United States Department of Transportation
i
Improved Grouts for Bonded Tendons in Post-Tensioned Bridge Structures
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1992-01-01
[PDF-2.07 MB]
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Abstract:Currently, there is a serious problem in the United States and elsewhere with the deterioration of concrete bridges due to corrosion induced by chloride intrusion into the concrete. Historically the problem has been associated with conventionally reinforced concrete bridge structures as opposed to prestressed or post-tensioned structures. However, corrosion of steel tendons in prestressed concrete structures is of greater concern because the structural integrity of the bridge relies on the high tensile loading of the tendons. Any corrosion or corrosion-induced cracking of the tendon could lead to catastrophic failure of the structure. Grout is the final line of defense against corrosion of the steel tendon. Accordingly, FHWA initiated this study (i) to develop and test new mixture designs for grouts, (ii) to develop and perform accelerated corrosion test methods on the new grouts, and (iii) to compare the corrosion performance of the new grouts with the standard grouts. Several modifiers and additives for grouts were examined, including: high-range water-reducers, fly ash, silica fume, latex polymer modifier, expansive agents, anti-bleed additives, and corrosion inhibitors. It was shown that these additives can greatly affect the fluidity, open-time, bleeding/segregation, chloride permeability, and mechanical properties of the grouts. Several experimental grouts were designed which provided improved properties compared to the more standard grouts presently being used. An accelerated corrosion test method (ACTM) was developed which evaluates the corrosion performance of steel tendons embedded in the grout. It was shown that any experimental grout that lowered the chloride permeability, increased the time for corrosion initiation and typically decreased the corrosion rate following initiation. The examination of the effect of calcium nitrite inhibitor required a modification of the as-specified ACTM, and the addition appears to produce the most significant improvement in corrosion performance of steel tendons embedded in grout, although the data for this comparison are limited.
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