Analysis of Circular Economy Interventions during the Demolition and Enabling Phase of a Construction Project: An Irish Case Study

Abstract

The global construction industry is the world’s largest consumer of raw materials and creates an estimated third of the world’s overall waste. A circular economy is one that aims to keep products, components and materials at their highest utility and value at all times. The Opera Square site development project is being utilised as a Lighthouse Demonstrator Project for the Circular Built Environment. The site is a brownfield site located in the heart of Limerick City. The transformational commercial development which commenced in 2022 consists of office, retail, residential and public buildings on a 3.7-acre site. During the demolition and enabling phase of the project, a number of buildings were demolished. Prior to demolition, a pre-demolition audit was undertaken. The purpose was to identify the type and quantities of the materials that would arise from the demolition works and possible opportunities to implement circular economy principles. This research paper will conduct a case study on the Opera Square project located in Limerick, Ireland, evaluating the circular economy interventions implemented during the demolition and enabling phase of the project. The study aims to assess the effectiveness of the interventions in achieving a diversion rate for construction and demolition material from landfill of 98% through on-site and off-site re-use of construction materials, the re-use of material as a piling mat diverted 87% of construction and demolition material from landfill. A life cycle analysis was undertaken and determined a reduction of at least 66% in the embodied carbon global warming potential compared to a business-as-usual construction practice for the piling mat. There are lessons learned from this project that can be applied to future projects, one being the full realisation of opportunities for further re-use of material through the end-of-waste and by-product mechanisms. Achieving the full potential of a circular economy in the built environment requires collaboration among stakeholders, with initiatives that promote community engagement being particularly impactful in creating both social, environmental and economic benefits through a Circular Economy.

Introduction

Circular Economy as a Climate Change Mitigation Measure

Climate change is having a significant impact on our planet. Sea levels are rising, and the intensity, frequency and duration of severe weather events is increasing. The main cause of climate change is the effects arising from anthropogenic emissions of greenhouse gases (GHG) warming Earth’s atmosphere [1]. The European Union (EU) has set a goal to reduce GHG emissions by 55% by 2030, compared to 1990 levels and to be climate neutral by 2050 [2].

The construction industry is expected to play a significant role in helping the EU reach its goal. Construction products account for over 30% of the EU’s total waste and the production of materials like cement, steel, aluminium and plastics contributes to 15% of the EU’s GHGs emissions [3]. Reducing GHG emissions from the construction industry is essential to meet the EU’s overall sustainability goals and moving to a circular economy (CE) through a transition from a linear economy to a CE has the potential to reduce up to 80% of these emissions and enhance the security of supply of primary raw materials [4].

In a CE economy, the construction industry designs and builds resource-efficient buildings. This is achieved by improving material efficiency, by prioritising re-use, recycling and repurposing of materials and designing structures for disassembly and resource management. The CE approach is applicable to an entire building’s life cycle.

For Ireland’s move to a CE to be successful, it must be supported by all stakeholders. These include economic operators in the value chain, policymakers, legal and technical actors, building users, facility managers and owners, design teams (engineering and architecture), contractors and builders, manufacturers of construction products, deconstruction and demolition teams, investors, developers and insurance providers, government, regulators and at each local authority.

Circular Economy Policy

A CE aims to keep resources in use for as long as possible by extracting their maximum value and through effective resource planning, recovering or regenerating products and materials at the end of their service life [5]. The principle of a CE prioritises waste prevention through adaptive re-use, refurbishing, repurposing and recycling resources to reduce resource scarcity and environmental degradation while minimising whole life carbon emissions [6]. A CE in the context of the built environment and the construction sector, refers to an economic system aimed at eliminating waste and designing and constructing buildings and infrastructure in a way that promotes re-use, recycling and the use of sustainable building materials. This approach also contributes to reducing the environmental impact of construction activities and supports the transition to a more sustainable and resource-efficient economy. By designing and constructing buildings and infrastructure utilising CE principles, the construction sector can address common societal goals whilst curbing the depletion of resources and the endless production of waste. Through eliminating waste in the design and construction of buildings and infrastructure by promoting re-use, recycling and sustainable building materials an effective CE would be at the heart of sustainable development. This in turn will help to achieve the following UN (United Nations) Sustainable Development Goals (SDGs) [7]:

• Goal 3 Good Health and Well Being.

• Goal 9 Industry, Innovation and Infrastructure.

• Goal 12 Responsible Consumption and Production.

• Goal 13 Climate Action.

In the European context, the European Green Deal is a key component of the EU’s agenda for sustainable growth. The Green Deal aims to boost the efficient use of resources by moving to a CE. It is the EU’s position that a CE will reduce pressure on natural resources, create sustainable growth and jobs and is essential to achieve the EU’s 2050 climate neutrality target. As part of this initiative, the EU has adopted a Circular Action Plan [8], focusing on resource-intensive sectors such as textiles, construction, electronics and plastics. The Circular Economy Action Plan (CEAP) is a comprehensive body of legislative and non-legislative actions adopted by the EU in 2020. It aims to transition the European economy from a linear to a circular model and maps out 54 actions, as well as four legislative proposals on waste. The EU adopted a new CEAP in March 2020, which is one of the main building blocks of the European Green Deal. The plan aims to reduce the EU’s resource consumption footprint and double its circular material use rate in the coming decade, while boosting economic growth.

The EU Taxonomy Regulation (EU) 2020/852 [9] is a classification system establishing a list of environmentally sustainable economic activities. It will be essential in helping the EU scale up sustainable investment and implement the European Green Deal. This Regulation was first published in the Official Journal of the European Union on 22 June 2020 and entered into force on 12 July 2020, establishes environmental objectives and safeguards required to meet the conditions for sustainable economic activity. As per Article 9 of the Regulation, the objectives are:

• 1. Climate change mitigation,

• 2. Climate change adaptation,

• 3. Sustainable use and protection of water and marine resources,

• 4. Transition to a circular economy,

• 5. Pollution prevention and control,

• 6. Protection and restoration of biodiversity and ecosystems.

The Regulation defines technical screening criteria for each environmental objective through delegated acts. Under the Regulation, for example, an activity under the climate change mitigation objective must achieve the environmental objectives by fulfilling the objective-specific screening criteria, while not negatively impacting the other five stated objectives. Taking the construction of a new building as it relates to the climate change mitigation objective for buildings larger than 5,000 m², the life-cycle Global Warming Potential (GWP) of the building resulting from the construction must be calculated through undertaking Life Cycle Analysis (LCA) for each stage in the life cycle. The GWP calculated must be available to investors and clients on demand. The GWP is communicated as a numeric indicator for each life cycle stage expressed as kgCO₂eq.,/m² (of net useful internal floor area) averaged for one year of a reference study calculation period of 50 years. The LCA data selection, scenario definition and calculations are carried out in accordance with EN 15,978: 2011 Sustainability of Construction Works - Assessment of environmental performance of buildings - Calculation method [10]. Where a national LCA calculation tool exists or is required for making disclosures or obtaining building permits, the respective tool may be utilised. Alternatively, other calculation tools may be used if they fulfil the minimum criteria laid down by the Level(s) framework [11]. Level(s) is a common framework across the EU; it establishes sustainability indicators for buildings across their entire lifecycle, aiming to provide a standard approach for users to understand, improve and optimise the environmental sustainability and performance of buildings [12]. The purpose of using a standard tool, using a standardised method in line with the EU Level(s) framework and the ISO standard EN 15,978, is to enable direct comparison both against benchmarks and between projects. The Level(s) objectives are to provide a common language by defining common indicators across projects and ensuring their comparability by measuring them using the same metrics and criteria. A second objective is to promote the use of LCA and Life Cycle Costing (LCC) to help understand the quantities and timings of environmental impacts in parallel with the most cost-effective approaches to reducing them.

In the Irish context, there is a Minister of State with responsibility for the Circular Economy at the Department of the Environment, Climate and Communications (DECC). The DECC on behalf of the Government of Ireland has launched Ireland’s first Whole of Government Circular Economy Strategy in 2022 [13]. The strategy is a key addition to the Irish Government’s drive to achieve a 51% reduction in GHG emissions by 2030 and carbon neutrality by 2050, as per commitments in the Programme for Government [14] and the Climate Act 2021 [15]. The Circular Economy and Miscellaneous Provisions Act 2022, which was signed by the President of Ireland in 2022 and has become law, underpins Ireland’s transition from a linear to a circular model [16]. This transition looks to retain the value of resources in use for as long as possible by extracting their maximum value and through effective resource planning, recovering or regenerating products and materials at the end of their service.

In the construction industry, clients and developers increasingly emphasise design practices that promote material sustainability and prioritise green strategies and practices related to:

• Material ingredients.

