*Article* **The Role of Earth Observation Satellites in Maximizing Renewable Energy Production: Case Studies Analysis for Renewable Power Plants**

#### **Mariarosa Argentiero <sup>1</sup> and Pasquale Marcello Falcone 2,\***


Received: 9 February 2020; Accepted: 5 March 2020; Published: 7 March 2020

**Abstract:** This paper is based on a novel approach towards clean energy production, i.e., space innovative applications toward sustainable development. Specifically, the role of Earth observation (EO) satellites in maximizing renewable energy production is considered to show the enormous potential in exploiting sustainable energy generation plants when the Earth is mapped by satellites to provide some peculiar parameters (e.g., solar irradiance, wind speed, precipitation, climate conditions, geothermal data). In this framework, RETScreen clean energy management software can be used for numerical analysis, such as energy generation and efficiency, prices, emission reductions, financial viability and hazard of various types of renewable-energy and energy-efficient technologies (RETs), based on a large database of satellite parameters. This simplifies initial assessments and provides streamlined processes that enable funders, architects, designers, regulators, etc. to make decisions on future clean energy initiatives. After describing the logic of life cycle analysis of RETScreen, two case studies (Mexicali and Toronto) on multiple technologies power plant are analyzed. The different results obtained, when projecting the two scenarios, showed how the software could be useful in the pre-feasibility phase to discriminate the type of installation not efficient for the selected location or not convenient in terms of internal rate of return (IRR) on equity.

**Keywords:** renewable energy; space industry; RETScreen

#### **1. Introduction**

Finding an effective way to deal with current resource depletion and climate change will require soon a complete transformation of existing unsustainable energy systems [1]. The space industry has come to represent an icon of knowledge-creation processes in technology-intensive industries [2]. The industry is not merely comprised of launches and satellites, but now includes direct consumer applications and personal entertainment [3]. Therefore, the space industry has some history of expansion, and its growth is expected to accelerate [4]. An input-output analysis is useful for predicting which industries will benefit from their growth and to inform the government, which may want to use this information for policy making or investment decisions [5]. For example, space tourism is becoming a topic of great media interest thanks to technological evolution in the aerospace sector and with the reduced costs of access to space [6]. Moreover, space-based applications are already helping emerging nations in reaching social equity, but often their demands come after the excellent attempts taken in industrialized nations to guarantee that all helpful space-based information and features are put to greatest use for social reasons [7]. Space applications are mainly based on closed-loop systems (i.e., circular), due to two main reasons: (i) to guarantee a satellite mission, the platform should

be autonomously powered; (ii) then, the spatial missions need regenerative processes to deal with limited available resources, for example air and water. Moreover, the very high costs for projecting and producing space technologies become more affordable when the system is reusable (to give an example, this is what happens for new launchers project). Therefore, the space industry is a clear example of a circular economy model.

The circular economy (CE) approach has the ambition of making better use of resources/materials through reuse, recycling and recovery with the aim of minimizing the energy and environmental impact of resource extraction and processing [8,9]. This mission is mainly pursued by redesigning the life cycle of the product, in order to have minimal input and minimal production of system waste [10]. A transition to a circular economy is required, not only because we need to overcome the limits of a linear economy, but also because scarcity of resources usually required a dependence on foreign countries on supply and a strong impact on environmental conditions due to virgin material extractions and "old" manufacturing process with no recycling objectives [11]. CE drives sustainable consumption and steers public and private investment, which eventually lead to sustainable development [12]. The sustainable development goals (SDGs) convey worldwide aspirations and urge all potential donors to help meet their difficulties [13]. Given the significant part that the space domain has already performed in growth initiatives and the excellent chance to increase its input, space operators are called on to take advantage of the momentum of the SDGs, not only to concentrate on how they can further participate, but also how they can become a more integrated component of a society struggling with growth in a wider global sense, thereby optimizing efficiency and input [14].

The following mapping, shown in Table 1, may be suggested to evaluate the space potential in order to pursue SDGs.


**Table 1.** Space contribution to SDGs [15].


**Table 1.** *Cont.*

Space technology has quickly followed and performed a significant part in economic development initiatives (coping with the majority of SDGs content) [16]. This is true in both emerging and industrialized countries. In emerging nations, where terrestrial infrastructure is often inadequate or missing, space-based applications give excellent benefits as they mainly eliminate the need for such infrastructure [17]. EO satellites are among the most relevant source of data even in industrialized countries, and they are often essential to guide policy governance providing information that is fundamental to watershed and fisheries management and to tracking pollution areas [18].

Through its SDG7 (affordable and clean energy) initiatives, the European Space Agency (ESA) promotes initiatives to guarantee inexpensive, safe, viable and contemporary energy for all. ESA is using its satellite technologies to create safe power alternatives that can substitute natural emissions producing greenhouse gasses that account for at least 70% of worldwide warming caused by human activity. Through the agency and its utility suppliers' extensive cloud booking operations conducted by ESA, consumers can build networks to support sustainable development in multiple industries, including energy, and assist in making the 17 SDGs a fact by 2030 [19].

Outside the European area, the National Aeronautics and Space Administration (NASA) has made a significant contribution to our awareness of Earth and the need for modern, greener technology in many ways. NASA's commitment to Earth, the atmosphere and green technologies continues today through solar arrays and fuel cells projects, EO satellite applications, more powerful spaceships, more efficient climate models and air, water and waste recycling processes. This is giving a strong enhancement for our planet's clean energy programs while advancing in highly technological research for science, aeronautics and space exploration tasks [20].

When talking about space technologies for clean energy generation, it is necessary to look at EO satellites for maximizing renewable energy production [21]. Satellites for EO provide a distinctive basis of data for anyone designing, implementing or assessing sustainable development initiatives. They can assist in reconstructing a sequence of occurrences by displaying a series of pictures over the span of a moment. High-resolution pictures can be used during a particular timeframe to investigate extremely focused phenomenon with a limited range of sight. In portraying national events that may involve more systemic and repeated compilation, low precision photography is easier.

Copernicus is the European Union (EU) EO and monitoring program, which looks to our planet and its environment for the ultimate benefit of all European citizens. It aims at providing accurate and easily accessible data to improve environment management and understanding of climate change effects [22]. Copernicus primarily draws on data collected from EO satellites, but it also depends on a large amount of information gathered in situ (meaning on-site or local) measurement systems made available by the Member States of the EU to the programme.

In Figure 1, the Sentinel family is displayed, which constitutes the space segment of the Copernicus program.

