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Article

Turning Agricultural Biomass Ash into a Valuable Resource in the Construction Industry—Exploring the Potential of Industrial Symbiosis

by
Olivera Bedov
1,
Ana Andabaka
2 and
Suzana Draganić
1,*
1
Department of Civil Engineering, Faculty of Technical Sciences, University of Novi Sad, 21000 Novi Sad, Serbia
2
Faculty of Economics and Business, University of Zagreb, 10000 Zagreb, Croatia
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(2), 273; https://doi.org/10.3390/buildings15020273
Submission received: 20 December 2024 / Revised: 14 January 2025 / Accepted: 16 January 2025 / Published: 18 January 2025
(This article belongs to the Special Issue Advances in the Implementation of Circular Economy in Buildings)
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Abstract

:
This paper presents a circular business model (CBM) designed to promote the valorization of agricultural biomass ash for producing an alternative binder in construction, aiming to reduce CO₂ emissions and landfill waste. The circular economy framework emphasizes regeneration and restoration to minimize resource and energy use, waste generation, pollution, and other environmental impacts. Aligned with these principles of sustainability, the construction industry, energy sector and food processing industry can establish a shared interest through industrial symbiosis. In the proposed CBM, waste from one industry becomes an input for another. The model leverages industrial symbiosis by using sunflower husk ash (SHA) as an alternative hydroxide activator for alkali-activated materials. A case study of companies in the Republic of Serbia that produce SHA as waste forms the basis for this model, featuring promising results of experimental testing of three alkali-activated mortars produced by activating ground-granulated blast furnace slag (GGBFS) with different SHA contents (15, 25 and 35 wt% GGBFS), instead of commercially available hydroxide activators. The potential of SHA as an alternative activator was assessed by testing flow diameter and compressive strength at 7 and 28 days of curing. The highest 28-day compressive strength was attained for the addition of 25% SHA (28.44 MPa). The promising results provided a valid basis for CBM development. The proposed CBM is stream-based, resulting from merging and upgrading two existing industrial symbioses. This study highlights the benefits of the CBM while addressing the challenges and barriers to its implementation, offering insights into the possible integration of agricultural biomass ash into sustainable construction practices.

