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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]

• 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]

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]

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]

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]

• Strengthening of RCA via cement slurry and biocement treatment was performed. • Both the control and treated aggregates are characterised for its possible use. • A novel method of fabricating concrete cubes with one aggregate has been developed. • Micromechanical property using nanoindentation was assessed at concrete interface. • RCA can be used to replace the NCA without compromising its performance. Variable quality of recycled aggregates especially attached mortars leading to weak interfaces is a primary drawback of recycled coarse aggregate (RCA). This investigation explores strengthening of such aggregates by biocement treatment and compares it with the conventional cement slurry treatment. The effect of the treatments on the aggregates has been recorded in terms of water absorption and mechanical properties. To study the concrete-aggregate interface, a novel method of fabricating concrete cubes with one aggregate has been developed. Damage evolution at the interfaces has been recorded with advanced monitoring techniques. Microstructural behaviour and elemental composition in the interface were also recorded. The test results show that the biocement treatment reduces the water absorption of RCA by about 71%. A microstructural study demonstrates that biocement, due to its considerably low viscosity, is able to penetrate the porous interfacial mortar within RCA and densify it. The micromechanical properties using nanoindentation provides more insights in improving of interfacial transition zones. The treatment improves the aggregates to a level that it can be used to replace the natural aggregates without compromising its performance. [ABSTRACT FROM AUTHOR]

The research aims at evaluating the effect of using recycled coarse concrete aggregates (RCA) on the basic properties of hot mix asphalt made with different grades of bitumen (60/70 and 80/100). First, recycled aggregate properties have been determined and compared to those of normal aggregates. Except for absorption, there were no significant differences between normal aggregates and RCA. Later, recycled aggregates were introduced in asphalt mixes using either 60/70 bitumen or 80/100 bitumen. In these mixes, natural coarse aggregate was partly (0%, 25%, 50% and 75%) or totally (100%) replaced by recycled aggregates. Replacement results show that the use of recycled aggregates increased the optimum bitumen content of the asphalt mixes. Properties and performance of mixes made from both grades of bitumen were compared. Although the increase of RCA percentage decreased the resilient modulus of the asphalt mixes, it increased their skid resistance. However, 60/70 bitumen increased the resilient modulus and skid resistance of the asphalt mixes compared to 80/100 bitumen. Mixes containing RCA show lower water sensitivity (stripping resistance) than RCA-free mixes. However, replacements up to 50% do not violate the 80% tensile strength ratio limit. Although the 50% replacement limit is acceptable, however, the volumetric properties were violated at this replacement ratio. Therefore, for both grades of bitumen, replacements more than 25% should not be used in hot mix asphalt for heavy traffic pavements. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregates (RCA) can be used as a replacement of natural aggregates for a concrete production to save natural sources and also to decrease amount of demolition waste which has to be landfilled. Precast production generates some percentage of defected elements which are carted off and recycled with other demolition waste. In this study defected elements are separately recycled into RCA with beneficial properties and used directly into new mixtures for precast elements. Results from testing of RCA and application into new concrete mixtures are presented. It was proved that the replacement of raw aggregates by RCA up to 20% has no negative influence on physico-mechanical properties of concrete. [ABSTRACT FROM AUTHOR]

Due to its considerably lower embodied carbon and making use of industrial by-products including fly ash and ground granulated blast-furnace slag, geopolymer concrete (GPC) is considered as a sustainable alternative to Portland cement (OPC) concrete. However, prior to granting GPC a green label and encouraging its widespread use, a number of other important possible impacts associated with this new material throughout its life cycle need to be further investigated. One of the important aspects of sustainability which has received little attention with regards to GPC is the end-of-life impact. While end-of-life strategies such as recycling and reuse have been widely investigated for conventional concrete, the applicability of such strategies to GPC has not been investigated. This paper presents the results of an experimental study conducted to investigate the recyclability of GPC. Basic properties of recycled geopolymer aggregates (RGAs) including water absorption, density and Los Angeles abrasion loss as well as the effects of size of RGA on these properties were investigated. In addition, the effects of the different replacement ratios of coarse RGA for coarse natural aggregates on the properties of the new recycled aggregate geopolymer concrete (RAG) including compressive strength, flexural strength and modulus of elasticity were investigated. The RGA and RAG properties were compared with those of recycled OPC concrete aggregate (RCA) and recycled aggregate OPC concrete (RAC) produced under relatively similar conditions. [ABSTRACT FROM AUTHOR]

