When we think about concrete's sustainable features, a few things automatically come to mind: durability, thermal mass, and recycled materials. Pollution control is usually not on the list. With advances in cement technology, concrete has reached an even greater green potential: cleaning itself and the air around it.
Photocatalytic cement, developed by Italcementi Group, has been available in Europe for a decade. Now Essroc, Italcementi's U.S. subsidiary in Nazareth, Pa., is making a name for the TX Active brand cement in North America.
TX Active includes two formulations. Self-cleaning TX Arca allows concrete to resist most environmental pollutants that gather on the surface and cause discoloration. TX Aria is also self-cleaning, and eliminates significant amounts of pollution—nitrogen oxide, sulfur oxide, and carbon monoxide— from the air.
When UV rays in sunlight contact concrete containing TX Active cement, they accelerate the natural oxidation process that decomposes organic and inorganic pollutants. This photocatalytic process keeps the pollutants from accumulating on the concrete's surface.
The environmental benefits vary. TX Arca attacks soot, grime, mold, mildew, bacteria, and other allergens to keep concrete structures clean and eliminate chemical cleaning solutions. TX Aria goes further by actually decreasing harmful air pollution.
George Spence was intrigued when he learned about TX Active cement at an annual Altus Group meeting. Spence, a regional manager for Greenville, S.C.- based precast producer Metromont, just needed the right project for the innovative material.
When Dalton State College approached Metromont about its new bell tower, Spence knew it was the perfect opportunity. As the campus's tallest structure, the 75-foot-high tower would be a focal point for the school. TX Active was attractive to the college both visually and financially, allowing the tower to maintain its bright façade without the hassle and expense of regular maintenance.
The tower is the first precast concrete project in the U.S. to use TX Active cement. Its 20 architectural precast segments were produced at Metromont's Hiram, Ga., plant.
Metromont's learning curve with the new cement was minimal. “TX Active handles exactly like portland cement,” says Spence. “We didn't make any changes in handling, batching, placing, or finishing.” The precaster had Essroc check its chemical admixtures for compatibility, as there are some chemicals that may react with TX Active, but they all passed the test.
Spence worked with the architect to ensure the tower's design would allow the cement to do its job. “We realized that a very light sandblast finish resulted in the maximum benefit from the cement's photocatalytic properties,” he says. “A heavy sandblast or retarded exposure of the aggregate would reduce the surface area of exposed TX Active.” The more cement matrix that is exposed, the better it reacts with sunlight to oxidize pollution and convert it to a water-soluble material that can be washed away by rain.
Metromont is spreading information about TX Active to architects. The producer markets its familiarity with the new cement, as well as its potential to earn Innovation in Design LEED credits.