1. Introduction

The effort to address the issues of climate change and sustainable development marked the decarbonization of the construction sector as a priority [1]. This resulted in the need for changing the supply and demand paradigm, i.e., transferring from a linear to a circular economy (CE). The CE is an economy model promoting regeneration and restoration concepts to minimize the use of natural resources and energy, waste generation, pollution and other negative impacts on the environment, i.e., to “decouple economic growth and resource use” [2]. The European Commission sees circularity as an essential part of a wider transformation of industry towards climate-neutrality and long-term competitiveness and emphasizes that greater circularity could be achieved through various strategies, including the implementation of industrial symbiosis (IS) [1]. Companies can follow the industrial symbiosis perspective by implementing various business models [3].
IS can be defined as synergistic interactions between companies where residuals from one industry can serve as a resource for the same or another one [4,5,6]. Through IS, otherwise diverse industries are enabled to establish collaborative activities for the exchange of materials, energy, water, by-products, information, services and sharing of facilities [3,6]. IS valorizes wastes and by-products and closes the loop between resources, materials, and products [5]. As such, it is acknowledged as a strategy for applying the CE paradigm at the meso-level [5] and represents a promising business model perspective [3].
The built environment sector is responsible for 37% of greenhouse gas emissions. These emissions are divided into operational and embodied carbon. The operational carbon is associated with building exploitation (function and maintenance). The embodied carbon comes from material production, the construction process, maintenance and refurbishment. The significant potential in the reduction of embodied carbon lies in the development and implementation of circular materials [7]. The most widely used building material is concrete, and there are no indications that any other material will take its place soon, in terms of performance, durability, cost or applicability. With global cement production being 4.2 Gt/y, the cement industry is responsible for 7–8% of total CO2 emissions in the world and has a very high consumption of natural resources [8]. One of the main strategies for decarbonizing the construction industry is the reduction or omission of cement from concrete through the development of alternative binders [7,9].
Alternative binders include alkali-activated materials (AAMs), which do not contain cement in their composition. AAMs are derived from raw materials rich in aluminosilicates, whose dissolution, rearrangement, condensation, and resolidification are initiated and accelerated by alkaline activators. The most used aluminosilicate-rich precursors are fly ash (by-product of coal-fired electricity plants), metakaolin (a product of dehydroxylation of kaolinite) and blast furnace slag (BFS) (by-product of iron production). Activators are usually a combination of alkali hydroxides and alkali silicates, mostly used in liquid form, where alkalis are sodium or potassium. Besides significantly lower CO2 emissions compared to Portland cement (PC), due to the absence of a cement clinker, AAMs can incorporate waste and industrial by-products as precursors, thus complying with sustainable development strategies [10]. Although BFS and fly ash already have a use value through application in blended cements, the usual clinker substitution is up to 50% for slag and 25% for fly ash, while higher substitutions are used for specific types of concretes with specific mix designs and performances [11]. Thus, a more appropriate application of BFS, for example, could be in AAMs [10]. Furthermore, the right mix design of concrete based on an alkali-activated binder can result in mechanical and durability properties comparable to PC concrete. This is why they have been comprehensively researched in the last few decades as a potential sustainable alternative to PC-based binders. Moreover, their potentially good long-term durability is evidenced by structures built in the former Soviet Union, China, and Northern Europe during the 1950s to 1980s; North America and the Netherlands in 1990s; and Australia in more recent times [10].
However, the disadvantages of AAMs include a lack of regulations and standards for application in construction [12], safety issues due to the use of highly caustic activating solutions [13] and the energy-intensiveness of activator production [14]. Almost the entire ecological footprint of AAMs is assigned to the production of chemical activators, which are also associated with the higher production costs of AAMs [15]. While standardization is an issue in policy making, the other mentioned issues are addressed in the scientific literature through designing AAM mixes with reduced activator content while maintaining satisfactory performance and replacing the conventional, chemical activators with alternative alkali and silicon sources. These sources are agricultural biomass ashes (ABAs), generated during the combustion process of agricultural biomass—waste derived from agricultural activities [8,16,17,18].
Agricultural biomass has a global value as an alternative fuel for energy production, and 140 Gt of these residues is produced per year, globally [19]. However, the combustion process results in significant amount of ABA, which is usually disposed of in landfills, causing significant environmental problems [20].
The focus of this article lies at the convergence of the issues of ABA landfilling and the search for alternative activators for AAMs to increase their sustainability. In the Autonomous Province of Vojvodina, Republic of Serbia, a significant amount of potassium-rich sunflower husk ash (SHA) is generated and landfilled by an edible oil production company and a heat and electrical plant. The idea of this research is to develop a circular business model (CBM) as a tool for promoting and supporting the valorization of locally available SHA as an alternative activator for AAMs, instead of commercially available hydroxide activators. The first phase of the presented research includes preliminary experimental testing of the consistency and 7- and 28-day compressive strength of slag-based alkali-activated (AA) mortars, containing 15, 25 and 35% SHA (by mass of slag), as an alternative activator. The experimental results indicated the promising potential of SHA application in AAM technology. Component materials for producing the AA mortars were provided by the participants of the CBM proposed in the second research phase, increasing the credibility of the experimental results as a valid basis for the CBM. The proposed model is based on merging two existing ISs and establishing a new one to form an industrial symbiosis network (ISN). The existing ISs are (1) between an edible oil production company, a heat and electric plant and a city, and (2) between steel, cement and concrete production companies. The new proposed IS is the focus of the research, linking the edible oil production company, the heat and electrical plant, and the cement production company to enhance resource efficiency and waste valorization. It was concluded that, aligned with the principles of sustainability, the construction industry and SHA producers can establish a shared interest through CE concepts, particularly IS.
The remainder of this article is structured as follows. Section 2 presents the theoretical background on IS as a CBM, existing industrial symbioses in the cement industry and the use of agricultural biomass ash in AAM technology. Section 3 describes the component materials used for the experimental research, applied experimental methods, and methods for the development of the CBM. Section 4 reports the experimental research results and proposed CBM. Section 5 discusses the results of the paper and provides an analysis of the potential stakeholders, drivers, and benefits of IS. Section 6 outlines the conclusions and emphasizes the key findings of the research.

