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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
J. TANESI
|
M. G. da SILVA
|
V. GOMES
duction of the product that meets the criteria of the specification
(Bickley et al. [10]).
3.2 Tactical analysis
3.2.1 Standards’ revision
The definition and selection of performance requirements have a
determining role in the durability of the structure because, simply
specifying the maximum water-binder ratio, compressive strength
and minimal cement content is not sufficient to guarantee the de-
sirable service life of the structure.
A clear example of the inadequacy of prescriptive specifications is
the minimum cement content requirement. It is not a requirement in
NBR 6118/2003 (ABNT [6]) but in NBR 12 655/2006 (ABNT [11]).
Not only this requirement is not sufficient to ensure the durabil-
ity, but could be even detrimental to it. This is because when a
minimum cement content is specified, the tendency is to exceed
it significantly, which could cause shrinkage and cracking issues,
in addition to neither being a sustainable nor a cost-effective deci-
sion. Some American agencies have already started the discus-
sion about the possibility of replacing the minimum cement content
by the maximum cement content (Simons [12]).
However, in Brazil, it is known that if the minimum content is not
specified, there is a risk that mixtures with cement content lower
than the technically appropriate would be used. That is why, in
performance-based specifications, there is a total change of tech-
nical responsibility, causing all involved to seek the best long-
term solution.
In order to develop a performance-based specification in Brazil, it
is imperative to change the current standards, in particular NBR
6118/2003 (ABNT [6]) and NBR 12 655/2006 (ABNT [11]).
The first suggested change would be the option to use three dif-
ferent types of specification: prescriptive, hybrid and performance-
based (Table 1), similar to the one presented in the Canadian stan-
dard CSA A23.1-04 (CSA [8]), which allows the use of two types
of specifications: performance and prescriptive. Nevertheless, in
the opinion of the authors what the CSA A23.1-04 (CSA [8]) calls
for performance specification is actually a hybrid specification. It is
also important to highlight that currently there is no real concrete
performance-based specification.
Performance-based specifications require the creation of more
detailed exposure classes than the existing classes in NBR
6118/2003 (ABNT [6]). In this case, a combination of current
3. Action plan for the creation and
implementation of concrete
performance-based specifications
in Brazil
Figure 1 shows a schematic of the action plan in the strategic level
(long-term), tactical (medium term) and operational (short term) for
the creation and implementation of concrete performance-based
specifications in Brazil.
3.1 Strategic analysis
The current situation of the Brazilian specifications is still far from a
performance-based approach, but should be redirected in that way
in order to obtain more durable concrete structures.
Environmental sustainability is another aspect to be considered.
The scarcity of raw materials and new environmental policies in-
creasingly stress the importance of the adoption of more innova-
tive solutions for the use of materials and resources available,
without, however, sacrificing the performance of the structure. En-
vironmental sustainability also requires the move in the direction
of performance-based specifications with the adoption of perfor-
mance indicators.
However, there is still a long way to reach a concrete performance-
based specification, as it requires mathematical modeling of dete-
rioration mechanisms in order to the estimate the service life of the
structure. This modeling should aim to guarantee the service life of
the project under the specific exposure conditions.
The specification of performance criteria which were not determined
with the use of mathematical models to predict the structure service
life does not constitute a performance-based specification, but rath-
er a hybrid specification. This is because, as with prescriptive speci-
fications, the criteria become subjective and not necessarily bound
to a particular service life or performance over time (Tanesi [2]).
The construction industry is a conservative industry, especially in
Brazil, that opposes to radical changes. It is also an industry that is
influenced by the interests of large corporations. The implementa-
tion of performance-based specifications requires a change of the
mindset of all involved in the process, mainly regarding technical
responsibilities.
This means that there should be a redistribution of risks and each
professional should have their responsibilities clearly defined.
However, if the producer and the contractor are expected to take
new risks, they anticipate to be given more freedom in the pro-
Table 1 – Suggested alternative method for specifying concrete based on CSA A23.1-04 (CSA )
Specification type
Requirements
Hybrid or
performance-based
n
requirements and criteria for structural safety
n
requirements and criteria for durability
n
environmental requirements
n
other requirements (color, texture, etc.)
Prescriptive
Same requirements in the current NBR 6118, provided
the requirements for exposure classes III and IV are revised.