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Review

Valorization of Agricultural Ashes from Cold and Temperate Regions as Alternative Supplementary Cementitious Materials: A Review

by
A. Sadoon
1,*,
M. T. Bassuoni
1 and
A. Ghazy
1,2,3
1
Civil Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada
2
Engineering Division, Public Works Department, Winnipeg, MB R3E 3P1, Canada
3
Department of Civil Engineering, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt
*
Author to whom correspondence should be addressed.
Clean Technol. 2025, 7(3), 59; https://doi.org/10.3390/cleantechnol7030059
Submission received: 10 May 2025 / Revised: 23 June 2025 / Accepted: 9 July 2025 / Published: 11 July 2025
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Abstract

The pursuit of sustainable alternatives to portland cement has become a global imperative within the construction sector, driven by the need to reduce carbon dioxide emissions and energy consumption. Among the promising alternatives, agricultural ashes have garnered attention for their potential as alternative supplementary cementitious materials (ASCMs), owing to their inherent pozzolanic properties when appropriately processed. However, the availability and utilization of these ashes have predominantly been concentrated in tropical and subtropical regions, where such biomass is more abundant. This review offers a comprehensive bibliometric analysis to identify and assess agricultural ashes (specifically switchgrass, barley, sunflower, and oat husks) that are cultivated in temperate and cold climates and exhibit potential for SCM application. The analysis aims to bridge the knowledge gap by systematically mapping the existing research landscape and highlighting underexplored resources suitable for cold-region implementation. Key processing parameters, including incineration temperature, retention duration, and post-combustion grinding techniques, are critically examined for their influence on the resulting ash’s physicochemical characteristics and pozzolanic reactivity. In addition, the effect on fresh, hardened, and durability properties was evaluated. Findings reveal that several crops grown in colder regions may produce ashes rich in reactive silica, thereby qualifying them as viable ASCM candidates and bioenergy sources. Notably, the ashes derived from switchgrass, barley, oats, and sunflowers demonstrate significant reactive silica content, reinforcing their potential in sustainable construction practices. Hence, this study underscores the multifaceted benefits of contributing to the decarbonization of the cement industry and circular economy, while addressing environmental challenges associated with biomass waste disposal and uncontrolled open-air combustion.

1. Introduction

The partial replacement of cement with supplementary cementitious materials (SCMs) is widely recognized as an effective strategy for alleviating the carbon footprint of concrete production [1,2]. However, the global supply of conventional SCMs (e.g., fly ash, slag, and natural pozzolans) falls short of meeting the growing demand for cementitious materials. This shortfall is attributed to factors such as stringent environmental policies aimed at reducing industrial greenhouse gas emissions or the unavailability of SCMs in certain regions. For example, Canada pledged, in 2016, to phase out unabated coal-fired power plants (the primary source of fly ash) by 2030, continuing a long-standing transition away from coal-based energy [3]. Consequently, national coal-fired electricity generation decreased by 66% between 2005 and 2021, replacing it with lower-emission natural gas or non-emitting power generation alternatives.
Agricultural waste-derived ashes (agro-ashes) have emerged as a promising class of alternative SCMs (ASCMs) due to their widespread availability, renewability, and sustainability. Global biomass production from agriculture is approximately 140 billion metric tons annually, which includes both primary crops and residues [4], and when subjected to controlled combustion, the resulting ashes may exhibit cementitious and pozzolanic properties. These properties stem from the presence of reactive oxides, particularly silica, alumina, and iron oxides, which enable the ash to chemically react with calcium hydroxide (Ca(OH)2) in a moisture-rich environment, forming secondary cementitious compounds [5,6]. Among these ASCMs, rice husk ash (RHA), palm oil fuel ash (POFA), and sugarcane bagasse ash (SCBA) are the most extensively utilized for partial replacement of portland cement in concrete [4,7]. However, the feasibility of incorporating these materials is largely dependent on regional agricultural practices, with their availability being particularly high in tropical and subtropical climates where such crops are extensively cultivated. For example, it is suggested that combusted agro-ashes might account for up to 15% of India’s cement production per year, while in Cuba, the percentage could reach nearly 80 % using SCBA [4]. Given the limitations in the availability of conventional SCMs, it is imperative to investigate the potential of agro-ashes from crops grown in temperate and cold climatic zones as potential sources of ASCMs. Biomass generated from agricultural activities contains a range of inorganic components that influence the composition and performance of the resulting ashes [8]. For instance, rice husk is known for its high silica content (85–95%) [9], making it particularly effective as a pozzolanic material. Similarly, agricultural residues or biomass crops from temperate and cold regions may also contain significant levels of silica (typically 50–70%), along with aluminum, calcium, and iron oxides, which contribute to their reactivity in cementitious systems. Understanding the mineral composition of biomass is essential in evaluating its potential as SCMs. Current reviews [4,6,8,10] have mainly concentrated on ASCMs from crops grown in tropical and subtropical regions, while largely overlooking those produced from crops cultivated in temperate and cold climates.

