Performance at high temperature of alkali-activated slag pastes produced with silica fume and rice husk ash based activators

Bernal, Susan A.; Rodríguez, Erich D.; Gutiérrez, Ruby Mejía de; Provis, John L.

doi:10.3989/mc.2015.03114

Cited by 77 publications

(44 citation statements)

References 40 publications

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“…In many existing studies on the durability and mechanical properties of AAS geopolymers regardless of "two-part" (i.e., liquid activators) or "one-part" (i.e., solid activators) mixing approaches, the use of GGBS and FA combination with a certain ratio as an aluminosilicate precursor achieves a geopolymer binder that can roughly meet the engineering requirements (Ismail et al, 2014;Bernal et al, 2015Bernal et al, , 2016Alrefaei and Dai, 2018;Alrefaei et al, 2019). The incorporation of highcalcium materials (i.e., to seed calcium species) with low-calcium raw materials (i.e., main source of alumina and silica) greatly affects the formation of the main binding gels (Bernal et al, 2016).…”

Section: Effect Of "Impurities" In Aas Geopolymermentioning

confidence: 99%

Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review

2019

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Chemically activated materials (often termed as geopolymer) have received attracting attentions in civil, material and environmental research fields as a toolkit alternative to traditional Portland cement in specific applications. This paper presents a comparative review on silico-aluminophosphate (SAP) geopolymers in terms of definition, chemistries involved during geopolymerization, mechanical performance, durability, environmental impacts, and their potentials in applications relative to conventional alkali-aluminosilicate (AAS) geopolymers. Recommendations for future applications are also highlighted. It is found that S-A-P gels with six-coordinated aluminum environment dominate in SAP geopolymers, while the aluminum in N-A-S-H gels formed in the AAS geopolymers is characterized by four-coordinated features. Besides, the slow performance development of SAP geopolymer matrix under ambient temperature curing can be compensated through incorporating additional countermeasures (e.g., metal sources) which allow the tailored design of such geopolymers for certain in-situ applications. Generally, the calcium-bearing C-(A)-S-H gels co-existing with N-A-S-H gels are dominant in AAS geopolymers, while the S-A-P gels enhanced by phosphate-containing crystalline/amorphous phases are the main products in SAP geopolymers. The SAP geopolymers show their environmental friendliness relative to the AAS geopolymers due to the utilization of phosphate activators that require lower production energy relative to silicate-containing activators. However, the higher cost of phosphate activators may confine the applications of SAP geopolymers in some exquisite or special fields.

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Section: Effect Of "Impurities" In Aas Geopolymermentioning

confidence: 99%

Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review

2019

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“…Alternative sodium silicate activators produced via sodium hydroxide digestion of rice husk ashes [19,20] or silica fume [21] have been utilised to produce alkali-activated slag cements whose microstructure is comparable to that of cements produced with commercial silicate solutions. The use of the alternative activators promoted the development of high mechanical strengths and improved performance when these cements were exposed to high temperatures [19,20]. These results demonstrated that the use of alternative silicate activators based on wastes such as rice husk ashes is a feasible path to replace commercial silicate solutions for the production of high performance alkali-activated slag materials.…”

