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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
Experimental analysis of reinforced concrete columns strengthened with self-compacting concrete
and connectors
shape of a “c” 140 mm wide, 35 mm high and a 70 mm extension.
Once fixed and involving the stirrups of the columns, they allowed
a 25 mm coating.
Figure 7 shows the location of connectors on the compressed face
of each column. They are represented by an ongoing line and also
show the thickness of the furrows and the distance between them.
Furrowing was needed to uncover shear reinforcement, thus en-
abling the connectors to be tied to the stirrups. The 110 mmwide
furrows were accomplished with the use of electrical demolition
hammer, manual hammer and metal pointer. With the stirrups in
place (Figure 8), the concrete surface was cleaned and the sub-
strate was wet in order to present a saturated dry surface. Struc-
tural adhesives were not used for bonding the substrate and the
strengthening concrete. Substrate scarification was carried out by
spraying only sand all over the compressed face of all the strength-
ened columns.
To the strengthening the columns, SCC was prepared to achieve
an average compression strength of 30 MPa at 28 days. Table 1
shows the proportion of materials used to produce a cubic meter
of concrete.
With regard to the slump flow test, the EFNARC (2002) recom-
mends that slump floow values ought to range from 650 to 800
mm. The concrete used to strengthen the columns showed slump
flow values of 760 and 750 mm for the first and second castings,
respectively (Figure 9). According to EFNARC (2002), the L-Box
test should have a h
2
/h
1
relation (height that concrete reaches
at the edge of the L-box/height that concrete maintains at the
beginning of the L-box) equal to 0.80. Dosed concrete revealed
values ranging from 0.81 to 0.84 (first and second castings, re-
spectively). Gomes et al. (2003) show Lt
20
values (reading of the
time concrete takes to reach a 20 cm marking on the L-box) rang-
ing from 0.5 to 1.5 seconds and Lt
40
values (reading of the time
concrete takes to reach a 40 cm marking on the L-box) ranging
from 2 to 3 seconds. The first casting revealed Lt
20
= 1 second
and Lt
40
= 2.5 seconds, whereas the second casting marked Lt
20
= 1 second and Lt
40
= 3 seconds.
Regarding the V-Funnel 5 min, EFNARC (2002) establishes a limit
ranging from 6 to 12 seconds and a difference between the first
and the second assays lower or equal to 3 seconds. The first cast-
cal to P6 and was made after a power outage had occurred in the
laboratory while performing tests on column P6.
Columns were cast horizontally and the tracing was dosed to
achieve an average compressive strength value of 30 MPa at
28 days. The conventional concrete used was pumped from the
concrete mixer to steel forms and mechanically compacted by an
immersion vibrator (25 mm diameter). During casting, 36 cylindri-
cal test samples measuring 150 mm x 300 mm were molded for
concrete characterization. Tests assessed compression strength,
tension by diametral compression and elasticity modulus. The col-
umns and the test samples were submitted daily to wet curing and
were covered with plastic canvas for seven days. After the seventh
day, the columns were removed from the mould and placed in the
laboratory until the date of the tests.
Figures 5 and 6 show the increase of the compressive strength of
concrete with the age of conventional concrete used in substratum
and the SCC used in reinforcement respectively.
The connectors were made from 5 mm diameter steel bars taken
from the same steel batch used for the stirrups of the columns
(Figure 5). With a total length of 350 mm, the bars were bent in the
Figure 4 – Stress-deformations curves
of 10 mm steel bars
Figure 6 – Concrete compression
strength of SCC with age curves
Figure 5 – Compression strength of substrate
concrete with age curves