Research Needs and Significance

Recent research has increasingly focused on the valorization of agro-residues as ASCMs, particularly in the context of reducing the environmental footprint of cement and concrete production. Among the most promising, but underutilized, sources of these residues are crops grown in temperate and cold climatic zones as potential ASCMs, such as those found across much of Canada and Europe. These crops are typically characterized by high silicon content (an indicator of pozzolanic potential upon combustion) and considerable calorific value (a measure of energy yield), which together make them attractive for dual purposes: (i) the production of pozzolanic ashes that may serve as ASCMs in concrete applications, and (ii) the generation of bioenergy through combustion. For example, Hosseini et al. [11] systematically classified a range of plant species that are well-adapted to colder climates based on two critical parameters: calorific value and silicon concentration. Their study identified several crops (i.e., switchgrass, barley, oat, and sunflower) as having ashes with particularly favorable properties. These crops produce biomass that, when subjected to controlled thermal treatment, yields ashes rich in amorphous silica, a key component in achieving pozzolanic reactivity in cementitious systems. For example, oats represent a compelling case due to both their agronomic prevalence and compositional characteristics. Oats are extensively grown in temperate and cold environments, with a global production exceeding 25.1 million tons annually, a significant portion of which is concentrated in North America and Northern Europe. The outer husk, a by-product of oat processing, has been found to contain silica concentrations exceeding 2% by weight [11]. Although this may appear modest compared to RHA, the volume of available biomass, coupled with optimized incineration parameters (e.g., 600 °C for 4 h [12]), offers substantial potential for producing reactive amorphous silica in the form of oat husk ash (OHA).
Despite these promising characteristics, the technical performance of such ashes within cementitious matrices remains relatively underexplored in the scientific literature. Most studies to date have focused on the physicochemical characterization of these ashes (assessing properties such as chemical composition [via X-ray fluorescence; XRF], phase crystallinity [via X-ray diffraction; XRD], and morphology [via scanning electron microscope; SEM]) while overlooking aspects of their practical performance, such as their effects on fresh properties (e.g., workability and setting time), mechanical strength development, and durability under aggressive environmental conditions (e.g., freeze–thaw, sulfate attack, chloride ingress). Consequently, this review seeks to address these research gaps by offering a comprehensive evaluation of agro-residues derived from crops grown in temperate and cold climatic zones as sustainable ASCMs. It aims to assess their chemical and physical characteristics, as well as their influence on fresh, hardened, and durability performance in cementitious systems. In doing so, the study not only contributes to the scientific understanding of these novel materials but also supports broader environmental objectives, including the reduction in greenhouse gas (GHG) emissions, the diversion of agro-residues from landfills, and the advancement of climate-adaptive construction practices. Ultimately, the integration of such residues into cementitious applications represents a viable pathway toward low-carbon concrete technologies aligned with circular economy principles. However, achieving this goal will require coordinated efforts in research, standardization, and policy development, ensuring that material innovation is matched by performance validation and industrial scalability.

2. Methodology

This study consists of three stages: (I) Collect data by using Scopus database to determine the number of publications of crops grown in temperate and cold climatic zones as potential sources of ASCMs. The inquiry was conducted in April 2025 and revealed that over the past three years, the number of publications has grown rapidly. The number of publications was approximately 167,844 studies when using the search keyword “switchgrass, barley, oat, and sunflower”. However, limiting search keywords specifically relevant to the SCMs or the ASCMs application resulted in a significantly reduced number of publications, totaling 49 documents. (II) A scientometric analysis was conducted on these 49 documents, specifically addressing the use of these resulting ashes as ASCMs. (3) Systematic review by analyzing data content and specifying processing methods, characteristics, effect on fresh properties, effect on hardened properties, and durability properties of concrete related to crops grown in temperate and cold climatic zones as potential sources of ASCMs.

3. Bibliometric Analysis

The analysis of publication data shows key research trends concerning the valorization of agro-residues from temperate and cold regions as ASCMs in concrete production. Notably, the leading contributions originate from countries such as Canada, the United States, and several European nations, as shown in Figure 1.
These regions are predominantly located in temperate to cold climatic zones, where harsh weather conditions and the availability of specific biomass residues have likely influenced the direction and intensity of related research activities. This trend reinforces the strategic importance of leveraging region-specific agro-residues as sustainable alternatives to traditional SCMs, contributing significantly to greenhouse gas (GHG) mitigation and the broader fight against global warming, complying with the UN sustainable development goals. The visualization of the keyword network map is shown in Figure 2 by utilizing VOSviewer (Version 1.6.20) software. The visualization not only reflects the current state of scientific inquiry in this field but also shows critical research gaps that must be addressed to fully unlock the environmental and technical benefits of utilizing temperate/cold-region agro-residues as ASCMs.
A co-occurrence analysis identified key topics, keywords, and research focus areas, emphasizing extensive studies on the mechanical properties, such as compressive strength, and the microstructure of cementitious mixtures incorporating cold-climate agro-residues. Among the agro-ashes investigated, sunflower husk ash and barley straw ash emerge as the most frequently studied cold-region by-products, followed by oat husk ash. These materials are examined for their pozzolanic activity, silica content, and synergy with traditional binders such as cement, lime, and fly ash. There is also an observable trend toward hybrid cementitious systems, integrating biomass-derived ashes with conventional SCMs like slag and fly ash to optimize performance and sustainability. Despite the promising physicochemical characteristics of these ashes (e.g., high silica content, suitable particle size, and amorphous structures), there remains a notable gap in the literature regarding their fresh, mechanical, and durability properties when incorporated into concrete. In particular, the lack of data on workability, setting times, sulfate resistance, and long-term performance limits their broader adoption within the construction industry. Therefore, future research should prioritize systematic experimental investigations to quantify these properties under standardized test protocols. These efforts are crucial to validate the technical feasibility of integrating temperate/cold-climate agro-ashes into low-carbon concrete production and to support evidence-based recommendations for industry-wide implementation.
Notably, switchgrass, despite being one of the earliest cold-region crops investigated for its potential as a source of reactive silica, is absent from the current keyword co-occurrence network in Figure 2. This omission can likely be attributed to the decline in recent research attention directed toward switchgrass-derived ash, as other agro-ashes have gained prominence. While studies in earlier years explored its pozzolanic behavior and silica content under various combustion conditions, the limited presence of switchgrass in the current literature suggests a stagnation in its development as a viable ASCM. This decline emphasizes the critical need to revisit and revitalize research on switchgrass ash and similar underexplored residues. Given the crop’s wide availability in cold and temperate climates and its previously demonstrated potential for high amorphous silica yield, switchgrass remains a promising candidate for sustainable ASCM development. Future investigations should focus on closing the knowledge gap by evaluating its mechanical, durability, and compatibility properties in cementitious systems. This would help determine its feasibility for practical applications and ensure that valuable resources are not overlooked in the pursuit of green construction materials.

4. Agro-Residues Derived from Temperate/Cold Climates

Research on ashes derived from temperate and cold-region crops began in 2009, initially focusing on switchgrass, as illustrated in Figure 3. However, it was not until 2022 that all crop sources were investigated (e.g., barley, sunflowers, and oat). The cumulative number of publications on this topic increased from 13 in 2019 to 49 in 2024, highlighting the growing interest in exploring novel ASCMs derived from the ashes of crops cultivated in temperate and cold climates, due to the pressing local unavailability of conventional SCMs. However, its performance in cementitious systems remains largely unexplored.