2. Background

2.1. Industrial Symbiosis as a Circular Business Model

A business model is a conceptual framework that represents how a company develops, delivers, and captures value, integrating its value proposition, strategy, market factors, and the roles of all involved actors to guide and analyze business activities [3,21]. It can relate to a company itself or to a network in which one company participates [3]. CBMs are focused on access to a product instead of ownership, the value of existing materials, components and products and a high level of collaboration between actors of a supply chain [22]. According to the CBM typology proposed by the OECD [22], there are five types of CBMs: (1) circular supply, (2) resource recovery, (3) product life extension, (4) sharing and (5) product service system.
IS is a sub-model of resource recovery CE models that is based on the valorization of waste materials to produce secondary raw materials, and it usually involves the collection of generated waste materials, sorting, i.e., separating waste into constituent materials, and secondary production to raw materials. Four extreme IS business models are identified in the literature, characterized on the basis of two governance features: (1) the need for coordination and (2) the centralization of control [3].
IS is characterized by high cooperation between the companies involved. The benefits of such relationships are multiple: economic, due to the increased competitiveness or decrease in waste treatment and disposal costs and decreased costs for input materials; environmental, due to the implications of waste reduction, the decreased use of fossil fuels, raw materials and decreased CO2 emissions; and social, due to increases in job creation [3,23]. The establishment of IS relations among companies can be seen as a good approach to enhancing the recovery of urban waste, closing material loops, and promoting resilience by reducing reliance on external resources [24].
The first implementation of IS dates back to the 1970s, in Denmark. It was formed between several manufacturing plants and the City of Kalundborg, which exchanged waste and resources. Through time, this IS spread to more companies across different industries [25]. In a broader context, entities between whom an IS relationship has been established form an ISN, which is part of an IS system involving a variety of actors—stakeholders, government, social actors, facilitators, and companies. Some authors emphasize the importance of IS for learning and innovation improvement within the network, stating that numerous examples of ISNs evolved beyond what was anticipated, encouraged by the initially formed networks [26].
Domenech et al. [27] conducted an overview of IS development in Europe, with a mapping of key networks, and a study of prevailing typologies of networks and characteristics (size, geographical distribution and main streams/resources traded). Three main groups of ISN were identified: (1) self-organized activity; (2) facilitated networks, and (3) planned networks. Biomass and agriculture by-products are the main types of waste streams common to most networks, along with chemicals, wood and wood pellets, plastics, reusable construction materials, equipment, inert waste, water, residual heat and steam. Furthermore, the type and characteristics of a waste stream, as well as its value and geographical distribution of resource recovery facilities, are the main determinants of geographical scope for different resource types. Geographical proximity is considered a facilitator for the realization of such a model; however, IS can be implemented for distant companies as well, if it is economically justified and if the infrastructure essential for the transaction of the materials or resources allows it [3]. Local proximity usually refers to cities [27], but is not strictly defined, since local distance depends on context [28].
Rentería Núñez et al. [29] conducted a literature review of business models for IS and noted that the most studied variables are the material flow and the possible strategies that companies can adopt to move toward IS. Various approaches were identified for material flow analysis, such as measurements of material circularity, the identification of industrial waste that has potential as input material for other companies, the evaluation of supply chains, cost-recovery assessments of the optimal combination of waste, and the development of material flow management tools. The analyzed IS strategies are mostly based on the development of business models, while the present tools and models are aimed at determining the region’s potential, the identification and evaluation of the possible IS, and the analysis of organizational changes.
Patricio et al. [24] identified two groups of approaches for the identification of potential synergies across a given region or development. The first group consists of discovery tools to identify potential partners based on input–output matching operation, while the second group includes uncovering tools for tracking resource flows between organizations.
The methodologies for IS implementation present in the literature also vary, from quantitative, qualitative, to mixed methodologies [29]. The methods for the quantification of IS impacts are the most widely used, with life cycle assessment being the most used in these assessments [23].

2.2. Existing Industrial Symbiosis in Cement Industry

The cement industry has already adopted IS concepts and is acknowledged as an important actor in ISNs [10,30]. Portland cement production is reduced nowadays, while cements with partial replacement of clinker with supplementary cementitious materials (SCMs) are taking over the market. Two main SCMs are slag, a by-product from the steel production industry, and coal fly ash, a by-product from energy production in thermal power plants [11]. Therefore, cement plants are part of an ISN, in which they receive supplementary cementitious materials (SCMs), e.g., fly ash, from power plants [31,32,33] and slag from iron and steel producing companies [32,34,35]. There are also examples where cement producing companies use multiple waste materials in one ISN as SCMs and fuel substitutions [24].
According to data from 2020, the highest number of published case studies on IS are about the manufacturing sector, where the chemical, cement, steel and iron industries have a significant place, along with the paper industry, power plants and refineries. Their main drivers for implementing IS are energy-intensiveness and high CO2 emissions [23].

