Today, the road construction profession is more than ever facing limited and increasingly expensive resources for component materials of asphalt mixtures, which has also led to the need for continuous research on the use of waste materials. One such potentially usable waste material is ash obtained by the combustion of wood biomass that is used to produce heat and electricity. The goal of this paper is to ascertain the possibility of using wood ash (WA) as the filler in asphalt concrete mixtures for the base-wearing layers of a pavement. The properties of Marshall stability (MS), quotient (MQ) and deformations, and the indirect tensile strength of water-conditioned samples and dry samples were tested on asphalt samples of an AC16 surf mixture with different contents of wood ash as the filler. The obtained values of MS and MQ indicate that a 50% content of bio ash in the filler results in an increase in asphalt’s resistance to the appearance of plastic deformations and greater tensile strength and in good asphalt resistance to the action of water.

The article describes the laboratory evaluation of mixtures of sand modified with wood fly ash (WFA) and additionally stabilized with different amounts of cement. Laboratory research includes determining the California Bearing Ratio (CBR), compressive and indirect tensile strengths of the mixtures, and the resistance of mixtures to freezing/thawing cycles. The aim of the research is to determine if WFA, an alternative material, can improve sand bearing capacity and contribute to strength development while reducing necessary cement amounts and satisfying the technical regulation for use in pavement base courses. The test results obtained show that WFA has a considerable stabilization effect on the sand mixture and improves its load bearing capacity. By adding a small quantity of the cement, the hydraulic reaction in the stabilized mixture is more intense and results in greater strengths and an improved resistance to freezing. The test results show that, by replacement of part of the sand with WFA (in the quantity of 30%), greater strengths can be achieved in relation to the mixture of only sand and cement. Additionally, the content of cement necessary for the stabilization of sand (usually 8–12%) is considerably reduced, which enables cost savings in the construction of pavement structures.

Stabilized mixes that are used in pavement structures are composed of aggregate bound with hydraulic binders (cement, lime) or bitumen. The most commonly used for the construction of base layers are mixes stabilized with cement. A long-standing construction practice for pavement structures was based on the use of quality granular materials for the construction of base layers. However, when designing the pavement structure and selecting materials, economy, sustainability, and environmental impact, in addition to their mechanical properties, should also be considered. Clear requirements and guidelines for sustainable development have imposed the need to explore the possibility of using non-standard materials in construction. Wood ash, which is formed as a residue from the combustion of biomass in the production of electricity and heat, is one of the newer and, in Croatia, less researched alternative materials that can be applied in construction. The paper describes compressive strength tests of mixtures of sand from the Drava River and cyclone wood ash stabilized with various contents of cement. The obtained results showed that with wood fly ash (in a content of 30 % mass.) in the stabilization mixture of sand, values of compressive strengths can be achieved within the required limits necessary for the construction of base layers of the pavement structure stabilized by a hydraulic binder.

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.

Rutting resistance of waterproofing-asphalt pavement systems on bridges Application of traditional waterproofing systems with thin asphalt courses results in occurrence of plastic deformities on traffic areas of bridges, especially in the form of rutting. The investigations comprised the analysis of the existing systems in exploitation, laboratory testing and on site measurements of relevant properties of individual system elements, as well as the system as whole, which have an impact to the resistance to rutting. The achieved results were controlled and confirmed on the waterproofing-asphalt courses system executed during construction of the Odra viaduct on the A11 motorway.