Rheological characterization and performance-related evaluation of paint sludge modified binders

Application of paints by spraying, extensively used in the automotive industry, generates a solid waste, known as paint sludge, which, if improperly managed, may lead to significant environmental and economic burdens. In the research work described in this paper, use of paint sludge for the production of modified bituminous binders for paving applications was investigated. In particular, expected field performance of paint sludge modified binders (PSMBs) was assessed and compared to that of neat bitumen and polymer-modified binders. PSMBs considered in the study were prepared in the laboratory by employing variable dosages of sludge coming from different painting plants and derived either from basecoat or clearcoat application. PSMB characteristics were evaluated by means of rheological tests which led to construction of master curves, determination of performance grade (PG) according to the SUPERPAVE scheme, detailed evaluation of resistance to permanent deformation by means of multiple stress creep recovery tests, and analysis of resistance to fatigue damage by making use of time sweep and linear amplitude sweep tests. Obtained results showed that use of automotive paint sludge for the production of PSMBs is a feasible, cost-effective and environmentally compatible alternative to currently adopted management solutions which consist either in incineration or in energy production in cement kilns. Although fluxing and stiffening effects were observed in the case of basecoat and clearcoat sludge, respectively, only minor variations were recorded in terms of PG, elastic response, stress sensitivity, fatigue resistance and fatigue ductility of neat bitumen.