2.3. Agricultural Biomass Ash in AAM Technology

Depending on the crop type, agricultural biomass can have different chemical compositions, and many types are rich in potassium (alkali) and silicon [17,36], which are of utmost importance in AAM technology. Depending on the chemical composition [36], ABA was experimentally tested as precursor or activator replacement. ABA rich in calcium acted as a precursor [37,38,39], while potassium- and silicon-rich ABAs had acted as an activators [17].
The activation of precursors with a complete or partial replacement of conventional silicate activators was proven viable for rice husk ash [18,40,41], and sugarcane straw ash, olive stone ash, maize ash, almond shell ash, nutshell ashes, hazelnut and mango seed-bar ashes were used as a replacement for hydroxide activators [16,41,42,43]. In the published research on potassium-rich ABA and BFS mortars, the ABA percentage in the mix was proportional to the compressive strength increase. The increased ABA content implies a higher content of K2O and soluble chemical compounds containing potassium [36], which will dissolve in the water added to the mix and form the activator, potassium hydroxide. The compressive strength also depends on other mix design properties (e.g., water-to-binder ratio) and the curing conditions. The highest content of biomass ash was 25% in respect to BFS content [44,45]. Curing at elevated temperature was found to be beneficial for compressive strength development. Most of the research proposes 7-day curing at 65 °C. After this period, samples were usually cured at 20 °C and 100% RH, or ambient humidity, until 28-day compressive strength testing [41,43,46]. In the study on slag-based mortars activated with 20% of almond-shell ash, the compressive strength after 7 days of curing at 65 °C was 36.44 MPa [47], while mortars with the addition of 25% of the same ash reached 44 MPa under the same curing regime [39]. De Moraes Pinheiro et al. [45] found that the addition of 25% of olive-stone biomass ash to BFS, instead of replacement results in compressive strength of 38.38 MPa after 7 days of curing at 65 °C.
To the best of the authors’ knowledge, apart from the mechanical properties, the durability properties of ABA-activated AAMs have not been tested in any research.
SHA has been proven as an inefficient supplementary cementitious material for PC concrete [48,49], and there is only one research paper addressing SHA an as alkali source for alkali-activated grouts [50], reaching a maximum of 21.27 MPa after 28 days, with an activator-to-water ratio of 0.8. In the absence of more results, there is a gap in the valorization of SHA.

3. Materials and Methods

This section is divided into two parts: (1) experimental research on SHA’s viability to act as a hydroxide activator in AAM systems and (2) the development of CBM model. The material’s potential for application in the construction industry is demonstrated through experimental testing of consistency and compressive strength. The results of the experimental work are followed by a proposal of the CBM, suggesting the development of an ISN.

3.1. Experimental Research

3.1.1. Materials and Mix Design

Ground granulated blast furnace slag (GGBFS), provided by Lafarge cement factory in Beočin, Serbia, was used as precursor for producing three AA mortars. SHA was provided by the edible oil producing company Victoria Oil in Šid, Serbia. The chemical compositions of the GGBFS and SHA were analyzed by X-ray fluorescence (Table 1). Quartz sand was used as an aggregate in accordance with EN 196-1: 2016 [51]. The GGBFS content was the same in all mixes. To assess the possibility of its use as a hydroxide activator instead of a chemical activator and its influence on the tested properties, SHA content was varied in three mixes, as following: 15, 25 and 35 wt% GGBFS. The mix proportion of the mortars was M(binder):M(aggregate) = 1:3, where the binder was calculated as the sum of GGBFS and the water-soluble content of SHA. The water-to-binder ratio (w/b) was 0.45 in all mixes. The SHA was added without any pretreatment.

3.1.2. Mixing, Sample Casting and Curing

To ensure the homogeneity of the component materials, GGBFS and SHA were mixed manually, with the addition of the standardized sand. The solid components were then added to water and mixed in the mixer, at high speed, for five minutes.
A set of three prismatic samples (40 × 40 × 160 mm) of each mix for compressive strength tests were cast in metal molds and sealed in polymeric films to prevent excessive moisture loss. The samples were demolded after 24 h, wrapped in polymeric films, and air-cured at ambient conditions until testing.

3.1.3. Testing Methods

The consistency of fresh AA mortar was determined in accordance with EN 1015-3: 2000 [52]. Compressive strength tests of prism mortar samples were conducted after 7 and 28 days of curing, in accordance with EN 1015-11:1999 [53].

