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15 pages, 3911 KiB

Open AccessArticle

Study of the Effect of Modification of Asphalt on the Rheological Properties Employing Microwave Radiation—An Aging Study

by Khalid Ahmed Owaid, Raghed Y. Ghazal and M. A. Abdelzaher

Recycling 2023, 8(5), 65; https://doi.org/10.3390/recycling8050065 - 26 Aug 2023

Cited by 6 | Viewed by 1955

Abstract

This study focuses on producing asphalt with improved rheological properties that differ from the original asphalt and are less affected by aging conditions. The rheological properties of Qayara asphalt were enhanced by modifying the asphalt using spent rubber tire (SRT) with different percentages [...] Read more.

This study focuses on producing asphalt with improved rheological properties that differ from the original asphalt and are less affected by aging conditions. The rheological properties of Qayara asphalt were enhanced by modifying the asphalt using spent rubber tire (SRT) with different percentages of anhydrous aluminum chloride. Percentages ranging from 1.0% by weight of the spent tire rubber were added after proceeding with the thermal crushing process. The percentages of anhydrous aluminum chloride catalyst were 0.4 and 0.8%, respectively. This mixture was microwaved at 270 watt of power for 4, 8, and 12 min, respectively. The measurements performed are plasticity, penetration, softening point, and penetration index. The previously mentioned measurements were also made on the modified asphalt one year after the modification process to understand the effect of aging conditions. The microstructure and thermodynamics have been characterized by FE-SEM and EDX measurements. This study provides good rheological properties of the modified bitumen binder that is aging-resistant. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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24 pages, 9422 KiB

Open AccessArticle

Life Cycle Assessment (LCA) of 3D Concrete Printing and Casting Processes for Cementitious Materials Incorporating Ground Waste Tire Rubber

by Matteo Sambucci, Ilario Biblioteca and Marco Valente

Recycling 2023, 8(1), 15; https://doi.org/10.3390/recycling8010015 - 20 Jan 2023

Cited by 20 | Viewed by 5681

Abstract

Ordinary concrete is an indispensable construction material of modern society which is used for everything from mundane road pavements to building structures. However, it is often used for non-load-bearing applications (for instance, insulating lightweight building units) where mechanical strength is not a priority. [...] Read more.

Ordinary concrete is an indispensable construction material of modern society which is used for everything from mundane road pavements to building structures. However, it is often used for non-load-bearing applications (for instance, insulating lightweight building units) where mechanical strength is not a priority. This leads to an avoidable depletion of natural aggregates which could instead be replaced by alternative waste materials capable of conferring to the material the desired performance while ensuring a “green” route for their disposal. Furthermore, the automation of production processes via 3D printing can further assist in the achievement of a more advanced and sustainable scenario in the construction sector. In this work, performance and environmental analyses were conducted on a 3D-printable cementitious mix engineered with ground waste tire rubber aggregates. The research proposed a comparative study between rubberized concrete mixes obtained by 3D printing and traditional mold-casting methods to achieve a comprehensive analysis in terms of the mix design and manufacturing process. To evaluate the environmental performance (global warming potential and cumulative energy demand) of the investigated samples, Life Cycle Assessment models were built by using the SimaPro software and the Ecoinvent database. The Empathetic Added Sustainability Index, which includes mechanical strength, durability, thermo-acoustic insulation, and environmental indicators, was defined to quantify the overall performance of the samples in relation to their engineering properties and eco-footprint. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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20 pages, 8081 KiB

Open AccessArticle

Upscaling of a Mechanochemical Devulcanization Process for EPDM Rubber Waste from a Batch to a Continuous System

by Larissa Gschwind and Carmen-Simona Jordan

Recycling 2023, 8(1), 8; https://doi.org/10.3390/recycling8010008 - 6 Jan 2023

Cited by 1 | Viewed by 2755

Abstract

The present work is a comparative study of the effects of mechanical shear, temperature, and concentration of a chemical agent on the devulcanization process of post-industrial ethylene propylene diene (EPDM) rubber waste. Devulcanization was carried out in a heating press (no shear), an [...] Read more.

