Materials selection for concrete overlays : the final report Page: 11
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Figure 2.2. Steel placed directly on top of existing pavement
Fibers
Fiber incorporation can provide improved flexural ductility and toughness, fatigue
capacity, and abrasion and impact resistance [19]. The effect of fibers in concrete on
compressive strength generally varies from a negligible increase or decrease to strength gains
around 20% [20, 21]. Also, fibers can be beneficial to reduce crack development, to slow crack
growth, and to delay debonding propagation while providing residual strength in pavements that
have already cracked [22]. Fibers are usually used in thinner overlays because of their high cost.
Fibers can bridge cracks in concrete and restrain them from opening thus increasing the
load ability of the concrete overlay [23]. Fiber-reinforced concrete pavements should have a
longer service life and require less maintenance than non-reinforced concrete pavements [24].
However, some past experiences have shown that negative effects can be expected from
fiber reinforced concrete overlays. The most prevalent effect is the cost. Addition of fibers will
tremendously increase the project cost, and, sometimes it is difficult to calculate cost-to-benefits
ratio of using fibers.
Another problem is the difficulty in handling fibers during construction. Fiber balling [23]
is a phenomenon that occurs when lack of effort to disperse the fiber in concrete matrix, bunched
fibers appear in the concrete overlay surface. Fiber balling not only reduces benefits from using
the fibers, but also, creates weak spots in concrete overlays.
Proper handling of fibers is required to increase performance in concrete overlays.
Increase in fiber dosage can lead to significant decrease in compressive and flexural strength.
However, without proper dispersion of fibers, the crack bridging benefits cannot be expected.
Polypropylene microfibers are produced either as cylindrical monofilaments or fine
fibrils with a rectangular cross section. Polypropylene microfibers can be in monofilament,
multifilament, or fibrillated form (Figure 2.3).11
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Kim, Dong H.; Fowler, David W.; Ferron, Raissa P.; Trevino, Manuel M. & Whitney, David P. Materials selection for concrete overlays : the final report, report, July 2012; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth303706/m1/31/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.