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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
Self-compacting concretes (SCC) – comparison of methods of dosage
In order to determine the water/cement ratio, the starting point es-
tablished was the compressive strength according to the amount
of water and cement used in each unit composition. For the defini-
tion of a family of concrete, three values for the water/cement ratio
were determined initially: one for the poor unit composition (w/c:
0.56), one for the rich (w/c: 0.39) and one for the intermediate unit
composition (w/c: 0.48), based on the previous knowledge about
the materials.
The amount of fines is determined for each specified water/cement
ratio and it is dosed to replace the cement, in volume. The method
establishes that a percentage of filler passing through the 0.075
mm sieve should be used in this stage. Fine sand was used as fine
material in order to achieve the SCC mixture. Since fine sand does
not have a significant amount of particles smaller than 0.075 mm,
it could not be included in the paste composition.
During the next step, the mortar for the mixture is prepared, by
defining the amount of fine aggregate in relation to the total volume
of mortar and then the basic amount of superplasticizer admixture.
The amount of fine aggregate was adjusted only for a water/ce-
ment ratio, the intermediate one, with the percentage found being
used for the others.
As a basic guideline, the method establishes that the volume of
fine aggregate in relation to the total volume of mortar should pref-
erably be not less than 35% and not more than 55%.
A regular sand and fine sand composition was defined as fine ag-
gregate. The choice of percentages for these materials was based
on the optimal granulometric curve of the aggregates. From there
it was concluded that the amount of fine aggregate which fit best
to the limit curve established by the method was the composition
made up of 80% of regular sand and 20% of fine sand.
In order to determine the amount of fine aggregate, the mortars
were assessed based on the flow test, which was adapted for
mortar. According to the test, the ideal amount of fine aggre-
gate in the mortar composition was 50% in relation to the total
volume, achieving satisfying test results when the amount of
admixture was 0.20% (considering only the amount of solids),
since the drainage time was 4 seconds and the flow was 240
mm. According to the method, the ideal amount of admixture
is the one which results in a mortar flow diameter between 200
and 280 mm and a draining time in the “V-funnel” between 3.5
and 10 seconds.
The mortar with intermediate amount of water/cement was used in
order to determine the amount of coarse aggregate for the prepa-
ration of an initial test mixture with 30% of coarse aggregate in
relation to the total volume of concrete. The method proposes an
amount of coarse aggregate between 27% and 33%, the optimal
value being the one which presents satisfying results on the work-
ability tests while reaching a 0.3% percentage of admixture (taking
into consideration only the amount of solids). Thus a value of 30%
was adopted, which was the midpoint between the proposed limits.
Using that percentage, a trial mixture with the intermediate unit
composition was created so as to verify the acceptability of the ad-
opted ratio, considering the initial amount of admixture determined
during the mortar stage.
A mixture made up of 50% 25 mm gravel and 50% 19 mm gravel
was used as coarse aggregate. These percentages were adopted
based on the granulometric analyses of the gravel.
Figure 3 shows the granulometric curve of the fine and the coarse
aggregate, according to the percentages adopted and the limit
curves imposed by the method for determining the granulometric
arrangement. As can be seen in Figure 3, the resulting granulo-
metric curve from the mix of aggregates used for the mixture is
within the limits recommended by the method. Were it not pos-
sible to fit any one of the aggregate compositions into the limit
curves, it would be necessary to specify other materials with differ-
ent granulometric characteristics and which enabled the feasibility
of the mixture.
According to the method, the amount of admixture in the mor-
tar represents a good indication of the results which will be
achieved in the concrete. Generally speaking, an increase of
roughly 0.1% in relation to the optimal amount of mortar is need-
ed. Following the guidelines regarding the amount of admixture,
the trial mixture contained initially 0.2% worth of superplasticiz-
er. The flow test showed that the mixture was not fluid enough,
which led to a gradual increase in admixture up to the maximum
admissible amount, i.e. 0.3% (considering only the amount of
solids). In case of unsatisfying results, the amount of coarse
aggregate should be altered in relation to the total volume of
Figure 3 – granulometric curve of the
composition of the aggregates used
in the Repette-Melo [2] method
Figure 4 – Flowchart of the
Tutikian & Dal Molin [3] method