Concrete and Circular Economy

Inhaltsverzeichnis

1. Frontmatter

2. Valorizations of Demolition Waste

   1. Demonstration of a Circular Building Process at Large Scale: Circboost Pilot Project in Norway

      Iveta Nováková, Sofija Kekez-Baran

      Abstract

      Concrete and construction sector are one of the biggest polluters on a global scale, generating excessive amounts of CO2 emissions and waste. One of the solutions that would alleviate this problem is implementation of circular construction process enabling efficient and low-carbon application of construction and demolition waste. Circular construction, as a pathway of circular economy, supports sustainability by lowering the carbon emissions, transportation needs, use of virgin materials, and landfilling of the waste. This paper demonstrates a circular building process at large scale following the example of the CircBoost Pilot project in Norway. The Norwegian Pilot is one of five that are developed within CircBoost, that deals with the selective demolition of an old slaughterhouse building, production of recycled concrete aggregate, and finally construction of the new museum building built predominantly with secondary raw materials including recycled concrete aggregates in Sortland municipality. This paper shows all stages of the circular building process and the administrative and technical aspects that are involved in the pre-demolition activities including the regular environmental mapping of the demolition structure and extensive concrete quality assessment via Schmidt hammer and core drill sampling, selective demolition using innovative methods, production of high-quality recycled concrete aggregates, and construction of the new structure with recycled concrete and other reused/recycled elements.

   2. Circular Economy in the Construction Sector: Challenges and Opportunities in Luxembourg and the Greater Region

      Monica L. Louie, Markus Schäfer

      Abstract

      Concrete used in the construction sector is made with natural aggregates such as sand, gravel, and crushed stone, sourced directly from the region's nature. These aggregates are mixed with cement and water to create a durable building material. Until today, only primary materials, such as crushed aggregates or river gravel, have been used in the national production of concrete. The construction and demolition (C&D) sector in Luxembourg and the Greater Region generates significant landfill waste. While current reuse and recycling efforts are in place to help reduce waste, they result in downcycling materials, underscoring the need for a circular economy approach. However, Luxembourg's accessible local river sand reserves may be exhausted within the next two decades due to urbanization along the Moselle River, emphasizing the urgency for sustainable solutions in construction materials. This research will focus on improving material recovery from existing construction through optical surveys to assess quality and remove low-grade materials. If the removal of low-grade materials is not feasible, the focus will shift to integrating a circular economy approach by designing products with the end-of-life stage in mind during the deconstruction and demolition processes. This ensures that materials can be easily separated, reused, or recycled without degrading their quality. This approach minimizes the need for raw resources and reduces environmental impact. Additionally, the research will examine C&D waste processing logistics, comparing centralized and decentralized recycling facilities. Non-mobile locations may offer better quality control and economies of scale, while mobile equipment could reduce transportation costs and offer localized solutions. Identifying the optimal strategy is crucial for efficient recycling and consistent quality. By addressing these technical, economic, and logistical challenges, this study aims to enhance the integration of recycled materials into construction, reduce reliance on virgin resources, and contribute to sustainable development in Luxembourg and the Greater Region.

   3. Recycling of Mineral Building Materials – Chances and Obstacles

      Anne Haller, Klaus Holschemacher, Jens Otto

      Abstract

      Civil engineering is the major consumer of natural resources like gravel. Therefore, the recycling of demolished building materials is of strongly increasing importance in the circular economy. For some materials, e.g. glass, the recycling process has already reached a very high and satisfying level. However, despite undisputed ecological advantages and political guidance, the application of recycled building materials is still encountering several obstacles in construction industry. It is to note that demolished mineral building materials are mostly applied as subgrade in road construction resulting in a downgrading and not in recycling or even upcycling of the valuable material.

      Based on the results of a questionnaire, chances and obstacles are analyzed in the context of recycling of mineral building materials. It becomes obvious that legal uncertainty, missing market transparency, and warranty risks are significant obstacles. Especially, in public tendering procedures, concerns are widely spread regarding quality and possible contamination of recycling materials. Measures like improvement of technical knowledge, unification of legal requirements, and support of innovative recycling technologies are needed and may result in an increased application of recycled mineral building materials in construction practice.

