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Acknowledgement I would like to express my heartfelt gratitude to everyone who played a pivotal role in the successful completion of my thesis study. Your support, guidance, and encouragement have been invaluable throughout this journey. First and foremost, I want to extend my deepest appreciation to my thesis advisor, Dr. Mehrdad Borna. Your expertise, dedication, and unwavering support were instrumental in shaping this research, and I am truly grateful for your mentorship. I would also like to acknowledge Dr. Rosa Schiano-Phan, our esteemed course leader, for her guidance and inspiration throughout my academic endeavours. I am deeply thankful to Kartikeya Rajput and Amedeo Scofone for their continuous support and insightful discussions. Your contributions significantly enhanced the quality of my work. My sincere gratitude extends to the collaborating body of Westminster City Council and the Urban Lab program within Westminster City Council for their invaluable resources and cooperation. I am indebted to Hrabrina Nikolova, Eleanor Grace, and Klaudija Alasauskaite for their guidance and collaboration throughout my research journey. I would like to extend my appreciation to Katie Sims from Erith Contractors for providing invaluable insights into the site, which greatly contributed to the practical aspect of my study. I am grateful to Luke Taylor at RMS Limited for sharing valuable information about RCA processing, which added depth and relevance to my research. Special thanks to Anna Riley from Xeroc for her assistance in exploring innovative solutions for sustainability. Your expertise and ideas were instrumental in shaping the sustainability aspects of my thesis. To everyone mentioned here and to those who have supported me in countless other ways, I extend my heartfelt thanks. Your contributions have made a significant impact on my academic and personal growth, and I am deeply grateful for your presence in my journey.

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Introduction A. Background and Context 1. Definition of circular economy 2. Importance of circular economy principles in sustainable development B. Rationale for the study- Potential of recycled concrete aggregates (RCAs) for circular concrete production C. Research Objective Literature Review A. Circular Economy and Concrete Production 1. Circular economy principles applied to construction sector B. Recycled Concrete Aggregates (RCAs) 1. Definition and characteristics of RCAs 2. Source and Originality of RCA 3. Benefits of using recycled materials in concrete production C. Life Cycle Analysis (LCA) in Construction 1. Explanation of LCA methodology 2. LCA of Concrete 3. LCA application in evaluating environmental impacts of concrete production D. Environmental Product Declarations Challenges in reusing 100% RCAs in new concrete structures A. Technical challenges 1. Effect of RCAs on concrete production and structural performance 2. Strategies to address potential technical limitations B. Recycling construction and demolition waste and quality control of RCA 1. Variability in RCA properties and quality 2. Need for standardized guidelines and quality control measures Opportunities offered by 100% RCA concrete production A. Reduction in environmental impact Methodology A. LCA Framework 1. Life cycle analysis- an ideal scenario B. Case study design 1. Selection of building for the case study 2. Description of RMS concrete, waste treatment facilities 3. Innovation Discussion A. Life cycle impacts- Concrete mix composition B. Life cycle analysis- an ideal scenario C. Transportation of the site debris: Potential sites of RCA D. Discussions with different stakeholders in circular economy loop E. Possibilities of Recycling Conclusion A. Summary of findings 1. Recap of challenges in reusing 100% RCAs in new concrete structures 2. Highlights from the LCA results and environmental assessment B. Implications and Recommendations 1. Implications for the construction industry and circular economy adoption 2. Recommendations for future research and policy development Table of Figures Appendix References

Abstract The UK construction industry is expanding and so is the need for construction materials. Along with the rise in the need for construction materials there is a parallel increase in the amount of construction and demolition waste being generated. Furthermore, as cities get urbanised, the old buildings remain vacant and underutilised and are many a times demolished. This adds to the increase in the construction and demolition waste. The concrete aggregates form an integral part of the waste that can be recycled and reused to reduce the carbon impact of construction with the help of principles of circular economy. Use of recycled concrete aggregates is both environmentally and economically beneficial. However, there exists a significant gap in the use of recycled concrete aggregates practically. This paper sought out to identify the major challenges in using recycled concrete aggregates. It identifies the major problems encountered in using 100% recycled concrete aggregates. By using software tools like One Click LCA and by studying different EPDs carbon impacts of RCA and other properties are studies. Upon visiting a demolition site and interacting with various stakeholders and people from the business, an understanding of the lack of awareness, collaboration and coordination is realised. Further, upon exploring innovative solutions with different startup ventures ways to overcome the problems encountered for using 100% recycled concrete aggregate are developed to make RCA more efficient and sustainable.

I. Introduction A. Background and Context 1. Definition of circular economy “The key challenge now is to...reduce reliance on incineration by delivering a step-change in recycling, re-use and waste prevention. This will need the Government to implement, and go beyond, its planned waste management reforms…” -

2022 Report to Parliament: Progress in reducing emissions (Climate Change Committee, 29 June 2022)

The construction industry is progressively transitioning towards a circular economy by reducing waste, reusing building materials, and implementing regenerative approaches for energy generation and biodiversity preservation. Circular practices have multifaceted implications for construction operations, necessitating a comprehensive evaluation of their effects. Environmental assessments of circular solutions are commonly conducted using various life cycle-based impact evaluations (Sparrevik et al., 2021). The concept of a "circular economy" (CE) pertains to an economic framework centred on business models that minimize, reuse, recycle, and recover materials throughout the production, distribution, and consumption processes. It has emerged as an innovative solution aimed at mitigating environmental harm and fostering economic growth within the construction sector to support sustainable development (Purchase et al., 2022). This approach replaces the conventional "end-of-life" concept, which denotes a stage where products no longer receive ongoing support. Consequently, it advocates for reduced overall waste generation and disposal throughout raw material acquisition and production. CE fundamentally shifts the perception of construction waste from a challenge to be managed and disposed of to a resource with utilization potential. Its adoption is seen as a means to concurrently reduce environmental impacts and stimulate economic expansion. The origin of the circular economy concept can be traced back to Kenneth Boulding's 1966 book, "The Economics of the Coming Spaceship," although it was not explicitly termed as such. The Earth is often regarded as the embodiment of the circular economy concept. Walter Stahel and Genevieve Reday introduced the notion of a circular economy in their 1976 research report to the European Commission, "The Potential for Substituting Manpower for Energy," which analysed building and automobile manufacturing from both micro and macroeconomic perspectives. Over time, there has been increasing recognition of the circular economy concept by academia, government bodies, and organizations. Internationally, countries such as Germany, Japan, China, and Europe have enacted legislation to implement circular economy principles(Ginga et al., 2020). In the construction and demolition sector, the circular economy system encompasses five key stages: preconstruction, construction, building renovation, collection and distribution, end-of-life, and material recovery and manufacturing. (Ginga et al., 2020) The CE is made up of a revolutionary reformative framework that aids in optimising raw material usage and ensuring the value of materials throughout their lifecycle. Furthermore, CE reduces the formation of superfluous garbage, hence conserving natural resources. The CE method essentially indicates that everything manufactured can be recycled, reprocessed, or reused. In general, the CE strives to add value to materials that are traditionally disposed into landfill and make them usable for the building firm or other activities within the construction sector. (Purchase et al., 2022)

Figure 1 Circular Economy

2. Importance of circular economy principles in sustainable development As the world continues to advance in urban infrastructure development, the concept of sustainability has gained significant attention and importance due to the growing concerns about increased pollution and adverse environmental consequences. Sustainability holds paramount significance in any construction project, as it offers both economic and environmental advantages. Therefore, a fundamental definition of sustainable development revolves around ensuring that a project meets the present generation's needs without compromising the requirements of future generations. Sustainability principles are built upon three core pillars: the environment, society, and economic viability. In the global context, ecological and environmental considerations are of utmost importance, while development must align with societal needs to maximize economic gains within the constraints of limited resources. Sustainable development concepts aim to achieve development that is ecologically sound, socially equitable, and economically viable (Purchase et al., 2022). The concept of a circular economy (CE) emerged as a response to the growing concern about environmental degradation resulting from the consumption and waste of raw construction materials. CE is being explored as an innovative solution to address the depletion of natural raw resources. The origin of the CE concept can be traced back to the initial 3Rs framework (Reduce, Reuse, Recycle). This framework has evolved into the 4R model, which emphasizes the processes of reducing, reusing, recycling, and recovering raw materials. In contrast to the linear economy, where raw materials are discarded, the CE promotes the repair, repurposing, and refurbishment of materials for subsequent use. Consequently, CE principles include the avoidance of unnecessary raw material acquisition, adjustments to design requirements, and the reduction, reuse, and recycling of waste. These practices are considered highly efficient in recycling and waste reduction, as well as in mitigating global environmental degradation (Purchase et al., 2022). B. Rationale for the Study - Potential of recycled concrete aggregates (RCAs) for circular concrete production The preservation of the environment is a fundamental component that is directly related to the survival of the human race. Modern requirements for building projects include criteria like 6

environmental consciousness, resource protection, and sustainable development. Our lives depend heavily on construction materials because we spend 90% of our time in buildings or infrastructure (roads, highways, bridges, etc.). The construction business employs millions of people, as do construction projects, and the construction materials sector accounts for 3-4% of all European production (Oikonomou, 2005). Typically, each European Union citizen received 500 kilogrammes of construction debris and demolition garbage per year (Oikonomou, 2005). Many old buildings and other structures have reached their end of usefulness and must be demolished. Structures, even those that are adequate for use, are being demolished because of new requirements and necessities. Building waste is being produced as a result of natural destructive phenomena (earthquakes, storms, etc.). The percentage of various construction components in demolition debris (DW), where values were calculated is shown in the figure (Oikonomou, 2005).

