Premature Concrete Deterioration in Texas Department of Transportation Precast Elements

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Title: Premature Concrete Deterioration in Texas Department of Transportation Precast Elements

Author(s): B. L. Lawrence, J. J. Myers, and R. L. Carrasquillo

Publication: Special Publication

Volume: 177

Issue:

Appears on pages(s): 141-158

Keywords: alkali-silica reaction; calcium aluminates; cast-in-place concrete; chert; ettringite; silica; steam curing; sulfate attack

Date: 1/1/1999

Abstract:
The occurrence of premature concrete deterioration found in Texas Department of Transportation (TxDOT) precast concrete elements and other types of concrete structures found in Texas has prompted TxDOT to conduct an investigation into the cause of this deterioration. TxDOT’s investigation of 69 prestressed concrete box beams, of which 56 are exhibiting various degrees of deterioration, includes a historical documentation review, chemical analysis and petrographic examination with both optical and scanning electron microprob microscopy. The cement mill that supplied the cement for the 56 beams that are deteriorating conducted an independent investigation. An overview of both investigations is presented. The investigation conducted by TxDOT revealed distress associated with pasted expansion. Ettringite was found throughout the concrete samples in the voids, cracks, gaps around aggregate particles and concentrations or nests exclusively within the cement paste. The presence of alkali-silica reaction (ASR) was also observed but little if any distress could be conclusively attributed to the ASR. The cement manufacturer’s investigation concluded that the main cause of distress was ASR and that delayed ettringite formation occurred as a secondary mechanism most likely resulting from poor construction practices. The varying conclusions of TxDOT’s and the cement manufacturer’s investigations typify the polarization of industry nation wide if not world wide over similar case studies involving this phenomenon described herein as premature concrete deterioration. Accordingly, the conclusion of this paper addresses some of the ramifications of not attaining a resolution to this problem.