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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
Guidelines for the development of concrete performance-based specifications in Brazil
1. Introduction
In 2009, following an international trend, Brazil approved its
first performance specification for residential
buildings (NBR
15 575/2008 [1]). It became effective in 2010 and aims to pro-
mote a paradigm shift, representing the evolution of the mindset
of the construction industry in Brazil. This specification deals
with performance of various systems of residential buildings of
up to five floors but not especifically with concrete as a material.
There is no consensus for the definition of performance speci-
fication and performance-based specifications (Tanesi [2]). In
the present paper, performance specifications are those speci-
fications that describe how the finished product should perform
over time, while performance-based specifications are speci-
fications that describe the desired levels of engineering prop-
erties (e.g., compressive strength and diffusion coefficient)
that are predictors of performance and appear in mathemati-
cal models that can be used to predict the performance from
combinations of predictors over the service life of the structure
(TRB [3], Tanesi [2]).
On the other hand, hybrid specification can be defined as a
specification that does not apply mathematical modeling to de-
termine the performance criteria or to predict the service life.
These specifications may be a combination of prescriptive rec-
ommendations and performance requirements and some of the
performance criteria are chosen based on technical recommen-
dations (Tanesi [2]).
The development and implementation of concrete performance-
based specifications are not easy tasks, especially in Brazil, due
to the lack of experience selecting the durability requirements
and criteria.
Nevertheless, some requirements widely used in prescriptive
specifications are in reality performance-based requirements,
such as slump (workability requirement related to constructabil-
ity), compressive strength and elastic modulus (requirements
related to structural safety).
In the past years, some papers have been published addressing
performance specification in the Brazilian context (Tanesi et al.
[4], Silva et al. [5]). This paper is a follow up to the previously
published papers and intends to provide guidelines for the de-
velopment of performance specifications in Brazil.
2. A critique on the prescriptive approach
in NBR 6118/2003
NBR 6118/2003 (ABNT [6]) brings exposure classes in the
same way as other international standards and specifications,
such as EN 206-1/2000 (EUROCODE [7]), CSA A23.1-04
(CSA [8]) and ACI 318-08 (ACI [9]). According to these class-
es, the Brazilian standard makes recommendations for maxi-
mum water-cement ratio, minimum compressive strength and
minimum cover.
Nevertheless, unlikely CSA A23.1-04 (CSA [8]) and EN
206-1/2000 (EUROCODE [7]), the exposure classes in NBR
6118/2003 (ABNT [6]) are very subjective and there are no
clear parameters to guide the specifier on how to choose the
correct exposure class.
In NBR 6118/2003 (ABNT [6]), the concrete quality is un-
derstood as directly related to water-cement ratio and com-
pressive strength. The Brazilian standard does not take into
account the type of cement used, the presence of supplemen-
tary cementitious materials, specified service life, curing qual-
ity, among other things. Despite the proven importance of
water-cement ratio with regard to durability, this is not the only fac-
tor that governs the various deterioration mechanisms in concrete.
Moreover the maximum allowed water-cement ratios allowed
by NBR 6118/2003 (ABNT [6]) are relatively high, especially
for the case of exposure class III. In this case, despite being a
high risk exposure class, a 0.55 water-cement ratio is allowed.
Since, unlikely in the USA, in Brazil, almost every single ce-
ment readily available in the market contains different contents
of blast furnace slag, it is surprising that the use of supplemen-
tary cementitious materials and their influence on the matrix
microstructure quality are not contemplated.
Finally, an important point is that the limits presented by NBR
6118/2003 (ABNT [6]) were determined on the basis of ex-
perience, empirical or not and not based on the understand-
ing and modeling of the deterioration mechanisms. Moreover,
since it does not specify a minimum service life, it is not pos-
sible to forecast what service life could be achieved if the NBR
6118/2003 (ABNT [6]) criteria are used. In this context, perfor-
mance-based specifications appear as a solution to achieve
the desired service life.
Figure 1 – Action plan for the creation and implementation of concrete
performance-based specifications in Brazil