Leaching performance of recycled aggregates

Because the production of aggregates for mortar and concrete is no longer sustainable, many attempts have been made to replace natural aggregates (NA) with recycled aggregates (RA) sourced from factories, recycling centers, and human activities such as construction and demolition works (C&D). This article reviews papers concerning mortars with fine RA from C&D debris, and from the by-products of the manufacturing and recycling processes of building materials. A four-step methodology based on searching, screening, clustering, and summarizing was proposed. The clustering variables were the type of aggregate, mix design parameters, tested properties, patents, and availability on the market. The number and the type of the clustering variables of each paper were analysed and compared. The results showed that the mortars were mainly characterized through their physical and mechanical properties, whereas few durability and thermal analyses were carried out. Moreover, few fine RA were sourced from the production waste of construction materials. Finally, there were no patents or products available on the market. The outcomes presented in this paper underlined the research trends that are useful to improve the knowledge on the suitability of fine RA from building-related processes in mortars.

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Strategies for a Circular Economy in the Construction and Demolition Sector: Identifying the Factors Affecting the Recommendation of Recycled Concrete

Sustainability ◽

10.3390/su13084113 ◽

2021 ◽

Vol 13 (8) ◽

pp. 4113

Author(s):

Valeria Superti ◽

Cynthia Houmani ◽

Ralph Hansmann ◽

Ivo Baur ◽

Claudia R. Binder

Keyword(s):

Circular Economy ◽

A Priori ◽

Recycled Concrete ◽

Recycled Aggregates ◽

Factors Affecting ◽

Structural Applications ◽

Adoption Of Innovation ◽

Decision Making Processes ◽

Behavioural Factors ◽

High Level

With increasing urbanisation, new approaches such as the Circular Economy (CE) are needed to reduce resource consumption. In Switzerland, Construction & Demolition (C&D) waste accounts for the largest portion of waste (84%). Beyond limiting the depletion of primary resources, implementing recycling strategies for C&D waste (such as using recycled aggregates to produce recycled concrete (RC)), can also decrease the amount of landfilled C&D waste. The use of RC still faces adoption barriers. In this research, we examined the factors driving the adoption of recycled products for a CE in the C&D sector by focusing on RC for structural applications. We developed a behavioural framework to understand the determinants of architects’ decisions to recommend RC. We collected and analysed survey data from 727 respondents. The analyses focused on architects’ a priori beliefs about RC, behavioural factors affecting their recommendations of RC, and project-specific contextual factors that might play a role in the recommendation of RC. Our results show that the factors that mainly facilitate the recommendation of RC by architects are: a senior position, a high level of RC knowledge and of the Minergie label, beliefs about the reduced environmental impact of RC, as well as favourable prescriptive social norms expressed by clients and other architects. We emphasise the importance of a holistic theoretical framework in approaching decision-making processes related to the adoption of innovation, and the importance of the agency of each involved actor for a transition towards a circular construction sector.

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Discrete Element Simulation Analysis of Biaxial Mechanical Properties of Concrete with Large-Size Recycled Aggregate

Sustainability ◽

10.3390/su13137498 ◽

2021 ◽

Vol 13 (13) ◽

pp. 7498

Author(s):

Tan Li ◽

Jianzhuang Xiao

Keyword(s):

Mechanical Properties ◽

Stress State ◽

Strain Curve ◽

Confining Pressure ◽

Recycled Concrete ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Aggregate Model ◽

Large Size

Concrete made with large-size recycled aggregates is a new kind of recycled concrete, where the size of the recycled aggregate used is 25–80 mm, which is generally three times that of conventional aggregate. Thus, its composition and mechanical properties are different from that of conventional recycled concrete and can be applied in large-volume structures. In this study, recycled aggregate generated in two stages with randomly distributed gravels and mortar was used to replace the conventional recycled aggregate model, to observe the internal stress state and cracking of the large-size recycled aggregate. This paper also investigated the mechanical properties, such as the compressive strength, crack morphology, and stress–strain curve, of concrete with large-size recycled aggregates under different confining pressures and recycled aggregate incorporation ratios. Through this research, it was found that when compared with conventional concrete, under the confining pressure, the strength of large-size recycled aggregate concrete did not decrease significantly at the same stress state, moreover, the stiffness was increased. Confining pressure has a significant influence on the strength of large-size recycled aggregate cocrete.

