"Unbound base layers are an important part of the pavement, which consume a considerable amount of granular stone material. Favorable grain size distribution of materials, necessary for the construction of unbound base layers, is achieved by selecting a suitable material from nature or favorable material composition is achieved through mechanical stabilization. The basic principle of mechanical material stabilization is the addition of finer or larger granular material to the material of unfavorable, uniform granulometric composition, which is inherently unstable. In designing economical pavement structures, the availability of local materials of natural or industrial origin is of great importance.
From natural local materials for the road construction in the area of Slavonia and Baranja, the Drava sand, a material of uniform granulometric composition of medium grain size D50 = 0.3 mm, is interesting and often in use. With the increasing number of biomass power plants in eastern Croatia, waste local material, wood ash, is also being created. Wood biomass ash, which is generated as a residue of biomass burning for electricity and heat production, is one of the newer and less explored alternative materials, which finds its application in construction as evidenced by the results of previous foreign studies. One possibility of using wood bio ashes in mixtures for unbound base layers is to modify / repair the granulometric composition of the base material. By combining the aforementioned local materials, that is, by designing a mixture of Drava sand and wood ash in appropriate proportions, it would be possible to obtain a mechanically stable mixture of increased load-bearing capacity for construction of unbound base layers.
In this paper testing of mixtures composed from different proportions of Drava sand and wood ash for unbound base layers is described with the purpose of proving the stabilizing effect of wood ash. "

unbound base layer; stabilizing effect; wood ash; Drava sand