Promoting resource conservation in road flexible pavement using jet grouting and plastic waste as filler

https://doi.org/10.1016/j.resconrec.2022.106633Get rights and content

Highlights

  • Design of hot asphalt mastics containing waste.

  • Waste plastics and jet grouting waste in substitution to limestone filler.

  • Analysis of rheological properties by assessing stiffness and rutting resistance.

  • Life cycle assessment of asphalt mastics.

  • Multi-weight method analysis for the selection of the best alternative.

Abstract

The circular economy aims to change the paradigm in relation to the linear economy by limiting the environmental impact and waste of resources, as well as increasing efficiency at all stages of the product economy; the recent warnings about waste pollution and the limits of natural resources are encouraging its development.

The purpose of this research is to investigate the potential environmental and mechanical benefits of reusing two different waste, namely jet grouting waste (JGW) and plastic waste (PW) for producing hot asphalt mastics made up of bitumen and filler: the JGW comes from the soil consolidation activities during pavement construction, while the PW, a mixture of high-density polyethylene, low density polyethylene, polypropylene and polyethylene terephthalate derives from a plastic recycling plant.

First, three mastics engineered by keeping constant viscosity and a filler over bitumen ratio of 0.3 for the asphalt mastic with limestone filler (LM), 0.29 for the mastic with JGW (JGWM) and 0.1 for the solution containing PW (PWM), were investigated through a dynamic shear rheometer to explore their rheological behavior.

Second main step concerned the life cycle assessment (LCA) of the three asphalt mastics that, in turn, are included into the base layer of a flexible road pavement by following ReCiPe impact assessment methodology.

Primary results in terms of mechanical performance demonstrated that: 1) JGWM outperformed LM in terms of complex shear modulus, which resulted 19% higher than that of LM in the temperature range below 30 °C, and 2) PWM returned on average 30% lower non-recoverable creep compliance at 50 °C under 0.1 and 3.2 kPa than remaining solutions under analysis.

LCA outcomes showed, on the one hand, that PWM had the best environmental performance, expressing the lowest damage to human health, ecosystems and resource availability indicators, returning on average 34% and 19% lower indicators than LM and JGWM, respectively. On the other hand, JGWM still represented an overall improvement of the environmental performance compared to LM, returning the best performance in terms of damage to human health, which lowers by 23%, due to the reduction of the output waste stream.

Introduction

The only way to safeguard the environment and natural resources is to take sustainable action. The take-make-dispose formula is no longer sustainable, and the effects of industrial practices are seriously affecting human health and the ecosystem. Therefore, a change based on the circularity of material flows is necessary in order to avoid intensive supply and waste production.

One of the first important benefits of the circular economy is related to waste management.

With a view to pursuing the circular economy objective in the road pavement construction area, many scholars are trying to study the benefits deriving from the substitution of raw materials in the grading curve with waste for making asphalt mixtures, i.e. steel slag as alternative aggregates (Chen et al., 2020; Lyu et al., 2021), construction and demolition waste as alternative aggregates (Contreras Llanes et al., 2021), red mud as a filler (Lima and Thives, 2020), waste jarosite as a filler (Islam et al., 2021).

One of the components of the asphalt mixture that affects the final performance is surely the asphalt mastic, i.e. binder plus filler passing 100% through the 0.063 mm sieve size, whose performance are under investigation by many researchers; above all, the benefits deriving by replacing traditional limestone filler with waste are carefully studied (Giustozzi et al., 2018; Veropalumbo et al., 2020; Varveri et al., 2021).

For example, Antunes et al. (2017) analyzed the delta ring and ball and water damage assessed through the mass ratio of filler particles separated from the mastic in the presence of hot water at 60 °C of asphalt mastics made up by using a brick powder as a filler deriving from construction and demolition waste (CDW) compared to limestone mastics. The filler over bitumen ratio was fixed to 0.6 for all the mastics. The delta ring and ball test showed how alternative mastics produced higher stiffness than the traditional one, on average +9%, while the mass ratio of filler particles separated from the mastic was very small and similar to that of limestone.