**Figure 1.** Copernicus EO satellite constellation [23].

Satellite programs for collecting climate data and, in general, for Earth monitoring are among the key sustainable development initiatives for SDGs, but this is not the end of the process: telemetry data properly post-processed are inserted in databases in order to allow very accurate analysis for certain type of project. For this scope, many software and tools have been developed with user-friendly interfaces, going from a basic-user level (a family that wants a domestic photovoltaic installation) to an advanced-user level (engineers working for investors in power plants or smart building programs). RETScreen, being the oldest tool conceived for exploiting databases of typical sets of data for Earth monitoring and consequently analyzing the feasibility of a power plant installation (traditional or renewable), has been adopted for describing how useful satellite missions are for renewable energy optimization in power plants, already existing or not [24].

The peculiarity of this study is to show how space-based research could produce significant enhancements to sustainability and, in particular, to renewable energy generation. Specifically, the novelty of this work comes from the emphasis given to one of the most innovative fields of study (i.e., space research) for finding solutions for our environment by trying to exploit already existing technologies to propose an innovative approach to clean energy generation. Our analyses show the results of two scenarios. The first one included a case study mixing multiple renewable technologies in a single installation; as a result, power, cost analysis, pollution analysis, financial analysis and risk analysis have been provided. The second scenario compared two equivalent (in terms of location and capacity) power plants, one provided with wind turbine and the other with photovoltaic technology.

The rest of the work is organized as follows. Section 2 introduces the materials and methods, Section 3 presents the results, whereas Section 4 discusses the findings; finally, Section 5 concludes.

#### **2. Materials and Methods**

Parameters should be accurately estimated in order to provide a reliable evaluation of renewable energy power plant installation. In Table 2, a typical set of data of the most significant parameters needed to evaluate Earth's conditions in order to better manage renewable resource plants is shown.


**Table 2.** Typical set of data for Earth monitoring [25].

These data are not easy to exploit. First, you will need to receive telemetry collected by sensors on-board the satellite. Then, you need to implement statistical and numerical models and choose the best in describing a specifying phenomenon, In the end, you will give as an input to the model, satellite data in a proper format (data normalization is always required). Only when you reach the final point, can the output data be collected in a larger database and help you in designing and optimizing energy plants and sustainable buildings.

In recent times, a spread of tools and software has been noticed, providing the evidence to how sustainability and, specifically, renewable energies are becoming relevant in our modern circular economy.

For example, Google, with its "Project sunroof" tool, allows you in a user-friendly interface to evaluate if it is convenient to build photovoltaic panels in a certain area, by using satellite data. It is not relevant to this point to list the high number of clean energy software that have been developed across the years, but it's important to speak about the most relevant ones and the way in which they provide useful results for an accurate analysis of renewable energies plants, thanks to the availability of large amount of satellite data (all of the Earth's surface is mapped with more than one sensor).

HOMER (Hybrid Optimization Modeling Software) is able to design and analyze the power systems combining traditional and renewable technologies. This tool is very accurate, but it requires too much input data to build a proper scenario, so it is mainly used not for the feasibility study phase, but for the manufacturing phase [26].

Further tools have been developed, as databases or atlases, depicting only a small set of parameters; among these tools, we found the NASA Prediction of Worldwide Energy Resource (POWER) project aimed to improve the current renewable energy data set and to create a new database from new satellite systems. The POWER project is mainly addressed to renewable and sustainable energy [27].

In the European area, the S2S4E Decision Support Tool (DST) has been developed as an operational climate service for clean energy. The DST generates climate information adapted through energy indicators derived from climatic variables such as wind speed, solar radiation, precipitation, temperature and pressure reduced to the average sea level. These indicators provide information on the expected variability in hydroelectric, solar and wind energy production, as well as on electricity demand in the future.

Last, but not least, one of the oldest and largest adopted tools for clean energy management is RETScreen, developed by the Canadian Government with NASA cooperation. In 1996, RETScreen clean energy management software was developed by Natural Resources Canada; after that, in 1998 the software package was carried on by the Canadian government.

The tool can be used for numerical analysis in areas such as energy generation and efficiency, prices, emission reductions, financial viability and hazards of various types of clean energy and energy-efficient technologies. This simplifies initial assessments and provides streamlined processes that enable funders, architects, designers, regulators, etc. to make decisions on future clean energy initiatives. This software is able to exploit post-processed satellite data and guides you through a very simple path from system project to cost analysis, in order to understand if, for example, some smart building or energy plant realization is feasible or not. It includes modelling for many renewable energy systems and the expected costs for the plant characteristics so you will be able to have an approximate, but flexible, estimate on the project you are working on.

The tool has already been used for projecting many installations all over the world: (i) to validate the techno-economic and environmental sustainability of solar PV technology in Nigeria [28], (ii) to evaluate and compare economic policies to increase energy generation capacity in the Iranian household consumption sector [29], (iii) to provide a technical, financial, economic and environmental pre-feasibility study of geothermal power plants in Ecuador [30] and (iv) to provide a preliminary determination of the optimal size for renewable energy resources in buildings [31].

RETScreen Expert software in its latest available version (7.0) has been adopted to provide useful case studies of projects involving renewable energies in contrast with standard power production. The open-source version (only viewer mode) has limited features, but it is still reliable for feasibility analysis of many projects, starting from smart buildings to power plants [32].

The first case study to be proposed is a multiple technologies power plant, combining geothermal and hydric power [33], as shown in Figure 2. In particular, water and geothermal power have been exploited in different percentages, so that the combination can provide 35,033 MWh as electricity export to the grid, reducing CO2 emissions by 15,676 tCO2 (equivalent tons of CO2).

**Figure 2.** Schematic of the integrated biphase back-pressure system [26].

The type of power plant and the location are the first step choices to go through. For this case study, the installation place is in Mexico.

Mexico's renewable energy contributes 26% of Mexico's electricity generation. The majority of renewable energy adoption comes from hydro, geothermal, solar and wind power. Long-term efforts are being made to increase the use of renewable sources of energy. The sum of geothermal energy used and extracted ranks Mexico as number four in the world.

Starting from a template of RETScreen software, latitude, longitude and altitude of both selected location (Mexicali) and the facility to be set is provided. The climate zone is individuated automatically to be that of Ensenada (the closest place to the facility being mapped for climate reference).

Mexicali is the capital of the Mexican state of Baja California. It covers an area of more than 13,000 km2 and it counts more than 900,000 inhabitants. The city is located on the border with the United States of America; in fact, its name is a crasis that derives from the union of the words México and California.

