Frost Depth and Frost Protection Capacity of Crushed Rock Aggregates Based on Particle Size Distribution.

A common road insulation practice in Norway is to use a layer of crushed rock material, which is called a frost protection layer (FPL). The current regulations allow a large variation of particle size distribution into this layer. This paper presents field investigations on frost insulation performance of crushed rock material with three distinct grading. A full-scale test site was built in Røros, Norway, with each FPLs composed of 1 meter of crushed rock aggregates and built as: Ro-3 section was a coarse dense-graded material (0/120 mm), Ro-1 section, a coarse open-graded material (40/120 mm) and section Ro-2, a fine dense-graded material (0/32 mm). The sections were monitored for two winters (2016-17 and 2017-18). The results showed a significant difference in frost penetration and capacities between the sections. For winter 2016-17, the frost depth reached 194, 136, and 175 cm in Ro-1, Ro-2, and Ro-3 sections respectively, for a surface freezing index of 22,630oC·h. For winter 2017-18, the frost depth reached 232, 171, and 209 cm in Ro-1, Ro-2, and Ro-3 sections respectively, for a surface freezing index of 36,683oC·h. The 0/32 mm material provided the best insulation capacity with a frost protection capacity of 443°C·h/cm. The frost protection capacity for the 0/120 and 40/120 mm material were of 253 and 85°C·h/cm respectively. The study showed that fine dense-graded material provided superior frost protection mostly due to the larger amount of water retained that increased latent heat. For similar road design and layer thicknesses, the coarse, well-graded material seemed to be the most cost-effective material adapted to Norwegian regions with F100 < 28,000°C·h. Coarse, open-graded material should be used in low FI areas, and convection effect should be taken into account. [ABSTRACT FROM AUTHOR]