Estudio de la idoneidad de un nuevo hormigón estructural fabricado con áridos ligeros reforzados con fibra de carbono sinterizados a partir de residuos

The suitability of three new lightweight aggregates containing carbon fiber residues (CAs) as components in structural lightweight concrete has been studied. Prismatic concrete specimens were prepared using these CAs as a coarse fraction. Additional specimens of normal-weight aggregate, commercial lightweight aggregate and mortar were prepared for comparison. The CA-concrete samples (CACs) have yielded compressive strength values between 35 and 55 MPa as well as low density and thermal conductivity results. Furthermore, the CACs have displayed the highest ratios of mechanical strength over density and the thermal conductivity, which means that there is a better balance between their mechanical and physical properties than in the other samples studied. These results indicate that the new CAs could have great potential for use in structural lightweight concrete, also complying with the principles of the Circular Economy.Este estudio pretende comprobar la idoneidad de unos novedosos áridos ligeros sinterizados con residuos de fibra de carbono (CAs) en la fabricación de hormigón ligero estructural. Se prepararon probetas prismáticas de hormigón, utilizando estos CAs como fracción gruesa, comparándose a su vez con probetas fabricadas con un árido convencional, un árido ligero comercial y mortero. Las muestras de hormigón con los áridos CA (en adelante CAC) han dado lugar a valores de resistencia a compresión entre 35 y 55 MPa, así como a resultados bajos de densidad y conductividad térmica, mostrando además las ratios más altas al relacionar estos tres parámetros. Esto indicaría por tanto un mejor equilibrio entre las propiedades mecánicas y físicas que los obtenidos en las otras muestras estudiadas. Estos resultados apuntan a que los nuevos CAs podrían tener un gran potencial para su uso en hormigón ligero estructural, cumpliendo además los principios de la Economía Circular

The H5 guide system - the latest innovative guide system at the ILL

The H5 program with the complete rebuild of the guide system and the upgrade or renovation of all instruments leads to a tremendous increase of the instrument performances. The improvement was obtained both in terms of more useful flux and upgrade of the different instruments (e.g. higher field density for IN15). In addition, the industrial application instrument D50 offers an addition to the ILL instrument suite (see p. 27 in this issue). With the commissioning of the new spin echo spectrometer WASP in 2016, the H5 program will be completed and a considerable improvement for the ILL instrument park will be finalized

Influence of polypropylene and steel fibres on thermal spalling and physical-mechanical properties of concrete under different heating rates

International audienceAbstractThis study investigates three concrete compositions: a control concrete, a reinforced concrete containing 60 kg/m3 of steel fibres, and a hybrid concrete containing 60 kg/m3 of steel fibres and 0.75 kg/m3 of polypropylene fibres. Cylindrical specimens were manufactured and subjected to two heating rates (10 °C/min and the ISO 834 fire standard) to study their spalling sensitivity. Moreover, unidirectional heat transfer and pressure measurements were performed on slabs heated at 10 °C/min to 600 °C. To understand the influence of fibres on spalling processes more clearly, the thermal properties were studied during heating and cooling: the gas permeability, compressive strength, and Young’s modulus of specimens were measured after a heating and cooling cycle at 0.5 °C/min. The results show that the spalling phenomenon was more severe for cylindrical specimens than for slabs. The addition of 60 kg/m3 of steel fibres had an unfavourable influence on spalling, especially during the ISO 834 fire test. The addition of 0.75 kg/m3 of polypropylene fibres allowed the concretes containing steel fibres to avoid spalling, regardless of the thermal loading conditions

Influence of steel and/or polypropylene fibres on the behaviour of concrete at high temperature: Spalling, transfer and mechanical properties

