Compressed earth blocks stabilized with glass waste and fly ash activated with a recycled alkaline cleaning solution

Sustainable alternatives are increasingly demanded as a sound response, from the construction industry, to the worldwide growing concerns with the environment. Such effort is justifiable by the degree of the contribution of this human activity to the problem, and it has thus propelled the development of a major trend in terms of funded research. The study reported in this paper focused on the physical-mechanical properties of compacted earth blocks formed by a common Portuguese silty clay (as the mineral skeleton), stabilized with a sustainable alkali activated cement exclusively produced from wastes and residues, including coal fly ash and glass waste, in a 50/50 wt ratio combination, and activated with an alkaline solution from the aluminium industry, using activator/precursor weight ratios of 0.50, 0.57 and 0.75. After optimising the alkaline activated cement (AAC), the AAC/Soil blocks were fabricated, using the response surface method to define their composition based on curing periods of 28 and 180 days at controlled ambient temperature. Uniaxial compressive strength (UCS) and several durability tests were performed, and the material was characterised using FTIR and SEM. The results evidenced the effectiveness of the alkaline cementing agent in forming a binding matrix for the soil particles. An average compressive strength of 17.23 MPa, in unsaturated conditions, was obtained for the blocks. The newly formed soil-binder structure was very capable to withstand wetting and drying cycles, ice-thaw cycles and erosion. The microstructure of the material was further analysed, using scanning electron microscopy and energy dispersive spectroscopy. The results demonstrated the real possibility of using this type of cement as a viable alternative to traditional soil stabilisation binders used in earth construction.This work was funded by the R&D Project JUSTREST-Development of Alkali Binders for Geotechnical Applications Made Exclusively from Industrial Waste, with reference PTDC/ECM-GEO/0637/2014, financed by the Foundation for Science and Technology - FCT/MCTES (PIDDAC).The research was supported by the GEO-DESIGN project, no17501, co-financed by the European Regional Development Fund (ERDF) through NORTE 2020 (North Regional Operational Program, 2014/2020)

Estabilización química de suelos - Materiales convencionales y activados alcalinamente (revisión)

The growing interest in the development of alternatives to the use of traditional binders in geotechnical applications, such as cement and lime, is largely due to the environmental challenges and associated costs in this type of applications. Alkali-activated binders emerge as one of the most sustainable alternatives, particularly because of their low energy consumption and in theory the low carbon footprint in their manufacture.  In addition, this type of binders have the possibility of using industrial waste and by-products as precursor materials in their production process. This article presents a state of the art of the various materials conventionally used in the chemical stabilization of soils and performs a review of published articles in relation to the implementation of alkali-activated binders. The technical feasibility, the environmental impacts associated, the challenges that must be overcome in order to position them as a sustainable alternative for geotechnical processes, and the advantages and disadvantages of its application are considered.El creciente interés por el desarrollo de alternativas frente al uso masivo de cementantes tradicionales en aplicaciones geotécnicas, tales como cemento y cal, se debe en gran medida a los retos ambientales y costos asociados en este tipo de aplicaciones. Los cementantes activados alcalinamente surgen como una de las alternativas de mayor sostenibilidad, particularmente por su bajo consumo energético y en teoría la baja huella de carbono en su fabricación; además, tienen la posibilidad de utilizar residuos y subproductos industriales como materiales precursores en su fabricación. Este artículo presenta un estado del arte de los diversos materiales empleados convencionalmente en la estabilización química de suelos y realiza una revisión de los artículos publicados en relación con la implementación de cementantes activados alcalinamente, su viabilidad técnica, los impactos ambientales asociados y los retos que se deben superar para lograr posicionarlos como una alternativa sostenible para procesos geotécnicos

Estabilização química do solo - materiais convencionais e ativados alcalinos (revisão)

The growing interest in the development of alternatives to the use of traditional binders in geotechnical applications, such as cement and lime, is largely due to the environmental challenges and associated costs in this type of applications. Alkali-activated binders emerge as one of the most sustainable alternatives, particularly because of their low energy consumption and in theory the low carbon footprint in their manufacture.  In addition, this type of binders have the possibility of using industrial waste and by-products as precursor materials in their production process. This article presents a state of the art of the various materials conventionally used in the chemical stabilization of soils and performs a review of published articles in relation to the implementation of alkali-activated binders. The technical feasibility, the environmental impacts associated, the challenges that must be overcome in order to position them as a sustainable alternative for geotechnical processes, and the advantages and disadvantages of its application are considered.El creciente interés por el desarrollo de alternativas frente al uso masivo de cementantes tradicionales en aplicaciones geotécnicas, tales como cemento y cal, se debe en gran medida a los retos ambientales y costos asociados en este tipo de aplicaciones. Los cementantes activados alcalinamente surgen como una de las alternativas de mayor sostenibilidad, particularmente por su bajo consumo energético y en teoría la baja huella de carbono en su fabricación; además, tienen la posibilidad de utilizar residuos y subproductos industriales como materiales precursores en su fabricación. Este artículo presenta un estado del arte de los diversos materiales empleados convencionalmente en la estabilización química de suelos y realiza una revisión de los artículos publicados en relación con la implementación de cementantes activados alcalinamente, su viabilidad técnica, los impactos ambientales asociados y los retos que se deben superar para lograr posicionarlos como una alternativa sostenible para procesos geotécnicos