Thanks to having plenty of water, gas and electricity, Mexicali counts two major power plants, Cerro Prieto Power Station, one of the world largest installed geothermal power plants, and Sempra Thermoelectric, a combined-cycle gas turbine (CCGT) power plant with two gas turbines, a steam turbine and a heat recovery steam generator (HRSG).

This case study is inspired by a biphase turbine installed in Cerro Prieto to maximize a geothermal well that produces power from both the steam and the water. It has increased the power production of the plant by more than 40%.

On August 20, 1997, this biphase turbine was synchronized with the Commission Federal de Electricidad electrical grid. From that time until May 23, 2000, a period of two years and nine months, the power plant was in operation. The grid was supplied by a total of 77,549 kWh.

Pending replacement of the rotor with a newly designed, higher power rotor and replacement of the bearings and seals, the power plant was subsequently put in a standby state.

In Table 3, location details for the selected location (Mexicali) have been divided into different categories, expressing respectively the climate data for the location area (Ensenada), the climate data for the selected facility (Mexicali) and the origins of the climate data.


After evaluating the type of plant and the location, the software displays the target to be achieved with this project, in terms of electricity to export to the grid, the total revenue and the emissions reduction, shown in Table 4.



After defining climate data related to the installation we decided to build, we have to deal with the benchmark module.

Benchmark metrics may derive from the RETScreen Benchmark Database index, company benchmarking initiatives, organisational expectations, market trends or any other relevant measure to better align the facility to performance goals.

The benchmark database collects indicative minimum and maximum energy production costs (also known as the "levelized cost of electricity" or LCOE) of different types of power generation systems; these costs come from considering the system operating conditions, the installation technology, the location and the operation and maintenance (O&M) costs of typical power plants already installed worldwide. There are also main factors used to measure the minimum and maximum range of values, for example fuel cost rate (for combustion power systems) and capacity factor (for renewable energy systems).

An example of benchmark analysis is provided in Figure 3:

**Figure 3.** Benchmark setting for energy production (screenshot by authors using RETScreen).

After completion of this high-level benchmark assessment, the user can then conduct a more comprehensive viability report to better estimate the facility energy savings, elimination of greenhouse gases (GHG) pollution, cost savings and/or output capacity.

The system partition for this case study is depicted in Table 5.



Toronto was chosen as the reference location, mainly because a lot of data are available and updated for Canadian territories (usually case studies or templates involving other countries are no more reliable especially for costs analysis). The city has both ground and satellite data to accurately map its territory characteristics. Moreover, Toronto is located in the extreme south-east of Canada, capital of the province of Ontario and most populous center of Canada with its 3,120,668 inhabitants. The city has shown its strong engagement in sustainable development, and in 2013, the City Council introduced a mandate to produce at least 5% of the electricity from renewable energy sources for all new installations. The use of solar photovoltaic, solar thermal, geothermal and biomass supports the environmental, energetic and economic objectives of the city.

Many initiatives have been set up for education and training of the community and even for helping in designing new smart buildings for commercial and personal use.

In Table 6, geographic and climate data for Toronto are provided.


**Table 6.** Location details for Toronto.

Wind turbine and photovoltaic plants, both of 1,000 kW, are considered.

For the wind turbine system, the electricity produced will be around 3,000 MWh.

As a benchmark for energy production costs, RETScreen values are quite accurate for many installations in Canada, so it was automatically set at 100 CA\$/MWh.

A benchmark analysis for the wind turbine case located in Toronto is shown in Figure 4.

**Figure 4.** Benchmark setting for energy production (screenshot by author using RETScreen).

Below, in Table 7, the initial target values of the proposed case are presented.


**Table 7.** Target to be reached with the proposed case.

The model of the wind turbine used for this project was manufactured by a Danish company, VESTAS. Many VESTAS turbines have been exported to Canada, as a symbol of European engagement in renewable energies.

The plant, using this wind turbine model, is able to produce 3197 MWh with initial costs of 2,309,703 CA\$ (CA\$/kW value is scaled with respect to the plant capacity and data are available in the software for defined range).

The electricity export rate value has been changing across the years. To give an example, many countries started with incentives for renewable energies investors, by rewarding them with a feed-in tariff or feed-in premium. In this way, the electricity was paid more for than the real cost per unit of the electricity exported to the central grid. Nowadays, this scenario is no longer relevant because bonuses for renewable energy plants have been largely reduced, so the actual price paid per MWh to sustainable power plants is similar to all other energy source plants.

Finally, the choice to put the electricity export rate at the same value as the benchmark energy production cost is good enough for an approximate evaluation.

Details about tailoring the wind turbine system are presented in Figure 5.

**Figure 5.** Tailoring the wind turbine system (screenshot by author using RETScreen).

For the photovoltaic system, the electricity produced will be around 1200 MWh and the benchmark value will be the same with respect to the previous project.

The initial target values of the proposed case are presented in Table 8.

**Table 8.** Target to be reached with the proposed case.


In Figure 6, a benchmark analysis for the photovoltaic case located in Toronto is shown.

**Figure 6.** Benchmark setting for energy production (screenshot by author using RETScreen).

The solar cells for this photovoltaic installation are made of mono-crystalline silicon. This system performs with a higher efficiency in terms of energy production and space occupied; moreover, this type of solar cell guarantees the longest lifetime for the whole project. On the other hand, this technology is more expensive than polycrystalline solar panels, and it could be damaged in the case of dirt, shadow or snow or sometimes it might not work properly in very hot locations. In addition, during the production process, a large part of the material becomes waste, so depending on the dimension of the project it could become unsustainable even if it is a renewable energy project.

Details about tailoring the photovoltaic system are presented in Figure 7.

**Figure 7.** Tailoring the photovoltaic system (screenshot by author using RETScreen).

#### **3. Case Study Results**

#### *3.1. Case Study 1*

Results are derived from a model comparison between the baseline scenario with the proposed alternative showing the difference in GHG emissions ("Gross annual GHG emission reduction"). Transmission and distribution (T&D) losses are automatically evaluated thanks to the largely populated database embedded in the software. An equivalence is shown in Figure 8 to better understand how much emission is being reduced (almost like 3,000 cars not used).

**Figure 8.** Emission analysis chart (screenshot by author using RETScreen).

A financial analysis is provided as a final step of this pre-feasibility study. Some parameters have been defined such as inflation rate, project lifetime, debt ratio, debt interest rate and debt duration. User-defined costs usually include O&M for the project lifetime or manpower for the installation. Incentives could be inserted, if available for the specific project.

