Page 44 - Riem-Vol6_nº3

396 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
Nonconventional concrete hollow blocks evaluation by destructive and non-destructive testing
CH/RHA curve shows the reactivity of this ash. It is observed
that RHA reacts slower than SF; however, RHA presented low
electrical conductivity, thus showing that it may indicate the for-
mation of CSH products. After 12 h, for both samples, it was ob-
served the electrical conductivity stabilization, with values close
to 0.5 mS.cm-1.
3.3 Ultrasonic pulse velocity (UPV)
Figures 6, 7 and 8 show the ultrasonic pulse velocity (UPV) values
across the concrete hollow blocks at three different directions, re-
spectively width, length and height.
At the width direction (Figure 6), UPV across the hollow blocks
with SF was higher than for other hollow blocks, which was
expected, as SF is commercially known as a pozzolan, which
presents high reactivity. It was observed that, as age increas-
es, there was a small UPV variation across the blocks. There
was a statistically significant difference among the UPV for all
of the blocks.
At the length direction (Figure 7), it was observed a similar be-
havior with those from Figure 6. However, control hollow blocks
and RHA-based hollow blocks showed no statistical difference be-
tween them, but both were statistically different when compared
to the SF-based hollow blocks, which showed the highest values
of UPV.
The same behavior was observed for the UPV at the height direc-
tion. UPV was higher across the SF-based hollow blocks.
RHA-based and SF-based hollow blocks present higher values of
UPV when compared to the control ones due to the “filler” physical
effect, with the filling of voids in concrete produced by the different
particles size.
Statistical analysis comparing the UPV values at 7 days among
the hollow blocks directions shows that there was a statistical
significant difference. For length and width, there is no statistical
difference; however, they showed statistical difference when com-
pared with the height direction. The same behavior was observed
when comparing UPV at 28 days. For the length and width direc-
tions, there is the effect of confinement of the wall mold, which
does not happen to the height direction.
3.4 Water absorption
According to the Brazilian standard (NBR 12118 [17]), the maxi-
mum water absorption for concrete hollow blocks must be 15%.
It is observed in Table 4 that the hollow blocks manufactured with
SF or RHA showed low water absorption, when compared to the
control ones.
If pozzolanic reaction occurs, the products reaction formed are
very effective in filling the capillary spaces, thus improving the me-
chanical strength and impermeability of the matrix (ASTM C55-11
[2]), as it was observed for the replacements tested.
Figure 6 – UPV of concrete hollow blocks
at the transverse direction (width)
0 7 14 21 28
1,8
2,0
2,2
2,4
2,6
UPV (Km/s)
Age (days)
Control
RHA
SF
Figure 7 – UPV of concrete hollow blocks
at the longitudinal direction (length)
0 7 14 21 28
1,8
2,0
2,2
2,4
2,6
UPV (Km/s)
Age (days)
Control
RHA
SF
Table 4 – Water absorption of hollow blocks
Concrete hollow blocks Water absorption (%) Standard deviation Coefficient of variation
Control
Cement/RHA
Cement/SF
11.56
8.97
8.67
–
1,81
–
–
17,22
–