Mechanical and environmental behavior of cement mortars containing ladle furnace slag

At present, steel production is mainly done in basic oxygen furnaces (BOF) and electric arc furnaces (EAF) (Pauliuk, S. et al, 2013, Morfeldt, J. et al, 2015). According to the statistics, it is expected that the use of electric arc furnaces to supply the demand for steel will prevail. In 2017, in Europe, 41% of steel was produced in electric arc furnaces, while in Spain, according to the Union of Steel Companies (UNESID, 2016), the percentage was almost 66% in 2016. In 2016 the European Union generated approximately 18.4 Mt of slag (black and white), of which 1.5 Mt was produced in Spain. In other words, the amount of white slag produced was about 286 thousand tons, approximately between 20 and 30 kg of slag per ton of steel (UNESID, 2016, Euroslag, 2016). Refining slag (white slag) is the second most abundant waste in steel production, and, to date, its final destination is still the landfill. This study has used ladle slag from refined steelworks, as a replacement for cement in different proportions (0, 25, 50 and 75%), for the manufacture of mortars. A broad characterization of the ladle slag has been carried out, as well as determining the mechanical, durable, and environmental properties of the manufactured mortars. The results show that using the ladle slag as a replacement for cement produces a decrease in compressive strength, but the expansion behavior remains below the stability limit. It also has been seen that the slag incorporated into mortars, evaluated by leaching test at 28 days, shows inert material behavior.Postprint (published version

Concrete with crumb rubber from used tyres

This study aims to determine the influence of the substitution of a variable volume of aggregates on a concrete by an equivalent quantity of crumb rubber (CR) obtained from used tyres. The physical and mechanical properties of different concretes, which were developed through laboratory tests, have been studied for this goal. The experimental method employed is based on the production of a reference concrete and six concretes where part of the conventional aggregate has been replaced by particles of CR, keeping the proportion water-cement and cement content per cubic meter of concrete constant. Intending to assess the influence of the volume of CR incorporated into a conventional concrete, a first group of specimens is created, replacing 5%, 10% and 15% of the volume of sand in the original mix by grains of rubber 1-4 mm. In order to study the influence of the size of the incorporated grains of CR, a second group of specimens is produced substituting the content of the gravel for grains of rubber 10-16 mm, which leads us to three other types of concrete. The addition of CR increases the rate of entrapped air due to the bad adherence between the cement paste and the CR grains. The consequence is a higher absorption and porosity. The compressive strength and the elasticity modulus decrease with the addition of rubber, but the tensile strength remains at the same level. The final conclusion of the study is that the use of concrete with CR is possible in several applications taking into account the limitations and advantages deduced from this experimental project.Postprint (published version

Long-term comparison between waste paper fly ash and traditional binder as hydraulic road binder exposed to sulfate concentrations

Sulfate attack is one of the drawbacks of cementitious materials for stabilized soils. In the current study, a durability comparison of stabilized soil with cement (Type IV) and waste paper fly ash (WPFA) was conducted. First, the treated soil’s unconfined compressive strength (UCS) was tested. Next, the treated soil was subjected to various wetting/drying cycles with various sulfate concentrations and temperatures for a year. In the meantime, samples were taken for DRX, FTIR, and TGA microstructural analyses. Additionally, samples were manufactured to track swelling over an 800 day period. The outcomes show that WPFA’s UCS remained constant. Furthermore, ettringite development can be seen in the microstructural studies, however testing on linear displacement over 800 days revealed no significant changes in swelling. Finally, SEM was used to verify the ettringite formation at 360 days in order to confirm the previous findings. All the results indicated that stabilizing soil with 5% of WPFA and 3% of cement IV is possible even in presence of high sulfate concentrations, while maintaining the durability of the structure.This research was funded by European Union’s Horizon 2020, grant number 730305.Peer ReviewedPostprint (published version

Efeito da pré-molhagem do agregado nas propriedades das argamassas com agregado reciclado deconcreto e agregado leve

