Using materials recovered from the waste stream typically results in less waste, pollution, and energy use than using virgin materials. From an environmental standpoint, post-consumer is typically considered preferable to pre-consumer recycled content because post-consumer recycled materials are more likely to have been diverted from landfills.
In some cases, we consider products with recycled content green but with some caveats regarding where they should be used. For example, rubber flooring made from recycled automobile tires should not be used in most fully enclosed indoor spaces due to the likelihood of VOC emissions.
Recycling can have downsides. For example, some studies show that curbside collection programs and some recycling processes use more energy than they save. Closed-loop recycling is generally preferable to “down-cycling,” in which a lower-grade material is produced—but due to contamination of waste streams and the difficulty of extracting high-value ingredients, down-cycling may be as good as it gets. At times recycling can re-introduce hazardous components. Some products, like copper and aluminum, include a high level of recycled content as a matter of course—which we applaud, but don’t consider justification for listing in GreenSpec. As more complete life-cycle information on recycled materials and processes becomes available, we use that to increase our scrutiny of recycled products.
Atlas Block with CarbonCure Technology
Atlas Block makes concrete masonry units, veneers, pavers, and landscaping products for residential and commercial applications that incorporate either CarbonCure CO2 sequestration technology or post-consumer recycled content. The CarbonCure Block System permanently sequesters CO2 as limestone within the concrete while still meeting ASTM/CSA industry quality standards. A typical 8-inch CMU contains approximately 15 grams of CO2 that would not otherwise be sequestered. The CO2 also acts as an accelerated curing agent that can reduce cement by up to 10%, energy consumption by up to 38% and reduce defect rates by up to 20%. Atlas Block also offers products that use 30% post-consumer recycled glass as aggregate. This glass aggregate, manufactured by Poraver, is powdered, mixed with magnesium oxide and other ingredients, and then heated so that it puffs into small lightweight spheres that are unaffected by alkali-silica reaction, which can weaken concrete. Atlas Block's recycled glass content varies depending on product, but does not impact the concrete's strength, according to the company.egate, manufactured by Poraver, is powdered, mixed with magnesium oxide and other ingredients, and then heated so that it puffs into small lightweight spheres that are unaffected by alkali-silica reaction, which can weaken concrete. Atlas Block's recycled glass content varies depending on product, but does not impact the concrete's strength, according to the company.
Brick is a durable building material, but it is fired at high temperatures, resulting in significant embodied energy. Some brick products are manufactured using less energy-intensive processes; there are others that safely incorporate waste and recycled materials; and reusing brick will extend its service life.
Products listed here use low-temperature manufacturing processes, incorporated recycled waste products, or are salvaged responsibly from old buildings for reuse in brick veneer. Note that not all salvaged, or “reclaimed” brick is suitable for reuse. Salvaged brick needs to be carefully removed from environmentally sound buildings to insure the bricks do not contain toxins or are damaged structurally. And “Salmon” brick taken from the interior of old buildings is too soft, fragile, and vulnerable to moisture for reuse as exterior brick veneer. If purchasing or specifying reclaimed brick, make sure you know what you're getting, and that it meets your project's needs.
Concrete masonry units (CMUs) are ubiquitous in construction and come in load-bearing varieties used primarily for foundations and exterior walls, and non-load-bearing varieties used on interior walls. CMUs are relatively inexpensive, offer good fire resistance, and are relatively easy to install and finish. They are also available with a finished face, which further reduces other finish materials.
While portland cement has high embodied energy and carbon dioxide emissions from manufacturing, CMUs make efficient use of that portland cement in a controlled manufacturing process—in contrast with cast-in-place concrete, which entails waste. In addition to aggregate, fly ash, silica fume, and other supplementary cementitious materials (SCMs) can also be added to CMUs to reduce the amount of portland cement and improve performance.
CMUs are also available that use carbon dioxide from other industries in their production, sequestering the carbon while improving the performance of the block. Use of recycled aggregate is also common in CMUs.
Products listed by GreenSpec use carbon sequestration; are designed for superior energy performance, such as by using expanded polystyrene insulation inserts; reduce material use by way of a finished exterior face, such as split-faced block; or contain recycled content, such as fly ash or glass aggregate.
Precast concrete unit paver can incorporate fly ash or alternative aggregrates as recycled content, and most products listed by GreenSpec here have at least 20% recycled content.
Consider the use of porous pavers that help manage stormwater runoff, reduce the urban heat island effect, and offer other benefits. GreenSpec includes some porous pavers with lower recycled content due to those environmental benefits.
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