Lisø PhD Dissertation Manuscript - NTNU

accelerated frost damage or frost decay for the thirteen stations, from highest to lowest, as
presented in Table 2 and illustrated in Fig. 4. A high frost decay exposure index (FDEI)
value indicates a high risk of frost decay or frost damage.
Annual average number of days with freezing point crossings (FPC)
100,0
90,0
80,0
70,0
60,0
50,0
40,0
30,0
20,0
10,0
0,0
Kristiansand (Kjevik)
Bergen
Bodø
Trondheim (Værnes)
Ørland
Stavanger (Sola)
Ålesund (Vigra)
Fig. 4. Frost decay exposure index (FDEI) for the thirteen example stations, presented in a combination
diagram. The annual average number of freezing events is given in columns, with values on the left side axis.
Values for the resulting average year total frost decay exposure index (see line) are given on the right side
axis. Weather data for the reference 30-year period 1961 – 1990 is used, summing 4-day rainfall prior to
freezing events.
The results can be assessed qualitatively as follows: Kristiansand and Bodø, on top
of the list for both 2-day, 3-day and 4-day sums of rainfall prior to freezing events, have
large amounts of rainfall coupled with a sizable number of freezing events per year, and
therefore represent the highest frost decay potential. Lastly, Røros and Karasjok have a
high number of freezing events, but a very small average rainfall, especially in winter
months. A few localisations are changing one place on the ranking dependent on the
number of days of rainfall counted. Bergen is especially to be noted, as it climbs from
number five when summing 2-day rainfall to number 2 on the ranking when summing 4day
rainfall, in particular due to extreme amounts of rain. Still, the bottom four
localisations on the ranking are independent of the number of days of rainfall summed
prior to days with freezing point crossings. This also applies for the top four localisations
on the ranking, when Bergen is left out of account, indicating a robust method of
characterising climates to promote frost decay. Damaging rain penetration in porous,
mineral building materials requires a long-lasting absorption of moisture. Subsequent and
repeated freezing events may destroy the material, or contribute to accelerated decay and
thus reduced lifetime, if the water content is higher than the critical degree of saturation for
the material at the time of freezing.
Tromsø
Page 8 of 13
Fruholmen
Lyngdal
Oslo
Røros
Karasjok
800,0
700,0
600,0
500,0
400,0
300,0
200,0
100,0
0,0
Frost decay exposure index (FDEI)