Page 45 - Riem-Vol6_nº3

397 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
M.S. RODRIGUES | G.C.S. FERREIRA | L. SHIROMA | A.L. BERALDO
3.5 Compressive strength of concrete hollow blocks
As expected, the compressive strength of the SF-based hollow
blocks was higher than the other ones (Figure 9). However, statisti-
cal analysis showed no statistically difference among the compres-
sive strength of the hollow blocks from the three different mixtures
employed (control, cement/SF, cement/RHA). Therefore, accord-
ing to this test, it is possible to produce hollow blocks with partial
replacement of Portland cement by RHA, without decreasing com-
pressive strength.
Based on the results of physical and mechanical tests, it was
observed that, in addition to the residues acting as pozzolans,
they may also perform as fillers, thus contributing to lower wa-
ter absorption and, therefore, increasing the durability of the
hollow blocks.
3.6 Correlation between UPV and compressive
strength
In order to obtain a correlation between UPV and compressive
strength, a simple regression was performed. UPV data are re-
lated to height direction that was also considered for destructive
test. The software used for regression analysis was Statgraphics.
Despite a positive tendency of the compressive strength
with respect to the UPV, the determination coefficient was
only 0.38, thus denoting a small dependence of the vari-
ables. The linear model presented by the software is pre-
sented by equation 2.
(2) UPV Rc    2177 ,2 1571 ,1
Rc = compressive strength (MPa);
UPV = ultrasonic pulse velocity (km.s-1)
4. Conclusions
The characterization of RHA showed high content of silica, low
content of potassium and high fineness, thus denoting its reactiv-
ity. However, this ash presents high LOI content, and XRD showed
a crystalline material with peaks of cristobalite and quartz. The
pozzolanic assessment of RHA showed pozzolanic reactivity when
evaluated by electrical conductivity in a CH /ash solution.
Non-destructive evaluation of the concrete hollow blocks showed
that the highest values ​of UPV were obtained across the SF-based
hollow blocks for three different directions. Statistical analysis
showed that, for length and height directions, the UPV for these
hollow blocks presents statistically significant difference when
compared to the others ones. RHA-based hollow blocks and SF-
based hollow blocks presented lower water absorption when com-
pared to the control ones.
Despite SF-based hollow blocks showing the highest values ​of
compressive strength, statistical analysis showed no statistically
significant difference among the types of hollow blocks. Data cor-
relation between UPV and compressive strength showed a small
determination coefficient (0.38).
5. References
[01] Brazilian Technical Standard Association – Rio de
Janeiro. NBR 6136 –Hollow concrete blocks for
concrete masonry. Rio de Janeiro, Brazil, 2006.
[02] American Society for Testing and Materials – C55-11,
Standard Specification for Concrete Building Brick.
2011.
[03] BS 6073/81 – Part 1 – Precast concrete masonry
units – Specification for precast for concrete masonary
units, 2011.
[04] Prassianakis, I.N.; Prassianakis, N.I. Ultrasonic
testing of non-metallic materials: concrete and marble.
Theoretical and Applied Fracture Mechanics.
Amsterdam, 42 (2004) 191-198.
Figure 8 – UPV of concrete hollow blocks
at the perpendicular direction (height)
0 7 14 21 28
1,8
2,0
2,2
2,4
2,6
UPV (Km/s)
Age (days)
Control
RHA
SF
Figure 9 – Compressive strength of blocks