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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 6
Pull Off test to evaluate the compressive strength of concrete: an alternative to Brazilian standard techniques
Figure 7 – a) Rebound hammer; b e c) Measurement points in the specimens
The simple compression test on cylindrical specimens was per-
formed following the procedures proposed in NBR 5739 [1] [Fig-
ure 8 (a)]. The simple compression test on prismatic specimens
was performed according to BS 12390-3 [3] [Figure 8 (b)]. For both
tests was adopted the loading speed of 0.4 MPa/s.
3.7 Pull Off test
The Pull Off test applied to concrete is not standardized in Bra-
zil. This study adopted the recommendations of BS 1881: Part
207 [13]. In this method, the traction is axially transmitted to
a metallic disc bonded beforehand into the concrete surface.
After a period of time enough to cure the epoxy resin used for
bonding the discs, a tensile force is applied to the disc using a
portable mechanical system [Figure 3 (a)]. The gradual increase
in tension can be directly observed on a scale (MPa), and the
maximum tension is logged, as soon as the pullout of concrete
happens. The equipment used for the tests was the Dyna Z 16E
Proceq [Figure 3 (b)].
For implementing the Pull Off test concrete slabs of 55 cm x 55
cm x 20 cm molded in the laboratory with the same concrete used
in the specimens of the resistance test were used. Nine readings
were performed on each slab. The amount of readings in each
slab was defined by recommendations of BS 1881: Part 207 [13].
Another factor in the sizing of the slabs is the recommendation
from the standard that discs should be set at a minimum of two
diameters to each other and positioned at a distance of a diameter
from the edges of the element to be tested. The material of the
discs used in the assay is aluminum and its dimensions are 25 mm
high and 50 mm in diameter.
The test was conducted with a surface cut of 5 mm deep according
to the dimension of the metallic disc. The execution of the cutting
was done to avoid the influence of the surface conditions of the
concrete, as in the case of carbonated surfaces.
Figure 8 – Compressive strength test (a) cylindrical specimens and (b) cubic specimens