PowerBlock Permeable Pavers FAQs
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How does the size and weight of PowerBlock compare to traditional permeable pavers?
PowerBlock permeable pavers are designed to be much larger than traditional pavers. Each block is about 1 square foot (11.75” x 13.7”) and weighs roughly 45 lbs at 4.5” thick. Traditional pavers vary in size, but they are typically around 3” thick, less than ½ square foot in area, and usually weigh between 5-8 lbs each. Having much larger dimensions makes PowerBlock more stable under traffic loads for longer lasting projects.
What colors are available?
PowerBlock’s standard color is light gray. Additional colors including tan, charcoal gray, and brick red are available. Custom colors are available on request. Coloring is added to the mix before PowerBlock is manufactured to keep the coloring consistent throughout the block and prevent the coloring from chipping or wearing off from traffic.
Is the block porous like pervious concrete?
PowerBlock is a solid concrete block. When installed, rainwater moves through the open joints between blocks, not directly through the block. The open joints remain unfilled, allowing the system to achieve surface infiltration rates over 1,000 inches/hour.
What is the Solar Reflective Index (SRI) for PowerBlock?
Solar Reflective Index is an indicator of a product’s ability to both reflect solar energy back into the atmosphere as well as release energy it has absorbed. SRI is affected by color, so PowerBlock permeable pavers will achieve different SRI’s based on the desired color. Testing has been performed for standard gray and tan colors, with the following values:
- Light Gray: 32
- Tan: 20
How long has PowerBlock been on the market?
PowerBlock permeable pavers were developed and released in 2017.
What is the design life of the block?
Most concrete pavements are designed for a 20-year service period with a life expectancy that extends well beyond that. PowerBlock exceeds this performance by using individual blocks that can articulate instead of cracking like a typical pavement would. With this in mind, most engineers anticipate the primary failure occurring in the system base (where the stone could become contaminated and/or become unstable) long before the individual blocks wear out. Since the base of PowerBlock is designed for both structure and capacity, the base layers are often significantly thicker than structurally required, reducing stresses on the subgrade. And with the addition of geotextiles to prevent contamination of the base, PowerBlock systems – with proper maintenance – often remain functional much longer than traditional pavements.
Where is PowerBlock made?
PowerBlock is currently made at plants in Virginia and Louisiana (we’re hoping to add New England in 2020), and it can be manufactured at virtually any facility capable of producing dry-cast concrete blocks.
Is PowerBlock rated for vehicular traffic?
PowerBlock is manufactured to meet a 4,000 psi requirement and blocks typically test significantly higher than this. At 4,000 psi, PowerBlock has been certified by an independent engineering firm to be capable of supporting vehicular traffic, including HS-20 and HS-25 loads. Contact your local ACF representative for a copy of this certification.
What applications can PowerBlock be used for?
PowerBlock is a wonderful surfacing material for a variety of applications, including (but, not limited to):
- Parking lots
- Parking stalls
- Drive isles
- Emergency access roads
- Residential & commercial applications
- Active roads with a max speed of less than 45mph
Does the open joint allow PowerBlock to be ADA compliant or acceptable for pedestrian traffic and high heels?
PowerBlock allows surface runoff to flow into the stone reservoir below the block through a ¼” open joint, which is the same size as a traditional expansion joint in any concrete sidewalk or pavement. This allows PowerBlock to meet ADA requirements, as well as be a suitable surface for pedestrian traffic – including pedestrians wearing high heels.
What is the surface infiltration rate of PowerBlock, and is there a benefit to having a surface infiltration rate that massively exceeds the rainfall rate?
The surface infiltration rate for PowerBlock is in excess of 1,000 inches per hour, which is the specified minimum acceptable rate for the installed system. While this rate greatly exceeds the rate of rainfall and virtually any run-on condition that may be created, this higher surface infiltration rate allows PowerBlock to easily keep up even during short intense burst events or (our favorite) rain bombs. Perhaps more importantly, massive surface infiltration rates extend the time period between maintenance activities. For example, if PowerBlock is 90% clogged, it would still be expected to achieve a surface infiltration rate of 100 inches per hour, close to where competing systems might function when brand new. Reducing maintenance headaches by extending maintenance cycles (typically 2-5 years) makes PowerBlock the “easiest to own” permeable pavement system available.
How does PowerBlock compare with standard permeable pavers or porous asphalt / concrete?
