Search

Diese Masterarbeit beschäftigt sich mit dem Thema Recycling-Baustoffe in der Beton- und Asphaltproduktion. Die Ziele dieser Arbeit sind die gesetzlichen Voraussetzungen, welche aktuell an Recycling-Baustoffe in der Beton- und Asphaltproduktion gestellt werden, zusammenzufassen sowie mögliche Maßnahmen zu erläutern, welche zu einer Marktdurchdringung von Beton und Asphalt mit erhöhten Anteilen an Recycling-Baustoffen führen. Die Thematiken Nachhaltigkeit, Ressourcenschonung und Recycling nahmen branchenübergreifend in den letzten zwei Jahrzehnten einen immer größeren Stellenwert ein. Durch diverse politische Zielvorgaben, Rahmenstrategien und Aktionsplänen gab es auch in der Baubranche ein großes Umdenken. Um die europäischen sowie nationalen Zielvorgaben erreichen zu können wird die Verwendung von Recycling-Baustoffen in Zukunft immer mehr in den Mittelpunkt der Beton- und Asphaltproduzenten rücken. Im ersten Kapitel wird die Thematik des Urban Mining erläutert und die angefallenen Bau- und Abfallmengen in Österreich aus dem Jahr 2018 dargestellt. Das Kapitel zwei verschafft einen Überblick über die Vorschriften, welche aktuell bei einem Abbruch bzw. Rückbau zu beachten sind. Im Fokus des dritten Kapitels stehen die gesetzlichen Voraussetzungen, Eigenschaften und Anforderungen, welche allgemein an rezyklierte Gesteinskörnungen gestellt werden. Im vierten und fünften Kapitel werden detailliert die bautechnischen Voraussetzungen und Anforderungen, die rezyklierte Gesteinskörnungen bei Verwendung im Beton oder Asphaltmischgut aufweisen müssen, erläutert. Aufgrund der Experteninterviews, welche mit renommierten Mischanlagenherstellern sowie Beton- und Asphaltproduzenten durchgeführt wurden, bietet das Kapitel sechs einen Überblick über die aktuelle Marktsituation. Des Weiteren werden abhängig vom Baustoff die zu setzenden Maßnahmen beschrieben, welche für einer Marktdurchdringung der RC-Baustoffe in der Beton- und Asphaltproduktion sorgen. This master thesis deals with the topic of recycled construction materials in concrete and asphalt production. The objectives of this thesis are to summarize the legal requirements currently imposed on recycled construction materials in concrete and asphalt production and to explain possible measures leading to a market penetration of concrete and asphalt with increased proportions of recycled construction materials. The issues of sustainability, resource conservation and recycling have become increasingly important across all industries in the last two decades. Various political targets, framework strategies and action plans have also led to a major rethink in the construction industry. In order to achieve the European and national targets, the use of recycled construction materials will become more and more important for concrete and asphalt producers in the future. In the first chapter, the topic of urban mining is explained and the construction and waste volumes in Austria from 2018 are presented. Chapter two provides an overview of the regulations that currently have to be observed during demolition or dismantling. Chapter three describes the legal requirements, characteristics and demands that are generally placed on recycled aggregates. The fourth and fifth chapters explain in detail the constructional requirements and specifications that recycled aggregates must meet when used in concrete or asphalt mixes. Based on expert interviews conducted with renowned mixing plant manufacturers and concrete and asphalt producers, chapter six provides an overview of the current market situation. Furthermore, depending on the construction material, the measures to be taken are described, which ensure a market penetration of recycled construction materials in concrete and asphalt production. vorgelegt von: Stefan Arthofer Auch als Printexemplar in der Bibliothek verfügbar Masterarbeit Wien, FH Campus Wien 2020

