Testing air & water benefits of unique cement blend

modotfeatureResearch team backed by Essroc, Lehigh Hanson, Iowa State Studies photocatalytic cement-bound pavement.

The Missouri Department of Transportation, in collaboration with the Federal Highway Administration (FHWA), the National Concrete Pavement Technology Center at Iowa State University’s Institute for Transportation, the Essroc Italcementi Group, and Lehigh Hanson, began in the fall of 2011 conducting extensive research on the environmental benefits of using concrete made with a new cement product in the construction of highways.

The cement used in the concrete was blended with photo-chemically-active titanium dioxide (TiO2) and is marketed under the trade name TX Active (supplied for this project by Essroc), which in turn is used in Lehigh Hanson's specialty cement TioCem on the West Coast and in its SmartCast Clean roof tile at Hanson Hardscapes in Canada. TiO2 is capable of reducing the environmental pollutants from vehicle exhausts. “To advance this pollution-reducing technology with TxActive in North America, Lehigh Hanson is excited to participate in this Air and Water Quality Impact research with the FHWA through the CP Tech Center,” said Lori Tiefenthaler, vice president, sustainability and marketing communications, Lehigh Hanson.

The research is intended to determine the benefits obtained from concrete paving materials made with cement blended with TX Active and to assess the overall impact of using this special concrete in highway construction projects. This work was done in combination with a Missouri Department of Transportation (MoDOT) two-lift paving demonstration project on Highway 141 in the St. Louis urban area. Two innovative applications are being studied: a photocatalytic concrete mainline pavement, and a photocatalytic pervious concrete shoulder pavement.

The mainline pavement material was applied using a two-lift paving strategy, which involved the placement of two wet-on-wet layers of concrete instead of a single, homogeneous layer. The lower, base-level layer was constructed with less expensive materials (e.g., a low cementitious-material content base lift), which was then overlaid with a thinner top wearing-course of concrete containing cement blended with TX Active, marking the first time the product has been used in pavement in the United States.

The shoulder pavement element of this research effort involves cement blended with TX Active. In this instance, the cement was used in a pervious concrete application. Together, this set of mainline and shoulder paving materials are believed to represent one of the most technically advanced and environmentally friendly concrete pavement systems ever employed. The project was constructed by St. Louis-based Fred Weber, Inc.

After several weather delays, the first pour took place at the end of October, consisting of mainline photocatalytic two-lift, measuring 24-ft. wide, 10-in. thick, and 1,500-ft. long. In the first week of November, the second pour on the third lane had the same measurements. A week later, a control section pour was done, measuring 36-ft. wide, 10-in. thick, and 1,500-ft. long; soon after, 12-ft.-wide concrete shoulders were put in place.

The final stage of the project, pervious concrete control and photocatalytic shoulders (with TX Active), were meant to have been poured immediately following the standard shoulders but had to be delayed due to weather until the spring of 2012. “The weather really pushed construction back, and we fought to get everything in yet this year,” says John Kevern, Ph.D., LEED AP, Assistant Professor of Civil Engineering, University of Missouri–Kansas City, and lead researcher, along with Dr. James Alleman of Iowa State.

When TX Active was first launched in the United States in 2008 (after launching in Europe two years earlier), Essroc promoted it directly to FHWA, an effort that eventually led to this research opportunity, according to Dan Schaffer, product manager for TX Active. “We highlighted the de-polluting activity of the product and its cost effectiveness in pavement based on the success of the technology in Europe, and before long FHWA and MoDOT were teaming up to do testing,” he explains.

Schaffer says the decision to use the dual-stage slipform for the pavement was simple, since the TX Active is triggered by sunlight and having 9-10 inches of the material would be a waste. “The base section does not contain the product, only the two inches on top,” he notes. “It was also important to make this pour happen on a busy street near downtown St. Louis, a high-pollution area, where a drop in air quality measurements could be noticed.”

Environmental impact numbers will be monitored for one year for both air and water quality, since the pervious pavement would presumably help contribute to clearer water in the area. The research monitoring is being accomplished by researchers at Iowa State and the University of Missouri–Kansas City who specialize in this area of environmental science. The test period will actually begin when Highway 141 opens up to traffic in mid-2012.

According to Schaffer, since Essroc has had several years of experience in Europe with the TX Active technology, the company was instrumental in helping set up the pours and testing regimens. "We brought in specialists from Italy to help select ideal locations for the pavement pours and define the parameters for testing," he says. "The company worked with local pavers to make sure they were certified to pour TX Active." — by Steven Prokopy