Production of high-quality coarse recycled aggregates through a two-stage jigging process

Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.4 - Per a 2030, modernitzar les infraestructures i reconvertir les indústries perquè siguin sostenibles, usant els recursos amb més eficàcia i promovent l’adopció de tecnologies i processos industrials nets i racionals ambiental­ment, i aconseguint que tots els països adoptin mesures d’acord amb les capacitats respectivesObjectius de Desenvolupament Sostenible::12 - Producció i Consum ResponsablesObjectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables::12.5 - Per a 2030, disminuir de manera substancial la generació de residus mitjançant polítiques de prevenció, reducció, reciclatge i reutilitzacióPostprint (published version

Characterization of Demolished Concretes with Three Different Strengths for Recycling as Coarse Aggregate

This paper presents a physical characterization for the recycling into new concretes of three comminuted concretes: C16/20 (“ordinary concrete”), C50/60 (“high strength concrete”), and C70/85 (“very high strength concrete”). The top size of the crushed concretes was 19.1 mm and the size range was 4.75 to 19.1 mm. The characterization was carried out with coarse aggregate liberation, to be prepared and concentrated in a gravity concentration process. The density distribution of the coarse aggregate, cement paste, and sand was carried out in different size ranges (4.75/19.1 mm; 4.75/8.0 mm; 8.0/12.5 mm; and 12.5/19.1 mm) for the three concretes studied. The form factor of the samples, as well as the porosity determination of particles in different density ranges, are presented. The obtained results indicate that the coarse aggregate liberation was more intensive for the low resistance concrete (C16/20), but a reasonable coarse aggregate recovery is possible for all concretes

Photocatalytic TiO₂-Based Coatings for Mortars on Facades: A Review of Efficiency, Durability, and Sustainability

Due to the urgent need for a more sustainable built environment and actions against climate change, this paper presents a literature review about photocatalytic TiO2-based thin layers to be applied on mortars in facades. Photocatalysis may be a potential strategy against current environmental and climate challenges by transforming or eliminating hazardous greenhouse gases from the atmosphere. The main subjects researched were the coatings’ efficiency (which encompassed their self-cleaning ability, depolluting effect, and antimicrobial properties), durability, and sustainability. The method was based on the systematic literature review approach. Self-cleaning ability was the most recurrent topic retrieved from published studies, followed by depolluting effect and durability. There are few investigations about antimicrobial properties considering TiO2-coated mortars in facades. However, sustainability studies through Life Cycle Assessment and Life Cycle Costing represented the most significant gap, even requiring broader surveys. The photocatalytic activity of the coatings is well-proven in the literature, although specific evaluations may be needed for each coating composition and testing condition to understand their performance. The type of contamination agents, TiO2 dispersion and characteristics, dopants, nanocomposites, and substrate are among the principal agents influencing the results; therefore, caution must be taken when comparing research. Mainly, adhesion and photocatalytic efficiency after ageing were studied on durability. More field exposures may be recommended. Regarding the trade-offs concerning the environmental impacts of TiO2-based coatings, it is urgent to clarify whether their overall outcome is indeed advantageous and to investigate their resilience regarding climate change scenarios

Relationship between Degree of Deformation in Quartz and Silica Dissolution for the Development of Alkali-Silica Reaction in Concrete

This paper presents research on the influence of quartz deformation in aggregates for the development of the alkali-silica reaction in concrete and its relationship with silica dissolution. The study also compares these characteristics with the field behavior of such rocks in concrete. The paper proposes parameters to classify the different degrees of deformation of quartz. Transmission electron microscopy showed the presence of walls even in slightly deformed quartz, which indicate the presence of the internal paths available to react with the alkaline concrete pore solutions and point to the potential development of an alkali-silica reaction. The presence of the deformation bands in the quartz grains leads to the alkali aggregate reaction occurring more rapidly. The visible spectrophotometer test was performed to evaluate the dissolution potential of the different samples of deformed quartz, which confirmed that the reactivity of the quartz increases as the deformation of the crystalline structure increases. The parameters established in the present study could be verified by analyzing the behavior of reactive and innocuous aggregates from the buildings

Influence of the Quartz Deformation Structures for the Occurrence of the Alkali–Silica Reaction

Defects in the crystalline structure of quartz facilitate the connection with the alkali hydroxides, since under a high alkalinity condition (e.g., in concrete), the Si-O bonds of quartz are easily broken. This study set out to investigate the influence of the deformation structures of quartz on its susceptibility to the alkali–silica reaction. A granite, a protomylonite, and a mylonite were selected for this study. Using optical microscopy, the quartz grains contained in these rocks were quantified and their texture characterized. The quartz samples extracted from the rocks were analyzed by magnetic nuclear resonance, to evaluate their potential for dissolving silica as well as changes in their atomic scale before and after the reaction with alkali hydroxides. These analyses were compared with the results of the accelerated mortar bar test. The study showed that the quartz with intense undulatory extinction and deformation bands denotes the most favorable condition to the development of the alkali–silica reaction. However, on an atomic scale, the slightly deformed grains were highly prone to react. Thus, in a high alkalinity condition, over a long period of time, any quartz tends to develop the alkali–silica reaction, regardless of the deformation degree of the grain

Demolished concretes recycling by the use of pneumatic jigs

Sampaio, C.H. et al., Demolished concretes recycling by the use of pneumatic jigs, Waste management and research, 38 (4) pp. 392-399. Copyright © 2020. DOI: 10.1177/0734242X20902835.Large quantities of construction and demolition waste is generated annually around the world. Part of this material is processed in recycling plants. After removing metals, fines and lights, the construction and demolition waste is crushed and sized and can be used as aggregates for low resistance concrete, for road sub-base, city landfill and other low value-added applications. For their use as coarse aggregate in structural concretes, construction and demolition waste must exhibit high densities and regularity of the material. This material usually is presented in demolished concretes. About 20% of the particles from demolished concretes can be used as coarse aggregates substituting part of natural aggregates in structural concretes. This article presents studies of demolished concretes recycling by the use of a pneumatic jig. All jigging tests were carried out with three different concretes produced in three strength classes: C16/20, ordinary concrete; C50/60, high strength concrete; and C70/85, very high strength concrete. Based on density distribution of the three concretes, there are reasonable masses with densities over 2.7¿g¿cm-3, particle density considered appropriate to the used as coarse aggregate for structural concretes. The concretes present different mass recoveries of the denser particles (different liberation). Coarse aggregates can be recovered with reasonable masses by the use of air jigs: About 65% for high strength concretes and about 75% for the low strength concrete. The jigging concentration efficiency depends on the concrete liberation, density and size distribution.The authors would like to thank the Brazilian National Council for Scientific and Technological Development (CNPq) for financial support. We are also very thankful to NORIE (Núcleo Orientado para a Inovação da Edificação), LEME (Laboratório de Ensaios Estruturais) and LEAMET (Laboratório de Estudos Ambientais para Metalurgia), research groups of the Federal University of Rio Grande do Sul, Brazil, where production and characterization of the concrete samples were carried out.Peer Reviewe