Recent progress in low-carbon binders

The development of low-carbon binders has been recognized as a means of reducing the carbon footprint of the Portland cement industry, in response to growing global concerns over CO2 emissions from the construction sector. This paper reviews recent progress in the three most attractive low-carbon binders: alkali-activated, carbonate, and belite-ye'elimite-based binders. Alkali-activated binders/materials were reviewed at the past two ICCC congresses, so this paper focuses on some key developments of alkali-activated binders/materials since the last keynote paper was published in 2015. Recent progress on carbonate and belite-ye'elimite-based binders are also reviewed and discussed, as they are attracting more and more attention as essential alternative low-carbon cementitious materials. These classes of binders have a clear role to play in providing a sustainable future for global construction, as part of the available toolkit of cements

Reactivity of Crystalline Slags in Alkaline Solution

© The Minerals, Metals & Materials Society 2019. Slags with varied amorphous and crystalline content, typical of iron and steel production, are generally underutilized. One promising reuse pathway for these wastes is chemical activation, producing alternatives to conventional building materials with lower embodied energy. The formation of a hardened binder is dependent on the slag mineralogy and, specifically, the reactivity of relevant phases. Reactivity can be understood by monitoring elemental dissolution rates through inductively coupled plasma (ICP-OES) analysis. Post-dissolution ICP analysis of activating solution and spectroscopic analysis of remaining solids was performed on several highly crystalline slags and on relevant synthetic minerals to track changes in chemical and phase composition. Amorphous and ionic phases have been observed as more reactive than other crystalline phases. This work aims to inform future studies on waste blending in alkali-activated systems, a promising avenue for valorization of industrial wastes with varied physicochemical properties. To this end, dissolution tests with varied initial Si, Al, and Ca concentrations in activating solution were also performed

Byproduct-based ettringite binder:a synergy between ladle slag and gypsum

Abstract Ladle slag (LS) is a byproduct from the steel industry that is usually reactive on its own and hydrates towards cementitious phases when mixed with water. However, these reaction products are often metastable, leading to micro-structural changes between 7 and 30 days after mixing. To address this issue, in this experimental investigation, a new binder was designed where LS was mixed with gypsum in order to deliver an ettringite-based binder (LSG). The experimental results revealed that the dominant crystalline phase of LSG was ettringite, which remained stable with no conversion at later stages. For better understanding of the ettringite-based binder, mortar characterization, mechanical properties, and durability of LSG were investigated. LSG showed good mechanical properties and excellent freeze-thaw resistance after 300 cycles, which is comparable to other calcium sulfoaluminate cements. Therefore, as a result, the byproduct-based ettringite binder synthesized herein could offer a solution to steelmaking byproducts with a low-CO2 binder, which could be used in a wide range of applications in the construction industry

Curing process and pore structure of metakaolin-based geopolymers:liquid-state ¹H NMR investigation

Abstract Geopolymers are emerging construction materials with lower carbon dioxide emissions compared to the conventional cementitious materials. The knowledge of the curing process and the related pore structures are important for optimizing the properties of these materials for different applications. The curing process and final pore structure are sensitive to the amount of used water, however the specifics are unclear. The curing process and pore structures of metakaolin-based geopolymers with a narrow water-to-solid (w/s) ratio (0.59–0.66) were monitored by nuclear magnetic resonance (NMR) relaxometry and cryoporometry. The 14-day curing process was investigated by monitoring the change of T₂ and T₁ relaxation times and water signal intensity. After the curing, the pore structures were characterized by 2D T₁-T₂ correlation and T₂-T₂ exchange measurements of absorbed water. The pore size distributions (PSDs) were measured with NMR cryoporometry and compared to nitrogen physisorption and mercury intrusion porosimetry (MIP) results. We found that the relaxation times decreased as the pore structure of the geopolymers matured during the curing while the dissolution and the condensation periods of the curing were distinguished by the changes in signal amplitude reflecting the proton density. After the curing, three distinct pore sizes and connectivity between pores were identified from T₁-T₂ and T₂-T₂ spectra. Their PSDs were measured, and they were found to correspond to two different pore sizes originating from the arrangement of clusters and defective pores. In the narrow w/s ratio (0.59–0.66), the curing times were the same for all samples when cured at 24 °C while the pore sizes were observed to increase as a function of the w/s ratio

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