The software gives four outcomes for evaluating financial viability:


As a result, financial feasibility is provided in Figure 9, together with the cumulative cash flow graph. Less than one year is needed to reach the equity payback.

**Figure 9.** Financial analysis chart (screenshot by author using RETScreen).

For risk analysis, the Monte Carlo method is applied. The possible combinations of input variables range from 500 to 5,000 values of pre and after-tax IRR equity, pre and after-tax IRR assets, equity payback, net present value (NPV) or energy production cost. The risk analysis allows the user to determine whether or not the volatility of the financial metric is appropriate by looking at the range of possible results. An excessive variance would imply the need to make further effort to reduce the volatility associated with the input variables that have been identified as having the greatest impact on the financial metric.

The applicant should enter an appropriate level of risk for the financial metric under consideration. The rate of risk feedback is used to assess the confidence interval (defined by the maximum and minimum limits) within which the financial predictor is expected to fall. The level of risk reflects the possibility that the financial predictor may slip outside this confidence interval.

Limits of the confidence interval are generally determined on the basis of the median value and the risk rate and are shown as "Minimum within the confidence level" and "Maximum within the confidence level". It is recommended that the individual reach a maximum risk level of 5%–10%, which are common values for the generic risk analysis.

The histogram lays out the array of possible values for the financial metric arising from the Monte Carlo simulation. The height of each bar reflects the rate (percent) of values that drop within the scope specified by the width of each bar. The value corresponding to the center of each range is plotted on the X axis.

Looking at the distribution of the financial metric, the consumer is able to quickly determine the volatility of the variable. In some instances, there is a lack of data to accurately map the graph. In the case of equity payback reached instantaneously, the outcome is the "n/a" (not applicable) symbol, and therefore this analysis will be missing.

#### *3.2. Case Study 2*

For this case study, we will analyze two sets of results depending on the system adopted (wind turbine or photovoltaics).

For the wind turbine case, the gross annual GHG emission reduction is 93%, comparable to 55 cars (traditionally fueled) no longer used.

Financial analysis shows, in Figure 10, that equity payback for the wind turbine power plant is reached after 3.5 years of the 25 years of the project's lifetime, but it should be taken into consideration that this analysis does not involve any incentive due to the rapid evolution of regulations, that it is progressively converting the initiatives for funding clean energy generation with initiatives for help in designing sustainable systems.

**Figure 10.** Financial analysis chart (screenshot by author using RETScreen).

For photovoltaic installation, the gross annual GHG emission reduction is 96%, comparable to 22 cars (traditionally fueled) no longer used. Even though the percentage is greater than the wind turbine case, we should consider that the electricity produced with photovoltaics is around one third of that produced by the other system, so effectively the CO2 reduction is minor.

Financial analysis shows, in Figure 11, that equity payback for the photovoltaic case is reached after 16.7 years of the 25 years of project's lifetime. For incentives and grants, the same consideration made for wind turbine system has been evaluated.

**Figure 11.** Financial analysis chart (screenshot by author using RETScreen).

#### **4. Discussion**

The first case study was only aimed at showing how RETScreen is powerful, even mixing different renewable technologies in one single power plant, optimizing the project on the base of the location characteristics. The second case study provided more evidence, reported in Table 9. The different outputs of the two installations (i.e., wind turbine vs. photovoltaic) are provided.


**Table 9.** Wind turbine vs photovoltaic in RETScreen.

It is possible to notice that, starting from a common baseline (same location, same power plant capacity, same project life and same evaluation for electricity export rate), that the electricity produced by the two power plants is sensibly different; in fact, the wind turbine system is much more efficient than the photovoltaics. Due to its higher efficiency in producing electricity, the correspondent gross annual emission reduction of greenhouse gases is bigger for the wind turbine with respect to the photovoltaic case. Findings emerged from our investigation can represent useful insights for policy makers. Specifically, besides looking at policy of direct regulations, other policy instruments that can indirectly support deployment of renewable energy resources in the long term should be adequately taken into account. These indirect strategies can be in the form of environmental taxes or of emission permits for energy produced by non-renewable sources, as well as the removal of subsidies given to fossil fuel generation [34]. Moreover, even though the total initial cost for the photovoltaic power plant is lower than for the wind turbine installation, it can be inferred from the financial indicators that the investment is much more convenient for the wind turbine project, which is able to cover its initial costs in a time 14% of the total lifetime; on the other side, with photovoltaics installation you will cover the costs after 70% of the project lifetime. Another aspect for policy makers to consider is looking at the financial issues that might prevent investment decisions. In this perspective, enhancing the green finance—i.e., the financing of investments that provide environmental benefits in the broader context of environmentally sustainable development [35]—may significantly contribute to guaranteeing capital flow in renewable energy sectors [36] so as to enhance the sustainability of the overall financial system [37] as well as to improve corporate planning strategies [38].

Overall, the aim of this study is not to evaluate which renewable technology is more affordable or efficient (it is very easy to find wind turbine for high-capacity systems and, on the contrary, projecting photovoltaic installation is usually aimed at small-capacity systems, such as houses), but to understand how the RETScreen software could be successfully adopted in decision-making processes in an early stage (e.g., pre-feasibility analysis), to effectively exclude inconvenient choices under determined constraints. From this perspective, a technique for optimizing a renewable energy network is developed using RETScreen software tool. It is built to maximize the size of an integrated hybrid energy system in buildings. Case studies for a single and an integrated renewable energy program may research the efficiency of the methods [39]. Another example of using RETScreen is to provide a techno-economic assessment of a certain type of renewable energy installation only after evaluating the environmental consequences of the selected energy systems through comprehensive life cycle assessment (LCA) with a more accurate tool [40]. To provide evidence for how it is valuable to move from traditional energy resources to renewable ones, another case study using RETScreen described how urban photovoltaic installations could improve sustainability in Saudi Arabia [41].

The significant number of analyses carried out with RETScreen is all thanks to the worldwide satellite missions providing data for Earth monitoring, even mapping areas where no ground-based information is available, due to territorial constraints (islands, mountains, etc.).

#### **5. Conclusions**

At the Conference of the Parties in December 2015 (Paris Agreement), 195 countries agreed to take urgent action to combat climate change by limiting global warming to well below 2 ◦C and pursuing efforts to limit it to 1.5 ◦C. The space industry, and related applications and tools, gives rise to a significant and innovative approach to clean energy generation; it is enough to think that starting from satellite missions, providing more and more accurate weather information, we are able to map every area of the globe, overcoming data limitation due to the lack of meteorological ground stations.

