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This paper provides an overview of literature on the multiple-time recycling of concrete waste and meticulously analyzes the research findings. The paper begins by reviewing the characteristics of recycled materials such as recycled coarse aggregate, recycled fine aggregate, and recycled powder obtained from concrete waste in relation to the recycling cycle. The influence of each of these materials on the mechanical properties and durability of next-generation concrete is analyzed. Moreover, this paper introduces strategies reported in the literature that aim to enhance the performance of multi-recycled concrete. Lastly, this paper identifies and highlights limitations and research gaps, while providing insightful recommendations to drive future exploration of multi-recycling of concrete.Highlight: Literature review on multi-recycling of concrete waste. Summary of effects of multi-recycling on properties of recycled materials/products. Review of strengthening methods for multi-recycled concrete. Identifying research gaps and proposing directions for future studies. [ABSTRACT FROM AUTHOR]

Acetic acid has been used to leach Portland cement paste, and the effect of acid concentration, liquid/solid ratio, temperature, and time on leaching of Ca, Al, Fe and Si is reported. The silica-rich solid residue (SR) remaining after leaching was washed, dried, and ground. This amorphous aluminosilicate has comparable pozzolanic reactivity to commercial supplementary cementitious materials (SCM) such as coal fly ash. The 28-day compressive strength of 0.5 w/b mortar containing 20% CEM 1 replaced with SR extracted from cement paste (63.6 MPa) was higher than the reference (51.2 MPa). The leachate from acid leaching contains high levels of Ca2+ ions, and these can sequester CO2 under controlled conditions to form vaterite, a spherical polymorph of CaCO3. Cement paste present in waste concrete can therefore be used to form a reactive silica-rich SCM in a process that sequesters carbon. The research has implications for the development of circular concrete. [ABSTRACT FROM AUTHOR]

The construction industry in Jordan plays a pivotal role in the national economy but also generates a significant amount of concrete waste, leading to environmental and health challenges. Current waste management practices involve landfill use and unregulated disposal, demonstrating the country's infrastructural shortcomings in concrete waste handling. Despite the recognized importance of the construction sector and the challenges of concrete waste management, more comprehensive studies need to focus on the practicality and benefits of recycling concrete within a circular economy framework in Jordan. This gap hinders the development of effective strategies that could mitigate environmental impacts, promote sustainability, and leverage economic and social benefits in the construction industry. Given the accelerating urbanization, increasing environmental awareness, and the pressing need for sustainable development goals, the timing for this study is critical. It aims to catalyze a timely shift toward more sustainable waste management practices that align with global sustainability trends and national priorities. This study aims to fill the knowledge gap regarding the practicality of recycling concrete within a circular economy context in Jordan and explore the hypothesis that adopting circular economy principles can enhance resource efficiency, reduce waste, lower greenhouse gas emissions, foster economic benefits, and create job opportunities within the sector. Methodologically, this research comprises an analysis based on literature, international comparisons, and technical, economic, and ecological explorations of concrete recycling in Jordan. The literature study establishes a foundational understanding of the current waste management landscape, the anticipated benefits of concrete recycling, and the challenges to its implementation. Furthermore, a technical analysis evaluates the quality and applicability of recycled concrete. The in-depth examination of Jordan's concrete waste problem highlights the urbanization challenges, regulatory gaps, and environmental, social, and economic impacts. Barriers, solutions, and recommendations are discussed through an interdisciplinary lens. This integrated approach supports the transition toward a sustainable, environmentally responsible, and economically viable construction sector. The findings could contribute to policy-making and the advancement of industry practices, ultimately promoting sustainable development in Jordan. [ABSTRACT FROM AUTHOR]

The clinker in cement largely determines the environmental footprint of concrete. Therefore, concrete recycling should focus on retrieving high-quality cementitious fractions to replace clinker. This requires a shift from current traditional recycling techniques towards innovative recycling methods, enabling recovery of not only clean secondary aggregates, but also residual cementitious fines (RCF), potentially eliminating the carbon dioxide emissions associated with them. The production and upcycling of RCF offer new implementation routes that were previously deemed unfeasible. However, the properties of RCF may vary based on their origin, affecting their replacement and upcycling potential. Consequently, assessing the original concrete quality, with a focus on the binder type, before demolition is important. A handheld x-ray fluorescence technique appears promising for this purpose. To achieve effective separation of clean secondary aggregates from the original cementitious content, innovative crushing and separation techniques are needed. Additionally, electrostatic separation shows significant research potential for further optimizing RCF.