Im Rahmen dieser Bachelorarbeit wird ein Teilgebiet von Beton, speziell die Betonzusammensetzung, die Klasseneinteilung und die Porenstruktur näher erläutert, um einen groben Überblick über den jahrhundertealten Baustoff zu verschaffen. Des Weiteren wird die Entstehung von Zementleim und die dahinterstehende chemische Reaktion, die Hydratation, erklärt, welche die Grundlage für die darauffolgende Karbonatisierung von Beton darstellt. Ein weiteres Kapitel dieser Bachelorarbeit ist der Entstehungsprozess der Karbonatisierung, sowie die daraus folgenden Auswirkungen auf die Eigenschaften von Beton. In diesem Zusammenhang werden die möglichen Bauwerksschäden zufolge der Korrosion sowie die Untersuchungsmethoden von Karbonatisierung erläutert. Speziell wird auf die Veränderung der Porenstruktur beziehungsweise des Porenvolumens vor und nach vollständiger Karbonatisierung, anhand eines eigenständig durchgeführten Versuches, eingegangen. Das Ziel dieser Untersuchung ist es festzustellen, ob und wie sich das Porenvolumen von Beton aufgrund der Karbonatisierung verändert. Im Zuge dieser Versuchsdurchführung wurde mit der Hilfe einer Reaktionskammer der chemische Prozess der Karbonatisierung nachgeahmt. Das verwendete Material für die Versuchsdurchführung war ein zertifizierter rezyklierter Betonabbruch, welcher einer Umgebungstemperatur von 40 Grad Celsius und einer Kohlendioxidzufuhr von 20 % ausgesetzt wurde. Die daraus folgende Veränderung des Porenvolumens wurde anhand eines Sättigungsversuches festgestellt. Das Ergebnis des Versuches weist nach der vollständigen Karbonatisierung eine Verminderung des Porenvolumens in der Höhe von 14,32 % auf. Infolgedessen lässt sich ein Zusammenhang zwischen der Karbonatisierung von Beton und der daraus resultierenden Reduktion der Porenstruktur beziehungsweise des Porenvolumens feststellen. Die erforschten Ergebnisse dieser Arbeit sollen als Grundlage für weitere wissenschaftliche Fragestellungen und Arbeiten dienen. Within the scope of this bachelor thesis, a sub-area of concrete, in particular the concrete composition, the class division and the pore structure, is explained in more detail in order to provide a rough overview of the centuries-old building material. Furthermore, the formation of cement glue and the underlying chemical reaction, hydration, is explained, which is the basis for the subsequent carbonation of concrete. A further chapter of this bachelor thesis is the development process of carbonation, as well as the resulting effects on the properties of concrete. In this context, the possible damage to the structure due to corrosion as well as the investigation methods of carbonation are explained. In particular, the change of the pore structure or the pore volume before and after complete carbonation is dealt with by means of an independently conducted experiment. The aim of this investigation is to determine whether and how the pore volume of concrete changes due to carbonation. In the course of this experiment, the chemical process of carbonation was imitated with the help of a reaction chamber. The material used for the test was a certified recycled concrete, which was exposed to an ambient temperature of 40 degrees Celsius and a carbon dioxide supply of 20 %. The resulting change in pore volume was determined by a saturation test. The result of the test shows a reduction of the pore volume after complete carbonation at the level of 14.32 %. As a result, a correlation can be established between the carbonation of concrete and the resulting reduction of the pore structure or the pore volume. The researched results of this work should serve as a basis for further scientific questions and work.

The recycling of concrete can reduce the environmental impact of Portland cement production and concrete construction, and decrease the damping and landfilling of demolition waste. Currently, concrete recycling is widely used for aggregate extraction [1], though concrete fines which are a mix of aggregate and the hydrated cement paste are not a part of the recycling process [1]. Research efforts have been directed to the production of new Portland cement from recycled fines, but most research attempts run into problems [2, 3].

In many countries, major portions of construction and demolition waste (C&DW) consists of concrete waste [1]. The uses of recycled aggregate from concrete waste include both base/sub-base infrastructure and structural applications. Each application requires a different quality and therefore, a different treatment. When concrete waste is crushed, a certain amount of paste/mortar from the original cement mortar remains attached to the aggregate particles, which forms a weak, porous and cracky layer [2]. The use of recycled aggregate in new concrete requires a beneficiation process, which separates the natural aggregate from the attached cement paste/mortar. The clean natural aggregate is used as recycled aggregate, while the attached cement paste/mortar is of no use. As a result, the majority of concrete recycling studies focus on the recycled aggregate only, clean from the attached cement paste/mortar. This work focuses on the old cement paste/mortar itself.

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.

La gran demanda de Cemento Portland Ordinario (CPO) debido al incremento de nuevas obras civiles y la generación de Residuos de Construcción y Demolición (RCD) causan un impacto ambiental negativo, por lo que una solución a esta problemática es el reciclaje de estos materiales para la producción de nuevos concretos. El reemplazo parcial de CPO por polvo de residuo de concreto (Concrete Waste Powder, CWP), proveniente del proceso de reciclaje de concreto, ha sido un enfoque sostenible. En esta investigación ser realizó la caracterización química y puzolánica del CWP mediante Fluorescencia de Rayos X (FRX), la prueba Frattini e índice de actividad de resistencia. Además, se evaluó la factibilidad de producir Concretos Autocompactantes (CAC) elaborados con CWP. El comportamiento de los CAC preparado con varias relaciones de reemplazo de CWP por CPO (en 0, 10, 20 y 30 %) proveniente de RCD, se evaluaron experimentalmente. Las propiedades de trabajabilidad se determinaron mediante las pruebas de flujo de asentamiento, embudo en V y caja en L. Las propiedades en estado endurecido de los CAC estudiadas incluyeron la resistencia a la compresión, la resistencia a la tracción indirecta, la resistencia a la flexión, la porosidad y la succión capilar. Los resultados experimentales de este trabajo mostraron que el CWP puede ser empleado con éxito como relleno en concretos autocompactantes, a pesar de disminuir la trabajabilidad y la resistencia mecánica.

Recycling concrete waste helps reduce the negative environmental impacts of construction activities. Worldwide, concrete recycling rates and available applications for recycled concrete var...

