The Phase I report identified materials combinations that were to be explored in Phases II and III. Phase II is ongoing through March 2011 and is evaluating cementitious materials combinations that will perform well in different environmental and climatic conditions. Phase II is focused on concrete mixtures that have the right properties in both the construction and hardened phases in cold weather, hot weather, freeze-thaw cycle conditions, and where road salts and corrosion may be factors in the life cycle of the concrete elements.
Phase III, started in June 2009, continues into June 2011 with field applications of ternary mixes in Utah pavements, Pennsylvania bridge decks, and potentially other applications in New Hampshire, Illinois, Mississippi, California, Iowa, Kansas and Wisconsin.
The complete Phase I report can be downloaded at http://www.intrans.iastate.edu/reports/ternary_mixes_phase1.pdf and a PowerPoint presentation from October 2009 on Phase I by Dr. Paul J. Tikalsky, P.E., chair and professor, Department of Civil and Environmental Engineering, University of Utah, may be downloaded at www.cptechcenter.org/t2/documents/03Tikalsky-TernaryMixes.pdf
Ternary Blends and Sawing
An earlier CP Tech Center study, Crack Development in Ternary Mix Concrete Utilizing Various Saw Depths, was funded by the Iowa Highway Research Board and was released in 2009.
Early entry sawing, which uses a lightweight machine to apply earlier and shallower cuts than conventional sawing, is believed to increase sawing productivity and reduce costs, the report says. But some early entry saw joints in Iowa have experienced delayed cracking, including delays of weeks or months after sawing.
“An urgent concern is whether early entry sawing could lead to late-age random cracking,” the report says. “This study was designed to investigate whether delayed random cracking may occur in pavements constructed using early entry sawing.”
Because cracking is related to stress development in concrete, the specific objective was to examine the stress levels that develop at pavements’ early entry sawing joints. The study found:
l Although most joints made using the early entry sawing method cracked later than the joints made with conventional sawing, all 30 joints examined in this study cracked within 25 days after paving.
l No random cracking was observed in the test section two months after construction.
l The average joint cracking time for early entry sawing was 12.3 days. The average joint cracking time for the joints made with the conventional sawing method was 2.2 days.
With the results of this study, agencies and the paving industry can identify potential late-age random cracking problems in pavements constructed with early entry sawing. Download the study at www.intrans.iastate.edu/reports/sawing.pdf
Ultra-High Performance Concrete
New concretes with high percentages of cement and silica fume, low water/cement ratios, and including steel fiber reinforcement, are being investigated by the FHWA.
Compressive strength in these new concretes is more than seven times that of conventional concrete, while tensile cracking strength is three times greater, FHWA reports. This emerging technology, known as Ultra-High Performance concrete (UHPC), has the potential to significantly impact the U.S. highway system.
Challenges remain, however, limiting widespread implementation of projects using this new technology, FHWA said in 2009. Among them are the lack of design code provisions, inadequate industry familiarity with the product, and high initial costs. “Addressing these issues will require significant knowledge transfer, industry support and buy-in, and greater reliance on life cycle costing,” FHWA says.
The first UHPC I-girder bridge opened to traffic in 2006 was the Mars Hill Bridge in Wapello County, Iowa. A second UHPC superstructure bridge opened to traffic in October 2008: the Cat Point Creek Bridge in Richmond County, Va. Also, a UHPC-decked girder bridge that opened to traffic in November 2008 was the Jakman Park Bridge in Buchanan County, Iowa.
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