Yinfei et al. (2020), instead, analyzed asphalt mastics made up by replacing limestone filler with hollow glass microsphere (HGM). The HGM was found to be a potential material to provide thermal resistance to the asphalt pavement, as well as increasing the fatigue life, on average +13% than a control mastic with limestone filler, evaluated by means of a linear amplitude sweep test under two strain levels of 2.5 and 5%.

Many efforts are also being made by researchers to introduce plastic waste for making road pavement layers (Viscione et al., 2022; Mishra and Gupta, 2020; Georgiou and Loizos, 2021), aiming not only to reduce the pollutants released in the environment but also to obtain new modifiers for bitumen (Ponnada and Krishna et al., 2020; Alghrafy et al., 2021; Chen et al., 2021) or use plastic particles as filler replacement for making asphalt mastics with superior performance than traditional ones (Veropalumbo et al., 2021b).

Ullah et al. (2021) studied the effect of using low density polyethylene (LDPE) and high-density polyethylene (HDPE) in substitution of 5%, 15% and 25% natural aggregates by evaluating different mechanical properties of the asphalt mixes containing them. The authors demonstrated that, when LDPE and HDPE replaced the natural aggregates, the Marshall stability increased up to 15% and, in particular, in correspondence of 15% HDPE addition, the highest value of resilient modulus was recorded, increasing by 168.5% in comparison to the control mixture with 100% natural aggregates.

Dalhat et al. (2019) focused the attention on a mix of recycled waste plastic (RWP) made up of 17% LDPE, 25% HDPE, 34% PET, 11% PP, 4% polyvinyl chloride (PVC) as substitute of the aggregates in a mixture for the binder layer. It was found that the 9.5% RWP is the optimum content to obtain an increase of dynamic modulus, on average 40% higher than the control mixture with 0% RWP, and a decrease of flow number by 66%.

Although the introduction of waste into the asphalt mixture has led to significant results from a mechanical perspective, it is fundamental to validate their adoption also from an environmental point of view. For this reason, many studies put the attention on the life cycle assessment (LCA) methodology (Araújo et al., 2014) for examining green benefits of different asphalt mixtures when waste is reused or recycled (Oreto et al., 2021a).

Vega et al. (2020), for example, investigated through LCA methodology the benefits of replacing natural aggregates with 30% CDW in the grading curve for making the asphalt mixture of a binder layer. The results showed that the mixture with CDW had lower global warming potential compared to the traditional mixture, thanks to lower amount of natural aggregates and 1 cm off the thickness for the pavement layer, keeping constant the service life.

Other researchers used LCA to assess the environmental benefits of using waste to modify asphalt binders and enhance the environmental performance of asphalt mixtures (Zhang et al., 2020; Piao et al., 2020); for example, (Samieadel et al., 2018) analyzed the production process of an asphalt mixture with 5% bitumen by the weight of aggregates considering two different bitumen: one modified with 10% bio-oil deriving from swine manure (by mass of the neat bitumen) and a neat unmodified bitumen. They found out that the production process of the modified asphalt mixture lowered by 82% the overall energy consumption of the life cycle compared to the asphalt mixture with neat bitumen.

Santos et al. (2018) compared the environmental performance of a traditional asphalt mixture with two mixtures containing a bituminous binder modified with 5% waste nitrile rubber from shoe sole (NBR) and 5% virgin poly (ethylene-co-vinyl acetate) (EVA), polymer by the weight of bitumen. The results showed that, while the asphalt mixture with 5% EVA worsened the environmental performance of the life cycle, up to 12% increase for the impact category freshwater eutrophication, the use of 5% NBR improved all the impact categories compared to the traditional asphalt mixture, in particular in terms of ozone layer depletion (−4%).

Although the waste derived from the demolition of existing buildings are reasonably analyzed in the field of road pavements, almost no studies dealt with the jet grouting waste (JGW), i.e. the residual of jet grout expelled together with the extracted mud during the soil consolidation operations. To date, the use of JGW is allowed by the Directive 1999/45/EC of the European Parliament and of the Council of 31 May 1999 concerning the approximation of the laws, regulations and administrative provisions of the Member States relating to the classification, packaging and labeling of dangerous preparations.

