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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
Probe penetration test applied for evaluating shotcrete compressive strength
ness and size of the coarse aggregate can affect the results
of the test, [1,2].
As an example that is practical and directed towards the construc-
tion of tunnels, the probe penetration resistance test adjusted by
a pneumatic system was employed by Iwaki, [8], for quality con-
trol of the compressive strength of a shotcrete structure, in which
a good correlation with strength values up to 30.0 MPa was ob-
tained. The strength limit of 30.0 MPa is associated with the ki-
netic energy level applied to the pneumatic system described by
Iwaki, [8]. In the case of the Windsor test, the strength limit is as
high as 40.0 MPa according to the same author.
The advantages of the probe penetration test include low cost;
simplicity, as it can be easily performed by a trained technician;
and speed when applying the test in structures that require a
high number of tests. Based on the above considerations, the
probe penetration test was chosen to evaluate the structure
analysed in the present study. The energy application system
of the probe penetration test used in this study consists of an
adaptation of the gun used in the Windsor test.
After defining the type of non-destructive test to be used in as-
sessing the shotcrete structure, the proposed methodology was
defined, as presented in the following section.
3. Methodology used to assess
the shotcrete structure
The proposed methodology is divided into two stages. The first
stage consists of defining the correlation curve of the non-destruc-
tive test, i.e., the relationship between the exposed length of the pin
and the compressive strength of the concrete. The second stage
involves in loco testing along the length of the tunnel. The com-
bined results of these two stages were used to determine which
parts of the structure had a compressive strength that was lower
in concrete, [1]. Pullout tests, such as the Lok-test and CAPO,
are widely used to assess the quality of finished concrete struc-
tures, [7].
Nonetheless, regarding shotcrete structures, pullout tests are
commonly used to estimate the compressive strength of con-
crete in its early stages, [8]. Moreover, Malhotra & Carino, [1],
the pullout test requires a long testing time. Based on these con-
siderations and the total length of the tunnel, the possibility of
using the pin pullout test in evaluating the shotcrete structures
was discarded.
Finally, the probe penetration test was considered. This test is
based on the absorption of the initial kinetic energy of the pin by
the concrete. In this case, a portion of the kinetic energy of the
driven pin is absorbed by the friction between the pin and the
concrete, and an additional portion of the energy is absorbed by
the concrete fracture, [2].
Similar to the rebound hammer test, the probe penetration test
is commonly used to evaluate the uniformity of the concrete
structure, [9]. Nevertheless, when the probe penetration test
is used to estimate the concrete strength, it is recommended to
defined a correlation curve for the tests results for the particular
concrete type to be investigated, [1,2,10].
One of the probe penetration tests reported in the literature
is that proposed by Al-Manaseer and Nasser, [11], the test
relies on a spring-loaded hammer similar to the one used in
the rebound hammer test. However, the most recognised pen-
etration test using a gun is the Windsor test, [6,12], which uses
a powder-actuated tool to project pins into the concrete. The
powder-actuated gun drives the steel-alloy probe (pin) into the
hardened concrete, and the exposed length is then measured.
In contrast to the rebound hammer test, the penetration test
is not strongly affected by the surface conditions of the con-
crete. Nonetheless, like the rebound hammer test, the hard-
Figure 2 – Equipment used in the probe penetration test: gun, pins, and cartridges (gunpowder)
Set of pins
Gun
Cartridges
Embedded pin