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Review

Utilizing E-Waste as a Sustainable Aggregate in Concrete Production: A Review

by
Gaurav Kumar
1,
Tushar Bansal
1,*,
Moinul Haq
2,*,
Utsav Sharma
3,
Amit Kumar
1,
Pooja Jha
1,
Dayanand Sharma
1,
Hesam Kamyab
4,5,* and
Edison Alejandro Villacreses Valencia
6
1
Department of Civil Engineering, Sharda School of Engineering and Technology, Sharda University, Greater Noida 201310, India
2
Interdisciplinary Research Center for Construction and Building Materials, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
3
Environmental Engineer, Uttar Pradesh Pollution Control Board, Noida 201304, India
4
Department of Biomaterials, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Chennai 600077, India
5
Faculty of Architecture and Urbanism, UTE University, Calle Rumipamba S/N and Bourgeois, Quito 170147, Ecuador
6
Departamento de Ciencias de la Tierra, Universidad de las Fuerzas Armadas ESPE, Sangolqui 1715-231B, Ecuador
*
Authors to whom correspondence should be addressed.
Buildings 2024, 14(8), 2495; https://doi.org/10.3390/buildings14082495
Submission received: 15 July 2024 / Revised: 31 July 2024 / Accepted: 8 August 2024 / Published: 13 August 2024
(This article belongs to the Section Building Materials, and Repair & Renovation)
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Abstract

:
The accumulation of electronic waste (E-waste) has become a significant global environmental issue, driven by the characteristics of the modern era and the ever-increasing use of electronic devices. Thus, a sustainable approach is necessary to overcome this issue. In this paper, an overview of utilizing E-waste as a sustainable aggregate in concrete production was comprehensively reviewed. The basic composition, characteristics, and production techniques were discussed. In addition to that, the colour, shape, size, aggregate crushing value, and water absorption of E-waste concrete were also discussed. Furthermore, the workability properties such as slump flow, mechanical properties (compressive strength, flexural strength, tensile strength) and thermal resistance of E-waste concrete identified by the various researchers were summarised. Based on the literature review, it is concluded that the shape and size distributions of E-waste particles greatly influenced the aggregate properties, and the percentage of replacement of E-waste aggregate affect the workability and mechanical and thermal properties of E-waste concrete.

1. Introduction

Electronic waste (E-waste) accumulation is an increasingly significant global environmental issue due to the characteristics of the modern period and the ever-growing use of electronic devices. E-waste consists of discarded electronic gadgets and products and is detrimental to the environment and human health on major levels due to its hazardous nature and improper disposal [1]. The waste generation for E-waste worldwide was 53.6 million metric tons in 2019 and it is expected to reach 74.7 million metric tons by 2030 [2]. In 2022, according to The Global E-waste Monitor 2024, a record 62 billion kg of E-waste was generated globally, which is equivalent to an average of 7.8 kg per capita per year. Specifically in Asia, 56 billion kg of E-waste was generated, which translates to 6.6 kg per capita per year. China contributed 12,000 million kg, while India generated 4100 million kg of E-waste, which resulted in the equivalent of 82.4 million kg of CO2 greenhouse gas emissions, 34.5 thousand kg of emissions of mercury and 26 million kg of plastics containing brominated flame retardants [3]. Thus, the situation requires urgent attention and equally immediate measures aimed at developing new sustainable approaches to the E-waste accumulation problem. The building sector, which consumes significant natural resources, must find a responsible way to use them while producing concrete, which is the second most utilised substance in the world after water [4]. The production of concrete consumes a significant number of resources and relies to a large extent on the quarrying of virgin aggregates such as sand and gravel, which impacts the environment negatively, amounts to the depletion of finite natural resources and disturbs biological processes [5,6,7,8,9,10,11,12,13]. In addition, the production of cement, a key ingredient of concrete, accounts for more than 8% of CO2 releases globally [14]. There is a need for resourceful ways of thinking to help us make progress toward sustainable construction and E-waste management. An example of scientific innovation in addressing this problem is to include E-waste in the production processes of concretes, in which the team can replace it with conventional aggregates. This system simplifies the search process internationally for sustainable E-waste management and seeks to reduce our reliance on virgin natural resources, which also favours the environment [15]. The utilization of different E-waste materials, viz., plastics, glass, and printed circuit boards (PCBs) in combination with concrete mixtures, has been a field of exploration by the scientific community [16]. Experiments based on these findings have shown that E-waste concrete can be used to replace some of the conventional aggregates in concrete effectively without substantially reducing the mechanical strength and durability of the material. The addition of E-Waste into concrete can solve a significant environmental issue and also make use of valuable resources. This alternative process not only addresses the issue of E-waste but also adheres to sustainable habits [17,18,19,20]. There are several benefits of using E-waste materials in concrete, such as preventing E-waste, reducing the need for new materials, and creating a circular economy that continuously reduces wastage and re-use, leading to a cheaper construction process [21] and reducing the environmental impact in both waste management and the construction sector. However, turning E-waste concrete into something more than a proof-of-concept will require cross-sectoral collaboration. This cannot be done by academics, lawmakers, business leaders and regulatory bodies independently. Physical challenges related to the collection and segregation of E-waste need to be solved. In addition, before using the mixture, setting out the guidelines and standards that are required is vital to ensure that its use in construction will be safe and effective. This paper presents a comprehensive review of the utilization of E-waste as a sustainable aggregate in concrete production or recycled concrete aggregate (RCA) based on composition, characteristics, and production techniques, the colour, shape, size, aggregate crushing value, water absorption, workability properties such as slump flow, mechanical properties (compressive strength, flexural strength, tensile strength), and thermal resistance of E-waste concrete.