In this study different mixtures of high strength concretes (70 MPa) were prepared with different naturesof aggregates, moisture content, length and dosage of polypropylene fibres (PPF) and steel fibres (SF) andsubjected to the standard ISO 834 fire. Concretes with 60 kg/m3 of SF show spalling while plain concrete(without fibres) and concrete with 0.75 kg/m3 of PPF and 60 kg/m3 of SF did not spall. Microstructure,thermal, hydric and mechanical properties of concretes were investigated. PPF increase the porosityand permeability of concretes. Steel fibres control crack development which reduce the stress relaxationphenomenon and the size of new pores

Influence of polypropylene and steel fibres on thermal spalling and physical-mechanical properties of concrete under different heating rates

International audienceAbstractThis study investigates three concrete compositions: a control concrete, a reinforced concrete containing 60 kg/m3 of steel fibres, and a hybrid concrete containing 60 kg/m3 of steel fibres and 0.75 kg/m3 of polypropylene fibres. Cylindrical specimens were manufactured and subjected to two heating rates (10 °C/min and the ISO 834 fire standard) to study their spalling sensitivity. Moreover, unidirectional heat transfer and pressure measurements were performed on slabs heated at 10 °C/min to 600 °C. To understand the influence of fibres on spalling processes more clearly, the thermal properties were studied during heating and cooling: the gas permeability, compressive strength, and Young’s modulus of specimens were measured after a heating and cooling cycle at 0.5 °C/min. The results show that the spalling phenomenon was more severe for cylindrical specimens than for slabs. The addition of 60 kg/m3 of steel fibres had an unfavourable influence on spalling, especially during the ISO 834 fire test. The addition of 0.75 kg/m3 of polypropylene fibres allowed the concretes containing steel fibres to avoid spalling, regardless of the thermal loading conditions

Influence of elevated temperature on properties of radiation shielding concrete with electric arc furnace slag as coarse aggregate

The development of value-added materials from by-product of the steel-making process can promotesustainability in construction to move towards a circular economy. The use of Electric Arc Furnace(EAF) steel slag as heavyweight coarse aggregate to develop sustainable radiation shielding concretecould provide both technical and economic benefits with less environmental impact. This contributioninvestigates the behaviour at high temperature of a sustainable radiation shielding concrete. Thermalbehaviour of EAF slag concrete was compared to another heavyweight concrete made of barite aggregatesand to a normal-weight concrete. On one hand, the thermal stability of the three different aggregates wasdetermined via simultaneous Thermogravimetry and Differential Scanning Calorimetry analyses andvisual observations after 10 C/min heating. On the other hand, the evolution of thermal conductivityof concretes during heating, the residual mechanical properties and the assessment of potential spallingoccurrence were investigated. Stereo-microscope and Scanning Electron Microscope pictures provideadditional explanations by showing the paste-aggregate interface after heating at 450 C. The results indicatedthat EAF concrete displayed less strength reduction at increasing temperature. This improved behaviouris attributed to both the strong bond between the paste and the aggregates, and the better thermalbehaviour of the EAF slag aggregates compared to barite aggregates

Influence of elevated temperature on properties of radiation shielding concrete with electric arc furnace slag as coarse aggregate

The development of value-added materials from by-product of the steel-making process can promote sustainability in construction to move towards a circular economy. The use of Electric Arc Furnace (EAF) steel slag as heavyweight coarse aggregate to develop sustainable radiation shielding concrete could provide both technical and economic benefits with less environmental impact. This contribution investigates the behaviour at high temperature of a sustainable radiation shielding concrete. Thermal behaviour of EAF slag concrete was compared to another heavyweight concrete made of barite aggregates and to a normal-weight concrete. On one hand, the thermal stability of the three different aggregates was determined via simultaneous Thermogravimetry and Differential Scanning Calorimetry analyses and visual observations after 10 \ub0C/min heating. On the other hand, the evolution of thermal conductivity of concretes during heating, the residual mechanical properties and the assessment of potential spalling occurrence were investigated. Stereo-microscope and Scanning Electron Microscope pictures provide additional explanations by showing the paste-aggregate interface after heating at 450 \ub0C. The results indicated that EAF concrete displayed less strength reduction at increasing temperature. This improved behaviour is attributed to both the strong bond between the paste and the aggregates, and the better thermal behaviour of the EAF slag aggregates compared to barite aggregates

