Freeze-thaw durability of recycled concrete from construction and demolition wastes

Road engineering is one of the most accepted applications for concrete including recycled aggregates from construction and demolition wastes as a partial replacement of the natural coarse aggregates. Amongst the durability concerns of such application, the deterioration due to freeze-thaw cycles is one of the most important causes decreasing the life span of concrete in countries with a continental climate. Moreover, the use of de-icing salts, which is a common practice to prevent ice formation on roadways and walkways, increases the superficial degradation of concrete due to frost-salt scaling. Thus, this paper aims to assess the resistance to frost salt with de-icing salts of two recycled concrete mixtures containing a 50% replacement of the conventional gravel by recycled aggregates both of mixed and ceramic nature, i.e. containing ceramic percentages of 34% and 100%, in comparison to a conventional concrete made with siliceous gravel. Therefore, the surface scaling was evaluated based on EN 1339 (2004) on 28 days cured cylinders, exposed to 7, 14, 21 and 28 freeze-thaw cycles in the presence of sodium chloride solution. Given that no airentraining admixture was used in any of the mixtures, the scaling of both conventional and recycled concretes exceeded the 1 kg/m2 limit established by the European standard. Nonetheless, for the casting surface, the recycled concrete with low ceramic content exhibited a similar behaviour to the conventional concrete, whereas the performance of the recycled concrete with high ceramic content was better. However, as expected, trowelled surfaces showed a worse performance and both recycled concretes had a lower freeze-thaw durability than the conventional mixture. In any case, the results suggested that the composition of the recycled aggregates could be used as a factor to limit the differences in performance between recycled and conventional mixtures

Improving the quality of various types of recycled aggregates by biodesposition

Demand for construction materials has been rising in recent decades in many countries around the world, placing a heavy burden on the environment in terms of both the natural resources consumed and the enormous flow of waste generated. In order to obtain a more sustainable construction, it is often suggested to reintroduce the industry’s own waste as input for the manufacture of new materials. In this study, the use of construction and demolition waste of concrete or mixed concrete/ceramic nature is investigated as a replacement of natural aggregates in concrete. The greater affinity of recycled aggregates for water directly affects the workability and/or the concrete strength and durability. One possible solution to reduce the aggregates water absorption is to apply a biogenic treatment with calcium carbonate-precipitating bacteria that consolidate the aggregate surface or the adhering mortar. Experimental results show that the biodeposition treatment reduced the recycled aggregate water absorption by generating precipitation in the pores and an impermeable outer layer, most effectively on the roughest particle surfaces. The largest decrease happened in the aggregates with the highest porosity. The biogenic layer had a good cohesion with the aggregates. The results of sonication indicated that the most effective treatment was on recycled concrete aggregates (RCA) instead of mixed aggregates (MA). Therefore, the treated RCA was used to make concrete for further investigation. The concrete made with bio-treated RCA had a denser structure, a decreased water absorption (around 1%) and an improved compressive strength (25%)

Análisis de cálculo de las cargas térmicas en silos metálicos mediante el Eurocódigo 1, los métodos clásicos y el método de los elementos finitos

Thermal loads cause important increases in the pressures exerted by granular material stored in silos. The Eurocode 1, part 4, establishes their importance, but it does not propose any calculation method that allows their quantification. In this work the authors try to overcome this difficulty analyzing and comparing different classic methods of calculation of thermal loads and models developed by the authors using the Finite Element Method.Las cargas térmicas provocan importantes aumentos en las presiones que ejerce el material granular almacenado en los silos; el Eurocódigo 1 parte 4, establece su importancia, pero no propone ningún método de cálculo que permita su cuantificación. En este trabajo se van a analizar y comparar diversos métodos clásicos de cálculo de cargas térmicas y modelos desarrollados por los autores usando el Método de los Elementos Finitos

Recycling Aggregates for Self-Compacting Concrete Production: A Feasible Option

[EN] The use of construction and demolition wastes (C&DW) is a trending future option for the sustainability of construction. In this context, a number of works deal with the use of recycled concrete aggregates to produce concrete for structural and non-structural purposes. Nowadays, an important number of C&DW management plants in the European Union (EU) and other countries have developed robust protocols to obtain high-quality coarse recycled aggregates that comply with different European standards in order to be used to produce new concrete. The development of self-compacting concrete (SCC) is another way to boost the sustainability of construction, due to the important reduction of energy employed. Using recycled aggregates is a relatively recent scientific area, however, studies on this material in the manufacture of self-compacting concrete have proven the feasibility thereof for conventional structural elements as well as high-performance and complex structural elements, densely reinforced structures, difficult-to-access formwork and difficult-to-vibrate elements. This paper presents an original study on the use of coarse recycled concrete aggregate (CRA) to obtain self-compacting concrete. Concrete with substitution ratios of 20%, 50% and 100% are compared with a control concrete. The purpose of this comparison is to check the influence of CRA on fresh SCC as well as its physical and mechanical properties. The parameters studied are material characterization, self-compactability, compressive strength, and tensile and flexural strength of the resulting concrete. The results conclude that it is feasible to use CRA for SCC production with minimal losses in the characteristics