• Locally sourced building materials; and.

• Low-emitting materials.

This shift towards sustainable design practices is influenced by demand from the investor and lender community, the global Environmental, Social and Governance (ESG) movement. These ESG concerns are influential in the real estate industry, impacting investment strategies, rental and capital growth potential and the vulnerability of assets to becoming obsolete in a world that will decide on capital-flows based on the least carbon footprint in the future [17].

By-products and End of waste in Ireland.

The concept of by-product and end-of-waste was established by the European Waste Framework Directive (WFD) [18] and adopted in domestic Irish law through Regulation 27 and Regulation 28 of the European Communities (Waste Directive) Regulations (2011) [19].

In Ireland, the Environmental Protection Agency (EPA) as the environmental regulator has responsibility for the following [20]:

• Waste Licensing,

• National Environmental Enforcement,

• Waste Management and Chemicals in the Environment,

• Water Management,

• Climate Science and Climate Change Environmental Monitoring and Assessment and the decision-making process for by-product and end-of-waste applications.

There are three levels of end-of-waste criteria that can be applied in Ireland [21]:

• EU level,

  • Criteria set the European Commission (EC) and is available to any producers in the EU.

• National level,

  • Criteria set by Member State, in consultation with the EC and available to any producer in that member stage, e.g. Republic of Ireland.

• Single case criteria

  • Single case is through an application to the EPA and the criteria is applicable to the producer either an individual organisation or group for which the criteria apply.

Although Regulation 27 by-products and Regulation 28 end-of-waste criteria are often discussed together they each have distinct practical and regulatory differences:

Regulation 27 allows an economic operator to decide, under certain circumstances, that a substance or object resulting from a production process, the primary aim of which is not the production of that item, may be regarded as a by-product and not a waste only if the following four tests are met:

• 1. further use of the substance or object is certain,

• 2. the substance or object can be used directly without any further processing other than normal industrial practice,

• 3. the substance or object is produced as an integral part of a production process,

• 4. further use is lawful, and the substance or object fulfils all relevant product, environmental and health protection requirements for the specific use, without leading to overall adverse environmental or human health impacts.

Regulation 28 sets out the grounds by which a material which is recovered from waste can be deemed to be no longer a waste. End-of-waste gives waste holders the opportunity to demonstrate a waste material can be ‘fully recovered’ and no longer be defined as waste, when:

• 1. the end-of-waste can be used as a “secondary” resource in place of and fulfilling the same role as a non-waste derived or virgin “primary” resource, or

• 2. new innovations can transform waste into a valuable resource, and

• 3. the fully recovered material can be used without causing overall adverse impacts to the environment or human health.

By-products can reduce waste growth by designating green-field soil and stone as by-product and a resource to be used again rather than as a waste. The end-of-waste process can reduce the need for virgin aggregates like crushed rock and sand & gravel that are used in concrete, by re-using what might otherwise be treated as waste material from demolition. The recovery process has to be done in a way that’s safe, in terms of both the environment and human health. The by-products and end-of-waste processes are the means by which those safeguards are implemented [22]. Advancing and embedding the concept of correctly designating by-products, along with increasing recycling rates through an end-of-waste process, can help the construction industry transition from a linear economy to a CE. This shift can contribute to the construction industry collective goal of reducing GHG emissions by improving resource efficiency.

Literature Review

The concept of a CE has become a significant school of thought in sustainable economics [23]. It is defined as an industrial system that is intentionally designed to be restorative or regenerative [24]. Since the start of 2020, the assets managed through public equity funds that have CE as the sole or partial focus have increased sixfold from USD 0.3 billion to over USD 2 billion [25]. Exploiting the CE can bring job creation, a more vibrant business environment, value creation through social entrepreneurship and reduced carbon emissions.

The concept of CE has gained traction in the construction industry to promote sustainable development, re-use, refurbishment, repurposing and recycling of resources (both construction and demolition waste) and supply chain management. An analysis of 486 articles undertaken by [26] Antwi-Afari et al., written over the last 10 years revealed gaps in research, particularly in areas such as circular product design, end-of-life considerations, economics and modular integrated construction. Their analysis identified a lack of practical approaches and holistic assessment tools for implementing the CE in construction [27]. In the field of research, there has been a noticeable emphasis on frameworks, systematic reviews and theoretical concepts rather than direct application of CE principles. While frameworks, systematic reviews and theoretical concepts play a crucial role in building a strong foundation of knowledge, there is a growing need to bridge the gap between theoretical understandings and practical application of CE principles. It is important to strike a balance between advancing theoretical frameworks and ensuring that research outcomes can be effectively applied to real-world situations.

A literature review by [28] Winans et al., revealed varying degrees of success and failure of CE projects, emphasising the need for integrated bottom-up and top-down approaches. Pomponi and Moncaster [29] identified a gap in existing research on the CE, finding that the research often focuses on macro- or micro-scale aspects, neglecting the meso-scale of individual buildings. They conducted a literature review to define key dimensions of CE in the built environment and highlighted the need for both bottom-up and top-down initiatives, interdisciplinary research, societal involvement and policy measures to enhance circularity in buildings.

In research conducted by Benachio et al. [30], they describe the four principles on which the CE is built upon as:

• designing products with their entire life cycles in mind,

• maximising product life cycles,

• recycling materials from end-of-life products, and

• reusing materials across diverse industries and value chains.

The building and construction industry’s significant use of raw materials, production of waste and emissions of greenhouse gases have highlighted the importance of implementing circular strategies, particularly in the re-use of construction materials. A recent study by Bellini et al. [31] on the Nøstebukten Brygge project in Norway explores the potential enhancement of the re-use process through improved data management. The study suggests an information-driven approach to re-use and underscores the possibility of applying the methodology to other projects. The study emphasises the necessity for further research to evaluate and standardise the CE framework to share data for use in circular construction projects.

The concept of CE in the built environment has attracted increasing attention, as it challenges traditional approaches and seeks to minimise waste while maximising economic value.

A systematic literature review by [32] Ossie et al., analysed 316 publications and identified key conceptual affinities and attributes contributing to the definition of CE. The review emphasised the importance of Construction and Demolition Waste Management (CDWM) and the prioritisation of environmental aspects. These findings suggest that a comprehensive understanding of CE is critical to prevent the misapplication of CE principles in the construction industry and to promote sustainable practices in a fair and unbiased manner [33].

Benachio et al., [34] conducted a content analysis of 45 published articles in four stages. The first stage was the definition of CE for the construction industry across the various articles. The second stage was the analysis of the stages of the life cycle included in the research; finding that research has focused primarily on the construction and operation stages of a building’s life cycle, with fewer concepts incorporated in the project design, material manufacture and end of life stages. The third stage was the analysis by research theme. Lastly, the fourth stage listed CE practices by life cycle stage. The research by [35] Benachio et al., found only one article considered all stages and most considered only one stage. This highlighted that research in the CE is still focused on applying the concepts of CE in the built environment in only one life cycle stage at a time.

Irrespective of focussing on one lifecycle stage or across a project lifecycle, performance indicators are required to assess CE. Although, what indicators should be measured is subject for debate as key performance indicators and numerical targets can be ambiguous and might lead to incorrect conclusions when determining success or otherwise of CE strategies [36]. This is compounded further when concepts and definitions within the CE remain open to interpretation e.g. recovery, re-use, recycle. Therefore, the principle of maintaining products, components and materials at their highest utility and value at all times should be used in determining appropriate performance indicators and targets [37].

Research by Salama [38] explores the potential for reusing concrete elements and materials from demolished buildings. The author presents the argument that reusing these elements could lead to a shift towards a more circular model in the construction industry. The study concludes that it is possible to change the linear life-cycle model to a cyclic one by applying Design for Disassembly (DfD) criteria to precast concrete systems and elements. The importance of incorporating circularity into the entire lifecycle of a building project is discussed and achieved more easily when there is early engagement in the concept stage of a project.

In a review of the origin of research papers on the topic of the CE, Benachio et al., [39] found in the EU numerous papers related to circular practices, which indicates the importance placed within the area on achieving environmental and climate objectives. The EU’s directives and regulations regarding national environmental and waste management policies target a bottom-up approach to tackle environmental sustainability challenges by implementing CE principles.

Research by Kirchherr et al. [40] on the CE in the EU highlights cultural barriers, particularly the lack of consumer interest as one of the primary obstacles to implementation. This challenges the common belief that technological barriers are the main obstacle, emphasising instead the need for a coordinated approach that addresses the complexity of cultural barriers and their impact on business models and consumer behaviour.