3.2. Development of Circular Business Model

Given the large amount of waste created during the combustion process of sunflower husks, the purpose of developing a CBM is to reduce the amount of landfill waste by transforming the by-product of combustion into a resource used in production by another company. The first step towards proposing a CBM was determining its purpose, value chain, materials, participants and other key stakeholders, and potential products. The second step was mapping and analyzing the flow of materials, based on the data from the case study. The third step was assigning the type of CBM and the analysis of the relationships between the participants. The model is focused on identifying the companies that would benefit from the resource exchange and would be willing to commit to the project realization. A strong foundation for the use of SHA as an input in the production of AA concrete and developing a CBM was provided by experimental research on SHA’s viability to act as a hydroxide activator in the AAM system. Testing the potential of SHA to be used as a binder by mixing it with another by-product provides a framework for developing an ISN, i.e., a business model that could provide several benefits not only for the companies involved but for the environment in which they operate as well.

4. Results

4.1. Experimental Research Results

The flow table test results are presented in Figure 1. The results for each mix are an average of two orthogonal diameter flow measurements. An increase in activator content, i.e., solid particles, resulted in a slight decrease in slump flow. The mixes were cohesive and displayed no segregation or bleeding. An example of a mortar mix after the flow table test is shown in Figure 2. The compressive strength results are presented in Figure 3.
The SHA25 mix had the highest compressive strength at 7 and 28 days of curing (18.44 MPa and 28.44 MPa, respectively). Mixes SHA15 and SHA35 reached the same compressive strength of approximately 16 MPa at 7 days of curing. However, mix SHA35 attained a slightly higher compressive strength than mix SHA 15 (25.22 MPa and 22.84 MPa, respectively) after 28 days of curing.

