66
D. Kocáb et al.
change L c in accordance with the American standard of ASTM C666/C666M—15
[15], the relative dynamic modulus of elasticity RDM n or the relative length change
ε L,n in accordance with one of the procedures described in the European standard
of CEN/TR 15177 [16] or the frost resistance coefficient in accordance with the
Czech standard of ˇ
CSN 73 1322 [17], which is the ratio of the flexural strength of
the test specimens after F-T cycles to the strength of the reference specimens (which
were not burdened with the F-T cycles). Another European document of RILEM TC
176-IDC [18] is almost identical to CEN/TR 15177 [16].
If there was a need to assess a concrete structure repair project (using the indicator
k SB ) with regard to sustainability, the situation would be significantly more complicated, namely for two reasons. For one thing, it would be rather problematic to assess
different repair options using k SB because there are other aspects as well than just
comparing the different concrete recipes; for another, it is complicated to determine
the frost resistance of concrete built in a structure. The following text deals with the
latter of the problems described.
3 Determining the Frost Resistance of Concrete
If concrete in a structure is exposed to repeated alternation of positive and negative
temperatures, its degradation occurs if it is also exposed to water or a high level
of moisture. If dry concrete is frozen and thawed in an environment with low air
humidity, no considerable negative impact is created [19]. With newly designed
concrete it is not difficult to check frost resistance—appropriate tests are done on
the test specimens, which results in determining the resistance level of the concrete
to freezing and thawing. However, if it is necessary to check this parameter in older
concrete built in a structure (e.g. during reconstruction or structural repairs), it often
poses a fundamental problem.
If the concrete structure or its part is in contact with water (road panels, railway
sleepers, water tanks etc.), the water gets into the porous structure of the concrete
due to its absorbability. If it freezes, there is a risk of micro cracks and later even
cracks occurring in the concrete. It is caused by water expansion as it changes from
liquid to solid state. Water present in the capillary pores in concrete starts to change
into crushed ice at the temperature of approximately −0.5 °C (the point when the
water starts freezing depends on the size of the pores; however, all the capillary water
should freeze at −12 °C) [20]. The volume of the ice formed is approximately 9%
larger than that of water in the liquid state. This water expansion in the form of ice
leads to internal stress development in the concrete, namely of the size of tens of
MPa. This results in the disruption of the inner concrete structure and subsequent
irreversible reduction in its fundamental material properties [21].
There are several ways of determining the frost resistance of concrete. There is a
limitation consisting in the fact that the testing is done almost solely on test specimens
made in moulds. The standard [15] is an exception allowing the testing of drilled
core specimens or prisms cut out of hardened concrete. In Europe, however, only
D. Kocáb et al.
change L c in accordance with the American standard of ASTM C666/C666M—15
[15], the relative dynamic modulus of elasticity RDM n or the relative length change
ε L,n in accordance with one of the procedures described in the European standard
of CEN/TR 15177 [16] or the frost resistance coefficient in accordance with the
Czech standard of ˇ
CSN 73 1322 [17], which is the ratio of the flexural strength of
the test specimens after F-T cycles to the strength of the reference specimens (which
were not burdened with the F-T cycles). Another European document of RILEM TC
176-IDC [18] is almost identical to CEN/TR 15177 [16].
If there was a need to assess a concrete structure repair project (using the indicator
k SB ) with regard to sustainability, the situation would be significantly more complicated, namely for two reasons. For one thing, it would be rather problematic to assess
different repair options using k SB because there are other aspects as well than just
comparing the different concrete recipes; for another, it is complicated to determine
the frost resistance of concrete built in a structure. The following text deals with the
latter of the problems described.
3 Determining the Frost Resistance of Concrete
If concrete in a structure is exposed to repeated alternation of positive and negative
temperatures, its degradation occurs if it is also exposed to water or a high level
of moisture. If dry concrete is frozen and thawed in an environment with low air
humidity, no considerable negative impact is created [19]. With newly designed
concrete it is not difficult to check frost resistance—appropriate tests are done on
the test specimens, which results in determining the resistance level of the concrete
to freezing and thawing. However, if it is necessary to check this parameter in older
concrete built in a structure (e.g. during reconstruction or structural repairs), it often
poses a fundamental problem.
If the concrete structure or its part is in contact with water (road panels, railway
sleepers, water tanks etc.), the water gets into the porous structure of the concrete
due to its absorbability. If it freezes, there is a risk of micro cracks and later even
cracks occurring in the concrete. It is caused by water expansion as it changes from
liquid to solid state. Water present in the capillary pores in concrete starts to change
into crushed ice at the temperature of approximately −0.5 °C (the point when the
water starts freezing depends on the size of the pores; however, all the capillary water
should freeze at −12 °C) [20]. The volume of the ice formed is approximately 9%
larger than that of water in the liquid state. This water expansion in the form of ice
leads to internal stress development in the concrete, namely of the size of tens of
MPa. This results in the disruption of the inner concrete structure and subsequent
irreversible reduction in its fundamental material properties [21].
There are several ways of determining the frost resistance of concrete. There is a
limitation consisting in the fact that the testing is done almost solely on test specimens
made in moulds. The standard [15] is an exception allowing the testing of drilled
core specimens or prisms cut out of hardened concrete. In Europe, however, only