PowerBlock is a larger, heavier block than traditional permeable, making it more stable in traffic areas (see question above on block size compared to traditional permeable pavers). It’s extremely durable and won’t spall under turning wheels like porous asphalt or concrete. PowerBlock uses open joints to achieve surface infiltration rates of over 1,000 inches per hour, which is 300% – 500% higher than other options. The extremely rapid movement of water off of the surface is critical to vehicular safety and pedestrian access while also extending maintenance cycles. While traditional porous pavements and permeable pavers must be cleaned every 3-12 months, PowerBlock maintenance cycles are typically between 2 and 5 years.
What base material is required, and what is the minimum base depth?
PowerBlock is designed to sit on a base of washed, angular AASHTO #57 stone (typically < 1.5” in diameter) with a minimum thickness of 6”. The base layer must be designed to meet both the volume requirements of the local regulations for permeable pavement as well as the structural requirements based on the surface use and subgrade bearing capacities. If the base depth reaches 12” or more, we recommend only the top 6” to be AASHTO #57 stone and a larger #2 stone to be used below that.
Can the stone base be used for structure and for storage?
Most permeable pavement designs utilize the stone base for both structure and stormwater retention/detention. PowerBlock designs work exactly the same way.
What type of geotextile envelope should be used to protect the stone base from contamination?
As with any detention system that utilizes stone for storage, wrapping the stone with a geotextile is critical to prevent soil intrusion into the open-graded stone which can plug the voids and structurally weaken the system. The ideal geotextile for permeable pavement applications is a woven monofilament such as the ACF M200, which combines separation and strength to support the saturated soils with high permeability rates to allow water to exfiltrate the system into surrounding soils. In some applications where more storage volume is needed in the base, but system depths are limited, R-Tank modules can be used below the base to meet storage requirements.
Is geogrid required under the blocks and the base stone?
No, it is not required. PowerBlock permeable pavers are typically installed on open-graded stone that doesn’t lock up like a road base material would, so some engineers find it preferable to utilize a geogrid, such as ACF BX11, at the interface between the stone base and the PowerBlock to prevent differential settlement of the blocks. While this layer of geogrid may support the installation process, it is not required.
What kind of material is used to infill the joints?
None! No stone. No sand. No chips or any other material should be placed in the PowerBlock joints. These ¼” joints remain open for runoff to quickly flow off the surface and safely into the stone base, away from vehicles and pedestrians. The open joints move water off the surface at over 1,000 inches / hour, 3-5 times faster than traditional permeable or porous systems.
Are perimeter edge restraints required?
Vehicular Applications – If the system edges are all full or half-size blocks, only minimal edge restraints are necessary. Using a stone & topsoil blend with seed may be adequate, or you may want to consider using #4 rebar or landscape edging to prevent blocks from moving. If there will be a radius on the edge or cut blocks smaller than a half-size block, a formal curb will perform best over time. If there are transitions between PowerBlock and traditional pavements, the best practice is to use a flush ribbon curb to separate the surfaces. This allows any future maintenance of the traditional pavement (milling, sealing, etc.) to be uninhibited by the interface.
Pedestrian / Landscape Applications – If the system edges are all full or half-size blocks, no special edging is required, and the blocks themselves will be stable enough. If there will be a radius along the edge or cut blocks smaller than a half-size block, using a minimal edge restraint such as a stone & topsoil blend with seed, #4 rebar, or landscape edging will work well.
Does PowerBlock only work in infiltration applications?
Measurable infiltration rates in the subgrade beneath PowerBlock are not required for a successful installation. Many permeable pavements have been installed throughout the world with underdrains to collect runoff and direct it to the storm sewer or additional treatment devices.
Are there any freeze/thaw issues with PowerBlock?
PowerBlock has not experienced any freeze/thaw issues, even in northern New England areas. Proper preparation of the base materials as detailed in the PowerBlock specification is critical to ensuring a successful installation.
Are there any heat expansion issues with PowerBlock?
PowerBlock has not experienced any issues with expansion or contraction, as the openings between blocks function as micro-expansion joints to mitigate these issues.
What is the maximum surface slope where PowerBlock can be installed?
PowerBlock can be easily installed on slopes up to 5%. If your project requires PowerBlock to be installed on grades steeper than 5%, there are a few design options that will make the steeper grades possible. Contact your local ACF Representative for assistance.
