With the aim to protect the ecosystem and to leave the earth with the same current resources for future generations, in the last decade, human activities have pursued more and more frequently and regularly the concerns regarding Eco-sustainability.
There are several tools that are used to support Eco-sustainability, such as “Green Purchases” (GPP – Green Public Procurement), which as defined in Europe, are “an approach according to which Public Administrations integrate environmental criteria in all the purchasing process phases, promoting the diffusion of environmental technologies and the development of environmentally-friendly products, through the research and the choice of results and solutions that have lower impacts on the environment throughout the entire life cycle”.
In this historical context, with reference to asphalt pavements, it should be noted that technologies have been developed towards solutions for enhancing the pavement’s service life, which should be considered in Life Cycle Analysis (LCA) too.
The most innovative technologies are:
- extended service life: increasing the service life of pavements up to 50 years. “Perpetual Pavements” have been introduced;
- rejuvenating and reusing asphalt derived from either demolishing or milling of existing asphalt layers (Circular Economy);
- reducing the energy consumptions and consequent emissions.
As evidence of this evolution in the road industry, Iterchimica Srl developed the formulation of an innovative product that contains graphene and a selected type of recycled hard plastics. This is shown in the followings.
In this part 1 of the article we deepen the theorical point of view while part 2, which will be online from wednesday April 1, will be focused on the application.
The PMA modification of asphalt mixes with Dry method
The chemical composition of bitumen is extremely complex and varies depending on both crude oil properties and manufacturing processes. In particular, the refining is increasingly driven to material recovery such as petrol, gas oils, heavy oils, etc., causing a continuous depletion of bitumen and its physical-mechanical performances.
At the same time, the ever-increasing traffic and loads have led to needs for constant increment in the performances of the various materials that compose a road section.
Regarding the asphalt pavements, in the last 40 years, solutions have been progressively sought in order to increase their performances through “modification”. For this purpose, countless modification methods and modifying typologies have been introduced e.g., neoprene (polychloroprene), natural and synthetic latex, plastomers of different nature, thermoplastic elastomers, etc.
However, the internationally acknowledged technologies are mainly two:
- polymer-modified Bitumen (PmB: Wet Method): according to regulation UNI EN 12597 it is defined as bituminous binder whose rheology is modified by use of one or more organic polymers. The performance is increased in comparison to the standard bitumen, which is ensured by the phase inversion obtaining through the processing in a specific modification plant (wet method). Afterwards, polymer modified bitumen is used in the production of asphalt mixes;
- direct modification of asphalt mixes (Polymer-modified Asphalt – PmA: Dry Method): the performance improvement is achieved by using a polymeric compound during the production phase of the asphalt mixture. That is, by using standard bitumen, the modifying polymer is introduced in the production cycle after the aggregates and before bitumen (Dry method).
With reference to Dry modifications, many polymeric compounds have been formulated in the last 15 years that require specifically studied formulations in which mixing the polymers of different nature and sometimes even the “doping” of the compound with other characterising materials, such as “graphene” is done.
Known since the 18th century, graphite is a layered material whose structure is formed by carbon atoms set together on the same level by covalent bonds, whereas the different layers are linked by Van der Walls’ interactions.
Deriving from the processing of graphite, discovered in 1947 by P.R. Wallace and further isolated in 2004 by A. Geim and K. Novoselov (Nobel Prize in Physics in 2010), graphene is a monolayer of carbon atoms (2D, the thickness corresponds to that of the atom) arranged in a honeycomb structure.
Such an organized structure gives high physical-mechanical properties to the it and any products containing that. These characteristics makes it excellent for products from several high technological fields such as electronics, aeronautics, medicine, astronautics, textile, sport, environment, and so on.
The main features are:
- thickness of an atom (106 times thinner than human hair, it is the thinnest material known to mankind);
- very high resistance (about 200 times that of steel);
- very high flexibility;
- excellent heat and electricity conduction (better than copper);
- huge light absorption;
- extremely high specific area (about 1.300 mq/g, but up to 3.100 mq/g).
