Sustainability of Concrete Structures in Terms …
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specimens from moulds are always tested. The principle of frost resistance determination is monitoring the decrease in a certain concrete property value after running
a certain number of F-T cycles with the presence of water. The Czech standard [17]
works primarily with flexural strength, which is logical—as soon as cracks or even
micro cracks appear in the inner concrete structure, the flexural strength immediately decreases. The standards [15, 16] determine the frost resistance of concrete by
monitoring changes in its dynamic modulus of elasticity or changes in the length of
the specimens after F-T cycles. Testing the concrete dynamic modulus of elasticity is
also suitable for this purpose as it is sensitive to changes in its inner structure quality.
The result is the relative dynamic modulus of elasticity (further marked as RDM).
4 The Experiment
As is clear from the previous text, the aim of the experiment was to determine the
frost resistance of concrete already built in a structure. It must be noted that the frost
resistance of concrete was tested without using chemical defrosting agents (some
of the above-mentioned procedures [16, 18] prescribe that concrete should be tested
using a sodium chloride solution).
4.1 Test Specimens and Material
As has already been mentioned, the European standards require that the testing
should be done using test specimens made in moulds, preferably prisms of 100 ×
100 × 400 mm. The document [16] does not set a requirement for the number of test
specimens. The standard [17] says that the number of test specimens depends on the
number of the F-T cycles planned. Generally, it can be stated that a suitable number
of test specimens that should be available is 9. When determining the frost resistance
of concrete in a structure, a problem usually already occurs during the sampling of
the specimens. It is very difficult to cut out a prism with the lateral dimensions of
100 × 100 mm of a standard core sample with a diameter of 150 mm—either the cut
out prism will have rounded edges or its lateral dimensions will be 95 × 95 mm at
best. For the test to be completely correct according to the standards, core samples
with a diameter of 160 mm or preferably 180 mm would have to be taken from the
structure. Moreover, the length of such a (undisturbed) core sample would have to be
almost 0.5 m (or its multiple) and the total length of the core samples (arranged one
after another) would have to be approx. 4.5 m. In addition, the core samples could not
be reinforced in the place where the 100 × 100 × 400 mm prism would later be cut
out, which means in its centre. It is very difficult, in some cases even impossible, to
obtain the test specimens required for frost resistance tests from almost any existing
concrete structure.
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specimens from moulds are always tested. The principle of frost resistance determination is monitoring the decrease in a certain concrete property value after running
a certain number of F-T cycles with the presence of water. The Czech standard [17]
works primarily with flexural strength, which is logical—as soon as cracks or even
micro cracks appear in the inner concrete structure, the flexural strength immediately decreases. The standards [15, 16] determine the frost resistance of concrete by
monitoring changes in its dynamic modulus of elasticity or changes in the length of
the specimens after F-T cycles. Testing the concrete dynamic modulus of elasticity is
also suitable for this purpose as it is sensitive to changes in its inner structure quality.
The result is the relative dynamic modulus of elasticity (further marked as RDM).
4 The Experiment
As is clear from the previous text, the aim of the experiment was to determine the
frost resistance of concrete already built in a structure. It must be noted that the frost
resistance of concrete was tested without using chemical defrosting agents (some
of the above-mentioned procedures [16, 18] prescribe that concrete should be tested
using a sodium chloride solution).
4.1 Test Specimens and Material
As has already been mentioned, the European standards require that the testing
should be done using test specimens made in moulds, preferably prisms of 100 ×
100 × 400 mm. The document [16] does not set a requirement for the number of test
specimens. The standard [17] says that the number of test specimens depends on the
number of the F-T cycles planned. Generally, it can be stated that a suitable number
of test specimens that should be available is 9. When determining the frost resistance
of concrete in a structure, a problem usually already occurs during the sampling of
the specimens. It is very difficult to cut out a prism with the lateral dimensions of
100 × 100 mm of a standard core sample with a diameter of 150 mm—either the cut
out prism will have rounded edges or its lateral dimensions will be 95 × 95 mm at
best. For the test to be completely correct according to the standards, core samples
with a diameter of 160 mm or preferably 180 mm would have to be taken from the
structure. Moreover, the length of such a (undisturbed) core sample would have to be
almost 0.5 m (or its multiple) and the total length of the core samples (arranged one
after another) would have to be approx. 4.5 m. In addition, the core samples could not
be reinforced in the place where the 100 × 100 × 400 mm prism would later be cut
out, which means in its centre. It is very difficult, in some cases even impossible, to
obtain the test specimens required for frost resistance tests from almost any existing
concrete structure.