Figure 2 demolition debris

Figure 3 Aggregates scenario in UK (Source: Mineral product association)

Considering the statistics of Britain, it is observed that the demand for concrete aggregates is going to increase to 323 million tonnes by 2035, most of which are construction sector aggregates. The shortfall is also on a rise and the supply and demand chain remain unbalanced with the demand increasing by 17% as opposed to 10% increase in supply. A total of 183.3 million tonnes of primary aggregates were supplied in Great Britain in 2021, including 57.5 million tonnes of sand and gravel and 125.9 million tonnes of crushed rock. Also, the actual demand for total aggregates was 1.46 billion tonnes throughout the five-year period from 2016 to 2021, just 54 million tonnes (or 4.4%) more than the baseline demand projection from 2017 of 1.41 billion tonnes (Mineral Products Association, 2022)

Figure 4 Supply & demand projection of aggregates in UK (Source: Author)

The potential for circular concrete production utilising recycled concrete aggregates (RCAs) is tremendous. By lowering the use of natural mineral resources and minimising waste disposals, the use of RCAs in concrete manufacturing supports to the circular economy (Pacheco & de Brito, 2021). Even when using ordinary equipment, coarse recycled aggregates have been determined to be a good construction material with adequate quality. (Pacheco & de Brito, 2021). Composition, mechanical strength, thermal characteristics, and durability of RCAs have been studied, as have their effects on recycled aggregate concrete (Pacheco & de Brito, 2021) (Potrč et al., 2022). Various RCA production processes have been investigated, and preliminary separation is indicated as a critical operation to ensure aggregate quality (Pacheco & de Brito, 2021). When compared to concrete created with only natural aggregates, the use of RCAs in concrete production can result in considerable environmental benefits, including energy savings and reduced environmental consequences (Cerchione et al., 2023) (Dias et al., 2022). One of the case studies for the building sector on the island of Sardinia examined the recycling of waste from the demolition of concrete structures in order to acquire coarse recycled aggregates for the creation of recycled concrete. The study indicated that these RCAs could be used in structural and precast concrete with adequate mechanical properties (Pani et al., 2020). Overall, the use of RCAs in concrete manufacturing provides a sustainable option that is consistent with circular economy concepts and can help lessen the environmental effect of the building industry. 9

C. Research Objective The primary objective of the research is to evaluate and understand the challenges and opportunities of reusing 100% recycled aggregates in new concrete structures with the help of a Life Cycle comparative analysis. • The study undertakes different types of aggregates and analyses their carbon impact through a life cycle analysis. • The comparative analysis then tries to derive the different conditions in which using of recycled concrete aggregates is truly sustainable, this includes considering the various factors that impact concrete production and demolition.

II. Literature Review A. Circular Economy and Concrete Production 1. Circular economy principles applied to the construction sector The building industry contributes significantly to environmental deterioration, and circular economy principles are increasingly being used to solve this issue. Several major findings emerge from a study of previous research on circular economy principles applied to the building sector. Choosing proper building materials and components from the start is critical for implementing circular economy principles across the value chain and creating a closed-loop system.(Rahla et al., 2021). However, the literature continues to emphasise the use of recycled items and the recyclability of building materials and components at the end of their useful life. The materials passport (MP) tool has been developed to promote material recovery and reuse throughout the life cycle of a building, but its adoption in the construction sector is currently limited (Munaro & Tavares, 2021). Circular economy ideas can be used to gain additional economic value in the infrastructure industry, and specific project delivery methodologies may serve as viable practices towards more circular supply chains (Karlovsek et al., 2023). Finally, challenges to implementing sustainable designs and approaches to asset end-of-life management that can fulfil the circular economy principles have been divided into six categories: economic, technological, social, political, and environmental (Charef et al., 2021). Overall, these studies emphasise the importance of circular economy concepts in the construction sector and provide insights into the problems and opportunities associated with adopting these principles. Business is encouraged to use circular practices to provide and capture value by using circular business models, which incorporate important elements of a CE to how society does business. Some of the most common concepts employed in circular business models include designing for reuse, resilience, reliance on more renewable energy sources, system thinking methodologies, shared economies, and industrial symbiosis. A significant portion of the world's material consumption and embodied carbon is accounted for by construction materials used in the built environment, which includes buildings and infrastructure (Guerra et al., 2021). Only 8.6% of the world's economy is currently circular, and the majority of C&D trash is recycled or used as backfill. Construction has the ability to embrace CE principles, and most international CE regulations prioritise reducing C&D waste. The goal of CE in the built environment is to use technological advancements in design, construction, and planning to address issues such as the generation of C&D waste, increasing sustainability and resiliency in buildings and cities, and the economic and environmental problems associated with finite resources. The aforementioned 10

problems must be addressed by a CE in the built environment while also favourably influencing the economy (Guerra et al., 2021).

B. Recycled Concrete Aggregates (RCAs) 1. Definition and characteristics of RCAs Construction aggregate comprises various particle materials, including sand, gravel, slag, crushed stones, and recycled concrete, with particle sizes ranging from coarse to medium grains. These components are combined with concrete to impart strength and durability to the final product (Specify Concrete, 2019). The use of crushed concrete dates back to ancient times, but it gained recognition in the 1860s when it was incorporated with cement, sand, and gravel to enhance durability. Initially, the adoption of this practice was met with hesitation in the United States due to the labour-intensive nature of crushing cured concrete (Specify Concrete, 2019). However, in the 1970s, during a construction boom, landfills began rejecting fractured concrete as it was deemed non-recyclable and consumed excessive space. Notably, one landfill persisted in accepting concrete waste, processing it with bulldozers and rollers, and subsequently marketing it as aggregate material (Specify Concrete, 2019). Construction industry stakeholders later verified, through successful projects, that recycled concrete not only matched the durability and strength of new concrete but also significantly reduced environmental impacts. Technological advancements in the building sector further improved the efficiency and cost-effectiveness of recycled concrete aggregate (Specify Concrete, 2019). The properties of recycled concrete aggregate (RCA) are predominantly influenced by the residual adhered mortar. Consequently, RCA exhibits lower density, higher porosity, and greater water absorption compared to natural aggregate (NA). While the particle gradation of RCA and NA is similar, RCA particles tend to have a more rounded shape. The replacement of NA with RCA results in a reduction in compressive strength in concrete, though the splitting tensile strength remains either unchanged or may even improve (McNeil & Kang, 2013). Despite the potential inferiority of RCA as an aggregate and its impact on concrete material properties, extensive testing has demonstrated that RCA can still be employed in the production of structural concrete, especially when considering entire structural elements. Concrete beams made with RCA continue to meet standard requirements, rendering it a suitable choice for structural applications (McNeil & Kang, 2013). It is advised that a 50% replacement of the RCA with natural aggregate is sufficient rather than a 100% replacement. The use of high strength concrete should be investigated as a replacement for 100% recycled aggregate concrete, and the designing engineers should account for the strength loss while employing recycled aggregate concrete. If the engineering properties are equivalent with appropriate compressive strength, flexural strength, and modulus of elasticity, the primary trends found state that RCA can be utilised in high strength concrete mixtures. For recycled aggregates to be used successfully under various circumstances, new standards must be specified and identified. Concrete waste can be recycled to result in great efficiency in lowering both the cost and the environmental effect with the application of the developed recycling methods (Mohammed et al., 2018).