This paper presents simulations of different concentration plants that use Inert Construction and Demolition Waste as feed to generate coarse aggregates from old concretes. Different feed materials were studied: CDW generated in Spain; low-strength concretes, C16/20, which are ordinary concrete used in civil construction; and high-strength concretes, C50/60, from specific demolitions, such as old viaducts and bridges. Granulometric and densimetric analyses were performed, and the composition of the granulometric fractions of the proposed concretes were analyzed based on previous studies carried out, to understand the materials that can be recovered and considered for reinvestment in the market. Investment analysis considering the CAPEX, OPEX, revenue, IRR, MIRR, NPV, and DPP of the different concentrating plants with varying streams of concentration to recover the materials of interest (coarse aggregates) are presented and discussed. The results of the analyses indicate greater viability in plants that use mobile plants and the use of water jigs. [ABSTRACT FROM AUTHOR]

Many researchers have investigated the solutions for the problem of solid waste in different ways. An example of that is reusing polyethylene terephthalate (PET) as reinforcement to concrete. Strapping plastic belts used to tie clay bricks while transportation in trucks are one of the common waste of construction that could be beneficial in enhancement of concrete flexural behaviour due to its high tensile strength. This paper is a trial to investigate the effect of utilizing waste strapping plastic belts on the flexural behavior of concrete. Concrete prisms (100*100*500mm) were reinforced with plastic belts as the main reinforcement for flexural strength. Five amounts of reinforcement were added to the concrete section in the tension zone (81, 67.5, 54, 40.5, 27 sqr mm). The reinforcement was included in concrete sections internally or externally using suitable glue. The behavior of the reinforced prisms was compared to plane concrete prisms (containing no reinforcement). Tests results showed an enhancement in flexural strength of concrete section while reinforcement ratio is increased externally. The addition of 81 mm² of plastic straps externally, increased the flexural strength by 21% compared to sections with 27 mm² reinforcement. The enhancement in flexural strength as internal reinforcement is added was limited. According to the flexural test of reinforced concrete prizms. Adding 81 mm² of plastic straps internally, reduced the flexural strength by 18% compared to sections with 54 mm² reinforcement due to the splitting of the cover as the area of the reinforcement increases. Increasing the number of belts in the section results in a sever reduction in the spacing between each two belts, leading to increase concrete cover tendency to split. For that, increasing the amount of plastic diversely affects connectivity for the internally reinforced sections. [ABSTRACT FROM AUTHOR]

The construction industry in Jordan plays a pivotal role in the national economy but also generates a significant amount of concrete waste, leading to environmental and health challenges. Current waste management practices involve landfill use and unregulated disposal, demonstrating the country's infrastructural shortcomings in concrete waste handling. Despite the recognized importance of the construction sector and the challenges of concrete waste management, more comprehensive studies need to focus on the practicality and benefits of recycling concrete within a circular economy framework in Jordan. This gap hinders the development of effective strategies that could mitigate environmental impacts, promote sustainability, and leverage economic and social benefits in the construction industry. Given the accelerating urbanization, increasing environmental awareness, and the pressing need for sustainable development goals, the timing for this study is critical. It aims to catalyze a timely shift toward more sustainable waste management practices that align with global sustainability trends and national priorities. This study aims to fill the knowledge gap regarding the practicality of recycling concrete within a circular economy context in Jordan and explore the hypothesis that adopting circular economy principles can enhance resource efficiency, reduce waste, lower greenhouse gas emissions, foster economic benefits, and create job opportunities within the sector. Methodologically, this research comprises an analysis based on literature, international comparisons, and technical, economic, and ecological explorations of concrete recycling in Jordan. The literature study establishes a foundational understanding of the current waste management landscape, the anticipated benefits of concrete recycling, and the challenges to its implementation. Furthermore, a technical analysis evaluates the quality and applicability of recycled concrete. The in-depth examination of Jordan's concrete waste problem highlights the urbanization challenges, regulatory gaps, and environmental, social, and economic impacts. Barriers, solutions, and recommendations are discussed through an interdisciplinary lens. This integrated approach supports the transition toward a sustainable, environmentally responsible, and economically viable construction sector. The findings could contribute to policy-making and the advancement of industry practices, ultimately promoting sustainable development in Jordan.