With a view to discover the possible reuse of other waste within asphalt mixtures and comparing their behavior with waste from different production cycles, the present research focuses on the investigation of the mechanical and environmental benefits of two sustainable asphalt mastics containing, in turn, plastic waste (PW) and jet grouting waste, considered alternative to the traditional limestone one, keeping boundary conditions constant as the viscosity, which implied different filler over bitumen ratio (f/b): a) JGWM made up by reusing JGW as a filler (f/b equal to 0.3), b) PWM made up by PW as a filler (f/b equal to 0.1), deriving from plastic bottles recycling plant and composed of a mixture of high density polyethylene, low density polyethylene, polypropylene and polyethylene terephthalate, c) LM made up by limestone filler (f/b equal to 0.3). The rheological performance of the three asphalt solutions here suggested are investigated through a frequency sweep test for defining the shear modulus at 0, 10, 20, 30, 40 and 50 °C in the frequency range from 0.1 to 10 Hz and Multiple Stress Creep and Recovery test for describing the non-recoverable creep compliance under 0.1 and 3.2 kPa stress levels at test temperature of both 40 and 50 °C.

With the aim to validate the consequent improvement of natural resource use and conservation, as well as pollution reduction, the LCA methodology (EN 14,040) is carried out for integrating the mechanical and environmental features of a road pavement base layer, whose asphalt mixture follows the composition of the three asphalt mastics solutions suggested one at time, and grading curve of the natural aggregates in compliance with the local technical specifications. As a conclusion of the research, the aim is to provide a mechanical-environmental integrated approach for comparing the asphalt mixtures performance starting from the evaluation of the asphalt mastics performance that obviously affect final asphalt mixture performance in which they are included (Aldagari et al., 2022; Kabir et al., 2021).

The revised decision tree of the end-of-waste strategy (EN 15,804) here adopted for pursuing the main goals of the research is shown in the Fig. 1 where mechanical and environmental benefits are well investigated and well connected for reaching the final best solutions.

Section snippets

Fillers

As mentioned above, two recycled wastes are here used as a filler for mixing hot asphalt mastics, as follows in the Fig. 2:a) Fig. 2a refers to a grinded plastics made up of HDPE, LDPE, PP and PET type coming from a recycling plastic plant that through an open-loop recycling process (Neo et al. 2021) produces plastic particles as a filler, with a final maximum size of 0.25 mm and percentage by mass passing at 0.063 mm sieve size falling within the range from 70 to 100% (EN 13,043); b) Fig. 2b

The rheological characterization of the asphalt mastics

The black diagram reported in Fig. 6 returns on the x-axis the phase angle δ values and on the y-axis the shear modulus G* values following the FS test (Grilli et al., 2017; Veropalumbo et al., 2021b): first of all it can be observed that for phase angle values lower than 55 ° the PWM solution requires the highest values of G *; this shows how PWM has a good elasticity even for medium-high values of the phase angle. On the other hand, it can be observed how JGWM appears like the best solution

Discussion

The study here presented aimed to point out the meaningfulness and relevance of recycling two specific waste as a filler, such as plastic waste obtained from grinded plastic bottles, and jet grouting waste from soil consolidation activities, for making sustainable and high-performing hot asphalt mastics for the construction of flexible road pavements’ base layers.

The rheological performance of three mastics was analyzed under an equi-viscosity constraint, which led to a filler over bitumen

Conclusions

In the present study, the environmental and mechanical feasibility of using waste plastic and jet grouting waste in substitution of traditional limestone filler into an asphalt mixture for a base layer of a flexible road pavement was assessed starting from the rheological analysis of the asphalt mastics containing them. The “cradle to site” approach was implemented to perform the life cycle assessment for valorizing the benefits of reusing in an innovative way the two wastes.

The findings that

CRediT authorship contribution statement

Francesca Russo: Conceptualization, Writing – original draft, Writing – review & editing, Supervision, Resources. Cristina Oreto: Conceptualization, Formal analysis, Data curation, Writing – review & editing, Resources, Visualization. Rosa Veropalumbo: Conceptualization, Methodology, Data curation, Investigation, Validation, Writing – review & editing, Resources.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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