A comparative environmental life cycle assessment of road asphalt pavement solutions made up of artificial aggregates

The construction and maintenance of road pavements entail detrimental impacts on the consumption of resources and damage to the natural environment but also make up an opportunity for the large-scale application of circular economy principles and innovative waste valorisation paths. The present study focuses on developing a comprehensive procedure to evaluate the technical and environmental sustainability of replacing high percentage of limestone aggregates with artificial aggregates from municipal solid waste incineration (MSWI) into hot or cold recycled asphalt mixtures for asphalt pavements. The technical feasibility of the designed mixtures was investigated in terms of the main physical and mechanical properties of both the raw materials and the asphalt mixtures with content of artificial aggregates or sand in the range 25-40 % by mass. The environmental feasibility of the asphalt mixtures was evaluated through the SEM-EDS technique, the analysis of the eluate of the leaching test and the ecotoxicity for living organisms. Afterwards, the life cycle assessment (LCA) was applied to detect the critical spots of the life cycle of 1 m2 of a 6 cm-thick binder layer with high percentage of artificial aggregates or sand built and maintained through 30 years analysis period according to 18 impact category indicators. The main results show that, recycling the artificial aggregates into hot asphalt mixtures has on average a negligible effect on the overall environmental performance of the life cycle, and appears to be detrimental only for the consumption of fossil resources due to the higher optimum bitumen content. Looking at the results for cold mixes, the introduction of the artificial aggregates has an effect on the predicted durability of the asphalt layers, which is maximized in the case of coarse artificial aggregates. Consequent environmental benefits regard the global warming potential, fossil resource scarcity and freshwater eutrophication indicators.

Leveraging Infrastructure BIM for Life-Cycle-Based Sustainable Road Pavement Management

The latest developments in the field of road asphalt materials and pavement construction/maintenance technologies, as well as the spread of life-cycle-based sustainability assessment techniques, have posed issues in the continuous and efficient management of data and relative decision-making process for the selection of appropriate road pavement design and maintenance solutions; Infrastructure Building Information Modeling (IBIM) tools may help in facing such challenges due to their data management and analysis capabilities. The present work aims to develop a road pavement life cycle sustainability assessment framework and integrate such a framework into the IBIM of a road pavement project through visual scripting to automatically provide the informatization of an appropriate pavement information model and evaluate sustainability criteria already in the design stage through life cycle assessment and life cycle cost analysis methods. The application of the proposed BIM-based tool to a real case study allowed us (a) to draw considerations about the long-term environmental and economic sustainability of alternative road construction materials and (b) to draft a maintenance plan for a specific road section that represents the best compromise solution among the analyzed ones. The IBIM tool represents a practical and dynamic way to integrate environmental considerations into road pavement design, encouraging the use of digital tools in the road industry and ultimately supporting a pavement maintenance decision-making process oriented toward a circular economy.

Exploring the effect on the environment of encapsulated micro- and nano-plastics into asphalt mastics for road pavement

A new environmental problem is represented by the huge transformation of plastic waste released into the environment into small fragments, the so called micro- and nano-plastics, due to atmospheric phenomena. The smaller the size of the plastic fragments, the more their spreading into environmental compartments. The aim of this study is to test encapsulation into asphalt mastics of waste plastic material (WPM) as sustainable strategy to obtain road flexible pavements and to evaluate the potential release in water of micro and nano plastics. A new mastic mixing method was developed to blend the WPM with the bitumen contained into a bitumen emulsion (BE60/40) by adopting low mixing temperatures. Three different WPM contents, equal to 5, 10 and 20% by the weight of the bitumen contained in the BE60/40, were adopted to produce the mastics; the mastics' rheological properties, obtained by frequency sweep and multiple stress creep and recovery tests, were compared to those of a traditional asphalt mastic containing limestone filler. The aging of asphalt mastics was analyzed by soaking them in water and gradually lowering and raising temperature between -10 and 60 °C at predefined intervals. The addition of WPM improved greatly the asphalt mastic performance; in particular, for a WPM content of 10%, the rheological response in terms of stiffness remained unchanged after the mastic underwent thermal excursions in water. Encapsulation of micro and nano plastics into mastics reduced of more than 99% their potential water release.