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Leaching Behaviour of Construction and Demolition Wastes and Recycled Aggregates: Statistical Analysis Applied to the Release of Contaminants

Applied Sciences ◽

10.3390/app11146265 ◽

2021 ◽

Vol 11 (14) ◽

pp. 6265

Author(s):

Alessandra Diotti ◽

Giovanni Plizzari ◽

Sabrina Sorlini

Keyword(s):

Particle Size ◽

Statistical Analysis ◽

Raw Materials ◽

Primary Source ◽

Recycled Aggregates ◽

Critical Parameters ◽

Material Particle ◽

Analysis Methodology ◽

Construction And Demolition Wastes ◽

Leaching Behaviour

Construction and demolition wastes represent a primary source of new alternative materials which, if properly recovered, can be used to replace virgin raw materials partially or totally. The distrust of end-users in the use of recycled aggregates is mainly due to the environmental performance of these materials. In particular, the release of pollutants into the surrounding environment appears to be the aspect of greatest concern. This is because these materials are characterized by a strong heterogeneity which can sometimes lead to contaminant releases above the legal limits for recovery. In this context, an analysis of the leaching behaviour of both CDWs and RAs was conducted by applying a statistical analysis methodology. Subsequently, to evaluate the influence of the particle size and the volumetric reduction of the material on the release of contaminants, several experimental leaching tests were carried out according to the UNI EN 12457-2 and UNI EN 12457-4 standards. The results obtained show that chromium, mercury, and COD are the most critical parameters for both CDWs and RAs. Moreover, the material particle size generally affects the release of contaminants (i.e., finer particles showed higher releases), while the crushing process does not always involve higher releases than the sieving process.

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Application of Construction and Demolition Waste in Civil Construction in the Brazilian Amazon—Case Study of the City of Rio Branco

Materials ◽

10.3390/ma14092247 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2247

Author(s):

Fernando da Silva Souza ◽

José Maria Franco de Carvalho ◽

Gabriela Grotti Silveira ◽

Vitória Cordeiro Araújo ◽

Ricardo André Fiorotti Peixoto

Keyword(s):

Mechanical Strength ◽

Raw Materials ◽

Amazon Region ◽

Construction And Demolition Waste ◽

Recycled Aggregates ◽

Federal State ◽

Construction Sites ◽

Demolition Waste ◽

Conventional Concrete ◽

Initial Adhesion

The lack of usable aggregates for civil construction in Rio Branco (capital of Acre, a Federal State in the Amazon region) makes the production and use of recycled aggregates from construction and demolition waste (CDW) an alternative of great interest. In this study, a comprehensive characterization of CDW collected from 24 construction sites of six building types and three different construction phases (structures, masonry, and finishing) was carried out. The fine and coarse recycled aggregates were produced and evaluated in 10 different compositions. The aggregates’ performance was evaluated in four mixtures designed for laying and coating mortars with a total replacement of conventional aggregates and a mixture designed for a C25 concrete with 50% and 100% replacement of conventional aggregates. CDW mortars showed lower densities and greater water retention, initial adhesion, and mechanical strength than conventional mortars. CDW concretes presented lower densities and greater resistance to chloride penetration than conventional concrete, with a small mechanical strength reduction. The recycled CDW aggregates proved to be technologically feasible for safe application in mortars and concrete; for this reason, it is believed that the alternative and proposed methodology is of great interest to the Amazonian construction industry, considering the high costs of raw materials and the need for defining and consolidating a sustainable development model for the Amazon region.

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Axial Stress-Strain Performance of Recycled Aggregate Concrete Reinforced with Macro-Polypropylene Fibres

Sustainability ◽

10.3390/su13105741 ◽

2021 ◽

Vol 13 (10) ◽

pp. 5741

Author(s):

Muhammad Junaid Munir ◽

Syed Minhaj Saleem Kazmi ◽

Yu-Fei Wu ◽

Xiaoshan Lin ◽

Muhammad Riaz Ahmad

Keyword(s):

Axial Stress ◽

Peak Stress ◽

Polypropylene Fibre ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Peak Strain ◽

