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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
J. J. L. Tenório | P. C. C. Gomes | C. C. Rodrigues | T. F. F. de Alencar
[25]. The higher water absorption of recycled aggregates was in-
fluenced by the presence of constituents red aggregate, which also
they influenced the specific mass.
In the figure 2, the content of fine and powdered materials is ob-
served to be higher in recycled sand, however, the recycled sand
demonstrated to be thicker than river sand, and could fit in the
grading zone used for natural fine aggregate. In figure 4, the recy-
cled coarse aggregates (G1 and G2) are observed to have similar
granulometries and which do not fit in granulometric zones of the
standard.
3.2 Compressive strength
Figure 5 shows the average of the results for the compressive
strength tests (fc) in samples.
In figure 5, it is possible to notice how the concrete, independent
of the aggregate type and specific mass of the recycled coarse ag-
gregate, obey the Abrams law, i.e., a higher w/c ratio corresponds
to a lower compressive strength, and in general, the RAC showed
compressive strength near the reference concrete. The accentu-
ated reductions of the strengths become evident to the negative
influence of the recycled aggregate G1, CDW origin and lower
specific mass, on the compressive strength of the concrete. The
strength values which were equaled or overcame the strengths of
the reference concrete were of the concrete with recycled G2 ag-
gregate, mixing G1 with CW, with larger density. In general, the
recycled aggregate concrete with larger specific mass (G2) had
compressive strength greater than those of concrete with recycled
aggregates of lower specific mass. And when w/c = 0.40 and 0.67,
the compressive strength of these concretes is also higher than
those of the concrete with natural aggregates.
The strengths of 19.0 MPa < fc < 23.5 MPa of the RAC with w/c =
0.67 were similar to the reference concrete. This displays that the
recycled aggregate and its characteristics (composition and specific
mass) were not the decisive factors for the strength, but the high
w/c ratio, which did with that the paste and the transition zone gov-
erned the strength. According to NEVILLE [26], the paste becomes
a more and more limiting factor of the strength with the increase
of the w/c ratio, which was also verified by CARRIJO [10]. Another
justification is that the recycled aggregate could have absorbed part
of the water mixture, reducing the effective of the w/c ratio of the
concrete and increasing its strengths. LEITE [27] and VIEIRA [28]
also observed that behavior to high w/c ratio. Whereas for concrete
with w/c = 0.50 and the strength of 28.0 MPa < fc < 33.0 MPa, RAC
showed values of lower strength than the reference concrete, in this
case, the recycled aggregate can be considered to be the limiting
factor to the strength. For concretes with w/c = 0.40 and strength in
the range 33.5 MPa < fc < 45.0 MPa, the influence of the aggregate
type in the strength of the concretes is more evident. The concrete
Figure � � �he �oncrete's compressive strength
Ta�le � � ��pt�re aspect of the recycled aggregates
Concrete
Type of recycled aggregates that appeared in the specimens
67MRG1
Non-rock grains + rock and non-rock grains detached
67MRG2
Non-rock grains + rock grains detached
67MNG1
Non rock grains
67MNG2
Non-rock grains and some rock grains
50MRG1
Non-rock grains
50MRG2
Non-rock and some rock grains
50MNG1
Non-rock grains
50MNG2
Rock e non-rock grains
40MRG1
Rock e non-rock grains
40MRG2
Rock and non-rock grains + a few detached rock grains
40MNG1
Non-rock + some detached rock grains
40MNG2
Rock and non-rock aggregates