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

Dynamical organization towards consensus in the Axelrod model on complex networks

We analyze the dynamics toward cultural consensus in the Axelrod model on scale-free networks. By looking at the microscopic dynamics of the model, we are able to show how culture traits spread across different cultural features. We compare the diffusion at the level of cultural features to the growth of cultural consensus at the global level, finding important differences between these two processes. In particular, we show that even when most of the cultural features have reached macroscopic consensus, there are still no signals of globalization. Finally, we analyze the topology of consensus clusters both for global culture and at the feature level of representation.Comment: 8 pages, 7 figures. Final version published in Physical Review

Precedentes administrativos das agências reguladoras: produção normativa como mecanismo de controle de políticas públicas

O presente trabalho ocupa-se em fazer um estudo acerca dos precedentes administrativos e sua aplicação. Depois, serão apresentados o conceito e os fundamentos constitucionais da teoria dos precedentes administrativos. Demonstrando a importância desse instituto para a aplicação dos princípios constitucionais da segurança jurídica e da isonomia, os quais devem pautar a atuação da Administração Pública. Este trabalho tem como objetivo verificar, por um lado, o papel dos órgãos reguladores em relação às Políticas Públicas, e por outro, a influência das Políticas Públicas no âmbito de atuação das Agências reguladoras. Partindo de uma abordagem conceitual, para em seguida explorar brevemente o arcabouço das Políticas Públicas e das Agências Reguladoras. Esse trabalho não ambiciona exaurir a discussão, mas incitar o leitor atento a reflexão sobre esses institutos

Mejoramiento del sistema de calidad de servicio al cliente en la Empresa Pública Municipal Mercado de Productores Agrícolas (EP-EMMPA) de la ciudad de Riobamba, provincia de Chimborazo año 2013.

El desarrollo del presente trabajo investigativo se elaboró en la Empresa Pública Municipal Mercado de Productores Agrícolas (EP-EMMPA), ubicado en la ciudad de Riobamba provincia de Chimborazo, es una empresa netamente de servicios, cuyo objetivo es garantizar la administración, operación y funcionamiento de las diferentes actividades que se vienen realizando en la misma. Para la elaboración del presente trabajo se realizó una minuciosa indagación, análisis y aplicación de una variedad de métodos, técnicas e instrumentos de investigación como la aplicación de encuestas y observación a todos los productores, comerciantes e intermediarios que trabajan en la empresa de esta manera se pudo conocer las causas y efectos del problema central: deficiente servicio al cliente, la actitud que demuestran los empleados no es la adecuada, falta de información sobre los cambios en la administración, los comerciantes no reciben un buen trato entre otros aspectos negativos que dan mala imagen a la institución. El propósito de esta investigación es mejorar la calidad en el servicio de atención al cliente en las diferentes áreas que mantengan una relación directa con los usuarios de la EP-EMMPA, debido a la importancia que tiene la satisfacción del mismo para el porvenir de la empresa. Por lo tanto, los resultados obtenidos a través de esta investigación permitirán gestionar sus actividades con mayor eficiencia, mejorar las políticas referentes al servicio que la empresa ofrece a sus clientes pilares fundamentales para lograr los objetivos y metas constituyendo de esta manera el beneficio de la calidad de atención al cliente. Luego de la extensa investigación realizada y con la ayuda de expertos en el tema se decidió proponer estrategias que permitan al talento humano de la empresa mejorar el servicio o atención al cliente, de esta manera ofrecer un servicio de calidad.The development of this research work was elaborated at the Empresa Pública Municipal Mercado de Productores Agrìcolas (EP-EMMPA), located in Riobamba province of Chimborazo, it is a company markedly of service, intended to ensure to the administration, operation and performance the different activities carried out in the enterprise For the preparation of this research work, a detailed inquiry, analysis and application of a variety of methods, techniques and instruments of investigations were carried out, such as the research and observation surveys application of all producers, dealers and middlemen who work in the business, therefore, causes and effects of the central problem could be known: the poor customer service, as well as the attitude shown by employees is not adequate, and the lack of information about changes in the administration, the businessmen do not get a good deal among other negative aspects give a bad image of the institution The purpose of this research is to improve the quality in the customer care service in different areas which maintain a direct relationship with other users of the company, EP-EMMPA, because of the importance of satisfaction for the future of the company. Therefore, the results obtained of the research will allow efficiently manage its business, improve the policies relating to the service that the company offers to its customers, fundamental pillars, for attaining the objectives and goals thereby constituting to the benefit of the customer service quality After the extensive research and with the help of experts in the field, it was decided to put strategies that enable the human talent of the company and improve the customer service, attention, so that provide a quality service