Separation is a fundamental step for concrete recycling, enabling not only the achievement of reliable and cleaner recycled aggregates but also the better re-use of the remaining concrete constituents. Recently, a new hydraulic binder produced from the hydrated cement paste contained in waste concrete, which is associated with lower processing temperatures and carbon dioxide emissions, has gained momentum in the history of concrete recycling. However, a decisive turning point for its application lies in the successful individualisation of the cement paste and aggregate initially contained in concrete debris. This paper describes a new patented method involving a mechanical comminution stage and a high-intensity magnetic separation process to obtain the cementitious fraction in concrete and retrieve cleaner fine aggregate. The efficiency of the proposed method was assessed through image analysis, thermogravimetry, X-ray diffraction and acid attack. In addition, cement pastes produced with the obtained recycled cement after thermal activation were characterised in terms of mechanical strength. Findings suggest that the proposed method effectively separated the main concrete constituents, especially when the waste material was reduced to the size range 150–500 μm. It was possible to obtain a recycled binder at the current laboratory scale with up to about 80% cement content by weight (nearly 90% in volume). Furthermore, a cleaner recycled fine aggregate, with minimal cement paste contamination, as low as less than 3 wt%, was also obtained. The mechanical strength of pastes with recycled cement retrieved from waste concrete was about 70% of that of reference pastes of equal water/binder produced with recycled cement from non-contaminated waste cement pastes.

This study investigated the environmental burdens concerning the recycling/recovery process of a wastewater treatment plant's construction material waste and biogas. Detailed data inventories of case studies were employed in several scenarios to explore the role of end-of-life treatment methods. The ReCiPe 2016 and the Greenhouse gas Protocol life cycle impact methods were conducted to measure the impact categories. The construction and demolition phases were considered for recycling potential assessment, while the operational phase was examined for assessing the advantages of energy recovery. Metal and concrete recycling show environmental benefits. Increasing the reprocessing rate requires more water consumption but results in: firstly, a decrease of 18.8% in total damage; secondly, reduces problematic mineral scarcity by 3.9%; and thirdly, a shortfall in fossil fuels amounting to 11.6%. Recycling concrete helps to reduce the amount of GHG emissions 1.4-fold. Different biogas treatment methods contribute to various outcomes. Biogas utilization for on-site energy purposes has more advantages than flaring and offsite consumption. Electricity and heat generation originating from biogas can provide 70% of the energy requirement and replace 100% natural gas usage. Biomethane production from biogas requires extreme power and more resources. Meanwhile, producing heat and electricity can offset 102.9 g of fossil CO2, and manufacturing biomethane contributes the equivalent of 101.2 g of fossil fuel-derived CO2. Reducing 10% of recovered electricity creation could rise 19.19% global warming indicator of the wastewater treatment plant.

The construction sector is one of the main consumers of raw materials and generates a high volume of waste within the European Union. The search for new materials that are more sustainable and respectful of the environment has become a challenge for countries with a high degree of industrialization. In this work, a study of the most relevant properties of masonry mortars made with recycled aggregates and reinforced with synthetic fibers was carried out. Three types of aggregates were used"”natural, concrete recycling and ceramic recycling"”and two types of reinforcing fibers: polypropylene and polyolefin. In this way, various tests of physical-mechanical characterization and a statistical analysis of the results were carried out. It has been shown that the mortars made from aggregate recycled concrete and reinforced with polypropylene fiber are the ones with the best properties for application in the construction sector, although without improving the properties of traditional mortars made from natural aggregate and without fibers. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Significant damage of some coarse aggregates due to microwave irradiation is neglected by most previous studies on microwave-assisted concrete recycling technique. Fracture behavior of commonly used coarse aggregates: granite and basalt were investigated by microwave heating tests. Heating rate of aggregates’ mineral components was tested respectively. Ilmenite was heated rapidly while other minerals were heated tardily. Larger temperature gradient was generated in basalt because of more ilmenite content to induce fracture, granite was not fractured yet. Most initial cracks in basalt extended along clockwise angle in Mode Ⅰ. Fracture of basalt occurred with more damage at higher power level.

Conventional methods for recycling demolition concrete and plastic waste do not allow recycling of 100% demolished concrete or large volumes of plastic waste. Furthermore, fresh raw materials for concrete manufacturing are still required, while it is projected that they will soon be in short supply due to ever growing consumption. This study focuses on producing a stabilized construction material with better mechanical strength than traditional concrete. A novel method for recycling demolished concrete and plastic waste by compacting concrete and plastic powders under various pressures and temperatures is proposed. The effects of forming conditions on the bending strength of the compacted plastic–concrete (CPC) are analyzed. Furthermore, the water absorption ability and micro-structure of the CPC are also determined. The experimental results confirm the feasibility of CPC and show promising aspects of CPC related to recycling both types of waste in concrete applications, achieving a closed loop for concrete recycling and a high-volume plastic recycling ratio. SEM results showed that the hot-pressing method ensures a good fusion between concrete and plastic particles. Almost all the specimens formed under different conditions possessed a superior bending strength than traditional concrete, and its strength remains stable with up to 75% plastic composition in the specimen. Therefore, the proposed method reveals the feasibility of large-scale plastics recycling in construction, and makes the CPC competitive with other construction materials.

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.