4.1. Switchgrass

Switchgrass is a perennial grass native to North America, thriving across a wide range of climates and soil types. It is primarily cultivated in the United States and Canada, with significant research and production efforts focused on its use as a bioenergy crop. In the U.S., switchgrass has been extensively studied for biomass production, with yields varying based on ecotype, location, and management practices [13]. For instance, lowland ecotypes like ‘Alamo’ have demonstrated annual biomass yields exceeding 28 megagrams per hectare in regions such as Alabama, Texas, and Oklahoma. While specific global production statistics are limited, switchgrass is recognized for its high biomass yield potential and adaptability, making it a promising candidate for bioenergy applications. Beyond its use as a biofuel source, recent studies have explored the potential of switchgrass combustion ash as ASCM. Combustion of switchgrass at approximately 411 °C yields about 5% ash by weight, which, after processing, exhibits pozzolanic properties suitable for partial replacement of portland cement in concrete [14]. Yet, further research is necessary to confirm these results with more tests related to fresh, mechanical, and durability properties to ensure consistent performance in the concrete industry.

4.2. Sunflower

Sunflowers are extensively cultivated worldwide, with significant production concentrated in Eastern Europe. As of the 2023/2024 crop year, Russia leads global sunflower seed production, contributing approximately 31% of the total output, equating to 17.1 million metric tons. Ukraine follows closely, accounting for about 28% with a production of 15.5 million metric tons. The European Union collectively produces around 10.13 million metric tons, representing 18% of global production [15]. Beyond their agricultural and economic significance, sunflowers have garnered attention in the construction industry for their potential as a source of ASCMs. Research has explored the feasibility of utilizing sunflower-derived ashes, such as shell sunflower ash (SSA) and sunflower stalk ash (SA), as partial replacements for cement in concrete. These studies have investigated various cement replacement levels, ranging from 2.5% to 20% by mass, assessing impacts on properties like compressive strength and flexural strength of concrete [16,17]. The incorporation of sunflower-derived ashes in low-carbon cementitious composites has demonstrated promising results, suggesting that these agro-ashes can serve as ASCMs. However, further research is necessary to optimize processing methods and replacement ratios to ensure consistent performance in various applications.

4.3. Oat

Oats are cultivated globally, with significant production in temperate regions. As of 2024, the European Union leads in oat production, contributing approximately 34% of the world’s total, equating to about 7.6 million metric tons. Canada follows with 15% (approximately 3.4 million metric tons), and Russia accounts for 13% (around 3 million metric tons) [18]. Beyond their nutritional value, oat husks—the outer shells separated during processing—have been investigated for their potential as ASCMs. When combusted under controlled conditions, oat husk ash (OHA) exhibits pozzolanic properties due to its reactive silica content. Studies have explored the partial replacement of cement with OHA, analyzing its effects on the fresh and hardened properties of cementitious composites. For instance, Ruviaro et al. [19] demonstrated that incorporating OHA can enhance certain mechanical properties of mortar cement and contribute to more sustainable construction practices. The utilization of OHA in concrete offers a promising avenue for reducing cement consumption and associated carbon emissions in the construction industry. However, further research is required to validate these trends through comprehensive testing of fresh properties, mechanical performance, and durability characteristics, in order to ensure consistent and reliable performance in concrete applications.

4.4. Barley

Barley is a key cereal crop cultivated globally, with substantial production in various regions. In the 2023/2024 crop year, the European Union (EU) led global barley production, accounting for approximately 33% of the total output, which translates to about 47.81 million metric tons. Within the EU, France, Germany, and Spain are notable contributors. Russia followed as the second-largest producer, contributing around 14% of global production, equivalent to 20.5 million metric tons. Other prominent barley-producing countries include Australia (8%), Canada (6%), and Turkey (6%) [18]. In addition to its agricultural applications, barley husks (remnants separated during grain processing) have been studied for their potential ASCMs. When subjected to controlled combustion, barley husk ash (BHA) demonstrates pozzolanic reactivity, primarily due to its high silica content. Khalil et al. [20] investigated the incorporation of BHA with ordinary portland cement (OPC) and found that replacing 15–20% of OPC with BHA significantly enhanced the blended cement’s properties. However, additional research is still required to validate these findings through further testing, particularly concerning the fresh, mechanical, and durability properties, to ensure consistent and reliable performance when incorporating BHA into concrete applications.

5. Processing Methods of Agro-Residues

Figure 4 presents a conceptual flowchart illustrating the integrated valorization pathway of agricultural residues into ASCM. The framework begins with the collection of switchgrass, oat husks, barley straw, and sunflower husks. Rather than being discarded or subjected to open-field burning, a practice that contributes to greenhouse gas emissions and environmental degradation. These residues are directed toward controlled combustion under optimized conditions. The resulting ash is then post-processed through grinding and sieving, followed by physicochemical characterization to evaluate its pozzolanic potential based on key parameters such as silica content, fineness, and loss on ignition. Once confirmed to meet performance criteria, the ash is incorporated into cementitious mixtures as a partial replacement for Portland cement, contributing to more sustainable concrete production without compromising mechanical or durability properties.
Agro-residues intended for use as ASCMs typically undergo one or a combination of thermal, mechanical, and/or chemical activation processes to enhance their reactivity. Among these, thermal treatment is the most prevalent method, with combustion temperatures generally ranging from 400 °C to 800 °C. Both the combustion temperature and the retention time are critical parameters that influence the final properties of the resulting ash, particularly in terms of phase composition and unburnt carbon content [21]. For instance, Sadoon et al. [12] examined the effects of varying combustion temperatures and retention times on the properties of OHA. Their study demonstrated that the highest amorphous silica content was obtained at a combustion temperature of 600 °C coupled with a retention time of 4 h, conditions that maximized the pozzolanic potential of the ash. Similarly, Wang et al. [22] conducted a systematic evaluation of switchgrass ash, concluding that 550 °C with a retention time of 4 h was optimal for achieving the maximum amorphous silica content. Table 1 shows various activation techniques to produce temperate/cold-region agro-ashes.
It is important to note that excessively high combustion temperatures can induce the crystallization of silica phases, such as cristobalite and tridymite, which significantly diminishes the pozzolanic reactivity of the ashes [23]. Therefore, careful control of the thermal treatment parameters is essential to preserve the amorphous nature of silica within the residues.
Table 1. Various activation techniques used to produce temperate/cold-region agro-ashes.
Table 1. Various activation techniques used to produce temperate/cold-region agro-ashes.
Thermal Treatment Switchgrass AshBarley Straw AshSunflower Husk AshOat Husk Ash
Type of Combustion Uncontrolled + ControlledUncontrolled + ControlledUncontrolled + ControlledUncontrolled + Controlled
Incineration Temperature (°C) 350–650500–700400–600500–900
Retention Time 1–4 h2–8 h3 h1–4 h
Grinding Process Vibratory pulverizing
mill for 30 s		Ball mill (0.5–2 h)-Ball mill for (5–30 min)
Ref. [14,22][24,25,26][16,17,27][12,19]
Following combustion, the resultant ashes often exhibit coarse particle sizes that do not conform to the fineness requirements specified in ASTM C618 [28]; the standard commonly referenced for evaluating the suitability of coal fly ash and natural pozzolans for use in concrete. Specifically, ASTM C618 mandates that at least 66% of the material must pass through a 45 µm sieve. To meet this criterion and enhance reactivity, mechanical grinding should be employed. This post-combustion grinding process not only reduces particle size but also increases the specific surface area, thereby promoting a higher rate of calcium silicate hydrate (C–S–H) formation during cement hydration [29].