Quality Assessment of Mixed and Ceramic Recycled Aggregates from Construction and Demolition Wastes in the Concrete Manufacture According to the Spanish Standard

[EN] Construction and demolition waste (CDW) constitutes an increasingly significant problem in society due to the volume generated, rendering sustainable management and disposal problematic. The aim of this study is to identify a possible reuse option in the concrete manufacturing for recycled aggregates with a significant ceramic content: mixed recycled aggregates (MixRA) and ceramic recycled aggregates (CerRA). In order to do so, several tests are conducted in accordance with the Spanish Code on Structural Concrete (EHE-08) to determine the composition in weight and physic-mechanical characteristics (particle size distributions, fine content, sand equivalent, density, water absorption, flakiness index, and resistance to fragmentation) of the samples for the partial inclusion of the recycled aggregates in concrete mixes. The results of these tests clearly support the hypothesis that this type of material may be suitable for such partial replacements if simple pretreatment is carried out. Furthermore, this measure of reuse is in line with European, national, and regional policies on sustainable development, and presents a solution to the environmental problem caused by the generation of CDW

Influence of the use of External Carbon Fiber Reinforcement on the Flexural Behavior of Prismatic Concrete Test Specimens. An Application for Repairing of Deteriorated Agricultural Structures

This manuscript reports a study of the capacity of polymer composites to increase flexural strength in concrete. The polymer composites reinforced with carbon fiber and bonded with epoxy adhesive were used in prismatic test specimens of mass concrete corresponding to two different morphologies. The aim was to simulate the restoration of deteriorating concrete agricultural structures in order to explore the viability of this alternative against replacing them. An increase was found in the strength of the elements tested, with a higher strength being observed in those test specimens presenting a modified geometry.NOThis research was funded by SPANISH MINISTER OF ECONOMY AND COMPETITIVENESS, grant number BIA2017-83526RThe authors acknowledge the technical support and material used for experiments donated by Sika Grou

Pre-Saturation Technique of the Recycled Aggregates: Solution to the Water Absorption Drawback in the Recycled Concrete Manufacture

The replacement of natural aggregates by recycled aggregates in the concrete manufacturing has been spreading worldwide as a recycling method to counteract the large amount of construction and demolition waste. Although legislation in this field is still not well developed, many investigations demonstrate the possibilities of success of this trend given that concrete with satisfactory mechanical and durability properties could be achieved. However, recycled aggregates present a low quality compared to natural aggregates, the water absorption being their main drawback. When used untreated in concrete mix, the recycled aggregate absorb part of the water initially calculated for the cement hydration, which will adversely affect some characteristics of the recycled concrete. This article seeks to demonstrate that the technique of pre-saturation is able to solve the aforementioned problem. In order to do so, the water absorption of the aggregates was tested to determine the necessary period of soaking to bring the recycled aggregates into a state of suitable humidity for their incorporation into the mixture. Moreover, several concrete mixes were made with different replacement percentages of natural aggregate and various periods of pre-saturation. The consistency and compressive strength of the concrete mixes were tested to verify the feasibility of the proposed techS

Effect of Design Parameters on Compressive and Split Tensile Strength of Self-Compacting Concrete with Recycled Aggregate: An Overview

[EN] One of the prime objectives of this review is to understand the role of design parameters on the mechanical properties (Compressive and split tensile strength) of Self-Compacting Concrete (SCC) with recycled aggregates (Recycled Coarse Aggregates (RCA) and Recycled Fine Aggregates (RFA)). The design parameters considered for review are Water to Cement (W/C) ratio, Water to Binder (W/B) ratio, Total Aggregates to Cement (TA/C) ratio, Fine Aggregate to Coarse Aggregate (FA/CA) ratio, Water to Solid (W/S) ratio in percentage, superplasticizer (SP) content (kg/cu.m), replacement percentage of RCA, and replacement percentage of RFA. It is observed that with respect to different grades of SCC, designed parameters affect the mechanical properties of SCC with recycled aggregates

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