As the construction sector is shifting towards circular economy models, the role of mineral construction materials as main waste fraction in terms of volumes is crucial. A characterization of this mineral stock, as well as the waste derived from it is decisive in ensuring the application of the best practices of circular economy. This paper describes a methodology for assessing the mineral building stock through a combination of geospatial and image analysis. By analysing old topographic maps, buildings are grouped according to their building age into different typologies and based on these maps the construction and demolition activity is evaluated. The mineral stock is assessed and estimations of the mineral construction and demolition waste (CDW) is generated for different stochastic scenarios. This methodology is applied exemplarily on the country of Luxembourg. It was found that the total mineral construction stock for Luxembourg is 276.75 Mt and has been growing at a rate of 20.81%–24.39% in the last 30 years. Furthermore, the study identified a mean age of the urban building stock of about 60 years and a typical maximum building lifetime of 122 years. Based on the stochastic projections the mineral CDW generated from the existing building stock is expected to be up to 226.9 Mt by 2100, while if future building scenarios are considered, it can be as high as 885.3 Mt. The annual CDW production is expected to be sufficient for a viable concrete recycling activity if regulations on the waste volume flows are made available.

Adding large-size demolished concrete lumps (DCLs) into the core of concrete-filled steel tubes (CFTs), a proposal by the authors and co-workers, has been demonstrated to be a practicable alternative means for old concrete recycling. This paper reports preliminary results of an experimental campaign newly implemented concerning the structural behavior of slender square steel tubular columns filled with DCLs and fresh concrete (FC). The replacement ratio of FC by DCLs and the load eccentricity were chosen as the two primary variables. The presented research focuses on the evaluation of the ultimate strength of the aforementioned columns. Design provisions in current codes of practice specified for conventional CFTs were used to check their applicability to the columns studied. The experimental outcomes indicate that: (1) the encasement by the outer square steel tube and the inherent cohesion between DCLs and FC ensured the integrity of inner concrete, thus the failure mode of the columns filled with FC and DCLs was similar to their counterparts filled with FC alone; (2) the initial stiffness, peak load, and post-peak response of the specimens appeared to be influenced only to a rather limited extent by the addition of DCLs; (3) the ultimate strengths of the concentrically and the eccentrically loaded specimens incorporating DCLs can be satisfactorily estimated by the design code Eurocode 4: 2004 and GB 50936-2014, respectively.

The volume of waste generated annually in concrete plants is quite large and has important environmental and economic consequences. The use of fresh concrete recyclers is an interesting way for the reuse of aggregates and water in new concrete production. This paper presents a study carried out for over one year by one of the largest ready-mix concrete producers in Brazil. This study focused on the evaluation of two recyclers with distinct material separation systems, herein referred to as drum-type and rotary sieve-type equipment. They were evaluated through characterization and monitoring test programs to verify the behaviour of recovered materials (aggregates, water, and slurry). The applicability of the recovered materials (water and aggregates) was also evaluated in the laboratory and at an industrial scale. The results obtained with the two types of recyclers used were equivalent and showed no significant differences. The only exception was in terms of workability. The drum-type recycler generated fewer cases that required increased pumping pressure. The analysis concluded that the use of untreated slurry is unfeasible because of its intense negative effects on the strength and workability of concrete. The reclaimed water, pre-treated to ensure that its density is less than 1.03 g/cm3, can be used on an industrial scale without causing any harm to the concrete. The use of recovered aggregates consequently induces an increase in water demand and cement consumption to ensure the workability conditions of concrete that is proportional to the concrete strength level. Therefore, the viability of their use is restricted to concretes with characteristic strengths lower than 25 MPa.

Construction and demolition waste typically comprises of a range of materials, the most dominant being concrete. Despite rapid growth in construction, the construction and demolition waste practices in Vietnam are not well documented. This paper addresses this gap by mapping and estimating construction and demolition concrete waste in Hanoi, and then more broadly in Vietnam. A review of the existing body of knowledge and research, stakeholder interviews, and field trips to construction sites were used to help in mapping construction and demolition waste practices. Material flow analysis was employed to assess material flows and recycling rates. Insights developed primarily demonstrated disposal practices used (e.g. landfill and recycling). Logistics pathways and processing quantities of informal and formal recyclers were also revealed. The findings concluded that current practices lacked; appropriate construction and demolition waste classifications; delegation; and control of waste flows by private companies. The major reasons for these issues were that; little efficiency or cost saving strategies were adopted by both public and private actors; bottlenecks exist in waste transport; little attention is given to value adding to concrete waste recycling; and government legislative and financial support for industry transformation is low. These insights are linked to areas for further research, where policy and business strategy opportunities in developing the concrete recycling industry across Vietnam could deliver better social, economic and environmental outcomes.

Waste concrete is the most predominant constituent material among construction and demolition waste. Current waste concrete recycling is limited to the use of recycled concrete aggregates as a road-base material and less as aggregates in new concrete mixes. Further, the production of recycled concrete aggregates results in the generation of a high amount of fines, consisting mainly of cement paste particles. Hence, this study aims to produce the cement mortars using the upgraded recycled concrete aggregates (sand granulometry) for the total replacement of natural aggregates and recycled concrete fines activated through a thermal treatment method as a partial cement substitution material. Cement mortar specimens were tested for their compressive and flexural strength, density and water absorption performance. The results showed that the combined usage of upgraded recycled concrete sand for total replacement of primary crushed sand and recycled concrete fines as partial cement replacement material is a promising option to produce cement mortars.