Is geogrid or geotextile needed under the blocks, under the stone base, or in both places?
A separation geotextile such as ACF M200 is required at the interface of the subgrade and stone base to prevent contamination of the stone. This material should also protect the vertical sides of the system from the in-situ soils. In addition, some engineers like to use a geogrid directly beneath the blocks. While this is perfectly acceptable and may facilitate installation, if the stone base is prepared properly it shouldn’t be necessary. In some cases where the subgrade is not competent, engineers may require over excavation and a combination of additional stone and geosynthetic materials be built up to provide a stable platform for the base materials.
Can I eliminate all of my drainage structures and catch basins by using PowerBlock?
Permeable pavements effectively turn the entire pavement into one large catch basin. This allows the elimination of virtually all of the traditional drainage components typically required. That said, a good design usually includes a backup plan, and including minimal overflow inlets that function in highly intense events or when the permeable pavements are neglected and clogged can help mitigate these issues.
Does PowerBlock provide stormwater quality treatment?
PowerBlock reduces runoff by converting impermeable surfaces to permeable ones, helping to maintain the hydraulic continuity of the pre-existing conditions where stormwater can infiltrate into the ground. Further, the stone base acts as an effective filter, trapping sediments and their sorbed pollutants to reduce contaminated discharges. Some regulations may even require a layer of sand or other fine material to be placed below the base to provide additional filtration. As a result, most states approve permeable pavements with significant pollutant reduction capabilities.
How do you overcome differential settlement between units?
Successful permeable pavement installations ALWAYS begin with successful base installations. While the #57 stone base used beneath PowerBlock won’t compact significantly, it does consolidate well. Installers should install base materials in 6-8” lifts and compact with a roller. When the final layer is placed and rolled, it should be finished with at least two passes of a plate compactor, one in the north/south direction, and a second in the east/west direction. Compaction is complete when the base is smooth and level with no movement of the base observed during compaction. This process will prevent differential settlement, and it is detailed step-by-step in the PowerBlock specification.
Should you protect adjacent non-permeable surfaces (like asphalt and concrete) from water intrusion?
Some engineers like to prevent runoff stored within the permeable pavement from entering adjacent traditional pavements that can be damaged by water. This separation can be accomplished with a standing curb or a geomembrane between the two pavements.
Does PowerBlock qualify for any LEED credits?
LEED is a rating system developed more than 20 years ago by the US Green Building Council. While specific products don’t generate individual credits, PowerBlock can help achieve the specific goals within the rating system, including:
- Sustainable Sites C6.1 & 6.2 (reducing runoff)
- Sustainable Sites C7.1 (reduce heat island effects)
- Materials & Resources C5.1 & 5.2 (locally and regionally sourced materials)
Can you paint parking lot lines on PowerBlock or stripe it for roads?
Yes, we have several case studies available that show how striping looks when applied to PowerBlock permeable pavers. Contact your local ACF representative for pictures or case studies.
How do you remove PowerBlock to install future utilities?
PowerBlock permeable pavers can easily be cut (just like a traditional pavement) for utility access. However, unlike traditional pavements, utility contractors can also simply remove the blocks that are obstructing access to utilities, and then replace the blocks on the #57 stone bedding.
Is PowerBlock resistant to road salt and other de-icing agents?
No, like all concrete products, sales and de-icing agents can cause significant damage to the surface. If salt is commonly used on the surfaces where PowerBlock will be installed, the blocks should be sealed after installation. (Follow the sealer manufacturer’s guidelines for application and subsequent reapplication as needed.) Sealing the blocks only boosts their ability to manage low concentrations of salt that might get tracked onto the pavement from adjacent streets. Instead of salt, the use of sand is recommended. Snow and ice tends to melt more quickly on permeable pavements, so a light sanding is usually adequate.
Do the gaps between PowerBlocks need to be filled with stone?
No, the joints between blocks remain open for rainwater to quickly run off the surface between blocks and should not be filled.
How do you cut PowerBlock?
Blocks can easily be cut by a chop saw with a concrete blade. Pieces smaller than ¼ block can be a little tricky to stabilize, so efforts should be made to avoid cutting pieces of that size or smaller. If small cut pieces of blocks are unavoidable, more significant edge restraints may be necessary.
How do you place PowerBlock around curves?