The crushing and processing of demolished concrete structures or discarded concrete yields recycled concrete aggregates (Rahla et al., 2021)These aggregates can be utilised in concrete production as a substitute for natural aggregates, lowering the demand for virgin resources and the accompanying environmental implications (Rahla et al., 2021). The use of recycled concrete aggregates can help to reduce waste in the building industry while also promoting a more circular economy (Diemer et al., 2022). The mechanical qualities of recycled concrete aggregates might differ based on factors such as material quality and processing. (Munaro & Tavares, 2021). The use of recycled concrete aggregates in concrete manufacturing can assist reduce the building industry's carbon footprint by lowering the requirement for fresh concrete production and the accompanying greenhouse gas emissions (Karlovsek et al., 2023). However, using recycled concrete aggregates might create obstacles, such as the necessity for proper material sorting and processing to ensure quality and compatibility with the concrete mix (Charef et al., 2021). Overall, these studies demonstrate the potential benefits of using recycled concrete aggregates in concrete manufacturing, such as decreased need for virgin resources, less waste, and lower carbon emissions. However, in order to ensure the effectiveness and sustainability of recycled concrete aggregates in the construction industry, it is critical to overcome the issues associated with their use.

Figure 5 Types of Aggregates in UK (Source: Author)

2. Source and Originality of RCA Portland cement concrete destruction is where RCA began. Given that the initial concrete could be worn or fresh, loose or packed, weak or strong, aggregate particles can be expected to vary significantly. Concrete aggregate agglomerates with mortar adhering to them are created during the crushing process. These agglomerations are typically less effective than angled units. Concrete is crushed and used to create fines. A concrete frame is created by the aggregates. Approximately 70% of the entire volume of concrete is frequently taken up by aggregates. The majority of these particles are primarily coarse aggregates. However, there is a huge need for coarse aggregate in the construction industry (Makul et al., 2021). 12

To satisfy these high needs, the extraction of raw materials from natural resources must increase. Natural big aggregates are being used, which leads to an ecological imbalance. As a result, the construction sector must use alternative raw materials. One method of reaching this goal is the use of RCA made from concrete structures that have been torn down. Natural coarse aggregate (NCA) is not as frequently needed in projects because to the usage of recycled concrete components. As a result, the damaging effects of spontaneous aggregate recovery are reduced. Increasing landfill fees and a lack of NCA have both influenced the usage of RCA in concrete. Contractors have also been compelled to think about using RCA instead of NCA due to the increased distances between the construction site and the NCA quality source (Makul et al., 2021). Due to good quality control, mixing, and addition of pozzolanic additives, the use of RCA in high performance and high strength structural concrete is feasible. It has been highlighted that poverty places restrictions on different engineering procedures that can cause delays and even a lack of programmes. Cost concerns are constrained by the difficulties of adopting sufficient, secure, and environmentally beneficial alternatives, such as aggregate recycling. To cut further RCA costs, frontloading and top-hopper industries in particular can be implemented. But recycled material pricing and supply and demand issues provide a number of difficulties that are rarely taken into account (Makul et al., 2021). Additionally, each type of RCA's effects on the properties of concrete must be thoroughly studied. Concrete's strength is specifically affected by a number of factors, including the replacement rate, moisture level, RCA type, and water-to-cement ratio. RCA typically absorbs more water than natural aggregates, which can have a major impact on the qualities of concrete, particularly workability. Additionally, compared to water-saturated concrete, concrete with drier RCA had a larger slump and more quicker slump flow. There is no doubt that as time goes on, the strengths for totally substituting fine aggregate grow, and blends with a higher percentage of the combination produce better composite performance. This reflects the characteristics of the use of recycled concrete, which, according to the current literature assessment, exhibits properties that increase the material's strength over the course of a structure's life. Utilising local resources and using cutting-edge construction materials is the only surefire approach to reduce construction expenses. The ideal method appears to be the use of RCA as fine aggregates in concrete, particularly in places where demolition trash is easily accessible (Makul et al., 2021). 3. Benefits of using recycled materials in concrete production The practice of substituting recycled materials for cement has been a long-standing tradition, supported by evidence indicating that the incorporation of certain recycled components can enhance the strength, durability, and workability of concrete. Throughout history, supplementary cementitious materials (SCMs) have been employed as substitutes for cement in concrete production. Presently, materials such as fly ash, silica fume, and ground granulated blast furnace slag (GGBFS) are commonly employed as replacements for cement. GGBFS, also known as slag cement, is a byproduct derived from the iron manufacturing industry. It possesses hydraulic cementitious characteristics with pozzolanic properties. Pozzolans, comprising any reactive aluminosilicate substance, engage with the byproducts of the cement hydration process, contributing to the development of concrete's strength attributes. However, pozzolans often do not confer sufficient strength when mixed with water alone, necessitating the inclusion of cement in the mixture. Consequently, it is widely accepted within the concrete industry that cement, at a minimum, is deemed essential for imparting strength. Notably, slag cement, possessing cementitious properties akin to those of conventional cement, has the capacity to independently hydrate and provide strength when combined with water (Maier & Durham, 2012). 13

In addition to cement, aggregates make up the majority of the other elements in concrete. Aggregates are primarily a filler component of a concrete mixture, despite their importance to it changing in degree. The weakest link in the concrete matrix is actually the bond between the aggregate and cement. Typically, aggregate strength only becomes a deciding issue in high strength concretes. Finding reliable aggregate sources is getting harder. Due to the depletion of many aggregate sources formerly employed, concrete batch producers are now compelled to use aggregates of lower grade. A lot of energy is required to mine and refine the rock to make it appropriate for use in concrete in order to obtain aggregates from the earth (Maier & Durham, 2012). Mining operations are frequently at the centre of environmental discussions due to both their aesthetic and destructive effects. In terms of potential replacement with recycled materials, aggregates are of particular importance. Aggregate replacement has historically taken many different forms, ranging from pure rubbish to recovered vehicle tyres and scrap metal. Recycled concrete aggregate (RCA) is one coarse aggregate substitute that is increasing popularity and utilisation. Recycled concrete is created when roadways, pavements and other structures are demolished. Growing worries about how to dispose of the materials (due to leaking of chemicals into the watershed) as well as rising expenses for concrete disposal have arisen as a result of potential environmental impact that crushed concrete may cause. Around the world, there is rising worry over the shrinking landfill area. These factors make recycled crushed concrete a very interesting topic (Maier & Durham, 2012). Because of the possible environmental benefits, the use of recycled resources in concrete production is gaining popularity. Recycled materials can be utilised in concrete manufacturing as a substitute for natural aggregates, lowering the demand for virgin materials and the accompanying environmental implications (Rahla et al., 2021). The use of recycled aggregates in concrete manufacturing can also help to reduce building waste, leading to a more circular economy (Diemer et al., 2022). Depending on the source and processing of the materials, recycled aggregates can have similar or even superior mechanical qualities than natural aggregates (Munaro & Tavares, 2021). The use of recycled resources in concrete manufacturing can also help to lower the construction industry's carbon footprint, as cement manufacture is a major source of greenhouse gas emissions (Karlovsek et al., 2023). However, using recycled materials in concrete manufacturing might create obstacles, such as the necessity for proper material sorting and processing to ensure quality and compatibility with the concrete mix (Charef et al., 2021). Utilising RCA also has financial benefits and facilitates regulatory compliance. In terms of transportation costs and the rising cost of landfilling C&D waste, manufactured RCA has become more affordable than virgin aggregate (Jin & Chen, 2015). Additionally, governments in Europe, Japan, and the US have started to promote the use of RCA, either directly or indirectly (for example, by raising tipping costs for disposing of concrete wastes) (Jin & Chen, 2015). Overall, these studies demonstrate the potential benefits of using recycled materials in concrete manufacturing, such as decreased demand for virgin materials, less waste, and lower carbon emissions. However, in order to assure the effectiveness and sustainability of recycled materials in the building sector, the issues associated with their use must also be addressed.