6. Physical and Chemical Properties of Agro-Ashes

Table 2 and Table 3 present a summary of the physical and chemical properties of ashes derived from various agro-residues cultivated in temperate and cold regions. These properties are primarily influenced by a combination of plant-specific characteristics, incineration temperature, and retention time during combustion. Reported specific gravity values typically range from 2.0 to 3.0, lower than cement (3.15), indicating that ash particles are lighter, which can influence volume batching and water demand. Most ashes exhibit mean particle sizes of 9–5 µm, except for sunflower (up to 200 µm). Finer ashes can fill voids more efficiently and enhance the pozzolanic reaction by increasing surface area. Most ashes tend to exhibit high specific surface area values (600–820 m2/kg), indicating significant reactive surface area. Lower values may correspond with lower pozzolanic reactivity unless further processed (e.g., grinding or calcining). The color of the resulting ash is strongly dependent on the extent of combustion and the structural form of silica present, as well as carbon content. Typically, the color transitions from black or reddish-gray to white as the temperature increases and decarbonization progresses [21,22]. This visual change serves as a qualitative indicator of the completeness of the combustion process. According to ASTM C618 [28], a material may be classified as a pozzolan if the combined content of silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3) exceeds 50% by mass. Moreover, the classification of pozzolans into Classes C, F, or N pozzolan is based on both their pozzolanic oxide content and their loss on ignition (LOI) values.
Upon examining the chemical compositions of these ashes, it is observed that most residues exhibit a pozzolanic oxide content near or exceeding the 50% threshold. Ashes derived from oat husk and switchgrass consistently exhibit high silica contents, typically ranging from 65% to 82%, which supports their classification as reactive pozzolans. In contrast, barley straw ash and sunflower husk ash demonstrate greater compositional variability, often characterized by elevated loss on ignition and alkali contents. These features may reflect incomplete combustion during processing and raise potential concerns regarding durability, particularly with respect to alkali-silica reaction susceptibility. Additionally, while the majority of ashes meet the LOI requirement of less than 11%, switchgrass ash shows an elevated LOI, likely attributable to insufficient retention time during combustion, which impedes complete oxidation of organic material [22]. Several ashes also display notable calcium oxide (CaO) contents, often exceeding 12% [21,22,23,24,25]. The presence of high CaO content is beneficial, as it may impart a latent hydraulic activity that can contribute to the development of hydration products independently of the pozzolanic reaction. It is also noteworthy that a few agro-ashes may exhibit high alkali content (Na2O + K2O > 20%) [16,25,30], which may significantly increase the total alkali load within the cementitious matrix. This raises concerns regarding the potential for alkali-silica reaction (ASR) when reactive aggregates are used in concrete. Furthermore, certain ashes, particularly those derived from sunflower shells, are characterized by elevated alumina (Al2O3) content. The availability of high levels of Al2O3 can stimulate additional reactions within the cementitious matrix, leading to the formation of calcium aluminate silicate hydrates (C–A–S–H) alongside the more conventional calcium silicate hydrate (C–S–H) phases [31,32]. Such reactions may positively influence both the mechanical performance and chemical stability of concrete containing these ashes.

7. Fresh Properties of Concrete Comprising Agro-Ashes

There is a notable scarcity of experimental data on the influence of agro-residues derived from temperate and cold-region crops on the fresh properties of concrete. Ruviaro et al. [19] investigated the influence of oat husk ash (OHA) on concrete workability across a range of calcination temperatures (500–800 °C). Their findings indicated a consistent decrease in slump values with increasing OHA content, regardless of the calcination temperature. At a 10% replacement level, slump values were nearly identical for all ash samples. However, at 20% replacement, a minimum 34% reduction in workability was reported relative to the control mix. Similar reductions in workability were also documented in studies involving sunflower seed shell ash, where increasing ash content led to more pronounced decreases in slump [11,12]. The reduction in workability is typically attributed to two main properties of the ashes: (a) coarse surface texture and angularity, which increase internal friction among paste components, and (b) high porosity, leading to greater water absorption [33,34].
However, some contradictory findings have emerged in the literature. For example, Cao et al. [35] reported an increase in workability with the inclusion of barley straw ash, even when the w/b ratio (0.38) and superplasticizer dosage (1.5%) were kept constant. Remarkably, a 17% increase in slump was observed with a 30% cement replacement, which they attributed to the ash’s high specific surface area (2100 m2/kg) and fine particle size (9 μm). These properties were thought to impart a “ball-bearing” effect, promoting better flow and dispersion within the mix. Nevertheless, this interpretation appears to contradict fundamental understanding of cementitious materials, where increased fineness and surface area, as well as particle shape irregularity, generally result in reduced workability due to elevated water demand and friction [36,37]. The disparity may stem from differences in particles’ morphology, chemical composition, or interaction with admixture systems, underscoring the complex and material-specific nature of different agro-ashes in concrete. In addition to workability, the effects of cold-region agro-residues on setting times and the rate of hydration remain largely undocumented in the literature. These parameters are critical for evaluating early-age performance, formwork removal schedules, and construction timelines, especially in cold climates where delays can be costly. The absence of such data highlights a significant research gap, and further studies are required to characterize the influence of these ashes on initial and final setting times, heat of hydration, and early-age strength development under different curing regimes. Addressing these gaps will not only improve the understanding of how these materials behave in cementitious systems but will also enable more reliable mix design optimization and facilitate their mainstream adoption as sustainable ASCMs in construction practices, under different climatic conditions.

