Page 58 - Riem-Vol6_nº2

229 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
A. C. MARQUES | T. N. BITTENCOURT | M. P. BARBOSA
creep test are similar to those from the compressive strength test,
the molds have some changes when compared to the usual ones
because of the metallic plates at the ends of the specimen (diam-
eter of 15cm and 2cm thick). So the molds were 15x34cm, in order
to keep the specimen 30cm height.
The metallic plates are placed at the ends of the specimen to en-
sure flatness and uniformity of the applied load. The upper plate
is solid and the lower plate has a hole and a slot (as prescribed in
NBR8224 [13]) which allows the passage of the embedded strain
gage cable. Furthermore, to ensure their attachment to the speci-
men, the bottom plate has a metal clamp. The mold also splits, in
order to facilitate the instrumentation procedures and has an orifice
because of the strain gage cable. In Figure 2, can be seen the
mold used for the creep test.
The procedure adopted for the creep test starts by setting the strain
gage in the mold, which is made by centralizing it in the longitudinal
axis of the mold. After closing the mold, oil is spread inside of it to
facilitate the removal of the specimen. After placed the concrete,
the upper plate is placed and leveled. These procedures are de-
tailed in Marques et al. [14].
Once casted, the specimens were kept in the molds until the date
of the test (14 or 49 days). The demold of each group was made
only at the test date and the loading was according to NBR8224
[13], i.e. the total load was applied in 30s and before the final
loading, it was preceded for two consecutive loading and unload-
ing cycles.
were previously oven-dried. The mixing of the concrete and the
specimens cast were made in the Laboratório de Estruturas e Ma-
teriais estruturais (LEM), of EPUSP. The fresh SCC tests were
made after mixing and before casting the test specimens. Those
tests were performed according to NBR15823-2 [7], NBR15823-4
[8] and NBR15823-5 [9].
The compressive strength, splitting tensile strength and modulus of
elasticity tests were made according to NBR5739 [10], NBR7222
[11] and NBR8522 [12], respectively, for 7, 14, 28, and 49 days.
Three specimens were casted for each test and for each age (total
of 36 specimens) The creep test was made according to NBR8224
[13], and was divided into two groups. The first group was loaded
at 14 days and the second one at 49 days. In Table 3 is shown the
amount of specimens for each group of drying creep test.
Besides the two ages at loading, tests were also made both inside
and outside a climated-controlled chamber at 60 ± 4% of humidity
and 23º ± 1 of temperature.
2.1 Procedures adopted for the drying creep test
The creep test uses cylindrical specimens of 15x30cm. The instru-
mentation used are embedded electrical strain gage from KYOWA,
type KM-120-120-H2-11W1M3. Although the specimens for the
Table 2 – Aggregates physical characteristics
Material
Test
Quartz sand
sand
Crushed Crushed
stone stone
(12.5mm)
Crushed
stone
(19mm)
Maximum aggregate size (mm) 0.60 2.40 9.50 19.0
Fine check sum (%) 1.40 3.10 0.50 0.80
Fineness modulus (%) 1.28 2.62 5.67 6.93
3 Specific gravity (g/cm ) 2.69 2.70 2.68 2.81
3 Bulk dry specific gravity (g/cm ) 2.66 2.65 2.63 2.79
3 Bulk SSD specific gravity (g/cm ) 2.67 2.66 2.64 2.80
Figure 1 – Aggregates gradation curves
Table 3 – Specimens for creep tests
Test Age (days)
14 49
Drying creep 2 2
Drying creep (out the
climated-controlled chamber) 2 2
Drying shrinkage 1 1
Drying shrinkage (out the
climated-controlled chamber) 1 1
Total 12