The novelty of this work comes from the emphasis given to one of the most innovative fields of study (i.e., space research) for finding solutions for our environment by trying to exploit already existing technologies, such as EO satellites or deep space exploration applications (them being mostly circular systems). Applying RETScreen software could be useful in the pre-feasibility phase to discriminate the type of installation that is not efficient for the selected location or not convenient in terms of IRR on equity. Results of our analysis indicate that, looking at the geographical context of our case studies, the wind turbine system is much more efficient than the photovoltaics in terms of financial indicators as well as the annual emission reduction of greenhouse gases.

There is a need to expand research based upon space exploration applications to develop capacity building and create less uncertainty for financing long-term projects to accelerate the circular economy framework. Governments and industry must increase R&D efforts to reduce costs and ensure space-based technologies' readiness for rapid deployment, while also supporting longer-term technology innovations.

**Author Contributions:** Conceptualization, M.A. and P.M.F.; methodology, M.A.; software, M.A.; validation, P.M.F., formal analysis, M.A.; investigation, M.A.; resources, M.A.; data curation, M.A.; writing—original draft preparation, M.A.; writing—review and editing, P.M.F.; visualization, M.A.; supervision, P.M.F.; project administration, P.M.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Abbreviations**


#### **References and Note**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

### *Article* **Towards Eco-Flowable Concrete Production**

#### **Maria Rashidi 1,\*, Alireza Joshaghani 2,\* and Maryam Ghodrat <sup>1</sup>**


Received: 20 December 2019; Accepted: 3 February 2020; Published: 7 February 2020

**Abstract:** Environmental concerns have increased due to the amount of unused/expired plastic medical waste generated in hospitals, laboratories, and other healthcare facilities, in addition to the fact that disposing of such wastes with extremely low degradation levels causes them to remain in the environment for extended periods of time. These issues have led researchers to develop more environmentally friendly alternatives for disposing of plastic medical waste in Australia. This study is an attempt to assess the impacts of using expired plastic syringes as fine aggregate on fresh and hardened characteristics of flowable concrete, which might provide a solution to environmental concerns. Six mixtures of flowable concrete with water-to-cement ratios of 0.38 were studied. It was found that using recycled aggregate in up to 20% can improve the workability and increase the V-funnel values of flowable concrete mixtures. However, using waste aggregates in more than 30% caused an inapt flowability. Adding waste aggregate at the 30%–50% replacement level led to a decrease in the L-box ratio. To verify the utility and the efficacy of this experiment, the connections between different rheological test measurements were also compared by implementing the Pearson correlation function. The mechanical properties of the mixes containing recycled aggregates were decreased at the age of seven days; however, at later ages, waste aggregates increased the strength at the 10%–30% replacement levels.

**Keywords:** flowable concrete; expired plastic syringes; rheological properties; mechanical behavior

#### **1. Introduction**

Numerous plastic products are being consumed with the development of society. However, large amounts of plastic waste pose a threat to the environment due to the very low biodegradability of plastic. It is necessary to develop a rational approach to waste disposal which addresses both the economy and environmental protection [1]. The use of recycled plastic aggregates in concrete can reduce the cost, alleviate an environmental problem, and save energy. In the last few decades, the recycling of waste materials has been a serious concern due to the boundaries of landfill spaces and the growing expenses. Based on a national report in 2016, Australia produced 59,000 tons of medical waste each year (Australia's report to the Basel Convention) [2]; disposable syringes made up a large proportion of the overall medical waste production. Plastic syringes contain a high percentage of plastic (about 90%), which means that they have high potential to be recycled. Currently, the main method instated by hospitals for expired plastic syringes is to pass expired plastic syringes through collection agencies, who dump them into landfills. However, recently, there have been significant increases in landfill levees, raising the price of non-recycled waste such as waste syringes.

There are opportunities for using these wastes in other fields, particularly in the construction industry. The field of research on the assessment of the application of plastic waste in concrete mixtures has gained popularity in the last few decades. The use of waste plastic bottles [3], waste PVC pipe [4], and shredded and recycled plastic waste [5–9] has been investigated by various researchers. Numerous studies have also been carried out on the usage of scrap rubber in both mortar and concrete [10,11]. In fact, using recycled plastic can improve concrete durability when used as fiber. It has also been found that using waste plastic as fiber in concrete leads to a growth in flexural and splitting-tensile strength [12,13]; at the same time, shrinkage and permeability decreased [14]. Other groups of researchers reported that increasing the amount of plastic waste causes a reduction in splitting-tensile, flexural, and compressive strength [15,16]. The main reason for this behavior is the incompatibility between the cement paste and plastic particles [15]. In addition, some researchers found that the shape of the plastic particles is a definitive parameter, in that sharp edges lead to a reduction in slump value [17]. On the other hand, adding plastic particles with a spherical shape enhances fluid ability.

It is observed that previous studies are mainly aimed at the properties of plastic waste as an aggregate substitution in ordinary concrete. Work related to self-compacting concrete containing plastic particles is relatively scarce. Just a few studies are found about the effect of plastic waste on the properties of self-compacting concrete. Overall, based on the detailed survey in the literature, it has been perceived that most of the research carried out so far is on assessing the implementation of plastic waste as a substitution for aggregate in ordinary concrete. There are relatively few studies found on fresh properties of flowable concrete with plastic particles; however, just a few studies have been done on the impact of plastic medical waste on properties of flowable concrete. This oversight is particularly unfortunate considering that flowable concrete has been increasingly used in stay-in-place formwork structures, concrete-filled steel columns, and prefabricated PVC walls and columns because of their light weight, construction simplicity, and their lower noise levels [18,19].

This study focused on integrating the expired plastic syringes into the matrix of flowable concrete mortar as a replacement for fine aggregate. The objective is to reduce the environmental footprint of expired plastic syringes and to avoid sending them into landfills. Recycled medical waste aggregate is produced from expired plastic syringes. This experimental study was done to evaluate the fresh and hardened properties of the flowable concrete with different proportions of fine aggregate substituted by shredded expired plastic syringes.

#### **2. Experimental Study**

The experimental study aims to promote the use of sustainable forms of flowable concrete by incorporating recycled aggregates from shredded expired plastic syringes and to develop information on their fresh and hardened mechanical properties.