CE can contribute to environmental sustainability by attracting both business and policymakers to sustainability efforts. However, more scientific research is required to ensure that the actual environmental impacts of CE can work toward global net-sustainability and reduce biodiversity loss [41]. The CE remains focused on technological solutions, driven by a promise of traditional economic growth at levels which are not environmentally sustainable. CE in general can have a positive effect because of lowered environmental impact but there is a risk of negative effects too if the circular strategy is based too heavily on bio-based materials without addressing proper sustainable sourcing and production. When natural habitats are replaced by industrial production of bio-based materials or if the production method itself requires large inputs of non-renewable energy sources or leads to the depletion of the national environment. Therefore, it is an imperative that we understand how best to implement CE principles in practice that fully consider sustainable development, placing environment at the forefront, with an emphasis on economic prosperity fulfilling lives in harmony with nature [42].

Research Gap

The results of the literature review show that a more detailed discussion of the specific strategies and best practices for implementing CE principles within the construction sector is required. There is an absence of evidence-based case studies dealing with CE principles in constructing the built environment within the Irish jurisdiction. This research paper employs a case study approach to examine CE measures within the construction sector, focusing on the demolition and enabling stages of the Opera Square project.

The Opera Square project in Ireland stands as a lighthouse demonstrator project for CE principles in the built environment. It explores CE opportunities through collaboration with various stakeholders during the demolition and enabling phase of the project (Contract A). Key measures presented include conserving raw materials by directly reusing materials both on-site and off-site, minimising the embodied carbon footprint by repurposing materials and investigating circularity options for subsequent project phases.

This research project aims to enhance understanding of CE implementation in construction and encourage the industry to regard waste streams as resource streams within a CE framework. This paper provides practical guidance through a demonstration for stakeholders constructing the built environment sector in Ireland and other jurisdictions. Achieving this aim can significantly advance our shared goal of reducing GHG emissions by improving resource efficiency through promoting a CE.

Circular Economy Construction (CE-CON) Demonstrator Project

This study and paper contributes to the Circular Economy Construction demonstrator project (CE-CON) which aims to utilise the Limerick Twenty Thirty Opera Square development as a Lighthouse Demonstrator Project for the Circular Built Environment. It is funded by the Environmental Protection Agency (EPA) and led by the Irish Green Building Council (IGBC) in collaboration with partners Atlantic Technical University (ATU), Limerick Twenty Thirty Designated Activity Company (LTT DAC) and the Southern Region Waste Management Office (SRWMO).

The CE-CON project objective is to explore CE opportunities across various stages, including demolition, design and construction. It will outline specific strategies and best practices necessary for implementing CE principles in the construction sector encouraging the industry to view waste streams as potential resource streams.

The key outputs of CE-CON include:

• a collection of demonstrator briefs that will guide future LTT DAC projects,

• evidence-based case studies and industry guidance intended to benefit the broader construction sector,

• inform national guidance, curriculum development and policy related to circular economy practices in construction.

Opera Square Project

Limerick Twenty Thirty DAC

Limerick is a city with a population of almost 95,000 people located in the mid-west of Ireland, on the River Shannon and covers an area of 59 km². It is located 200 km from the capital, Dublin and is Ireland’s third largest city. In 2014, Limerick City and County Council (LCCC) published the Limerick 2030 Vision: An Economic and Spatial Plan for Limerick [43].

The Plan is an economic and spatial framework for the redevelopment and growth of Limerick City Centre. Key to the delivery of the Plan is the development of a number of strategic sites. LCCC established LTT DAC in 2016 to undertake development of these strategic sites that will act as anchors for enterprise and development for the region in Ireland.

Opera Square was identified as a strategic site, a key objective of the Opera Square project is to restore and regenerate a site within the city centre that has been vacant for decades into a modern-day world-class mixed-use development.

Opera Square Site

Opera Square is a brownfield site located in the heart of Limerick City Centre in the functional area of LCCC. The site, as indicated within the red boundary in Fig. 1, occupies the majority of a city block bounded to the west by Patrick Street and Rutland Street, to the north by Bank Place, to the east by Michael Street and to the south by Ellen Street. It contains various building structures dating from the 18th to the 20th century. The perimeter of the site, bordering Rutland Street, Patrick Street and Ellen Street is predominantly made up of terraced buildings dating from the Georgian period. There are several buildings on the site with varying levels of heritage value. These include structures listed on the Record of Protected Structures and in the National Inventory of Architectural Heritage (NIAH).

The main redevelopment plan involved the demolition of all the twentieth-century buildings and later additions to the rear of existing heritage structures to facilitate new-build elements and proposed renovation and adaptive re-use of the Protected Structures and the other structures of heritage value within the site.

The Opera Square project will be delivered across specific parcels in five phases (A-E), consisting in total of the following:

• One Opera Square, a 14,000m² building, 6-storey, comprising office, retail and a restaurant.

• A hotel, which is 4,700m² and consists of 110 rooms and a restaurant.

• A new 4,410m² City Library and café.

• Four Opera Square, a 2,580m², 5-storey office (flex space).

• Parcel 3B, which comprises six one-bedroom Georgian apartments and retail.

• A 14-storey landmark office building of 12,300m².

• The refurbishment of the Granary building (2,715m²) constructed in 1870 into offices and a restaurant.

• An 8,000m² basement for 133 car spaces including e-charging capabilities and 495 bike spaces.

Further elements of the development include the provision of a significant amount of open amenity space, associated public realm works and the provision of additional access routes to enhance the site’s overall permeability. The development also includes environmental improvement works to the adjacent public streets.

Fig. 1

Opera Square is a brownfield site located in the heart of Limerick City Centre

The buildings highlighted with red infill in Fig. 1 indicate twentieth-century buildings and later additions to the rear of existing heritage structures which are not designated as being of heritage value. These structures were demolished in the demolition and enabling phase (Contract A).

Research Methods

Aim and Scope

This research paper employs a case study methodology to examine CE measures identified, considered, deployed or considered and not progressed within the Opera Square project. The focus of this paper is on the initial stages of the project (demolition and enabling phase Contract A).

The use of case study research methodology is common among scholars when presenting research on CE. Johansson [44] characterised case study research methodology by its in-depth and comprehensive exploration of a single or small number of units (cases) of analysis. This approach emphasises the real-life context of the study and relies on multiple sources of data to ensure the reliability and validity of findings through triangulation of the data to develop, build and present the case study findings. The case study research methodology is beneficial for investigating phenomena that are challenging to replicate in experimental or theoretical settings by providing valuable, detailed, practical insights into various aspects of a research problem in a setting that allows the full appreciation of all influences in a real-world setting.

Research by Merli et al. [45], demonstrates the distribution of articles based on research methodologies with Modelling (32.12%) and Case Study (28.32%). In the case study category, there is a significant number of papers that focus on the application of CE.

The approach to implementing CE principles within Opera Square examines the following cases:

• Utilisation of a pre-demolition audit to assess construction and demolition waste for re-use and recycling, including its integration into the overall project and its contribution to material efficiency.

• Direct re-use of materials on-site and off-site.

• Life cycle assessment of the circular interventions through the repurposing of material from the demolition phase as a piling mat in a future project phase.

• Investigation and implementation of end-of-waste and by-product determination criteria, along with exploring circularity options for subsequent project phases.

The aim is to enhance understanding of CE implementation in construction and to encourage the industry to regard waste streams as resource streams within a CE framework. This paper provides practical guidance as a demonstration for stakeholders in the built environment sector in Ireland. Achieving this aim can significantly advance our shared goal of reducing GHG emissions by improving resource efficiency and promoting a CE.

The Methodological Process

The data collection and analysis method for this paper on the Opera Square development involved an initial phase of on-site engagement with the project team. Site visits were conducted to monitor and gain a comprehensive understanding of the overall project. Activities included:

• Attend weekly project design and progress meetings,

• Conduct a literature review focusing on the following areas:

  • CE principles and policies in the built environment.

  • Existing regulations in Ireland and abroad

  • Case studies implementing CE principles, with particular emphasis on the demolition phase and strategies that could be applied to the Opera Square project.

• Compile and verify data related to the demolition phase of the project,

• Identify and review relevant data sources and construction documents,

• Undertake a Life Cycle Analysis on demolition and enabling phase,

• Conduct interviews with design teams and contractors to gather valuable data in the preparation of best practice factsheets for the industry,

• Develop a Project questionnaire survey to understand their experiences in implementation of circular principles in the construction industry in Ireland,

• Identify lessons learned.

Remote access to construction documents and drawings was facilitated through the construction document management software platform used by the construction and design teams. The methodological process is illustrated in Fig. 2.