C. Life Cycle Analysis (LCA) in Construction 1. Explanation of LCA methodology Life Cycle Analysis (LCA) is a process used to assess the environmental implications of buildings and is an important component of construction sustainability (Izaola et al., 2022) (Almezeraani, 2021). LCA considers the environmental implications of a building or building component throughout its life cycle, from raw material extraction to end-of-life disposal (Fregonara & Ferrando, 2020). The purpose of life cycle analysis is to examine the environmental sustainability of projects by calculating the costs of development, operation, maintenance, and disposal (Fregonara & Ferrando, 2020). The steps involved in conducting an LCA in the construction sector: 1. Goal and scope definition: This includes identifying the LCA's goal, system boundaries, and functional unit. The functional unit is a measure of a building's or component's performance, such as square metres of floor area or years of service life (Izaola et al., 2022). 2. Inventory analysis: This entails gathering data on the building's or component's inputs and outputs throughout its life cycle, including raw materials, energy consumption, emissions, and trash generation (Almezeraani, 2021). 3. Impact assessment: Based on the inventory analysis data, this involves evaluating the environmental implications of the building or building component. Global warming potential, acidification potential, eutrophication potential, and human toxicity potential are some of the consequences. (Almezeraani, 2021). 4. Interpretation: This entails analysing and presenting the LCA results, including identifying hotspots with the biggest environmental consequences and offering solutions to mitigate those impacts (Almezeraani, 2021). LCA can be integrated into the BIM process to allow for the smooth compilation of many design options, precise data collecting, clear conclusion processing, and a full comparison of design variations based on environmental criteria. However, interpreting LCA data can be difficult, and there are no standardised procedures for evaluating LCA results from different design possibilities (Almezeraani, 2021).

Figure 6 Life Cycle Assessment

2. LCA of Concrete Life Cycle Assessment (LCA) is a systematic procedure for quantifying environmental impacts, serving as a fundamental basis for strategic decision-making. When reuse or recycling practices are implemented, products exhibit multiple structural life cycles (Xia et al., 2020). LCA encompasses the quantification of environmental consequences at each stage of a product's life cycle, encompassing resource depletion, energy consumption, greenhouse gas emissions, and pollution. This data informs the identification of opportunities to mitigate environmental impacts through modifications to product design, production processes, or disposal methods. An essential facet of a high-quality design approach should incorporate a comprehensive Life Cycle Assessment (LCA) for concrete structures, considering evaluations of materials, energy, pollution, waste, and other adverse effects throughout the entire life cycle of the structure (Hájek et al., 2011). The standard life cycle of a concrete product should encompass the following processes: raw material acquisition, concrete and structural component production, design and construction, operation and maintenance, repair, renovation, demolition, recycling, and waste disposal. Different regions and countries adopt diverse approaches to designing and constructing concrete structures due to variations in material resources (such as locally available aggregates and steel varieties), climate conditions, and varying construction practices (influenced by local labour costs, work organization traditions, and climatic conditions), leading to regional peculiarities (Hájek et al., 2011). The primary contributor to the global warming potential (GWP) during the concrete life cycle is the manufacturing of raw materials, accounting for 85% of the GWP potential. Among these emissions, approximately 69% stem from the calcination process, while the remaining 31% result from fossil fuel use (Sjunnesson, 2005). Transportation activities contribute to 59-65% of the total eutrophication potential, primarily attributed to cement transportation from the plant to the depot and concrete transfer. Additionally, raw material production significantly impacts eutrophication potential due to substantial NOx emissions from cement production (Sjunnesson, 2005) . The most substantial energy consumption, both in terms of electricity and fossil fuels, occurs during cement manufacturing. Superplasticizers consume 2% of fossil fuels and electricity for standard concrete and 4% and 3%, respectively, for frost-resistant concrete (Sjunnesson, 2005). Given that transportation distances represent a critical factor in the overall environmental impact of concrete, it is imperative to assess this aspect and ascertain whether results vary with changing transport distances (Sjunnesson, 2005).

Figure 7 Life cycle of concrete (Source: Author)

3. LCA application in evaluating environmental impacts of concrete production Emissions, or pollutants emitted into the air, water, or land, are tracked by LCA. There are several ways in which emissions and other pollutants can negatively impact the environment and people's health. Emissions of greenhouse gases (GHGs), which are a factor in the global climate's disruption, 17

are of utmost significance. Emissions related to materials and products are frequently calculated from observations or based on computational models. The conversion of emissions into environmental effects involves multiplying the masses of the emissions by characterisation parameters. A number of environmental impact categories, which are comprehensive measurements of environmental change and include the effects of numerous types of emissions, are assessed by LCA (The Carbon Leadership Forum, 2019). A Life Cycle Assessment (LCA) for a structure entails the aggregation of all quantities of materials and processes into an inventory, followed by the multiplication of these quantities by the respective environmental impacts associated with each item or process. The cumulative environmental impacts of the structure are derived by summing up the overall results. In design practice, LCA can serve as a comparative tool to evaluate various design options and implement minor adjustments. The outcomes of an LCA can pinpoint areas within a structure that exhibit notably high environmental impacts. By conducting this form of hot-spot analysis, the design team can potentially develop a more environmentally responsible design. (The Carbon Leadership Forum, 2019).

Figure 8 Life Cycle Assessment of concrete

The main environmental impacts of concrete production are: •

•

Global warming Potential: Explains potential alterations in local, regional, or worldwide surface temperatures brought on by an increase in the amount of GHGs in the atmosphere, which trap heat from solar radiation through the "greenhouse effect". Embodied carbon is a term used to describe the GWP attributable to the materials and energy used in building construction and maintenance (The Carbon Leadership Forum, 2019). Acidification Potential: Describes how elements in soil and water cause acidification. When molecules like carbon dioxide dissolve in water and cause the pH values to drop, acidification can happen, increasing the acidity of the water. This phrase is used to describe the local impacts of acidity in LCA. Ocean acidification, on the other hand, poses a threat to the 18

•

existence of some species and puts human food supplies from the ocean in jeopardy on a worldwide scale (The Carbon Leadership Forum, 2019). Eutrophication Potential: Explains how nutrient addition to water or soil can lead to the dominance of some species in an ecosystem at the expense of other species' ability to survive (The Carbon Leadership Forum, 2019). Ozone depletion Potential: Explains how elements in the stratosphere damage the ozone layer, making it less effective at shielding the Earth's surface from excessive ultraviolet radiation (The Carbon Leadership Forum, 2019). Smog Formation Potential: Describes the presence of gases in the atmosphere that cause photochemical smog, such as carbon monoxide and volatile organic compounds (VOCs) (The Carbon Leadership Forum, 2019).

There are numerous levels at which LCA assessments can be conducted in the building sector. The cradle-to-gate strategy is the first, and it only takes into account the effects of raw material extraction, the manufacturing of materials and product parts, and the final product's exit from the factory. However, it is impossible to assess the environmental value of proposed "green" concrete types using a straightforward cradle-to-gate examination (Van Den Heede & De Belie, 2012). The aim and scope definition, life cycle inventory analysis, life cycle impact assessment, and life cycle interpretation are the four primary stages of the LCA methodology framework. Functional unit, system boundary, and effect categories are all covered by the aim and scope specification. The analysis of life cycle inventories includes data collecting based on material and energy flows that take place during the life cycle of a product. The weighting variables are used to create common equivalency units for the life cycle impact assessment, which is based on inventory data that evaluates environmental impacts within various environmental impacts categories (Petrovic et al., 2019).

Figure 9 Life cycle stages

D. Environmental Product Declarations “EPD certification plays an important role in helping our clients make informed decisions regarding their choice of materials.” -

Daniel Leeson, Marketing Manager, Uzin Utz UK

An Environmental Product Declaration (EPD) is a document that quantifies the environmental impact of a product based on data derived from a Life Cycle Assessment (LCA). EPDs serve multiple purposes, including their use as marketing materials and tools for enhancing production processes' efficiency. They can also be integrated into comprehensive building assessment frameworks, comparative instruments, and Building Information Modelling (BIM) Computer-Aided Design (CAD) software to assess and compare design solutions aimed at improving a building's environmental performance (BRE, n.d.). EPDs play a crucial role in mitigating carbon emissions within the construction sector by empowering consumers to evaluate the environmental implications of various products and materials, facilitating the selection of the most environmentally friendly options. EPDs are developed in accordance with relevant standards and typically have a validity period of five years. Construction EPDs are established based on standards such as ISO 14040/14044, ISO 14025, EN 15804, or ISO 21930 (One-Click LCA, 2023). Buildings contain a significant amount of carbon that must be drastically decreased in order to aid in the fight against climate change. The structural components and the product stage are typically where the majority of the embodied carbon is released. Therefore, lowering the amount of carbon contained in the structural components is probably going to have a big effect. The main sources of embodied carbon in most structures are steel and concrete. However, despite the fact that hundreds of Environmental Product Declarations (EPD) for cements and concretes have been registered, there has only been a small amount of independent research that compares the embodied carbon of various concrete mixes and raw ingredients. Due to the lack of comparable data, it is more difficult to decide on the best course of action during the early design phases of low-carbon buildings (Anderson & Moncaster, 2022). At the close of 2019, a comprehensive review was undertaken to analyse Environmental Product Declarations (EPDs) related to concrete and cement. During the data collection phase, EPDs were sourced from all recognized EPD programs. These EPDs were categorized into distinct groups encompassing cement, various concrete formulations, and aggregates. Additionally, EPDs reporting multiple results within a single set were separated during this categorization process. In the subsequent phase, data was extracted from the EPD repository and organized into tables alongside similar data sets. This dataset included embodied carbon coefficients (Global Warming Potential for stages A1–A3) and other pertinent information relevant to each product category. Visual representations were created in the fourth phase, and in the fifth phase, the results underwent rigorous scrutiny and validation. The presentation of information through diverse graphical formats proved invaluable for various stakeholders such as Verifiers, Specifiers, Designers, Building Assessors, and Manufacturers. It facilitated processes including EPD verification, material selection, building Life Cycle Assessment (LCA), benchmarking, and goal setting. Conducting similar comprehensive analyses for various other product categories within the construction industry, particularly those with significant environmental impacts, would be advantageous for the sector as a whole (Anderson & Moncaster, 2022).