This research examines damage experienced by concrete recycling factories of construction concrete residuals. The study integrates three analytical methods: Pareto Charts, Ishikawa Diagrams, and FMEA Tables. Pareto charts are employed to identify dominant types of damage. Ishikawa diagrams pinpoint potential causal factors, including human, machine, method, and environmental elements. The FMEA Table assesses the impact, frequency, and ease of detection level for each causal factor. Data for analysis were gathered through interviews, observations, and document studies. The results of the Pareto analysis reveal four dominant types of damage: damage to recycling screws, cyclone pumps, vibro screens, and WLC sensor components. Potential causal factors for each component are identified in the Ishikawa Diagram. These factors encompass human, machine, method, and environmental elements. Further, the FMEA Table analysis uncovers several factors contributing to a high-risk priority number. These factors include poor component quality, operational errors, overloading, and insufficient maintenance. The analysis results conclude that it is necessary to enhance quality control design by employing more reliable components and integrating sensors for overload detection. Additionally, the study emphasizes the need to improve the current quality control system by incorporating quality checkpoints and ensuring that users are adequately prepared to execute the operation and maintenance processes at the concrete recycling plant.

Abstract The west section of the Governor Mário Covas São Paulo Metropolitan Road Ring was opened to traffic in 2002. The original pavement was a jointed plain concrete pavement with dowelled joints and a design flexural strength (or modulus of rupture) of 4.5 MPa. Premature failure of the concrete slabs was observed not only by engineers and users, but also reported by the media. Concrete slabs soon started being demolished and replaced. Many of the removed slabs were taken to a nearby recycling plant for crushing. However, the resulting recycled concrete aggregate was not used in the manufacturing of the new slabs. There were concerns that the potential presence of detrimental chemical substances had caused the early deterioration of the slabs. If that were true, using recycled aggregates obtained from the original concrete could result in the same issues in the new mix. This paper describes a feasibility study on recycling the original concrete for use as aggregate in new concrete slabs. The first goal was to verify the presence of fluorite as detrimental substance in the existing concrete because there was a suspicion among concrete technologists engaged on mixture design during the construction. Chemical analysis using X-ray fluorescence spectrometry did not show the presence of chemical components detrimental to concrete durability. Therefore, the second goal was to accept the material for recycling and discuss mix proportions, strength, stiffness, fracture toughness, and fatigue. Although some of the concrete properties were affected by the inclusion of recycled aggregates in the mix, the results indicate that it is possible to use recycled aggregates produced from the original concrete to cast new concrete slabs, however requiring greater thicknesses. The fatigue performance of recycled mixtures points out the demand for thicker and eventually more expansive design solutions.

Investigations of the CO2 Storage Potential of Recycled Concrete Aggregates and Cement Samples under Forced Carbonation The production of concrete, in particular the cement contained as a binder, causes a high proportion of human induced climate‐impacting gas emissions. Studies show that the decarbonization of limestone causes at least 8 % of global CO2 emissions, which underlines the acute need for action and research. Due to the current building and infrastructure stock and its increasing obsolescence or replacement, the amount of available demolition material is constantly increasing. In many cases, this material consists of high‐quality concrete that could be reused as recycled aggregate in the production process to conserve primary raw material sources. Most of this crushed concrete is not carbonized. This means that this potential could be used as a CO2 sink in the course of a recycling process. The recycled and carbonized material can be used as a substitute for natural grains. Due to the admixture as aggregate in the course of the concrete production, the degree of carbonation is irrelevant for steel corrosion or related problems. The main objective of this work was to investigate the CO2 absorption capacity of concrete waste in order to quantify its use as a potential carbon sink. The test series show that the ecological footprint of concrete can be significantly reduced by exploiting its carbonation potential by storing more than 1.3 % CO2 of the original mass after 24 hours. [ABSTRACT FROM AUTHOR]

Introducing the principles of circular economy into the concrete industry would significantly contribute to the sustainability of this sector. Even though recycling ranks below waste elimination, the generation of concrete waste is inevitable, and modern recycling strategies cannot efficiently tackle waste concrete fines (WCF) that represent an enormous environmental burden. Inspired by recent advances in self-healing concretes and biocementation of loose soil, we propose harnessing bacteria for bonding WCF to form artificial rocks that could be used as construction material. The devised technology brings many obstacles that can be tackled based on extensive research offered in this critical review, focused mostly on different bacterial metabolic pathways resulting in calcite precipitation and their environmental impacts. The most frequently exploited pathway in materials engineering, ureolysis, was employed to demonstrate the technical feasibility of WCF recycling using Sporosarcina pasteurii. Despite promising results of this demonstration, an alternative approach must be sought to reduce the negative environmental impact associated with the use of ureolytic bacteria as it exceeds potential benefits. Such an approach could be based on the use of by-products from other industries to replace laboratory-grade chemicals, or on utilization of different metabolic pathways, such as carbonic anhydrase or methane oxidation. [ABSTRACT FROM AUTHOR]