8. Effect on Hardened Properties of Concrete

Compressive Strength

The incorporation of agro-ashes as partial replacements for cement has been widely explored to enhance the sustainability of concrete while maintaining or improving its mechanical properties. Among the most studied residues (i.e., RHA, POFA, and SCBA), numerous investigations have demonstrated consistent improvements in compressive strength, particularly at replacement levels below 20% [17,24,38,39,40,41,42,43,44,45]. These enhancements are commonly attributed to the pozzolanic reactivity of the ashes, which contribute to the formation of additional calcium silicate hydrate (C–S–H) gel, densifying the microstructure and improving load-bearing capacity.
In contrast, agro-ashes sourced from temperate and cold climates (i.e., switchgrass ash, barley husk ash, oat husk ash, and sunflower husk ash) have demonstrated less consistent or even adverse effects on compressive strength, particularly at early ages or at higher replacement dosages [14,16,27,30]. This difference may be linked to lower pozzolanic activity, incomplete combustion, or the presence of inhibitory phases such as unburned carbon in the ash. For example, Sadoon et al. [12] reported that cement mortar containing 20% OHA achieved comparable compressive strength to the control mortar mix after 90 days of curing, with only a 5% reduction in strength. The mixture had a water-to-binder (w/b) ratio of 0.454, and the strength parity at later ages suggests potential long-term pozzolanic activity, though the early-age strength gains were limited.
Conversely, Wang et al. [14] observed a declining trend in compressive strength with increasing substitution levels of switchgrass ash, particularly evident at a 20% replacement level and w/b ratio of 0.55, where a 19% reduction in 28-day strength was reported. These results indicate that not all agro-ashes exhibit the same reactivity or compatibility with cement hydration processes. Similarly, sunflower husk ash has been associated with strength reductions, even at lower substitution levels. In one study, the incorporation of 5% and 10% sunflower husk ash into concrete at a w/b of 0.5 led to reductions in both compressive and flexural strength, with the 10% replacement yielding a 57% decrease in compressive strength and a 38% reduction in flexural strength after 28 days of curing [30]. These significant declines highlight the potential inhibitory effects of certain ash compositions or physical properties when used in concrete formulations. Furthermore, Grubeša et al. [16] evaluated the compressive strength of concrete incorporating sunflower husk ash at varying levels (5%, 7.5%, and 10%) under the same w/b ratio of 0.5. At 28 days, all replacement levels exhibited a downward trend in strength, with the 10% substitution resulting in a 17% reduction compared to the control mix. Interestingly, at 90 days, the mix containing 5% sunflower husk ash showed a 13% strength gain over its 28-day value, although it still remained 6% lower than the control. This suggests delayed pozzolanic activity or continued hydration facilitated by the finer ash particles over extended curing periods.
Table 4 summarizes the compressive strength data collected from multiple studies, presenting the range of strength improvements or reductions associated with various agro-ashes agricultural ashes from temperate and cold regions at 28 days of curing, along with the corresponding w/b ratios. It was observed that ashes with high amorphous silica content and fine particle size (e.g., oat husk ash) tended to exhibit superior pozzolanic activity, which contributed positively to strength development, particularly at later curing ages. In contrast, ashes with elevated LOI or insufficient fineness (e.g., sunflower husk ash) demonstrated limited reactivity, which often resulted in lower compressive strength. The variability in performance underscores the material-specific nature of these ashes and the importance of tailored mix design strategies, ash processing conditions (e.g., calcination temperature and duration), and compatibility assessments with chemical admixtures and cement types. The findings presented reinforce the need for more comprehensive investigations to identify optimal processing techniques and mixture proportions that can unlock the full potential of cold-climate agro-residues as effective ASCMs.

9. Durability Properties

Durability is a critical performance criterion for concrete, particularly in infrastructure exposed to aggressive environmental conditions. The incorporation of these ashes (i.e., switchgrass ash, sunflower husk ash, oat husk ash, and barley husk ash) into concrete requires thorough evaluation of key durability parameters. However, the literature on the performance of these ashes in long-term durability aspects is still emerging. This section synthesizes available data while highlighting critical gaps in knowledge.

9.1. Transport Properties

The effect of temperate and cold-climate agro-residues on the water absorption capacity of concrete remains insufficiently explored, and the available findings exhibit considerable variation [27,46]. These discrepancies may stem from differences in the chemical composition, microstructural characteristics, and particle fineness of the ashes, as well as variations in testing protocols and curing conditions. For instance, the incorporation of 10% barley straw ash into magnesium oxychloride cement composites was found to marginally enhance water resistance by 7% and decrease water absorption by 2.11%, suggesting a densifying effect of the ash [46]. Conversely, ultra-fine sunflower husk ash, when used at high replacement levels (25% and 50%) with a w/b ratio of 0.45, significantly increased water absorption after 28 days of curing, up to 47% higher than the control [27]. This divergence underscores the material-specific nature of agro-ashes and the need for more standardized evaluation to understand their role in capillary porosity and pore connectivity in hardened concrete.
Chloride ions ingress is a primary cause of steel reinforcement corrosion, particularly in structures exposed to marine environments or de-icing salts. Reducing chloride penetrability in concrete structures is, thus, essential for extending their service lives. While numerous studies have shown that more common agro-residues such as RHA, SCBA, and POFA can significantly reduce chloride ion penetrability through pore refinement and supplementary C–S–H formation [47,48,49,50], no published data was found on the resistance for concrete containing ashes derived from temperate or cold-region crops to chloride ions infiltration. This trend highlights a critical research gap, especially since cold climates frequently expose concrete to de-icing agents, an environment where chloride ingress is a serious concern. Evaluating these ashes under standardized test methods (e.g., ASTM C1202 [rapid chloride penetrability test]) would be essential for understanding their suitability to such exposure conditions involving chloride-based salts.