Most installers build great looking curves by installing PowerBlock beyond the finished edge and cutting the curve in-place. This has proven to be much easier than trying to pre-cut blocks to fit a desired radius. If small cut pieces of blocks remain after the curve is cut, more significant edge may be necessary to hold them in place.
How much extra PowerBlock should I order to account for waste?
For rectangular projects, using a 5% waste factor should be adequate. However, if your project is narrow (a sidewalk, for example) or includes a significant percentage of curved edges, a higher waste factor of 10-15% will be more appropriate.
What is the minimum temperature needed to install PowerBlock?
We do not specify a minimum required temperature for installation. However, the base materials must not be frozen in order to be fully compacted, and improperly installed (and frozen) base materials will be reflected in the PowerBlock surface when the base thaws.
What role does freight play in pricing?
As you might imagine, freight is not inexpensive for any permeable pavement. That’s why we always provide pricing that includes freight costs to the installation site. Your local ACF Representative can help determine the cost of freight as well as the number of trucks needed to complete your delivery.
If the blocks are not fitting close enough to the curb, what can I do?
PowerBlock permeable pavers fit perfectly against curbs with a vertical face. If your curb has been poured with a sloped face, you may have a gap between the blocks and the curb. While the engineer of record should be consulted for a final decision, using a small stone (> ¼”) to fill the gap can provide a simple solution. The best solution, of course, is prevention. Good planning and communication with the curb installer along with an accurate block layout plan are critical to a good installation.
Can I install PowerBlock in the first phase of construction to use as an access road, or do I need to wait until the end?
Like other stormwater Best Management Practices (BMPs), PowerBlock permeable pavers should be installed at the end of the project to prevent contamination. If it must be installed before the site is fully stabilized and significantly complete, there are some rigid covering options that can be added to protect the system. Contact your local ACF representative for assistance with these options.
How do I perform maintenance on PowerBlock?
Maintenance is performed with a vacuum sweeper truck, like the Elgin Whirlwind (which we highly recommend). These trucks are capable of generating enough suction to remove sediments and debris from between the blocks without disturbing the large base stone materials. And since the joints remain open by design, once the vacuuming is done, the maintenance is complete with no additional work required.
How do I know if / when maintenance is needed?
ACF recommends that maintenance occur if the surface infiltration rate of more than 75% of the pavement surface falls below 10% of the specified rate. Even at this rate, PowerBlock would be removing water at 100 inches per hour, but it’s best to complete maintenance before the system completely ceases to function. We also recommend maintenance be initiated if there is any significant surface ponding on the pavement that persists for more than 24 hours. This information can be found in the PowerBlock specification.
What is the typical maintenance schedule and is there a benefit to more frequent maintenance cycles?
Due to PowerBlock’s extremely high surface infiltration rate, most currently installed projects are using a 2-5 year maintenance schedule. Where your project falls within this range will depend largely on the volume of run-on coming from adjacent impervious surfaces as well as nearby trees and plants that contribute biodegradable materials to the pavement.
Some clients, particularly those that own a vacuum truck, prefer to perform more frequent, preventive maintenance before any of the obvious maintenance triggers occur. Taking this approach minimizes the amount of time involved in each cleaning effort and can be a terrific approach, particularly in areas with significant tree cover.
Can a snow plow be used on PowerBlock?
Yes, snow plows can safely operate on PowerBlock pavements. Ideally, operators will use a rubber tip or a puck (to raise the metal edge of the plow) to prevent excess wear on the surface. However, the heavy, interlocking blocks will remain stable even under metal plows, and the uniform color throughout the block will help minimize the appearance of any chipping that might occur.
Can salt be applied to PowerBlock when needed?
Salt is not recommended. In cold climates the blocks can be sealed in place with a salt-guard. However, this does not make the blocks salt-tolerant. Rather, it boosts their ability to manage low concentrations of salt that might get tracked onto the pavement from adjacent streets. Instead of salt, the use of sand is recommended on the blocks. Snow and ice tends to melt more quickly on permeable pavements, so a light sanding is usually adequate.
Can sand be applied to PowerBlock with its open joints?
Yes. Sand is recommended in place of salt of de-icing agents as it will not damage the blocks. While most of the sand applied will eventually end up in the open joints between the blocks, it can easily be removed during normal maintenance operations.
Can de-icing agents be used on PowerBlock?
De-icing agents are particularly hard on concrete products and are not recommended.