This year’s Construction Specifications Institute convention had a number of interesting seminars for the “geeks-like-me crowd” usually found at CSI gatherings, but the presentation that grabbed my attention was “Smog Eating Cement.” Besides sounding like a 1950’s horror movie, the seminar title promised some interesting information about new green technologies. Promised, and as it turned out, delivered.
As often is the case, the cutting-edge in product innovation seems to come from Europe, this time from ESSROC Italcementi Group, as represented by Dan Schaffer. And the key to “Smog Eating Cement” is not an actor in a lizard suit but photocatalytic nanotechnology, a term with nothing at all to do with the scary movies of my childhood and everything to do with the future of our practice. Schaffer discussed results showing a 40% to 60% reduction in certain air pollutants from early studies of mock-ups and real projects where photocatalytic cement was used in buildings, paving and infrastructure. Photocatalysis is defined as a reaction that uses light to activate a substance (catalyst) to modify the rate of a chemical reaction without the substance itself being involved in the reaction. Nanotechnology has been incorporated in building materials for a few years now. In the area of glazing alone, many of us are very familiar with self-cleaning glass and advanced coatings that block ultraviolet or infrared light. In fact titanium dioxide (TiO2), which is the catalyst in self-cleaning glass used to break down dirt or pollution that can then be washed off by rain water, is also the basis for photocatalytic cement. One of the first uses of photocatalytic cement in a concrete structure was Dives in Misericordia Church in Rome, designed by Richard Meier and completed in 2003, which used TiO2 throughout the mix. Italcementi’s Dan Schaffer pointed out that this cast-in-place example is probably not practicable for most projects. Since the TiO2 catalyst works only in the presence of ultraviolet light (UV) and UV only penetrates a short distance into the concrete, the benefit of the TiO2 rapidly diminishes further into the structure. In fact a thin surface layer, probably no more than 30 mm thick, is all that is required. Any more depth is wasted, especially at a cost of perhaps $1 per sf for each inch of thickness.
Schaffer suggested that cost effective applications for photocatalytic cement are precast concrete, tilt up slabs, and paver blocks. In these applications, a thin layer of photocatalytic concrete is placed first then backed up by much less expensive regular concrete mix. Because his company focuses mainly on concrete cements, Schaffer focused the seminar mainly on concrete, but he made the point that the photocatalytic technology could lend itself to any cementitious product. After seminar discussion suggested other possible uses: stucco, mortar, concrete masonry units and tiles, cementitious paints, and cementitious siding and roofing.
So, is this new technology viable for our current projects? Based on the seminar, I think it is something to consider. Can we afford it? The obvious right solution is reducing to elimination the harmful pollutants we humans put into the air in the first place, but until that happens, “smog eating cement” might just be a product we can’t afford NOT to consider. Especially if you remember, like I do, how the results of our pollution led to those science fiction monsters in the first place.
In a recent webinar, I encountered the term “greenwashing,” a practice whereby manufacturers and their product representatives overstate or misstate the sustainable attributes of their products. A study quoted in the webinar mentioned the greenwashing “sin of the hidden trade-off.” That’s when a product has significant benefits but also contains hidden and sometimes offsetting negative features. For a good example of this, take a good look at the massively hyped Eco-rock by Serious Materials, a substitute for gypsum board which “uses 80% less energy to produce than gypsum drywall.”
Now, gypsum board is not a particularly onerous product from a green standpoint – after all it has high recycled content, it can be recycled, and most impressively, it can be made synthetically using a byproduct from coal burning flue gas. In fact, most recently constructed gypsum board production facilities are located near coal-fed power plants to make use of the synthetic gypsum byproduct.
Still, the manufacturer of Eco-rock makes a valid point: gypsum board has high embodied energy. On the production line, gypsum needs to be crushed, dried, ground, and calcined; a process requiring a lot of resources and fuel, perhaps as much as 200,000 btu for each sheet of gypsum wallboard. Multiply that number by the 25 billion square feet of wallboard produced in the United States in a typical year, then multiply again by the savings claimed by Eco-Rock, and all of a sudden you are looking at a new product that could truly revolutionize construction.
Best of all, according to Serious Materials’ literature, Eco-Rock “…meets 100% of ASTM C-1396 physical drywall properties…” except for the “…early text of C-1396, which specifies the gypsum content of the board.” There you have it, a perfect 100% substitute for gypsum board as verified by standardized testing, along with that huge embodied energy savings. So, where’s the hidden trade-off? To find out, it is important to remember how and why gypsum board (“drywall”, “sheetrock”, “plaster board”, etc.) came to be the ubiquitous wall surface it is today, and how it works as a passive fire resisting element.
A century ago plaster was the typical interior wall finish, applied either directly to masonry structure or over wood or other types of lath attached to framing studs. In either application, plaster provided a smooth, durable, and flat surface that was also to some extent fire resistant. When gypsum board was developed and became readily available, it offered several obvious advantages. It was lighter than plaster, faster to apply and finish, and required much less water. Moreover, it had a tremendous ability to provide a high level of passive fire resistance within a relatively thin and lightweight product.
And the reason gypsum has excellent fire resistance is that during the energy-rich process of its manufacturing, crystallized water becomes chemically bonded within the gypsum. As fire begins to affect gypsum board in a wall assembly, the temperature of the product is raised in a linear fashion until the water within the product begins to sublime – that is it turns from a solid component directly into a vapor. This change in state within the material consumes a tremendous amount of heat energy from the fire side without raising the temperature further on the safe side, and thus allows a couple of thin layers of gypsum board to provide fire resistance quantifiable by an ASTM E-119 test as code requires.
So with standard gypsum board, it is precisely the embodied energy from its manufacturing process released later on in a fire that prevents the spread of that fire. And therein lies the hidden downside of EcoRock. When Serious Materials first introduced the product as a concept, it was intended to be made available in a 5/8” thick ASTM C 1396 Type X version with a 1-hour ASTM E-119 fire resistance rating, as well as a 1/2” thick non-rated version. However, recent information obtained from the manufacturer indicates that the 5/8” Type X product will not be manufactured. My informed guess is that since it is not a gypsum product and therefore cannot take advantage of sublimation energy, Eco-Rock will be hard-pressed to provide a tested assembly fire resistance comparable to gypsum board.
So the sin of EcoRock greenwashing seems to be not in misstating what is said, but in the hidden downside, in what is unsaid but implicit. We expect gypsum board to provide fire resistance, and apparently EcoRock does not do that. Although the energy saving benefits and physical performance properties of the product may be exactly as stated, I would not consider EcoRock as a direct substitute for applications where one would typically use gypsum board until we see an ASTM E-119 test from Serious Materials.
[Originally published on the Cannon Design blog - visit my friends at CannonDesign.com ]