9.2. Resistance to Freezing and Thawing Cycles

Freeze–thaw resistance is a key property for exposed concrete serving in cold regions, where repeated cycles can lead to microcracking, scaling, and eventual structural degradation. Despite its relevance, very few studies have assessed the freeze–thaw durability of concrete incorporating agro-ashes [51,52]. This lack of investigation is likely due to the historical focus on concrete comprising tropical ashes used in hot climates, where freeze–thaw cycles are not a concern. With the growing interest in temperate- and cold-region agro-residues, it is imperative to assess their behavior under cyclic freezing conditions. The air-void system, internal pore pressure, and moisture transport mechanisms associated with such ashes may significantly influence freeze–thaw performance of concrete. Future research should prioritize this durability aspect to ensure safe and long-lasting use of these materials in concrete serving under cold climates.

9.3. Sulfate Attack

Sulfate attack poses a major durability threat to concrete, especially in soils or groundwater rich in sulfates. The literature generally reports that ashes from tropical agro-residues enhance sulfate resistance due to reduced calcium hydroxide content, the formation of additional C–S–H, and improved pore structure [53,54,55,56,57,58,59,60,61,62]. However, the effect of agro-ashes from cold and temperate regions on sulfate resistance has not been systematically examined. Given that some temperate region ashes may contain alkalis, soluble salts, or poorly combusted organic content, their influence on sulfate durability may vary significantly. A comprehensive evaluation, including mass loss, expansion, and microstructural degradation, is necessary to confirm their suitability in sulfate-rich environments.

9.4. Alkali–Silica Reaction (ASR)

The alkali–silica reaction (ASR) is a deleterious phenomenon characterized by the reaction between alkalis in the pore solution and reactive silica in aggregates, leading to expansive gel formation and cracking. Incorporation of agro-ashes such as RHA, SCBA, and POFA has been shown to mitigate ASR-induced expansions, primarily by reducing pore solution alkalinity and consuming calcium hydroxide through pozzolanic reactions [63,64,65,66,67]. However, temperate and cold-region agro-ashes have not been thoroughly assessed for their performance in mitigating ASR. Elevated alkali levels (particularly in the form of K2O and Na2O) were identified in certain ashes (e.g., sunflower husk ash) where values exceeded 15%. These high alkali contents were noted to increase the risk of alkali–silica reaction, especially when reactive aggregates are used. In contrast, ashes such as oat husk ash and switch ash were shown to possess significantly lower alkali content and higher reactive silica, which have been demonstrated in previous studies to reduce ASR potential through the consumption of calcium hydroxide (CH) and the reduction in pore solution alkalinity. Systematic investigations using established test methods (e.g., ASTM C1260 [mortar-bar method] and C1567 [accelerated mortar-bar method]) are needed to ascertain the role of these ashes in ASR-prone environments.
Overall, the performance of concrete incorporating agro-ashes from temperate and cold regions remains underexplored, and inconsistent results were reported from limited studies. While some ashes exhibit promise at enhancing specific properties, such as water resistance and long-term strength gain, others may pose risks due to increased permeability or chemical reactivity. A holistic (standard and combined) testing approach remains essential to evaluate concrete produced from these materials across all key durability domains (e.g., water transport, chloride ingress, sulfate exposure, freeze–thaw cycles, ASR susceptibility, combined exposures comprising chemical attacks with cyclic environments) before they can be reliably implemented in structural applications across diverse climates.

10. Sustainability and Circular Economy Integration

Inefficient waste management and associated environmental pollution are exhausting societies’ precious renewable resources [68], underscoring the need for sustainable strategies that repurpose agro-ashes into functional materials. Rice husk ash has been widely studied and utilized as a low-carbon SCM, with reported CO2 emissions for its production ranging from 100 to 200 kg CO2 per ton of ash [69,70]. Given the comparable characteristics with oat husk ash, which can provide a basis for evaluating the potential of agro-ashes derived from temperate and cold-climate crops to contribute to reductions in CO2 emissions. Both types of husks serve as protective outer layers of grains and share similar lignocellulosic composition (i.e., cellulose, hemicellulose, lignin, and silica), calorific value (approximately 12.0–16.0 MJ/kg), and optimal combustion temperature range (500–700 °C). Therefore, it is reasonable to project that OHA, when produced at scale under optimized conditions, would exhibit similar emissions profiles. In contrast, traditional portland cement production is associated with substantially higher emissions, typically in the range of 800–1000 kg CO2 per ton, according to the U.S. Environmental Protection Agency (EPA) [71]. This stark disparity highlights the environmental benefit of integrating these agro-ashes into cementitious systems. Nevertheless, while drawing parallels between OHA and RHA provides a practical framework, the actual carbon footprint of agro-ashes derived from temperate and cold-climate crops requires direct quantification. Accurate life cycle data must be collected under controlled production conditions, particularly for large-scale applications. Small-scale trials often rely on assumptions that may not accurately reflect operational realities, such as energy consumption, feedstock variability, emissions control, and waste handling, which are critical for reliable environmental assessments.
The growing emphasis on establishing a circular economy nationally and globally necessitates innovative strategies to manage the significant volumes of agro-residues generated annually. Rather than relying on disposal or low-value applications, current approaches should focus on strategic reuse and valorization to produce high-value products, supporting both environmental sustainability and economic development. Historically, agro-residues were primarily employed as animal fodder, either in their natural state or after basic modifications. However, the nutritional limitations of certain residues (e.g., the low digestibility of rice straw due to its high silica and lignocellulosic content) have prompted the search for alternative uses [72]. Applying these residues as organic fertilizers has proven beneficial, enhancing soil fertility, improving soil structure, and boosting crop yields by increasing organic matter content [73]. More recently, bio-brick production has emerged as a promising utilization pathway. Manufactured from agro-residue materials, bio-bricks offer a sustainable, low-cost, and eco-friendly solution for building insulation [74]. With a thermal conductivity around 0.27 W/m·K, they provide effective thermal and acoustic insulation, although their mechanical properties render them unsuitable for structural load-bearing applications.
In parallel, the thermal conversion of biomass into energy remains a widely practiced and evolving method. Conventional combustion rapidly oxidizes organic matter in the presence of oxygen, releasing energy, carbon dioxide, and water [75]. Advanced thermal processes, notably pyrolysis, have been introduced to optimize energy recovery. Pyrolysis involves the decomposition of biomass at 400–600 °C in an oxygen-free environment, producing biochar, bio-oil, and syngas. Technologies such as fluidized bed reactors, rotary kilns, and fixed bed systems are employed for these reactions [76]. Nonetheless, the scalability of pyrolysis is challenged by high preparatory costs and complex operational requirements. Another advanced and sustainable method for converting lignocellulosic biomass into value-added bioproducts is hydrothermal treatment, which offers an efficient pathway to support low-carbon development [77]. Operated below 300 °C, this process decomposes hemicellulose, cellulose, and lignin, with outcomes influenced by temperature, retention time, and the chemical environment (e.g., acidic, alkaline, or oxidative). The breakdown of natural biomass barriers leads to significant changes in composition and structure, yielding materials with high carbon content, tunable morphologies, oxygen-rich functionalities, and low levels of impurities. These modified characteristics enable the production of diverse bioproducts, including wood vinegar, briquette fuels, adsorbents, electrode materials, and catalysts. However, the resulting solid and liquid fractions are often chemically complex and may require further processing [78]. A strategic pathway was suggested herein, and it lies in the production of ASCMs from agro-residues using the controlled combustion of agro-residues at temperatures between 500 °C and 800 °C, which results in the formation of silica-rich ashes. These ashes can partially replace cement in concrete mixtures, contributing to the development of low-carbon construction materials. Biomass combustion can be efficiently carried out in dedicated systems such as moving-grate boilers or fluidized bed combustors, generating thermal energy alongside ash [79]. In practical terms, agro-residues could substitute up to 20% of traditional fossil fuel inputs based on calorific value. Additionally, integrating ash valorization into cement production facilities, either as standalone units or within existing plants, offers a synergistic opportunity to advance both energy sustainability and material circularity in the construction industry. The energy pathway further enables the generation of heat, steam, or electricity, while the residual ashes from combustion can be valorized as ASCMs for low-carbon concrete production as shown in Figure 5.

