In Croatia, the design of pavement structures primarily considers the traffic load. However, if the subgrade soil is frost susceptible and if the hydraulic conditions are unfavourable, the originally designedpavement structure shouldbe additionally tested to determine the impact of freezing. If there is a risk of freezing, certain technical measures have to be planned within the pavement structure or under it in order to avoid the risk of freezing or to significantly lower the impact of freezing. In Croatia the pavement testing concerning freezing is carried out in the following manner.
Based on the soil mechanics characteristics, the pavement materials and subgrades are grouped into one of the following four groups according to their freezing susceptibility (in compliance with the national standard HRN U. E1. 012):
G1 – lightly susceptible (gravel) containing 3-10% of particles smaller than 0.02 mm.
G2 – lightly to moderately susceptible (gravel, sand) containing 10-20% of small particles.
G3 – moderately susceptible (gravel, sand, clay with PI higher than 12) containing over 20%, i. e. over 15% of particles smaller than 0.02 mm.
G4 – highly susceptible (dust, very fine dusty sand, clayey dust) containing over 15% of particles smaller than 0.02 mm.
According to the national standard HRN U. C4.016, it is established whether the hydrological circumstances are favourable or not.
Fig. A.1 Contour map with air freezing index (FI) for the territory of Croatia (Srsen et al. 2004). Reproduced by permission of the Croatian Association of Civil Engineers
Then the freezing depth is determined according to the national standard HRN U. B9. 012. It is required to determine the Freezing Index (FI) for that purpose. The FI value is taken from the freezing index contour map shown in Fig. A.1. That map is derived from an IGH study on Freezing Index determination for national roads in 2003, elaborated in cooperation with the Metrological and Hydrological Service. The study is based on the data on the highest and lowest air temperatures noted in 39 meteorological stations in Croatia in a period of 25 years (1976-2000) (Srsen et al. 2004).
The freezing depth under the pavement surface is read from a diagram based on FI and from the data on pavement thickness (designed or completed), its spatial mass and humidity and from data on the soil type under the pavement.