Reinforcing concrete to keep it from
cracking is nothing new --even
the earliest civilizations used natural fibers
to inhibit cracking in masonry structures. Today, synthetic-fiber reinforcement
is available to reinforce non-structural concrete applications with superior
results. Currently, the most widely-accepted form of reinforcement is
welded-wire fabric (WWF), a mesh of steel wires, steel fibers, polymeric nets
and polymeric fibers that are placed in concrete. However, synthetic-fiber
reinforcement avoids the increased labor costs and difficulty in placement.
Synthetic-fiber reinforcement prevents cracks in concrete, small-diameter
synthetic fibers (nylon, glass, steel or polypropylene) are now being added to
concrete to reduce shrinkage cracking by more than 80% according to independent
lab tests. Reducing cracks improves concrete impermeability, increases its
toughness and long-term weather ability, and can reduce callbacks in concrete
slab floors, decks, driveways, and walks. The placement, curing, or finish
characteristics of the concrete are not affected by the addition of fibrous
reinforcement. Larger-diameter synthetic fibers (steel or polyolefin), added at
higher content by volume (0.5% to 1.5% respectively), also enhance hardened
flexural strength, but at increased cost. Fibrous reinforcement is primarily
used to reduce cracking in non-structural concrete applications.
However, steel fibers rust and can cause surface discoloration. Adding fibers
to the concrete during mixing can add to the cost of concrete, but avoids the
labor cost and time to place reinforcing steel. Fibrous concrete reinforcement
reduces concrete cracking and permeability, and increases strength, impact
resistance, and durability of concrete non-structural slabs. This research
studies the effect of using steel fibers and polypropylene fibers in
reinforcing prisms (100x100x400) mm, and slabs (500x500x50) mm for testing
drying shrinkage and drop ball impact loading, then compare results with plain
concrete. Test results indicated that the presence of synthetic fibers enhance
significantly the shrinkage and impact resistance properties.