11. Limitations and Challenges

Incorporating agro-ashes derived from temperate and cold-climate crops as SCMs presents notable environmental and performance advantages, particularly for concrete applications in cold-weather regions [8,9,80]. However, the successful implementation of these materials in practice necessitates careful consideration of several key factors to ensure optimal performance. One critical aspect is the potential influence of agro-ash incorporation on setting times and early-age strength development. Cold ambient conditions inherently delay hydration and strength gain, and the inclusion of agro-ashes, depending on their reactivity and fineness, may further exacerbate these effects. Consequently, adjustments to mix designs and construction practices may be required to meet early-age performance criteria. Ensuring consistent quality of the agro-ash is equally important, necessitating controlled combustion processes to yield ash with stable chemical composition and high amorphous silica content, which is essential for pozzolanic reactivity. Optimizing mixture proportions through systematic trial batching is essential to determine appropriate replacement levels, achieving a balance between workability, mechanical strength, and durability under environmental stressors typical of cold climates, such as freeze–thaw cycles and exposure to de-icing salts. Moreover, proper curing methods are vital to mitigate the detrimental effects of low temperatures on hydration and strength development. Techniques such as the use of thermal blankets, heated enclosures, or chemical accelerators can significantly improve the early-age performance of agro-ash-modified concrete. By addressing these challenges holistically, the integration of agro-ashes as SCMs can not only meet structural and durability requirements but also contribute meaningfully to sustainable and resilient construction practices in cold-climate regions.

12. Conclusions and Recommendations

This article offers a comprehensive review of agro-ashes as emerging supplementary cementitious materials, with a particular focus on underexplored residues derived from crops grown in temperate and cold climates. Through a critical evaluation of ashes produced under diverse environmental conditions, this review examines their physicochemical properties, activation processes, and performance implications when incorporated into concrete systems. The key findings are outlined as follows:
  • Global Research Trends: Bibliometric analysis indicates that research leadership in this field is concentrated in Canada, the United States, and various European nations. Among the most widely studied agro-residues are switchgrass, barley, sunflower husk, and oat husk ashes. Importantly, the body of literature in this area has experienced notable growth, with the number of publications more than doubling over the past three years, highlighting the escalating global interest in identifying sustainable alternatives to conventional Portland cement.
  • Knowledge Gaps and Bibliometric Insights: The bibliometric evaluation highlights encouraging progress in the chemical and physical characterization of these ashes. However, comprehensive data on their fresh, mechanical, and especially durability properties in concrete applications are still lacking. Addressing these gaps is vital to facilitate the transition from laboratory-scale research to full-scale implementation.
  • Processing Techniques: The conversion of agro-residues into reactive ashes typically involves a combination of thermal, mechanical, and chemical treatments. Thermal treatment is the most common approach, wherein controlled combustion at temperatures between 500 °C and 800 °C promotes the transformation of crystalline silica phases into amorphous silica, thereby enhancing the pozzolanic reactivity of the resulting ash. This transformation is critical for achieving effective performance as an SCM by facilitating improved cementitious reactions within the concrete matrix.
  • Pozzolanic Classification Criteria: In accordance with ASTM C618, a material is classified as a pozzolan if it satisfies the following requirements: (a) a minimum of 66% of the material must pass through a 45 µm sieve, (b) the combined content of SiO2, Al2O3, and Fe2O3 must exceed 50%, and (c) the loss on ignition (LOI) must be less than 11%. These parameters provide a standardized framework for assessing the suitability of ashes for use as SCMs.
  • Fresh and Mechanical Properties: Agro-ashes frequently lead to a reduction in workability due to their porous structure, angular morphology, and irregular particle shape, which increase internal friction and water demand within fresh concrete mixtures. In addition, their incorporation may result in extended setting times. When used as partial cement replacements, typically at dosages up to 20%, these ashes have demonstrated the potential to achieve comparable compressive strength to conventional mixes. Nevertheless, there is a pressing need for systematic experimental investigations to evaluate their mechanical performance under varying mix proportions, curing regimes, and exposure conditions to support their broader implementation in sustainable construction practices.
  • Durability Considerations: While several ashes show promise in preliminary studies, there is a notable lack of data regarding their long-term durability, including resistance to sulfate attack, alkali-silica reaction (ASR), freeze–thaw cycles, and chloride ingress. This research gap limits their widespread adoption and warrants targeted investigation.
  • Sustainability and Circular Economy Integration: Incorporating agro-ashes into construction materials aligns with circular economy principles by minimizing dependence on portland cement, a major contributor to global industrial CO2 emissions. Emerging innovations should focus on the valorization of agro-residues through controlled combustion, enabling a dual benefit: renewable energy generation and the production of low-carbon construction materials. This integrated approach not only facilitates the development of low-carbon concrete but also strengthens the interconnection between the agricultural and construction sectors, advancing sustainability across both industries.
The advancement of agro-residues as ASCMs still requires interdisciplinary collaboration, active involvement from industry stakeholders and policymakers, and the development of standardized protocols to ensure consistent performance and safety. The role of technical organizations and standardization bodies is crucial in translating research findings into practical guidelines, standards, and codes that can drive sustainable transformation within the construction sector.