Sustainable asphalt mastics made up recycling waste as filler

The continuous growth of waste is generating worldwide more and more increasing related environmental concerns. Anything that is not recycled or recuperated from waste represents a loss of raw materials and other production factors used in the manufacture, transport and consumer phases of the product. This research explored the potential of three waste namely Construction and Demolition (CD) waste, Fly Ash (FA), and Jet Grouting (JG) waste as fillers in comparison to the traditional limestone one for making hot asphalt mastics for road pavement, through a rheological analysis and environmental compatibility tests towards the release of potentially toxic elements. A total of eight asphalt mastics were prepared by using two filler-to-binder weight ratios (f/b) of 0.5 and 1 for blending each filler with a neat bitumen 50/70 penetration grade. The Frequency Sweep test and the Multiple Stress Creep and Recovery (MSCR) test were carried out to investigate the rheological properties of the asphalt mastics. Asphalt mastics containing FA and JG fillers were found to be more mechanically and environmentally efficient than traditional limestone mastic in particular by adopting an f/b equal to 1 where it was observed higher complex shear modulus values, G*, (on average 50% compared to the traditional asphalt mastic) and lower non-recoverable creep compliance values, Jnr, (on average 35% compared to the traditional asphalt mastic) at all test temperatures investigated. Based on the suggested ranking methodology, CD emerged as the filler performing in the same way of the traditional one. All the waste containing mastics, showed up noticeable environmental compatibility, being the potentially toxic elements completely immobilized into the mastics' structure e practically not releasable into acidic water, highlighting the waste recycling for road pavements as primary strategy to immobilize hazardous wastes.

Life Cycle Assessment of Sustainable Asphalt Pavement Solutions Involving Recycled Aggregates and Polymers

The pursuit of sustainability in the field of road asphalt pavements calls for effective decision-making strategies, referring to both the technical and environmental sustainability of the solutions. This study aims to compare the life cycle impacts of several pavement solution alternatives involving, in the binder and base layers, some eco-designed, hot- and cold-produced asphalt mixtures made up of recycled aggregates in substitution for natural filler and commercial recycled polymer pellets for dry mixture modification. The first step focused on the technical and environmental compatibility assessment of the construction and demolition waste (CDW), jet grouting waste (JGW), fly ash (FA), and reclaimed asphalt pavement (RAP). Then, three non-traditional mixtures were designed for the binder layer and three for the base layer and characterized in terms of the stiffness modulus. Asphalt pavement design allowed for the definition of the functional units of Life Cycle Assessment (LCA), which was applied to all of the pavement configurations under analysis in a "from cradle to grave" approach. The LCA results showed that the best performance was reached for the solutions involving a cold, in-place recycled mixture made up of RAP and JGW in the base layer, which lowered all the impact category indicators by 31% on average compared to those of the traditional pavement solution. Further considerations highlighted that the combination of a cold base layer with a hot asphalt mixture made up of CDW or FA in the binder layer also maximized the service life of the pavement solution, providing the best synergistic effect.

Investigating the environmental impacts and engineering performance of road asphalt pavement mixtures made up of jet grouting waste and reclaimed asphalt pavement

As a response to the reduction of environmental pollution and energy consumption in the maintenance or building of a road pavement, this research aims to provide innovative asphalt mixture solutions when designing asphalt base layers containing solidified Jet Grouting Waste (JGW) particles. This involved adding (or not) solutions made up from Reclaimed Asphalt Pavement (RAP) obtained by milling old pavements. The first step focused on a JGW and RAP leaching test before going on to design two non-traditional mixtures: a) a hot asphalt mixture made by replacing 4% of the limestone filler by the total weight of the aggregates with JGW (HMAJ), mixing all of them at a high temperature (160 ÷ 180°C), and b) a cold asphalt mixture made by adding 3% JGW as a filler, 70% RAP (CMRAJ), and 27% limestone by the total weight of the aggregates at low temperatures (40 ÷ 50°C). These innovative mixtures were investigated from the point of view of engineering performance by ascertaining their physico-mechanical features and environmental impact through a Life Cycle Assessment (LCA) test. Further comparison with traditional ones was then carried out using a hot mix asphalt (HMA) and a cold mixture made up from RAP, substituting a portion of the limestone aggregates (CMRA). Such mixtures are subject to special tender specification requirements. Engineering performance assessment showed that, compared with HMA, when JGW is added to both hot and cold mixtures, the ITS is 11% higher for HMAJ and CMRAJ, and cumulative strain is reduced by 17% for HMAJ and 39% for CMRA, while the cold asphalt mixtures (CMRA and CMRAJ) showed greater stiffness levels (on average 50%) at all test temperatures (10, 25, and 40°C). LCA analysis provided significant results for the solutions being compared. Specifically, use of HMAJ as the base layer helped save 65 g/m³ of CO₂ compared with HMA, at the same time helping to reduce 29.7 kg of CO_2eq./m³ global warming potential. On the other hand, the use of CMRA as the base layer, again compared with the HMA, helped save 45 g/m³ of phosphorous compound emissions in water. In terms of terrestrial ecotoxicity and human non-carcinogenic toxicity, the best performance was obtained using a CMRAJ mixture, whose indicators showed a 60% reduction compared with the HMA solution base layer.