The present work is a comparative study of the effects of mechanical shear, temperature, and concentration of a chemical agent on the devulcanization process of post-industrial ethylene propylene diene (EPDM) rubber waste. Devulcanization was carried out in a heating press (no shear), an internal mixer (low shear), and a co-rotating twin screw extruder (high shear) at temperatures ranging from 100 to 200 °C. The efficiency of pure dibenzamido diphenyl disulfide (DBD) and a commercial devulcanizing agent, Struktol A89^®, containing DBD were studied. Based on the results, the devulcanization process was upscaled from 40 g per batch to a continuous process with a capacity of 270 g/h. The parameters were fine-tuned regarding flow rate, screw speed, and temperature. Blends of virgin rubber (VR) and 25, 50, and 75 wt% recyclates were compared with blends of VR and 25, 50, and 75 wt% of untreated RWP. The quality of the recyclate was determined by rheometer tests, SEM images, TGA, and mechanical properties. The best results were obtained with 2 wt% DBD in the extruder with a temperature profile of 120 to 80 °C, 50 rpm, and 4.5 g per minute (gpm). The tensile strength and strain at break of the recyclate already met the requirements of DIN EN 681-1:2006 for the production of sealing systems. The compression set and Shore A hardness were restored by mixing recyclate with 25 wt% VR. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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20 pages, 2289 KiB

Open AccessArticle

Release of PAH from Secondary Products Made from End-of-Life Tire Recyclates into 20% Aqueous Ethanol as Assessment of Human Dermal Absorption

by Stefan Hoyer, Lothar Kroll, Benny Fischer, Kai Pisulla and Albrecht Seidel

Recycling 2023, 8(1), 6; https://doi.org/10.3390/recycling8010006 - 30 Dec 2022

Cited by 1 | Viewed by 2531

Abstract

Compliance with the legal limits set at the European level for the content of polycyclic aromatic hydrocarbons (PAH), which are harmful to human health and the environment, is of central importance for the recycling of rubber, particularly end-of-life tires (ELT), into secondary products, [...] Read more.

Compliance with the legal limits set at the European level for the content of polycyclic aromatic hydrocarbons (PAH), which are harmful to human health and the environment, is of central importance for the recycling of rubber, particularly end-of-life tires (ELT), into secondary products, e.g., elastic fall protection mats or anti-slip mats for the transport sector. However, different regulations associated with different analytical methods apply to newly produced tires on the one hand and secondary products made from ELT on the other. Given these discrepancies, ELT can potentially contain levels of PAH, which can be problematic when reused in consumer products. The total PAH content, however, is not without doubt a reliable risk indicator, which should ultimately be based primarily on the transfer of the substances from the product into the skin of human beings or their release into the environment. Accordingly, additional studies are required to determine the extent to which migration-based measurements are more suitable for risk assessment and how the PAH content correlates with migration. Complementing the recently published results of PAH content in different types of ELT, this study investigates the release of PAH for a range of typical secondary materials composed entirely or partly of ELT. In the present study, migration tests with 20% aqueous ethanol were applied, a methodology that has been shown in previous investigations by others to reflect human skin exposure well, and the resulting migration rates of PAH are determined. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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22 pages, 4172 KiB

Open AccessArticle

Properties of Rubberized Concrete Prepared from Different Cement Types

by Lamiaa K. Idriss and Yasser Abdal Shafey Gamal

Recycling 2022, 7(3), 39; https://doi.org/10.3390/recycling7030039 - 12 Jun 2022

Cited by 8 | Viewed by 3379

Abstract

At present, global waste tire generation considerably exceeds consumption. Moreover, waste rubber tires (WRTs) are a cause of concern, as huge volumes are being discarded and buried, thus causing serious environmental pollution. Rubberized waste concrete (RWC) is a type of environmentally friendly construction [...] Read more.

At present, global waste tire generation considerably exceeds consumption. Moreover, waste rubber tires (WRTs) are a cause of concern, as huge volumes are being discarded and buried, thus causing serious environmental pollution. Rubberized waste concrete (RWC) is a type of environmentally friendly construction material. The main challenge encountered when manufacturing rubberized concrete is the low adhesive properties between the cement paste and rubber particles. This paper demonstrates the effects, through experiments, of using waste tire rubber instead of recycled coarse aggregate (RCA) on two types of cement, i.e., sulfate-resistant cement (SRC) and ordinary Portland cement (OPC), where SRC is a specially blended cement designed to improve concrete performance and workability in the most aggressive environments. All tested samples contained 10% silica fume (SF) and 0.2% fly ash (FA), and the substitution of recycled aggregate content with waste rubber tier (WRT) at different percentages of 100%, 75%, and 50% was evaluated. The research investigated the synergistic effect on the workability and mechanical properties of various cement types with different amounts of rubber aggregate. It was found that the sulfate-resistant (SRC) type can increase the compressive strength than OPC with a percentage of 25% with the same content of WRT at concrete mix. Moreover, ductility and cracking behavior are improved, and it appears that it is also possible to make lightweight rubber aggregate concrete with this type of mixture.. Using this type of cement, it is possible to restore satisfactory ductility to the waste tires, thus facilitating a reduction in the formation of potential plastic cracks. Moreover, the indicative compressive strength development for SRC with recycled rubber in concrete positively contributes to a reduction in formed cracks. However, SEM microstructural analyses suggest a higher proportion of C–S–H intermixed with sulfate reaction phases of SRC rubberized mortar than those of OPC; thus, given that crystal growth results in a decreased percentage of air voids rather than decreased internal cracking, it is clearly shown that the average crack width increases in OPC mortar compared with SRC. Finally, t-testing was used as an inferential statistical tool to determine whether there is a sizeable distinction between the properties of the two categories of materials, OPC and SRC, by comparing the mean and standard deviation of the values for compressive and tensile strength. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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17 pages, 5638 KiB