2. Methodology

2.1. Review Framework

This section discusses the systematic methodology used to carry out a literature survey on E-waste sustainability aggregate in concrete production. The review process includes a literature search, the application of inclusion and exclusion criteria, the extraction and analysis of data (if applicable), as well as assessments of the data’s quality.

2.2. Literature Search

In order to find all related studies, an exhaustive search of the literature was conducted from different academic databases. English language articles were considered from the following databases: Google Scholar, ScienceDirect, PubMed & IEEE Xplore, and Web of Science. The keywords used in the search strategy were identified as unique words or phrases such as “E-waste concrete”, “sustainable aggregate”, “concrete mix design”, “mechanical property testing methods”, “influence of different environmental conditions on E-waste aggregates”, and “durability factors affecting engineering properties”.

2.3. Inclusion and Exclusion Criteria

To maintain a high standard of quality and relevance, inclusion and exclusion criteria were applied during the selection process. The criteria for inclusion consisted of studies published in peer-reviewed journals or conference proceedings, research related to the utilization of E-waste as an aggregate in concrete manufacturing, and studies that possessed quantitative data on workability, mechanical properties, and durability potentiality regarding the E-waste concrete. The exclusion criteria were papers that did not discuss concrete or construction materials, articles without empirical data and experimental results, non-peer-reviewed items including opinion pieces, editorials, and grey literature, as well as research about the environmental impact of E-waste that only considers its environment-friendly use in the production of concrete.

2.4. Data Extraction and Analysis

The selected articles underwent a meticulous data extraction process to ensure all relevant information was captured and analyzed systematically. The key aspects extracted from each study included E-waste type and proportion, workability metrics, mechanical properties, and durability indicators.

2.5. Need for a Consistent Methodological Framework

This review highlights a significant challenge in the current body of literature: the variation in methodological approaches across different studies. This variability complicates the comparison of results and the drawing of meaningful conclusions. To address this issue, it is essential to establish a consistent methodological framework. The proposed standardised parameters are aggregate characteristics (size, shape, and type of E-waste used in the concrete mix), mix proportions (specific ratios of E-waste aggregates to other components in the concrete), mechanical properties (standardised tests for compressive strength, flexural strength, and tensile strength), durability indicators (consistent metrics for water absorption, thermal resistance, and long-term durability) and workability (uniform methods for measuring slump and other workability-related properties). By standardizing these parameters, future research can provide more reliable and comparable data, enhancing the overall understanding of the viability and performance of E-waste concrete. This approach will also facilitate meta-analyses and systematic reviews, contributing to the development of best practices in the use of E-waste as a sustainable construction material.

3. E-Waste and Its Composition

E-waste is the term used to describe any obsolete electronic/electrical devices. These range from large household appliances such as refrigerators and air conditioners to everyday devices such as mobile phones, personal stereos, and computers. There are 10 different categories of E-waste based on the European Waste Electrical and Electronic Equipment (WEEE) Directives 2002/96/EC and 2012/19/EU [22], as shown in Table 1. The composition of E-waste is shown in Figure 1.
E-waste is made up of a multitude of different parts that differ depending on the product being considered. These components consist of more than 1000 substances, which are segregated into “hazardous” and “non-hazardous”. E-waste has a hazardous component as waste from electronics generally consists of heavy metals (including mercury, lead, and cadmium) and hazardous substances (for example, brominated flame retardants, PVC). Grant et al. [23] found that the hazardous constituents of E-waste can pose extensive problems for human health. These mainly pertain to growth, cellular function, thyroid function, lung function, and reproductive health. Less harmful metals, plastics, and even glass typically fall under the class of non-hazardous materials. Table 2 shows the hazardous characteristics of E-waste and their origins [24]. As there are so many high-value and toxic substances in E-waste that are harmful and difficult to decompose, they must be properly collected, treated, and managed to avoid the risk of their impact on the environment and human health. These steps can be taken by recyclers and facilities, which are required by United Nations Environment Programme (UNEP) rules to make a concerted effort to recycle and reuse obsolete EEDs. Furthermore, rare and valuable materials in EEDs should only be disassembled and recovered if reuse is not an option. It is advised that facilities and recyclers adhere to the recycling, renovation, and disposal procedures, as mentioned in Figure 2.