#### *2.1. Materials and Mix Properties*

Cement type I with a fineness of 2850 cm2/gr and a specific gravity of 3.16 was added to the mixture as the main cementitious material. The chemical composition of the cement is shown in Table 1. The natural coarse aggregate was limestone gravel with a nominal maximum size of 12.5 mm. The specific gravity and water absorption of the coarse aggregate in flowable concrete were 2.82 and 1.95%, respectively. As a fine aggregate, concrete aggregate with a maximum size of 4.75 mm was added to the mixture. In addition, the fine aggregate had a specific gravity and water absorption of 2.67 and 2.51%, respectively. The physical properties of the aggregates are shown in Table 2. The natural aggregate gradation is shown in Figure 1 with black lines. Moreover, the recycled coarse and fine aggregates are shown in Figure 1 with solid and dashed red lines, respectively. a High-Range Water-Reducing Admixture (HRWRA) with a polycarboxylic-ether base and a specific gravity of 1.09 was used in this study. The HRWRA was used in flowable concrete mixes to reach the flowability target, i.e., the initial slump flow of 650 ± 25 mm.


**Table 1.** Chemical and physical properties of Type I cement.


**Figure 1.** Sieve analysis of coarse and fine aggregates for both natural and recycled aggregates.

#### *2.2. Preparation of Expired Plastic Syringe Aggregate*

The flowable concrete mixes of the experimental program were produced using natural aggregates and aggregates from shredded expired plastic syringes. The recyclability of the syringes' bodies and needle attachments were considered initially; this provided a relatively wide scope of materials, e.g., plastic, metal, and rubber. Plastic syringes (50 and 10 mL used in this study) have a high plastic content (around 90%). About 400 expired 50 and 10 mL plastic syringes with different brands and manufacturers were collected from hospitals, laboratories, and dental clinics all around the greater Sydney region. The unused syringes were then shredded by a 1.5 kW jaw crusher, as shown in Figure 2a; the steel needle parts were then removed by a 2 ton Beaver Permanent Magnet Lifter (Figure 2b).

**Figure 2.** Waste plastic sample preparation.

Figure 3 represents the plastic types that exist in expired plastic syringes: Rubber, white, green, and crystal plastic. As can be seen from Figure 3, the crushed particles of the rubber plunger are bigger in size when compared with other plastic particles. The microstructural properties of the four plastic types were examined in order to understand the elements that exist in each type.

**Figure 3.** Types of plastic in the expired plastic syringes collected from hospitals and vet clinics.

#### *2.3. Microstructural Properties of Waste Plastic Syringe Composites*

Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) tests of ground expired plastic syringes were carried out to analyze the elements existing in these wastes. Four types of plastic particles, including rubber, crystal plastic, green plastic, and white plastic were visually detected and examined. The elemental analyses of these four plastic particles are reported in Figure 4. Samples were X-ray mapped using a JEOL JXA-8600 super probe SEM with an "AMPTEK" EDS silicon drift detector [20]. SEM allows greater magnification, resolution, and depth-of-field than those of an optical microscope. X-ray microanalysis was used to identify, locate, and quantify the elements that compose a specimen, as shown in Figure 4. The results showed the elemental differences between the

different plastic particles in expired syringes. As can be seen from Figure 4, carbon is the dominant element in all plastic particle types detected in expired syringes except rubber particles, in which SiO2 plays a governing role, followed by CaO and SO3. Previous studies displayed that adhesion between rubber parts and the cement paste seems to be substantial for the product properties [21].

**Figure 4.** Scanning electron microscopy (SEM) micrographs and energy-dispersive spectroscopy (EDS) microanalysis of materials in expired/waste plastic syringes.

#### *2.4. Mixture Proportion*

The binder content for this study was 500 kg/m<sup>3</sup> with a constant water-to-cement ratio of 0.36. In this experimental study, different series of flowable concrete mixtures incorporating expired plastic syringe particles as a replacement for aggregates were designed. Replacement levels for waste materials were 10%–50% of the fine aggregate weight. The mixture proportions of the flowable concrete with recycled aggregates are presented in Table 3. The mix ID consists of two parts: The number is the replacement percentage and R is the sign of replacement. For example, 20R denotes the mixture with the recycled aggregate replacement of 20% of the weight of the sand.


**Table 3.** Mix proportion of flowable concrete using natural and recycled aggregates (kg/m3).

SP: Superplasticizer, RA: Recycled aggregate, CA: Natural coarse aggregate, and FA: Natural fine aggregate.

ASTM C 192 [22] allows aggregates to be dried to the saturated-surface-dry (SSD) condition instead of oven-dried. In this study, towels were used to dry the surface moisture from aggregates to add them into the mix in the SSD condition. The dosage of HRWRA is presented with respect to the cementitious material content (by weight) in Table 3. In addition, Figure 5 displays the procedure of the mixing used to prepare the flowable concrete mixes. Natural and recycled aggregates were mixed before batching the concrete mixture.

**Figure 5.** Details of the mixing procedure for flowable concrete with recycled aggregates.

During the first 24 h after pouring, samples were covered with a wet towel at room temperature. Afterward, samples were placed in a lime-saturated water bath at 23 ± 2 ◦C, where they were kept until the test day. On the test day, specimens were removed from the water bath and brought to SSD condition before they were tested.

#### *2.5. Test Practices*

#### 2.5.1. Workability Measurements

The superplasticizer (SP) was adjusted in order to prepare a homogeneous mix with a slump flow diameter of 650 ± 25 mm, as described in the ASTM C 1611 standard [23]. The slump flow T500 test was carried out to take the measurement of the flowable concrete flowability with no obstructions. The purpose of this test was to measure both the flow speed and flow time [24,25]. The T500 time can present the viscosity of the flowable concrete. After preparing the base plate and clean cone, the cone was filled with no agitation or roding. After 30 seconds, the cone was picked up vertically with no interference with the concrete flow, as shown in Figure 6a. To measure the T500 time, the time is started right after the cone case is in contact with the base plate, and timekeeping is continued until the

concrete reaches a diameter of 500 mm. The greatest diameter of the flow spread was recorded as the slump flow [26].

**Figure 6.** Workability tests: (**a**) Slump flow and (**b**) V-funnel.

The V-funnel was tested based on the BS EN 12350 standard to take a measurement of the flowability through a confined area with no blockage under its own weight. Then, the time that the concrete took to flow through the apparatus (TV) was recorded. Figure 6b presents the method of performing the V-funnel test.