Recently, studies on multiple recycling of concrete have been attracting attention. In general, multiple recycling increases adhered mortar content of aggregate, consequently, the water absorption of the multiple recycled aggregate is increased, and the slump of concrete with the multiple recycled aggregate is reduced. Therefore, this study attempted to offset the slump loss by increasing the plasticizer dosage, and investigated the effect of the increased plasticizer dosage on the various properties of multiple recycled aggregate concrete. The properties investigated included slump, air content, density, compressive strength, splitting tensile strength, ultrasonic pulse velocity, and capillary absorption. The results showed that all selected properties of the multiple recycled aggregate concrete were lower than those of reference concrete at the same plasticizer dosage due to the lower quality of the multiple recycled aggregate. However, the slump could be improved by adjusting the amount of plasticizer, and furthermore, within a certain range, the increase of the plasticizer dosage improved the density, sorptivity, and mechanical strength, demonstrating the multiple recycled aggregate concrete could achieve requirements for the use of structural concrete. [ABSTRACT FROM AUTHOR]

In this study, we explored the potential of microbiologically induced calcite precipitation (MICP) for enhancing the microstructural integrity of waste concrete fines (WCF). Traditionally, ureolytic bacteria, such as Sporosarcina pasteurii , have been widely used in MICP due to their ability to produce calcium carbonate via urea hydrolysis, but this process generates ammonia, raising environmental concerns. As an alternative, we employed the carbonic anhydrase pathway using Bacillus pseudofirmus and Bacillus cohnii to induce biomineralization without ammonia byproducts. We examined three types of WCF materials and found that samples containing gypsum facilitated the formation of AFt phases (ettringite/thaumasite crystals) when treated with these bacteria, significantly increasing WCF cohesion and forming strong conglomerates. Comparative analysis revealed that facultative anaerobes exploiting the carbonic anhydrase pathway outperformed ureolytic bacteria in strengthening the material. Investigations into pre-compaction and feather fiber reinforcement did not yield improvements in strength and stiffness. [ABSTRACT FROM AUTHOR]

The growing importance of a circular economy also holds possibilities for concrete. Some of the principles of circularity, like the re-use of "waste" as secondary raw material and the optimisation of the design with regards to lifespan, environmental impact and re-use, can be applied. Several technological innovations in this domain are in an advanced stage of development. However, the transition from research to full commercial applications is held back, mostly due to the absence of documented experience and the lack of a technical framework (prescriptions). In order to accelerate the adoption of new technologies, the Belgian Building Research Institute (BBRI) started the project "Circular.Concrete". In this paper, the results are presented of validation tests regarding 1) smart crushing technology, 2) the carbonation of recycled aggregates, 3) concrete using only recycled aggregates and 4) the use of alternative binders and supplementary cementitious materials.

Multidisciplinary approach is used to evaluate concrete with recycled concrete aggregates (RCA) from technical, environmental impacts and product circularity perspectives. Two RCA replacements investigated, RAC50: fine aggregates; RAC100: both coarse, fine aggregates. Reference, recycled concretes have same cement content, similar workability and compressive strength requirement, proven experimentally. RCA is sourced from pre-fab element discards of a Swedish plant, the logistical alternatives requiring environmental impact analysis. Alternatives are RCA crushing at plant and crushing at a different location including transportation. LCA shows transportation is second largest contributor after cement in all impact categories. RAC alternatives show lower total impact than reference concrete due to RCA replacement. A circularity index for concrete based on economic value of recirculated aggregates; supplements LCA for sustainability reporting. Circularity index results: RAC100 > RAC50 > RC. Combining circularity index with LCA helps optimize recycling process with regard to amount of recycled material and logistics respectively. [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregate (RCA) from construction and demolition (C&D) waste is a rational way towards better sustainability in the construction industry. By using concentrated solar energy for the heating, thermomechanical beneficiation of concrete waste has been shown here to produce high-quality RCA. In this pioneering study, demolished concrete was heated using solar radiation concentrated through large reflectors and cast iron receivers, and subsequently scrubbed to yield coarse and fine RCA, with properties similar to those of pristine aggregates and much better than those obtained from just mechanical crushing. The concrete produced using these beneficiated aggregates is seen to meet the requirements for typical structural applications. [ABSTRACT FROM AUTHOR]