Thermal stability of different siliceous and calcareous aggregates subjected to high temperature

The goal of this study is to improve the knowledge of the deterioration of aggregates subject to high temperature phenomena and to characterise the physical and chemical transformations they undergo. Twenty one (21) aggregates of different mineralogical composition were exposed at temperatures up to 750 °C. The behaviour of siliceous and calcareous aggregates undergoing high temperature has been examined with respect to the evolution of physical, chemical and mineralogical properties

Estudio del comportamiento de concreto asfáltico con residuos siderúrgicos como agregados

Spa: El auge de la construcción de grandes obras de ingeniería ha impulsado la demanda del acero, lo que ha generado un incremento en la producción de residuos siderúrgicos, situación que causa problemas ambientales debido a su acumulación y no disposición adecuada. Igualmente, la explotación de recursos naturales no renovables como los agregados pétreos están generando deterioro en el medio ambiente; si a esto le sumamos que las regulaciones ambientales para la explotación de estos materiales no renovables son cada vez más estrictas generando incremento significativo en los costos de producción. En consecuencia, esto lleva a un cambio de paradigma: utilizar materiales no convencionales y emplear técnicas de reciclajes de los pavimentos existentes. El uso de residuos industriales en diferentes procesos debe estar enfocado hacia el desarrollo sostenible y la protección del medio ambiente. Durante el proceso de la fabricación de acero se producen diferentes residuos entre los cuales se encuentran la escoria de horno al oxigeno (BOF), escoria de horno de arco eléctrico (EAF) y polvo de alto horno (BFD). Esta investigación analiza la conveniencia técnica del uso de la escoria BOF y escoria EAF como agregado grueso y estudia la alternativa del uso de BFD como agregado fino, para fabricar mezclas asfálticas en caliente para pavimentos, como una alternativa para mitigar los problemas ambientales derivados de la acumulación de residuos siderúrgicos y de la explotación de materiales no renovables, como la grava y la arena. Para lograr el objetivo, se analizaron once tipos de mezclas asfálticas, una mezcla con materiales convencionales y diez mezclas sustituyendo parcial (50%) y totalmente (100%) el agregado grueso por escoria BOF y escoria EAF y el agregado fino por BFD. El diseño de las mezclas se realizó con la metodología Ramcodes, la cual se basa en el principio del polígono de vacíos. Mediante ensayos se evaluaron las características del diseño preliminar y verificaron las propiedades de desempeño de cada una de las mezclas. También se estudia y analiza la posibilidad de modificar el cemento asfáltico con polvo de escoria de horno de arco eléctrico (EAFD), Para lo cual se realiza el estudio reológico añadiendo 3%, 6% y 10% de EAFD y se compara con los resultados del cemento asfáltico base. Se realizan los ensayos con el reómetro de corte dinámico DSR para determinar los parámetros G* y δ en los cementos asfáltico originales, envejecidos en el horno rotatorio de película delgada (RTFO) y en el horno de envejecimiento a presión (PAV). También se realiza el ensayo de recuperación elástica a diferentes esfuerzos MSCR, el cual mide las propiedades viscoelásticas del cemento asfáltico envejecido a corto plazo en RTFO. Los resultados de este estudio confirman el uso de escoria BOF y escoria EAF como agregado grueso e indican la factibilidad del uso de BFD como agregado fino, para reemplazar parcialmente los agregados convencionales, en la fabricación de concretos asfálticos para uso en carreteras. Respecto a las propiedades mecánicas, las mezclas cumplen con los requerimientos del INVIAS para un nivel de tránsito NT-3, como son estabilidad, flujo y propiedades volumétricas. Asimismo, las propiedades de desempeño (susceptibilidad a la humedad, susceptibilidad a la deformación permanente, módulo resiliente y fatiga) presentaron un buen comportamiento.DoctoradoDoctorado en Ingeniería y Ciencia de los Materiale