A Survey to Determine the Impact of Changes in Specifications and Construction Practices on the Performance of Concrete in Bridge Decks

About the report:

In response to its own research and observations in the early 1960's the Virginia Department of Highways mounted an intensive and extensive effort to improve the performance of concrete in bridge decks. Major elements of this effort included (1) a training and certification program for Department and industry personnel and (2) improved and upgraded specifications for both materials and construction practices. In 1972 a survey was made of 129 randomly selected bridges constructed after 1966, when all the improvements had been formally instituted. The performance of these bridges was compared with that of a similar sample that had been surveyed in 1961. In addition to the visual observation of performance measurements of electrical corrosion potentials and depth of concrete cover, were made in the 1972 survey. Based upon this survey the following conclusions and recommendations were drawn: (1) The frequency of early bridge deck scaling has been dramatically reduced by the upgrading of specification requirements and construction practices. Several specific changes such as increased air contents, use of linseed oil treatments as well as increased awareness of the problem all contribute to this improvement. Because concrete susceptible to scaling usually exhibits the defect at an early age this is an encouraging result The elimination of scaling was a major target of the specification upgrading effort. The success of this effort is evident. (2) Transverse and random cracking are indicated to be more frequent than before the upgrading. The reason for the increase in transverse cracking is not apparent and there is other evidence that the indicated increase in random cracking is related to closer observation and differences in classifications rather than to real causes. The severity of cracking does not seem serious enough to warrant attention. Real differences if any will become more apparent with time. (3) The frequency of all other defects is very low. Based upon previous studies this will undoubtedly increase with age, traffic, etc., but experience suggests that serious problems are indicated at comparatively early ages. (4) The measured average cover over reinforcement is fortunately significantly greater than that specified. For the two levels of cover specified, 8 and 16 percent of the measurements are less than required. This is believed to reflect an acceptable level of control. (5) Ninety-five percent of the spans have average corrosion potentials below 0.20 volt which indicates no active corrosion. On one percent of the spans the average values are above 0.40 volt which suggests the presence of active corrosion. The potential for corrosion will increase with age and exposure to deicing chemicals.

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