Fort Pitt Bridge
We were selected as the concrete suppler for two major reconstruction projects of the Fort Pitt Bridge, a major artery into the City of Pittsburgh.
The first phase was the temporary patching of the bridge deck prior to total reconstruction of the bridge. This aspect of the job allowed us to pioneer the AAA Accelerated mix design. The district engineer approached us about developing a mix design that would attain the minimum f’c of 4500 psi in 24 hours. This was a very unique design prior to this job. The key point was that PennDOT would issue a contract to remove and replace specific sections of the bridge deck on Friday night starting at 6:00PM and would have to reopen the deck at 6:00AM Monday morning.
The liquidated damages were approximately $30,000 / hour for every hour after 6:00AM that the bridge was not opened. We developed the mix design and utilized heat signature and maturity data as a part of the quality assurance for the concrete being placed. As it turned out, we were able to attain the required 4500 psi in less than 24 hours, averaging in the 18 hour time frame.
The second phase, several years later, was the total reconstruction of the bridge. We provided thousands of yards of bridge deck concrete. In an effort to help elongate the concrete life cycle, we utilized specific percentages of Supplementary Cementitious Materials (SCM) in order to help reduce the potential of concrete cracking and elongate the strength development in the concrete. The concrete was specifically optimized with the cementitious replacements as well as the particle size distribution of the aggregate. In combination we were able to reduce the shrinking potential of the concrete. This specific type of concrete was later implemented on a state wide level, known today as AAAP Bridge Deck concrete.