4. E-Waste to Construction Materials: Production Techniques

The construction industry has been seeking to use crushed recycled E-waste as an alternative to other aggregates in concrete production as a sustainable solution. It utilises E-waste plastic components, Cathode Ray Tubes (CRTs), and Printed Circuit Boards (PCBs) from outdated digital devices. E-waste plastics recycling can be done with chemical modification [26], mechanical recycling [27], thermal process [28], etc. In the chemical transformation method, polymer chains are degraded by hydrolysis, pyrolysis, etc. Thus, it works well for materials such as MMA and PET. Mechanical recycling, which refers to granulating or shredding and heating above a desired temperature to produce recycled aggregates, is suitable for high-density polyethene (HDPE) and PET that have been sorted by type. Also, PET and HDPE can generate microplastics in construction and built environments. This microplastic pollution can contaminate soil and water and pose ecological risks. Due to their smaller size, there is risk of potential entry into the food chain, impacting wildlife and ecosystems [29]. Plastic is melted down at high temperatures through a process called thermal processing to create new items that do not change the chemical structure of the plastic [30]. Scientists have developed methods for the synthesis of aggregates, such as mixing plastic from shredded E-waste and fillers such as sand or quarry fines and fly ash. This mix is milled and heated to melt the plastic (at about 200 °C) and encapsulate the fillers, then it is formed into slabs and crushed into fine and coarse aggregates [26,27]. Ullah et al. [30] adapted the process by washing, shredding, and melting small plastic parts at 200 °C, then casting the plastic into “plastic rocks”, which are then crushed into synthetic aggregates by sieving out impurities. CRTs, by themselves, can be recycled to produce lightweight concrete aggregate in addition to plastics, but CRTs need to be treated because of the existence of lead. A CRT waste recycling method was developed by a researcher in Hong Kong. The method involved dismantling and separating the components of CRT, crushing the lead-containing glass, and washing the lead-containing glass with nitric acid to recover lead. Then, the funnel glass was melted/annealed to spherical pellets or crushed into angular aggregate [28]. Another possible source of recycled aggregate is printed circuit boards (PCBs) from E-waste. PCBs have metals such as copper that can be recovered by recycling [31]. The non-metallic portion left could be shredded, heat-treated, and used as fine aggregate in concrete [32]. Recently, a few studies have been published on the use of milled PCB powder as a partial replacement for cement in concrete for the enhancement of strength and durability [16]. The recycling of plastics, CRTs, and PCBs within the construction industry consequently aids in sustainable waste management and reduces the environmental impact of E-waste [16,26,27,28,30,31,32,33]. Using these E-waste recycled aggregates in the production of concrete prevents E-waste from going to landfills and also saves natural resources. Nevertheless, more research is needed in order to improve recycling procedures and guarantee the functioning as well as the durability of recycled concrete made with E-waste aggregates.

5. Properties of Concrete with Recycled E-Waste

Researchers around the world are working on sustainable building material solutions that include E-waste and its several extracted components. The before-mentioned solution is achieved by using waste materials to improve the fresh properties of concrete while affecting the hardened properties differently. Increased properties emerge especially due to materials such as fly ash, waste glass and steel slag. However, more investigations are needed in order to further utilise the alluring strength properties of E-waste concrete, which is very much essential to embrace on a wider scale into construction practices. It is eco-friendly in approach and promotes environmental sustainability, helps conserve natural aggregates, reduces pollution, etc. Among such studies, a few [34,35,36] are pivotal. Table 3 shows the E-waste studies performed by the various researchers based on different parameters.

5.1. Colour, Shape, Size, Aggregate Crushing Value, and Water Absorption of E-Waste Concrete

E-waste concrete utilises electronic waste by-products such as plastics and other non-metallic components, which impact the aesthetic and physical performance of the concrete [30,50]. It has been indicated that the colour and water absorption characteristics of concrete can be sustained by the use of E-waste in its formation. However, the non-metallic coatings or polymeric components and hydrophobic materials such as plastics could change the intensity of the colour and reduce its absorption in the case of hydrophobic materials [30,51]. The shape and size distributions of E-waste particles will also influence aggregate properties and may therefore need further processing or pretreatments to achieve success [14,52].

