Page 140 - Riem-Vol6_nº2

311 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
D. L. ARAÚJO | A. R. DANIN | M. B. MELO | P. F. RODRIGUES
Here, fb is the average bonding stress, Fmax the pull-out load, ld the
bonding length, and φ the diameter of the steel bar.
This same conclusion can be reached when comparing the
normalized bonding stress, obtained by the relation between
the bonding stress and splitting tensile strength of the concrete
(Figure 5). In this case, a reduction of up to 45% in the normal-
ized bonding stress is noted with the addition of 2% of steel fibers,
showing that the bonding stress is not influenced by the increase
of the tensile strength of the concrete provided by these fibers. A
possible justification of this is the short length of the bonding por-
tion of the bar (50 mm) as compared to the length of the fibers (35
mm), which does not allow the mobilization of the fiber before the
pull-out of the bar.
The same behavior was observed by other researchers [8], who
found that the addition of 0.75% (60 kg/m3) of steel fibers with 35
mm length and aspect ratio equal to 64 increased by maximum
Table 2 – Properties of fresh concrete
Fiber volume
(%) Test specimen
Slump (mm) Air content (%) 3 Density (kg/m ) Slump Flow (cm)
Properties
0
1
2
CP10.5.0.A1
CP10.5.0.A2
CP10.10.0.A1
CP10.10.0.A2
CP20.10.0.A1
CP20.10.0.A2
CP10.10.0.A3
CP10.10.0.A4
CP20.10.0.A3
CP12,5.10.0.A1
CP12,5.10.0.A2
CP12,5.10.0.A3
CP16.10.0.A1
CP16.10.0.A2
CP16.10.0.A3
Average
CP10.5.1.A1
CP10.5.1.A2
CP10.10.1.A1
CP10.10.1.A2
CP10.10.1.A3
CP10.10.1.A4
CP20.10.1.A1
CP20.10.1.A2
CP20.10.1.A3
Average
CP10.5.2.A1
CP10.5.2.A2
CP10.10.2.A1
CP10.10.2.A2
CP20.10.2.A1
CP20.10.2.A2
CP10.10.2.A3
CP10.10.2.A4
CP20.10.2.A3
Average
–
–
–
–
–
185
150
175
140
163
115
70
50
85
80
2.40
1.90
1.80
1.10
1.80
1.90
1.60
1.30
1.00
1.45
1.70
1.20
1.60
0.80
1.33
2330
2332
2316
3318
2324
2396
2395
2404
2390
2396
2455
2453
2457
2455
2455
65
64
69
69
67
–
–
–
–
–
–
–
–
–
–