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1. Introduction
The heterogeneity of the composition; the specific mass with lower
density; the adhered mortar quality and the amount of adhered
mortar and the variability of the properties are all important char-
acteristics of recycled aggregates, which represent obstacles not
only for their use as well as for the reliability of the same in con-
cretes used in structural applications (Lovato et al. [1], Etxeberria
et al. [2], Tabsh et al. [3], Kwan et al. [4], Cabral et al. [5]).
The consequences of these characteristics are observed in the recy-
cled aggregates themselves. Their properties normally do not obey the
norms commonly destined to natural aggregates (QUEBAUD et al. [6]);
and in the recycled aggregate concretes (RAC) made with the same
aggregates tend to give less work, be weaker, more deformed (smaller
module of elasticity), more porous and more permeable (Tabsh et al.
[3], Etxeberria et al. [2]). In the case of recycled aggregate concrete,
more cement needs to be added to the concrete made of 100% of recy-
cled aggregate in order to achieve the same workability and compres-
sional strength as conventional concrete (Etxeberria et al. [2]).
In the aggregates, the porosity affects more of their properties
(MEHTA and MONTEIRO [7]) and two of them reflect well their
level of porosity and are of relatively easy determination: the wa-
ter absorption and the specific mass. In the concrete, its strength,
durability, shrinkage and permeability suffers direct influence from
the number, type, size and distribution of pores present in the ag-
gregates, cement paste and transition zone (BASHEER et al. [8]).
As outlined by Kou et al. [9], the porosity of recycled aggregate con-
crete (RAC) is normally higher than that of natural aggregate concrete
(NAC) due to the adhered mortar present in the recycled aggregates.
The porosity and the pore size distribution are the most important char-
acteristics of the pore system of concrete which influences the penetra-
tion of external substances to the interior of the concrete. Therefore it is
important to understand the development of the pore system in order
to assess the durability properties of the recycled aggregate concrete.
Based on the criteria commonly related to the water absorption,
specific mass or values of Los Ángeles abrasion, it is an important
beginning given by the Science of Materials that is the existent
inversely proportional relation between porosity and the mechani-
cal strength of that material, valid in several materials and also in
concrete and ceramic (MEHTA and MONTEIRO [7]).
Many studies, norms and recommendations have been proposed
or established forms of classifying the recycled aggregate accord-
ing to the percentage of each phase (concrete, mortar, ceramic
etc.). With the intention of assuring a smaller variation of the phas-
es, the norms and recommendations have defined criteria that
must be obeyed with recycled aggregates (e.g. values of water ab-
sorption). The classification is usually made in visual form and the
definition of the best phase begins with the selection of aggregates
with stronger and more resistant materials (e.g. concrete), which
are also more resistant and can be used in applications of larger
importance. One of the reasons for which the concrete is seen as
more resistant is because it has rocks.
The classification based on the visual criteria which is limited be-
cause of each phase of CDW has its own variability. For instance,
it is possible to find concretes of different strengths produced
with different water/cement (w/c) ratios, and different amounts of
coarse aggregates, originated from rocks of different resistances.
The studies of CARRIJO [10] and ANGLE [11] prove these facts.
The concrete properties with recycled coarse aggregate of CDW,
separated by specific mass, showed a larger relation with the den-
sity rather than with the visual criteria called “grey aggregate” or “red
aggregate”, demonstrating the fallibility of the visual classification
system. The density separation (d) done by CARRIJO [10] was
based on the specific mass of the aggregates or, in other words,
each aggregate inside a certain order of specific mass (d < 1.9 kg/
dm³, 1.9 kg/dm³ < d < 2.2 kg/dm³, 2.2 kg/dm³ < d < 2.5 kg/dm³ e d
> 2.5 kg/dm³) has grains with specific mass of that order so that its
denser aggregates, for instance, a great part of them are grains of
rock. The concrete showed improvement in its properties (compres-
sive strength, elasticity module, etc.) with the increase of the specific
mass of the recycled aggregates. The compressive strength of the
recycled aggregate concrete (RAC) was less resistances in com-
parison to the conventional concrete, and decreased as the density
of the aggregates decreased. However, concrete made with aggre-
gates of density ranges between d > 2.5 kg/dm³ and 2.2 kg/dm³ <
d <2.5 kg/dm³ showed resistance values close to those of conven-
tional concrete. Furthermore, the RAC obey the Abrams Law.
1.1 Objectives
An experimental study was developed in order to evaluate the me-
chanical and durable concrete properties produced with recycled
coarse aggregates from different specific mass and compared to
those obtained with natural aggregates with the possible objective
of obtaining recycled aggregate concretes (RAC) appropriate for
applications in concrete with properties to structural concrete.
2. Materials and experimental program
2.1 Material
Samples of mineral fraction from the CDW were obtained from
around the city of Maceió and from the CW of the Laboratory
of Structures and Materials (LSM) of the Federal University of
693
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
Figure � � �ec�c�e� coarse
aggregates composition