Fig. 2

The methodological process

The research included flexibility to respond to emerging opportunities on the Opera Square project. The overall CE-CON research output is the evaluation of CE interventions in this case study and their design, to generate a collection of demonstrator briefs that will guide future LTT DAC projects and industry guidance factsheets intended to benefit the broader construction sector.

Case Study Description

The scope of the demolition and enabling phase (Contract A) works was outlined in a performance specification that was issued in May 2020 for tender for the demolition and enabling of the project site. The scope of work included various tasks such as surveys, site-setup, hoarding installation, traffic and pedestrian management, site-clearance, building stabilisation, demolition of structures, sewer construction, hazardous material investigation and site grading.

The Contract A work prepared the site for future project phases. The performance specification highlighted the importance of preserving and storing special conservation pieces. The contractor was required to develop a project-specific Construction Environmental Management Plan (CEMP). The plan included a Construction and Demolition Waste Management Plan (CDWMP), an Environmental Emergency Preparedness and Response Plan (EEPRP), measures to ensure protection of surface waters during works, measures for the management of invasive species and measures for the protection and management of bat species.

The section in the performance specification outlining Waste Management Requirements was particularly important as it placed a requirement to divert at least 75% of construction and demolition waste from landfill, noting that this number must exclude Alternative Daily Cover (ADC). ADC (in the context of landfilling) is the term used to describe material spread over deposited waste at the end of each working day.

The contract documentation also referred to a pre-demolition audit, the first of its kind at this scale in Ireland, which was underway at the time of contract negotiation. The pre-demolition audit included estimating the quantities of demolition waste and identified markets or potential uses for that demolition waste before the demolition works commenced. The pre-demolition audit was shared with the contractor post tender (pre-contract signing), and the contractor was requested to co-operate collaboratively on this pilot project with LTT DAC and SRWMO to which the contractor agreed.

In October 2020, the pre-demolition audit was published and in the same month the tender process closed and the first phase of the Opera Square project, demolition and enabling phase (Contract A), was awarded to the construction company.

Data Collection

Pre-demolition Audit

The pre-demolition audit aimed to identify and evaluate the type and quantities of materials to be deconstructed and/or demolished. The audit also provided recommendations on their further handling. The audit process comprised two phases, namely a desk study followed by field survey.

The desk study involved reviewing available information and documentation pertinent to the building, including the age of the building, design documents, documentation of use, a list of hazardous substances, the surroundings and access. The study aimed to identify the construction date/period, dimensions, construction typology, composition, type of materials, location of machinery and installations and details of hidden or difficult to access spaces. The audit team also referred to design and planning documentation, particularly the registered findings of asbestos surveys and heritage reports.

The field survey involved a visual inspection of the site and buildings and where necessary, minor invasive works. The survey comprised a site visit to develop a material inventory, identifying, quantifying and locating material types in each building such as floor coverings, electrical fittings, interior walls and false ceilings, to inform recommendations on re-use and recycling.

In summary and based on discussions with the lead auditor, ‘the desk top study allowed the identification of quantities, and the field survey determined material type.’

The audit aimed to determine materials, quantities and type, for re-use or recycling and to consider factors such as safety, time, economic feasibility and market acceptance. The audit recognised that existing buildings were a material resource and the utility and value of their components, elements and materials should be maintained for as long as possible. The audit provided the necessary information to plan and manage demolition and disassembly work to deliver best practice approaches to resource recovery.

On-site Re-use

The foundation of EU waste management is the five-step Waste hierarchy (Fig. 3), established in the Waste Framework Directive [46]. It establishes an order of preference for managing and disposing of waste. ‘Preparing for Re-Use’ is high in the Waste hierarchy.

Fig. 3

Waste hierarchy from Waste Framework Directive

‘Preparing for Re-Use’ is enabled when materials are inspected, cleaned, or repaired in recovery operations, a further refinement is when materials are directly re-used without additional processing in a like for like process. Direct re-use of materials is crucial for achieving a CE due to its potential to reduce waste and significantly minimise the consumption of new resources.

During this research, it was noted that while the contract documents stipulated an overall requirement to divert at least 75% of construction and demolition waste from landfill, there were no specific targets for on-site re-use of construction and demolition waste or material specific diversion targets. The absence of such targets for the construction team to pursue when seeking to re-use material without it leaving the site should be a lesson learned from this project. Such targets would have challenged the construction team to implement circularity principles, including optimised lifecycle performance and longer use life of construction and demolition resources.

On Opera Square, demolition on site was carried out systematically and involved the removal of several buildings and support areas. These included the existing industrial/warehouse/workspace buildings towards the centre of the site, office buildings, modern additions and extensions to the rear of the Granary Building, which is a Protected Structure. Also included were existing structures to the rear of heritage structures fronting onto Rutland Street, Patrick Street and Ellen Street. Additionally, the existing Ellen Street surface car park and the modern-day buildings 6/7 Rutland St., were removed to facilitate the widening of the existing east-west access route into the site. The process of demolition included soft stripping of the buildings and the use of mechanical excavators for the demolition of the buildings.

Re-use of Steel on Site

In the construction stage of Opera Square, virgin steel was imported for temporary works. The pre-demolition audit indicated the availability of steel sections post demolition. An opportunity may have arisen if material-specific re-use and onsite re-use targets were stipulated for the steel recovered from the demolition process. These steel elements were sent off-site for traditional recycling. Through source segregation and initial identification of opportunities for the re-use of the steel there was potential to stockpile and re-use steel on-site.

An enabler for this would have been a target or key performance indicator (KPI) on the re-use of steel from the demolition and enabling phase (Contract A) in future stages of the development. To achieve this, resource and waste management planning must occur upfront during master planning, especially when projects have multiple stages where tender documents are not all in place simultaneously. Focusing solely on a particular phase of a project, without full consideration for opportunities across an entire project lifecycle, should be avoided. This is especially relevant where a significant initial element of the project involves demolition and enabling works.

Re-use of Demolition Material in a Piling Mat

The material resulting from the demolition process, outlined above, commonly referred to as the ‘crushed’ material, was composed of crushed concrete (in-situ), blocks (concrete), bricks (engineering), red brick and some natural stone. This material was stockpiled on-site and underwent testing to confirm its adherence to the material grading requirements of the 6F2 fill material, as stipulated in Table 6/2 of the Transport for Infrastructure Ireland (TII) Specification for Road Works, Series 600-Earthworks [47]. As a result, it was deemed suitable for on-site re-use in a piling mat (Fig. 4). By reusing 15,003 tonnes of this crushed material classified as 6F2, for the haulage road build-up and piling mat layer on Opera Square, a significant amount of construction and demolition waste was diverted from landfill.

Fig. 4

Piling Mat spread across the Opera Square site

During this research it was observed that the re-use of demolition material in the piling mat achieved a very high on-site re-use rate. If the piling mat option had not been available to re-use such a large volume of material on-site, this demolition material would have been transported off-site. This would have potentially resulted in the loss of a higher-value construction material to a lesser-value backfilling operation, with off-site transport costs to the project and associated GHG emissions.

The material was re-used even though the contract documentation did not have an on-site re-use target. Within this project, it made economic sense to do so as the demolition material did not have to be hauled off-site to a recovery facility and an option for re-use of the material was available. Therefore, it is evident how important it is for a client with a vision to deliver a project with a CE focus to engage and deploy a construction team that is open to exploring such re-use options and the success the engagement can bring.

It must be noted how important it is in construction projects, where the enablers for re-use may not align as well as on Opera Square; during the development of specifications clients should consider setting re-use and recycling targets for construction and demolition waste and its material-specific fractions.

Site-specific targets for re-use and recycling targets with a determination of the quantity of materials that can leave the site should be specified. These targets can only be achieved by preparing for re-use, recycling and other material recovery at the earliest stage of the project life cycle, ideally before the construction phase begins.

On-site Re-use (Future Phase of Project)

Cobblestones removed from the passageways to Patrick St. and Rutland St., a historic Limestone door case to 6 Rutland Street (Fig. 5) and three pallets of old Georgian red brick were palletised on-site for re-use in later phases of Opera Square. These are currently stored on-site for future re-use in passageways and repairs to chimneys or gables of the Georgian buildings.

Fig. 5

Limestone door case to 6 Rutland Street

Off-site Re-use

Direct Re-use

A total of 852 tonnes of natural stone recovered as part of the demolition process, from Opera Square, have been re-used across a range of projects throughout Limerick City and County, including:

• Repairs to the Canal Harbour Building used 2,000 red bricks (Fig. 6).

• In the construction of a stone sculpture (Fig. 7).

• In the construction of natural stone walls (Fig. 8).