The emerging sustainable development movement in the construction industry requires the recycling of waste materials to reduce the negative environmental impact of construction activities. In many countries, old concrete, a major waste stream generated from the demolition of obsolete buildings/structures, is being recycled. However, for various reasons, progress toward concrete recycling varies from country to country. This paper discusses the current status of concrete recycling in the U.S. construction industry based on results from a two-part questionnaire survey. The first part of the survey collects information on the recycling practices of surveyed concrete companies. The second part adapts questions from a study conducted in Australia and Japan to examine the awareness, benefits, difficulties, and recommended methods related to concrete recycling. The findings showed that although recycling old concrete is common in the U.S., its application is mostly limited to backfill and pavement base; using waste concrete in new concrete production is not widely applied. There are also similarities and differences in the perceptions of concrete recycling between U.S. concrete companies and their counterparts in Australia and Japan. [ABSTRACT FROM AUTHOR]

The production of reactivated cementitious materials is an option for the recycling of hydrated-cement-rich fines discarded during recycled aggregate production. Reactivation is based on a thermal process where calcium silicate hydrates present in the fines decompose forming new hydraulic compounds. In the reported study, materials reactivated at temperatures between 660 °C and 940 °C were characterized using X-Ray diffraction and particle size analysis, and evaluated as binders using a central composite experiment to model the effects of reactivation temperature and reactivated material substitution level on the flowability, compressive strength and expansion of mortar mixtures. Reactivation temperature effects correlated with the relative concentration of reactive phases, particularly a stabilized form of alpha'-C 2 S identified in the materials. Substitution effects depended on the supplementary material tested, and lacked significant interaction with reactivation temperature. In the region explored, mortars based on materials produced at 800 °C, 40% substituted by silica fume, achieved highest strength but lowest flowability. [ABSTRACT FROM AUTHOR]

One of the main environmental challenges in the construction industry is a strong social force to decrease the bulk transport of the building materials in urban environments. Considering this fact, applying more in-situ recycling technologies for Construction and Demolition Waste (CDW) is an urgent need. The European C2CA project develops a novel concrete recycling technology that can be performed purely mechanically and in situ. The technology consists of a combination of smart demolition, gentle grinding of the crushed concrete in an autogenous mill, and a novel dry classification technology called ADR to remove the fines. The feasibility of this recycling process was examined in demonstration projects involving in total 20,000 tons of End of Life (EOL) concrete from two office towers in Groningen, The Netherlands. This paper concentrates on the second demonstration project of C2CA, where EOL concrete was recycled on an industrial site. After recycling, the properties of the produced Recycled Aggregate (RA) were investigated, and results are presented. An experimental study was carried out on mechanical and durability properties of produced Recycled Aggregate Concrete (RAC) compared to those of the Natural Aggregate Concrete (NAC). The aim was to understand the importance of RA substitution, w/c ratio and type of cement to the properties of RAC. In this regard, two series of reference concrete with strength classes of C25/30 and C45/55 were produced using natural coarse aggregates (rounded and crushed) and natural sand. The RAC series were created by replacing parts of the natural aggregate, resulting in series of concrete with 0%, 20%, 50% and 100% of RA. Results show that the concrete mix design and type of cement have a decisive effect on the properties of RAC. On the other hand, the substitution of RA even at a high percentage replacement level has minor and manageable impact on the performance of RAC. This result is a good indication towards the feasibility of using RA in structural concrete by modifying the mix design and using a proper type of cement. [ABSTRACT FROM AUTHOR]

