Lessons Learned from Bridge Repair with Steel Fiber-Reinforced Shotcrete and Overlays

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Title: Lessons Learned from Bridge Repair with Steel Fiber-Reinforced Shotcrete and Overlays

Author(s): J. Wong and P. D. Carter

Publication: Special Publication

Volume: 268

Issue:

Appears on pages(s): 139-154

Keywords: corrosion protection; high-performance concrete; overlays; repair cracking; shotcrete; steel fiber-reinforced concrete.

Date: 3/1/2010

Abstract:
The use of steel fiber-reinforced, silica-fume-modified concrete overlays and shotcrete for bridge repairs has long been the standard for Alberta Transportation (AT). Approximately 200 provincial bridges have been repaired with steel fiber reinforced, silica-fume-modified materials since 1984, mostly to decks, which had been exposed to aggressive conditions including freezing and thawing, de-icing salts, and moisture. The purpose of using steel fiber in bridge concrete repair materials was primarily to prevent or reduce repair cracks and to improve durability. Standard fiber lengths were 25 mm (1 in.) for shotcrete and 50 mm (2 in.) for overlays with standard fiber dosages of 60 km/m3 (100 pounds/yd3). Most of the repairs were done with superplasticized, silica-fume-modified, low water-cement ratio concrete mixes. This paper reports on the early historical development of the repair method basics and the lessons learned from monitoring bridge repairs. Conclusions are presented from AT’s Level 1 and Level 2 inspection data. Level 2 data quantifies several repair performance indicators, such as wide cracks, stains, delamination, spalls, patches, and debonds, as well as a breakdown of numerical condition ratings on important bridge elements. Crack data from Level 2 inspections was available from 154 silica fume modified bridge deck overlays, 124 of which contained steel fiber. The crack data was analyzed to assess the performance of fibers in reducing the amount of easily visible cracks: those wider than 0.3 mm (0.012 in.). The results showed that the steel fibers resulted in significant crack reduction and improved overlay durability and service life.