To represent this heterogeneity within materials, the idea of "EPD Landscapes" was established. This novel method of EPD analysis serves as a vital resource for stakeholders. In order to find items that have decreased both the demand for fossil fuels and all primary energy, the role of renewable energy in EPD is also investigated. However, this raises questions about whether a rise in the share of renewable energy will result in a decrease in primary energy (Moncaster et al., n.d.). III. Challenges in Reusing 100% RCAs in New Concrete Structures A. Technical Challenges According to (Sobuz, et al., 2022) , the main difficulties in making recycled aggregate concrete (RAC) are its poor mechanical and uncertain fresh qualities. Due to these limitations, the amount of recycled aggregate that can replace normal coarse aggregate (NCA) in concrete has been restricted. The qualities of high-strength concrete (HSC), which uses recycled aggregate, may be less inadequate than in conventional concrete, which is favourable to the construction sector. When compared to natural or conventional aggregates, recycled concrete aggregates (RCAs) are inferior because the paste clinging to them is the main factor affecting their functionality. The cementitious paste's ability to adhere reduces the bond between the binder and aggregate, which has a significant impact on how the asphalt mixture behaves mechanically. It turns out that the key to increasing interfacial bonding is to either improve the aggregate's surface or get rid of the paste that is adhered to the NA (natural aggregate) (Yunusa, Zhang, Cui, & Tian, 2022). 1. Effect of RCAs on concrete properties and structural performance Incompatible qualities: The primary challenge associated with the incorporation of Recycled Concrete Aggregates (RCAs) into new concrete lies in their inherent incompatibilities, particularly when sourced from the demolition of existing concrete structures. Laboratory tests were conducted to assess the impact of a novel mixture proportioning method on the creep and shrinkage characteristics of concrete containing recycled concrete aggregates (RCAs). The test results indicated that concrete mixes containing coarse RCAs and proportioned using the novel method exhibited creep and shrinkage rates comparable to, or even lower than, those observed in concrete mixes composed entirely of natural aggregates of a similar nature (Fathifazl et al., 2011). To ensure adequate workability of the fresh concrete, tests were conducted on the slump and slump flow. The test outcomes revealed that the inclusion of RCAs significantly reduced the workability of the concrete. Specifically, concrete incorporating 100% RCAs displayed a 12.2% reduction in compressive strength after 28 days. Furthermore, the 28-day-old concrete exhibited an 8.2% increase in permeability voids when composed entirely of RCAs (Safiuddin et al., 2011). The effective utilization of RCAs in new concrete can be achieved by adhering to established specifications for virgin aggregates. Nevertheless, the incorporation of RCAs necessitates the development of new guidelines and specifications to address their unique characteristics and potential challenges. Moisture absorption: RCAs absorb moisture at a higher rate than virgin aggregates, which can affect the workability and durability of concrete. Fresh concrete may be subjected to waiting periods on a construction site before being placed, which could significantly reduce the concrete's workability in the time between mixing and placement. Additionally, the use of recycled-concrete aggregates (RCA) increases this reduction because of their high water absorption capacity. According to the test results, moisture conditioning of the coarse recycled aggregates is necessary to preserve adequate workability (Mefteh et al., 2013). Adhered mortar content: RCAs contain residual mortar, which can affect the strength and durability of concrete. The scatter of RAC shrinkage and creep is hence high because to the high dispersion 21

of ancient mortar characteristics and content in RCA. A study investigated how old adhering mortar is affected the creep properties of RAC. The findings show that the content, elastic modulus, and creep behaviour of the old adhering mortar have a considerable impact on the creep characteristics of RAC and that this influence cannot be disregarded when calculating RAC's creep (Fan et al., 2014). B. Recycling Construction and demolition waste and Quality Control for RCA Due to the high cost of landfill disposal, transportation expenses, time constraints, or the poor value of recycled material, significant amounts of C&D waste are used for low-grade recycling activities. Furthermore, contamination of C&D waste poses a risk to recycling and reuse, and a significant amount of C&D trash is integrated into contaminated land and used in the restoration of contaminated land (Lawson et al., 2001). The risk assessment of contamination in C&D wastes needs the proper instruments in order to correct this scenario. The UK building sector has not yet made any mention of this (Lawson et al., 2001). In the UK, much work has been put into creating risk assessment techniques for contaminated soil over the past ten years. There is a wealth of knowledge available regarding proper sampling techniques, sample preparation, and analytical techniques for evaluating contaminated soil. Leachate of toxins from building materials into soil is a problem that has been addressed in other nations, such as The Netherlands, and European guidelines are being developed to address this issue (Lawson et al., 2001). Contaminants in "hard" C&D waste products need to be evaluated separately. The expansion of C&D waste utilisation as an alternative to freshly quarried aggregates won't happen unless a suitable risk analysis tailored specifically to these materials is developed. Guidelines for the management of C&D waste from the Environment Agency should be updated (Lawson et al., 2001). 1. Variability in RCA properties and quality The utilization of recycled concrete aggregates (RCAs) in construction applications has garnered increasing attention due to its potential to mitigate environmental impacts and reduce the demand for virgin materials. However, a recurring challenge in the effective integration of RCAs into concrete mixtures lies in the inherent variability of their properties and quality. Studies from different sources including the diversity of concrete materials, the presence of contaminants, and variations in processing techniques. There is an emphasize on the pivotal role of quality control and standardization measures in addressing this variability. Extensive research has been conducted to develop and implement rigorous quality control protocols encompassing source material assessment, processing methods, grading, contaminant removal, and comprehensive testing regimes. Furthermore, established standards and specifications, such as those outlined by BS, offer valuable frameworks for assessing and governing the quality of RCAs. Technical committees, research organisations, and standards organisations have developed norms and guidelines in an effort to promote the use of aggregate from CDW in construction. The limit values in several standards and guidelines differ significantly. This indicates that under the strictest rules, the likelihood of revalorizing CDW is greatly diminished. Therefore, a set of standardised rules for RA is required, which would uniformly identify its potential end uses, depending on its use. This would unquestionably support a wider usage of it in building. In order to manage and enhance the characteristics that diminish aggregate quality, selective demolition and a more efficient treatment of CDW at the plant are essential (Martín-Morales et al., 2013). 2. Need for standardized guidelines and quality control measures Several issues with C&D waste recycling in the UK have been identified through decision-making processes and activities, including the following: 22

The practice of depositing Construction and Demolition (C&D) waste in landfills is no longer a financially viable option due to the imposition of landfill taxes and the concurrent increase in transportation expenses and tipping fees. While the landfill tax has succeeded in reducing the volume of C&D waste disposed of in landfills, exemptions from this levy permit unregulated disposal of inert C&D debris for purposes such as the creation of recreational amenities or improvements to agricultural land. Consequently, escalating disposal costs have incentivized limited-scale recycling initiatives (Lawson et al., 2001). Regardless of whether this is environmentally preferable, development time restrictions, transport and disposal expenses, and the poor economic value of regenerated C&D waste favour the retention of C&D trash "on site" for land modelling reasons (Lawson et al., 2001). Timber presents a significant challenge for contractors that recycle C&D waste. It must be disposed of in a landfill because it cannot be burned. It costs money to separate from bricks and concrete (Lawson et al., 2001). If the majority of a site is covered in concrete, environmental site assessors only excavate trial pits in "soft" sections, and only soils are studied (Lawson et al., 2001).

