrete pavers for its heavily trafficked downtown city center in the early 1980s, officials of this city of 54,000 wanted to know they’d be getting the most for their money. Not only did the resulting installation meet aesthetic and functional goals, it has since become a model of low-maintenance cost savings that has proved durable well beyond its projected lifespan of 20 years.

At the time of its completion in 1983, the $3 million, 150,000 sf (13,900 m²) Main Street project, which included roadway and sidewalks constructed on the full width of the road allowance, was hailed for its aesthetic contribution to a revitalized downtown business and retail district. When surveyed eight and 16 years later, the pavement was found to be performing exceptionally well under high traffic and extreme weather conditions, with little evidence of distress, despite minimal maintenance needed. In fact, after 12 years, a city official confirmed that there had been no maintenance at all. In addition, a 1999 life cycle cost analysis that compared the concrete paver installation with a local control section of hot-mix asphalt pavement found a difference of about $76,000/lane-km in maintenance costs favoring the concrete pavers.

Thirty-two years later, the installation is still performing, though finally ready for replacement, says Adam Lacombe, P. Eng, North Bay senior capital program engineer. The city is budgeting for a paver replacement to begin in 2017 or 2018. “Main Street has always been the centerpiece of the city, and the [pavers] set it off,” he says. “We are [considering] replacing them for their aesthetic quality and lifespan.”

Extreme Applications

The Main Street project was conceived at a time when the city of North Bay was planning to update its central business district with a more people-friendly scale and unified appearance. As part of the transformation, approximately 50 percent of the on-street parking was recommended for removal. In its place, designers envisioned wider sidewalks, boulevard areas and the addition of trees and planting areas, new benches, underground wiring and new streetlights.

Aiming to attract shoppers to a refreshed retail destination at a time when traditional Main Street businesses were losing business to shopping malls, North Bay’s Engineering and Public Works Departments gave interlocking concrete pavers first consideration in part for their potential to create an aesthetic identity for the district. But another major goal was to find a pavement that could handle an expected traffic volume of 8,000 vehicles per day (5 percent delivery trucks and buses), as well as snow removal and harsh weather conditions.

In North Bay, temperatures can range from −40 C in winter to 35 C in summer, and punishing freeze-thaw cycles occur throughout the winter months, with frost depths of up to 8 ft (2.4 m). The Main Street roadway would be subject to approximately 300 tons of salt annually, as well as the regular impact of the carbide steel blades used on snow-removing graders, slushers and plows.

At the time of the project’s conception, interlocking concrete pavers were already in use in high-load, harsh-weather projects around the world, and were just beginning to gain wider interest for heavy-use projects in North America. Just one year before the North Bay Main Street pavement was installed, 610,000 sf (56,700 m²) of interlocking concrete pavement was used in what is now called the Pier IX Terminal, in Newport News, VA. This facility handles ground storage of coal, so the pavers are subject to high loads from coal storage piles and abrasive loads from steel-tracked bulldozers. This provided an example of durability in an industrial setting.

North Bay officials had some experience with concrete pavers, which had successfully performed in an area around city hall for five winters under de-icing salts. But that area was not subject to vehicular traffic, so additional evidence was sought to prove the material and its installation could withstand projected traffic load and environmental conditions long-term.

A seminar that brought in experts from Australia, England and the Netherlands demonstrated to North Bay stakeholders how pavers had performed successfully under extreme loads and weather conditions in container ports, airports and roadways. Presenters offered compelling evidence that, when designed and executed correctly, the installation would withstand the rigors of a heavily trafficked Northern Ontario Main Street.