The most difficult production challenge of graphene was that of finding a process that allows to obtain a high-quality and high-purity final product, in order to achieve the best performance and to eliminate extraneous chemical substances.
Used to produce the graphene-based supermodifier, hereby presented, graphene G+ (named ITC1) is produced by Directa Plus and is composed of extremely pure graphene nanoplatelets with enhanced morphological and structural properties. G+ is obtained through a patented production process that takes advantage of a unique technique: Plasma Super Expansion.
Starting from natural graphite, each phase of the process (expansion, exfoliation and exsiccation) creates graphene nanoplatelets that can be further reused in powder, flakes, paste or dispersed in liquid.
This physical transformation allows to obtain a product that is:
- composed of 100% graphene, free from solvents or other chemical substances, and of constant quality;
- certified, non-toxic and compliant with REACH requirements.
Graphene-based polymeric supermodifiers for asphalt mixes
Complied with the concepts of recycling and “Perpetual Pavements”, over the last five years the Iterchimica’s R&D Department has dealt with the performance evolution of polymeric compounds for the Dry modification of asphalt mixes, analysing the Life Cycle Assessment (LCA) of asphalt pavements and pursuing mainly the following objectives:
- high-efficiency production;
- energy consumption reduction;
- material recovery;
- versatile modifications with Dry technologies in the production of asphalt mixes;
- use of graphene to improve performances as compared to traditional polymeric compounds.
Commercially known as Gipave®, the graphene-enhanced supermodifier is produced through an efficient, sustainable and innovative system. The research was part of the Ecopave Project 2014-2020, financed by Regione Lombardia, and was carried out in collaboration with the University of Milan-Bicocca (study of the Life Cycle Assessment – LCA), Directa Plus (graphene producer) and G.Eco (selection and recovery of the hard plastics).
This new product is composed of specific polymers and graphene in order to improve significantly the physical-mechanical properties of the asphalt pavements, both compared to the PmB traditional technology and the PmA technologies applying Dry method, which are currently in use.
This super modifier is in the form of grey-black coloured granules with an average diameter of 1.0-4.0 mm and is composed of:
- selected recycled plastics: deriving from the recovery of objects composed of “hard plastics” (for example toys, bins, boxes, tubes, tables and chairs, etc.). They are industrially treated according to a patented process that includes also the techno-selection depending on the specific physical-chemical characteristics (however, not all hard plastics can be used, but only part of them). The techno-selected hard plastics are therefore selected from the traditional disposal circuit, which ends at the waste-to-energy plants;
- functional base: is composed of additives of different nature, which are a part of the super modifier. The physio-chemical composition is protected by industrial secrecy;
- graphene: the one that was used is G+ (named ITC1) and is composed of extremely pure nanoplatelets of graphene (please refer to the previous chapter).
The innovation is patented and eco-sustainable
Considering the innovative nature of this product, there are three patents, which prove its uniqueness:
- graphene production method: it allows to obtain a total purity (held by Directa Plus, more details in the following sections);
- Gipave® Formulation: protected by industrial secrecy, it was developed for the first time by the R&D Department of Iterchimica Srl;
- the recycling process of hard plastics: it consists of in the selection of specific hard plastics and their recycling in the polymeric super modifier production, which prevents their disposal to energy-to-waste plants.
In terms of environmental impact reduction, it is important to point out that:
- the formulation involves the use of graphene that is produced without solvents or other chemical products (production with plasma);
- the techno-selection allows the recycling of hard plastics that are usually considered non-recyclable and non-reusable, avoiding their disposal at waste-to-energy plants;
- the super modifier is produced at lower energy consumption, minimising emissions in the atmosphere;
- the asphalt mixes modified with the mentioned technology have a long service life (Perpetual Pavement), reducing the use of non-renewable raw materials and decreasing road maintenance over the time;
- the materials deriving from the demolition of existing asphalt pavements containing the graphene-based super modifier are re-usable as any other asphalt;
- the life cycle assessment is extremely positive in comparison to the production processes of asphalt mixes, used so far.