Modern comminution research and development are mainly product driven rather than material driven. An opinion that is gaining acceptance throughout the comminution community is that it is desirable for the comminution field to evolve toward material driven process design. To this end, this paper introduces the concept of mechanical texture, which corresponds to those textural properties of materials that have a direct bearing on their mechanical and fracture properties, which in turn should be the primary target for comminution process research and equipment design. The paper shows that mass specific fracture energy Ecs is a fracture parameter that is highly sensitive to variations in material texture, leading to selecting Ecs as a sound mechanical texture index. The paper then shows that, in the case of concrete, a set of specific features of the fracture porosity that can be measured inside concrete texture correlate highly with Ecs , thereby defining mechanical texture for concrete comminution. The demonstration that it is possible to establish a direct link between textural properties of concrete and macroscopic properties relevant to comminution shows that material driven comminution process modeling and design are possible and should be encouraged. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new process for concrete recycling is developed in the context of the European C2CA project. [•] The process aims to reduce the impact of construction and demolition waste by in situ mechanical recycling of EOL concrete. [•] The process applies autogenous milling and ADR to extract high-grade 4–16mm recycle aggregate from crushed concrete. [•] Results show that the +4mm recycled aggregate compares favorably with natural aggregate. [ABSTRACT FROM AUTHOR]

Highlights: [•] The properties of waste materials (RCA and SSA) are studied and compared to normal aggregate. [•] The use of RCA adversely affects the properties of concrete, but the use of SSA enhances the properties of concrete. [•] Concrete containing both RCA and SSA is studied. The mechanical properties of RAC are enhanced. [•] Environmental problems can be reduced. [Copyright &y& Elsevier]

Abstract: Demolished concretes to be recycled show great diversity in property with regard to residual potential of resistance to the environmental effects such as frost action, when they are used in a new concrete as aggregate. There seems to exist no appropriate test method fitting specific characteristics of the recycled concrete aggregates with respect to the fair judgement of their unbound state frost durability. This fact rises another important prejudice against performance of recycled concrete aggregates compared to virgin alternatives. This study deals with reliable identification of frost susceptibility of recycled concrete aggregates. An unbound frost durability test with a mild pre-drying procedure (at 50°C) was performed on recycled concrete aggregates originated from both air-entrained and non-air-entrained type of source concretes. The procedure distinctly identified the non-durable recycled coarse aggregates in parallel to freezing and thawing durability results of the concretes incorporating identical aggregates. Sulfate soundness test gave misleading results in judgement of the unbound state frost durability due to the highly disruptive physicochemical effect of the method on the recycled concrete aggregates, regardless of the air void characteristics of the materials. [Copyright &y& Elsevier]

Abstract: Environmental problems have been considered to be serious in the construction industry. Waste management pressures are pressing very hard with alarming industrial warming signals. Among the different types of construction and demolition wastes, concrete is about 81 percent of the volume of construction and demolition waste in Australia. To minimize the concrete waste generated from construction activities, recycling of concrete waste is one of the best methods to improve the environment. However, situations of concrete recycling in different countries vary considerably. Japan is a leading country in recycling concrete waste, with 100 percent recycling of the wastes that are used for new structural applications. This paper investigates the current concrete recycling situations in Australian and Japanese construction industries. A questionnaire survey and structured interviews were conducted. In comparing the current concrete recycling situations between Australia and Japan, it should be noted that major difficulties found from Australian and Japanese construction industries are on different phases of the transition to recycling of construction wastes. Therefore, it is suggested that the Australian construction industry should be: i) developing a unified policy in concrete recycling; ii) providing financial governmental support; iii) developing clear technical specifications or standards on the use of recycled aggregate for structural applications. [Copyright &y& Elsevier]

Studies have been conducted on the repeated recycling of recycled coarse aggregates and recycled fine aggregates obtained from concrete waste, but no research has been conducted on the repeated recycling of recycled powder as a partial replacement for cement, which is pointed out as a major source of CO 2 in the concrete industry. This paper investigates the closed-loop recycling potential of construction wastes by evaluating the effects of repeated use of concrete powder generated in the production of recycled aggregates on the selected fresh and hardened mechanical properties of concrete. Through a series of concrete making and crushing, once-, twice-, three times-recycled concrete powder of less than 150 μm was collected and used as a partial replacement for cement in concrete matrices at replacement levels of 10%, 20% and 30%. According to the experiment results, the replacement ratio and the number of recycling of concrete powder are parameters that affect the properties of concrete, and in particular, the replacement ratio is more affected than the number of recycling. The strength of concrete containing 10–20% concrete powder surpassed the target strength by up to 21% over three times of recycling, and the cost and environmental benefits increase in proportion to the number of concrete powder recycling. This study can contribute to the valorization of construction waste by providing a new initiative for multi-recycling of concrete powder and a closed-loop recycling system for construction waste. • Potential of multi-recycled concrete powder as a cement substitute was evaluated. • Properties of concrete with repeatedly recycled concrete powder were investigated. • Multi-recycling of RP slightly reduces the properties of fresh, hardened concrete. • The environmental and cost benefits increase with the number of recycling. [ABSTRACT FROM AUTHOR]