Recycling addresses environmental issues associated with solid waste by minimizing overall resource consumption and environmental impact. In the construction industry, concrete recycling is crucial because concrete is the most dominant waste of construction and demolition waste. However, its implementation is at a low level in numerous countries becauseconstruction managers refuse to adopt concrete recycling in practice. This study’s objective is to identify factors that are affecting decisions in adopting concrete recycling from the constructionmanagers’ perspective. To achieve this objective, open-ended interview data with constructionmanagers are analyzed. Eleven factors affecting decisions in adopting concrete recycling inure identified. The factors are recycling factories, availability of raw material, quality, cost, reliable standard, government encouragement, legally, acceptance factor, proper planning, skilled workforce, and management. This research contributes to the body of knowledge in the analysis of factors that influence the acceptance of concrete recycling from industry practitioners’ perspectives, which could help researchers and industry practitioners develop strategies to reduce the rejection of concrete recycling among construction managers. The findings of this research would help improve the success of adopting concrete recycling in the construction industry.

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 outcomes of mortar-aggregate under microwave irradiation. Four different aggregates are selected that widely used as aggregates in concrete. The temperature variations of mortar and aggregate under different heating times and microwave power inputs are obtained. The crack formation, propagation and material damage during the heating process are illustrated. Push-out tests are conducted after microwave heating process to investigate the interface mechanical behavior of aggregate and mortar. The physical properties of recycled aggregate, including apparent density, porosity, water absorption, toughness and adhered mortar percentage after microwave treatment methods are evaluated. 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.

Microwave heating is an attractive new technique for concrete treatment due to its high efficiency and low energy consumption. This paper provides a comprehensive review of the scientific and technical achievements of microwave-assisted concrete treatment. The research progress is classified into microwave heating mechanism, experimental studies and numerical studies. The theoretical fundamentals for the microwave-assisted concrete heating process are investigated in detail, covering areas such as the microwave heating characteristics, governing equations, dielectric properties and multi-field coupling effects. Several attractive microwave applications for concrete treatment are summarized, including microwave-assisted concrete recycling, microwave-accelerated concrete curing, microwave-assisted concrete drilling, and microwave-assisted nondestructive monitoring. Future efforts, as well as theoretical and technical challenges for industrial applications of microwave for concrete treatment, are discussed, which providing guidance for the development of microwave applications for concrete treatment.

Overexploitation of natural limestone used in wet flue gas desulfurization (WFGD) process has led to multiple ecological impacts. To reduce consumption of natural limestone, waste concrete powder (WCP) generated in waste concrete recycling plants were used as an alternative desulfurization absorbent for SO2 controlling. The SO2 absorbing performance of WCP with different particle size is evaluated in a stirred tank reactor with an fixed flat gas–liquid interface at 600 rpm, operated in gas-phase continuous operation mode. The results indicate that the slurry prepared as WCP dissolved in water is strongly alkaline and rich in Ca2+ species. The SO2 in flue gas was effectively removed by the WCP slurries, reaching a desulphurization efficiency of above 98%. Under acidic conditions produced upon dissolving SO2 in the slurry, the Ca2+ ions releasing process of WCP particles involves two stages: a primarily sharp increasing period and a following stable stage. Because of the Ca-rich cement hydrates concentrate in the finer parts of the WCP particles, the Ca2+ ions releasing capacity of WCP increases as its particle size decreases, resulting in a higher desulphurization capacity of finer WPC particles. The Ca2+ ions releasing process is well described by Fick's first law and pseudo-second order model. The Ca2+ ions released combine with SO42- to form insoluble gypsum. As the particle size of WPC decreases, the desulphurization capacity increases in the range of 0.44–0.73 (gSO2 /gWCP). The study provides new and efficient materials for SO2 controlling in waste flue gas and offers an innovative solution for the disposal of WCP also.

This paper aims to assess the influence of calcined dredging sediments (CFC) from Antwerp port as a new SCM on the mechanical properties and shrinkage behaviour of concrete, where cement is replaced by 20, 30 and 40 wt% of CFC. Experimental results are compared with the current prediction models. CFC blended cement develops lower cumulative heat, compared to an OPC reference mix, resulting in a lower temperature development. Although the strength development of a CFC concrete mix is slower than that of an OPC reference mix, CFC concrete reaches higher compressive strength values after 28 days. Both autogenous and total shrinkage are reduced by using CFC blended cement. The development of the mechanical properties can be well described using the model from Eurocode 2, provided that the cement type dependent parameters were adjusted according to the new blended cement system. The existing shrinkage prediction models are also parametrised. All considered drying shrinkage models describe well the drying shrinkage development, while for autogenous shrinkage, the Bazant B4 model appears to be the best predictor. The results clearly support the use of CFC as a new SCM for the production of sustainable cement and concrete.

The rapid industrial development and global population growth of the past century have resulted in an exponential increase of resource consumption and thus caused elevated CO2 emissions that, in turn, are held responsible for global warming and associated environmental problems that require urgent solutions. Specifically, increase of cement production causes CO2 pollution and generates a significant amount of concrete waste. Waste concrete, the major component of construction waste, can be efficiently recycled and is mainly used as a roadbed or backfill material. However, as no further resource recycling is expected for waste concrete, more efficient and productive recycling systems are sought after. Herein, waste concrete powder is used to produce added-value inorganic building materials, namely recycled cement and solidification. The characteristics of recycled cement (manufactured through calcination) are evaluated in terms of free lime content, mineral composition, density, color, flow test and strength, and the performance of recycled cement is found to be identical to that of ordinary Portland cement. X-ray diffraction and compressive strength analyses of the solidification manufactured through hydrothermal synthesis show that blocks of the desired strengths can be produced by adjusting the degree of consolidation and curing conditions. Based on these results, this study proposes a concrete waste recycling system to reduce the amount of construction waste and prevent resource depletion.