Evaluation of Mechanical Characteristics of Cement Mortar with Fine Recycled Concrete Aggregates (FRCA)

[EN] One of the growing demands in concrete manufacture is the availability of natural fine aggregates, which account for 35% to 45% of the total concrete. An alternative method of disposal of fine recycled concrete aggregates (FRCA) generated from demolition and construction waste (C&DW) is their usage in mortar and the development of recycled mortar. The main aim of this research work is to evaluate the viability of incorporating FRCA from urban C&DW for the manufacture of cement-based mortars. Simple processing techniques like washing and sieving are adopted to improve the FRCA quality. Physical and chemical characterization of ingredients is carried out. In total four mixes of 1:3 (cement: sand) mortar with partial replacement of normalized sand with FRCA (0%, 25%, 50%, and 100%) are evaluated for mechanical properties. Water to cement ratio for all four mortar mixes are determined by fixed consistency. Mechanical and physical properties like density, compressive strength, and flexural strength are studied for various curing periods, and the result is that the optimum usage of FRCA is 25% based on a 90-day curing period.SIReutiliza S.L. for offering the recycled and natural aggregate used in this study free of cost. Eduardo Torroja Institute for Construction Science and FCT for financial support

Effect of pores on the mechanical and durability properties on high strength recycled fine aggregate mortar

[EN] Larger consumption of natural fine aggregates (NFA) leads to an increase in cost, energy, and negative environmental impact. On the contrary, the larger production of construction waste results in the generation of recycled fine aggregate (RFA), which requires safe disposal. The aim of study, is to the hunt for such alternatives, compares the mortar mechanical and durability properties with and without RFA. High strength mortar specimens were produced with mix proportion as 1:3 using RFA as partial replacement for NFA as 0%, 25%, 50% and 100%. The mechanical and durability performance of all specimens was assessed in the terms of compressive strength, flexural strength, water absorption and mercury intrusion porosimetry. Mechanical performance is confirmed by microscopic studies. The main results display that the mortar with 25% of RFA, performed better, which are related to pore structures and their distribution. It is noted that the, pores also increase with the increase in RFA content. The effect of pores on the strength and their relationships are assessed.SIAuthor wish to thank for the supports and guidance given by faculties from University of Leon, Leon, Spain and Coimbatore Institute of Technology, Coimbatore, Indi

Self-healing concrete with recycled aggregates

[EN] The higher water absorption of recycled aggregates is the main drawback which hinders the reuse of this secondary material, limiting its acceptance in the construction market. This study proposes the microbially induced carbonate precipitation (by using Bacillus sphaericus) to improve the quality of mixed and ceramic recycled aggregates. This precipitation has contributed to a weight increase and has unleashed a waterproofing response, most effectively on the roughest particle surfaces. High ceramic content aggregates profited from a greater biodeposition, leading to a remaining amount of precipitates is more deeply fixed in cementitious materials. The pore-filling effect was detected by SEM, supporting the waterproofing result. The use of biotreated aggregates led to more fluid recycled concrete consistencies when the same amount of mixing water was used. Without water adjustments in the concrete mixture, the presence of calcium carbonate lessened long-term compressive strength, although strength development was accelerated, with higher early-age (7 days) values than observed for concrete bearing untreated recycled aggregate

Paving with Precast Concrete Made with Recycled Mixed Ceramic Aggregates: A Viable Technical Option for the Valorization of Construction and Demolition Wastes (CDW)