5.2. Workability of E-Waste Concrete

The workability of concrete is an essential property in construction considered in the determination of practical uses such as mixing, placing, compacting, and finishing. The addition of E-waste to the concrete mix presents interesting challenges and advantages concerning its workability as well. The consistency of concrete flow has been influenced by studies that involved utilizing E-waste plastic partly as a substitute for the coarse aggregates. For example, Manjunath [50] reported that the slump value decreased from 75 mm for the control mix to 60 mm on the introduction of 5% E-waste plastic. This decrease in slump value indicates that E-waste concrete will need more effort for compaction in order to have proper density and uniformity. A similar finding was also reported by Suchithra et al. [41]. On gradual replacement of natural coarse aggregates by E-waste plastic aggregates such as 10% partial volume replacement, the slump value was decreased from 90 mm to 65 mm. This reduction underscores that adjustments in the mix design, such as changes in water-cement ratio or use of superplasticisers, may be necessary in order to increase workability without affecting concrete strength and serviceability [52]. Ullah et al. [30] found that the issues related to workability could be reduced by incorporating a superplasticiser. Their experiments revealed that concrete with 15% E-waste content workability increased from 50 mm without a superplasticiser to 70 mm with a superplasticiser. The strait-laced outline of E-waste plastic particles is one of the reasons for their decreased workability. The rough surface texture and irregular shape of E-waste particles also increase internal friction within the concrete mix, which leads to decreased flowability in concrete mix [53]. It was found that the workability was decreased from 80 mm to 55 mm slump when E-waste plastic was used as a replacement of 20% natural aggregates, and the mix was modified to retain the workability as per requirement. Further, the variation in the density of conventional aggregates with E-waste plastic affects the segregation and bleeding tendencies of concrete. The investigation showed that the bleeding rates were greater than the criterion level of 2 mm. The bleeding could be controlled to this level if the mix proportion was adjusted and by the addition of supplementary cementitious materials [45]. This was confirmed by a lab-based study conducted by Sabau and Vargas [54], which also cited slump to have reduced from 85 mm in concrete to 50 mm when 30% of the mix was replaced with E-waste plastic. This dramatic drop underscores the need for the addition of high-range water reducers to enable flowability. Santhanam et al. [55] studied the impact of E-waste plastic on the fresh properties of concrete and revealed that when aggregate E-waste plastic is replaced by 20% natural aggregate, the slump decreases from 75 mm to 55 mm. However, the incorporation of fly ash as a supplementary cementitious material could help to enhance the workability of the mix, justifying the requirement of mix design strategies that encompass the workability and mechanical properties of E-waste concrete. Figure 3 shows the values of slump flow identified by the various researchers at different E-waste content levels. From Figure 3, it is observed that the workability decreases with increasing E-waste content. Also, it is noticed that exceeding 30% of E-waste content in concrete could significantly reduce the workability and make the concrete mix difficult to handle, place, and compact [56].

5.3. Characteristic Strength of E-Waste Concrete

The incorporation of E-waste in concrete mixes has been of growing interest because of its environmental benefits and concrete properties [30]. Many studies have reported on characteristic strength, an essential property that determines the compressive strength likely to be attained by a concrete mix, with the incorporation of E-waste materials. Manjunath [50] studied the optimum replacement of E-waste plastic as a partial replacement of coarse aggregates in concrete with the characteristic strength of concrete. They found that the addition of 5% of E-waste plastic into coarse aggregates reduced minimal compressive strength from 30 MPa (for the control mix) to 28.5 MPa. Kumar and Baskar [45] found the characteristic strength to reduce from 32 MPa for the control mix to 29 MPa at a 10% replacement level. At 20% replacement, the strength even reduced to 25.5 MPa. The higher content of E-waste plastic, which lowers the compressive strength, may be due to the lower specific gravity and the higher porosity of E-waste materials compared to conventional aggregates. Needihdasan et al. [52] performed a study on E-waste concrete by adding the superplasticisers. They found that 15% E-waste with superplasticiser showed a compressive strength of 27 MPa comparted to 24 MPa without superplasticiser. There followed a study by Arivalagan [53] performed on concrete up to replacement of 25% E-waste plastic. However, the reduction in characteristic strength was much greater in his results where the strength reduced to 22 MPa at 25% replacement compared to the control mix of 31 MPa. This substantial drop signifies the need to optimise the mix design to strike the right balance between the advantages of using E-waste with the mechanical properties demanded in a structural application. Further, Kumar and Baskar [45] mentioned ways to improve the performance of E-waste concrete by the addition of supplementary cementitious materials (SCMs). Sabau and Vargas [54] found that the initial compressive strength of concrete was lower in the case of E-waste, however, when investigated at age 28 days, E-concrete showed strength comparable to conventional concrete. The 28-day compressive strength was 21 MPa at a 30% replacement level but increased to 24 MPa at 90 days, which revealed that E-waste concrete can attain appreciable strength values beyond its normal curing period. Needhidasan et al. [57] studied the amalgamation of E-waste plastic and M-Sand in concrete. They found that a totalizing mix with 15% E-waste along with M-sand reaches up to 28 MPa for characteristic strength in comparison with a 30 MPa normal mix. The small amount of decrease shows that cement can be replaced with other materials to make concrete acceptable in strength for different uses by combining them. Figure 4 shows the compressive strength of different E-waste concrete identified by the various researchers. Based on the studies mentioned in Figure 4, it is concluded that the compressive strength of E-waste concrete decreases with increasing E-waste. This is due to several factors, including the increased porosity and lower density of E-waste aggregates, which weaken the concrete matrix. However, the incorporation of chemical admixtures, supplementary cementitious materials, and fine-tuned mix design can offset such reductions. The potential environmental advantages of recycling E-waste in concrete are promising, but the mechanical properties are of concern and must be properly addressed for use in structural concrete.
Also, there are several reasons for the reduction in compressive strength of concrete modified with E-waste plastic aggregates.
  • Physical properties (as E-waste plastic aggregates are lighter and stiffer in contrast to natural coarse aggregates): this difference induces stress concentration zones in the bulk of the concrete, which leads to the formation and propagation of cracks and, as a result, reduces the compressive performance of the material as a whole [30].
  • Hydrophobic nature: As E-waste plastic aggregates exhibit a hydrophobic nature, this will not allow sufficient moisture to penetrate and hydrate the aggregate during the curing process, totally drying up the excess moisture, hence allowing dry out over time, meaning that the concrete becomes less dense and has a lower compressive strength [57].
  • Surface texture: the smooth surface texture of E-waste plastic aggregates leads to a relatively poor bond formation between the mortar and the aggregates [45].
  • Density and segregation: E-waste plastic aggregates have a lower density than the normal aggregate and tend to migrate towards the top surface during the casting process, including vibration for compaction. This form of segregation causes a non-homogeneous distribution of aggregates in the specimen, which reduces the compressive strength [58].
In this regard, various recent investigations have been carried out to include E-waste in concrete so as to overcome the reduction in compressive strength. Several researchers have proposed different techniques to increase the structural characteristics of upgraded concretes with E-waste, summarised as follows:
Needhidasan et al. [59] performed an experimental investigation on adding fly ash as an admixture in E-waste plastic concrete. When they substituted 8 to 12% coarse aggregate partial volume with E-waste plastic and added fly ash, there was an increase in 28-day compressive strength from 0.18% to 3.75%. This improvement is probably because of the densification and reduced porosity achieved by fly ash at the ITZs because of its filler effect. Rohini and Padmapriya [60] recommended the application of microbiologically induced calcite precipitation (MICP) as an innovative technique to enhance the strength of E-waste-enhanced concrete. When 0%, 1%, and 2% bacteria were introduced into 15% E-waste plastic concrete, the compressive strength increased by 6.26%, 8.41%, and 5.95% as shown in their results. The bacteria’s presence promotes the formation of calcium carbonate in the concrete, aiding in greater strength and self-healing properties. Santhanam et al. [55] studied mixes of high-strength concrete formulations with up to 16% E-waste plastic to the extent of coarse aggregates together with the superplasticiser polycarboxylate ether. The results showed that 12% and 16% E-waste aggregates improved the compressive strength of concrete by 1.27% and 6.75%, respectively. Use of a superplasticiser might have resulted in better workability and packing efficiency, which in turn aided the compressive strength. These studies then begin to provide collective evidence that the modification in the properties of concrete due to the addition of E-waste, with the selective use of raw materials like steel slag, fly ash, bacteria, etc., along with superplasticisers, can nullify the weaknesses of concrete and improve on its sound functionality. These advances in concrete practice are being proved by evidence worldwide.