Open AccessArticle

Treatment of Scrap Tire for Rubber and Carbon Black Recovery

by Alaa Sultan Abdulrahman and Fawzi Habeeb Jabrail

Recycling 2022, 7(3), 27; https://doi.org/10.3390/recycling7030027 - 20 Apr 2022

Cited by 9 | Viewed by 4936

Abstract

In this study, a chemical dissolution treatment was used to recover rubber and carbon black (CB) from truck tire scrap, with gas oil acting as the solvent and 4-Hydroxy-TEMPO acting as the catalyst for the chemical reactions. Montmorillonite clay was used to separate [...] Read more.

In this study, a chemical dissolution treatment was used to recover rubber and carbon black (CB) from truck tire scrap, with gas oil acting as the solvent and 4-Hydroxy-TEMPO acting as the catalyst for the chemical reactions. Montmorillonite clay was used to separate the rubber solution from the CB and the other non-dissolved tire additives. The recovered rubber and CB were characterized together with the original scrap tire sample by XRD, SEM, BET and thermal analysis, as well as FTIR and ¹H NMR spectral analyses. Characterization of the chemical structure of the recovered rubber showed that the main functional groups of styrene−butadiene rubber blend with natural rubber. The thermal behavior and crystalline structure of the recovered rubber, as well as its morphological images, showed that the properties of the rubber sample were acceptable and similar to natural rubber. The recovered CB characterizations showed that the sample after pyrolysis was a highly crystalline nanocomposite structure with a high specific surface area and scattered pores. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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20 pages, 14477 KiB

Open AccessArticle

Effect of Ground Tire Rubber (GTR) Particle Size and Content on the Morphological and Mechanical Properties of Recycled High-Density Polyethylene (rHDPE)/GTR Blends

by Ali Fazli and Denis Rodrigue

Recycling 2021, 6(3), 44; https://doi.org/10.3390/recycling6030044 - 1 Jul 2021

Cited by 23 | Viewed by 6591

Abstract

This work investigates the effect of ground rubber tire (GRT) particle size and their concentration on the morphological, mechanical, physical, and thermal properties of thermoplastic elastomer (TPE) blends based on recycled high-density polyethylene (rHDPE). In our methodology, samples are prepared via melt blending [...] Read more.

This work investigates the effect of ground rubber tire (GRT) particle size and their concentration on the morphological, mechanical, physical, and thermal properties of thermoplastic elastomer (TPE) blends based on recycled high-density polyethylene (rHDPE). In our methodology, samples are prepared via melt blending (twin-screw extrusion followed by compression molding) to prepare different series of blends using GTR with three different particle sizes (0–250 μm, 250–500 μm, and 500–850 μm) for different GTR concentrations (0, 20, 35, 50, and 65 wt.%). The thermal properties are characterized by differential scanning calorimeter (DSC), and the morphology of the blends is studied by scanning electron microscopy (SEM). The mechanical and physical properties of the blends are investigated by quasi-static tensile and flexural tests, combined with impact strength and dynamic mechanical analysis (DMA). The SEM observations indicate some incompatibility and inhomogeneity in the blends, due to low interfacial adhesion between rHDPE and GTR (especially for GTR > 50 wt.%). Increasing the GTR content up to 65 wt.% leads to poor interphase (high interfacial tension) and agglomeration, resulting in the formation of voids around GTR particles and increasing defects/cracks in the matrix. However, introducing fine GTR particles (0–250 μm) with higher specific surface area leads to a more homogenous structure and uniform particle dispersion, due to improved physical/interfacial interactions. The results also show that for a fixed composition, smaller GTR particles (0–250 μm) gives lower melt flow index (MFI), but higher tensile strength/modulus/elongation at break and toughness compared to larger GTR particles (250–500 μm and 500–850 μm). Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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14 pages, 1296 KiB

Open AccessFeature PaperArticle

Ground Tire Rubber Recycling in Applications as Insulators in Polymeric Compounds, According to Spanish UNE Standards

by Marc Marín-Genescà, Jordi García-Amorós, Ramon Mujal-Rosas, Lluís Massagués Vidal, Jordi Bordes Arroyo and Xavier Colom Fajula

Recycling 2020, 5(3), 16; https://doi.org/10.3390/recycling5030016 - 2 Aug 2020

Cited by 14 | Viewed by 6021

Abstract

In the present research, we investigated the conceivable outcomes of using ground tire rubber (GTR) particle polymeric blends. Special methods of restoring tires that are no longer in use include GTR retreading, GTR blending destined for recycling to attain raw substances utilized in [...] Read more.