   4. IFC-Based Demolition Schedule Optimization

      Melody Njuguna, André Mantelatto, Artur Kuzminykh, Tomo Cerovšek, Manuel Parente, José Granja, Miguel Azenha

      Abstract

      Demolition scheduling, where material circularity is prioritized, has the twin goals of sequencing the order of works done and assigning the correct labour teams to do this work, while minimizing cost and time. The topics of Building Information Modelling and Evolutionary Algorithms have been studied at length separately, however, this paper explores the potential of their joint use in the creation of a new way to optimize the aforementioned goals. The paper proposes a method of performing schedule and multi-objective resource optimization based on IFC models and with the use of a precedence matrix. A chromosome repair strategy is created, whereby the domain knowledge carried within the precedence matrix is incorporated into the fitness function, using which NSGA-II generates multiple results bearing optimal schedules that consider both costs and time. This method is then successfully implemented on a case study of a high-rise building. The findings show the potential of the proposed method for demolition scheduling, and proposals are made for strategies to build upon this method.

   5. Recyclability of Demolished Diaphragm Wall Material

      Thomas Pichler, Christian Müller, Konrad Bergmeister, Klaus Voit

      Abstract

      To protect natural resources, circular economy in the construction industry has to be further established. In many cases today, demolition material from concrete structures is recycled in a very low value or landfilled. In urban areas, where the temporary construction pit system is used during the construction phase, large volumes of demolition concrete are produced at the end of the construction period. This concrete waste should be recycled to high quality recycled concrete aggregates (RCA) in the sense of urban mining. In this research project, the material from a demolished diaphragm wall is investigated for its recyclability and further production of watertight structural walls in the infrastructure sector. In particular, the workability of the material in concrete production as well as the hardened concrete properties such as watertightness and permeability are parameters that are investigated during the research. The tests will be carried out on test specimens as well as on test walls. By establishing the recycling process, the material could be processed and reused on the construction site. This helps to reduce the use of natural resources and conserve areas that would otherwise be used for landfilling.

   6. Performance of Recycled Concrete Aggregates in Gravel-Cement Mixtures: Strength, Shrinkage, and Durability Analysis

      Oussama Atoui, Azer Maazoun, Ahmed Siala

      Abstract

      The depletion of high-quality natural aggregates due to excessive quarrying presents a major challenge in sustainable road construction. This study investigates the incorporation of recycled concrete aggregates (RCA) into gravel-cement mixtures for pavement base layers. Four formulations were de-veloped with 0%, 25%, 50%, and 75% RCA, while maintaining a fixed cement dosage of 4%. Laboratory testing included compressive strength, flexural strength, indirect tensile strength, shrinkage, and water absorption. The results showed that increasing RCA content reduced compressive strength by up to 10.6% (from 3.5 MPa to 3.1 MPa at 28 days) and flexural and tensile strengths by 15.6% and 10.4%, respectively. However, all mixtures exceeded the mini-mum strength required for pavement base layers (≥2.5 MPa at 28 days). Shrink-age strain decreased by up to 20%, and water absorption increased moderately but remained within acceptable limits. These findings confirm that gravel-cement mixtures with high RCA content can meet mechanical and durability requirements while offering environmental and economic benefits.

   7. Establishing an Efficient Method for Quantifying the CO2-Uptake Potential of Recycled Aggregates

      Johannes Hron, Oliver Zeman, Konrad Bergmeister

      Abstract

      The extensive resource extraction and the enormous global CO₂-emissions of the construction industry are becoming increasingly a challenge with regard to the aim of a sustainable future. Recycling of construction and demolition waste (CDW) can contribute significantly to the conservation of resources. The existing building stock therefore has to be considered as a raw material depot for future construction activities. Forced carbonation of recycled concrete aggregates (RCA) is a novel methodology and if additionally carried out in the course of processing, the aspect of climate protection can also be considered. Regarding forced carbonation, first industry implementations have already taken place and an increased future application is emerging. One difficulty is the uncertainty of the existing CO₂-uptake potential of the RCA. Main influencing factors for the achievable storage potential are the grain size and the duration of the CO₂ exposure time as well as the appropriate ambient conditions like humidity of the grains and CO₂ concentration. An exact determination is essentially possible after the carbonation has taken place by measuring masses before and after carbonation monitoring the experimental conditions. The present study shows a simply applicable and efficient method for determining the CO₂-uptake potential on material samples which can be taken from the still existing construction stock before demolition. Available data show the possibility of determination also for RCA from different sources, showing an influence of concrete quality and natural exposure time after processing the demolition concrete waste.

