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Concrete for both cast-in-place and precast construction plays a vital role in the development of the highway infrastructure in Texas. Historically, Texas has enjoyed a consistent supply of quality concrete because of the availability of economical and high-quality aggregates and cementious materials. However, recent discoveries by the Texas Department of Transportation (TxDOT) of premature concrete distress in concrete elements has raised significant concerns regarding current standards and specifications for concrete materials and construction practices.
In late 1995, 69 precast concrete box beams fabricated in San Marcos, TX became the subject of a comprehensive concrete evaluation effort to determine the cause of premature concrete distress in 56 of the 69 beams. This was TxDOT's first experience with the distress mechanism referred to as delayed ettringite formation. As a result of the investigation, the 56 distressed beams were rendered unsuitable for use.
Since the box beam case study, TxDOT has identified a number of other structures exhibiting similar signs of distress. Four of these structures have been evaluated petrographically. In each case, the distress was attributed to DEF. The increase in the number of structures with this problem has prompted TxDOT to expand its investigation. This includes conducting an extensive in-house research program, sponsoring a round-robin investigation of the box beam concrete, and funding research. As a result of the initial findings, TxDOT is presently considering changes to the cement, aggregate, and construction specifications for mitigation of this problem.
This paper addresses the key elements of TxDOT's continuing investigation and research efforts regarding the problem of premature concrete distress in Texas. Emphasis is placed on the growing nature of the problem in Texas, technological advances in evaluation techniques, and mitigating measures presently under consideration by TxDOT.
Precast concrete fabrication engineer, Texas Department of Transportation, Materials and Tests Division, Austin, TX
Associate research engineer, Texas Transportation Institute, Texas A&M University, College Station, TX
Professor of civil engineering, Construction Materials Research Group, University of Texas at Austin, Austin, TX
Associate research scientist, Department of Geology and Geophysics Electron Microprobe Lab, Texas and A&M University, College Station, TX
Stock #: CCA10511J