4.2. Proposed CBM

The proposed CBM presents an ISN as a result of merging two existing ISs:
  • An edible oil production company (Victoria Oil, Šid) and Heat and electric plant, and Sremska Mitrovica town (TE-TO Sremska Mitrovica),
  • Steel, cement and concrete production companies.
Victoria Oil is a factory for processing oil crops. The company produces raw and refined oils, biodiesel and protein meal. The processing capacity for sunflower is 220.000 tons annually and 1.200 tons of sunflower a day. The production capacity of the refinery plant is 300 tons of refined oil a day. The edible oil bottling plant has a capacity of 14.000 bottles an hour. Victoria Oil exports sunflower oil to the countries of the Balkan region, as well as to the EU countries Austria, Slovakia, Italy, Holland, Slovenia, Croatia, Hungary and Greece. During the sunflower seed processing, a significant amount of sunflower husks are generated [54]. They are considered as waste, but their low natural moisture (9%) and good thermal properties (average 18 MJ∙kg−1) make them suitable as biomass energy source [55]. In 2007 Victoria Oil invested in a biomass boiler to produce energy for production and operating [54]. Each year, 720 tons of waste, i.e., SHA, is generated in the combustion process of sunflower husks [56]. Although the concept of the valorization of agricultural waste as a SCM has been researched and proven viable for other crop residues in the Vojvodina region [57], with no recognized use value, SHA is disposed of in landfills.
Some of the sunflower husks from the production process at Victoria Oil are sold to the heat and electric plant TE-TO in Sremska Mitrovica, a city in the southwest part of Vojvodina. In 2012, the company constructed a second boiler plant, which uses sunflower husks as an energy source to produce heating for the city. The boiler plant has a capacity of 18 MWt. This has resulted in a production cost for thermal energy that is approximately 20% lower compared to the previously used fuel—natural gas [58]. Annually, 240 tons of generated SHA in the heat production process is also deposited on landfill [56]. Therefore, 960 tons of SHA is generated annually from these two companies.
The second IS underpinning the proposed CBM is established between a steel production company and a cement producer. In the region of SHA producers, there are the HBIS Group steel production factory, Smederevo and the Lafarge cement plant, Beočin. They have a long-standing IS relationship involving the steel production company supplying BFS to the cement plant to produce clinker-reduced cement. Lafarge then markets its product (cement) to various consumers, with concrete producers being the primary example in the proposed CBM. This symbiotic relationship is highlighted because it already exists and serves as a foundation for a potential new collaboration. Specifically, the cement plant could introduce a new product to its portfolio, based on a combination of SHA and slag, targeting the same customer base, i.e., concrete producers.
The proposed CBM is a stream-based approach [25], meaning the new relationships in the joint CBM are based on the flow of SHA. The developed CBM is presented in Figure 4. The main participants in the CBM are an edible oil production company, a heat and electric plant, a city and steel, cement and concrete production companies. The process flow and relationships between CBM participants are presented with arrows. They are divided into two groups by color: red arrows symbolize a waste material from one company that becomes an input for another, and green and grey arrows stand for companies’ final products produced from the received input material. Each arrow is followed by the name of an output material (e.g., sunflower husks, blast furnace slag) or by a final product (e.g., energy, heat) of that process. Furthermore, solid lines present existing relationships between CBM companies, while the dashed lines correspond to new relationships that the model proposes.
The existing relationships between CBM constituents remain uncompromised. The proposed CBM establishes two new symbiotic relationships: one between an edible oil company and a cement production company (with a distance of 60 km), and another between a heat and electric plant and a cement production company (with a distance of 40 km). These relationships relate to SHA transfer, instead of its landfill. Consequently, the cement production company will obtain an input material for developing a new product for an already existing relationship with a concrete producer, i.e., a 100% waste-based binder made from SHA and GGBFS, along with cement. The new relationships for the transfer of SHA do not rely on the development of a completely new production process. Instead, they are based solely on the transfer of waste that is already being generated, which is favorable for the IS concept [25].
The relationships in the proposed CBM present internal and external resource interdependencies. Internal dependency occurs within the edible oil production company, since it uses waste generated during sunflower seed processing to produce energy for operating the factory. External interdependency forms through relationships between the edible oil production company and the heat and electrical plant, and between the steel production company and the cement producer. It is an interdependency on a strategic level due to the use of the waste material of another company or another process within the same company to generate a product [3].
An important characteristic of SHA is that it can be used as alternative activator in an AAM system without any pretreatment, which is proved in the presented experimental research on slag-based mortars. This results in cost savings for the cement producer and transaction costs within the CBM, due to the lower coordination needed [3].
The described IS is the basis of the proposed CBM and will have continuous potential in the future. Sunflower is a dominant crop among the industrial plants in the Republic of Serbia, with 45.2% of the total agricultural area under cultivation with industrial plants. In 2022, sunflower was planted in 251.155 ha of agricultural land, of which 88.5% is planted in the region of Vojvodina. From 2013 to 2022, the area of agricultural land planted with sunflower increased every year by 3.3% on average [59].
In support of the promising performance of SHA-activated AA mortars, the development of a CBM for this product would enable various benefits. On a global level, there is a great potential of SHA as an alternative activator in AAM technology, as the total world production of sunflower in 2021 was approximately 56 million tons and the harvested area was 29 million ha [60]. Agricultural biomass holds immense potential as a valuable alternative fuel for energy production. By adding use value to SHA, other edible oil producers in the region could be motivated to invest in alternative fuel system. The benefits of using SHA are manifested in the reduction of CO2 resulting from fuel and cement reduction, the elimination of landfilled waste, savings in raw materials stemming from the replacement of cement, and significant cost savings.