This paper evaluates the feasibility of preparing self-compacting concrete (SCC) by incorporating waste concrete recycling materials (WCRMs). Some or all of the natural materials were substituted with WCRMs, such as recycled coarse aggregate (RCA), recycled fine aggregate (RFA) and recycled powder (RP). Nine SCC mixtures were produced, including eight self-compacting recycled concrete mixes and one control mix without WCRMs. The SCC mixes were designed with four different RCA replacement rates (0%, 25%, 50% and 100%) along with a constant amount of RFA (10%) and varying percentages of RP (10% and 20%). The water/binder ratio was designed as 0.4 for all the SCC mixtures. The workability properties (e.g., flowability, viscosity and passing ability) and mechanical properties (e.g., compressive, splitting tensile and flexural strengths) of self-compacting recycled concrete were investigated. The findings indicate that the substitution ratio of WCRMs will affect the workability and mechanical behavior of SCC. This study demonstrates that the decline in the workability and mechanical behavior of self-compacting recycled concrete results from the cooperation of WCRMs. When natural materials are substituted and the amount of WCRMs is limited, the workability of self-compacting recycled concrete can satisfy the European standard EFNARC (2005). Meanwhile, this study also finds that the self-compacting recycled concrete can achieve acceptable mechanical performance when compared to the ordinary SCC without WCRMs.

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.

Concrete is a building material commonly used for ages. Therefore, in the result of repairs or demolition of building structures, large amounts of concrete rubble are created, which requires appropriate management. The aim of the realized research was to determine the influence of heat and mechanical treatment of concrete rubble on the properties of recycled aggregate concrete. The research experiment included 12 series, with three variables: X1&mdash, roasting temperature (300, 600, 900 &deg, C), X2&mdash, time of mechanical treatment (5, 10, 15 min), X3&mdash, content of coarse recycled aggregates (20, 40, 60% by volume). Two additional series containing recycled aggregate without treatment and natural aggregate were also prepared. Established properties of individual aggregates have confirmed a positive effect of thermo-mechanical treatment. Then, based on the results of compressive strength, flexural strength, Young&rsquo, s modulus, volumetric density, water absorption, water permeability and capillarity, the most favourable parameters of heat and mechanical treatment of concrete were determined. The test results showed that appropriate treatment of concrete rubble allows to obtain high-quality coarse aggregate and valuable fine fraction. This was also confirmed by the macro- and microscopic observations of the aggregate and separated cement paste. Works realized on the concrete recycling method resulted in obtaining a patent PAT.229887.

Reusing of fine particles of waste concrete (FPWC) is a disturbing problem for waste concrete recycling process. In this study, the FPWC developed from waste concrete was used as an innovative absorbent to remove phosphorus (P) from wastewater. The results showed, with the change of particle size of the FPWC, the maximum phosphorus binding capacity of the FPWC varies in the range of 1.07–4.96 mg P/g. The P-removal ability of FPWC increases as its particle size decreases, because of the FPWC with smaller particle size has more Ca-rich and porous hardened cement paste (HCP) powder. A “components separation” mechanism was proposed to explain the change of HCP powder content in FPWC with different particle size distribution. Both the Thomas and Yoon-Nelson model can be used to describe the P-removal behaviors of FPWC. The phosphorus removal mechanism is that the Ca2+ and OH− can release from HCP powder and forms a local alkaline condition with high Ca2+ concentration. The condition was beneficial to the formation of Ca5(PO4)3(OH) which could be attached on the surface of the FPWC. Based on the Fick’s law, the Ca2+ release behavior form FPWC can be separated into two stages, and it could be described by pseudo-second order model. Totally, FPWC developed from waste concrete blocks exhibited sufficient potential in phosphate removal.

Concrete recycling is an important element of sustainable development. Demolished concrete lumps (DCLs) can be blended with fresh concrete as a filler, but achieving good compactness of the...

13th international Symposium on Concrete Roads, BERLIN, ALLEMAGNE, 19-/06/2018 - 22/06/2018; The opportunity of developing concrete pavements with a high rate of recycled concrete aggregate was recently studied within the French national project RECYBETON. According to the French rational pavement design, it is necessary for that purpose to evaluate the impact of recycling on flexural fatigue behaviour of concrete. The state of the art review shows a trend for an endurance decrease when including recycled aggregates in concrete. Nevertheless, only few reliable data are available in the literature and in particular with a sufficient number of specimens to take into account the scattering of fatigue life span, which is of paramount importance for pavement design.This presents papers presents a series of fatigue tests on concrete including high rates of recycling. In a first case only the coarse natural aggregates were replaced by recycled aggregate, while in a second case all the granular skeleton (sand and coarse particles) were replaced.Tests carried out in this study seem to confirm that high recycling rates lead only to a slight deterioration in the fatigue behavior of pavement concretes. The papers concludes by giving typical fatigue behavior parameters for pavement design and shows that only a slight increase in cement content per m2 can compensate the decrease in fatigue behavior.