Reutilisation of the construction and demolition (C&D) wastes as aggregate in concrete is a vital step towards sustainability as it prevents depletion of natural resources as well as alleviates wastes. However, the attached mortar on the aggregate surface renders certain shortcomings like excessive water absorption, high porosity, and weak interfaces. Recycled aggregates can be treated to improve these shortcomings. However, the minimisation of the drawbacks involves huge energy, materials, and cost. Moreover, the efficacy of such adopted method is sometime questionable, and which needs further research. This study demonstrates bio-treatment of recycled coarse aggregate (RCA) as a means of upcycling and compares it with conventional cement slurry treatment. A novel spraying technique has been applied that significantly economises biocement treatment. The experimental results show that biocement treatment reduced the water absorption by 70%. The treatment has filled the pores of RCA and has prevented water absorption. In contrast, cement slurry coating treatment shows increase in water absorption of RCA by 19%. The compressive strength of concrete with 100% biocement treated RCA surpasses that of concrete with natural coarse aggregates. The genesis of this dramatic improvement in case of biocement has been established through micro-scale studies including scanning electron microscopy and energy-dispersive X-ray spectroscopy. The cost analysis demonstrates that RCA upcycled with biocement treatment is more economical than natural aggregates or cement treated ones. Findings of the present study led to the conclusion that 100% replacement of natural coarse aggregates can be achieved by upcycling C&D wastes as coarse aggregate through bio-treatment. [ABSTRACT FROM AUTHOR]

Due to the potential for significant process benefit, microwave assisted concrete recycling is highlighted by many scholars and engineers over the world recently. In this paper, a multi-field model is established to simulate the microwave heating process of concrete specimen with single-particle aggregate by using of COMSOL Multiphysics. The validation of this model is verified by comparison with temperature from experiment. Mechanical properties of aggregate-mortar interface during microwave heating process was experimentally investigated. Electric, temperature, stress field evolution and moisture transformation during microwave heating process are discussed in detail. Temperature and stress gradient at mortar-aggregate interface influenced by microwave heating power, frequency and duration are analyzed and graphically presented, which are the dominant factors to achieve the interface debonding. Based on the comparison between concrete absorbed energy and temperature variation, energy efficiency for microwave heating concrete is also briefly discussed. Results of this investigation could provide a multi-field understanding for the microwave treatment on concrete.

The reuse and recycling of materials can make an important contribution to the conservation of natural resources in the sense of a circular economy. This applies in particular to high quality recycling, supporting the material use of waste and closing product cycles. The construction sector is the most important sector in terms of available volume of materials for recycling. However, the largest share of recycling (RC) materials goes predominantly into road construction and underground engineering. This research developed a dynamic model and used a simulation tool to calculate future building material flows in the German construction sector of residential buildings to explore the medium- and long-term potential for RC concrete. The results show that, by increasing the RC rate of concrete to produce recycled aggregates for concrete (RAC) from currently 1.5% to 48%, up to 179 million tons of sand and gravel could be saved until 2060. If the current maximum secondary input rate of RAC of 45% is increased to 70%, the savings could rise over another 66 million tons. If a secondary input rate of 100% is applied, RAC could completely fulfill the demand for sand and gravel for new residential building in Germany from 2045 onwards. The approval of RC concrete for more concrete strength and exposure classes is required to avoid a surplus of RAC and a rapid exhaustion of landfill capacities in the future. [ABSTRACT FROM AUTHOR]

The growing importance of a circular economy also holds possibilities for concrete. Some of the principles of circularity, like the re-use of "waste" as secondary raw material and the optimisation of the design with regards to lifespan, environmental impact and re-use, can be applied. Several technological innovations in this domain are in an advanced stage of development. However, the transition from research to full commercial applications is held back, mostly due to the absence of documented experience and the lack of a technical framework (prescriptions). In order to accelerate the adoption of new technologies, the Belgian Building Research Institute (BBRI) started the project "Circular.Concrete". In this paper, the results are presented of validation tests regarding 1) smart crushing technology, 2) the carbonation of recycled aggregates, 3) concrete using only recycled aggregates and 4) the use of alternative binders and supplementary cementitious materials. [ABSTRACT FROM AUTHOR]

Microwave assisted concrete recycling is highlighted by a large number of research groups all over the world due to its potential for significant process benefit. In this paper, systematic experiments are established to study the microwave heating and aggregate recycling of dried and saturated concrete, respectively, investigating the effect of moisture content on heating results. The heating characteristics, cracks propagation, concrete damage and micro-structure variations were demonstrated. The temperature was higher in dried concrete under microwave heating, while the concrete damage and mortar-aggregate interface debonding were firstly occurred in saturated concrete. Recycled aggregates could be obtained by the combinations of mechanical process and microwave treatment in dried sample. While in saturated concrete, aggregates could be easily separated under relatively sufficient microwave power input. The results show that water content has the vital influence on concrete heating and aggregate separation results. The properties of recycled aggregates were tested to evaluate its further applications. The experimental results can provide a new approach to improve the microwave-assisted concrete aggregate recycling efficiency through the increment of water content. [ABSTRACT FROM AUTHOR]