   8. Microstructural and Micromechanical Study of the Interfacial Transition Zone of Recycled Concrete by Combined Nanoindentation and SEM-EDX Technique

      Feng Li, Göran Forbrig, Florian Kleiner, Luise Göbel, Christiane Rößler, Elske Linß

      Abstract

      The macroscopic properties of concrete are largely determined by its microstructure and micromechanical properties. As the most vulnerable structural element in concrete, the interfacial transition zone (ITZ) has a significant influence on the macro-mechanical behavior of concrete. The use of recycled aggregates, which exhibit higher porosity, lower density and higher water adsorption, results in concrete with distinct properties compared to natural concrete. The aim of this study is to investigate the ITZ in both natural and recycled concrete using a combination of nanoindentation and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Firstly, the concrete samples were analyzed using SEM to identify areas with a typical ITZ. Backscattered electrons (BSE) are employed to resolve the microstructure of these regions and the thickness of the ITZ, taking into account the porosity distribution. Subsequently, the indentation modulus and the hardness of the ITZ were determined. According to the distribution of the porosity and modulus, the thickness of the ITZ is determined to amount to 50–70 μm. The results show that the ITZ in recycled concrete has higher porosity and lower indentation modulus than that in natural concrete. The obtained results were further analyzed using clustering method (i.e. k-means). The micromechanical investigations allow for the identification of five different material phases with spatially varying properties.

   9. Evaluating the Influence of Recycled Concrete Fine Fineness on Fresh and Hardened Properties of Mortar

      Bayram Tutkun, Farshad Ameri, Daniella Mehanni, Katalin Kopecskó, Zaid Khaiqani, Ildikó Merta

      Abstract

      Recycled fine (RF), a by-product of construction and demolition (C&D) waste, has limited application in cementitious materials due to its coarse particle size and low reactivity. This study investigates the effect of RF fineness on the fresh, mechanical, durability, and environmental properties of mortar. Mortar mixtures were prepared by replacing 25% of the cement with RF ground for 30, 60, and 90 minutes. To evaluate the influence of RF fineness, fresh properties were assessed through flow table tests, while hardened properties were examined using compressive and flexural strength tests at 28 days, rapid chloride migration tests for durability, and hardened density measurements. SEM and XRD analyses were conducted to characterize the morphology and mineralogical composition of RF, while an environmental assessment quantified CO₂ emissions. The results demonstrate that increasing RF fineness enhances its reactivity and filler effect, leading to a 13–23% reduction in compressive strength losses and a 20% decrease in the chloride migration coefficient, indicating an improved microstructure with increased fineness. SEM analysis confirmed that finer RF exhibits a more uniform and less angular morphology, which enhances its interaction with cement hydration products. Additionally, the need for superplasticizer decreased as RF fineness increased due to morphological improvements. The environmental assessment showed that RF utilization reduced CO₂ emissions by 23% per cubic meter, highlighting its potential as a sustainable alternative in cementitious materials. Strength efficiency analysis indicated that finely ground RF can maintain an optimal balance between mechanical performance and environmental impact. These findings suggest that finely ground RF can improve mechanical and durability properties while reducing environmental impact.

3. Eco-friendly Binders with Low CO2-emission

   1. Frontmatter

   2. LC3-Based Concrete with High Recycled Sand Content: Unveiling its Mechanical and Durability Potential

      Ahmad Jan, Lucia Ferrari, Nikola Mikanovic, Mohsen Ben-Haha, Elisa Franzoni

      Abstract

      Developing green concrete with the employment of recycled fine aggregate (RFA) and limestone calcined Clay cement (LC³) could be a promising and economical method for the reduction of the environmental impact of buildings, by reducing CO₂ emission related to cement production and providing a viable alternative to natural resource depletion. This study was carried out to examine the mechanical and physical properties of LC³–based concrete, using different proportions of limestone, calcined clay, and cement clinker, with 100% natural coarse aggregates and 50 vol% of RFA substitution. The fresh state behavior was evaluated by the slump test, and the target slump was obtained by adjusting the superplasticizer dosage. The 28-day mechanical and durability properties including compressive strength, water absorption and capillary water absorption rate of different concretes were investigated. The results highlight that LC³ binders show better mechanical properties than reference commercial cement with both natural and recycled sands. Considering the superior mechanical properties and environmental advantages, combining LC³ binders with RFA for concrete production seems an effective approach for a sustainable development of the construction industry.

