CIRCULAR ECONOMY FOR TRANSPORT INFRASTRUCTURES: RECYCLING WATERPROOFING MEMBRANES TO PRODUCE LONG LASTING ASPHALT MATERIALS

Overall, in this research study recycling feasibility of waterproofing membranes waste into bituminous materials was evaluated. Firstly, optimized dosages of membrane waste in bituminous binder and mixtures were determined in laboratory. Then, at optimized dosages, membranes waste modified bituminous mixtures were also produced at asphalt plant to validate the laboratory test results. Based on all laboratory test results, it can be concluded: Addition of membranes waste in bituminous materials by dry mixing method (direct mixing in bituminous mixtures) is more economical and easier in comparison with wet mixing methodology. As wet mixing method consist of more energy consumption due to homogenization of membranes waste by standard shear mixer prior to addition in neat paving bitumen and again high shear mixing to prepare final MW-modified blends. Moreover, wet modification results in a less homogeneous and stable binder leading to uncertainties and inconsistent final performance. DSC test results showed, melting temperatures of three basic constituents’ materials i.e., membrane waste bitumen, glass fibers and polyester fibers were 163.89 °C, 257.8 °C and 251.32 °C, respectively. Hence, glass/polyester fibers will not be melted at conventional bituminous mixtures paving temperature (160-180 ˚C) and provide reinforcement to distribute stresses over large area to increase durability of pavement structures. Membranes industrial production waste in paving bitumen decrease its Pen Grade up to 50% and increase its softening point 17-26% due to presence of polymer-modified bitumen and glass/polyester fibers in membranes waste. So, it leads to increase in stiffness while reducing ductility of paving bitumen. At higher temperatures 165 ˚C, viscosity test results are not correlated to membranes waste dosages due glass/polyester fibers locally interaction with neat paving bitumen. However, all MW modified bitumen blends have relatively higher values of viscosity that leads to higher bituminous mixtures production temperatures to guarantee adequate workability of MW modified bituminous mixtures. Moreover, geometry of viscosity measuring spindle slightly affect the viscosity test results as all measuring methods results different viscosity values, but all values are less than max allowable limit for PG classification i.e., 3 Pa.s. Rheological investigation showed, industrial production membranes waste 15-20% increase stiffness as well as elasticity of neat paving bitumen while 10% MW-modified blend have similar rheological behavior like neat bitumen. End of life MW-modified bituminous mixtures (either 0.5% or 2% by weight of mix) did not affect the workability and the moisture resistance of the investigated bituminous mixtures. End-of-life MW-modified bituminous mixtures were characterized by higher indirect tensile strength, stiffness and permanent deformation resistance with respect to the corresponding reference mixtures. Moreover, higher the MW content, higher the performance of bituminous mixtures. MW shreds led to a positive effect also regarding the fatigue cracking resistance at lower strain levels; however, MW modified materials were characterized by a higher strain sensitivity likely due to the presence of hard brittle binder. Overall, plant produced membranes PW modified bituminous mixtures have similar compaction behaviour, relatively higher moisture damage resistance, similar stiffness modulus, higher high temperature performance and relatively better fatigue resistance in comparison with reference mixture (i.e. not containing membrane wastes).