Author Contributions

Conceptualization, A.S.; methodology, A.S., M.T.B. and A.G.; validation, A.S., M.T.B. and A.G.; formal analysis, A.S., M.T.B. and A.G.; investigation, A.S., M.T.B. and A.G.; data curation, M.T.B. and A.G.; writing—original draft preparation, A.S.; writing—review and editing, M.T.B. and A.G.; supervision, M.T.B. and A.G.; project administration, M.T.B. and A.G.; funding acquisition, M.T.B. and A.G. All authors have read and agreed to the published version of the manuscript.

Funding

The authors highly appreciate the financial support from Mitacs (Mitacs Accelerate program) and the City of Winnipeg.

Data Availability Statement

The main data are already included in the article. Please contact the corresponding author for further information.

Conflicts of Interest

The authors declare no conflicts of interest that could have influenced the reporting of results and discussions.

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Figure 1. Potential contributing countries by percentage share of publications related to the utilization of temperate/cold-climate agro-residues as ASCMs: (a) Switchgrass, (b) Barley, (c) Oat, and (d) Sunflower.
Figure 1. Potential contributing countries by percentage share of publications related to the utilization of temperate/cold-climate agro-residues as ASCMs: (a) Switchgrass, (b) Barley, (c) Oat, and (d) Sunflower.
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Figure 2. Network visualization of the co-occurrence analysis of keywords.
Figure 2. Network visualization of the co-occurrence analysis of keywords.
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Figure 3. Cumulative publication statistics for cold-regions candidates’ crops.
Figure 3. Cumulative publication statistics for cold-regions candidates’ crops.
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Figure 4. Flowchart outlining the processing steps for the valorization of agro-residues into concrete production.
Figure 4. Flowchart outlining the processing steps for the valorization of agro-residues into concrete production.
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Figure 5. The valorization of agro-residues through combustion for dual purposes: energy generation and production of low-carbon construction materials.
Figure 5. The valorization of agro-residues through combustion for dual purposes: energy generation and production of low-carbon construction materials.
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Table 2. Physical properties of various temperate/cold-region agro-ashes.
Table 2. Physical properties of various temperate/cold-region agro-ashes.
Properties Switchgrass AshBarley Straw AshSunflower Husk AshOat Husk Ash
Specific gravity -2.092.7–2.92.16–2.33
Specific surface Area (m2/kg) 625-817580
Mean particle size (μm) 6595–2005–13
Ref. [14,22][24,25,26][16,17,27][12,19]
Note: ‘-’ indicates that this information was not mentioned in the references.
Table 3. Chemical composition (% of mass) of temperate/cold-region agro-ashes.
Table 3. Chemical composition (% of mass) of temperate/cold-region agro-ashes.
Chemical Composition Switchgrass AshBarley Straw AshSunflower Husk AshOat Husk Ash
SiO267.221.2–62.62–5165.2–81.9
Al2O30.72.7–5.90–11--
Fe2O30.32.4–3.80–160.2–0.3
CaO 12.310–11.412.8–23.33.2–3.6
Na2Oeq ** 0.93.9–27.611.5–24.91.5–1.8
SO3--1.8–2.50–14.51.4–8.4
MgO 22–2.34–14--
P2O51.25.7–5.90–4.8 0–1
Others 0.30.40.1–0.30.1–0.3
LOI 14.84.60–25.51.5–5.2
Pozzolanic * 6827–722–8982–87
Ref. [14,22][24,25,26][16,17,27][12,19]
* Pozzolanic oxides (SiO2 + Al2O3 + Fe2O3). ** Na2Oeq = Na2O + 0.658 K2O.
Table 4. Compressive strength of temperate/cold-region agro-ashes.
Table 4. Compressive strength of temperate/cold-region agro-ashes.
Parameters Switchgrass AshBarley Straw AshSunflower Husk AshOat Husk Ash
Optimum replacements 10%5%5–25%20%
Strength improvement at 28 Days -26%-6%
Strength reduction at 28 Days−14%-−25%-
w/b0.550.380.34–0.50.45
Ref.[14,22][24,25,26][16,17,27][12,19]
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Sadoon, A.; Bassuoni, M.T.; Ghazy, A. Valorization of Agricultural Ashes from Cold and Temperate Regions as Alternative Supplementary Cementitious Materials: A Review. Clean Technol. 2025, 7, 59. https://doi.org/10.3390/cleantechnol7030059

AMA Style

Sadoon A, Bassuoni MT, Ghazy A. Valorization of Agricultural Ashes from Cold and Temperate Regions as Alternative Supplementary Cementitious Materials: A Review. Clean Technologies. 2025; 7(3):59. https://doi.org/10.3390/cleantechnol7030059

Chicago/Turabian Style

Sadoon, A., M. T. Bassuoni, and A. Ghazy. 2025. "Valorization of Agricultural Ashes from Cold and Temperate Regions as Alternative Supplementary Cementitious Materials: A Review" Clean Technologies 7, no. 3: 59. https://doi.org/10.3390/cleantechnol7030059

APA Style

Sadoon, A., Bassuoni, M. T., & Ghazy, A. (2025). Valorization of Agricultural Ashes from Cold and Temperate Regions as Alternative Supplementary Cementitious Materials: A Review. Clean Technologies, 7(3), 59. https://doi.org/10.3390/cleantechnol7030059

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