Evaluation of Cracking Performance of Bridge Decks Incorporating Nonmetallic Fibers

Abstract

The Minnesota Department of Transportation (MnDOT) identified 20 monolithic (onecourse) bridge decks, constructed between 2015 and 2018, for cracking surveys to investigate the effectiveness of nonmetallic fibers in reducing bridge deck cracking. Of the 20 monolithic decks, 13 were constructed with concrete mixtures containing nonmetallic fibers and seven without fibers. Of the bridge decks constructed with nonmetallic fibers, nine are supported by precast-prestressed concrete girders and four are supported by steel girders. Of the decks constructed without fibers, six are supported by precast-prestressed concrete girders and one is supported by steel girders. The first portion of the report (Chapters 1 through 4) presents a description of the crack survey procedures, followed by information about the decks. A comparison of the decks is then made by converting the survey results to equivalent crack densities at 36 months of age. The second portion of the report (Chapters 5 and 6) investigates the effects of paste content, fibers, and construction procedures on the cracking performance of the 20 bridge decks surveyed in this study using comparisons with the results of crack surveys of 74 other bridge deck placements, conducted in Kansas, Virginia, and Indiana. Results show that for the decks surveyed in this study, the majority of cracks that contributed to crack density had lengths greater than 1 ft and there is no apparent correlation between the use of fibers and crack width. Low cracking bridge decks require the use of concrete with a low paste content (27.1% or less), and when the paste content is 27.1% or less, there is no significant difference in the average 36-month crack densities between bridge decks with and without fibers. More generally, good construction practices are needed for low-cracking decks, and with poor construction practices, even decks with low paste content, with or without fibers, can exhibit high cracking