Issue 30

V. Veselý et alii, Frattura ed Integrità Strutturale, 30 (2014) 263-272; DOI: 10.3221/IGF-ESIS.30.33

Pre-dried Surface Samples

Wet Surface Samples

T31A T31B T31C T39A T39B T39C T86A T86B T86C T88A T88B T88C

T1A T1B T1C

-10 el. resistivity difference   [k  cm] 10 30 50 0.00 0.20

-10 el. resistivity difference   [k  cm] 10 30 50 0.00 0.20

T63A T63B T63C T69A T69B T69C

0.40

0.60

0.80

1.00

0.40

0.60

0.80

1.00

relative effective crack length  eff [-]

relative effective crack length  eff [-]

a) b) Figure 5 : Relationship between the concrete electrical resistivity difference,   , and the relative effective crack length,  eff , for the pre-dried (a) and the wet surface (b) samples evaluated at the notch (n) level.

Pre-dried Surface Samples

Wet Surface Samples

160

160

T31A T31B T31C T39A T39B T39C T86A T86B T86C T88A T88B T88C

T1A T1B T1C

0 ultrasound passing time t [  s] 40 80 120

0 ultrasound passing time t [  s] 40 80 120

T63A T63B T63C T69A T69B T69C

0.00

0.20

0.40

0.60

0.80

1.00

0.00

0.20

0.40

0.60

0.80

1.00

relative effective crack length  eff [-]

relative effective crack length  eff [-]

a) b) Figure 6 : Relationship between the ultrasound pulse passing time, t , and the relative effective crack length,  eff

, for the pre-dried (a)

and the wet surface (b) samples evaluated at the notch (n) level.

D ISCUSSION OF RESULTS

T

here were two sets of samples subjected to testing in order to indicate the difference between the dried and wet surface on the results of concrete electrical resistivity as well as ultrasound pulse passing time. As was mentioned above, the samples have been cured by saturation in lime water. The pre-dried samples have been removed from the curing tank one day before testing in order to let the surface dry out. Wet samples were stored in lime-water tank until the experiment took place. These samples have been kept wet between the subsequent testing cycles by treating the surfaces with wet sponge. Both test series were conducted at different ages of the concrete specimens. Thus, differences in conditions between the tests on the two specimen sets went from three sources: i) the time period between the specimen removal from the storage tank and the testing, ii) the existence of the wet sponge-based treatment of sample surfaces before the (resistivity) test, and iii) the age of concrete specimens. However, based on the nature of results of the conducted tests, it is not possible to precisely distinguish the effect of the individual source. Thus, the analysis is limited to the overall difference between the two specimen sets. Electrical resistivity measurements Fig. 5a) illustrates the overall pre-dried samples performance in terms of the difference between the resistivity value in the central (cracked) part of the specimen and the average of its values in its side (intact) parts,   , versus the relative effective

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