Best Practices Defined

The manufacturers, designers, engineers and installers involved in the Main Street installation set their sights on creating a state-of-the-art model showcase for what was recognized as a high-profile project. The pavers were manufactured to resist abrasion and freeze-thaw conditions, meet compressive strength and absorption standards, and were subject to a salt immersion test. Installation included a compacted subbase and base, edge restraints in the form of cast-in-place concrete curbs, concrete collars around utility structures such as manholes to offer a stationary restraint for the pavers, a herringbone pattern to provide the greatest degree of interlock (except in the crosswalks, which use a running bond pattern), and a slight crown in the roadway to allow for natural settling and drainage after construction. Sub-drains were utilized in some locations and surface water was designed to flow to catch basins and storm sewers.

During construction, installers performed regular density checks of the base with a nuclear density gauge to achieve the specified level of compaction that is critical to long-term performance. Nearing the end of installation, a plate compactor was used to force bedding sand into the joints and to facilitate the process of paver interlock, which in turn enables the transfer of vehicular load from paver to paver.

From today’s perspective, the North Bay Main Street project helped define best practices for interlocking concrete pavement manufacture and installation, some of which later became ASTM and CSA standards, including those for compressive strength, freeze-thaw durability and dimensional durability, and remain in use today.

Test of Durability

At eight years post-construction, an engineering consultancy performed a detailed condition survey and non-destructive deflection testing of the Main Street pavement. The survey found that about 4 percent of the approximately 57,000 sf of pavement surveyed had depressions concentrated in an area that had been subject to improper repair of the base when reinstalled after utility repairs. Another section that showed spalling resulted from incomplete joint filling and subsequently pavers losing interlock. Aside from this, the report concluded that the pavements provided “excellent performance…surface deformation occurs in less than 1.5 percent of the pavement areas surveyed,” and that the pavers were in “very good to excellent condition.”

Sixteen years after completion, in 1999, a geotechnical engineering consultant performed another condition survey that included a comparison with a local control section of asphalt pavement. It concluded that the interlocking concrete pavement showed little evidence of distress, with pavement condition indexes (PCI) for tested sections averaging 70 on a scale of 0 to 100 (with 100 showing no distress).

At 20 years, North Bay Public Works confirmed that the pavement was expected to be serviceable for another 15 to 20 years with only minimal maintenance anticipated.

A Cost-Effective Option

As part of the 1999 survey, a 40-year model was used for a life cycle cost analysis comparing the pavers and an asphalt street model that concluded rehabilitation of the pavers would be required at Year 21 in order to maintain a pavement PCI of 60. For the asphalt pavement, rehabilitation would correspond to years 18, 27 and 36 to maintain a PCI of 60.

At a 4 percent discount rate (corresponding to a secure investment of 6 percent and inflation of 2 percent), interlocking concrete pavements were shown to be more cost-effective than asphalt pavements. The study did not reflect costs to the public in downtime from routine maintenance and repairs. Interlocking concrete pavers can have a significant benefit in terms of reduction of these user delay costs because traffic can be restored very quickly after repair; also, less maintenance downtime is required over the pavement’s lifespan.

Since 1983, North Bay has continued using interlocking concrete pavers in public sidewalks, boulevards, its train station and lengthy promenades along its award-winning Lake Nipissing Waterfront Park. In 2010, it added a one-block section of pavers in a roadway that complements nearby Main Street and sets off a roadway island park. Likewise, cities across the United States and Canada have since chosen pavers for a variety of low- and high-impact projects, taking advantage of their endurance, aesthetic qualities and green attributes, more recently including permeable installations that aid in stormwater management.

The details of North Bay’s Main Street pavement rehabilitation are still to be determined as the city works on a new land use and urban design plan, says Mr. Lacombe. A rough estimate for replacing the pavement, including design and construction, is currently $2.4 million, he says.

North Bay faces the same decisions as hundreds of cities across North America: how to replace an aging downtown roadway in a way that’s economical in the short and long term, while taking into account aesthetic and environmental considerations, and the needs of stakeholders. The Main Street project offers strong evidence that interlocking concrete pavers are suitable for high-impact applications, and can be the most cost-effective pavement solution when considering total cost of ownership over the long term.