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1. Introduction
In recent years, aspects related to durability, maintenance, ret-
rofitting and strengthening of structures have been highlighted
in the national scenario. Buildings with useful life below ex-
pectations, ageing of large structures, which already operate
within the limits of stability and security (some of our bridges
and viaducts, for example), and the lack of periodic inspections
and preventive maintenances are factors which compete for the
relevance of concepts related to strengthening and retrofitting
of structures.
A retrofitted and/or strengthened structure must present perfor-
mance higher than the presented before the intervention. In this
way, the development of new technologies and techniques, more
secure and efficient, arouse attention of researchers in various
fields.
As a technique to strengthen structures of reinforced concrete,
the application of CFRP is interesting, and has being accepted,
owing the advantages, notably those related to the high resis-
tance/weight ratio, immunity to corrosion, facility and rapidity of
application. In Brazil, large structures have already been strength-
ened with CFRP. However, the already existing knowledge can
be better conceived with a view to potentiating this technology.
Thus, the present paper intended to, as a construction innova-
tion, develop a technique of flexural strengthening of RC beams,
comprised of a process of previous retrofitting of the structure, by
elaborating and applying a composite of high performance based
on Portland cement and short steel fibers, intended to construct a
so-called transition layer. With this layer, as shown in Figure [1],
it is expected to reconstruct the tension zone of the RC beams
in order to better explore the properties of resistance of strength-
ening with sheets of CFRP and, possibly, to enhance the beam
performance as a whole.
It is known (Bian & Maalej [1], Ferrari [2], Leung [3]) that the
strengthening of RC beams with CFRP sheets is susceptible to
the appearance of a fragile, premature and extremely undesir-
able failure, because it prevents the total use of the strength prop-
erties to the polymer tensile.
Such form of failure anticipates the collapse of the strength-
ened beam by failure in the mechanisms of stress transfer. One
of these mechanisms concerns to the localized debonding of
strengthening (designated in the literature as peeling off), from its
anchoring zone or zones with excessive concentration of flexural
and/or shearing cracks. More significant increments of resistance
only can be achieved if the premature forms of failure were pre-
vented (FIB [4]).
Thus, with the proposed and presented in the study, it is imagined
to withdraw a part of tensile zone of beams to be strengthened
(frequently damaged by mechanical action, corrosion, natural
wearing), as illustrates Figure [2], in order to reconstruct it with
a high performance cement-based composite. For this purpose,
it is assumed that the retrofitted part will form a transition layer,
whose characteristics would be more appropriate for the applica-
tion of the flexural strengthening with CFRP sheet.
2. High performance cement-based
composite
In this section, are presented the experimental methodology and
the results obtained in the development of a cement-based com-
posite with characteristics more appropriate to reconstruct the ten-
sile zones of RC beams, also serving as substrate to bond the
CFRP. It is expected, with this composite, to constitute the transi-
tion layer in order to control better the cracking of concrete and
to delay the premature debonding of the polymeric strengthening.
According to Ferrari [5], the modifications resulting from the addi-
tion of steel fibers to concrete, at relatively low rates (a maximum
of 2%), are restricted only to the post-peak stage of the loading
history. According to Ferreira [6], under such conditions, the steel
fibers are not sufficient to inhibit the matrix cracking process which
precedes the maximum load (subcritical growth of crack).
Thus, aiming to improve the cement-based composite behavior
during the pre-peak stage of resistance, it is studied the effect
of incorporating steel microfibers into conventional steel fibers,
in an attempt to modify the composite in its microstructure and
consequently to improve the process of stress transfer from ma-
trix to fibers.
597
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
Figure � � ��he�e o� strengthening with CFRP sheets and transition layer
transition layer conected to the
concrete and reinforcements
transition layer control the
beam cracking
strengthening with sheet of
CFRP bond the transition layer
V. J. FERRARI | J. B. DE HANAI