A circular economy-based model for assessing the sustainability of construction and demolition waste management

In an effort to tackle climate change and decrease the consumption of natural resources, more and more industries worldwide are adopting circular economy principles. The construction industry is no exception; however, the implementation of these principles is beyond satisfactory levels. As a consumer of more than half of the extracted materials and a contributor to more than a third of waste, the construction industry hides great circular economy potential. In recent years, the scientific community has devoted a great effort to investigate different aspects of construction and demolition waste (CDW) management. The assessment of key aspects of sustainability, such as the economic, environmental and social aspects, were particularly studied, mainly to find the optimal management alternative that would be the least detrimental to the environment and the society. However, the available studies rarely included all three pillars of sustainability. Moreover, management alternatives that were assessed included only recycling, backfilling and disposal in most cases, leaving the treatment options that support circular economy principles such as reuse and high-quality recycling unexplored. Additionally, most of the studies performed sustainability assessments on statistical data of CDW quantities that are often unreliable and may significantly underestimate the sustainability performance. The main objective of this research was to propose a new model for the sustainability assessment of CDW management and the selection of the optimal CDW management alternative. To achieve this objective, the following specific goals were addressed: 1) setting up a unique material stock database that includes the types and quantities of materials embedded in buildings; 2) proposing possible CDW management alternatives; 3) proposing a model for estimating future quantities and composition of CDW; 4) proposing a model for assessing the sustainability performance of the proposed alternatives; 5) comparing and ranking of CDW management alternatives; 6) analysis of the ranking results and selecting the optimal CDW alternative. The model was tested in a case study for the management of CDW from residential buildings in Serbia. In this case study, three alternatives: the current CDW management (BAU), the alternative that aims to achieve the EU average CDW recovery rates (EU28(2018)) and the alternative that implements circular economy principles in CDW management practices (CE) were evaluated and ranked. Each alternative was ranked against four different decision-makers scenarios: economic, environmental, social and holistic. The model includes the integration of the existing and widely used methods: bottom-up inventory analysis and dynamic stock modelling for the estimation of the material stock and CDW quantities and composition, Cost-Benefit Analysis for sustainability assessment and Multi-Criteria Decision-Making Analysis (Analytical Hierarchy Process - AHP) for ranking of the CDW alternatives and choosing the optimal CDW management alternative. The implementation of the model in the case study for CDW management in Serbia yielded three sets of results. The first set of results was related to the creation of a unique material stock database that included the list of materials embedded in residential buildings built between 1946 and 1990 with detailed specifics (geometry and physical characteristics). Based on this, viii the total weight and the composition of the materials embedded in these buildings were calculated. The total weight of material embedded was estimated to be 714.6 million tonnes, out of which 601.1 million tonnes were embedded in single-family house (SFH) buildings and 113.5 million tonnes of materials were embedded in multi-family house (MFH) buildings. The materials with a share of over 80% belong to the mineral fraction (concrete, bricks, tiles, ceramics). The second set of results included the potential waste quantities and composition when these buildings in Serbia are renovated or demolished. Depending on the renovation alternative, the total amount of waste in the period 2021—2046 ranged between 40.2 and 41.1 million tonnes, with an average annual contribution between 1.5 and 1.6 million tonnes. The sensitivity analysis of the waste quantities showed that these quantities might range between 0.89 and 2.5 million tonnes if the demolition rate changes up to 30%, while the renovation rates do not bring significant changes to the amount of waste. The highest share of the waste stream (67%) is made up of clay and concrete-based materials. Consequently, the