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Curing of concrete bridge decks requires saturated burlap for 7 days.
Pennsylvania's Experience with HPC Bridge Decks
Patricia Miller, Pennsylvania Department of TransportationIn October 2000, the Pennsylvania Department of Transportation (PennDOT) started its research and development of a high performance concrete (HPC) specification for bridge decks. This research was done in conjunction with the Pennsylvania Transportation Institute (PTI) at the Pennsylvania State University. Currently four out of the eleven Engineering Districts of PennDOT are using some aspect of the HPC concept for bridge decks. This article contains a timeline of events leading to our current status.
In 2001 and 2002, a PennDOT concrete mix for HPC bridge decks was developed. This mix had a water-cement ratio of 0.43, a design strength of 4000 psi (28 MPa), and an air content for the freshly mixed concrete of 6%.
In 2002 and 2003, several bridge decks were constructed using this concrete mix. During this time, 25 full-scale concrete mixes were produced and a full battery of tests was performed on them to determine the mixtures' workability, durability, and other parameters that would impact the long-term performance of the concrete. A Best Engineering Practices Guide for bridge decks was also developed. It included engineering guidelines and design aids on the following concrete properties: compressive strength, strength development, chloride penetration, shrinkage, alkali-silica reaction, freezing and thawing durability, scaling resistance, modulus of elasticity, creep coefficient, and tensile strength. Engineering long-life concrete highway structures was also included in the guide.
During 2004, PennDOT’s specifications book (Publication 408) was revised to include the best practices as identified through the research at that time. Some of the revisions were as follows:
As part of the research done by PennDOT and PTI, 10 bridges were constructed on I-99 during the 2005 and 2006 construction season. Each bridge was instrumented with temperature sensors, strain gages, and grounding clamps for half-cell potential measurements. Instrumentation was placed on the girders, inside the deck, and in locations surrounding the deck. These instruments were used to monitor the short- and long-term performance of the bridge decks. A weather station was used to document ambient conditions. Construction of these decks was monitored and multiple early age deck condition surveys were conducted.
Between 2001 and 2007, 21 bridges, including the 10 on I-99, were constructed with HPC decks throughout Pennsylvania. Information and data collected from these bridge decks and future decks will be analyzed. These data and other industry data will be used to modify the existing HPC bridge deck specification. Some of the changes that are being considered are:
For more information about PennDOT's experiences, see HPC Bridge Views Issue No. 45 or contact the author at email@example.com.
HPC Bridge Views, Issue 56, July/Aug 2009