This study tested the hypothesis that concrete produced with recycled concrete aggregate (RCA) has increased cracking resistance compared to concrete incorporating natural aggregates. Two sources of RCA were used: (1) a laboratory created RCA produced by crushing previously produced laboratory concrete; and (2) a field RCA obtained from a demolished airfield pavement. Mechanical properties, and shrinkage and cracking due to drying of concrete produced with RCA replacement were studied. Adequate compressive strength (39.3–43.4 MPa), splitting tensile strength (3.7–4.4 MPa), and modulus of elasticity (27.2–28.3 GPa) were obtained in mixtures including coarse RCA, even at 100% replacement levels. The use of RCA did not significantly increase the drying shrinkage of concrete. It was shown that the use of RCA significantly reduced the cracking risk of concrete from “high” to “moderate-high” when incorporated into a high cracking risk mixture.

In this work, fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures were studied, in which synthetic fibers were used. Eight different SCLWACs were prepared, in which, as aggregates, different combinations of fine and coarse expanded clay were tried, also partially replaced by either quartz sand or aggregate coming from concrete recycling. SCLWACs were characterized at the fresh state by means of slump flow, V-funnel and L-box tests, and after hardening by means of compression, splitting tension and bending tests, and drying shrinkage measurements. Strength class of LC 45/50 was obtained by using synthetic macrofibres when the oven dry density of SCLWAC was about 1600 kg/m 3 , while if the oven dry density of SCLWAC was lower than 1250 kg/m 3 a strength class of LC 25/28 was reached as well. Tensile and flexural strength values were consistent with concrete strength class, while the elastic modulus was quite low with respect to normal weight self-compacting concrete (SCC). The post-cracking behavior of SCLWAC was strongly improved by the addition of synthetic macrofibers, which provided strain-hardening effect similar to that achievable by means of steel fibers, even if characterized by a sensibly lower weight. In conclusion, SCLWACs showed excellent combination of mechanical and functional properties.

Current state-of-the-art concrete recycling technology provides decision makers with the option to produce coarse recycled concrete aggregates (RCAs) with different qualities through variations in the number of crushing stages or the use of beneficiation processes available. Variations in the recycling process may significantly affect the economic and environmental impacts of the concrete recycling strategy. This, together with variations in transportation requirements from one project to another, makes it impossible to draw general conclusions about the sustainability of a concrete recycling strategy. This paper proposes a computational method for identifying the optimal concrete recycling method by considering the trade-off between costs, energy use and carbon dioxide emissions of concrete recycling in a particular project. After estimating the amount of various grades of the recyclable concrete available using the data made available by building information models, a computational algorithm is applied to identify alternative feasible concrete recycling methods to produce different RCA qualities and to estimate the costs, energy use and carbon dioxide emissions associated with each recycling method. The latter will then serve as decision-making criteria for selection of the best feasible concrete recycling method. The proposed computational method is applied to an illustrative example.

Betong är idag och har länge varit det allra vanligaste byggnadsmaterial i Sverige. Det är ett robust och mångsidigt byggnadsmaterial med flera fördelar. Detta arbete är en experimentell studie av betongavfall från Hedareds sand & betong för betongprogrammet RE: Concrete och Högskolan i Borås. Betongavfallet krossas till ny ballast och därefter siktas och gjuts till ny betong enligt olika betongrecept. Försöken sker i betonglabbet i Högskolan i Borås för att krossa och tillverka betong. Grundreceptet har tillhandhållits av Hedareds sand & betong. Syftet med arbetet har varit att undersöka möjligheterna för att kunna använda återvunnen betong i nya bärande konstruktioner. Målet var att bevisa att det var tekniskt möjligt att åstadkomma en 100 % ersättning av ballast med återvunnen betong och få fram ny betong som passar den bärande stommen i en byggnad. Olika egenskaper undersöktes så som tryckhållfasthet för den nya betongen och partikelfördelning samt vattenabsorption för ballasten med målet att uppnå likvärdigt resultat som för referensbetongen. Resultatet visar att det är möjligt att kunna återvinna betong till 100 %. Arbetbarheten är bra i flertal försök men bör förbättras för att uppnå likvärdig arbetbarhet som referensbetongens. Referensbetongens tryckhållfasthet är 59 MPa och bästa tryckhållfasthet som erhållits för återvunnen betong är 57,2 MPa. Detta tyder på ett positivt resultat och den återvunna betongen i denna studie kan ersätta naturgrusballast i en bärande konstruktion till 100 %. Concrete is and has been for a long time the most common building material in Sweden. It is a robust and multipurpose building material with several advantages. This report is about an experimental study of concrete waste from Hedareds sand & betong. The concrete waste is crushed to a new aggregate and then sifted and casted into new concrete. The study was conducted in the Concrete Laboratory at University of Borås for crushing and casting of concrete. Recipes are supplied by Hedareds sand & betong as a starting point, which is later modified gradually to achieve better results. The purpose of this study is to investigate the possibilities for using recycled concrete in new constructions. It is also examined if the recycled concrete is technically sustainable and if the workability is good enough for using in load bearing structures. Different properties are studied such as compressive strength, particle distribution, water absorption and workability to achieve equivalent results as the reference concrete. The result obtained in this study shows that it is possible to recycle concrete by replacing aggregates to 100 % in new concrete. Workability is good in several tests, but it should be improved to achieve the same workability as the reference concrete. The reference concrete's compressive strength is 59 MPa and the best compressive strength obtained for recycled concrete is 57.2 MPa. This indicates positive results and the recycled concrete in this study can replace ordinary concrete in a load bearing construction.