Fig. 6

Canal Harbour Building

Fig. 7

Natural Stone from Opera Square in the construction of a stone sculpture

Fig. 8

Natural stone from opera square

Additionally, the Limerick City Build regeneration project has been able to use the stone in a stone mason training scheme (Fig. 9). The successful re-use of this material has undoubtedly contributed to the sustainable development of the community. This is an example of the societal, environmental and economic benefits that were forthcoming due to CE interventions on the Opera Square project. Other examples of Off-site re-use include:

• Palisade metal fencing panels re-used by the Richmond Rugby Club (Fig. 10).

• Timber-framed internal division wall with glass panels re-used in local offices.

• Gates and stone pillars re-used by Limerick Civic Trust (Fig. 11).

Fig. 9

Using stone recycled from Opera Square (Credit: Richard Lynch photography: Opera Square sustainability programme gives old building materials a new life)

Fig. 10

Palisade metal fencing panels

Fig. 11

Gates and stone pillars re-used by Limerick civic trust

By-product on Opera Square

In Ireland, the EPA, as the Irish environmental regulator, published a guide to submitting a by-product notification under Article 27 of the European Communities (Waste Directive) Regulations 2011 [48]. During the development of Opera Square, a basement void was excavated to approximately 5 m below ground level across a large part of the site. This excavation generated excess soil and stone that was not required on site, which was initially intended for disposal/recovery at an authorised waste facility until the client LTT DAC identified it as potentially a valuable resource that could be re-used in an upcoming flood relief scheme (FRS) in the functional area of the Local Authority. The bedrock removed to facilitate the creation of the basement void was also identified as a resource, which could potentially be a by-product to be utilised for local road projects under the remit of the Local Authority. A by-product notification to the EPA was considered for the soil, stone and the bedrock excavated for basement void from the Opera Square project.

By-product: Soil and Stone

Before re-use could be confirmed, it was important to determine the soil classification and whether the material fell under the remit of a by-product. The excavation area underwent a series of tests, including assigning a Waste Acceptance Criteria (WAC) classification and the creation of an excavation plan, also known as a dig plan. Further information on the function of a dig plan is provided in Sect. 4.6. This classification informed discussions with the Local Authority for possible re-use of the material in the FRS and in planning for off-site disposal/recovery at an authorised waste facility if re-use was not feasible.

The contractual testing regime was undertaken to identify potential routes for appropriate material disposal. The testing involved intrusive investigation techniques and sample collection by a specialist contractor according to best practice standards and guidance, including WAC, to classify the soil as Inert, Non-Hazardous or Hazardous for off-site re-use, disposal or recovery at an appropriate authorised waste facility. This contractual testing regime did not satisfy the geotechnical requirements to meet material suitability on an FRS. Instructions in the contract would have been required to meet the FRS specific testing requirements, which would have impacted the project programme.

As part of investigating the re-use of the Soil and Stone through a by-product notification to the EPA. It became apparent that there was a gap between the material excavation schedule and the proposed recipient being ready to receive. Stockpiling of this material off-site would, therefore, have become a requirement, which raised the question of how to classify the material for transport in the intervening period while waiting on the determination by the EPA. The material would have to be transported as a by-product material, but that brings risk to all parties because if the EPA disagrees with the assumption that it meets by-product requirements, then the material would have to be disposed of after it has been subjected to interim storage charges.

In addition to the misalignment between the testing regime, availability of the material and classification for transport, further challenges were identified. Interim storage would necessitate obtaining the appropriate permissions and licences to accommodate the holding of by-product material. Furthermore, the planning approval process was not in place for the FRS, so it would be incorrect to say the future use of the material is certain.

By-product: Bedrock

A by-product application was also considered for bedrock material excavated for the basement void, but the application did not progress. Despite the bedrock material being suitable for road projects, many existing road projects in Ireland under the Local Authorities’ remit accept only ‘finished products’. In this context, ‘finished products’ mean aggregate that is ready to use in its final application instead of arriving at its intended use site and requiring mechanical resizing through crushing and screening. In order to realise this opportunity, the bedrock excavated for the basement void must be crushed to a smaller size before shipping from Opera Square. The tender document and project contract did not place a requirement on the Contractor to crush and stockpile material onsite and therefore the programme delays which would have emanated out of crushing and stockpiling onsite were not accounted for within the project costs and programme and could have potentially increased costs. If the rock had to be resized before shipping, operating a mobile crusher on the Opera Square site to crush the bedrock would require authorisation through the planning process. The environmental impact of a mobile crusher must be considered at the project’s planning stage, included in the tender development stage and inserted into the project contract documents. These considerations underscore the complexity of managing excavated materials, which must be considered as early as possible in a project lifecycle for a successful outcome if a by-product determination is sought.

Ultimately, the commencement of discussions was too late for both by-product opportunities (soil, stone and bedrock) to start, as the material needed to be removed from the Opera Square site to protect the project programme. Had these opportunities been explored during the planning, design and tender development stage and therefore included within the project contract documents there would have been an increased likelihood that the facilitation of a by-product process could have been accommodated to include facilitating a by-product notification and response time from the EPA.

An early assessment of the cost benefit at project planning stage would have allowed time to identify further uses of the materials and permit additional work to be costed appropriately and time allocated in the project schedule. The absence of cost benefit analysis for these materials in the earlier stages of the project was a factor in not achieving these opportunities and is a valuable lesson which can be applied in future projects.

It should be noted that Local Authority guidance on the re-use of materials on road projects was interpreted differently by two consultants with respect to the requirements for crushing on-site or off-site. This suggests that the existing guidance could be improved to provide clear criteria for assessing re-use material.

Another barrier to the re-use of bedrock on Opera Square was the timeline for processing a by-product application. Specified timelines for processing applications would allow project programming to be developed, providing opportunities for re-use without a project delivery schedule.

End-of-waste on Opera Square

The EPA grant single-case decisions on the application of the end-of-waste regulation in accordance with Regulation 28(3) of the European Union (Waste Directive) Regulations 2011. An application to the EPA and the criteria set within the response is applicable to the producer, either an individual organisation or group to which the decision applies.

In the demolition and enabling phase (Contract A),15,003 tonnes of concrete, brick and concrete blocks were crushed and graded to 6F2 classification [49] and spread throughout the top 600 mm of the full area of the site as a piling mat to support piling rig enabling downstream Contract B works (Fig. 12). After the piling work was completed, the project moved on to the next phase, involving a bulk excavation for a basement void.

Fig. 12

Piling rig on mat

Prior to commencement of the bulk excavation, the excavation area underwent a series of tests, as described in 4.5.1 including a Waste Acceptance Criteria (WAC) of soil and stone originating from Opera Square. The classification led to the creation of a dig plan (Fig. 13).

Fig. 13

Dig Plan (Extract)

A dig plan is a site map with grid references corresponding to a grading indicated by colour as described in the soil classification report including the type of landfill which is suitable for accepting the material: an inert landfill, a non-hazardous landfill, or a hazardous waste landfill, in accordance with EPA guidance [50].

On Opera Square a total of 4,524 tonnes of non-hazardous material was identified as suitable as an end-of-waste material. In order to realise this opportunity, the construction team identified an environmental company (ENVA Ireland Ltd.), as holding a single case decision from the EPA to produce recycled aggregate from crushed concrete. The EPA provided the single case decision in accordance with Regulation 28(3) of the European Union (Waste Directive) Regulations 2011, which states that the recycled aggregate, subject to the application made by ENVA Ireland Limited on 3rd February 2021 and produced at an appropriately authorised waste facility, will cease to be waste if it complies with the end-of-waste criteria for the production of recycled aggregate by ENVA Ireland Limited.

Through the end-of-waste process the material was excavated from the 600 mm piling mat layer and relocated to various sites in Limerick County. The material was utilised in two key projects:

• the Foynes freight rail line works, where it served as a base layer for a construction compound,

• and a local sports club that used it for a car park upgrade.

The successful re-use of this material has minimised the need for virgin resources, demonstrating just one of the examples of resource efficiency benefits that emerged from circular interventions in the Opera Square project.

In this case, the material has thus far had three life cycles, first as a building, then as a piling mat and now as a base layer for a construction compound and a local sports club car park upgrade. As a lesson learned, there may have been ways to optimise recovery and re-use of this material on Opera Square and in future projects, if a protective layer or geo-membrane had been installed to separate the crushed material from the soil to promote higher recovery rates.

Results

Pre-demolition Audit

The data on materials recorded in the pre-demolition audit and the actual values recorded in the project’s waste tracking software, Smart Waste, during the demolition and enabling phase (Contract A) are presented in Table 1. Smart Waste is a web-based platform, and it is utilised for quantifying, reporting and managing construction site waste. Smart Waste relies on the manual user input of data and therefore does not operate in real-time. Not all material categories identified at the pre-demolition audit were segregated during the demolition and site clearance works, leading to their classification as General waste in Smart Waste.