waste composition (waste streams) and the possible treatments of these waste streams determine the sustainability performance of three proposed CDW management alternatives for Serbia. The third set of results was related to the sustainability performance and the ranking of CDW management alternatives. The direct outputs of the Cost-Benefit Analysis (financial and economic net present value) identified cash flow balance and potential economic, environmental and social benefits to the waste operators and the society for each alternative for Serbia. The current CDW management alternative in Serbia was the worst option. The financial and the economic net present values were negative in this alternative, which implies that managing waste under this alternative will not benefit the waste operator or society. On the other hand, the CE alternative was identified as the best option, with both of these indicators positive. The ranking of alternatives with the Multi-Criteria Decision-Making Analysis resulted in the optimal CDW management alternative under different decision-making preferences. In the environmental and holistic decision-making scenarios, the CE alternative was ranked as the optimal, while the current waste management alternative was ranked as the optimal solution under the economic and social preferences. In addition, the sensitivity analysis applied to the sustainability performance revealed several critical variables such as the demolition rate, discount rates, capital and operational costs and unit prices of recovered bricks and aggregates. These are the variables that should be carefully considered when waste management strategies are planned. The case study showed that efficient CDW management practice depends on active participation and partnership of all stakeholders, from policymakers to researchers and practitioners. All these stakeholders may find the proposed model useful from different management aspects. The policymakers may use this model to evaluate the effects of the stricter implementation of the existing regulations and the promotion of new regulations such as the carbon and landfill taxes or even landfill bans for recyclable waste fractions. More advanced instruments would include reusing and recycling subsidies and the implementation of green procurement provisions in public contracts. And finally, in lack of financing for better waste management practices, carefully planned and contracted public-private partnerships may be the right answer that will, in the end, benefit all partners, the environment and the society.Kao odgovor na klimatske promene i smanjenje potrošnje prirodnih resursa sve više industrija širom sveta usvaja principe cirkularne ekonomije. Građevinska industrija nije izuzetak, međutim primena ovih principa je daleko ispod zadovoljavajućeg nivoa. Zahvaljujući činjenici da troši više od polovine iskopanog materijala i da generiše više od trećine otpada, građevinska industrija ima veliki potencijal za primenu principa cirkularne ekonomije. Naučna zajednica je u skorije vreme, posvetila mnogo napora istraživanju različitih aspekata upravljanja otpadom od građenja i rušenja, posebno procenama aspekata održivosti, kao što su ekonomski, ekološki i društveni aspekt, kako bi pronašla optimalnu alternativu za upravljanje ovim otpadom koja bi bila najmanje štetna po životnu sredinu i društvo. Međutim, dostupne studije retko uključuju sva tri stuba održivosti. Štaviše, alternative za upravljanje koje su procenjivane u studijama su u većini slučajeva uključivale samo recikliranje, nasipanje i odlaganje na deponiju, zanemarujući pri tome opcije tretmana otpada koje podržavaju principe cirkularne ekonomije, kao što su ponovna upotreba i recikliranje koje rezultira kvalitetnim recikliranim agregatom. Dodatno, većina studija je analizirala održivost opcija za upravljanje otpadom od građenja i rušenja na osnovu statističkih podataka o količinama koji su često nepouzdani i mogu značajno potceniti rezultate. Glavni cilj ovog istraživanja je predlaganje modela za procenu održivosti alternativa za upravljanje otpadom od građenja i rušenja i izbor optimalne alternative. Kako bi se postigao ovaj cilj, postavljeno je nekoliko pojedinačnih ciljeva: 1) formiranje jedinstvenog fonda građevinskog materijala, baze podataka o tipu i količini materijala ugrađenih u zgrade; 2) predlaganje mogućih alternativa za upravljanje otpadom od građenja i rušenja; 3) predlaganje modela za procenu budućih količina i sastava otpada od građenja i rušenja; 4) predlaganje modela za procenu održivosti alternativa za upravljanje otpadom od građenja i rušenja; 5) poređenje i rangiranje alternativa za upravljanje otpadom od građenja i rušenja; 6) analiza rezultata