Civil Engineering Reference
In-Depth Information
same angle a, as the ribs on the bar. The radial component of this compressive
force is offset by a tensile ring that appears in the concrete surrounding the
bar, generating internal longitudinal cracks. in the absence of transverse
reinforcement, these cracks grow outward through the entire cover, causing
brittle or splitting failure at the concrete surface. if the concrete is well
confined by the transverse reinforcement, however, failure occurs because
the bar breaks away from the surrounding concrete. The result is pull-out
failure (see Fig. 17.11).
Fernández-Jiménez
and Palomo
(2009) also compared bonding in alkali-
activated fly ash concrete to bonding in portland cement concretes (see Fig.
17.11). Some of the findings are given in Table 17.3. In the alkali-activated
fly ash concrete (H-FA-N and H-FA-W), failure occurred in the matrix,
whereas in oPc concrete (H-ce-a), pull-out failure was observed.
(a)
(b)
(c)
17.11
(a) Apparatus used in the pull-out test; (b) fly ash concrete
activated with NaOH + Na
2
SiO
3
, in which the matrix failed; and (c)
fly ash concrete activated with NaOH, in which the 16-mm diameter
steel bar failed (Fernández-Jiménez and Palomo, 2009).