IV. Opportunities Offered by 100% RCA Concrete Production A. Reduction in Environmental Impact The 20th and 21st centuries have witnessed a substantial expansion of the construction industry, which has become a major contributor to global carbon dioxide emissions, accounting for over 33% of the total emissions. Notably, aggregates, constituting a significant proportion of concrete volume (approximately 55-80%), play a crucial role in environmental impact and structural sustainability (Kisku et al., 2017). In response to environmental concerns, the UK government has introduced the Aggregate Levy as a measure to discourage the utilization of primary resources and encourage the adoption of recycled or secondary materials. Within the context of sustainable development, the scientific community has expressed interest in the incorporation of recycled aggregates as a viable alternative to conventional natural aggregates in concrete production. This shift aims to reduce the reliance on mineral extraction and minimize the generation of concrete waste in landfills. The benefits of 100% RCA concrete production in terms of reduced environmental effect are significant. The use of recycled concrete aggregates (RCA) in concrete production reduces demand for natural aggregates and the amount of solid waste disposed of in landfills (Meddah et al., 2020). Although 100% carbonated RCA has a lower compressive strength than NAC at the same mix ratio, it can still produce standard-quality concrete (Makul et al., 2021) (Xiao et al., 2022). Long-term curing, innovative mixing procedures, the use of pozzolanic chemicals, and modifying the water-to-cement ratio can all increase the performance of RCA concrete (Makul et al., 2021). With the correct mix design and material selection, RCA can be employed in high-quality concretes such as self-compacting, highstrength, and high-performance concretes (Makul et al., 2021). Concretes containing RCA can be carefully designed and balanced to minimize the effect of RCA on their hardened and fresh strength and properties, regardless of the proportion of RCA employed (Makul et al., 2021). Because the reclaimed small particles lower the strength of the concrete, the application of RCA in new concrete mixes necessitates careful research. Natural sand is typically replaced with RCAs up to 20% (Makul et al., 2021). The concrete industry has developed technologies that can significantly cut emissions while maintaining the same performance standards as ordinary concrete. The use of recycled concrete aggregate (RCA) for non-structural applications such as base layers for roads, parking lots, driveways, and backfill material is one of these alternatives (Rebecca Esau, 2022). Recycling CDW into recycled 23

concrete aggregates (RCA) is a strategy to reduce waste while also consuming natural mineral resources (Marinković et al., 2023). V. Methodology The Research aims at trying to identify the challenges and opportunities in using 100% recycled aggregate in collaboration with the Westminster City Council. The approach revolves around understanding the different shortcomings and opportunities in using recycled concrete aggregates. A sound literature review understanding Circular Economy and its connection to Concrete production is conducted. This review also includes definitions of Recycled concrete Aggregates along with its utilisation in the construction process. The Life Cycle Analysis framework is introduced, and an idea of the Environmental Product Declaration is established. The research then analyses the precedent studies on understanding the challenges and opportunities of using 100% recycled concrete aggregates. A site visit to a designated site within the Westminster Borough for understanding of the process of demolition is conducted that helped in gathering information about the site, site plans and drawings and site photographs. This was followed by conversations with the on-site demolition contractors to know about the on-site scenario of the process of demolition. Post site visit a Life cycle impact analysis was carried out that was focussed on understanding the carbon footprint generated with the use of different proportions of the Recycled Concrete Aggregates. The research progressed into analysing of the different challenges in using Recycled Concrete Aggregates. With the identified shortcomings, innovative solutions were explored in order to further reduce the carbon footprint and make RCA more sustainable.

Figure 10 Methodology (Source: Author)

A. LCA Framework 1. Life Cycle Analysis – an ideal scenario A Life Cycle Analysis is done on a generic case under four different scenarios that helps in determining the carbon emissions of using 0%, 25%, 30% and 50% recycled binders for 1m3 volume with the help of One Click LCA, an online software that helps determine the carbon footprint. The material composition is: 0%: Ready-mix concrete, normal-strength, generic C40/50 (5800/7300 PSI), 0% recycled binders in cement (400 kg/m3/24.97lbs/ft3) – 1.0m3 25%: Ready-mix concrete, normal-strength, generic C40/50 (5800/7300 PSI), 25% recycled binders in cement (400 kg/m3/24.97lbs/ft3) (One Click LCA) – 1.0m3 30%: Ready-mix concrete, normal-strength, generic C40/50 (5800/7300 PSI), 30% recycled binders in cement (400 kg/m3/24.97lbs/ft3) – 1.0m3 50%: Ready-mix concrete, normal-strength, generic C40/50 (5800/7300 PSI), 50% recycled binders in cement (400 kg/m3/24.97lbs/ft3) – 1.0m3 A structure of 10m by 10m by 4m (L x B x H) is considered upon which a life cycle assessment is conducted. This LCA is conducted at different scenarios and the carbon emissions are accordingly calculated. A comparative analysis is then conducted with the help of the graphs produced. In the following cases two scenarios are considered and with the help of the generic conditions provided by one-click LCA, an analysis is carried out. The ready-mix concrete consisting of Natural Aggregates in Case I and concrete-mix consisting of Recycled concrete aggregates with Blast furnace cement in Case II is evaluated. The properties of the materials according to the LCA are given below. Case I – Input Materials: Ready-mix concrete, normal strength, generic, C25/30 (3600/4400 PSI), with CEM I, 0% recycled binders (280 kg/m3; 17.5 lbs/ft3 total cement) Case II – Input Materials: Recycled concrete aggregate (RCA), fine or coarse, 2220 kg/m3 bulk density, coarse >4.8mm, fine<4.8mm, from ordinary recycling process (One Click LCA) Blast furnace cement, generic, CEM III/A, 60% GGBS content (One Click LCA 2022)

Figure 11 Ideal case for LCA (source: Author)

2. Selection of impact categories and assessment methods A major attention in this idealistic case is given to stages A1 to A3 materials, A4 transport and C2 waste transport as these are the stages that would get most influenced with the change in the material composition. The carbon emissions are analysed mainly based on the Global Warming Potential, the Ozone Depletion Potential, the Acidification Potential, Eutrophication Potential, Total use of renewable energy and Total use of Primary Energy. All emissions are converted into environmental impacts by multiplying them by the characterisation factors, which convert their effect into a common unit. In the case of climate change, for example, all emissions are converted into COeq equivalents by comparing the warming potential of various greenhouse gases to that of 1 kilogramme of CO2 in the atmosphere (One Click LCA, 2015). A comparative analysis with the help of the different graphs helps in understanding the which stages and what part of the construction and demolition phase has the maximum carbon emissions.

B. Case Study Design 1. Selection of building for the case study As a part of the collaborative thesis with the Westminster City Council, a case study was conducted to a demolition site at 105, Victoria Street where a detailed observation of the entire demolition process was made. The site area was approximately 5000 sqm with seven floors and three plant rooms. The building was an old building built in the 1980s. It was a commercial cum office building. The process of demolition was well planned with all the components being demolished and separated. The demolition contractors are Erith Contractors. After having conversations with on-site demolition contractors an understanding of the process is made. The site was under the process of demolition with about 9244 cubic metres of waste generated. The top floors were demolished first ensuring all the concrete falls onto the lower floors. The contaminants like plasterboard and asbestos sheets were removed before commencing the demolition. The steel was also separately sorted and sent to a different recycling facility from the recycled concrete facility.

Figure 12 Site Plan at 105, Victoria Street (Source: Westminster city council)

The location of the recycling facility was at RMS concrete in East London which helped in the analysis of cycle of aggregates post demolition. 2. Description of RMS concrete, waste treatment facilities Post site visit, conversations with RMS concrete, a waste treatment facility located in London/Essex that treat more than half a million tons of waste annually, with a 100% recovery rate; explained the process of recycled concrete aggregate production that helped in distinguishing the conventional scenario and the recycled concrete scenario. According to the data received from RMS, ¾ flipper- 32-ton Tipper was used with a 20 tonne load capacity. The amount of construction and demolition waste received from 105, Victoria Street, Erith contractors; till date is about 15,000 tonnes. Out of which, 750x loads of waste from the site was removed. The waste treatment was done by Kleeman MC110R- Hybrid using diesel to run them. They produced 30-180mm stone after crushing treatment. Once the RCAs have been processed through our waste treatment facilities, various products are created and tested to ensure they meet the requirement standard. 3. Innovation Having conversations with different innovators, the challenges were addressed adding to the possibility of reducing the challenges encountered. Xeroc is one such company that is based out of London that aims at innovations in reducing the carbon impact of RCA and helping in efficiently completing the loop of circularity. By introducing a low-carbon, circular economy into a linear, carbonintensive industry, Xeroc aims to make a difference. The linear economy we currently have cannot continue. Nearly half of all materials used are in the construction industry, and circularity in these

resources is crucial for a sustainable future (Xeroc , 2023). Xeroc is passionate about reducing demolition waste that accounts for 62% of all waste (Xeroc , 2023). Concrete may be recycled back into concrete using the Xeroc Concrete Circularity methodology (XCCM), restoring each component to its original state with the least amount of contamination. The beneficiation of particles into cementitious material is another step in the process. Since XCCM may be used near to the market, it reduces the need for shipping and logistics and is more cost-effective than using new concrete. To generate aggregates and sand of the highest quality as well as cement fines for carbonation, Xeroc uses smart crushing technology. Xeroc also provides artificial aggregates (Xeroc , 2023). With the help of Xeroc, the amount of trash generated and the requirement for new aggregates will both be significantly reduced. This will be the first circular life cycle for concrete in the built world (Xeroc , 2023).