To prevent rapid climate change, it will be necessary to reduce net anthropogenic CO2 emissions drastically. This likely will require imposition of a tax or tradable permit scheme that creates a subsidy for negative emissions. Here, we examine possible niche markets in the cement and steel industries where it is possible to generate a limited supply of negative emissions (carbon storage or sequestration) cost-effectively.Ca(OH)2 and CaO from steel slag or concrete waste can be dissolved in water and reacted with CO2 in ambient air to capture and store carbon safely and permanently in the form of stable carbonate minerals (CaCO3). The kinetics of Ca dissolution for various particle size fractions of ground steel slag and concrete were measured in batch experiments. The majority of available Ca was found to dissolve on a time scale of hours, which was taken to be sufficiently fast for use in an industrial process.An overview of the management options for steel slag and concrete waste is presented, which indicates how their use for carbon sequestration might be integrated into existing industrial processes. Use of the materials in a carbon sequestration scheme does not preclude subsequent use and is likely to add value by removing the undesirable qualities of water absorption and expansion from the products.Finally, an example scheme is presented which could be built and operated with current technology to sequester CO2 with steel slag or concrete waste. Numerical models and simple calculations are used to establish the feasibility and estimate the operating parameters of the scheme. The operating cost is estimated to be US$8/t-CO2 sequestered. The scheme would be important as an early application of technology for capturing CO2 directly from ambient air. [Copyright &y& Elsevier]

• Thermo-mechanical beneficiation process for crushed concrete. • Quality parameters and acceptance criteria for optimizing recycling. • Tuning of beneficiation based on process efficiency and aggregate quality. • Yield of high-quality RCA, comparable with pristine natural aggregates. • Illustration of potential reuse of RCA fractions in new concrete. In order to move towards a circular economy, it is relevant to maximize the usage of waste materials in construction activities. One such resource that could be extracted from abundant waste are Recycled Concrete Aggregates (RCA). Many methods have been proposed in the last few decades to improve the quality of RCA, with limitations in terms of energy demand or low yield. In the present study, an attempt has been made to employ thermo-mechanical beneficiation to obtain high-quality coarse and fine aggregates, with high yield (>90%). Heating temperature, feed size and residing duration are variables that have been optimized. When waste concrete chunks are heated for about 60 min at 500 °C (932°F) and milled with steel ball charge, the resulting RCA fractions conform to the limits set by stringent codes and guidelines. The beneficiated coarse RCA thus obtained could give concrete performance comparable to that of pristine granite aggregate concrete. [ABSTRACT FROM AUTHOR]

• Microwave is introduced to assist the concrete aggregate recycling. • Temperature field evolution, crack propagation, samples damage and interface properties of concrete are investigated. • The chemical content and micro-structure variations could promote the mortar- aggregate interface debonding. • Energy consumptions and recycled aggregate properties are evaluated to illustrate the efficiency of microwave heating. • Microwave heating tests on standard concretes are conducted to prove its practical applications. 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 investigate the heating process of mortar-aggregate under microwave irradiation. Four different aggregate types are selected that widely used as aggregates in concrete to represent different kinds of aggregates. The temperature field of both mortar and aggregate under different heating time and microwave power input are obtained. The crack formation, propagation and material damage during the heating process are graphically presented. XRD tests and SEM analysis are carried out to clarify the chemical content and microstructure variation around the aggregate-mortar interface before and after microwave heating. The mechanical properties of recycled concrete are evaluated through the UCS tests. Energy consumptions are tested during the heating process. The applications of microwave recovering aggregates from standard concretes are conducted based on the results obtained in the simplified concrete. The research proves that microwave irradiation could weaken the bonding between mortar and aggregate effectively, which provide a contribution and reference for the further application of microwave-assisted aggregates recycling. [ABSTRACT FROM AUTHOR]