Cementos híbridos basados en la activación alcalina de subproductos del carbón

Este estudio se propuso la producción de un material cementicio alternativo de bajo impacto ambiental a partir de la evaluación de dos subproductos de la combustión del carbón. Se elaboraron dos cementos híbridos basados en la activación alcalina de una ceniza volante (FA) y una escoria de parrilla (BS) y adicionados con cemento portland (OPC) hasta en un 30%. FA y BS contienen hasta un 16% de inquemados. Para la optimización de la resistencia a la compresión se utilizó la Metodología de Superficie de Respuesta (MSR). El geopolímero BS alcanzo alta resistencia a la compresión (>100 MPa a 28 días) y el geopolímero FA reporto 30 MPa al aplicar curado térmico. La adición de OPC contribuyo a modificar el método de curado. En el caso del hibrido basado en FA (HFA), se observó un incremento significativo en la resistencia a niveles hasta de 65 MPa a 28 días sin aplicar el curado térmic0This study focuses on the production of an alternative cementitious material with low environmental impact through the evaluation of two-coal combustion by-products. Hybrid cements based on the alkali activation of fly ash, (FA) and boiler slag (BS) blend with a proportion of Portland cement (OPC) up to 30% were produced. FA and BS contain an unburned material up to 16%. Response Surface Methodology (RSM) was used to optimize the compressive strength. BS geopolymer achieved high compressive strength (>100 MPa at 28 days) and FA geopolymer reached 30 MPa with thermal curing. The addition of OPC helped modify the curing method. In the case of hybrid based on FA (HFA), there was a significant increase in the compressive strength with levels ranging up to 65 MPa at 28 days without requiring a thermal curin

Application of electric arc furnace slag as an alternative precursor to blast furnace slag in alkaline cements

In steel manufacturing, electric arc furnaces are increasingly common, as they use mostly scrap metal as ore source. Thus, blast furnace slag (BFS) is decreasing, while electric arc slag (EAFS) is proportionally increasing. This study focuses on the potential of EAFS in alkaline cements, as precursor or aggregate. Different EAFS/BFS mixtures, some including fly ash (FA), were activated with a NaOH solution, and characterized from a mechanical and microstructural perspective. Selected pastes were used to prepare mortars, using EAFS as aggregate. Results showed that EAFS alone doesn’t deliver an adequate strength. However, when combined with BFS and FA, it formed compact matrices with significant mechanical strength and lower hydration heat. The use of EAFS as aggregate produced higher strength than obtained with silica sand. EAFS showed the potential to be applied as a precursor in alkaline cements, and the combination of BFS/EAFS yielded higher compressive strengths than obtained with BFS alone.This research has been financed by the project “RENEw – REsiduos Na construção para uma Economia circular”, operation number POCI-01-0247-FEDER-033834, financed by the European Regional Development Fund (ERDF) through COMPETE 2020 (Competitiveness and Internationalisation Operational Programme). This study was also partially supported by the Ministry of Science and Innovation and FEDER under research project PDC2021-120771-I00. One of the authors also acknowledgements the concession of the JIN project (Ref. PID2020-116738RJ-I0) funded by the Ministry of Science and Innovation (Projects I + D + I 2020)

One-part hybrid cements from fly ash and electric arc furnace slag activated by sodium sulphate or sodium chloride

An innovative hybrid cement, based on type F fly ash (FA), iron and steel slag (ISS) and Portland cement (OPC), is proposed in the present paper. The precursors were activated by powder-form elements – sodium sulphate or sodium chloride – forming what is known as a ‘one part geopolymer’ cement, which was then evaluated considering both mechanical and microstructural perspectives. Results showed that, in these conditions, the reactivity of the ISS is lower than that of the FA, with or without the presence of the activators. In the ternary pastes formed by 50%ISS +25%FA + 25%OPC and 25%ISS +25%FA + 50%OPC, with no activator included, both the ISS and the FA reacted due to its inherent pozzolanic activity. The presence of the powder-form activators increased the mechanical strength of the pastes (which are known as “hybrid cements”, since an activator and OPC are simultaneously present), relatively to the no-activator pastes. Furthermore, the inclusion of Na2SO4 or NaCl increased and decreased the activation rate, respectively, relatively to the equivalent binder hydrated with water (i.e. without the presence of an activator). Regardless, in both cases, strength values above 40 MPa and 35 MPa, after 28 days curing, were obtained. In the hybrid cements, the activators first reacted with the OPC phases; with the activator anions originating products such as calcium sulphate, ettringite or Friedel's salt (depending on the activator type), which increase the density of the matrix and, therefore, the resulting mechanical strength. Furthermore, in the presence of the Na+ cation, local NaOH is generated, increasing the alkalinity of the medium and, consequently, accelerating the reaction of the ISS and FA, which further improves the mechanical strength. Behind every combination, a C-(A)-S-H gel is the main reaction product.This research has been financed by the project “RENEw - REsiduos Na construção para uma Economia circular”, operation number POCI-01-0247-FEDER-033834, financed by the European Regional Development Fund (ERDF) through COMPETE 2020 (Competitiveness and Internationalisation Operational Programme). The research was also supported by the Ministry of Science and Innovation and Universities (Spain) and by FEDER funds, that subsidize the Project PID2019-111464RB-100, and by the European Union, that subsidize the Project LIFE FREEDON (LIFE19 ENV IT 000165)