Literature Survey on Shear in FRC Beams - On Shear Behavior of Structural Elements Made of Steel Fiber Reinforced Concrete - page 40

3.14.2 Manufacturing of HCS Made with FRC

Adding bers are

added before any free water. However, to use this type of concrete to produce
Hollow Core Slabs (HCS) by extrusion it would be necessary to make the concrete
mix slightly wetter [ 101 ].
ACI Committee 544 [ 102 ] and JCI [ 103 ] recommended that

bers in a concrete mix with zero slump concrete is possible if

bers should be
added to the concrete mix as the nal component after all other ingredients have
been introduced. However, with this mixing procedure

bers remained together.

Therefore, Paine [ 101 ] proposed to add nally the water. With this method no

balling of bers.

Initially, in 1996, Peaston and Paine FRC was performed with the extrusion
machine with no apparent dif

bers occurred due to the scouring action of aggregates on the

culties but, it was detected a lack of compaction on
the top surface of the HCS [ 101 , 104 ]. Some years ago, in 1999, Peaston et al. [ 104 ]
ensured that extruded HCS with FRC could be practicable but it was detected that
the ber orientation was not random and was strongly in fl uenced by the extrusion

process.
Recently, Cuenca and Serna [ 105 , 106 ] has ensured that it is possible to produce

ber-reinforced concrete Hollow Core Slabs (HCS) without encountering technical
problems.

3.14.3 Advantages of Adding Fibers into Concrete Mix
for HCS Production

Fibers considerably improve the shear strength of HCS and also help to maintain
strength after shear cracking giving more ductile shear failures. Fibers may also
improve the bond between strand and concrete resulting in greater dowel resistance
to shear. This is a key advantage given the impossibility of placing transverse
reinforcements on HCSs [ 101 , 105 , 106 ]. Fibers improve mechanical behavior of
the concrete giving a solution to overcome shear failure since bers are capable of

increasing element strength to its full fl exural capacity, thus attenuating Kani ' s

valley [ 105 , 106 ].

3.14.4 Shear Behavior of HCS

The shear failures were abrupt, brittle and occurred with little or no warning. As a/d
increased the explosiveness of the failure increased. Figure 3.14 compares the
failure mechanisms of the slabs, showing how a tendency for fl exural-type failures

increased with a/d and ber volume [ 101 ].