   3. Carbon Storage Capacity Evaluation of Incineration Ash

      Marie-Laure Heyndrickx, Beibei Sun, Veerle Boel, Stijn Matthys

      Abstract

      The growing volume of waste materials poses significant environmental challenges, while CO2 emissions from cement production contribute to global warming. This study explores the potential of using incineration ashes, in particular fly ash (FA) and bottom ash (BA), in construction materials, both to reduce landfill waste and to capture CO2 through carbonation curing. While bottom ash has been used in construction (limited to low grade applications), most fly ash is landfilled. By incorporating bottom ash into carbonation curing, CO2 can be captured during the curing process, providing environmental and economic benefits. This research investigates the carbon sequestration capacity of bottom ashes as well as fly ashes of municipal solid waste incinerator (MSWI) and co-combustion (CC) ashes under accelerated carbonation conditions. Using techniques such as XRF, TGA and mass uptake analysis, the results show that finer particles and higher CO2 curing concentrations improve carbonation efficiency. From the tested materials these results also highlight optimal carbonation conditions and suggest a strategy for the use of incineration ash in carbon curing concrete, providing guidance for sustainable construction applications. MSWI FA, as studied in this work, showed the highest sequestration potential.

   4. Effectiveness of Cement Replacement Materials at Different Cement Content and Water-Cement Ratio

      Rita Nemes, Anna Szijártó

      Abstract

      The binder material in conventional concrete is cement. In addition to its binding properties, it also provides the finest particle size range in the mix. The cement content in normal concrete fundamentally influences strength and durability. Higher strength and better durability require a higher amount of binder. Cement is the most polluting and energy-intensive component of concrete. The most effective way to reduce CO₂ emissions is to lower the cement content in concrete. Green cement with low clinker content can be used but directly utilizing cement replacement materials (CRM) is even more effective. Well-established CRMs include blast furnace slag cement and pozzolan cement, but using local materials is particularly beneficial. In many cases, this will depend on the geographical location or the state of the industry. It is even better if waste materials or industrial by-products are used. Our experiments used low and high water-cement ratios (0.45–0.65) in mortars at low and high cement contents (360 and 500 kg/m³) as reference series and then pure Portland cement was partially replaced with CRM. Both are wastes from the production of construction elements that should be recycled in other sectors of the construction industry. The use of marble powder is still less widespread, limestone flour being more common. Their optimal and maximum potential applications were investigated, and they were compared with other cement replacement materials using both our own results and results from the literature.

   5. Quarry Waste Composition Effect on Mechanical Performance of Eco-Friendly Binders

      Lobna Benzina Mechmeche, Ramy Belhadj, Abderraouf Trabelsi, Mongi Ben Ouezdou

      Abstract

      A large amount of the building sector carbon footprint is caused by the manufacturing of cement, a vital component of concrete. New techniques for its production are continuously being developed to lessen its environmental impact. Using natural waste materials to partially replace cement is one such technique. This work primary goal is to correlate the used quarry waste mineral composition to the produced concrete mechanical performance at 28-day age: X-ray diffraction (XRD) analysis was used to investigate the quarry material components. It is an easy accessible by-product of stone crushing processes. It was exploited in a partial substitution procedure of the classical cement binder. Concrete samples were made using 2 different waste quarry powders P₁ and P₂ respectively at 2 cement substitution rates: 10% and 20% of the cement weight. P₁ is a limestone based material whereas P₂ powder is a clay based one. Both powders were baked at 650 °C during 6 h before use. Sodium silicate Na₂SiO₃ and sodium bicarbonate NaHCO₃ alkaline activators were respectively added to the concrete mix at a 20% dosage of the waste amount. Experimental test results illustrate that the substituting powders have positive effects on the 28-day compressive strength (Rc₂₈). The Rc₂₈ growth rate obtained in the case of P₁ waste ranged between 11.6% and 24.3% compared to the reference sample (with no cement substitution). For P₂ clay based waste, the compressive strength increase rate reached 6.2% at a substitution rate of 20% when the activator was Sodium Silicate. In order to understand how the waste powders have helped to increase concrete compressive strength, the XRD analysis was adopted. It seems that calcium, Silica and Zinc presence in the quarry waste have helped to enhance the cement hydration process resulting in additional hydrates that reinforce concrete structure. This study emphasizes the possibility of recycling quarry waste materials in manufacturing low environmental impact concrete without sacrificing its mechanical performance. The findings show that substituting up to 20% of the cement binder could preserve the compressive strength.

