ZEMCH 2015 - International Conference Proceedings | Page 782

Experimental results
For each realized mixture fresh and hardened tests were performed. In particular, workability
tests and entrapped air as well as density measurements were carried out in the fresh state. Compressive tests were also executed on the hardened concrete.
Fresh properties
Workability is generally described as the amount of internal work required to fully compact the
wet concrete without reducing its quality. The most common test for the measurement of this
property is the slump test (UNI EN 12350 2003). However, considering steel fibre reinforced concrete, this test is not considered the most appropriate for quantitative measures of workability
(ACI 544.2R 1989). For that reason slump measurement has been used as a quality control test to
monitor the concrete consistency from batch to batch. Although the slump test does not directly
measure the work required to compact the concrete, it gives good indications on the workability
in terms of comparison between concrete mixes and, above all, is simple to perform. A minimum
of two slump tests were performed on the fresh concrete for each mixture. According to (UNI EN
206-1 2006), the class of consistency for each average slump values (mean value of two data) was
identified. The percentage of entrapped air in the concrete sample was measured according to
(UNI EN 12350 2003) as well as the fresh concrete density. The fresh properties of each concrete are
resumed in Tab.2.

Table 2: Fresh properties
Slump

Fluidity

Air

Density

[mm]

grade

[%]

[kg/m3]

PC

190

S4

3.2

2387

ISFC

170

S4

3.0

2399

RSFC

200

S4

2.7

2416

Hardened properties
As reported in (ACI 544.2R 1989), the presence of fibres alters the mode of failure of the specimens by making the concrete less brittle. Fibres usually have only a minor effect on compressive
strength. After a minimum curing period of 28 days, all the tests were performed according to the
(UNI EN 12390 2003). The experimental compression strength (Rc) and corresponding coefficient
of variation (C.O.V.) of the realized concrete are summarized in Table 3,
Table 3: Hardened properties
Rc

Density

[MPa]

[kg/m3]

PC

43.6 (±0.2)

2408

ISFC

48.8 (±0.8)

2400

RSFC

47.8 (±0.3)

2393

It can be observed that compressive strength for reinforced concrete specimens is slightly higher
than that found for the control mix, while closer values were found for both recycled and industrial steel fibres. However, as found in (ACI 544.2R 1989; CNR-DT 204/2006 2007; Model Code 2010)
and in the available literature (Olivito et al. 2010; Buratti et al. 2011), it can be concluded that the
presence of fibres have only a minor effect on compressive strength of the reinforced concrete.

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ZEMCH 2015 | International Conference | Bari - Lecce, Italy