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

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

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

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

Experimental study of the effect of the thermal conductivity of EAF slag aggregates used in asphaltic concrete of wearing courses on the durability of road pavements

Electric Arc Furnace (EAF) steel slag is the basic material used to obtain good quality aggregates in different layers of road pavements. Many scientific papers have reported on the high frictional and abrasion resistance of this material. EAF slag aggregates are hard, dense, chemically stable and have good adhesion with bitumen, all characteristics related with its high alkaline character. These properties are important in hot mix asphalt for wearing courses where high wear is present and optimal skid resistance is required. In some EAF slags, calcium and specially magnesium oxides are not completely combined, and upon contact with moisture convert into the corresponding hydroxides that could lead to volume changes. Only EAF slags with less than 3,5% expansion are used in Europe as aggregates for asphalt concrete or hot mix asphalt. In this paper, we present the experimental results of a study evaluating the consequences of the lower thermal conductivity of the EAF slag aggregates used in Catalonia (Spain). These aggregates have the necessary mechanical and chemical properties, as well as a very low expansion (0,5 to 1,5%). The EAF slag aggregates have a lower thermal conductivity (0,85-1,20 W/mK) than natural aggregates, such as granite that are used in wearing courses (1,60-1,80 W/mK). This property of the EAF slag aggregates can represent up to 30% less conductivity in asphalt concrete or hot mix asphalt. The different levels of depth in the wearing course with slag aggregates will be at lower temperature. This is especially important during the spring, summer and early fall months in the interior territories of the Mediterranean Coast, when due to the high temperatures the modulus of the mix in the wearing course is lower. The layer containing EAF slag is stiffer and the pavement has a better ability to resist the tendency to develop ruts and deformations.Postprint (published version

Effects of the mineralogical composition and particle size distribution of ladle furnace slag as a cement/fine aggregate replacement in concrete

Ladle furnace slag (LFS) shows excellent potential for valorization. Despite this, landfills are typically its final destination, mainly because of technological barriers in its valorization process. This work examines the potential use of LFS as a partial cement/fine aggregate replacement, focusing on the effects of LFS composition and particle size distribution on concrete physico–mechanical properties. Chemical/mineralogical characterization of raw/hydrated samples, fresh-/hardened-state concrete properties, and volumetric instability tests were evaluated. Our results show reduced mechanical performance with LFS replacement, reaching compressive strength values of 32–42 MPa after 28 days. LFS mineralogical characterization reveals the absence of free CaO and the presence of periclase with its hydration/carbonation products. Therefore, the weathering/maturity process mainly affects free CaO. Furthermore, the observed volumetric instability issues were within the Code on Structural Concrete (Spanish abbreviation: EHE) established limits (0.04%), suggesting that the remaining periclase could be responsible for this expansive behavior.Peer ReviewedPostprint (published version

Waste paper ash as an alternative binder to improve the bearing capacity of road subgrades

The interest on alternative hydraulic road binders to replace cement is increasing these days aiming at reducing the carbon footprint of road projects. The PaperChain project, an EU funded project under the H2020 programme, tackles the use of one of these fly ashes, Waste Paper Fly Ash (WPFA), a waste stream coming from the energy recovery of paper rejects and sludge, as alternative binder for subgrade stabilisation and cement-modified subbase layers. WPFA has been extensively tested at laboratory scale and demonstrated at real scale in three field tests covering the three types of stabilised soils recognised in the Spanish Road Regulations, complying with all technical requirements. Nonetheless, the complete replacement of cement by WPFA is a challenge from the design point of view. This paper focuses on the construction and monitoring of one of those cases, specifically the one allocated for the pavement subgrade with the highest bearing capacity. Pairs of cement and WPFA-stabilised laboratory specimens have been tested showing a different hardening pattern and different reaction modulus evolution. Field-testing (load plate tests) and compressive resistance results confirmed this trend. These differences can result in positive effects on cracking development thanks to the slower hardening speed during the first days but the current design values should be reviewed when applied to WPFA, given the notable differences expected over the long term.This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 730305. The authors would like to thank SAICA and the Laboratorio de Carreteras de Aragón de la Dirección General de Movilidad e Infraestructuras del Gobierno de Aragón for their support.Postprint (published version

Diseño de mezclas de hormigón reciclado mediante el método Volumen de Mortero Equivalente (EMV): Validación bajo el contexto español y su adaptación al método de diseño de Bolomey

El nuevo método para el diseño de hormigón con árido reciclado (HAR) es usado para comprobar su posibilidad de uso bajo el contexto español. Primeramente, se realiza una extensa campaña experimental, para analizar las posibilidades de su aplicación, usando dos áridos reciclados de hormigón (ARH) españoles. En la segunda etapa se elabora una adaptación del método a la metodología propuesta por Bolomey (1), con 20% de reemplazo en peso de árido grueso natural (AN) por ARH, para así cumplir con las recomendaciones estipuladas en la Instrucción de Hormigón Estructural (EHE 2008). Para determinar y analizar las propiedades del hormigón, se llevaron a cabo ensayos de asentamiento, contenido de aire, densidades, módulo elástico y resistencias a compresión. Finalmente, se concluye que el uso del nuevo método es viable, y que su adaptación produce hormigones con similares o mejores características que los elaborados para hormigón con árido convencional (HAC) y HAR convencionales.Peer ReviewedPostprint (published version

Soil stabilization using waste paper fly ash: precautions for its correct use

This paper deals with the valorization of waste paper fly ash (WPFA) as a binder for soil stabilization. The mineralogical characterization shows the presence of free lime, as well as some non-reactive and cementitious phases. The hydration of lime is an expansive reaction and can be problematic in soil stabilization. Therefore, to study its effect on stabilized soil, an in-house experimental set-up is proposed to measure the possible expansion. Furthermore, to study the effect of water reduction and delay time on strength, unconfined compressive strength with different mixes is conducted. The obtained results showed that using WPFA causes expansion in stabilized soil, but a delay time of 30 min, after mixing the material with water and then compacting it, can decrease the expansion. Additionally, decreasing the water content by a point of Proctor can be essential for improving the strength in soil samples, even reaching the same strength values as control samples cured at 7 days. Finally, all the results obtained in this study have shown that WPFA is a suitable material for use as a binder for soil stabilization while reducing its optimum water content, adding a proper delay time, and taking into consideration WPFA’s expansive behavior at the moment of its use.The study presented in this paper is part of the Paperchain Project. This project has received funding from the European Union’s Horizon 2020 research and innovation program, under grant agreement no. 730305.Peer ReviewedPostprint (published version

Recycling silicon solar cell waste in cement-based systems

This is a study of the recycling of crystalline solar cells by incorporating them in cement matrices. The hydration process of a mixture of calcium aluminate cement (CAC) and solar photovoltaic cell waste was researched and analyzed. The nature of the hydration products of various compositions of these mixtures was evaluated at a temperature of 20 1C by analyzing the samples through X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The total porosity and mechanical strength development of these materials were also determined. It was revealed that the presence of a solar cell residue of up to 5% in the cement matrices does not result in new hydration products that are different from those derived from the normal hydration of the CAC cement. Moreover, the material developed can be considered as an expansive cement blend because it releases H2 at early stages. The presence of waste causes a decrease in the mechanical strength and an increase in the total porosity of this material, but it can be used for applications such as thermal insulationPeer ReviewedPostprint (published version