5.4. Flexural Strength of E-Waste Concrete

This section describes the studies performed by various researchers based on flexural strength parameters. Rathore and Rawat [61] considered the use of 5%, 10%, 15%, 20%, 25%, and 30% E-waste plastic aggregates in place of coarse aggregates in M20 grade concrete. Moreover, the flexural strength was also investigated for plastic aggregates from E-waste according to changes in size (0–10 mm, 10–15 mm and 15–20 mm). They found that the 28-day flexural strength increased by 15% among E-waste plastic aggregates with sizes less than 10 mm, while the 10–15 mm size was included for comparison as the control sample. For another attempt, the increase in the 28-day flexural strength of concrete containing 10% E-waste plastic aggregates was 1.14% higher than the control specimen [50]. Furthermore, it possessed a splitting tensile strength which was comparable to a control sample of concrete when tested with 20% E-waste plastic aggregates. On the other hand, the 28-day flexural strength of concrete decreased by 7.48%, 11.67% and 15.41% with the addition of 12%, 17%, and 22% E-waste plastics, respectively, compared to the control specimen, as reported by Needhidasan et al. [57]. Kumar and Baskar [45] found that the flexural strength of concrete with 10–50% E-waste plastic in place of CA decreases by 11.11–37.38% as compared to the control specimen. However, the decrement in the bending strength of E-waste concrete can be improved by various methods such as adding admixtures and biomineralisation, which can attain a flexural strength equal to or even greater than that of normal concrete. Table 4 shows the studies performed by various researchers on the flexural strength of E-waste concrete based on the percentage replacement of E-waste aggregates and aggregate size.

5.5. Tensile Strength of E-Waste Concrete

This section describes the studies performed by the various researchers based on tensile strength. Numerous research works found that an increase in E-waste plastic waste proportions in the concrete mix reduces the splitting tensile strength of concrete. The most remarkable reductions reported were decreases in ultra-lightweight of 23.51%, 30.97%, and 32.46% at 10%, 15%, and 20% aggregate inclusion levels, respectively [30]. In the M40 grade concrete tested by Needhidasan et al. [59], strength decreased with increasing content of E-waste aggregate, but strength increased between 7 and 28 days in most cases, the highest increase coming later. Kumar and Baskar [45] observed a wide range of strength loss between 8.06% and 47.89% for 10–50% E-waste replacement in concrete. E-waste-enhanced concrete exhibits a higher ductility than normal concrete, which, prior to the failure of a structure, calls for a warning, and thus is a significant safety component as observed from investigations by Kumar and Baskar [58]. While most of the studies show a decrease in splitting tensile strength with the addition of E-waste, there are some exceptions in which increases in splitting tensile strength coincide with specific percentages of E-waste inclusion.

