In the construction business, doing something right the first time saves money over the long term. Over the last 50 years, pressure from contractors for faster-setting concrete has lead to incremental compromises in quality. In 1995, R. L. Blaine published his 1994 survey of 387 North American cements. Compared to Blaine’s similar 1954 survey, there has been a great increase in the early strength—this is bad, because greater early strength increases the risk of cracking.

After writing more than 30 concrete-related papers based on 50 years of experience in the business, I know the subject well. Which is why, when T-REX was approved back in 2001, I took a keen interest in their concrete specifications. Concerned about the use of fast-setting concrete, I wrote a letter to Gov. Bill Owens warning him that the 16 new bridges of the 1.6-billion-dollar T-REX project would have a cracking problem unless a slow-hydrating Portland cement was used. My letter was answered two months later by a Colorado Department of Transportation materials engineer who explained that the risk of cracking would be controlled by adding fly ash to the concrete mixture. On July 30, 2002, Franklin St. Bridge was the first T-REX bridge to open—within three months, it developed 260 cracks even though 15 and 20 percent fly ash was used and the concrete was placed at night.

In Sept. of 2002, Sen. Ben Nighthorse Campbell sent a letter at my behest to Norman Mineta, Secretary of Transportation, warning of the cracking risk to the remaining bridges. In Nov., the letter was answered by the associate administrator for infrastructure, Federal Highway Administration, who said that the cracking problem was related to a design problem, not the cement. They reduced the spacing of the construction joints in the sidewalk from nine feet to four feet. The barriers, which previously had no construction joints, were redesigned with joints spaced at four feet.

Now, as I write these words in April, 2007, it is obvious to all that these corrective measures did not work. All 16 bridges are currently cracked. I firmly believe the problem was the cement, not the design: The sidewalk cracks in the Washington St. Bridge are worse than the cracks in the sidewalks of the Franklin St. Bridge, which had to be removed and replaced; the four-foot barrier sections have cracked; the pillars show crazing from drying shrinkage and have been camouflaged with grey paint; and many decks are cracked.

My solution to this problem is a more crack-resistant cement, such as was used in the 1950s when CDOT built 232 bridges. The 149 bridges that remain in their original state have withstood the test of time—none are cracked. And a solution like this could be adopted—the cement committee for the American Society for Testing and Materials International (ASTM) may approve a new and more crack-resistant cement to be called Type VI. The proposed new cement has a maximum limit of 3200 psi on the 7-day strength. In 2003, only 45 percent of the 75-member committee voted for Type VI cement. But in 2004 the count was 61 percent affirmative, and in 2005, 78 percent were in favor. There are nine remaining negative voters and each one must be voted as non-persuasive by a two-thirds margin for the cement to be approved. The cracking of the T-REX bridges has significantly strengthened the case for the proposed Type VI cement, so while it has been costly for our region, it may be good for the national interest. Perhaps the best news is that the Federal Highway Administration has reversed its position and is now supporting the effort for a more crack-resistant Portland cement.

For more information, please contact Dick Burrows at Burrows340@aol.com

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