rangiranja i izbor optimalne alternative za upravljanje otpadom od građenja i rušenja. U tu svrhu, ovaj model je testiran na stambene zgrade u Srbiji. Alternative koje su procenjivane i rangirane su: alternativa sa sadašnjim načinom upravljanja otpadom od građenja i rušenja (BAU), alternativa koji teži da dostigne prosečne evropske procente iskorišćenja ovog otpada (EU28(2018)) i alternativa koji primenjuje principe cirkularne ekonomije u upravljanju otpadom od građenja i rušenja (CE). Svaka od ovih alternativa je rangirana u skladu sa različitim prioritetima donosioca odluka: ekonomskim, ekološkim, društvenim i sveobuhvatnim. Model koje je predložen integriše postojeće metode koje su široko u upotrebi. Za procenu fonda građevinskog materijala i količinu i sastav otpada od građenja i rušenja korišćena je analiza inventara zgrada i dinamičko modeliranje fonda zgrada, dok je za procenu održivosti i rangiranje alternativa korišćena analiza troškova i koristi i višekriterijumska optimizacija. Primena modela na izabranu studiju slučaja je dala tri grupe rezultata. Prva grupa rezultata predstavlja kreiranje jedinstvene baze podataka koja sadrži listu materijala ugrađenih u stambene zgrade u periodu od 1946. do 1990. godine sa detaljnom specifikacijom geometrije i fizičkih karakteristika zgrada. Na osnovu ovoga izračunata je ukupna količina i sastav materijala ugrađenog u stambene zgrade. Ukupna težina materijala koji je ugrađen u stambene zgrade iznosi 714.6 miliona tona, od čega se 601.1 milion tona odnosi na zgrade namenjene xi porodičnom stanovanju, a 113.5 miliona tona na zgrade namenjene višeporodičnom stanovanju. Materijali koji u ovom fondu materijala učestvuju sa preko 80% pripadaju materijalima mineralnog porekla (beton, opeka, keramika). Druga grupa podataka se odnosi na moguće količine otpada kada se ove zgrade renoviraju ili sruše. U zavisnosti od alternative renoviranja, ukupna količina otpada u periodu 2021—2046 varira između 40.2 i 41.1 miliona tona, sa prosečnim godišnjim prinosom od 1.5 do 1.6 miliona tona. Analiza osetljivosti ovih rezultata je pokazala da se ove količine mogu kretati u opsegu od 0.89 do 2.5 miliona tona ukoliko se stopa rušenja promeni za 30%, dok stope renoviranja nemaju značajniji uticaj na količine otpada. Najveći udeo u količini otpada (67%) imaju materijali na bazi opeke i betona. Shodno tome, sastav i mogući tretmani ovog otpada određuju troškove i prihode tri predložene alternative za upravljanje otpadom od građenja i rušenja u Srbiji. Treća grupa rezultata se odnosi na analizu troškova i koristi i rangiranje alternativa za upravljanje otpadom od građenja i rušenja. Rezultati analize troškova i koristi su identifikovali alternativu sa sadašnjim načinom upravljanja kao najlošiju opciju. Negativna vrednost finansijske i ekonomske neto sadašnje vrednosti impliciraju da upravljanje otpadom od građenja i rušenja u ovoj alternativi ne donose korist ni operatoru otpada ni društvu. Sa druge strane, CE alternativa se pokazala kao najbolja opcija u kojoj su obe neto sadašnje vrednosti pozitivne. Rangiranje alternativa pomoću višekriterijumske optimizacije je rezultiralo izborom optimalna alternative u različitim scenarijima odlučivanja. U ekološkom i sveobuhvatnom scenariju odlučivanja CE alternativa je rangirana kao optimalna, dok se u ekonomskom i socijalnom scenariju odlučivanja, sadašnji način upravljanja otpadom od građenja i rušenja pokazao kao optimalna opcija. Dodatno, analiza osetljivosti procene održivosti je otkrila nekoliko kritičnih parametara kao što su stopa rušenja, diskontne stope, kapitalni i operativni troškovi i jedinične cene opeke za ponovnu upotrebu i recikliranog agregata, koji se moraju pažljivo razmotriti kada se planiraju strategije za upravljanje otpadom od građenja i rušenja. Studija slučaja je pokazala da efikasno upravljanje otpadom od građenja i rušenja zavisi od aktivnog učešća i partnerstva svih zainteresovanih strana, od istraživača do političara i praktičara. Model predložen u ovom istraživanju bi mogao da bude koristan svima. Političari bi mogli da ga koriste prilikom razmatranja strožijih kontrole i bolje primene postojeće regulative kao i promovisanja novih zakonskih instrumenata kao što su porez na emisiju ugljen-dioksida i porez na odlaganje na deponiju ili čak zabrana odlaganja na deponiju otpada koji se može reciklirati. Napredniji instrumenti bi mogli da uključe podsticaje za ponovnu upotrebu i recikliranje kao i primenu zelenih nabavki u javnim ugovorima. I konačno, u nedostatku finansiranja boljih opcija za upravljanje otpadom, pažljivo planirana i ugovorena javno-privatna partnerstva bi mogla da budu odgovor koji bi koristio svim partnerima, kao i životnoj sredini i društvu