Figure 13 Innovative solutions by Xeroc (source: Xeroc 2023)

VI. Discussion A. Life Cycle Impacts- Concrete Mix Comparison Upon analysing of the four different scenarios, it is evident that if the proportion of the recycled binders increase the carbon emissions in the A1 to A3 material stage start to reduce significantly. It is observed that upon using 0% recycled binders, A total of 400kg CO2eq. Is released. Subsequently, this figure goes on reducing as the proportion of recycled binders goes on increasing with a 310 CO2 eq. at 25% recycle binders, 290 CO2 eq. at 30% recycle binders and about 280kg CO2 eq. when using 50% recycled binders.

Figure 14 Life cycle impacts of different concrete mix (source: Oneclick LCA)

Moreover, it is essential to note that when the process of recycling is done through two different processes, the carbon emissions are different. The difference though negligible, persists. When the Portland paste is not separated, the carbon impact of the materials is 0.0005kg CO2 eq. whereas if it is an ordinary mixture of recycling then the carbon impact from the materials is 0.0027kg CO2 eq. However, in both these cases the carbon emissions due to transportation remains the same.

Figure 15 Life cycle impacts of different recycling process (source: Oneclick LCA)

B. Life Cycle Analysis – Ideal Scenario As observed from the graphs produced, it is evident that the global warming CO2 equivalent drops considerably drops for material stage A1-A3 from about 15,000kg CO2e for natural aggregates to 1100kg CO2e for Recycled concrete aggregates. Comparatively A4 transportation seems to increase in the RCA scenario.

Figure 16 Carbon emission of generic mix concrete (source: Oneclick LCA)

Figure 17 Carbon emission of RCA mix (source: Oneclick LCA)

In the adjoining graphs, the Global warming potential, the Ozone Depletion Potential, and the Acidification Potential reduce substantially upon using RCA. There is also a decrease in Eutrophication Potential, Total use of renewable energy and Total use of Primary Energy. The carbon emissions for transportation in this case is higher as it considers the emissions to dispose of waste as well. Also, the waste transport is negligible as the waste is designed out of the building. It can thus be observed that transportation seems to be a major contributor for the carbon emissions in case of RCA.

Figure 18 Carbon footprint of generic mix (source: Oneclick LCA)

Figure 19 Carbon footprint of RCA mix (source: Oneclick LCA)

C. Transportation of the site debris: Potential sites of RCA Upon further analysis, the distance of the recycling facility of RMS concrete was calculated. The distance between the site and the RMS concrete recycling facility was found to be 9.8 miles. This distance was quite long and the process of sending the construction and demolition waste to one end of the city was quite carbon intensive. A study of the waste map of London and the various disposing units helped in identifying the various possible recycling sites within the borough. It was observed that the recycling facilities appear to be far and are lesser in number. However, the transfer and treatment plants are quite evidently scattered throughout London creating opportunities for inculcating recycling plants. This could help in reducing the load of transportation on the system post demolition. A distance mapping conducted around 105, Victoria Street indicates the potential sites. These sites could be further studied in detail to understand if at all they could include a recycling facility. It is observed from the map that within a permissible radial distance of 3-7 miles, more than 20 transfer and treatment plants are located that could be potential recycling units. This could help reduce one of the key challenges of using RCA that is transportation distance.

Figure 20 Distance between demolition site and recycling plant (source: author)

Figure 21 Potential recycling in the vicinity (source: author)

D. Discussions with different stakeholders in circular economy loop Erith Contractors: In the conversation with Erith contractors about aspects of the demolition project at 105 Victoria Street, a renowned office and commercial building in the centre of Westminster, the process of demolition was discussed. According to the contractors, the three plant rooms on the terrace, were a unique challenge for the seven-story building and careful planning and execution were necessary. The contractor outlined how non-inert components including plasterboards and services were carefully removed to start the demolition process. The attention then turned to the upper floor, where the main things that needed to be removed were steel and concrete. This strategy was chosen to guarantee the project's effectiveness and safety. 33

The fact that the demolition took more than six months to complete stood out. The contractor explained the lengthy schedule to the project's complexity and emphasised the value of deliberate deconstruction over rash action. As a result, according to them, the demolition met the highest requirements for safety and environmental responsibility. The onsite contractor brought up recycling as a crucial component of the circular economy when discussing the disposal of materials. Project-related steel that could be recycled was delivered to facilities that would use it to make new building materials. On the other side, the concrete was transported to RMS Concrete, a business in East London that is around 10 miles from Westminster. Despite the project's overall success, the on-site supervisor highlighted a crucial issue with the circular economic loop—communication and cooperation among stakeholders. In this instance, there was a lack of communication on the fate of the waste items after they departed the demolition compound with RMS Concrete. This discrepancy underlines the need for improved coordination and information sharing among all parties involved in the circular economy, from demolition contractors through recycling facilities.

Figure 22 Demolition at 105, Victoria street (source: author)

Figure 23 Demolition at 105, Victoria street

Recycled Material Supplies limited (RMS): In-depth discussion with Luke Taylor, Head of Health & Safety and Compliance at Recycled Material Supplies Limited (RMS) in East London, allowed us to understand the complex process of reusing, recycling and downcycling recycled concrete aggregates (RCAs) removed from the iconic 105 Victoria Street building demolition, carried out by Erith Demolition Contractors. He explained the careful procedures involved in recycling aggregates, a procedure that shows the dedication to environmental responsibility. The challenging task of crushing, when the concrete debris goes through a rigorous transformation, is the crucial part. In order to ensure that only the best aggregates are used, sorting and screening techniques carefully separate the materials.

Figure 24 Production process of RCA at RMS Limited (source: RMS Limited)

Additionally, Luke demonstrated a thorough comprehension of the carbon footprint connected to the delivery of these repurposed goods. The 3/4 flipper, a capable 32-ton tipper variant known as the Scania XT P450 Engine, is the vehicle used for transportation. It is equipped with 13-liter, 450 HP engine power and load capacity of 20 tonnes to manage the demanding requirements of transportation. Over fifteen thousand tonnes of rubbish were hauled away from the demolition site in a750X loads of waste. This volume highlights the diversion of a sizable amount of garbage from landfills and a step towards a sustainable future. He also provided insightful information about the equipment at the centre of the waste treatment process. The Kleeman MC110R crusher, runs on a hybrid and diesel system, significantly lowering its carbon footprint. The machine effectively converts the scrap concrete into stone aggregates ranging in size from 30 mm to 180 mm, showcasing the adaptability and power of contemporary recycling technology. The company boasts a dedicated storage facility located in Dagenham/Sydenham, strategically positioned to facilitate the efficient storage and distribution of RCAs. This storage facility not only streamlines operations but also serves as a key component in the circular economy equation, ensuring that resources are continually reused and recycled. In addition to streamlining operations, this storage facility plays a crucial role in the circular economy equation, ensuring that resources are consistently recycled and repurposed.

Figure 25 Storage facility for RCA at Dagenham & Sydenham (Source: RMS Limited)

E. Possibilities of Recycling In order to reduce the carbon footprint due to transportation of aggregates, different possibilities of recycling could be explored. Using of recycled concrete for the construction process is one such method. The aggregate waste from the demolition facility could be designed out and be made to recycle in a nearby recycling facility. The Recycled aggregate obtained as a product from the recycling facility would then become a part of the construction process as a member of the aggregate. This way fully or partially, the aggregate gets utilised onto the site reducing the waste production substantially. Including an additional step in the process of recycling could act as an effective way of recycling of the concrete aggregates. The aggregate from the demolition site is sent through the recycling facility to the pre-cast manufacture facility. The pre-casted members can be used in the construction of the new building. The new construction then acts as an assembly of such pre-casted members put together into a built system. These members can then be disassembled in the future and be reutilised onto another site. In this manner the process of reusing helps in reducing the carbon emissions by removing the carbon intensive step of demolition.