5.6. Thermal Resistance of E-Waste Concrete

This section describes the studies performed by various researchers based on the thermal resistance of E-waste concrete. Given that human and economic losses could potentially be high, it is essential to evaluate the behaviour of concrete structures in the event of a fire [62]. Understanding the thermal resistance of concrete is essential in the fire design of structures [53]. The most common way of examining the performance of concrete under fire is to assess the loss of compressive strength or weight changes. The limited literature review on the thermal resistance of E-waste aggregate concrete is summarised as follows:
Ullah et al. [30] evaluated the thermal resistance of concrete containing 10–20% E-waste plastic aggregates under 150 °C and 300 °C for 1 h. While the compressive strength decreased, the rate of reduction for specimens with E-waste aggregate was lower than for conventional specimens. The strength reduction was 24.41 and 21.42% for the control and 20% E-waste plastic aggregate mix, respectively, at 150 °C. Kumar and Baskar [63] exposed concrete to 100 °C, 200 °C, and 300 °C for 1 h in the case of E-waste plastic aggregates. No colour change and no visible surface cracks in the specimens were observed when it was tested at 100 °C. Fewer cracks were observed at 200 °C. When it was subjected to 300 °C testing, it exhibited cracks at 45°. Specimens that received E-waste aggregate had a 35% strength retention at 300 °C after 28 days of curing, and the concrete with a ratio of E-waste aggregate still exhibited 50% of its strength even when subjected to 300 °C testing. The study conducted by Danish et al. [38] indicated that concrete made with E-waste plastic aggregates was thermally more stable than control concrete with a compressive strength reduction of 24.14–28.57% at 150 °C and 41.37–42.85% at 300 °C, respectively. All specimens retained up to 50% residual strength, however, regardless of strength degradation signifying the possible advantage of E-waste aggregates for improving thermal resistance in structures. Pauzi et al. [46] demonstrated comprehensible evidence about the fire-resistance behaviour of concrete with E-waste subjected to temperatures from 200 to 800 °C for 1 and 2 h. At 200 °C and 400 °C for one hour, they reported an increase in compressive strength compared to ambient temperatures, which can be attributed to the accelerated hydration reactions. At greater temperatures, the specimens had a marked reduction in their compressive strength, which was due to the recovery of Ca(OH)2 and the regeneration of C–S–H gel taking place, so they were becoming less bonded with E-waste aggregates and mortar. However, it is worth noting that E-waste aggregate concrete showed better thermal resistance than that of conventional concrete up to a certain level of replacement of E-waste aggregates and up to a certain temperature. This is due to the fact that the E-waste aggregates take longer to achieve a steady electromotive force, which permits them to remain exposed to heat for an extended period. This outcome further validates the effectiveness of E-waste aggregates in building concrete walls that keep the temperature of the rooms within the acceptable range during different atmospheric conditions at any time of the year. Yet, because several parameters (e.g., aggregate type and exposure conditions) are interdependent, more extensive analysis is needed to properly understand how E-waste aggregates may affect the fire resistance of concrete structures.

6. Discussion

6.1. Workability of E-Waste Concrete

Workability of concrete as determined by slump tests also plays a vital role in assessing the ease with which the mix can be mixed, placed and finished. The literature on E-waste indicated that the incorporation of E-waste reduces workability significantly in concrete mixtures. The decrease in workability with the increase of E-waste content is mainly due to surface texture, which is rough and irregular, leading to high internal friction, resulting in less flow ability. Furthermore, the hydrophobic character of most E-waste substances, especially plastics, acts to lessen actual water articles in combination [64], which lowers or retards workability. Therefore, to help optimise mix designs and increase practical utilization of E-waste concrete, it is necessary to be able to understand the underlying mechanisms as well as thoroughly evaluate how different types and percentages of E-waste affect these properties.

6.2. Mechanical Properties of E-Waste Concrete

The mechanical properties of concrete itself, including the strength in compression and flexure and perhaps tension as well, are not only important for its performance but also provide a guide to quality. It has been found from studies that as the E-waste proportion increases, these properties often are decreasing. Kumar and Baskar [45] also revealed that the compressive strength decreased drastically when scaled to 100% E-waste substitution. The reduction in strength is attributed to several reasons, such as the increased porosity and density of E-waste aggregates that led to deterioration in the concrete matrix. Additionally, the smooth and hydrophobic surfaces of E-waste particles are a barrier to effective bonding with cement paste, while stiffness differences between E-waste versus natural aggregates result in stress concentration zones that trigger crack initiation and propagation [65].

