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While pervious concrete was first used over 100 years ago, it has taken until recent years for it’s application to become more commercially mainstream. Thanks to the sustainable trend in building practices, and organizations like the EPA and USGBC*, it is becoming a more widely used material.
Pervious concrete is made of aggregate and a paste of cementitious materials and a specific amount of water. There is little to no sand found in pervious concrete because it inhibits the ability for the paste to leave voids. Think of it like a rice krispie treat. The paste is the marshmallow filling that attaches to the aggregate (rice) while not filling in the holes between.
Typical flow rates for pervious concrete are 480 inches per hour or 5gallons/square foot/min. This means it is both more economically and more environmentally smart than regular concretes because it allows stormwater to filter through its layer back into the soil, recharging groundwater levels immediately. The open pore system also greatly reduces heat island effect caused by impervious concrete.
The economics side of this means that because of this immediate filter and removal it drastically reduces – if not entirely mitigates – the need for retention ponds, swales, or other stormwater management systems. This not only lowers the overall cost of the project, but lets you use the land which would have been swales more efficiently for building use – something which becomes very economically obvious if swales are replaced by rentable offices or apartments. It could also remove any stormwater impact fees that government agencies are starting to implement from the project costs.
Pervious concretes are typically seen as parking lots or other pavements, sidewalks and paths, and residential roads/alleys/driveways. Increased study of its composition in recent years, however, has seen it also implemented as tennis courts, foundations for greenhouses/hatcheries, patios, low water crossings, slope stabilizations, zoo floors, artificial reefs, swimming pool decks, seawalls, and noise barriers (it has very good acoustic properties). Places in Europe have even used it for load-bearing walls.
Because of the makeup and the faster drying time, the entire process is done on-site, which means the ingredients can (and should) come from a local source, helping the local economy. This also makes it more easily adaptable to different regions.
Due to the fact that its main uses are still for locations where there will be interactions with cars, questions about what happens to oil and other liquids arise. Because of the way the pervious pavement forms, however, instead of pooling the liquids, it acts as a filtering device. The oil which might leak from a car is filtered through the voids in the surface. It does not merely run through like water, but attaches itself as a layer on top of the hardened edges of the void. Natural bacteria and fungi then break down the oil. Studies have shown that up to 99% of oil introduced in this way will be biodegraded.
While pervious concrete is not typically used for high traffic locations, like main roads or places where heavy semis will maneuver, the normal composite used can safely hold 3000psi – the weight of a fire truck. Special mixes can be made that allow it to hold more, and the introduction of subgrade aggregate also increases its strength.
The rice krispie treat look also aids vehicle traction, especially during inclement weather. The porosity ensures the filtration which also eliminates spraying and pooling of water. Because of its more rugged surface, however, it is important to know that it shouldn’t be used where highly abrasive machinery will be used – like a snow plow that digs all the way down to concrete surface.
In general, a smaller amount of shrinkage during drying occurs and the minimal cracks that might occur have no effect on the structural integrity of the concrete. In colder climates, the implementation must be designed so that the voids would not ever become fully saturated. This is typically achieved by putting in 8-24″ of sublayer rock.
Pervious concrete can last 20-40 years with little to no maintenance, compared to other concretes or asphalts which continuously need resurfaced. The main source of maintenance is the prevention of clogging the voids through annual vacuuming and/or pressure washing.
*The use of pervious concrete is listed as a “Best Management Practices” by the EPA and will help achieve LEED credits SS-C6.1, 6.2; SS-C7.1; WE-C1.1; MR-C4.2, 4.2; and MR-C5.1, 5.2.
Tankless water heaters use more energy during the time in which they’re on, meaning that for the time in which they’re running, they’re costing more money. The upside is that they’re running much less frequently, as in: only when you need it instead of all the time.
The tankless heaters cost more for purchase and installation than tank heaters, but their lifespan is double and efficiency higher. This means that, while there is a higher initial cost, the homeowner is saving money every month with their new tankless heater over the lifespan of the tankless heater (avg 20 yrs).
There are currently tax rebates for the purchase and installation of tankless water heaters with an energy factor (EF) of .82 or higher in a primary home. What was once a $300 rebate on the stimulus plan, is now 30% of purchase and installation cost up to $1,500. The new tankless heater must be installed by December 2010.
Maine also has tax rebates for the purchase and installation of a tankless water heater. Improvements to the home’s energy efficiency by 25% will result in a rebate of 30% up to $1,500. Improvements of 50% energy efficiency will cover 50% of the product and installation cost up to $3,000. The funds will be available on a first-come, first-serve basis to those who meet the requirements.