The J-ring test was also used to measure the passing ability of flowable concrete to fill spaces within the formwork. The J-ring setup includes a slump cone in the middle of a cage of rebar, as shown in Figure 7. This test method was conducted based on the EFNARC specifications and ASTM C1621 [27,28]. The slump cone is filled with concrete and lifted, and the circular flow of concrete is measured. The J-ring flow test represents the passing ability by measuring the difference in the concrete flow diameters (d2–d1)) [29].

**Figure 7.** The J-ring test apparatus for testing the passing ability.

In addition, the L-box test was used as a measurement of the workability of flowable concrete in the presence of obstacles by reinforcing bars in accordance with the BS EN 12350 standard. The L-box test setup has an L-shaped rectangular-section box, as shown in Figure 8. The horizontal and vertical parts are separated by a gate, which is removed after the upright part is filled with flowable concrete. The concrete heights at the vertical part (H1) and at the end of the horizontal part (H2) were recorded. The magnitude of H2/H1 represents the flowable concrete flowability in the presence of obstacles.

**Figure 8.** The L-box setup for workability measurement.

The European Federation of National Associations Representing for Concrete (EFNARC) specification defines specific requirements for the flowable concrete material, its composition, and its application. The test procedures that are applied to characterize the properties of flowable concrete have upper and lower limits, as shown in Table 4. The reason is that all flowability limits should be evaluated to fulfill all requirements.


**Table 4.** Flowable concrete property requirements according to the European Federation of National Associations Representing for Concrete (EFNARC) [27].

#### 2.5.2. Mechanical Tests

The compressive strengths of flowable concrete specimens were measured at the ages of 7, 28, and 91 days based on ASTM C39. The flowable concrete was cast in 100 × 200 mm cylinders. Concrete specimens with dimensions of 300 × 100 × 100 mm were cast for flexural strength tests (using a beam with three-point loading) based on the committee C-9 of ASTM C78 [30]. Finally, cylinders with a diameter and height of 100 and 200 mm, respectively, were cast for splitting-tensile tests based on the ASTM C496 [31].

#### **3. Experimental Results**

#### *3.1. Fresh Properties*

Figure 9 illustrates the required HRWRA dosage to reach the slump flow target, 650 ± 25 mm, in each mix. However, the horizontal free flow was changed for flowable concrete mixtures with recycled aggregates. The incorporation of 50% of recycled aggregate caused the highest demand for HRWRA. There was a greater water absorption by using more waste plastic aggregate. For flowable concrete specimens with 30% or more plastic content, the water absorption percentage was significantly greater than those of other specimens with no waste materials. Therefore, samples with greater replacement percentages tended to absorb more water on their surfaces and consequently increased

the water demand of the mixtures. Therefore, the lubricant effect of water decreased and the cohesion of flowable concrete mixes increased, which required a higher level of HRWRA to yield the anticipated slump flow. The average slump flows for 10%–20% recycled aggregate replacements were equal to or greater than that of the control sample. This shows the advantages of using recycled aggregate to improve the workability of flowable concrete by only adding up to 20% waste materials. However, 30%–50% replacement decreased the slump flow in comparison with that of the control sample. Al-Hadithi and Hilal reported that slump flow diameters ranging from 650 to 780 mm were obtained for the Self Compacting Concrete (SCC) with plastic waste replacement [32].

**Figure 9.** The SP dosage of flowable concrete mixtures to achieve target slump flow.

For all the mixes, although the HRWRA percentage increased with an increased amount of waste aggregate to maintain an acceptable slump, a reduction in the slump flow was seen with increasing waste material content. In addition, the time that the concrete took to achieve the slump flow of 500 mm was measured (T500). Figure 10 shows that the T500 increased from 2.02 seconds for the control flowable concrete to 2.12, 2.26, 2.15, 2.73, and 3.34 for flowable concrete with 10%–50% replacements. Although the plastic waste aggregate did not change the slump flow excessively, the homogeneity of the concrete decreased. The comparison between the T500 and V-funnel flow times of the control sample and flowable concrete at different replacement ratios confirmed that adding waste aggregate significantly increased the flow time.

**Figure 10.** Results of the T500 and V-funnel tests.

The viscosity of flowable concrete was measured by the V-funnel test. Based on the specifications, a longer V-funnel flow time indicates a flowable concrete with greater viscosity. Moreover, those mixtures with shorter V-funnel flow times (i.e., low viscosities) are prone to having segregation [33]. As shown in Figure 10 with a dashed line, using waste aggregates increased the

V-funnel flow time of flowable concrete; thus, the viscosity of SCC would be increased. The minimum value for the V-funnel was 8 seconds, which corresponded with a 10% aggregate replacement. Therefore, all of the flowable concrete mixtures were greater than the minimum EFNARC requirement (i.e., 6 seconds). However, using waste aggregates for more than 30% kept the V-funnel values greater than 12 seconds, which indicated an inappropriate flowability and a viscosity too high for being flowable. Al-Hadithi and Hilal found that the addition of waste plastic increases both T500 slump flow and V-funnel flow times [32].

Figure 11 shows the results of the L-box test. In this test, the L-box values of the mixes, indicating the flowabilities of the mixes, ranged between 0.8 and 1. The mixes with the lower waste aggregate replacement ratios had higher L-box ratio than those with the higher replacement ratios, indicating higher flowability and workability of the mixtures. Addition of waste aggregate at a 30%–50% replacement level decreased the L-box ratio in comparison to that of the control specimen. According to Albano et al., having a higher absorption capacity in mixtures with plastic aggregates can influence the porosity [34]. This behavior can cause an increase in viscosity, as is evident from the reduced L-box ratio magnitudes. The L-box ratio of the mix 10R was greater than those of other mixtures, which indicates that 10% replacement of waste aggregate was more successful in improving workability in comparison with other replacements. Al-Hadithi and Hilal also reported the same trend in L-box testing [32].

**Figure 11.** The L-box test results.

The results of the J-ring test also confirmed the results obtained by the L-box, V-funnel, and slump flow tests (see Figure 12). The maximum reduction of mixtures in slump flow in the J-ring test was not higher than 50 mm, except with 50R. Brameshuber and Uebachs [35] reported that a flowable concrete mixture with an acceptable passing ability should have a blocking index (difference between J-ring flow and slump flow) of less than 50 mm to not see any blockage. Figure 12 demonstrates the influences of recycled aggregate on the J-ring flow results; i.e., the passing ability was decreased for 20%–50% replacements as the J-ring flow decreased. On the contrary, the J-ring flow was improved at the 10% waste aggregate replacement level, which shows a greater passing ability compared to that of the control sample. The higher percentage of waste materials made the concrete less workable and increased the potential of blocking. Due to the angularity and rough surface texture of the waste aggregate, the passing ability of flowable concrete was decreased by its friction. Safiuddin et al. reported the same behavior when using construction waste aggregates [36].

