An affordable housing project under construction on Melrose Avenue in the Bronx, is using 5,000 psi CMUs with Pozzotive replacing 25% of the portland cement.
Back in 2003, Lou Grasso, of Kingston Block & Masonry Supply, paid a visit to Bob Fox, FAIA, of Cook + Fox Architects in New York City. Grasso had a line of nice-looking, polished-face concrete masonry units (CMUs) and he was hoping to interest Fox in specifying it in a project. Instead, Grasso was shown to the door. “Unless a product is sustainable,” Grasso remembers Fox telling him, “we’re not interested.”
Rather than simply accepting that rejection and moving on to a more promising client, Grasso looked at his company’s product and set out to reinvent it. Six years later he introduced Pozzotive Plus, a line of CMUs and concrete facing brick that breaks new ground in the use of recycled materials.
Grasso developed a pozzolan (a material, such as fly ash, that exhibits cementitious properties when combined with calcium hydroxide) from 100% recycled glass. The glass, which can be of any color or type (from beverage glass to window glass), is ground in a multi-step process to an extremely fine powder (10–15 microns). In this form, the material (with the trade name Pozzotive) can be substituted for 30% of the portland cement in the CMU and concrete brick formulas.
Pozzotive significantly reduces the embodied energy and carbon intensity of concrete block; each ton of portland cement replaced with Pozzotive saves about one ton of CO2
emissions. Pozzotive also helps reduce efflorescence (whitish deposits on concrete that form when soluble salts migrate to the outer surface of concrete), according to Grasso, and it produces stronger block.
Grasso wanted to go further than simply replacing some of the portland cement in his products, however, so he looked at the aggregate he was using and realized that he could substitute at least half with aggregate produced from post-consumer concrete and brick demolition waste. Kingston’s Pozzotive Plus line of CMUs and brick uses both the recycled glass Pozzotive and the recycled aggregate.
The aggregate is collected at a construction and demolition waste transfer station in Brooklyn and barged up the Hudson River to Ravena, New York, where it is processed into aggregate of the proper size for block manufacture, then trucked 40 miles to the company’s manufacturing plant in Kingston. Grasso has produced block with up to 100% recycled aggregate, but to ensure performance consistency, the company typically sticks with a 50% mix.
Pozzotive Plus concrete facing brick uses post-consumer recycled aggregate and recycled-glass Pozzotive.
Pozzotive Plus CMUs and brick, like the company’s standard products, are available with a ground, polished face for more decorative applications—offering the benefit of “structure as finish.” The polished faces are typically sealed with an acrylic with low levels of volatile organic compounds (VOCs), though one wonders if a zero-VOC sodium silicate hardener of the type used in polished concrete floors could be used satisfactorily (and affordably) in this application (see
EBN Feb. 2006
To date, the Pozzotive Plus CMUs, which were introduced in the spring of 2009, have been used in two multi-family affordable housing projects in New York City. The concrete facing brick in the same line was rolled out at the Urban Green Expo in New York City in September 2009. Grasso hopes eventually to convert his entire operation to the Pozzotive Plus formulation. “I can hardly wait for it to be all green,” he told
Meanwhile, Bob Fox, who inspired this whole product line, is now one of its biggest fans. “I think it’s terrific,” he told
. Fox likens Grasso to Ray Anderson, who led the carpet industry in a shift to more sustainable practices, suggesting that Grasso might do the same for the concrete masonry industry. While Fox does not incorporate a lot of masonry materials into his buildings, he told
that whenever he finds the opportunity, he will certainly specify Pozzotive Plus.
For more information:
Kingston Block & Masonry Supply
November 1, 2009