Microwave heating is a novel and promising method to remove mortar that adheres to aggregates in recycled concrete. A systematic experiment was carried out to evaluate the heating results of mortar-aggregate composite materials after microwave heating with different power and irradiation times. It was revealed that the surface temperature and heating rates of the mortar and aggregate linearly increased with the irradiation time and powers level. After microwave treatment, macrocracks generated along the mortar–aggregate interface and penetrated the mortar matrix until the mortar broke. Moreover, based on the push-out tests, it was found that the interface bond strength of mortar-aggregate after microwave treatment was much lower than that of the untreated specimens. The influence of the temperature difference on the residual bond strength is also discussed in this study. The parametric study confirmed that the bonding strength between mortar and aggregate after microwave heating is reduced. This experimental investigation could provide a basis and reference for microwave-assisted concrete recycling for industrial applications. [ABSTRACT FROM AUTHOR]

The reuse and recycling of materials can make an important contribution to the conservation of natural resources in the sense of a circular economy. This applies in particular to high quality recycling, supporting the material use of waste and closing product cycles. The construction sector is the most important sector in terms of available volume of materials for recycling. However, the largest share of recycling (RC) materials goes predominantly into road construction and underground engineering. This research developed a dynamic model and used a simulation tool to calculate future building material flows in the German construction sector of residential buildings to explore the medium- and long-term potential for RC concrete. The results show that, by increasing the RC rate of concrete to produce recycled aggregates for concrete (RAC) from currently 1.5% to 48%, up to 179 million tons of sand and gravel could be saved until 2060. If the current maximum secondary input rate of RAC of 45% is increased to 70%, the savings could rise over another 66 million tons. If a secondary input rate of 100% is applied, RAC could completely fulfill the demand for sand and gravel for new residential building in Germany from 2045 onwards. The approval of RC concrete for more concrete strength and exposure classes is required to avoid a surplus of RAC and a rapid exhaustion of landfill capacities in the future.

Large quantities of construction and demolition waste is generated annually around the world. Part of this material is processed in recycling plants. After removing metals, fines and lights, the construction and demolition waste is crushed and sized and can be used as aggregates for low resistance concrete, for road sub-base, city landfill and other low value-added applications. For their use as coarse aggregate in structural concretes, construction and demolition waste must exhibit high densities and regularity of the material. This material usually is presented in demolished concretes. About 20% of the particles from demolished concretes can be used as coarse aggregates substituting part of natural aggregates in structural concretes. This article presents studies of demolished concretes recycling by the use of a pneumatic jig. All jigging tests were carried out with three different concretes produced in three strength classes: C16/20, ordinary concrete; C50/60, high strength concrete; and C70/85, very high strength concrete. Based on density distribution of the three concretes, there are reasonable masses with densities over 2.7 g cm−3, particle density considered appropriate to the used as coarse aggregate for structural concretes. The concretes present different mass recoveries of the denser particles (different liberation). Coarse aggregates can be recovered with reasonable masses by the use of air jigs: About 65% for high strength concretes and about 75% for the low strength concrete. The jigging concentration efficiency depends on the concrete liberation, density and size distribution. [ABSTRACT FROM AUTHOR]

This study investigates the potential of microbially-induced calcite precipitation (MICP) in converting waste concrete fines (WCF), an underutilized byproduct generated during the crushing of old concrete, into construction material. WCF samples treated with Sporosarcina pasteurii DSM 33 for periods ranging from 14 to 90 days exhibited up to an 11% increase in CaCO 3 content, compared to a control group treated with a saline solution. The formation of CaCO 3 crystals also resulted in a 15% reduction in porosity and, most importantly, enhanced the integrity of the WCF conglomerates, reaching 20% of the stiffness of autoclaved aerated concrete. These results suggest that MICP could be used for the valorization of WCF, aligning with sustainability and circular economy goals. [Display omitted] • MICP process enhances CaCO 3 content in waste concrete fines (WCF). • S. pasteurii DSM 33 accelerates CaCO 3 crystallization in WCF. • MICP treatment modifies porosity, suggesting improved durability. • Long-term MICP treatment increases mechanical strength of WCF conglomerates. • MICP presents a promising potential for sustainable use of waste concrete. [ABSTRACT FROM AUTHOR]