5. Discussion

The results of the experimental testing revealed that SHA can be utilized as an alternative activator for BFS, achieving compressive strengths comparable to those reported in the literature.
Although the literature suggests curing at higher temperature for enhancing the compressive strength, the presented experimental research favored ambient curing, due to savings in energy costs, which is in line with concepts of CE and CBM. This is why the 7-day compressive strength of all three tested mixes is significantly lower than the same compressive strengths of mortars activated with different ABAs (olive-stone biomass ashes—38.38 MPa [45], 29.90 MPa [46], almond shell ash—36.44 MPa [47]). The 28-day compressive strength of SHA15, SHA25 and SHA35 is comparable to the mixtures cured at 65 °C for 7 days in which the slag content was replaced with 25% ABA (olive-stone ash—33.0 MPa [61]). The differences in compressive strength can be explained by a lower water-to-binder ratio in the mixes in the literature, the chemical composition of the ABA (i.e., potassium content) and the solubility of ABA [47]. The same effect of increased compressive strength due to curing at higher temperatures can be expected in SHA-activated mortars. It is not clear why compressive strength decreases after an increase in SHA content above 25%; it could be a consequence of excessive amounts of alkalis, leading to the early formation of dense hydration products that block further reaction [62]. However, this phenomenon is not the subject of the presented research and will be further investigated in future research, along with the mechanical and durability properties of the proposed binder on a concrete level.
Stakeholder engagement, motivation, and openness to the IS approach are crucial for fostering initial cooperation [28,63]. In the developed CBM, the existing relationships between industrial players show that they are already familiar with the presented concept of cooperation and its benefits, making them more prone to overcome barriers and adopt the proposed model of the ISN. For example, the cement industry is already actively contributing to the implementation of the CBM at various stages of the production process and adopting synergistic practices with other industries.
This type of CBM offers cost reductions and waste management improvement, which are main drivers among companies, according to the interviews conducted by Domenech et al. [27] (decreasing resource costs (64% of responses), reducing generated waste (55% of responses) and prevent waste landfilling (32% of responses)). Furthermore, it is an answer to the increasing need to turn to CE in the construction sector.
Apart from industrial partners, the successful implementation of IS calls for the engagement of a wider range of stakeholders, especially public authorities. For the proposed model, creating the legal framework to support the use of alternative binders is a necessary step toward developing more sustainable solutions in concrete production and overcoming the most significant barriers towards implementing the model [64]. Moreover, public sector support by using the top-down approach would demonstrate the recognized potential of ISNs to unlock new business opportunities [5,65]. The facilitation framework could include the local government, i.e., the region, which would be a part of the ISN by using the heat from the plant, which creates SHA as a by-product of heat production. By facilitating the use of SHA as an alternative binder in the cement industry, the city would benefit from diverting industrial waste from landfills and could also lead by example by promoting CE processes in the urban area. Another important actor in the facilitation process in Serbia could be the Chamber of Commerce, which promotes better waste management practices, CBMs and low-carbon concrete. The Center for Circular Economy of the Serbian Chamber of Commerce organizes free professional services and consulting for companies in the field of the circular economy with the support of the German Agency for International Cooperation (Deutsche Gesellschaft für Internationale Zusammenarbeit—GIZ) [66]. The city and the Chamber of Commerce are often perceived as impartial and have a vested interest in the prosperity, sustainability, and development of the industrial sector [28], and they could promote the establishment of the IS network to reap its benefits.
Given the appropriate regulatory and facilitation framework, the proposed business model of using the SHA for the reduction or replacement of the chemical activators could increase AAMs’ competitiveness as sustainable alternatives to PC concrete worldwide. However, the specificities of each case must be taken into consideration, and a broader, systemic perspective is necessary to fully leverage the benefits of CEs and ISs [3].
Developing innovative environments for engagement and partnership, as well as actively including a wider range of stakeholders, plays a vital role in enhancing the multiplier effect associated with the implementation of IS [28]. In England, the publicly funded National Industrial Symbiosis Programme (NISP) was established in 2005 to promote the efficient use of underused or undervalued resources (including energy, waste, water, and logistics) among different industrial sectors. The outcomes of this programme in the period from 2005 to 2013 include more than GBP 37 million worth of public investment, the creation of over 10,000 permanent jobs, a decrease of 42 million tons in carbon emissions at a cost of only GBP 0.65 per ton, and total savings of GBP 1 billion by reducing disposal, storage, transport, and purchasing costs. Furthermore, this world’s first national IS initiative successfully diverted 47 million tons of industrial waste from landfills, reused 1.8 million tons of hazardous waste, preserved 60 million tons of virgin materials, and saved 73 million tons of industrial water [67,68]. The remarkable achievement of the NISP shows that governments can play a crucial role in promoting IS by encouraging collaborative exchanges between companies that are advantageous for all parties involved and engaging facilitators to implement the program across different regions.
Based on the analysis of 28 IS projects, Sommer [28] emphasized the role of facilitation as one of the most important elements serving as a driving force for enhancing awareness, identifying potential opportunities, and collaboratively executing IS initiatives. Different actors could serve as potential facilitators, such as industrial park owners/managers, the municipality or the Chamber of Commerce, the association of a cluster of companies established by the partners involved, hubs for circularity [28] or leading experts on IS.

