Binding mechanism and properties of alkali-activated fly ash/slag mortars

Chi, Maochieh; Huang, Ran

doi:10.1016/j.conbuildmat.2012.11.003

Cited by 335 publications

(105 citation statements)

References 35 publications

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“…There are a few published studies on geopolymer mixes with a variant combination of FA and GGBS in the mixture [9,16,17,[23][24][25] and in most of these studies promising results were achieved. However, in these studies high volumes and concentrations of corrosive sodium silicate and/or sodium hydroxide have been used leading to geopolymer products with potential health and worker safety issues during application [14].…”

Section: Introductionmentioning

confidence: 99%

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Development of geopolymer mortar under ambient temperature for in situ applications

Al-Majidi

Λαμπρόπουλος

Cundy

et al. 2016

Construction and Building Materials

293

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Geopolymer concrete technology involves production of more environmentally friendly waste material-based concrete which could be a viable solution for conventional concrete replacement. Typical fly ash-based geopolymer concrete however requires high temperature curing treatment in order to develop sufficient early strength properties, which is considered a severe limitation for cast-in-place concrete applications. Most previous studies on geopolymer concrete have focused on the properties of concretes pre-hardened by heat curing and/ or by aggressive chemical treatment (e.g. alkali activation using concentrated sodium hydroxide (NaOH)). The current study presents an extensive experimental investigation on the mechanical and microstructural properties of geopolymer concrete mixes prepared with a combination of fly ash and slag cured under ambient temperature. 'User friendly' geopolymer mixes were produced using fly ash (FA) and Ground Granulated Blast furnace Slag (GGBS) mixed together with potassium silicate with molar ratio equal to 1.2 (as the activator) and water. The results indicated that heat curing treatment can be avoided by partial replacement of fly ash with slag. The compressive strength of the examined mixes was found to be in the range of 40-50MPa for 40 % and 50 % GGBS replacement mixtures respectively. Moreover, the flexural and direct tensile strengths of geopolymer mixes are considerably improved as the GGBS content is increased.Based on FTIR and SEM/EDS analysis, the inclusion of a higher content of GGBS resulted in a denser structure by formation of more hydration products.Keywords: Fly ash, slag, ambient temperature, user friendly geopolymer mortar *Manuscript Click here to view linked References 2 IntroductionThere are many environmental issues associated with the production of Ordinary Portland cement (OPC), such as consumption of 5% of natural resources, and generation of 5-7 % of total global anthropogenic carbon dioxide emissions [1][2][3][4]. This has led to an urgent need for the development of alternative materials that may provide technically viable alternative solutions to conventional cementitious concrete, with more favourable environmental credentials. Geopolymer concrete manufacture is one of the most promising techniques which has been developed in the last few years. Utilization of geopolymer materials can reduce 80% of greenhouse gas emissions associated with material production, and overcome issues related to cement production and unregulated disposal of industrial materials by recycling these materials in geopolymer manufacture [5][6][7].Geopolymers are inorganic by-product materials, rich in silicon (Si) and aluminium Five different mixtures of geopolymer mortar proportions were examined with various ratios of GGBS to total binder (10%, 20%, 30%, 40% and 50 %, Table 2). Based on preliminary experimental studies undertaken during the current project, the optimum mix design (in terms of mechanical strength and workability) was achieved using water, alkaline activator...

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Section: Introductionmentioning

confidence: 99%

“…The main reaction product of alkali-activated cements for GGBS is calcium silicate hydrate (C-S-H) while for FA it is amorphous hydrated alkali-aluminosilicate [16]. Alkali activated slag has high strength but issues related to rapid 3 setting and insufficient workability along with high values of dry shrinkage have been reported [17].…”

Section: Introductionmentioning

confidence: 99%

Development of geopolymer mortar under ambient temperature for in situ applications

Al-Majidi

Λαμπρόπουλος

Cundy

et al. 2016

Construction and Building Materials

293

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“…Puertas et al [16] studied the strength behavior and hydration products of fly ash/slag pastes activated with NaOH and found that the compressive strength of the specimen with 50% fly ash/50% slag activated with 10 M NaOH solution and cured at the temperature of 25 ℃ was more that 50 MPa at the age of 28 days. The fly ash/slag ratio is the most relevant factor on the strength development [9]. Zhao et al [17] studied the strength of alkali-activated 20% fly ash/80% slag blended cement and found that the compressive strength of the cement mortar is up to 49MPa and flexural strength 8.4 MPa at the age of 28 days.…”

Section: Introductionmentioning

confidence: 99%

“…The major binding phase in alkali-activated GGBFS [6] is calcium silicate hydrate (C-S-H) [7] while alkali-activated class F fly ash is the amorphous hydrated alkali-aluminosilicate [8]. These two types of cements have been investigated to substitute for binder to compose cementless mortar or concrete because of their special characteristics and the typical representation of alkali-activated cements [9].…”

Section: Introductionmentioning

confidence: 99%

Mechanical and Microstructural Characterization of Alkali-Activated Materials Based on Fly Ash and Slag

Chi¹,

Liu²,

Huang³

2015

IJET

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“…100 µm 100 µm 100 µm (a) (b) (c) A number of researchers have reported distinct products from FA and GGBS alkali activation, with the latter resulting in the formation of a denser C-S-H type gel (Chi and Huang, 2013;Gunasekara et al, 2015;Ismail et al, 2014;Li et al, 2013). The phase shown in Figures 6 and 7 has similar morphology to such gels.…”

Section: Advances In Cement Researchmentioning

confidence: 99%

Chemical aspects related to using recycled geopolymers as aggregates

Chaliasou

Heath

Paine

et al. 2018

Advances in Cement Research

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Despite extensive research into sustainability of geopolymers, end-of-life aspects have been largely overlooked. A recycling scenario is examined in this study. This requires an investigation of alkali leaching potential from a geopolymeric matrix. To study the feasibility of geopolymer cement (GPC) recycling, the migration of alkalis was evaluated for the first time on a microstructural level through energy dispersive X-ray (EDX) scanning electron microscopy (SEM) elemental mapping and leaching tests. Macroscale impacts were assessed through an investigation of Portland cement (PC) mortar properties affected by alkali concentration. Leaching tests indicated that alkalis immediately become available in aqueous environments, but the majority remain chemically or physically bound in the matrix. This type of leaching accelerates the initial setting of PC paste. Elemental mapping and EDX/SEM analysis showed a complex paste-aggregate interfacial transition zone. Exchange of calcium and sodium, revealed by the maps, resulted in the migration of sodium into the PC paste and the formation of additional calcium-silicon-based phases in the geopolymeric matrix. Strength values of mortars with 25% and 50% recycled aggregates (RA) showed negligible differences compared with the reference sample. Screening tests indicated a low potential for GPC RA inducing alkali-silica reaction. Transport of GPC RA alkalis and the underlying mechanisms were observed. This transport phenomenon was found to have minor effects on the properties of the PC mortar, indicating that recycling of geopolymers is a viable reuse practice.

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Binding mechanism and properties of alkali-activated fly ash/slag mortars

Cited by 335 publications

References 35 publications

Development of geopolymer mortar under ambient temperature for in situ applications

Development of geopolymer mortar under ambient temperature for in situ applications

Mechanical and Microstructural Characterization of Alkali-Activated Materials Based on Fly Ash and Slag

Chemical aspects related to using recycled geopolymers as aggregates

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