This paper examines the suitability of partially replacing natural aggregate, sand, (NA) with recycled concrete aggregate (RCA) or lightweight aggregate (LWA) in mortars, under the hypothesis that pre-wetting aggregates would produce improvement in mortar properties. Fresh mortar properties such as density, entrained air content, consistency and heat of hydration, as well as hardened mortar properties such as dry density, compressive and flexural strength, and dimensional instability at 0% and 100% saturation were determined. The results show that mortars made with natural aggregate (75%) and recycled concrete aggregate (25%) have similar properties to mortars made with only natural aggregate (100%) and that pre-wetting the aggregates does not influence the properties of mortars significantly. Therefore, partial replacement with recycled concrete aggregate is a viable alternative for producing mortar.Peer ReviewedPostprint (published version

Estudio de hormigones con adición de polvo de neumàticos fuera de uso (NFU)

Pese a las diversas aplicaciones ya estudiadas con los neumáticos fuera de uso, el elevado volumen de los mismos producido anualmente como residuo, justifica el investigar sus nuevas posibilidades de uso. Asimismo, es cada vez más importante en encontrar aplicaciones en las que la incorporación de dichos residuos represente un valor añadido desde el punto de vista del desempeño del producto final. En este contexto, se considera que la producción de nuevos hormigones con polvo de neumático fuera de uso (polvo de NFU) con propiedades optimizadas, representa un avance significativo, no solo de cara a una mejor gestión de residuos, como también para la producción de hormigones con mejores prestaciones. Las partículas del polvo de NFU contribuyen para la producción de una microestructura más flexible, dando lugar a un hormigón más resistente a las deformaciones por flexión y con mayor resistencia a la fatiga; que a su vez el hormigón con polvo de NFU presenta una mejora significativa de su capacidad térmica y acústica

Migration of calcium hydroxide particles from the matrix to the cellulosic fibres in cement mortar based composites

Postprint (published version

Hilbert fractal curves for HTS miniaturized filters

This work presents novel compact High Temperature Superconductor (HTS) microstrip resonators based on Hilbert fractal curves. Their miniaturization performance has been investigated, emphasizing the parameters which allow to obtain a good trade off between compact size and quality factor. Hilbert resonators with different arrangements have been designed and assessed by using full wave simulators. In order to experimentally verify our analysis, a four pole quasi elliptic filter, in the cascade quadruplet configuration, with f0 close to 2.45GHz, have been fabricated by patterning a 10x10mm2 YBCO film on MgO substrates. Minimum insertion losses of the order of (0.1-0.2) dB have been measured.Peer Reviewe

Miniaturization of superconducting filters using Hilbert fractal curves

This work presents novel compact high-temperature superconductor microstrip resonators and filters based on the Hilbert space-filling fractal curve. Several Hilbert resonator configurations have been assessed by using a full-wave electromagnetic simulator and their miniaturization performance has been investigated, emphasizing the parameters which allow obtaining good tradeoff between compact size and losses. These resonators have proved to be useful for filter design. A four-pole 2.45-GHz quasi-elliptic filter and a four-pole 1.9-GHz Chebyshev filter have been realized by patterning 10 mm/spl times/10 mm Y/sub 2/Ba/sub 3/Cu/sub 7-/spl delta//O thin films on MgO substrates. Insertion losses of the order of 0.2 dB have been measured, showing good agreement with the simulations.Peer Reviewe

Impacto ambiental en el ámbito de los materiales de construcción

El proceso de lixiviación en sí es universal, ya que cualquier material expuesto al contacto con el agua filtrará los componentes de su superficie o de su interior en función de la porosidad del material considerado. El contenido total de contaminantes no es determinante para valorar el verdadero impacto ambiental de una sustancia y su aplicación. La lixiviación depende de diversos factores, que deben ser tenidos en cuenta a la hora de aplicar los resultados de laboratorio a la realidad del escenario concreto pero a la vez habrá que establecer elementos de referencia valorables a través de ensayos de laboratorio y tomar decisiones simplificadoras. El estudio del impacto ambiental por lixiviación es una herramienta que permite tomar decisiones respecto al uso, tratamiento o vertido de residuos y debe extenderse también a los materiales de construcción. El equipo ponente se centra en la actualidad en el estudio de la lixiviación de los materiales obtenidos a partir de residuos y pretende contribuir al conocimiento general y a la necesaria divulgación