Foamed bitumen bound mixtures with steel slag, foundry sand and bottom ash: a laboratory investigation

The recycling of industrial wastes in road infrastructures represents a possible solution to two important and delicate questions: the growing problem of the disposal of industrial by-products and the need of finding alternative materials to the traditional quarried stone used for road construction. The paper describes an experimental investigation on foamed bitumen bound mixtures for road pavements, with the aggregate matrix completely composed by industrial by-products, as electric arc furnace steel slags, waste foundry sands and bottom ash from municipal solid waste incineration, used with different proportions. The study has been articulated in a laboratory analysis of the physical and leaching properties of each recycled granular material and in the following mechanical characterization of the foamed bitumen bound mixtures, in terms of indirect tensile strength and stiffness modulus tests. Both the mechanical test have been also performed in wet conditions, in order to investigate the moisture sensitivity of the mixes. The results of the tests (indirect tensile strength and stiffness modulus up to 0.85 MPa and 8,570 MPa, respectively, depending on the mixture) have been compared with the requisites for acceptance of the main Italian Contract Specifications, that demonstrated that the analyzed marginal materials are suitable for use as integral substitutes of natural aggregates, in the production of foamed bitumen bound mixtures for road bases and sub-bases