74
D. Kocáb et al.
cycles are not the same—the drop in the tensile splitting strength tends to be lower,
see [27, 28]. Thus, assessing the concrete frost resistance is not so strict, which could
compensate for the above negative impacts (thus substituting the tolerance in the
sense of the standard [26]).
When assessing a concrete structure repair project in terms of sustainability with
frost resistance being among the parameters used for calculating the sustainability
indicator k SB , the assessment criterion (i.e. the limit value for deciding whether
a concrete is frost resistant) is virtually superfluous. Important is that the frost resistance parameter substituted into the k SB calculation should be obtained by an identical
method regardless of whether it is RDM by [16] after 100 F-T cycles or, e.g., the
frost resistance coefficient by [17] after 50 F-T cycles. The only problem is, when
assessing the suitability of each concrete structure repair project in terms of sustainability, how to deal with the relevant calculation of k SB (thus, with the input values
other than the frost resistance parameter) or of some other sustainability criterion.
This could, however, be the subject of another paper, or a book.
6 Conclusions
Determining the frost resistance of concrete in a structure is not an easy matter.
On the contrary, it has some pitfalls, of which the most serious one is obtaining
a relevant number of relevant test specimens. In the ideal case, the test specimens
should be 9 in number, being 100 × 100 × 400 mm prisms. They can be used to
determine the relative dynamic modulus of elasticity (and, from it, RDM) as well as
flexural strength, which is used to calculate the frost resistance coefficient. To this
end, however, 9 core samples had to be taken from the structure with a diameter
of 160–180 mm and length of at least 450 mm. The cores would also have to be
without reinforcement and cracks, which, in a vast majority of structures, is next to
impossible. Another (feasible) variant is using cores of a smaller diameter (such as
100 mm) to prepare test cylinders 150 mm or 200 mm long. These can then be used
to determine the RDM while testing the flexural strength can be replaced by testing
the tensile splitting strength.
It should be stressed that, in any case, to prepare the test specimens, core sampling
and circular cutting will be required, which will inevitably entail a risk of micro
cracks occurring in the test specimen concrete. This, along with the fact that the
surface of the test specimens will be created by a cut with exposed aggregate, can
have a negative impact on the frost resistance test. A serious problem, especially in
older structures, can also be the considerable variability of concrete in its volume or
the use of different concretes in different (even if structurally identical) parts of the
construction—as was the case in the above experiment.
The result of a concrete frost resistance test can be used as one of the basic
parameters in assessing concrete structure repair projects in terms of sustainability.
It would enter the calculation of the sustainability indicator k SB as a performance
D. Kocáb et al.
cycles are not the same—the drop in the tensile splitting strength tends to be lower,
see [27, 28]. Thus, assessing the concrete frost resistance is not so strict, which could
compensate for the above negative impacts (thus substituting the tolerance in the
sense of the standard [26]).
When assessing a concrete structure repair project in terms of sustainability with
frost resistance being among the parameters used for calculating the sustainability
indicator k SB , the assessment criterion (i.e. the limit value for deciding whether
a concrete is frost resistant) is virtually superfluous. Important is that the frost resistance parameter substituted into the k SB calculation should be obtained by an identical
method regardless of whether it is RDM by [16] after 100 F-T cycles or, e.g., the
frost resistance coefficient by [17] after 50 F-T cycles. The only problem is, when
assessing the suitability of each concrete structure repair project in terms of sustainability, how to deal with the relevant calculation of k SB (thus, with the input values
other than the frost resistance parameter) or of some other sustainability criterion.
This could, however, be the subject of another paper, or a book.
6 Conclusions
Determining the frost resistance of concrete in a structure is not an easy matter.
On the contrary, it has some pitfalls, of which the most serious one is obtaining
a relevant number of relevant test specimens. In the ideal case, the test specimens
should be 9 in number, being 100 × 100 × 400 mm prisms. They can be used to
determine the relative dynamic modulus of elasticity (and, from it, RDM) as well as
flexural strength, which is used to calculate the frost resistance coefficient. To this
end, however, 9 core samples had to be taken from the structure with a diameter
of 160–180 mm and length of at least 450 mm. The cores would also have to be
without reinforcement and cracks, which, in a vast majority of structures, is next to
impossible. Another (feasible) variant is using cores of a smaller diameter (such as
100 mm) to prepare test cylinders 150 mm or 200 mm long. These can then be used
to determine the RDM while testing the flexural strength can be replaced by testing
the tensile splitting strength.
It should be stressed that, in any case, to prepare the test specimens, core sampling
and circular cutting will be required, which will inevitably entail a risk of micro
cracks occurring in the test specimen concrete. This, along with the fact that the
surface of the test specimens will be created by a cut with exposed aggregate, can
have a negative impact on the frost resistance test. A serious problem, especially in
older structures, can also be the considerable variability of concrete in its volume or
the use of different concretes in different (even if structurally identical) parts of the
construction—as was the case in the above experiment.
The result of a concrete frost resistance test can be used as one of the basic
parameters in assessing concrete structure repair projects in terms of sustainability.
It would enter the calculation of the sustainability indicator k SB as a performance