Model za procenu održivosti upravljanja otpadom od građenja i rušenja zasnovan na principima cirkularne ekonomije

In an effort to tackle climate change and decrease the consumption of natural resources, more and more industries worldwide are adopting circular economy principles. The construction industry is no exception; however, the implementation of these principles is beyond satisfactory levels. As a consumer of more than half of the extracted materials and a contributor to more than a third of waste, the construction industry hides great circular economy potential...Kao odgovor na klimatske promene i smanjenje potrošnje prirodnih resursa sve više industrija širom sveta usvaja principe cirkularne ekonomije. Građevinska industrija nije izuzetak, međutim primena ovih principa je daleko ispod zadovoljavajućeg nivoa. Zahvaljujući činjenici da troši više od polovine iskopanog materijala i da generiše više od trećine otpada, građevinska industrija ima veliki potencijal za primenu principa cirkularne ekonomije..

Circular Economy in Construction and Demolition Waste Management in the Western Balkans: A Sustainability Assessment Framework

Population growth, consumerism and linear (take-make-dispose) economy models have been piling up waste for decades. The construction industry is also based primarily on linear economy models, but the good news is that most of the waste can be re-used or recycled. So far, numerous models for managing construction and demolition waste in a sustainable way have been developed, but only a few models have included circular economy approaches. The main objective of this study is to propose an integrated framework for the sustainability assessment of CDW management. Apart from the economic, environmental and social aspects of sustainability, this model also includes circular economy principles. The proposed framework is based on the integration of existing methods: bottom-up materials stock approximation; cost–benefit analysis for criteria calculation; and scenario and multi-criteria decision-making analysis for sustainability. It is suggested that the European average recovery rates should be used for future scenario development. With higher re-use and recycling rates, the potential for the circularity of the recovered waste grows. In an effort to increase circularity in the region, particular attention was devoted to customize the framework and examine its potential for use in the Western Balkan countries. The framework may also be useful in countries with immature construction and demolition waste managemen

COVID-19 Struggle and Post-COVID-19 Recovery: Exploring the Governance, Success, and Digital Transition in Construction Projects in Serbia

Construction, one of the largest global economic sectors, has been severely challenged by the economic uncertainties brought on by COVID-19. Since 2020, pandemic-related disruptions and remedial measures have made its historically low performance even more difficult. As a result, recent research mainly addressed these negative consequences on the construction sector. In contrast, this paper aims to identify mitigation strategies recognised as good practices on construction projects in Serbia, in addition to detecting disruptions and quantifying their effects on cost and time overruns. A particular emphasis is given to how the pandemic hastened digital transition and encouraged the adoption of modern project management practices. The research was carried out through a survey of two rounds, conducted one year apart, to obtain an in-depth overview. The findings indicated that, although it had an impact on construction projects, the pandemic was not particularly harmful, because of widely used remedial measures and modern project management techniques. However, the pandemic did not modernise project implementation substantially nor significantly increase the use of cutting-edge digital technologies. Nevertheless, it encouraged project managers to think about introducing new approaches in project management, where digitisation is the new normal. The research findings may indicate to academia and practitioners what strategies may assure a project’s implementation even in enormously changed conditions, such as during a pandemic

Urban mining potential in Serbia: Case study of residential building material stock

As governments worldwide attempt to develop sustainable waste management strategies, massive amounts of waste have been accumulating. However, developing an effective waste management strategy requires a thorough understanding of waste types and quantites. The existing efforts to identify waste flows in the built environment are unsuitable for countries with non-reliable statistics as they mostly use location-specific parameters such as data on construction, renovation, demolition activity, and generation rates from the literature. The types and quantities of materials embedded are rarely considered. This study aims to fill the identified gap by estimating the quantities of different material types embedded in Serbian residential building stock. It will do so by calculating the volume and weights of building elements and their materials using information from a detailed building stock typology. The results show that the amounts of materials embedded vary significantly from district to district, ranging from 10 in Toplička District to 96.9 million tons in Belgrade. The mineral materials are the highest contributors to the material embedded, implying that future waste management strategies should focus on them. Apart from the formulation of location-specific circular economy and waste management strategies, these results may be useful for planning energy efficiency retrofitting activities, deconstruction and reversible design strategies

Development and Implementation of Evaluation Framework for Quality Enhancement of Outcome-Based Curriculum

Evaluation to improve teaching and learning is essential for achieving the objectives of higher education programs. While structural and organisational aspects of teaching are frequently assessed, programme evaluation tools are rarely matched to specific learning objectives and competence levels that students are expected to achieve. Driven by the shortcomings of previous unstructured surveys on the quality of teaching at our Faculty, we created a curriculum improvement framework based on the evaluation tool that compares the level of competence that students perceive they achieved in each of the courses, and the level of competence that professors attribute to their courses by quantifying the learning outcomes using Bloom’s taxonomy. In our two year study, which included seven teachers who teach 16 courses and 38 and 24 students in two consecutive years, this framework provided the educators with the indicators for quality enhancement based on the difference between students’ and teachers’ evaluations. Based on indicator values, the teacher implemented improvements on two pilot courses. In the second round of surveys, we were able to measure the success of improvements. Our findings indicate that the proposed framework and evaluation tool are simple to implement and can be used as indicators and starting points for improving the quality of teaching. In this way, we provide a practical framework for others wishing to enhance their teaching and their students' learning

