determined by subtracting the instantaneous elastic strain due to
the specimen loading and the strain due to the autogenous shrinkage
from the total strain. The basis of the strain measurement is 500 mm
at the middle of the specimen (Fig. 1).
2.2.2. Creep in tension
Creep tests in tension have been developed by other researchers
[7–14]. The IFSTTAR creep test in tension was designed and developed
in 2008 in the frame of an industrial research project conducted for
Institut de Radioprotection et de Sureté Nucléaire (IRSN) to investigate
the endogenous tensile creep of concrete nuclear power plants. The
test duration did not exceed 3 days [15]. The design of the tensile
creep device adopted a frame-type flail arm lever (Figs. 2 and 3). To reduce
the maximum applied load and maintain good loading sensitivity
with a reasonable size for the loading frame, a 5/1 ratio was selected for
the lever arms. This tensile creep machine allows testing of cylindrical
specimens with a diameter of 13 cm and a length of 500 mm.
Specimens for testing are protected from drying during the test
using two layers of self-adhesive aluminum sheet. The specimen is
connected to the machine frame by bonding and bolting. The specimen
is glued to aluminum heads that are connected to the machine
frame by bolting (Figs. 2 and 3). A bonding system for the heads
was designed to ensure proper alignment of the tensile axes of the
specimen (Fig. 4).
With the 5/1 ratio chosen for the lever arm, a mass of 1300 kg is
necessary to apply a maximum force of 65 kN. To obtain a load sensitivity
threshold of 1%, 100 disks of 13 kg each were chosen to achieve
the desired maximum force (Figs. 2 and 3). A sensitive aspect of this
device concerns the connecting points of the fail. To obtain a proper
test, it is essential to minimize parasitic forces due to friction. The solution
retained for these connecting points is bull socket joints (Fig. 5).
Three longitudinal displacement transducers were positioned at
120° on the central part of the specimen. The basis of measurement
was 300 mm (Fig. 3).
As for the study on the basic creep in compression, autogenous
shrinkage tests were performed on specimens identical to those
used for creep tests at the same time as the basic creep tests in
tension and using the same protection technique against drying.
The creep strain is conventionally determined by subtracting to
the total strain, the instantaneous elastic strain due to loading and
the strain due to autogenous shrinkage, as for creep in compression.
2.3. Test program
2.3.1. Compression tests
To measure basic creep, five specimens were tested at concrete
ages of 64 days (n = 3) and 7 days (n = 2). Of the three specimens
tested at 64 days, two were loaded at 50% and one at 70% of the
average compressive strength of concrete measured at 64 days. The
determined by subtracting the instantaneous elastic strain due to
the specimen loading and the strain due to the autogenous shrinkage
from the total strain. The basis of the strain measurement is 500 mm
at the middle of the specimen (Fig. 1).
2.2.2. Creep in tension
Creep tests in tension have been developed by other researchers
[7–14]. The IFSTTAR creep test in tension was designed and developed
in 2008 in the frame of an industrial research project conducted for
Institut de Radioprotection et de Sureté Nucléaire (IRSN) to investigate
the endogenous tensile creep of concrete nuclear power plants. The
test duration did not exceed 3 days [15]. The design of the tensile
creep device adopted a frame-type flail arm lever (Figs. 2 and 3). To reduce
the maximum applied load and maintain good loading sensitivity
with a reasonable size for the loading frame, a 5/1 ratio was selected for
the lever arms. This tensile creep machine allows testing of cylindrical
specimens with a diameter of 13 cm and a length of 500 mm.
Specimens for testing are protected from drying during the test
using two layers of self-adhesive aluminum sheet. The specimen is
connected to the machine frame by bonding and bolting. The specimen
is glued to aluminum heads that are connected to the machine
frame by bolting (Figs. 2 and 3). A bonding system for the heads
was designed to ensure proper alignment of the tensile axes of the
specimen (Fig. 4).
With the 5/1 ratio chosen for the lever arm, a mass of 1300 kg is
necessary to apply a maximum force of 65 kN. To obtain a load sensitivity
threshold of 1%, 100 disks of 13 kg each were chosen to achieve
the desired maximum force (Figs. 2 and 3). A sensitive aspect of this
device concerns the connecting points of the fail. To obtain a proper
test, it is essential to minimize parasitic forces due to friction. The solution
retained for these connecting points is bull socket joints (Fig. 5).
Three longitudinal displacement transducers were positioned at
120° on the central part of the specimen. The basis of measurement
was 300 mm (Fig. 3).
As for the study on the basic creep in compression, autogenous
shrinkage tests were performed on specimens identical to those
used for creep tests at the same time as the basic creep tests in
tension and using the same protection technique against drying.
The creep strain is conventionally determined by subtracting to
the total strain, the instantaneous elastic strain due to loading and
the strain due to autogenous shrinkage, as for creep in compression.
2.3. Test program
2.3.1. Compression tests
To measure basic creep, five specimens were tested at concrete
ages of 64 days (n = 3) and 7 days (n = 2). Of the three specimens
tested at 64 days, two were loaded at 50% and one at 70% of the
average compressive strength of concrete measured at 64 days. The
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