The Norwegian road construction specifications limit the amount of fines below 20 micrometre for gravel materials in the pavement to a maximum 3 per cent. This is based on the frost susceptibility criterion from Casagrande and only the material smaller than 19 mm is considered. Experience has shown that when the fines content smaller than 20 micrometre is limited to 3 per cent, none or very little deterioration due to gravel quality has taken place. However, in many cases no damage has occurred even with fines content up to 4-5 per cent, even when drainage conditions have been unfavourable. However, the problem with the gravel may not be the capillary suction and subsequent freezing. An increase in the water content of the base gravel material due to external infiltration during spring thaw, and consequently building up of pore pressure and reduction in shear stength under traffic load may be a much larger problem. The article describes different methods for thin section preparation of base gravel specimens and discusses their stability properties studied in thin section with regard to pore and grain structure, influenced by grain size distribution and the total amount of fines. (A)
Samenvatting