An integrated solution for increased circularity in buidlings. A methodological framework

The transition from a linear to a circular economy still poses a significant challenge worldwide. The abundance of materials measured in billions of tonnes is transferred annually within the economy, with minimal materials being cycled back. The construction sector uses approximately half of the materials extracted while generating more than a third of the total waste. The current circular potential in the construction industry is yet to be exploited. This paper addresses the issue of materials embedded in buildings and the possibility of their reversible capacities. The main objective of this paper is to develop a systemic methodological framework on how to create, collect, process and present data which may support a better recovery of the embedded building materials, especially their reuse and high-quality recycling during the renovation and demolition processes. The proposed framework defines a methodological approach for developing an interactive digital solution, a digital map, to increase circularity in a built environment by integrating spatial data and building information models (BIMs). To this end, a four-step methodological approach is introduced: (1) development of BIMs for the existing building stock; (2) allocation of material inventory data to BIMs; (3) calculation of circular economy indicators; and (4) digital solution integration into 3D Geographic Information Systems (GIS). This map may facilitate maximising the circular potential of buildings, encourage data transparency and increase their availability to a wide range of market players. It could be imbued with tools such as a digital building logbook with which it could share data

A digital solution for unlocking the urban mining potential of the residential building stock through the integration of BIM and GIS

The construction industry consumes up to half of the excavated primary resources and generates one-third of total waste annually, impacting the environment and society. To reduce this impact, maintaining the primary resources in some form within the economy as long as possible is essential. One of the ways to do this would be to recover waste products and cycle them back into the economy as a secondary resource, either through reusing or recycling. This implies carefully planned waste recovery strategies based on the knowledge of the materials embedded in constructions. The solutions that encourage data transparency and increase the availability of data on this knowledge to all potential stakeholders across many industries could contribute to creating more effective strategies. Digital technologies are the primary tool in the development of such solutions. Integrating Building Information Modelling (BIM) and Geographic Information Systems (GIS) provides the power to achieve this. The main objective of this paper is to develop and validate a digital solution that compiles, systematizes and represents the buildings’ material inventory data at the municipal level. To this end, a three-step methodological framework was introduced: (1) development of BIMs for the existing building stock; (2) allocation of material inventory data to BIMs; and (3) integration of a digital solution into 3D GIS. A residential building in one of the central municipalities of Belgrade, Serbia, was selected as a case study to evaluate the proposed concept. The BIM model was reconstructed from aerial and terrestrial scans (Scan-to BIM), and its semantic enrichment with the data on building type, construction period, type of built-in materials, their service lives and material quantities acquired from several publicly available sources. When fully implemented at the urban scale level and validated in the interaction with public administration, NGOs from the housing sector and end-users, the platform could be a valuable tool which may maximize the circular potential of each material embedded in buildings and help in more effective policymaking and could be used for benchmarking and progress tracking of achieving strategic goals set within these policies

Cost-oriented analysis of fibre reinforced concrete column-supported flat slabs construction

Fibre reinforced concrete (FRC) is increasingly being used in elements with high structural responsibility, the constructed FRC column-supported flat slabs (CSFSs, hereinafter) with partial or even total substitution of reinforcing steel bars being a supporting evidence for that statement. These pioneer experiences provide encouraging results with respect to resource optimization and construction time reduction without jeopardising the structural reliability. Despite such promising achievements, the use of FRC in CSFSs is still limited in the building sector. To provide an additional impulse for the use of FRC, a comprehensive comparison between FRC and traditional reinforced concrete (RC) technologies for CSFSs in terms of execution procedure and overall costs is needed. With this in mind, an industrial-oriented study was carried out with the main objective of elaborating a simplified method for the preliminary comparison of RC and FRC solutions. This method permits to assess the major amount of the required reinforcement (flexural reinforcement) followed by an evaluation of the time saving effect due to the partial or total substitution of reinforcing steel bars by fibres. For this purpose and for the sake of generalization, several databases were examined and 33 interviews with experts on in situ construction were conducted so that a wide range of productivity rates and other particularities could be identified. Based on the proposed method, a case study was analysed in order to indicate the potential direct costs (materials + labour) for a number of RC and FRC solutions using data from the examined databases and conducted interviews. The results reflect an increment of direct costs for both fibre and hybrid (fibre + reinforcing steel bars, HFRC) solutions; however, these increment can be compensated by the reduction of the construction period and, as a consequence, time-dependent costs (i.e., preliminaries, equipment costs, overheads, and finance costs). The outcomes of this research are meant to provide support to designers and construction planners with regard to the suitability of using FRC for CSFSs