Stress Strain ◽

Polypropylene Fibres ◽

Aggregate Concrete

The addition of macro-polypropylene fibres improves the stress-strain performance of natural aggregate concrete (NAC). However, limited studies focus on the stress-strain performance of macro-polypropylene fibre-reinforced recycled aggregate concrete (RAC). Considering the variability of coarse recycled aggregates (CRA), more studies are needed to investigate the stress-strain performance of macro-polypropylene fibre-reinforced RAC. In this study, a new type of 48 mm long BarChip macro-polypropylene fibre with a continuously embossed surface texture is used to produce BarChip fibre-reinforced NAC (BFNAC) and RAC (BFRAC). The stress-strain performance of BFNAC and BFRAC is studied for varying dosages of BarChip fibres. Results show that the increase in energy dissipation capacity (i.e., area under the curve), peak stress, and peak strain of samples is observed with an increase in fibre dosage, indicating the positive effect of fibre addition on the stress-strain performance of concrete. The strength enhancement due to the addition of fibres is higher for BFRAC samples than BFNAC samples. The reduction in peak stress, ultimate strain, toughness and specific toughness of concrete samples due to the utilisation of CRA also reduces with the addition of fibres. Hence, the negative effect of CRA on the properties of concrete samples can be minimised by adding BarChip macro-polypropylene fibres. The applicability of the stress-strain model previously developed for macro-synthetic and steel fibre-reinforced NAC and RAC to BFNAC and BFRAC is also examined.

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Characterisation and Life Cycle Assessment of Pervious Concrete with Recycled Concrete Aggregates

Crystals ◽

10.3390/cryst11020209 ◽

2021 ◽

Vol 11 (2) ◽

pp. 209

Author(s):

Adilson C. Paula Junior ◽

Cláudia Jacinto ◽

Thaís M. Oliveira ◽

Antonio E. Polisseni ◽

Fabio M. Brum ◽

...

Keyword(s):

Environmental Performance ◽

Treatment Plant ◽

Recycled Concrete ◽

Pervious Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Positive Contribution ◽

Concrete Aggregates ◽

Recycled Concrete Aggregates

The search for environmental preservation and conservation of natural resources gives rise to new concepts and viable technical solutions on the path to sustainable development. In this context, this study’s main objective is to analyse the influence of recycled concrete aggregates (RCAs) on the development of pervious concrete, whose use as a floor covering represents an excellent device to mitigate the urban soil sealing phenomena. For this, mechanical and hydraulic tests were carried out, in addition to microstructural analyses and the assessment of its environmental performance. The results obtained were compared to reference studies also involving the incorporation of recycled aggregates. A pilot-scale case study was conducted, involving a parking space lined with pervious concrete moulded “in situ”. In laboratory tests, permeability coefficients and mechanical strengths compatible with the literature and above the normative limit for light traffic were found. The case study demonstrated higher permeability than in the laboratory, but the flexural strength was lower, being indicated only for pedestrian traffic. The environmental assessment showed that the RCA represents a positive contribution to the environmental performance of pervious concrete. Still, attention should be given to the recycled aggregate transport distance between the concrete plant and the RCA treatment plant.

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Predicting Compressive Strength of Concrete Containing Recycled Aggregate Using Modified ANN with Different Optimization Algorithms

Applied Sciences ◽

10.3390/app11020485 ◽

2021 ◽

Vol 11 (2) ◽

pp. 485

Author(s):

Amirreza Kandiri ◽

Farid Sartipi ◽

Mahdi Kioumarsi

Keyword(s):

Compressive Strength ◽

Optimization Algorithms ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Tree Model ◽

Grasshopper Optimization Algorithm ◽

Compressive Strength Of Concrete ◽

Grasshopper Optimization ◽

Artificial Neural Network Ann ◽

Industry Needs

Using recycled aggregate in concrete is one of the best ways to reduce construction pollution and prevent the exploitation of natural resources to provide the needed aggregate. However, recycled aggregates affect the mechanical properties of concrete, but the existing information on the subject is less than what the industry needs. Compressive strength, on the other hand, is the most important mechanical property of concrete. Therefore, having predictive models to provide the required information can be helpful to convince the industry to increase the use of recycled aggregate in concrete. In this research, three different optimization algorithms including genetic algorithm (GA), salp swarm algorithm (SSA), and grasshopper optimization algorithm (GOA) are employed to be hybridized with artificial neural network (ANN) separately to predict the compressive strength of concrete containing recycled aggregate, and a M5P tree model is used to test the efficiency of the ANNs. The results of this study show the superior efficiency of the modified ANN with SSA when compared to other models. However, the statistical indicators of the hybrid ANNs with SSA, GA, and GOA are so close to each other.

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