Table 1 Estimated and actual materials quantities from demolition and enabling phase (Contract A) in tonnes (t)

Re-Use of Material on Opera Square

The project’s performance specification for waste management during the demolition and enabling phase required the contractor to divert at least 75% of demolition construction waste from landfill. It is evident that this target was successfully achieved.

The crushing and re-use of the crushed material in the construction of the piling mat alone represents a recovery rate of 87% of the overall material generated. Additionally, the off-site direct re-use of materials from the Opera Square project fostered local community development and social sustainability by directing the benefits of material re-use to the community by providing raw material stone to a local stone mason training scheme. The direct re-use of the material helped address social challenges by providing opportunities for skill development and community empowerment. The direct re-use of the stone across wall building projects in Limerick City and County is an example of circularity in motion and a break from a linear use of resources (Sect. 4.4.1).

The overall project percentage of material diverted from landfill rises to 98% when re-used material, recycled and recovered material on the project is considered, as described in Table 1. The diversion from landfill of such significant quantities of construction and demolition waste is one of the key achievements of this project.

Life Cycle Assessment of On-site Re-use

Life Cycle Assessment (LCA) is the compilation and evaluation of the inputs, outputs and potential environmental impacts of a product or system throughout its life cycle [51]. LCA accounts for material, energy and waste flows associated with a product or process over its entire life cycle. LCA is one of the best-known tools for assessing the environmental impact of construction activities.

The approach to the assessment covers all stages of the building life cycle. It is based on data obtained from information modules in Environmental Product Declarations (EPD) and other information necessary (e.g. material quantity) for carrying out the assessment [52]. An EPD, is a document that transparently reports the environmental impact of a product or material, based on LCA.

LCA quantifies the inputs and resulting environmental impacts at each process step, providing meaningful data to determine if an alternative product or process has less environmental impact.

Environmental impact is assessed by assigning known emissions or multiplying emission factor rates to each input to a process. Emission factors are available from various sources such as EPDs, government agencies and published research.

The basic principles of the LCA methodology for evaluating GHG emissions throughout a building’s life cycle are described in the following standards:

• ISO 14040 Principles and Framework for Life Cycle Assessment.

• ISO 14044 Requirements and Guidelines for Life Cycle Assessment.

• ISO 14067 Greenhouse gases — Carbon footprint of products — Requirements and guidelines for quantification.

• ISO 14025 Environmental labels and declarations — Type III environmental declarations — Principles and procedures.

• ISO 21929-1 Core Indicators for Assessing Sustainability Performance of Buildings related to design, construction, operation, maintenance, refurbishment and end of life.

In Europe, the European Committee for Standardisation (CEN) Technical Committee CEN/TC 350 was established under a mandate from the European Commission to provide a method for voluntarily delivering environmental information for construction. CEN/TC 350 promotes a standardised approach for EPD schemes in Europe, ensuring that comparable environmental information is generated and used without creating trade barriers for member states of the EU.

Since its inception in 2004, CEN/TC 350 has developed a suite of European Standards covering the assessment of sustainability for construction products, buildings and the wider built environment, including:

• ISO EN 15978:2011 Sustainability of Construction Works — Assessment of Environmental Performance of Buildings (Calculation Method).

• ISO EN 15804 Sustainability of Construction Works — Environmental Product Declarations.

The ISO EN 15978:2011 standard models all elements of a building across its entire lifecycle. The methodology outlined in the standard breaks down the lifecycle of a building into its stages and corresponding modules (Fig. 14).

Fig. 14

ISO EN 15978:2011, Life cycle stages [53]

The purpose of the LCA in this research is to calculate the embodied carbon in GWP saved through the re-use of materials in the demolition and enabling phase (Contract A) as measured in kgCO₂eq., across the A1 to A5 modules (Fig. 14), encompassing Cradle to Practical Completion of the piling mat on the Opera Square project.

The LCA boundary is modules A1 to A5, this incorporates the product stage modules A1 to A3 and the construction process modules A4 and A5, as defined in ISO EN 15978:2011 [54] and illustrated in Fig. 14. These boundaries have been deliberately chosen, as the piling mat is made from aggregate, a construction product; and therefore, it is necessary to include both the Product and Construction Process phases.

The boundary for Modules A1 to A3 addresses the Cradle to Gate processes related to the materials and services used in construction. The A4 to A5 Construction Process stage accounts for the processes from the factory gate of various construction products to the Practical Completion of the construction work on the piling mat.

The following analysis does not account for the embodied carbon emissions from removing the crushed material off-site and subsequent embodied carbon emissions in other projects. However, it is noteworthy that in the case of the Opera Square project, the piling mat material has moved from Opera Square for re-use as a base layer for a construction compound on a different project and a local sports club car park upgrade. The material has thus far had three life cycles, first as a building and as a piling mat on the Opera project and subsequently re-used as a base layer. The scope of this research paper does not look at future movements of the material post their use in the piling mat.

The output from the LCA in this project will determine the reduction in embodied carbon in a comparative study between the Opera Square project’s re-use strategy and a traditional business-as-usual approach in constructing the project’s piling mat. The Opera Square project’s re-use strategy reflects actual events on-site. The calculation for embodied carbon is based on the demolition and crushing of 15,003 tonnes of material on site, spread evenly over the entire site of 10,800 m² to create a piling mat 600 mm deep. The LCA for the business-as-usual approach accounts for the embodied carbon of the same mass of virgin material (15,003 tonnes) in constructing the project’s piling mat.

The on-site re-use of 87% of the demolition material on the project was a significant achievement and consisted of 15,003 tonnes of demolition material crushed and re-used on site in the piling mat out of the total 17,248 tonnes tracked through Smart Waste, as described in Table 1.

The Opera Square project’s re-use strategy is beneficial and different to a traditional business-as-usual approach where virgin material would have been brought to the site for the piling mat. The on-site re-use of the demolition material in the piling mat meant that new virgin materials were not required for the piling mat. Considering that the piling mat is 600 mm deep over the entire site of 10,800 m²; this equates to approximately 6,480 m³ of material. Given that a standard truck for excavated material removal holds circa 8 m³, this would have resulted in approximately 810 truckloads of material that did not need to be hauled to or from the Opera Square site and illustrates the societal, environmental and economic benefits that arose from circular interventions on the Opera Square project with approximately 1,620 truck movements avoided through Limerick City and Environs.

LCA of Opera Square project’s Re-use Strategy

In the demolition and enabling phase (Contract A), the twentieth-century buildings and later additions to the rear of existing heritage structures were demolished and crushed on-site utilising excavators with mechanical shears and crushing plant and equipment. It is common for excavators and crushers to monitor and record their usage hours and fuel consumption. Clients can use this data retrospectively for environmental reporting or to support decisions that may have an environmental aspect or allow more accurate estimation of future cost, consumption and emissions from similar work. Unfortunately, on Opera Square, fuel (diesel) consumption is unavailable for the demolition and crushing works. A key lesson learned from this process is the value of having fuel consumption data available and in a form that can be reviewed as required during the life of future projects.

To obtain fuel consumption figures for this research comparable to the demolition and crushing activities at the Opera Square project, generic Irish data [55] is used in the LCA, derived from an EPD for a similar process for producing a precast concrete wall in Ireland. The results presented in the EPD are based on a weighted average of the concrete mixes and steel reinforcement used in their wall product as manufactured by Moore Concrete in 2021 [56]. The scope of the EPD incorporates the product stage modules A1 to A3 Cradle to Gate and Module C1 De-construction and Demolition within the End of Life stage.

In the Opera Square project’s re-use strategy, all material originated on site and therefore A4 Transport module was not applicable. Additionally, the A5 Construction Installation Process module for the piling mat has been excluded from both LCAs since the same construction installation process would likely have occurred in both Opera Square project’s re-use strategy and a business-as-usual approach.

The EPD states that for Module C1, the precast concrete structure was assumed to be demolished and crushed on the site where it was installed. The EPD provides fuel consumption data indicating that 3.6 L of diesel are consumed per m³ of concrete during the demolition process and 0.22 L of diesel per m³ during the crushing process, which operates at a capacity of 300 tonnes per hour, as described in the EPD.

The fuel data from the EPD is used to estimate emissions from the Opera Square project’s demolition and crushing processes. While making these assumptions, it is essential to note that actual data is irreplaceable. Although the crushing process may be comparable, the equipment, capacities, productivity, processing methods and other factors can vary significantly. Additionally, sorting, demolishing and processing large, reinforced concrete components in situ and on the ground add further complexity. It is a challenge to calculate post works an accurate fuel consumption rate per m³ during demolition as each project presents unique considerations such as building type, structural components, site conditions, equipment and site logistics.