6.3. Durability of E-Waste Concrete

Concrete applications, with respect to long-term exposure of environmental conditions, pose concerns in terms of durability. The higher E-waste content increases the porosity of concrete, which in turn makes it more vulnerable to environmental degradation (freeze-thaw cycles and chemical attacks). Further, curing with low moisture penetration of the E-waste materials will reduce density and fill voids due to the hydrophobic behaviour of concrete [64].

6.4. Environmental and Health Impacts

This utilization of E-waste in concrete has an important environmental advantage beyond the reduction of disposal and the conservation of natural resources as well. On the other hand, increased E-waste content may increase the likelihood of heavy metal and brominated flame-retardant leaching which are potential environmental and health hazards. Hence, one needs to be careful in balancing the environmental benefits vs. the risks entailed with increase E-waste content.

6.5. Practical Implications and Feasibility

The feasibility and practical implementation of E-waste concrete require careful consideration of the availability of E-waste, processing techniques, and regulatory support. Ensuring a reliable supply of E-waste through partnerships with recyclers and waste management authorities is essential. Additionally, higher E-waste content necessitates more extensive processing and quality control measures to ensure consistent performance [63].

6.6. Economic Aspects

The economic feasibility of incorporating E-waste in concrete will depend on the balance between processing cost and possible savings not only due to the reduction of natural aggregate required, but also the decrease in disposal costs resulting from landfilling. Consistent systematic economic analyses are required for large scale construction work to decide the cost-effectiveness of E-waste concrete.

7. Conclusions

This research presents useful revelations and suggestions for sustainable construction practices by providing a full-fledged analysis of the viability of recycling E-waste in concrete and exhibiting an overview of various approaches for the production of concrete aggregate from E-waste. The colour, shape, size, aggregate crushing value, water absorption, and workability properties such as slump flow, mechanical properties (compressive strength, flexural strength, tensile strength), and thermal resistance of E-waste concrete have been discussed. The influence of incorporating E-waste in the form of coarse and fine aggregates in concrete mixes experimentally demonstrated effects on workability, mechanical properties, and durability. Based on the literature review, it is concluded that engineered E-waste aggregates show potential in improving workability by their typically smooth surfaces, while un-processed E-waste plastic aggregate could create difficulties with moisture movement. E-waste plastic aggregate-laden concrete also shows a diminishing trend in the mechanical properties with an increase in replacement levels owing to the reduced density and increased porosity of E-waste aggregates.

