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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
lected previously. Since assessing performance of in-place
concrete may not be always practical, surrogate tests may be
used for acceptance. In addition, another set of tests may be
specified to verify the concrete delivered is similar to the pre-
qualified mixture. The acceptance criteria should be statically
based and tolerance or minimum /maximum values should be
specified. The actions to be taken, in case the criteria are not
met, should be clearly stated. The point of sampling should be
clearly defined, as well (ACI [38]).
3.2.3 Hybrid specifications
A transition in the direction of performance specifications
is necessary. For such, an intermediate stage should be
implemented, where the maximum allowed water-binder ra-
tio should be decreased and other requirements should be
specified. This can be an efficient and relatively simple way
to guarantee a better microstructure and, as a consequence,
increase the service life of the structures, before the Brazil-
ian industry is ready for the implementation of performance-
based specifications.
An example of hybrid specification is a document that specifies the
compressive strength and maximum total charge in Coulombs as
requirements instead of water-binder ratio. One of the most com-
monly specified requirements in hybrid specifications is the maxi-
mum total charge.
ASTM C 1202-05 (ASTM [17]) presents a qualitative classification
regarding the risk of chloride penetration. However, since this clas-
sification is very broad, it can potentially put quite different mixtures
at the same level of risk of chloride penetration. This classification,
therefore, is not sufficiently sensitive to microstructural differences
that may occur, nor it is appropriate to ensure durability and does
not consider the exposure conditions of the structure.
The current hybrid specifications normally do not use the C 1202-05
(ASTM [17]) classification but stipulate a maximum total charge passed
at particular age. A value of 1500 Coulombs to 56 days has been shown
to be appropriate for most cases with similar exposure conditions of ex-
posure classes III and IV of NBR 6118/2003 (ABNT [6]).
3.3 Operational analysis
As previously presented, implementation of performance-based
specifications in Brazil requires a change of mentality in the indus-
try. In order to promote this change, it is recommended the cre-
ation of workshops and seminars so that the performance-based
concepts, as well as their implications, advantages and disadvan-
tages can be presented to engineers, contractors and owners.
In addition, according to Bickley et al. [10], it is necessary:
n
creation of qualification/certification programs that establish re-
quirements for a quality control management system, qualifica-
tion of personnel and requirements for the concrete plants;
n
Producers and contractors partner to ensure the right mixture
is developed, delivered and installed;
n
Performance requirements be measured by a set of tests at the
various stages of the process (pre- qualification of mixture and
quality control);
n
A clear set of instructions is created presenting actions to be
taken when concrete does not meet the performance criteria,
including penalties and bonuses;
n
Reliable mathematical models are developed and calibrated
based on data from long-term exposure to the Brazilian condi-
tions (environment and materials).
4. Conclusions
This paper proposed the creation of performance-based specifica-
tions, as well as hybrid specifications in Brazil. In order to accom-
plish it, the current Brazilian standards, especially NBR 6118/2003
and NBR 12655/2006 must be changed.
Among the necessary changes, NBR 6118/2003 should allow the
use of performance-based specifications and, in this case, the re-
quirement for maximum water-binder ratio should be eliminated.
New exposure classes were proposed, taking into consideration
various mechanisms of deterioration.
The need of mathematical modeling to predict service life and
some of the challenges related to performance-based specifica-
tions implementation were analyzed.
The process of choosing performance requirements and crite-
ria was discussed. The constructability, structural safety, dura-
bility, sustainability and special requirements were analyzed.
In addition, a methodology to determine the performance cri-
teria was proposed.
5. References
[01] ASSOCIAÇÃO BRASILEIRA DE NORMAS
TÉCNICAS. NBR 15 575-1: Edifícios habitacionais de
até cinco pavimentos - Desempenho - Parte 1:
Table 3 – Mathematical models for
performance requirements related to durability
Requirement
Are there mathematical
models to correlate
this requirement with
service life?
Chloride diffusion
coefficient
Yes
Charge (ASTM C 1202)
No
Electrical resistivity
No
Carbonation coefficient
Yes
Absorption
No
Shrinkage
No
Cracking
No
Expansion due
to sulfate attack
Yes
Expansion due to alkali
silica reaction
Yes
Abrasion resistance
No