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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
B. F. TUTIKIAN | M. PACHECO
This test was performed at 28 days, and, in order to keep a coher-
ent comparison between the performance diagram properties, the
same compressive strength ranges selected for the other catego-
ries were maintained.
Based on the data shown in Fig. 11, it can be concluded that the
Repette-Melo method, 2005 [2], presented a chloride ion penetra-
tion 9.8% lower than did Tutikian & Dal Molin, 2007 [3] and 17.4%
lower than did Nan Su et al., 2001 [1].
The amount of water in relation to the cement consumption in the
mixture is an important factor which impacts concrete porosity,
which in turn has a direct impact on chloride ion penetration. Thus
it should be noted that the Repette-Melo method, 2005 [2], pro-
vided a water/cement ratio of 0.46, against 0.51 in Tutikian & Dal
Molin, 2007 [3] and 0.50 in Nan Su et al., 2001 [1]. Those results
were achieved by setting the compressive strength at 91 days at
48.8 MPa, which is the value defined by the experiments done by
the Nan Su et al. method, 2001 [1]. That value was adapted to
match the behavior equations identified Tutikian & Dal Molin, 2007
[3] and Repette-Melo, 2005 [2].
4.3 Non quantitative aspects reported in
the executation of the methods of dosage
Among the non quantitative aspects observed during the proce-
dures for obtaining SCC through the methods performed during
the experimental program, it was observed that in the procedures
defined by Nan Su et al., 2001 [1] the calculation of cement con-
sumption depends solely on the required compressive strength.
During the experimental work, in order to determine the proportion
of cement in the SCC mixture, it was established that the compres-
sive strength at 28 days, according to the formula, would be 55
MPa, which resulted in an amount of cement corresponding to the
adopted strength. However, it can be verified that this process did
not work properly, since the result for compressive strength at 28
days for this method was 44.8 MPa, which is 18.5% less than the
value defined in the proposed empirical formula. It is known that
there are several types of cement, aggregates, binders and admix-
tures which impact the final strength, and, in case it is intended to
establish a universal equation to calculate cement consumption, all
the aforementioned variables must be included.
In order to define the amount of admixture, which is an important
factor in cost composition for the SCC mixtures, the Repette-Melo
method, 2005 [2], determines an establishment of the proportions to
be used, firstly during the paste stage, then during the mortar stage
and finally in the concrete. These early studies, in order to obtain
the best performance from the admixture in the mixture, ended up
creating a slower and more troublesome procedure for the dosage
of concrete. It was verified, through other methods, that such ex-
periments have little effect on the amount of admixture. In Tutikian &
Dal Molin, 2007 [3], for instance, which does not make use of such
processes in order to achieve the superplasticizer consumption, a
percentage 21% smaller of material in the mixture was obtained, in
contrast to what was found by Repette-Melo, 2005 [2]. Thus it can be
said that the ideal and optimal content of the admixture depends on
the interaction of all elements in the unit composition, i.e., cement,
sand, gravel, and that is only possible in the concrete stage.
The Repette-Melo method, 2005 [2], in order to determine the
coarse aggregate, proposes that the values used should range
from 27% to 33% in relation to the total volume of concrete. That is
a rather empirical procedure, since the worker in charge of the dos-
age will have seven alternatives for the choice of amount of coarse
aggregate in the mixture. That engenders doubt during the choice,
as happened to Nan Su et al., where an intermediate percentage
was selected.
5. Final Considerations
In this study, three methods of dosage for the manufacturing of
SSC were compared technically and economically, using the same
materials. In view of the proposed goals, after the lab work, it can
be concluded that:
n
From this study, it was verified that, in order to dose SCC with
aggregates found in the South of Brazil, the method which pre-
sented the smallest cost and higher compressive strengths at
the ages of 7, 28 and 91 days was Tutikian & Dal Molin, 2007
[3], while the one which reached the highest chloride ion pen-
etration and highest compacity and modulus of elasticity was
Repette-Melo, 2005 [2]. During tests performed in the fresh
state, all methods tried obtained mixtures which fit in the re-
quired self-compactibility class;
n
However, it should be noted that during the comparisons made
between Repette-Melo, 2005 [2] and Tutikian & Dal Molin,
2007 [3], the characteristics which involve the propagation
velocity of the ultrasound achieved very similar results, i.e.,
the results may be considered identical due to the number of
samples analyzed;
n
Regarding workability verification, it is observed that the values
achieved for each method of dosage tried could be adjusted, as
long as the proportion of superplasticizer admixture is increased.
That was not done in this study, since the amount was set to
achieve the values of the established self-compactibility class.
These considerations are only valid for the concretes dosed in
this study, with materials from the South of Brazil, determined ac-
cording to the presented proportions. It should be noted that the
mechanical properties may suffer alterations if other materials are
used, or higher or lower amounts of admixture are used, for in-
stance. The criteria and compared aspects suggested may be use-
ful instruments in selecting, among various methods with poten-
tially the same answers, the one which best fits reality or specific
needs for applications.
6. References
[01] SU, N.; HSU, K.C.; CHAI, H.W. A simple mix design
method for self-compacting concrete. In: Cement and
Concrete Research, n. 31, p. 1799-1807, 2001.
[02] MELO, K. A. Proposição de método de dosagem de
concreto autoadensável com adição de fíler calcáreo.
Dissertação de mestrado, UFSC, 2005.
[03] TUTIKIAN, B. F. Proposição de um método de dosagem
experimental para concretos autoadensáveis.
Dissertação de doutorado, Universidade Federal do
Rio Grande do Sul, Porto Alegre, 2007.
[04] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS.
NBR 15823: Concreto autoadensável. Rio de Janeiro,
2010.
[05] GRÜNEWALD, S. Performance-based design of
self-compacting fibre reinforced concrete.