8. Future Recommendations

E-waste incorporation into concrete production seems a promising approach to enhancing sustainable construction. Yet, there are numerous applications that need improvement and testing before these advantages can be adequately realised. Further research might be carried out to assess the mix designs (i.e., admixtures) for superplasticisers and supplementary cementitious materials (SCMs), the contributions of workability, strength, and durability together. It is also recommended that long-term durability studies should be carried out to know the behaviour of E-waste concrete in different environmental conditions, particularly quanta cycle and moisture ingress with time, so as to make sure whether it will still intact or not. The environmental impacts and benefits of E-waste for use in concrete remain unknown, hence comprehensive life cycle assessments (LCAs) should be undertaken to quantify the complete impact of using E-waste as well as to provide a holistic view of its end-of-life fate. Economic analyses will also be necessary in order to assess the cost-effectiveness of E-waste concrete on a large scale, including not only processing costs but those incurred during transportation and quality control measures, weighed against any potential savings due to less use of natural aggregates. Pilot projects and field trials would emerge as feeder systems providing relevant on-site evidence in terms of application and performance, thus further confirming activities carried out at laboratory scale whilst proving feasibility to the parties concerned from industry. Furthermore, research should investigate the results of E-waste content in concrete over 30% as higher ratios could produce visibly lowering workability, other mechanical and durability properties, and an environmental impact or/and health risk. To address these issues, the utilization of high E-waste content concrete needs to be practiced based on innovative solutions through advanced additives and alternative processing methods for practical acceptability followed by sustainable feasibility. Machine learning techniques such as an artificial neural network (ANN) can be used to forecast the construction activities and concrete performance as well.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Buildings 14 02495 g001
Figure 1. General composition of E-waste.
Figure 1. General composition of E-waste.
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Figure 2. Waste management cycle adopted from [25].
Figure 2. Waste management cycle adopted from [25].
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Figure 3. Slump flow of E-waste concrete at different content [45,50,53,54,57,58].
Figure 3. Slump flow of E-waste concrete at different content [45,50,53,54,57,58].
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Figure 4. Compressive strength of E-waste concrete [45,50,53,54,57,58].
Figure 4. Compressive strength of E-waste concrete [45,50,53,54,57,58].
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Table 1. Ten different categories of E-waste on the basis of European WEEE directives 2002/96/EC and 2012/19/EU.
Table 1. Ten different categories of E-waste on the basis of European WEEE directives 2002/96/EC and 2012/19/EU.
CategoryDescriptionExamples
Large Home AppliancesMajor household appliances and electronicsRefrigerators, washing machines, air conditioners, dishwashers, microwave ovens
Small Home ElectronicsMinor household gadgets and electronicsTVs, DVD/Blu-ray players, stereo systems, alarm clocks, blenders, coffee makers
IT & Telecom EquipmentInformation technology and telecommunication devicesComputers, laptops, modems, routers, mobile phones, landline phones
Consumer ElectronicsElectronic devices for entertainment and personal useRadios, MP3 players, digital cameras, camcorders, game consoles
Lighting ProductsLamps and lighting equipmentLED bulbs, fluorescent tubes, halogen lamps, neon signs
Electronic ComponentsIndividual electrical and electronic partsTransistors, capacitors, resistors, printed circuit boards, wires, cables
Toys & RecreationElectronic toys, leisure, and sports equipmentRemote-controlled toys, drones, fitness trackers, electronic games
Medical DevicesMedical and biomedical equipmentThermometers, blood pressure monitors, diagnostic tools, imaging scanners
Control SystemsMonitoring and control instrumentsIndustrial control systems, thermostats, sensors, relays, microcontrollers
Automated DispensersAutomatic dispensing machinesSoap dispensers, water dispensers, vending machines, ATMs
Table 2. Hazardous characteristics of E-waste and their origins.
Table 2. Hazardous characteristics of E-waste and their origins.
ContaminantOrigins
Halogenated Flame Suppressants (BFRs: PBDEs, PBBs)Electronic devices
Polychlorinated Biphenyls (PCBs)Dielectric liquids, lubricants, coolants in generators, capacitors, transformers, luminescent illumination, rotary aerators, dish cleaning machines, electric motors
Dioxins (PCDDs, PCDFs) Dioxin-analogous PCBsCombustion derivatives Dielectric liquids, lubricants, coolants in generators, capacitors, transformers, luminescent illumination, rotary aerators, dish cleaning machines, electric motors
Polycyclic Aromatic Hydrocarbons (PAHs)Combustion derivatives
Plumbum (Pb)Printed circuit boards, cathode ray tubes (CRTs), illumination bulbs, televisual displays, solder, galvanic cells
Chromium (Cr)Anticorrosive coatings, data tapes, floppy disks
Cadmium (Cd)Switches, connectors, printed circuit boards, galvanic cells, infrared detectors, semiconductor chips, ink or toner photocopying machines, cathode ray tubes, mobile communication devices
Hydrargyrum (Hg)Thermostats, sensors, monitors, cells, printed circuit boards, cold cathode luminescent lamps, liquid crystal display (LCD) backlights
Zinc (Zn)Cathode ray tubes, metallic coatings
Nickel (Ni)Galvanic cells
Lithium (Li)Galvanic cells
Barium (Ba)
Beryllium (Be)		Cathode ray tubes, luminescent lamps Power supply units, computing machines, X-ray apparatuses, ceramic components of electronics
Table 3. Different parameters identified by the various researchers.
Table 3. Different parameters identified by the various researchers.
Reference CSFSSPSTRDW
[37]✓✓✓......
[38]✓......✓✓
[39]✓..✓..✓..
[40]✓....✓✓..
[41]✓..✓......
[42]✓....✓✓..
[43]......✓✓..
[44]......✓....
[45]✓....✓....
[46]✓....✓....
[47]✓....✓✓..
[48]✓....✓✓..
[49]✓..✓..✓..
[16]✓..✓..✓..
CS: Compressive strength; FS: Flexural strength; SPS: Split tensile Strength; TR: Thermal resistance; D: Durability; W: Workability.
Table 4. Flexural strength of E-waste concrete.
Table 4. Flexural strength of E-waste concrete.
Study Reference% E-Waste Plastic AggregatesAggregate Size (mm)Change in 28-Day Flexural Strength (%)Additional Comments
[61]5%, 10%, 15%, 20%, 25%, 30%<10, 10–15, >15+15% (for <10 and 10–15 mm)Compared to control
[50]10%Not specified+1.14%Similar tensile strength with 20%
[57]12%, 17%, 22%Not specified−7.48%, −11.67%, −15.41%Compared to control
[45]10–50%Not specified−11.11% to −37.38%Decrease as % increases
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Kumar, G.; Bansal, T.; Haq, M.; Sharma, U.; Kumar, A.; Jha, P.; Sharma, D.; Kamyab, H.; Valencia, E.A.V. Utilizing E-Waste as a Sustainable Aggregate in Concrete Production: A Review. Buildings 2024, 14, 2495. https://doi.org/10.3390/buildings14082495

AMA Style

Kumar G, Bansal T, Haq M, Sharma U, Kumar A, Jha P, Sharma D, Kamyab H, Valencia EAV. Utilizing E-Waste as a Sustainable Aggregate in Concrete Production: A Review. Buildings. 2024; 14(8):2495. https://doi.org/10.3390/buildings14082495

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Kumar, Gaurav, Tushar Bansal, Moinul Haq, Utsav Sharma, Amit Kumar, Pooja Jha, Dayanand Sharma, Hesam Kamyab, and Edison Alejandro Villacreses Valencia. 2024. "Utilizing E-Waste as a Sustainable Aggregate in Concrete Production: A Review" Buildings 14, no. 8: 2495. https://doi.org/10.3390/buildings14082495

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