Materials selection for concrete overlays : the final report Page: 12
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Figure 2.3. Different forms of polypropylene fibers
Microfibers are effective in controlling plastic shrinkage and settlement cracking. The
fibrillation process greatly enhances the bonding between the concrete and the polypropylene
fibers and can provide residual strength in pavement that has already cracked [6].
Polypropylene macrofibers are coarse fibers that allow greater surface area contact within
the concrete, resulting in increased interfacial bonding and flexural toughness. Polypropylene
macrofibers can be used as secondary reinforcement and can provide greater post-crack strength
and concrete slab capacity. Additional benefits include improved impact, abrasion, and shatter
resistance.
Polyester fibers are available only in monofilament form. They commonly have
relatively low fiber content and are used to control plastic shrinkage-induced cracking. Synthetic
fibers do not absorb water and therefore do not affect the mixing requirements.
Steel fibers are primarily made of carbon steel, although stainless steel fibers are also
manufactured. Perhaps the biggest advantage of steel fibers is their high tensile strength and
their ability to bridge joints and cracks to provide tighter aggregate interlock, resulting in
increased load-carrying capacity. Steel fiber reinforced pavements exhibit excellent toughness
and pre- and post-crack capacity [19].
The aspect ratio is an important parameter influencing the bond between the concrete and
the fiber, with longer fibers providing greater bond strength and toughness, often at the expense
of workability. Steel fibers may also have certain geometric features to enhance pullout or
anchorage within the concrete mixture. These features may include crimped or hooked ends or
surface deformations and irregularities (Figure 2.4).12
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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/m1/32/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.