Experimental Tests on Hollow Core Slabs Made with FRC - On Shear Behavior of Structural Elements Made of Steel Fiber Reinforced Concrete - page 122

Table 7.3 Concrete mechanical properties
Series Concrete f c (MPa) f R1 (MPa) f R2 (MPa) f R3 (MPa) f R4 (MPa)

I TC 54.2 - - - -

FRC-50 50.4 2.75 2.85 2.83 2.66

II TC 43.8

- - - -

FRC-50 38.2 4.25 4.66 4.70 4.37

FRC-70 35.9 5.74 6.03 5.80 5.47

Average values

bers was used in the daily HCS production in the precast
industry that provided the FRC elements. Mechanical properties were controlled in
one concrete sample by means of the compressive strength test on 150

Concrete without

×

300 mm

cylinders (EN 12390-3) and the fl exural tensile strength test (EN 14651). The latter

were obtained with the exural tensile strength (f R,j ),

which corresponds to the crack mouth opening displacements (CMOD) linked to
the crack openings of 0.5, 1.5, 2.5 and 3.5 mm (j = 1, 2, 3, 4 respectively).
Table 7.3 provides the mechanical properties of the different concrete mixes. All
the values were obtained as an average of three specimens made with two different
samples for each concrete type, 28 days after casting. As it can be observed in
Table 7.3 there is a big difference between the results of same types of concrete,
probably because of different casting conditions and very different external tem-
peratures as Series I and Series II were produced in different seasons. Also, it is very
important to know that the concrete was made in a precast plant during its normal
cycle of production and some little details could be changed to adapt the concretes
of our Series to the needs of the company.

fl exural test: the residual fl

7.2.3 HCS Production

A continuous slab was casted. It occupied a complete lane in which prestressed
strands were positioned; the machine received the concrete and HCS were formed
by extrusion (Fig. 7.2 ).
As expected [ 2 ], some problems initially occurred when a new concrete type was
produced. The initial problems were related with the introduction of

bers into a
very dry concrete mix to obtain an optimum concrete ready to use in the extrusion
process. Yet after the preliminary adjustments in the process, these problems no
longer appeared and a good surface aspect was achieved (Fig. 7.3 ). This fact
demonstrates that it is possible to produce FRC Hollow Core Slabs in a normal
daily production cycle of a precast plant.
Only some slabs had an undulated surface, webs of different widths and defects
on the slab surface, which were created in some zones where

bers blocked the

extrusion machine. These stretches were thrown away.