In the present research, we investigated the conceivable outcomes of using ground tire rubber (GTR) particle polymeric blends. Special methods of restoring tires that are no longer in use include GTR retreading, GTR blending destined for recycling to attain raw substances utilized in other industrial application production processes, and the valorization of GTR for power/energy generation. The recycling of end-of-life tires enables the recovery of rubber, steel, and fibers, all of which are valid on the market as raw materials to be used for other processes. There are methods to recycle GTRs in a clean and environmentally friendly way. In the present research, several industrial applications of GTR polymer blends were developed and compared with standard values from the Spanish Association for Standardization (UNE) and the International Electrotechnical Commission (IEC). In order to analyze the viability in many of the industrial applications selected, certain compounds obtained from the GTR polymer blends were analyzed regarding their use in nine low requirement insulator applications. The research and analysis developed in this manuscript used standard values from the UNE and IEC, and these standard values were compared with the test values. The obtained results were used to provide an application list that could be helpful for industrial applications. In this research, the pre-owned polymers were as follows: polypropylene (PP), high-density polyethylene (HDPE), polystyrene (PS), acrylonitrile butadiene-styrene (ABS), ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), and polyamide (PA). The filler used was GTR with particle sizes lower than 200 microns. The amounts of GTR particles in the compound materials were 0% (raw polymer), 5%, 10%, 20%, 40%, 50%, and 70% (the latter being found in polymeric blends). We discovered six plausible modern applications of GTR polymer blends as indicated by the UNE and IEC standards. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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13 pages, 4503 KiB

Open AccessFeature PaperArticle

Tire Recycled Rubber for More Eco-Sustainable Advanced Cementitious Aggregate

by Matteo Sambucci, Danilo Marini and Marco Valente

Recycling 2020, 5(2), 11; https://doi.org/10.3390/recycling5020011 - 11 May 2020

Cited by 25 | Viewed by 8249

Abstract

This research focused on using ground tire rubber (GTR) with different grain sizes as a replacement for the mineral aggregates used in a cement-based mixture suitable for extrusion-based Additive Manufacturing. The use of two types of GTR particles and the possibility to apply [...] Read more.

This research focused on using ground tire rubber (GTR) with different grain sizes as a replacement for the mineral aggregates used in a cement-based mixture suitable for extrusion-based Additive Manufacturing. The use of two types of GTR particles and the possibility to apply rubberized mixtures in advanced manufacturing technologies are the innovative aspects of this work. At the base of this strategy is the possibility of achieving cementitious aggregates, which would potentially be improved regarding some technological-engineering requirements (lightness, thermal-acoustic insulation, energy dissipation capacity, durability) and environmentally sustainable. The integration of waste tires into cement-based materials is a promising solution for the reuse and recycling of such industrial waste. In addition, this approach may involve a considerable reduction in the use of natural resources (sand, water, coarse mineral aggregates) needed for the building materials production. The purpose of the research was to investigate the effect of sand-GTR replacement on certain chemical-physical properties of mixtures (permeable porosity, surface wetness, and water sorptivity), closely related to material durability. Besides, the role of rubber on the printability properties of the fresh material was evaluated. GTR fillers do not alter the rheological properties of the cement material, which was properly extruded with better print quality than the reference mixture. Concerning chemical-physical characterization, the GTR powder-granules synergy promotes good compaction of the mixture, hinders the cracks propagation in the cement matrix, decreases the permeable porosity, improves the surface hydrophobicity and preserves optimal water permeability. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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Review

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14 pages, 2427 KiB

Open AccessReview

Recycling of Rubber Wastes as Fuel and Its Additives

by Ahmed Akbas and Nor Yuliana Yuhana

Recycling 2021, 6(4), 78; https://doi.org/10.3390/recycling6040078 - 1 Dec 2021

Cited by 27 | Viewed by 13329

Abstract

Economic, social, and urban developments generally require improvements in the transportation sector, which includes automobiles such as trucks, buses, trailers, airplanes, and even bicycles. All these vehicles use rubber tires. After consumption, these tires become waste, leading to enlarged landfill areas for used [...] Read more.