   6. A Study on Utilization of Mussel Shells in Cement Mortar: Enhancing Sustainability and Mechanical Properties

      Monika Verma, Francesco Colangelo, Ilenia Farina

      Abstract

      The construction sector faces huge pressure to adopt sustainable practices and reduce its environmental impact. This study explores the innovative use of mussel shells, a by-product of the seafood industry, silica fume and fly ash in cement mortar to enhance both sustainability and mechanical properties. Two important issues are addressed by the integration of these waste elements: efficient waste management and the creation of sustainable building materials. Mussel shells were processed by cleaning, oven dried at 60°C temperature for 24 h and grinded to achieve a suitable particle size for use as a partial replacement by weight of cement. Silica fume and fly ash, known for their pozzolanic properties, were used to partially replace sand. Various mix designs were prepared with different proportions of mussel shells (10%, 20%, 30%), silica fume (5%), and fly ash (5%). Mechanical tests, including compressive strength and flexural strength were conducted to evaluate the performance of the modified mortars after 7, 14 and 28 days. The results demonstrate that the combined use of mussel shells, silica fume, and fly ash significantly enhances the mechanical properties of cement mortar. Notably, the mix with 10% mussel shells, 5% silica fume, and 5% fly ash exhibited a remarkable increase in compressive and flexural strengths, achieving a 20% and 25% improvement, respectively, compared to the other mixes. In conclusion, the synergistic use of mussel shells, silica fume, and fly ash in cement mortar presents a promising approach to achieving sustainability and improved mechanical properties in construction materials. This research opens avenues for further exploration and optimization of alternative materials in the construction industry.

   7. Strength Properties of Water-Cured One-Part Geopolymer Concrete Containing Platinum Slag Aggregate

      Babatunde L. Ajayi, Mustapha B. Jaji, Adewumi J. Babafemi

      Abstract

      Using waste materials in concrete production is a sustainable approach to mitigate carbon emissions, reduce waste and environmental pollution, lower costs, and preserve natural resources. This study investigates the potential of one-part geopolymer concrete (OGPC) produced with ground granulated corex slag and naturally abundant metakaolin as a binder, combined with Polokwane platinum slag (PPS) aggregate as a replacement for natural fine aggregate (Malmesbury sand). The workability, mechanical properties (compressive, flexural, and splitting tensile strengths), and morphology of water-cured OGPC with varying PPS aggregate contents (0%, 25%, 50%, 75%, and 100%) were examined. The results indicate that increasing PPS aggregate content progressively improved workability, with a 23.8% improvement at full replacement. The compressive strength result shows an optimal sand replacement level of 50% having 26.7 MPa and 30.8 MPa, at 7- and 28-day, respectively, with a 4.8% improvement compared to the control at 28 days. However, higher PPS aggregate inclusion (75% and 100%) led to an 8.5% and 8.8% decrease in the compressive strength, respectively. At 7- and 28-day, the splitting tensile strength (STS) remained comparable to the control up to 50% PPS aggregate inclusion but declined by 20.6% with full sand replacement. Flexural strength exhibited a different trend, with a 6.4% reduction at 50% PPS aggregate and further decreases by 13.7% and 21.3% at 75% and 100% PPS inclusion, respectively. In conclusion, PPS aggregate can replace up to 50% of natural sand by volume in one-part metakaolin-based geopolymer concrete, offering potential benefits in reducing aggregate costs and minimising environmental pollution.

   8. Eco-Friendly Mortars with Barite and Hydraulic Lime Under Thermal Exposure: Study of Morphology, Physical and Mechanical Properties

      Majed Noumi, Khaled Saidani, Lasaad Ajam

      Abstract

      The study evaluates the impact of barite and hydraulic lime on the physical and mechanical properties of mortars exposed to high temperatures. Six mortar formulations were developed, incorporating a volumetric substitution of 0% or 33% of cement with hydraulic lime, and 0%, 50%, or 100% of sand with barite, these formulations conduct to obtain more eco-friendly mixtures than conventional cement-based concrete. The physical properties (density, ultrasonic pulse velocity, water absorption by immersion and capillarity) and mechanical properties (dynamic modulus of elasticity, compressive strength, and tensile strength) were measured after exposure to 20 °C, 300 °C, and 600 °C. A surface and microscopic morphological analysis of the samples, using scanning electron microscopy (SEM), was also conducted. The results indicate that the addition of barite increases the density and water absorption of the mortars. Barite improves the tensile strength while decreasing the dynamic modulus of elasticity at high temperatures. At 300 °C, the incorporation of barite and hydraulic lime increases compressive strength, while a significant decrease is observed at 20 °C and 600 °C. Compressive strength remains stable for reference mortars and those with 50% barite but decreases with 100% barite and in the presence of lime. Furthermore, the combined use of barite and hydraulic lime visibly improves the morphology of the mortars after exposure to elevated temperatures. These results demonstrate that barite and hydraulic lime can enhance the resilience of mortars subjected to thermal stress, thus contributing to more durable and high-performing construction materials.