materialsArticle Paving with Precast Concrete Made with Recycled Mixed Ceramic Aggregates: A Viable Technical Option for the Valorization of Construction and Demolition Wastes (CDW) Andrés Juan-Valdés 1,* , Julia García-González 2, Desirée Rodríguez-Robles 3, Manuel Ignacio Guerra-Romero 1, Fernando López Gayarre 4, Nele De Belie 5 and Julia M. Morán-del Pozo 1 1 Department of Agricultural Engineering and Sciencies, University of León, 24071 León, Spain; [email protected] (M.I.G.-R.); [email protected] (J.M.M.-d.P.) 2 Department of Agriculture and Feeding, University of La Rioja, 26006 Logroño, Spain; [email protected] 3 Department of Agronomy and Forestry Engineering, University of Extremadura, 06007 Badajoz, Spain; [email protected] 4 Department of Construction, Campus de Gijón, University of Oviedo, 33203 Gijón, Spain; [email protected] 5 Magnel Laboratory for Concrete Research, Ghent University, 9052 Ghent, Belgium; [email protected] * Correspondence: [email protected]; Tel.: +34-987-291000 Received: 4 December 2018; Accepted: 18 December 2018; Published: 21 December 2018 Abstract: This research aimed to prove the feasibility of producing two types of precast elements widely used in construction, such as curbstones and paving blocks, using recycled concrete made with a 50% substitution of the natural gravel by recycled mixed aggregates with a significant ceramic content (>30%). In order to prove the quality of such mass concrete recycled precast elements, two different mixes were used: the first one was a conventional concrete mix provided by Prefabricados de Hormigón Pavimentos Páramo S.L., one of the collaborating companies in this study, and the other was a mixture in which wt 50% of the natural coarse aggregates were substituted for recycled mixed aggregates ceramic (RMAc). This recycled aggregate is a heterogeneous mixture of unbound aggregates, concrete, ceramic, etc., used as a secondary recycled aggregate and commonly produced in a lot of recycling plants in many European countries. This material was supplied by Tecnología y Reciclado S.L., the other collaborating company. Both mixtures were representative in order to establish the comparative behavior between them, taking into account that smaller percentages of replacement of the natural with recycled aggregates will also produce good results. This percentage of substitution represents a high saving of natural resources (gravel) and maintains a balanced behavior of the recycled concrete, so this new material can be considered to be a viable and reliable option for precast mass concrete paving elements. The characterization of the recycled precast elements, covering mechanical, microstructural, and durability properties, showed mostly similar behavior when compared to the analogous industrially-produced pieces made with conventional concrete.This work has been financially supported by the Spanish Ministry of Economy and Competitiveness through the research projects grants BIA2013-48876-C3-3-R and BIA2017-83526-R.The authors would like to thanks the companies Prefabricados de Hormigón Pavimentos Páramo S.L. and TEC-REC: Tecnología y Reciclado S.L., who participated in this study

Recycled Precast Concrete Kerbs and Paving Blocks, a Technically Viable Option for Footways

[EN] The linear economy paradigm in place to date has to be seriously challenged to give way to a new school of thought known as the circular economy. In this research work, precast kerbs and paving blocks made with recycled concrete (RACC-mixture) bearing 50 wt% mixed recycled aggregate (masonry content of 33%) and an eco-efficient cementitious material as 25 wt% conventional binder replacement were evaluated to assess their intrinsic potential to replace traditional raw materials, in keeping with circular economy criteria. Therefore, precast products were subjected to mechanical strength, durability and microstructure tests and were compared to conventional concrete units (CC-mixture and commercially available precast elements). Although a class demotion was observed for water absorption and some decreases in flexural strength (26%), splitting tensile strength (12.8%) and electrical resistivity (45%) and a lower class water absorption were registered, and the recycled mixture also exhibited a greater performance in terms of compressive strength (6%), a better abrasion resistance classification and a comparable porosity and microstructure, which ensures a good concrete durability. In any case, the results showed that precast pieces were European standard-compliant, thus supporting the viability of the mixed recycled aggregates and eco-efficient cementitious replacement in footways

Evolución de pacientes alcohólicos egresados del servicio de deshabituación durante los años 2014 y 2015

Introducción: el propósito del tratamiento del paciente alcohólico es la rehabilitación mediante actividades de reeducación, readaptación y la reinserción social, siendo la abstinencia absoluta de alcohol la condición para lograrlo, además con la dispensarización se establecen procedimientos  para desarrollar  acciones de seguimiento y control.Objetivo: determinar la evolución  de   los pacientes alcohólicos egresados del Servicio de Deshabituación  al alcohol y otras drogas del Hospital psiquiátrico de la provincia Mayabeque. Métodos: se realizó un estudio descriptivo, transversal, en el Hospital Psiquiátrico Provincial “Crisanto Betancourt Hernández”, municipio Güines, provincia Mayabeque, durante los años 2014 y 2015. Después de aplicar, los criterios de inclusión y exclusión, al universo de 87 pacientes, se seleccionaron 50 por un muestreo probabilístico simple aleatorio. Se estudiaron las variables de tiempo de abstinencia, recaídas, recursos terapéuticos utilizados y dispensarización en el primero y segundo nivel de atención. La información se obtuvo por la observación, entrevistas y revisión documental de los archivos estadísticos.Resultados: el 34 % de los pacientes se mantuvo en abstinencia entre uno a tres meses, el 46% con recaídas evaluadas de regular; el acamprosato fue el fármaco más utilizado (28 %) y el 100 % fueron dispensarizados en el segundo nivel de atención.Conclusiones: el tiempo de abstinencia que predomina es de uno a tres meses, la recaída fue evaluada de regular, como recursos terapéuticos el acamprosato es el fármaco más utilizado y efectivo. Todos los pacientes fueron dispensarizados en la atención secundaria de salud