Evaluation and Mitigating Measures for Premature Concrete Distress in Texas Department of Transportation Concrete Elements

摘要

Concrete for both cast-in-place and precastconstruction plays a vital role in the development of the highwayinfrastructure in Texas. Historically, Texas has enjoyed aconsistent supply of quality concrete because of the availabilityof economical and high-quality aggregates and cementiousmaterials. However, recent discoveries by the Texas Departmentof Transportation (TxDOT) of premature concrete distress inconcrete elements has raised significations concerns regardingcurrent standards and specifications for concrete materials andconstruction practices.In late 1995, 69 precast concrete box beams fabricated in SanMarcos, TX became the subject of a comrehensive concreteevaluation effort to determine the cause of premature concretedistress in 56 of the 69 beams. This was TxDOT's firstexperience with the distress mechanism referred to as delayedettringite formation. As a result of the investigation, the 56distressed beams were rendered unsuitable for use.Since the box beam case study, TxDOT has identified anumber of other structures exhibiting similar signs of distress.Four of these structures have been evaluated petrographically. Ineach case, the distress was attributed to DEF. The increase in thenumber of structures with this problem has prompted TxDOT toexpand its investigation. This includes conduction an extensivein-house research program, sponsoring a round-robininvestigation of the box beam concrete, and funding research. Asa result of the initial findings, TxDOT is presently consideringchanges to the cement, aggregate, and construction specificationsfor mitigation of this problem.This paper addresses the key elements of TxDOT's continuinginvestigation and research efforts regarding the problem ofpremature concrete distress in Texas. Emphasis is placed on thegrowing nature of the problem in Texas, technological advancesin evaluation techniques, and mitigating measures presently underconsideration by TxDOT.