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.

The paper summarizes results of pilot fatigue testing of concrete slabs resting on granular base in testing box. The project aimed at verification of recent findings that fatigue resistance of concrete slabs is much higher than that predicted by using concrete fatigue characteristics from beam testing. Paper presents additional testing results that confirm enhanced fatigue resistance of concrete slabs. Further research is envisioned to supplement pilot testing results and to receive new results also on fatigue resistance under concrete recycling scheme.

Recycling End of Life (EOL) concrete into high-grade aggregate for new concrete is a challenging prospect for the building sector because of the competing constraints of low recycling process cost and high aggregate product quality. A further complicating factor is that, from the perspective of the environment, there is a strong societal drive to reduce bulk transport of building materials in urban environments, and to apply more in situ recycling technologies for Construction & Demolition Waste. The European C2CA project investigates a combination of smart demolition, grinding of the crushed concrete in an autogenous mill to increase the liberation of cement mortar from the surface of aggregates and a novel dry classification technology called ADR to remove the fines. The feasibility of this recycling process was examined in a demonstration project involving 20,000 tons of EOL concrete from two office towers in Groningen, the Netherlands. Results show that the +4 mm recycled aggregate compares favorably with natural aggregate in terms of workability and the compressive strength of the new concrete, showing 30% higher strength after 7 days.

While concrete recycling is practiced worldwide, there are many unanswered questions in relation to ultrafine particle (UFP; Dp < 100 nm) emissions and exposure around recycling sites. In particular: (i) Does recycling produce UFPs and in what quantities? (ii) How do they disperse around the source? (iii) What impact does recycling have on ambient particle number concentrations (PNCs) and exposure? (iv) How effective are commonly used dust respirators to limit exposure? We measured size-resolved particles in the 5–560 nm range at five distances between 0.15 and 15.15 m that were generated by an experimentally simulated concrete recycling source and found that: (i) the size distributions were multimodal, with up to ∼93% of total PNC in the UFP size range; and (ii) dilution was a key particle transformation mechanism. UFPs showed a much slower decay rate, requiring ∼62% more distance to reach 10% of their initial concentration compared with their larger counterparts in the 100–560 nm size range. Compared with typical urban exposure during car journeys, exposure decay profiles showed up to ∼5 times higher respiratory deposition within 10 m of the source. Dust respirators were found to remove half of total PNC; however the removal factor for UFPs was only ∼57% of that observed in the 100–560 nm size range. These findings highlight a need for developing an understanding of the nature of the particles as well as for better control measures to limit UFP exposure.

The process of recycling concrete rubble is accompanied by the formation of a large amount of fine fraction, which cannot be reused as aggregate. The results of research on the possibility of using recycled cement mortar (RCM), obtained during concrete recycling, as a cementitious supplementary material, are presented. The experimental research was carried out on the basis of two variables determining the recycling process: X1&mdash, temperature (range of variation 288&ndash, 712 &deg, C) and X2&mdash, time (range of variation 30&ndash, 90 min) of thermal treatment of concrete rubble. The experiment included 10 series of new composites made with RCMs subjected to different variants of thermal treatment, and two additional control series. The best treatment parameters were determined based on the assessment of selected physical and mechanical properties of the new cement composites, as well as the analysis of characteristics and microstructure of RCM. The test results showed that proper thermal treatment of concrete rubble makes it possible to obtain a high-quality fine fraction, which has the properties of an active addition and can be used as a partial replacement for cement in mortars and concretes.

Current development megatrends are aimed at finding a balance between the economy, social and environmental aspects. It is also required that the economic processes that are undertaken should be highly effective in these three dimensions. Both the finite amount of the natural resources and the need to manage the construction and demolition waste, while the constant demand for the concrete mix, makes it necessary to develop knowledge and practice in the field of concrete recycling. One of the main issues in the recovery of concrete aggregate is the presence of impurities. Aggregate treatment is a possible solution, but these are energy consuming and costly processes. Therefore, there is a need to estimate their impact on concrete parameters. Such knowledge is necessary for assessing the need for additional aggregate treatment processes. Harmful aggregate impurities are materials that hinder the curing of the concrete, reduce its strength and tightness, cause splinters, violate the anti-corrosion protection of reinforcement. The paper analyses the type of impurities in RCA, as well as its sources and their influence on the technical parameters of the concrete. Six concrete mixes with the same content of coarse aggregate and water-cement ratio were prepared for the research. The first mix contained only natural aggregates, while the second mix was replaced in half by recycled aggregates. In subsequent samples, the recycled aggregate in 5% by volume was successively replaced with: glass, brick, foamed polystyrene and a mixture of these impurities. Both impurities and the recycled aggregate were prepared in 2/8mm fractions. The obtained results were compared to the results presented in the literature.