Section: Brief Overview Of Alkali-activated Slag Materialsmentioning

confidence: 99%

Advances in near-neutral salts activation of blast furnace slags

Bernal

2016

RILEM Tech Lett

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The utilisation of near-neutral salts as activators to produce alkali-activated slag cements offers several technical advantages, including reduced alkalinity of the binders, minimising the risk associated with handling of highly alkaline materials, and better workability of the fresh paste compared to that of sodium silicate-activated slag cements. Despite these evident advantages, the delayed setting and slow early-age mechanical strength development of these cements have limited their adoption and commercialisation. Recent studies have demonstrated that these limitations can be overcome by selecting slags with chemistry, which is more prone to react with near-neutral salts, or by adding mineral additives. A brief overview of the most recent advances in alkali-activation of slags using either sodium carbonate or sodium sulfate as activators is reported, highlighting the role of material design parameters in the kinetics of reaction and phase evolution of these cements, as well as the perspectives for research and development of these materials.Keywords: Alkali-activation; Blast furnace slag; Sodium Carbonate; Sodium sulfate; Characterisation Brief overview of alkali-activated slag materialsAlkali-activated cements are materials produced via the chemical reaction of a poorly crystalline aluminosilicate powder, and a highly alkaline solution, to form a hardened solid. These materials have been studied for more than a century, and in the past decades one of the main drivers for their development has been the potential environmental benefits associated with their production [1]. Alkali activated cements are usually produced from industrial wastes or byproducts such as blast furnace slag derived from the ironmaking industry, fly ashes from the coal combustion process, among others [2], and are now commercialised in several places around the world [3]. These materials can develop desirable properties including high mechanical strength [4], good retention of integrity when exposed to high temperatures [5] and acidic media [6], if properly formulated and cured. Significant advances have been made over the past decade in understanding alkali-activated slag materials at micro-and macroscopic scales, as discussed in recent reviews [7,8], particularly for those materials produced with sodium silicate solutions as alkali-activator. The influence of formulation parameters such as chemistry of the slag [9, 10], type of activator [11], addition of metakaolin [12] or fly ashes [13], on the microstructural development and therefore performance of these materials have been the main focus of study in recent years. The application of advanced analytical techniques, including synchrotron X-ray diffraction [14] and X-ray fluorescence microscopy [15], along with thermodynamic modelling [16], have revealed detailed information about the chemistry and phase assemblage of these cements, allowing the development of descriptive models for the activation processes of slags (Fig. 1). Figure 1. Simplified schematic diagram of the alk...

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“…fast hardening, high and early compressive strength, optimal acid resistance and long term durability (9)(10)(11). However, the performance of the final product in these applications is heavily reliant on the physical properties of geopolymers and more specifically, the microstructure and porosity.…”

Section: Introductionmentioning

confidence: 99%

Contributions to the study of porosity in fly ash-based geopolymers. Relationship between degree of reaction, porosity and compressive strength

2016

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ABSTRACT:The main contribution of this paper relates to the development of a systematic study involving a set of parameters which could potentially have an impact on geopolymer properties: curing temperature, type of activating solution, alkali metal in solution, incorporation of slag (Ca source) and type of slag used. The microstructures, degrees of reaction, porosities and compressive strengths of geopolymers have been evaluated. Geopolymers prepared with soluble silicate presented a more compacted and closed structure, a larger amount of gel, lower porosity and greater compressive strength than those prepared with hydroxides. On the other hand, Na-geopolymers were more porous but more resistant than K-geopolymers. Although there is an inverse relation between degree of reaction and porosity, between compressive strength and porosity it is not always inversely proportional and could, in some cases, be masked by changes produced in other influencing parameters. RESUMEN: Contribuciones al estudio de la porosidad de geopolímeros basados en cenizas volantes. Relación entre grado de reacción, porosidad y resistencia a compresión.La principal contribución de este documento es el desarrollo de un estudio sistemático implicando una serie de parámetros que podrían afectar a las propiedades de los geopolímeros: temperatura de curado, solución activadora, metal alcalino de la solución, incorporación de escorias (fuente de calcio) y tipo de escorias. Se han evaluado: microestructura, grado de reacción, porosidad y resistencia a compresión. Los geopolímeros preparados con silicatos presentaron un microestructura más densa y compacta, una mayor cantidad del gel geopolimérico, menor porosidad y mejores propiedades mecánicas que los preparados con hidróxidos. Los geopolímeros preparados con sales de sodio fueron más porosos pero más resistentes que los preparados con sales potasio. Aunque existe una relación inversa entre el grado de reacción y la porosidad, en algunos casos, la relación entre resistencia y porosidad es inexistente ya que puede estar enmascarada por cambios producidos por otros parámetros que afecten a la reacción.

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Performance at high temperature of alkali-activated slag pastes produced with silica fume and rice husk ash based activators

Cited by 77 publications

References 40 publications

Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review

Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review

Advances in near-neutral salts activation of blast furnace slags

Contributions to the study of porosity in fly ash-based geopolymers. Relationship between degree of reaction, porosity and compressive strength

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