The emissions for demolition were also estimated using the guidance published by the Royal Institution of Chartered Surveyors (RICS) in relation to whole life carbon assessment [57]. The carbon emissions factor for demolition in the RICS guidance is based on monitored case studies in central London. The RICS carbon emission factor for demolition is 3.4 kgCO2e/m2 of Gross Internal Floor Area (GIFA). It represents carbon emissions from on-site deconstruction and demolition activities, including energy consumption for site accommodation and plant use. This carbon emissions factor was multiplied by the GIFA of the demolished structures and was used to provide an estimated figure of embodied carbon in GWP in the demolition process.

The Opera Square project’s re-use strategy, for the demolition and enabling phase (Contract A) implemented an approach that utilised aggregate sourced from the crushing of on-site materials in the construction of the piling mat. Table 2 presents the modules forming the LCA for the Opera Square project’s re-use strategy in the construction of the piling mat.

Table 2 LCA modules in Opera square project’s re-use strategy

The mass of material as recorded in Smart Waste and displayed in Table 1 in the Concrete and Blocks material category is 15,003 tonnes (1 tonne = 1,000 kg) of crushed material.

Using the density of reinforced concrete, which is 2,500 kg/m³, as the average density of the crushed material, leads to an estimated total volume of 6,001 m³ of crushed material. The emission factor for diesel consumed in heavy goods vehicles (HGVs) is 2.68 kgCO₂eq/litre of diesel, as outlined in Table 4C of Annex 4 of Ireland’s National Inventory Report [58].

Table 3 Module A3 Opera square project’s re-use strategy

The embodied carbon in GWP from diesel consumption for the Opera Square project’s re-use strategy during the demolition of the buildings, which generated 15,003 tonnes of material, are estimated to be 61,436 kgCO2eq. which is thereby attributable to creating the aggregate used in the construction of the piling mat. It is important to note that this embodied carbon in GWP estimate for the demolition may vary based on the actual machinery used and construction practices. Access to actual fuel consumption data would enhance the accuracy of this analysis. An estimate of the demolition emissions based on the RICS carbon emissions factor was also calculated to create two estimates of the emissions in the Opera Square project’s re-use strategy.

The RICS carbon emissions factor for demolition for module C1 is 3.4 kgCO₂eq/m² of GIFA. For Project Opera, a demolition GIFA of 9,985 m² was estimated from planning stage drawings. These buildings are the source of the 15,003 tonnes of material for the aggregate used in the construction of the piling mat. Consequently, it is estimated that the resulting embodied carbon in GWP of 33,948 kgCO₂eq., is generated for demolition of the buildings, which is thereby attributable to creating the aggregate used in the construction of the piling mat.

Utilising two different sources to estimate the embodied carbon in GWP attributable to the demolition and crushing process creates a range of values in GWP for the re-use strategy on the Opera Square project, as presented in Table 4. The calculated embodied carbon in GWP from the demolition and crushing process will vary based on the sources used. The calculated embodied carbon in GWP from the Opera Square project’s demolition and crushing processes based on the fuel data emissions based on the EPD amount to 61,436 kgCO₂eq, while the RICS carbon factor yields a figure of 33,948 kgCO₂eq., in constructing the piling mat.

Table 4 Estimate of embodied carbon in GWP Opera square project for demolition phase

The differences in the embodied carbon in GWP from the Opera Square project’s demolition and crushing processes may be attributable to several factors. The RICS guide notes that its carbon factor is based on monitored case studies in central London without specifying details about the construction materials used. In contrast, the fuel data emissions from the EPD are based on reinforced concrete.

In addition to the inherent differences in material properties, accurately estimating the extent of the demolition area is challenging due to the presence of various rubble walls and differing densities in the materials on the original Opera site, which are not available in the planning stage drawings which helps explain the discrepancy between the two estimates of the emissions for the demolition phase of the project. Therefore, the author has chosen to report a range of embodied carbon GWP for constructing the piling mat in the Opera Square project’s re-use strategy.

LCA of Business-as-usual Approach Strategy

The LCA for the business-as-usual approach considers the embodied carbon associated with 15,003 tonnes of virgin material in constructing the piling mat. It also includes the A4 transport emissions from truck movements that transport this material to Opera Square. In addition to the embodied carbon emissions attributable to utilising virgin material, the emissions resulting from demolition and crushing activities, as well as the transport of excavated materials off-site, are also included in the total embodied carbon GWP for business-as-usual. These emissions are considered enabling work necessary to prepare the site for constructing the piling mat. They are included in determining the total emissions associated with the business-as-usual approach. The emissions from enabling work are limited to those related to demolition, crushing and transporting excavated material off-site. This study does not examine the future movements of the (virgin) material after its use in the piling mat.

In the LCA for the business-as-usual approach, the average value of GWP as measured in kgCO₂eq., for the Product Stage (Fig. 14), which includes Modules A1 to A3, are taken from Ireland’s National Inventory of Generic Construction Materials Database [59]:

• Aggregate: Average A1 to A3, GWP 0.005 kgCO₂eq./kg

The National Inventory of Generic Construction Materials Database was developed to provide an understanding of the environmental impacts associated with various building materials used in construction. This inventory aims to serve as a resource for estimating the carbon emissions produced during the manufacturing processes of common materials such as concrete, brick, steel, concrete blocks, insulation, slate, stone, windows, doors, plasterboard and flooring. To create this inventory, the IGBC commissioned Cambridge Architectural Research (CAR), a team of life cycle assessment specialists.

CAR conducted a comprehensive review of the Irish market for building materials to assess the carbon emissions linked to their production [60]. Environmental data was gathered for each material and weighted averages for their carbon impacts, resulting in a detailed report and database mentioned above. The report and database are available for public access on the IGBC website [61]. For materials not directly researched by CAR, the inventory incorporates data from the Inventory of Carbon and Energy (ICE) Database [62]. ICE is a credible source that provides generic carbon information based on EPDs and is hosted by the University of Bath. The inventory is a valuable tool for professionals in the early stages of building design.

In the business-as-usual approach, transportation emissions would be generated from removing excavated material to a landfill, which is assumed to be located 20 km away from Opera Square site. Additionally, transport emissions would also come from delivering virgin aggregate to form the piling method. The construction team for the Opera Square project has confirmed that, under normal operations, virgin aggregates in a business-as-usual approach would be transported to the site from a quarry located 9 km away. On-site observations by the author indicate that the most common type of transportation for materials on the Opera Square project, both on-site and off-site, was a rigid tipper truck, similar to the Scania model with 450–550 horsepower, as illustrated in Fig. 15. These trucks are equipped with Euro 6 standard engines and have a load capacity ranging from 16 to 32 tonnes. Figure 15 is a snapshot from the Opera Square site and shows the type of rigid tipper truck in question.

Fig. 15

Rigid tipper trucks operating on the Opera Square site

The Institute of Structural Engineers guidance document [63] provides the following emission factor for A4 Transport module:

• Average laden truck emissions in the UK: 0.0001074 kgCO2eq/kg/km.

An additional source of data for the transport emissions in the LCA of the business-as-usual approach strategy for A4 Transport module is the INDICATE methodology database, which was developed as part of the INDICATE project. The INDICATE project is a research collaboration involving various organisations in Ireland and international experts [64]. The aim of the collaboration is to create a national database of projects in Ireland, Spain and Czechia. It uses a transparent tool to ensure data completeness and accuracy. This methodology establishes baseline data for buildings, allowing policymakers to set carbon limits based on a full lifecycle assessment.

The database provides the following emission factor for A4 Transport module:

• Average laden truck emissions: 0.0001065 kgCO2eq/kg/km.

In this paper, an average of the two figures is adopted for the business-as-usual LCA:

• A4 Transport module business-as-usual LCA: 0.0001069 kgCO2eq/kg/km.

Table 5 presents the A4 Transport module emissions, including the embodied carbon in GWP for transporting the equivalent mass of virgin material required to construct the piling mat at Opera Square, as well as the removal of the demolished material to a landfill (assumed to be 20 km away). The inclusion of emissions associated with transporting excavated materials ensures accuracy in determining business-as-usual emissions, as these emissions must be considered as enabling the construction of the piling mat.