Economic, social, and urban developments generally require improvements in the transportation sector, which includes automobiles such as trucks, buses, trailers, airplanes, and even bicycles. All these vehicles use rubber tires. After consumption, these tires become waste, leading to enlarged landfill areas for used tires and implying additional harm to the environment. This review summarizes the growth of rubber recycling application and the sustainability of using waste rubber in the construction field. Furthermore, we provide methods to convert rubber waste to fuel or fuel additives by using tire-derived fuel and concentrate to pyrolysis, which are environmentally friendly and efficient ways. The related parameters such as temperature, pressure, and feedstock composition were studied. Most research papers observed that 500 °C is the optimal temperature at atmospheric pressure in the presence of a specific type of catalyst to improve pyrolysis rate, oil yield, and quality. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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22 pages, 5843 KiB

Open AccessFeature PaperReview

Functionalization of Crumb Rubber Surface for the Incorporation into Asphalt Layers of Reduced Stiffness: An Overview of Existing Treatment Approaches

by Christina Makoundou, Kenth Johansson, Viveca Wallqvist and Cesare Sangiorgi

Recycling 2021, 6(1), 19; https://doi.org/10.3390/recycling6010019 - 8 Mar 2021

Cited by 12 | Viewed by 6326

Abstract

The substitution of mineral aggregates with crumb rubber (CR) from waste end-of-life tires (ELTs) in the asphalt concretes, has been considered a sustainable paving industry approach. The rubber has been used to construct pavements with proven enhanced resilience and improved durability. However, some [...] Read more.

The substitution of mineral aggregates with crumb rubber (CR) from waste end-of-life tires (ELTs) in the asphalt concretes, has been considered a sustainable paving industry approach. The rubber has been used to construct pavements with proven enhanced resilience and improved durability. However, some issues related to the rubber’s surface adhesion or swelling may arise with these practices and generate complications (binder consumption, temperatures, mixing times). One possible solution to overcome the materials’ compatibility problems is to pre-treat the CR’s surface before its incorporation into the asphalt mixes to allow a surface functionalization that can enhance coverage and cohesion inside the mixes. The physical treatments using radiations-based beam are already exploited in the plastic recycling industries avoiding the use of chemicals in considerable amounts. Such treatments permit the recovering of large quantities of polymer-based materials and the enhancement of interfacial properties. This article provides an overview of existing surface treatments of polymers and especially rubber, including gamma ray, UV-ozone, microwaves, and plasma. Several studies have shown an overall improvement of the rubber surface’s reactive properties due to contaminant removal or roughness enhancement attributed to cross-linking or scission reactions occurring on the rubber’s surface layer. With those properties, the asphalt mixes’ phase stability properties are increased when the pre-treated rubber is incorporated. The treatments would permit to increase the CR quantities, yet reduce the layer stiffness, and improve the durability and the sustainability of future advanced road pavements. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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20 pages, 6060 KiB

Open AccessReview

Crumb Rubber as a Secondary Raw Material from Waste Rubber: A Short Review of End-Of-Life Mechanical Processing Methods

by Vjaceslavs Lapkovskis, Viktors Mironovs, Andrei Kasperovich, Vadim Myadelets and Dmitri Goljandin

Recycling 2020, 5(4), 32; https://doi.org/10.3390/recycling5040032 - 1 Dec 2020

Cited by 37 | Viewed by 16137

Abstract

Despite technological developments, modern methods for the disposal of end-of-life tires most often involve either their incineration in cement kilns or the destruction of tires in special landfills, demonstrating a lack of sustainable recycling of this valuable material. The fundamental role of recycling [...] Read more.

Despite technological developments, modern methods for the disposal of end-of-life tires most often involve either their incineration in cement kilns or the destruction of tires in special landfills, demonstrating a lack of sustainable recycling of this valuable material. The fundamental role of recycling is evident, and the development of high-efficiency processes represents a crucial priority for the European market. Therefore, the investigation of end-of-life rubber processing methods is of high importance for both manufacturers and recyclers of rubber materials. In this paper, we review existing methods for processing of end-of-life tires, in order to obtain rubber crumb, which can later be used in the production of new industrial rubber goods and composites. We consider processes for separating end-of-life tires into fractions (in terms of types of materials) using chemical, mechanochemical, and mechanical methods to process the materials of used tires, in order to obtain crumb rubber of various fractions and chemical reactivities. Full article

(This article belongs to the Special Issue Recycling of Rubber Waste)

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