Page 42 - Riem-Vol6_nº3

394 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
Nonconventional concrete hollow blocks evaluation by destructive and non-destructive testing
of age, according to Brazilian standard NBR 12118 [17]. Blocks
were soaked in water at 23+5 °C during 24 h, and then, they were
weighed in saturated condition. Block’s absorption was calculated
according to equation 1.
(1) 100 .
s
s h
m
mmw 

w (%) = water absorption;
mh = block saturated mass (kg);
ms = block dried mass (kg).
2.7 Compressive strength
The test was conducted in a universal testing machine model
DL30000, with device displacement of 2 mm.min-1. The results
of the compressive strength (MPa) were obtained by dividing the
maximum load (N) by the area of section (mm2), obtaining the av-
erage of repetitions, in accordance with standard. Data were ana-
lyzed by statistical software (Statgraphics). Average comparison
was performed using the Tukey test at 5% of significance level.
3. Results and discussion
3.1 Residues characterization
Chemical composition and LOI of the residues are shown in Table
2. RHA shows high content of silica, thus corroborating the analy-
sis presented by others researchers (Krishnaro [18], Bui [19]). Po-
tassium content was low for both samples, which is a favorable
aspect, as the presence of potassium may cause problems with
alkali-aggregate reaction in the cement matrix. However, LOI for
RHA was high. According to the Brazilian standard (NBR 12653
[20]), pozzolan maximum content must be 6% of LOI.
XRD patterns of SF and RHA are presented in Figures 2 and 3,
respectively. As expected, crystalline phases were not identified
for SF, and the amorphous material is evidenced. Peaks of cristo-
balite and quartz were observed at RHA diffractogram, showing
the crystalline phases formation, probably as a consequence of
non-controlled burning. The more crystalline ashes, the lower its
reactivity (John [21]).
Table 3 and Figure 4 show the particle size distribution and par-
ticle size curve, respectively. It is observed that SF has the small-
est particles size when compared to RHA; however, RHA has
90% of its particles below 80 µm, and it presents small average
diameter. Materials with a high fineness may show high reactivity
in contact with calcium hydroxide (NBR 12118 [17]). Moreover,
employed: a control (100% of Portland cement), blocks with RHA
and blocks with SF. The percentage of replacement of Portland
cement by ashes was 10%. The ratios used in mixtures are pre-
sented in Table 1.
The materials were placed in a mixer, and after complete mixture’s
homogenization the mixture was pressed in a pneumatic machine
Permac model MB0100. The pressure of the piston was 50 MPa.
Hollow blocks were produced with dimensions of 390 x 190 x 140
mm, classified as M-15 block, according to Brazilian standard NBR
6136 [1]. The cure was performed in a laboratory environment with
temperature range of 23+5 °C.
2.5 Ultrasonic pulse velocity (UPV)
The same hollow blocks were tested by nondestructive test and
then by the destructive one. UPV was recorded once a week
during 28 days before the destructive test. An Ultrasonic Tester
Steinkamp, model BP7, with exponential transducers with a reso-
nance frequency of 45 kHz was employed. Measurements were
carried out in three directions of the blocks, height, length and
width, as showed in Figure 1.
Statistical analysis was conducted by the Statgraphics Software,
version Centurion XV.I. UPV’s data were evaluated statistically
aiming to obtain correlations with the compressive strength allow-
ing applications for the control of material quality.
2.6 Water absorption test
The blocks were subjected to the water absorption test at 28 days
Figure 1 – Directions of the measurements:
height, length and width
Table 2 – Chemical composition of RHA and SF
Na O2 MgO Al O2 3 SiO2 P O2 5 SO 3 Cl K O2 CaO MnO Fe O2 3 LOI
SF
RHA
0.17
0.09
0.37
0.37
0.08
0.19
95.2
86.8
0.12
0.66
0.28
0.09
0.21
0.03
1.22
1.67
0.48
0.65
0.04
0.21
0.10
0.09
1.68
9.12