Reuse of paint sludge in road pavements: Technological and environmental issues.

This paper presents some of the results obtained in a research project focused on the use of paint sludge (PS) as a modifying agent in the production of bituminous binders for paving applications. The scope of the project was to provide an innovative, sustainable and profitable solution to waste management problems which automotive industries have to face worldwide as a result of the production of PS. The authors applied for a patent which defines the industrial process for the production of PS modified binders (PSMBs). Measurements and analyses which were considered relevant for the assessment of technological feasibility included evaluation of: PS physical characteristics, PSMB high-temperature viscosity and PSMB storage stability. Environmental issues were addressed by considering PS chemical composition, gaseous emissions during PSMB production, and leaching behavior of bituminous mixtures containing PSMBs. Obtained results show that with a proper adaptation of the PSMB production process (i.e., PS drying at a higher temperature than 105°C) it is possible to comply with technological and environmental requirements such as those related to storage stability and to gaseous emissions during PSMB production and laying of bituminous mixtures. Leaching tests, aimed to evaluate runoff water quality, show no substantial difference in the release of substances in water between standard bituminous mixtures and bituminous mixtures prepared with PSMBs.

A Sustainable Cold-Recycled Solution for the Surface Finishing of Unpaved Rural Roads.

This paper presents the results of an experimental investigation which was carried out with the purpose of assessing the performance-related properties of an emulsion-based cold-recycled mixture to be employed as a sustainable solution for the surface finishing of unpaved rural roads. This mixture contained significant quantities of recycled components (reclaimed asphalt and mineral sludge), and its composition was fine-tuned by following an innovative mix design procedure. Properties of these mixtures were studied by means of laboratory tests which considered key parameters, such as flowability, indirect tensile stiffness modulus, indirect tensile strength, moisture susceptibility and resistance to permanent deformation. It was found that, by means of the proposed mix design procedure, optimal dosages of the recycled components can be identified, thereby ensuring the achievement of the desired properties in terms of high workability and adequate stiffness and strength.

Experimental Evaluation and Modeling of Physical Hardening in Asphalt Binders.

The research described in this paper deals with the experimental evaluation and modeling of physical hardening in asphalt binders. The term physical hardening refers to a reversible phenomenon occurring at low temperatures that causes time-dependent changes in viscoelastic properties. The experimental approach, followed to quantitatively assess physical hardening, was based on flexural creep tests carried out by means of the Bending Beam Rheometer at various temperatures and conditioning times. The results obtained confirmed that hardening phenomena have a significant influence on the creep response of asphalt binders, to an extent that can be quantitatively assessed by referring to the appropriate rheological parameters and by applying the loading time-conditioning time superposition principle. The experimental data were fitted to a mechanical model proposed in the literature (composed of a single Kelvin-Voigt element) and thereafter to an improved model (with two Kelvin-Voigt elements in series). Both models were assessed in terms of their prediction accuracy. The improved model was found to better describe physical hardening effects in the case of both short- and long-term conditioning. Practical implications of the study were finally highlighted by referring to possible ranking criteria to be introduced in acceptance procedures for the comparative evaluation of asphalt binders.

Cost analysis and environmental assessment of recycling paint sludge in asphalt pavements.

Paint sludge (PS) is a waste product coming from spray application of paints in automotive industry. For the first time, this work assessed the economic costs and environmental impacts connected to recycling PS in bituminous binders for asphalt pavement applications. Previous works have demonstrated that PS could be used as a replacement of up to 20% (w/w) of neat bitumen in the production of hot mixture asphalts (HMAs), without worsening the technical performances of pavements. The annual production of PS from Italian automotive plants (3000 t/year) could be accommodated in a paved area of 1.64 km2 that, when employed in local roads, with an average width of 5 m, corresponds to approximately 330 km. Costs for treating PS to be prepared for recycling resulted in 144 €/t raw PS. This cost was of the same order, or even less, of that required for PS incineration or disposal in a landfill for hazardous waste (250-300 €). The LCA analysis revealed that the production of HMAs by employing a binder that contains 20% (w/w) of PS, reduced the gross energy requirement (GER) and global warming potential (GWP) indexes by 15% and 39%, respectively, compared to an HMA produced with the traditional process.

A preliminary investigation into the physical and chemical properties of biomass ashes used as aggregate fillers for bituminous mixtures.

Fly and bottom ashes are the main by-products arising from the combustion of solid biomass. Since the production of energy from this source is increasing, the processing and disposal of the resulting ashes has become an environmental and economic issue. Such ashes are of interest as a construction material because they are composed of very fine particles similar to fillers normally employed in bituminous and cementitious mixtures. This research investigates the potential use of ash from biomass as filler in bituminous mixtures. The morphological, physical and chemical characteristics of 21 different ashes and two traditional fillers (calcium carbonate and "recovered" plant filler) were evaluated and discussed. Leaching tests, performed in order to quantify the release of pollutants, revealed that five ashes do not comply with the Italian environmental re-use limits. Experimental results show a wide range of values for almost all the investigated properties and a low correlation with biomass type in terms of origin and chemical composition. Furthermore, sieving and milling processes were found to improve the properties of the raw material in terms of grading and sample porosity. The effectiveness of these treatments and the low content of organic matter and harmful fines suggest that most of the biomass ashes investigated may be regarded as potential replacements for natural filler in bituminous mixtures.

Rheological characterization of xanthan suspensions of nanoscale iron for injection in porous media.

Nanoscale zerovalent iron (NZVI) represents one of the most interesting reagents for the remediation of contaminated aquifers, but its application is hindered by a lack of colloidal stability. Prior studies have shown that nanoscale iron slurries can be successfully stabilized against aggregation and sedimentation through dispersion in xanthan solutions; thus, further research was carried out by focusing on the flow behavior of xanthan-modified NVZI suspensions. This work aims at understanding the rheological properties of NZVI-xanthan suspensions, which have been extensively tested under two different flow conditions: simple shear flow and flow through a porous medium. According to both experimental approaches, the suspensions show a shear thinning behavior that is dependent on iron concentration. These rheological properties are explained by referring to the microstructure of the colloidal system. Flow equations have been formulated and solved in radial coordinates in order to demonstrate the feasibility of such suspensions in field scale applications.