**Figure 12.** Results of the recycled aggregate on the J-ring flow of concrete.

In order to verify the utility and efficacy of using waste plastic materials, the correlations between different rheological test measurements were calculated by employing the Pearson correlation method, as shown in Table 5. The correlation coefficient is a number between −1 and +1. This number can specify how strongly two factors are correlated to each other. Coefficients of -1 and +1 designate great negative and positive correlations, respectively [37]. In this study, an absolute value of a correlation coefficient of greater than 0.8 was considered as a robust correlation. In addition, a correlation coefficient of less than 0.5 was considered as a weak correlation.


**Table 5.** Pearson correlation numbers of fresh properties.

The correlation coefficients between the slump flow, J-ring, L-box, and V-funnel were greater than 0.8, which shows a strong correlation. However, the T500 test was weakly correlated with other rheological factors. These relationships between the fresh properties were considered as a strong correlation. The effects of using the waste aggregate in flowable concrete by different levels of replacement were identical. In other words, the rheological properties (stability, mobility, and compactability) were improved in the same manner.

#### *3.2. Mechanical Tests*

The compressive strengths of samples were measured at the ages of 7, 28, and 91 days. As can be seen in Figure 13, at the age of 7 days, samples containing recycled aggregates resulted in lower compressive strength values than that of the control sample. However, at the age of 28 days, using waste aggregates increased the compressive strengths of the samples beyond those of the control mix, except for the 30%–50% replacement percentages. Safi et al. reported that the compressive strength of self-compacting mortars decreased with the increase in plastic waste content at all curing times [38]. At 30% and 50% substitution of waste, the percentages of reduction of compressive strength were 15% and 33%, respectively. Other authors found that, compared to control mixes, up to 72% reductions in compressive strength were observed for concrete with 20% replacement [39,40].

**Figure 13.** Results of the compressive strength test.

The same trend was seen in the tensile test. As shown in Figure 14, using waste materials as aggregates reduced the splitting-tensile strength of SCC excessively. By using waste products instead of natural aggregates, in comparison with the control sample, the splitting-tensile strengths of samples decreased by 22.3% by adding 50% waste. In addition, Figure 15 shows that the average value for the flexural strength test of the control samples was higher than for other samples except 40R after 7 days. However, after 28 days, for flexural strength, there was a great improvement in 20%–50% replacement percentages, as shown in Figure 15. The highest increase was in the SCC samples by adding 40% waste materials, as the flexural strength increased by 25.8%. Adding 10% waste materials did not change the flexural strength and decreased it insignificantly. The flexural strength decreased by 35% by adding 10% waste products. Other authors reported that the flexural tensile strength decreases with the increase in plastic waste content. Authors found that this is due to the low resistance of the waste [41].

**Figure 14.** Results of the splitting-tensile strength test.

**Figure 15.** Results of the flexural strength test.

The analysis of variance (ANOVA) is shown in Table 6, which indicates whether the strength differences between samples containing waste replacement and the control sample are significant. As this evaluation was done within the samples in one group, it is called an omnibus test. Based on a defined level of 0.05, when the significance factor with waste materials is less than or equal to 0.05, there is a significant difference between this and the strength of the control sample. Otherwise, samples with significance factors of higher than 0.05 have an insignificant difference with the control sample [42,43]. When adding waste materials, the compressive strengths and splitting-tensile strengths of flowable concrete samples were decreased, but the magnitudes of strength did not change noticeably at small replacement levels. Table 6 shows that the percentage reduction of 50R compared to the control sample was significant for both compressive and splitting-tensile strengths. Based on statistical analysis, all significance factors are larger than 0.05 for replacing waste materials up to 40%. This indicates that almost all compressive and splitting-tensile strength values were in the same range. Based on ANOVA, adding 10% waste materials decreased the flexural strength significantly compared to that of the control sample. While using waste materials to replace more than 10% of the fine aggregates had a slight impact on the flexural strength compared to that of control sample, no notable changes were observed in improving the flexural strength at 28 days.


**Table 6.** Effects of waste materials on the compressive, splitting-tensile, and flexural strengths of flowable concrete samples after 28 days.

\* The mean difference is significant at the 0.05 level.

#### **4. Limitations and Future Directions**

The legal requirements for different management methods of plastic medical waste along with additional recommended controls and explanations are considered as the key limitations for efficient management of these kinds of wastes.

The lack of strategic planning among the responsible organizations is a big issue, and there is minimal level of awareness among some hospital staff regarding the risks to the environment resulting from inappropriate management of unused plastic medical waste.

The future avenues for efficient waste management at healthcare facilities would include the better education of healthcare workers and standardized sorting of medical waste streams; hence, further research is required given the trend in increased medical waste production with increasing global GDP.

#### *Role towards Sustainability*

The main role of this research with respect to sustainability is to introduce a more sustainable method of the usage of expired/unused plastic medical waste and puts forward appropriate countermeasures for the acting facilities operation, performance management and other aspects. The environmental and economic burden related to the management of unused plastic medical waste is huge. The data presented in this research pointed out that using expired plastic syringes as fine aggregate in the production of flowable concrete might provide a solution to environmental concerns, in addition to mediating the cost of the waste treatment.

There are a number of moves that governments could make to improve expired plastic syringe treatment and disposal. Firstly, governments should standardize explicit classification of expired plastic/glass syringes and IDUs (injection drug units) and tightly regulate the disposal of each type to prevent their dumping. In addition, governments need to provide healthcare facilities with incentives for reducing sharp production through adequate procurement of staff training and putting into place an accurate database regarding the level of demands that each hospital has in order to avoid over-ordering syringes and other medical devices. Lastly, governments should increase research funding in the area of medical waste reduction and treatment though research grants and industry research partnerships.

#### **5. Conclusions**

This study explored the properties of flowable concrete made with shredded waste plastic syringes as fine aggregate. The following conclusions can be drawn:


**Author Contributions:** Formal analysis, A.J. and M.G.; Funding acquisition, M.R.; Investigation, M.R.; Methodology, A.J. and M.G.; Writing—original draft, A.J. and M.G.; Writing—review and editing, M.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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