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%)

Mechanical behaviour of grapevine wood affected by Xylotrechus arvicola

[EN] The cerambycid insect Xylotrechus arvicola is considered a pest that affects the wood of the grapevine (Vitis vinifera) in the major wine areas of the Iberian Peninsula. The larva of this insect perforates the grapevine wood, resulting in structural and biomechanical failure of the vine plants. Vine samples from wood damaged by X. arvicola larvae were picked up from different vineyards and grape varieties. Compressive and flexural tests were performed in order to assess the mechanical behaviour of the wood samples. Total length of the cracks in wood samples (TLCWS) that appeared on the surface of the grapevine wood samples after the mechanical tests was measured. Compressive strength (CS) and flexural strength (FS) decreased with the increase of the cross-sectional area (CSA) of both branches and trunks, regardless of damage condition or water content. Moreover, the resistance was lower in damaged wood. In addition, this was verified through the linear regression coefficients of the interaction CS x CSA and FS x CSA. TLCWS in branches and trunks of damaged samples was greater that in undamaged samples. Also, TLCWS within the same damage condition and part of the plant was higher in dry samples than in fresh samples. The damaged wood would show a higher vulnerability to common mechanical stress suffered by the grapevines in the field including heavy winds, fruit overweight or harvesting machines shaking (when mechanically collected). Larvae of this insect altered the mechanical behaviour of the trunk and branches of grapevine wood. The mechanical strength of wood was more negatively affected when the CSA of the branches and trunks increased. Longer TLCWS was found in affected wood

A sustainable production of natural hydraulic lime mortars through bio-amendment

.This article examined the effect of a bioproduct suspension obtained from fermentation of biodiesel’s crude glycerol when used to formulate natural hydraulic lime mortars, as a fluid replacing the mixing water. The bioproduct was used either sonicated or non-sonicated and two volumes of mixing fluid were tested. The aim was to assess the advantages and drawbacks that could be achieved with a waste-based bioproduct, instead of petrochemical-based additions. The investigation revealed a positive effect on workability, producing mortars with a lower mixing fluid content, improving the mechanical performance. Finally, the bioproducts reduced the mortar water absorption by gravity and capillary.S

Ensayos de hormigones fabricados con polvo de corcho

[ES] Este trabajo de investigación tiene por objeto conocer algunas propiedades físicas y mecánicas de un hormigón elaborado en laboratorio, adicionándole diversas proporciones de polvo de corcho. Las propiedades del material resultante, si bien carecen de la resistencia mecánica que caracteriza al hormigón, parecen interesantes para su uso en ciertas aplicaciones de la ingeniería agronómica tales como en la fabricación de piezas para solados de parques infantiles y jardines, o en los cubículos de ciertas construcciones ganaderas, extremos que es preciso analizar y comprobar

Zamoranos en Cuba

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2012-201

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

Influence of Design Parameters on Fresh Properties of Self-Compacting Concrete with Recycled Aggregate—A Review

[EN] This article presents an overview of the bibliographic picture of the design parameter’s influence on the mix proportion of self-compacting concrete with recycled aggregate. Design parameters like water-cement ratio, water to paste ratio, and percentage of superplasticizers are considered in this review. Standardization and recent research on the usage of recycled aggregates in self-compacting concrete (SCC) exploit its significance in the construction sector. The usage of recycled aggregate not only resolves the negative impacts on the environment but also prevents the usage of natural resources. Furthermore, it is necessary to understand the recycled aggregate property’s role in a mixed design and SCC properties. Design parameters are not only influenced by a mix design but also play a key role in SCC’s fresh properties. Hence, in this overview, properties of SCC ingredients, calculation of design parameters in mix design, the effect of design parameters on fresh concrete properties, and the evolution of fresh concrete properties are studied.S

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