6. Conclusions

This paper proposes a CBM for supporting the valorization of locally available waste from biomass energy production—SHA as an alternative activator of AAMs. The proposed model is based on a case study of IS in the Autonomous Province of Vojvodina, Serbia. The CBM participants are an edible oil production company, a heat and electrical plant, a city, a steel production company, a cement factory and a concrete production company. The valid basis for the model is provided by preliminary experimental research on GGBF-based AA mortar mixes activated with different SHA contents. The promising potential of SHA application in AAM technology is confirmed by assessing consistency and compressive strength at 7 and 28 days of curing. The highest compressive strength was attained for the addition of 25% SHA (by GGBFS mass), reaching 28.44 MPa at 28 days of curing. However, further research on mechanical and durability properties at the concrete level are essential to confirm the suitability of the proposed sustainable solution for concrete production.
The CBM is a result of merging and improving two existing IS relations: an edible oil production company and a heat and electric plant, and a steel and iron production company and a cement company. It is a stream-based model that could effectively contribute to the reduction of environmental problems caused by SHA landfilling by providing the SHA to cement producers.
This paper highlights the multiple benefits of such a model: economic benefits due to a decrease in waste disposal costs and lower costs for input materials; environmental benefits due to the reduction of waste landfilling, a decreased use of fossil fuels and raw materials and decreased CO2 emissions; and social benefits due to increased job creation, as well as development and innovation.
The main barrier for the implementation of the proposed CBM and use of AAMs in the construction industry is the lack of a legal framework and standards for AAMs. This is why public sector support by using the top-down approach is necessary to facilitate this kind of ISN in the construction industry.
Improving the sustainability of construction materials such as concrete is an imperative for decarbonization and is proposed by European Commission framework. The reduction or replacement of the chemical activators would increase AAMs’ competitiveness as sustainable alternatives to PC concrete. Valorizing locally available waste would have several positive outcomes: a reduction of CO2 emissions and material costs, the reinforcement of CE concepts in the construction sector, and waste management improvement by moving it up the hierarchical scale, from the lowest level—disposal—to the highest level—prevention.

Author Contributions

Conceptualization, O.B. and A.A.; methodology, O.B., A.A. and S.D.; validation, O.B. and A.A.; formal analysis, O.B.; investigation, O.B., A.A. and S.D.; resources, O.B. and S.D.; data curation, O.B., A.A. and S.D.; writing—original draft preparation, O.B., A.A. and S.D.; writing—review and editing, O.B., A.A. and S.D.; visualization, O.B.; supervision, A.A. and S.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

This article is based upon work from COST Action Implementation of Circular Economy in the Built Environment (CircularB), CA21103, supported by COST (European Cooperation in Science and Technology). The research has also been supported by Provincial Secretariat for Higher Education and Scientific Research in Vojvodina through project “Development of new binders based on agricultural and industrial waste from the area of Vojvodina for the production of eco-friendly mortars”.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Flow-table test results of SHA activated mortars.
Figure 1. Flow-table test results of SHA activated mortars.
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Figure 2. An example of AA mortar mix after flow table test—SHA25. (a) Top view; (b) side view.
Figure 2. An example of AA mortar mix after flow table test—SHA25. (a) Top view; (b) side view.
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Figure 3. Compressive strength of SHA activated mortars, after 7 and 28 days of ambient curing.
Figure 3. Compressive strength of SHA activated mortars, after 7 and 28 days of ambient curing.
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Figure 4. Schematic representation of developed CBM.
Figure 4. Schematic representation of developed CBM.
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Table 1. Chemical composition of GGBFS and SHA.
Table 1. Chemical composition of GGBFS and SHA.
OxideSiO2Al2O3Fe2O3CaOMgOSO3K2ONa2OMnOTiO2
GGBFS38.1910.280.3137.049.690.750.870.390.520.37
SHA5.341.191.0312.969.949.7144.760.680.06-
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Bedov, O.; Andabaka, A.; Draganić, S. Turning Agricultural Biomass Ash into a Valuable Resource in the Construction Industry—Exploring the Potential of Industrial Symbiosis. Buildings 2025, 15, 273. https://doi.org/10.3390/buildings15020273

AMA Style

Bedov O, Andabaka A, Draganić S. Turning Agricultural Biomass Ash into a Valuable Resource in the Construction Industry—Exploring the Potential of Industrial Symbiosis. Buildings. 2025; 15(2):273. https://doi.org/10.3390/buildings15020273

Chicago/Turabian Style

Bedov, Olivera, Ana Andabaka, and Suzana Draganić. 2025. "Turning Agricultural Biomass Ash into a Valuable Resource in the Construction Industry—Exploring the Potential of Industrial Symbiosis" Buildings 15, no. 2: 273. https://doi.org/10.3390/buildings15020273

APA Style

Bedov, O., Andabaka, A., & Draganić, S. (2025). Turning Agricultural Biomass Ash into a Valuable Resource in the Construction Industry—Exploring the Potential of Industrial Symbiosis. Buildings, 15(2), 273. https://doi.org/10.3390/buildings15020273

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