Page 28 - Riem-Vol6_nº2

199 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
R. MASCOLO | A. B. MASUERO | D. C. C. DAL MOLIN
central portion of the discharge (midpoint), according standards
recommendations, as reference for representing the variation be-
tween the collection points of every batch. Thus there has been
shown the percentage differences of points 1, 2, 4 and 5 in relation
to the center point.
From the comparative shown in Figures 2 to 4 it is observed the
absence of a specific profile that can represent the variation of the
compressive strength along the discharge of ready mix concrete.
There are profiles constants, with less than 2% difference between
the points, and other profiles with high percentages of variation of
approximately 10% along the five sampled points.
In table 2 is showed a summary, with the percentage of occur-
rences of variation of compressive strength of each point relative
to midpoint, where it can be seen that over 85% of cases are con-
centrated in the zone of ± 5% from the central point. It is also pos-
sible to note that there is a tendency of values ​​greater than the
resistance to P3.
Based on these results of compressive strength is not possible to
affirm that the samples collected as recommended by NBR 7212
[9] and NM33 NBR [10], which exclude 15% initial and final of the
total volume of concrete-mixer for testing purposes, have the best
representation of the concrete, since this points do not always
present the greatest resistance of batch.
Considering the recommendation of ABECE [14] where the resis-
tance variation should not differ more than 15% compared to the
central point, the lots analyzed fully satisfy this criterion.
It is possible see in Figures 2-4 that there is a tendency to reduce
the consistency along the 5 points for each batch of samples,
which is more explicit when viewing the summary of variations
in the consistency of each point relative to the central, as shown
in table 3.
From the data of Table 3 is perceived that the variations in con-
sistency between points are more concentrated in the region
Figure 4 – Profile of variations in compressive strength, consistency and coarse aggregate content - lots 9 to 13
* P1 to P5 correspond to collection points within each batch
* The percent variation of compression strength are given from potential resistance of each sampling point relative to the central point (P3),
taking as the reference.
Table 2 – Summary of percentage of occurrence
of the compressive strength of each point relative
to point P3
Zone P1 P2 P3 P4 P5
<-10% 0% 0% - 0% 0%
-5-10% 8% 0% - 0% 0%
até -5% 38% 31% - 38% 31%
até 5% 46% 69% - 54% 62%
5 a 10% 8% 0% - 8% 8%
>10% 0% 0% - 0% 0%