Table 5 Module A4 embodied carbon in GWP for transport

Table 6 Business-as-usual approach LCA modules in the construction of the piling mat

Table 7 Modules A1, A2, A3 and A4 embodied carbon in GWP for business-as-usual approach in the construction of the piling mat

The business-as-usual approach in constructing the piling mat using virgin aggregate sourced from a local quarry would have led to an embodied carbon in GWP of 121,525 kgCO2eq. The embodied carbon produced during the demolition and crushing processes are summarised in Table 4. The overall embodied carbon in GWP for the business-as-usual approach is presented in Table 8.

Table 8 Total embodied carbon in GWP for business-as-usual

The embodied carbon in GWP for the Opera Square project’s re-use strategy in the construction of the piling mat is estimated to be in the range of 155,473 kgCO2eq., to 182,961 kgCO2eq., depending on whether the fuel data or RICS guidance is used in calculating the emissions from the crushing and demolition process.

Table 9 presents the estimated range in embodied carbon for the Opera Square project’s re-use strategy and for the business-as-usual case. This shows that adopting a re-use strategy can lead to estimated savings of 66–77% in embodied carbon in GWP compared to a traditional business-as-usual approach.

Table 9 Range in reduction of embodied carbon in GWP in constructing the piling mat

The reduction does not include the embodied carbon offset which results from using the material as a base layer for a construction compound on a different project and a local sports club car park upgrade. This aspect falls outside the scope of the LCA boundary for this research project. However, the re-use of the material will have additional positive environmental impacts on those projects due to the circular interventions implemented in the Opera Square project. It is worth noting that the demolition material moved forward from Opera Square has thus far undergone three life cycles: initially as a building, as a piling mat on Opera Square project, and subsequently as a base layer for a construction compound and a local sports club car park upgrade.

To put the estimated savings from the Opera Square project into context, a reduction of 121,525 kgCO2eq is equivalent to:

• approximately 110 economy flights from London to New York by one person;

• or approximately 50 people, to stop driving their car for one year in Ireland;

• or the carbon sequestered by 86 acres of forests in Ireland in one year.

Discussion and Conclusion

This research paper aimed to conduct a case study on the Opera Square project located in Limerick, Ireland, evaluating the circular economy interventions implemented during the demolition and enabling phase of the project. This research provides an evidence-based case study to allow the LTT DAC organisation and the construction sector to benchmark the Opera Square development and future projects by providing numerical results. The output from the LCA in this project has determined the reduction in embodied carbon in a comparative study between the Opera Square project’s re-use strategy and a traditional business-as-usual approach. The direct comparison of this work with existing literature is difficult, as there are few case studies published on CE interventions during demolition in the construction sector.

The Opera Square project achieved a diversion rate of 98% of construction and demolition waste from landfills through recycling materials and the on-site and off-site re-use of construction materials. Additionally, the project achieved an estimated reduction in embodied carbon emissions of 121,525 kgCO₂eq. This was accomplished by implementing a re-use strategy to form the project piling mat, utilising materials available on-site during the demolition and enabling phases of the project. The results of this research will support data-driven decision-making in assessing future construction methodologies and their environmental impact. Future work should include a cost-benefit analysis of each strategy.

A limitation of this research was the availability of data for estimating the emissions from the demolition and crushing process. It should be noted that to achieve a fully circular economy, collaboration is required and therefore, goal setting at the earliest stage is key. These goals should include a requirement to report regularly on the greenhouse gas emissions associated with onsite activities across the full life cycle of the project. It is vital that that data, if available, is shared with clients at the earliest opportunity and a key lesson learned from this process is to ensure this data is available and in a form that can be reviewed if required. In this research, to obtain fuel consumption figures comparable to the demolition and crushing activities at the Opera Square project, generic Irish data was used in the LCA, derived from an EPD for a similar process for producing a precast concrete wall in Ireland. Further research should follow where fuel consumption measured in real-time for demolishing and crushing in a similar process can be compared to the values in this research paper.

It is advised that the earlier circular opportunities and interventions are considered, the greater their potential impact and ease of implementation. If a client, advised by a project team, formulates their ambitions and objectives at the start of the planning and tender development stage, the chance that they will be considered in the design development and implementation stages increases. The CE strategy should be guided by a client’s sustainability strategy, market forces and benefit analysis.

The diversion of such significant quantities of construction and demolition waste (98%) from landfills is one of the key achievements of this project. The implications of the data will enable LTT DAC to benchmark against other projects and Construction and Demolition Waste Statistics for Ireland, as published by the Environmental Protection Agency.

The opportunity to utilise bedrock from the basement void as a by-product for large civil engineering projects encountered significant challenges because the testing regime, material specifications, and standards related to the intended use of excavated materials were not known early in the project. It is essential to fully understand the testing regime, material specifications and regulations related to the intended use of excavated materials early in a project. This involves planning sufficient time for testing and separating materials from a building so that they can be reused in their entirety in the most appropriate application.

There is a long-established approach in Ireland to accepting only ‘finished products’ on road projects. While outside the remit of this research, Local Authorities in Ireland must review their ‘finished products’ approach as it does not align with the government approach to facilitating circular economy principles. Road projects by their nature go through a lengthy planning process thus allowing time for the management of imported excavated materials in any form.

On the Opera Square project, the commencement of discussions was too late for both by-product opportunities (soil, stone and bedrock) to start, as the material was already being removed from the Opera Square site. Investigating these opportunities should have commenced during the planning and tender development stage and inserted into the project contract documents to allow the scope to include facilitating a by-product notification and response time from the EPA. Earlier project planning would also have allowed time to identify further uses of the materials and permit additional work to be costed appropriately and time allocated in the project schedule.

It is important to note that CE practices have other far-reaching impacts. The reduced environmental impact of truck movements should not be overlooked. Increased truck traffic in urban areas impacts local traffic patterns and congestion, particularly during peak hours. Reducing truck movements creates a safer environment for pedestrians, cyclists and other road users. Noise pollution is another important factor related to truck movements. The sound of trucks, especially during early morning or late-night hours, can be disruptive to nearby residents and businesses. This can lead to complaints from the local community. Trucks are typically a significant source of greenhouse gas emissions and air pollutants in urban settings. Increasing the frequency of truck movements can exacerbate these issues. Implementing a re-use strategy for managing materials reduced the need for truck movements of new materials for the Opera Square project in Limerick city.

The demolition material, in this case, has moved forward from Opera Square. The material has thus far had three life cycles, first as a building, then as a piling mat and now as a base layer for a construction compound and a local sports club car park upgrade. The offset carbon in kgCO₂eq., through the subsequent use as a base layer in the construction compound and car park has not been accounted for within the LCA boundary for this research project but will have additional positive environmental impacts on those projects. Therefore, the reduction in GWP due to the re-use of construction products on the Opera Development is underestimated.

Additional Lessons learned from this project include:

• If selective demolition is a client requirement to enable recovery of materials the client must appropriately include it in contract documentation when CE principles are a client expectation of a demolition project.

• Including circular requirements, practices and principles in contract documentation at the concept stage can lead to a significant reduction in the environmental impact of the construction process.

• The pre-demolition audit process is the best tool for establishing effective material recovery strategies and options. This output from the pre-demolition audit should occur in the early planning stage to integrate material recovery and re-use considerations into scope and project contract documents.

• Integrating material recovery and re-use considerations into project contract documents ensures the opportunity is provided to cost and schedule the works required to realise the opportunities.

• Setting clearly defined definitions and targets linked to KPIs for material re-use within a project is important to promote accountability in material recovery.

• The establishment of separate recovery targets for each waste stream will enhance environmental outcomes.

• Early collaboration at the concept stage among stakeholders, contractors, clients and waste consultants is integral to the success of the waste management process.

• The methodology for resource and waste characterisation, continuous communication and a transparent waste-tracking approach are crucial for maintaining efficiency and managing costs.

• In the Irish context, it is important to integrate end waste and by-product requirements from the tender development stage into scope and project contract documents. In addition, the time required for an EPA determination must be considered in future discussions regarding by-product determination to avoid impacts on project schedules.

• Ultimately, well-prepared scope and project contract documents that address material re-use will enhance a project's execution and environmental outcomes.

Future Work

There is further opportunity to study the social and community aspects of implementing CE principles in practice. Additionally cost benefit analysis is important when making the case for CE interventions and should be at the forefront of further research. Further work should include a cost-benefit analysis of each strategy and overall re-use strategies, including retention of older structures versus new builds incorporating scoring factors that adequately represent cost and heritage value of buildings.

Future work to be undertaken as part of the CE-CON project includes contract analysis for different phases of the Opera project, and a survey of project stakeholders.

As previously stated, the generation of demonstrator briefs and industry guidance factsheets that will guide future LTT DAC projects and the broader construction sector will be a key output from the CE-CON research project. Further lifecycle analysis may be carried out to track the secondary and subsequent future re-use of the material, primarily from the piling mat.