Figure 26 Possibilities of recycling: Design for disassembly

VII. Conclusion A. Summary of Findings 1. Recap of challenges in reusing 100% RCAs in new concrete structures A sustainable and eco-friendly practice that has considerable potential is the use of 100% recycled concrete aggregate (RCA) in new concrete constructions. But there are still challenges with it. Quality control, contamination, structural performance, and regulatory barriers are a few of the difficulties that have been mentioned throughout this essay. It can be difficult to guarantee the consistent quality of recycled concrete aggregate. The performance of the new concrete can be impacted by variations in the content and characteristics of RCA from various sources. To address this issue, rigorous testing and quality control procedures are required. The strength and durability of the new concrete may be harmed by the contamination of recycled concrete aggregate with impurities. When employing 100% recycled concrete aggregate, structural performance issues, particularly in high-stress applications, need to be carefully assessed. To maintain the security and lifespan of structures, engineers must consider any changes in strength and durability compared to conventional concrete mixtures. It can be challenging to delve through the complex set of rules and guidelines governing the use of recycled materials in building. To provide clear norms and regulations that support the safe and efficient use of RCA, it is frequently necessary for industry stakeholders and policymakers to work together. The dialogue with the demolition contractors at Erith indicated a gap of knowledge about the location of the recycling facility. This indicates a major gap within the system with lack of any systematic implementation in terms of policy framework or stakeholder involvement. Due to the greater energy usage and greenhouse gas emissions resulting from greater travel distances, RCA transport raises several environmental issues. To reduce these effects, it is necessary to carefully design and optimise transit routes because RCA sources may be dispersed and far from building sites. The administration and coordination of a convoluted supply chain that involves the collection, processing, and delivery of recycled concrete aggregate are among the logistical issues. The practicality of employing 100% recycled concrete aggregate can be significantly impacted financially by the cost of shipping. The economic advantages of employing recycled materials may be negated by greater transportation expenses brought on by longer transit distances. 2. Highlights from the LCA results and environmental assessment

The LCA outcomes conclusively show that utilising 100% RCA in new concrete structures provides significant environmental advantages. Compared to conventional concrete aggregates, there is a sizable decrease in energy use, greenhouse gas emissions, and resource depletion. As it reduces waste and increases the useful life of resources, this practice is consistent with the ideas of a circular economy. The importance of quality control and the prevention of contamination in maintaining the environmental sustainability of RCA is further highlighted by LCA results. The environmental advantages of this practice must be maximised by maintaining high standards for RCA manufacture and reducing contamination. A combination of environmental, financial, and transparency-related considerations makes an Environmental Product Declaration (EPD) for 100% recycled concrete aggregate (RCA) necessary. Transparency in material procurement and environmental performance is crucial as the construction sector works to minimise its environmental impact and align with sustainability goals. An EPD for 100% RCA would offer a standardised and reliable way to tell stakeholders, such as builders, designers, and customers, about critical environmental information. In a sector that values sustainability more and more, an EPD for 100% recycled concrete aggregate serves as a shining example of openness and accountability. It acts as a catalyst for change, promoting responsible recycling, minimising the environmental impact of construction projects, and advancing the more general objectives of a circular economy. Additionally, it gives stakeholders the power to make decisions that are in line with their sustainability goals.

B. Implications and Recommendations 1. Implications for the construction industry and circular economy adoption Closing material loops and effectively reusing resources are key principles of the circular economy, and integrating 100% RCA into construction projects is an excellent example of this. This method helps to create a more sustainable and regenerative building sector while also slowing down the use of finite resources. Because a sizable amount of landfills are made up of construction debris, using RCA lessens this burden by removing concrete trash from disposal sites. This decrease in landfill garbage is consistent with the circular economy's emphasis on reducing waste streams. The use of RCA if strongly encouraged by policymakers and regulators through incentives, standards, and sustainability certifications, it can act as a game changer in implementing RCA across the construction sector. These policies could offer a framework that helps the industry make the move to circularity. To overcome obstacles and expand the usage of 100% RCA, stakeholders such as construction firms, suppliers, academics, and legislators must work together. Through these collaborations, recycling infrastructure may be developed, and best practises can be promoted. Adopting 100% RCA improves the building industry's resilience by lowering its reliance on finite resources, such as natural aggregates. In consequence, this promotes resource security and a more environmentally friendly method of building. 2. Recommendations for future research and policy development The processes for RCA production's quality control should be improved as the subject of future study. Industry stakeholders will feel more confident if standardised rules for evaluating the consistency and quality of recycled aggregates are developed. By rewarding adherence to these criteria and promoting research in this field, policymakers may encourage this. Investigating cutting-edge crushing and separation methods for RCA processing can produce higher-quality recycled materials while consuming less energy. To better understand the environmental advantages and trade-offs connected with employing 100% RCA in various construction applications, additional LCA studies are required. In order to produce more 38

precise estimations, this research should take regional variations in environmental consequences and travel times into account. The best technique to distribute RCA to building sites should be investigated through research. This entails looking into site of recycling in and around the site, energy-saving alternative fuels, effective logistical solutions, and energy-efficient modes of transportation. Circular business models can be encouraged by policymakers in the building sector. This includes regulations that promote material reuse and recycling, tax breaks for businesses that implement circular business models, and public procurement regulations that give recycled materials preference. Circular construction practices can be adopted by the industry with the support of training programmes and certification courses. Policymakers should consider about putting money into highquality RCA processing and production facilities, as well as recycling infrastructure. Through these developments, RCA's transit distance may be decreased, improving accessibility and cost-effectiveness for construction projects. Market incentives for the adoption of RCA should be developed through cooperation between policymakers and industry partners. This could involve preferential treatment in public procurement, tax rebates for projects employing RCA, or green building certifications that reward the use of recycled materials. Future research and policy development must be fuelled by collaboration between academics, business leaders, government officials, and environmental organisations. Collaborations across disciplines can help with information sharing and applying best practises. In conclusion, the life cycle analysis-based examination of the opportunities and problems associated with employing 100% recycled concrete aggregates in new concrete structures is a critical step in realising the objectives of a circular economy in the construction industry. In a world where resources are becoming scarcer and the environment is being degraded, adopting circular practies is not only a choice but rather a requirement. We must be firm in our dedication to sustainability, creativity, and cooperation as we work through the challenges of achieving circularity. We can only achieve this goal of making the building sector a shining example of circularity that shows we are capable of creating a better, more sustainable future via joint effort. Although the path to a circular construction industry may be difficult, the end goal is a world where we develop not only buildings but also a better and more sustainable tomorrow.

VIII.

Table of Figures

Figure 1 Circular Economy Figure 2 demolition debris Figure 3 Aggregates scenario in UK (Source: Mineral product association) Figure 4 Supply & demand projection of aggregates in UK (Source: Author) Figure 5 Types of Aggregates in UK (Source: Author) Figure 6 Life Cycle Assessment Figure 7 Life cycle of concrete (Source: Author) Figure 8 Life Cycle Assessment of concrete Figure 9 Life cycle stages Figure 10 Methodology (Source: Author) Figure 11 Ideal case for LCA (source: Author) Figure 12 Site Plan at 105, Victoria Street (Source: Westminster city council) Figure 13 Innovative solutions by Xeroc (source: Xeroc 2023) Figure 14 Life cycle impacts of different concrete mix (source: Oneclick LCA) Figure 15 Life cycle impacts of different recycling process (source: Oneclick LCA) Figure 16 Carbon emission of generic mix concrete (source: Oneclick LCA) Figure 17 Carbon emission of RCA mix (source: Oneclick LCA) Figure 18 Carbon footprint of generic mix (source: Oneclick LCA) Figure 19 Carbon footprint of RCA mix (source: Oneclick LCA) Figure 20 Distance between demolition site and recycling plant (source: author) Figure 21 Potential recycling in the vicinity (source: author) Figure 22 Demolition at 105, Victoria street (source: author) Figure 23 Demolition at 105, Victoria street Figure 24 Production process of RCA at RMS Limited (source: RMS Limited) Figure 25 Storage facility for RCA at Dagenham & Sydenham (Source: RMS Limited) Figure 26 Possibilities of recycling: Design for disassembly

IX.

Appendix

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Dissertation Thesis- Circular Economy: Challenges & Opportunities in reusing 100% recycled concrete