Investigating causes and determine repair needs to mitigate falling concrete from bridge decks.

PDFTech ReportRC-1567108621Bridge decksConcrete bridgesCorrosionNondestructive testsField testsLaboratory testsSpallingFreeze thaw testsMichiganMichigan. Dept. of Transportation. Office of Research and Best PracticesGrace, NabilJensen, ElinLawrence Technological UniversityNTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and StructuresNTL-HIGHWAY/ROAD TRANSPORTATION-Construction and MaintenanceUS Transportation CollectionThis study developed a procedure to identify concrete bridge decks that are exhibiting the characteristics associatedwith falling concrete. Field exploratory work on reinforced concrete bridge decks was supported by analytical andlaboratory investigations. The field work included visual inspection, non-destructive tests, and sampling of full-depthcores and powder samples from the bottom of the bridge deck. Chief variables assessed were the chance of corrosionby the half-cell potential, chloride content at the location of the bottom reinforcement, and the concrete pH level. Thechloride diffusivity was estimated from the chloride profile. The laboratory investigation was performed on bridgedeck beams. The beams were constructed from concrete containing chloride levels known to cause corrosion as well asfrom a control concrete. Beams were subjected to freeze-thaw or saltwater followed by repeated loading to simulatefield conditions. The following characteristics were quantified: chance of corrosion, corrosion rate, chloride content,flexural response as a function of environmental exposure and repeated loads, and ultimate strength. The size of theporous zone around the reinforcement was determined using an environmental scanning electron microscope. Finally, astrategy was developed to assess if a bridge deck exhibited the characteristics associated with falling concrete. Thestrategy included visual inspection of cracking and spalling, assessment of chance of corrosion, chloride content, andpH levels. If any of these measures exceed critical levels a service life calculation needs to be performed. Based onexisting mathematical models, the time to corrosion initiation and time to corrosion cracking can be predicted. Theresulting time is then compared to the age of the bridge. From this information proper planning for future repair needscan be made