• An effective and cheap method of sorting and recycling EoL concrete into clean aggregates introduced. • ADR and HAS technologies provide a prospective future to fully close the materials' loop and to effectively implement circular economy in the construction sector. • ADR and HAS are mobile technologies and this prompts additional benefit for on-site recycling of EoL concrete waste. • Concrete made with coarse and fine recycled aggregates processed by ADR and HAS display comparable compressive strength as the reference concrete. Currently, natural resources are consumed at an alarming rate than their production (United Nations Environment Programme, 2014). This imposes unprecedented pressure on the environment. The problem seems to get worse with the present increase in population and demand for infrastructures. To alleviate these and other related problems, a circular approach to construction material flow is crucial. Recycling construction and demolition wastes (C&DW) to generate high-quality materials is essential to ensure materials circularity in the construction sector. This article, therefore, describes the development of two large-scale technologies called Advanced Dry Recovery (ADR) and Heating Air classification System (HAS). ADR and HAS are industrial-scale technologies aimed to recycle End-of-Life (EoL) concrete into coarse, fine and ultrafine particles. While ADR is used to sort out clean coarse aggregates, HAS is used to produce clean fine aggregates by heating and separating the ultrafine hydrated cement components. The process parameters and the quality of aggregates are briefly described. Accordingly, concrete made of recycled coarse and fine aggregates displays comparable mechanical properties as the reference concrete which is made of natural aggregates. Both technologies are designed to be mobile so that EoL concrete wastes are processed at the site of demolition or close to ready-mix concrete plants, reducing the heavy traffic related to construction activities. These technologies, in general, have a potential in increasing sustainability and thereby greening the construction sector. This is by far a convenient contribution towards sustainable development and a big step towards closing the recycling loop in the construction sector. [ABSTRACT FROM AUTHOR]

The carbonation mechanisms of ground, hydrated cement pastes that mimic recycled concrete fines are investigated under direct wet carbonation. The carbonation is a sequential processes including dissolution of the hydrates, transport of the dissolved material to the precipitation sites and precipitation of the reaction products. During the first stages of carbonation, when portlandite reacts, the reaction is limited by the amount of dissolved CO 2 and potentially by the calcite precipitation rate. When portlandite is depleted, the kinetics is dominated by the dissolution of other hydrates and diffusion of calcium into the solution. The main carbonation products are calcite and an alumina-silica (hydrate) gel. The hydrotalcite-like phase appears to be stable towards carbonation under the experimental conditions employed in this work. The CO 2 concentration and the paste composition have a limited influence on the reaction mechanisms as well as on products formed. [ABSTRACT FROM AUTHOR]

• The recyclability of geopolymer concrete in Portland cement concrete is studied. • Elastic modulus decreased 4% and 13% at 20% and 50% recycled content respectively. • Up to 20% recycled aggregate has no significant effect on flexural strength. • Compressive strength decreased only 14% at 20% recycled aggregate content. • Compressive strength decreased significantly at 50% and 100% recycled content. The available literature on recycling of geopolymer concrete is currently limited to application of recycled geopolymer aggregates as coarse aggregates for new geopolymer concrete. This paper highlights an alternative waste management strategy for geopolymer concrete construction and demolition waste by illustrating the suitability of recycled geopolymer aggregates for full or partial replacement of coarse natural aggregates in the widely used Portland cement concrete. The properties of Portland cement concrete and geopolymer concrete made with varying contents of coarse geopolymer recycled aggregates (0%, 20%, 50% and 100% coarse natural aggregates replacement) are investigated and compared with those of Portland cement concrete containing recycled Portland cement concrete aggregates. The results indicate that up to 20% replacement of coarse natural aggregates with recycled geopolymer concrete aggregates results in only insignificant reductions in the modulus of elasticity, flexural strength and volume of permeable voids as well as a moderate reduction in compressive strength of Portland cement concrete. The negative effects of varying amounts of recycled geopolymer concrete aggregates on the properties of Portland cement concrete is however found to be slightly more significant than those caused by same proportions of recycled aggregates produced from Portland cement concrete waste. Furthermore, incorporation of coarse recycled geopolymer concrete aggregates is found to lead to more significant negative effects on properties of Portland cement concrete than geopolymer concrete. These include respectively 21%, 8.3% and 3.4% further reductions in compressive strength, modulus of elasticity and flexural strength of RAGC compared to RAG at 100% coarse aggregate replacement ratio, highlighting a higher compatibility between geopolymer recycled aggregates and geopolymer binder than Portland cement binder. [ABSTRACT FROM AUTHOR]