• An overarching framework, conforming to the ISO standards, for LCA/LCC-type eco-efficiency assessment is proposed. • An impact assessment step is added in LCC to identify the cost stressors at different life cycle stages. • Innovative routes for high-grade concrete recycling within three EU projects (C2CA, HISER, and VEEP) were compared. • Reducing cement and sand in new concrete by using recycled fines and treating waste on-site are most eco-efficient. The increasing volume of Construction and demolition waste (CDW) associated with economic growth is posing challenges to the sustainable management of the built environment. The largest fraction of all the CDW generated in the member states of the European Union (EU) is End-of-life (EOL) concrete. The most widely applied method for EOL concrete recovery in Europe is road base backfilling, which is considered low-grade recovery. The common practice for high-grade recycling is wet process that processes and washes EOL concrete into clean coarse aggregate for concrete manufacturing. It is costly. As a result, a series of EU projects have been launched to advance the technologies for high value-added concrete recycling. A critical environmental and economic evaluation of such technological innovations is important to inform decision making, while there has been a lack of studies in this field. Hence the present study aimed to assess the efficiency of the technical innovations in high-grade concrete recycling, using an improved eco-efficiency analytical approach by integrating life cycle assessment (LCA) and life cycle costing (LCC). Four systems of high-grade concrete recycling were analyzed for comparison: (i) business-as-usual (BAU) stationary wet processing; (ii) stationary advanced dry recovery (ADR); (iii) mobile ADR; (iv) mobile ADR and Heating Air Classification (A&H). An overarching framework was proposed for LCA/LCC-type eco-efficiency assessment conforming to ISO standards. The study found that technological routes that recycle on-site and produce high-value secondary products are most advantageous. Accordingly, policy recommendations are proposed to support the technological innovations of CDW management. [ABSTRACT FROM AUTHOR]

Highlights • Cementitious pastes with large amounts of recycled concrete fines were examined. • Thermal activation of recycled concrete was avoided by using additives. • Addition of fly ash and slag resulted in higher tensile strength in bending. • Presence of recycled concrete in cement pastes resulted in shrinkage mitigation. Abstract Construction and demolition waste recycling for production of new concrete is usually limited to the use of coarse aggregates, and efficient utilization of fine subsieve fractions remains an unresolved issue. In the presented research, Portland cement pastes containing 50% finely ground recycled concrete, blended with lime, fly ash, or blast furnace slag, were studied. SEM-BSE microscopy, EDX analysis, and porosimetry were employed for investigating their microstructure, individual stages of hydration were detected using calorimetry, shrinkage was optically monitored in the early stages of hardening, the evolution of Young's modulus was assessed using the resonance method, and strength was determined from destructive tests. The study suggests that recycled concrete fines can be incorporated into cementitious composites in large amounts and even improve their properties, especially when blended with fly ash or blast furnace slag. Substitution of Portland cement in the studied pastes by recycled concrete led to a compressive strength deterioration, but also a reduction of shrinkage, and an increase of the tensile strength in bending by up to 26%. [ABSTRACT FROM AUTHOR]

Copyright of Waste Forum is the property of Czech Environment Management Center (CEMC) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose:To present a comparative life cycle assessment (LCA) of natural and recycled coarse aggregates used in concrete production.Methods:LCA was used to compare the environmental impacts of three alternative of procurement of coarse aggregates for concrete production: extraction and processing of natural aggregates; recycling of demolished concrete either using a fixed or a mobile plant. Site-specific data supplied by companies were used to model the life cycle of these aggregates. A sensitivity analysis was also made for the critical stages of these three life cycles.Results and conclusion:This paper presents and analyses innovative LCA data of production of coarse aggregates, both natural and recycled (from mobile or fixed recycling plants). The recycling process of aggregates has to be optimised, following a selective demolition of buildings that maximises waste recovery, reuse and recycling. The use of these aggregates in the production of concrete is more favourable than natural aggregates only in terms of land use and respiratory inorganics, but coarse recycled aggregates can present a better environmental performance than natural ones if fine recycled aggregates are also used in concrete production instead of being sent to a landfill. These results are, however, very sensitive to the transportation distances. [ABSTRACT FROM AUTHOR]

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Mineral sequestration stabilizes carbon dioxide in carbonate form, its thermodynamic ground state. In the case of waste concrete, it produces precipitated calcium carbonate, a commodity. We propose an indirect, aqueous process consisting of six steps: (i) recovery of waste cement (primarily calcium silicate hydrate) from waste concrete, (ii) leaching of calcium from waste cement using hydrochloric acid, (iii) purification of the leachate through alkalinity addition, (iv) precipitation of calcium carbonate via aqueous reaction with sodium carbonate, four of which were investigated here. The omissions include regeneration of hydrochloric acid and sodium hydroxide solutions from sodium chloride solution through bipolar membrane electrodialysis and absorption of CO 2 by sodium hydroxide solution. Hydrochloric acid was capable of leaching all the calcium ions present in the fines when the stoichiometric amount was added. Results showed up to 70% of the total calcium ions recovered were associated with waste cement with the remainder from limestone in the aggregates. A bright, high-purity PCC was produced after purification to pH ∼11. The high-purity PCC particles were larger than what is typically used in paper manufacturing (∼2 μm) with metastable morphology. The particle size was reduced to ∼2 μm when the purification stopped at pH 9.0 and a magnesium containing PCC was produced; the morphology remained stable in de-ionized water for 24 h. [ABSTRACT FROM AUTHOR]

