Do you think there should be a separate ASTM category for concrete blocks, pavers, and other elements that incorporate non-traditional green ingredients?
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Not too long ago, the idea of shipping a green block was a bad thing. It meant that the unit hadn't been fully cured and may not have enough compressive strength to comply with specifications.
In today's frenzy of developing new sustainable construction techniques, the term green block is taking on new meaning. Like all segments of the concrete production industry, block producers are struggling to develop business approaches to capture their share of the green building construction market.
One aspect of the greening of the block process has been an effort to include non-traditional materials as ingredients. Currently, ASTM C 90, Standard Specification for Loadbearing Concrete Masonry Units, covers units made “from hydraulic cement, water, and mineral aggregates, with or without the inclusion of other materials.” Note that the percentage of the ingredients in a mix design is left entirely to the producer.
The specification does specifically list common green ingredients such as pozzolans and blast furnace slag cement. These must meet the applicable ASTM standard. And C 90 also allows other non-listed constituents as long as they are “previously established as suitable for use in concrete masonry units and shall conform to applicable ASTM standards.”
But what about potential ingredients that haven't been used before in the blockmaking process? The standard allows producers to incorporate new materials as long as the producer can document that the product “by test or experience, not to be detrimental to the durability of the concrete masonry units or any material customarily used in masonry construction.”
It's this aspect of the standard that is intriguing and baffling to innovative producers.
Not every potential ingredient can be a good thing. For example, take the effort of a producer who was approached by a neighboring manufacturing facility to help solve a waste stream problem. The manufacturing plant contacted the producer's QC department to consider including a plastic aggregate generated by a shot/paint process. The results of some preliminary lab testing suggested that the material could be used.
Despite the initial success, the producer dropped the project. Staffers discovered the plastic product had been reported as a production waste material to the EPA. As such, should the producer include the plastic aggregate in any product, it would have to submit a special RECLA report seeking permission to have the waste material cross state lines.
Fortunately for an industry steeped in conservatism and strong product performance, there's a ready resource to help answer the question of how to best select ingredients in block production that transforms one man's trash into another man's treasure.
The staff at the World Center for Concrete Technology (WCCT), with support from the faculty at Alpena Community College (ACC), both in Alpena, Mich., have guided both producers and manufacturers in developing our next green building stones. In the last two years, they have taken on a number of proprietary research efforts. They expect the trend to increase.