In the Netherlands, yearly 20 Mt Construction- and Demolition waste (CDW) is being produced mainly consisting of concrete and masonry rubble. This is two third of the yearly production of concrete (33 Mt). Currently, less than 1 Mt/year of the 20 Mt/year CDW is recycled in new concrete (mainly as coarse recycled concrete aggregates). This preliminary study being part of a larger study, is aiming to increase that amount, amongst others by focusing on use of the fine recycled concrete aggregates. Fine recycled concrete aggregates (fRCA) appear promising for (partial) replacement of natural fine aggregates (sand) and cement in new concrete. Nevertheless, they can be expected to have adverse properties and components that may reduce the performance of the concrete. Their physical, chemical and mechanical properties, which thus may significantly differ from that of natural sand, are still far from being fully investigated. The present paper focusses on characterization of physical properties of fRCA for finding the most critical indicators for fRCA quality. The tests include particle size distribution, morphology, BET surface area, solid density and water absorption of individual and total fractions (0–0.25 mm, 0.25–4 mm and 0–4 mm). The tests are performed on three fRCAs with different origin. Natural river sand with 96 wt.% of SiO2 was also studied to provide a baseline for comparison. Experimental results showed that, on the one side, the particle size distribution, surface area and amounts of individual fractions of fRCAs are significantly different from that of natural sand and that there is a large difference between each other. This is caused by variations of the parent concrete properties and by the type of recycling technique and processes (one step or multiple steps crushing). On the other side, fRCAs have comparative solid densities, which were still lower than that of natural sand. It was also shown that difference in water absorption between fractions 0.25–4 mm and 0–4 mm is very small in all three fRCAs groups. The results of this study will be used for future correlations between investigated properties of fRCAs with properties of concretes with fRCAs. This will be investigated in the next stage of the project, such that these correlations can enable production of durable concretes with fRCAs and assist recyclers in optimization of their production processes based on quality control of fRCAs.

Enormous amount of Construction and Demolition Waste (CDW) are yearly generated in Europe and the predominant material constituent is concrete. Despite the urgency of creating a sustainable solution for End Of Life (EOL) concrete waste treatment, there has not been a large driving force for recycling it into prime grade materials. The C2CA concrete recycling process aims at a cost effective system approach to recycle EOL concrete to hardened cement and clean aggregates. This recycling process consists of a combination of smart demolition, gentle grinding of the crushed concrete in an autogenous mill, and a novel dry classification technology called Advanced Dry Recovery (ADR) to remove the fines. The main factors in the C2CA process which may influence the properties of Recycled Aggregates (RA) or Recycled Aggregate Concrete (RAC) include the type of Parent Concrete (PC), the intensity of autogenous milling (changing the amount of shear and compression inside of a mill) and the ADR cut-size point (usage of +2 mm or +4 mm RA in the new concrete). This study aims to investigate the influence of implied factors on the quality of the RA and RAC. To conduct the study, first of all, three types of concrete which are mostly demanded in the Dutch market were cast as PC and their fresh and hardened properties were tested. After nearly one year curing, PC samples were recycled independently varying the type of PC and intensity of the autogenous milling. Experimental variables resulted in the production of eight types of RA. The physical, mechanical and durability properties of the produced RA were tested and the effect of the experimental variables on their properties were investigated. According to the results, the type of PC is a prevailing parameter for the final properties of RA, in comparison with the milling intensity. Moreover, it is observed that a variation in the milling intensity mostly influences the properties of RA produced from a lower strength PC. Furthermore, the performance of the RA in the new concrete was studied. Four types of RAC were produced based on the modified recipe of their corresponding PCs. For the modification of the recipes, water absorption and density of RA were taken into account while the amount of applied cement and consistency class was kept similar to the corresponding PC. Experimental results show that the RAC samples compare favourably with PC. Among various autogenous milling intensities, milling at medium shear and compression delivers better properties for RA and RAC. Good performance of RAC with the incorporation of 2–4 mm ADR fines and RA, confirms the possibility of setting ADR cut-size point on 2 mm. [ABSTRACT FROM AUTHOR]