The influence of alkalinity on activation and microstructure of fly ash

Li, Dongxu; Chen, Yi-Min; Shen, Jing; Su, Jiaohua; Wu, Xiaofu

doi:10.1016/s0008-8846(00)00252-0

Cited by 81 publications

(39 citation statements)

References 7 publications

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“…pulverised combustion, fluidised combustion), technology of off-gasses desulfurisation. Fly ash reactivity in cement or in fly ash-lime pastes is low at room temperature and strictly depends on its properties, amount and conditions of hardening [21,38,[43][44][45]. This by-product can react with Ca(OH) 2 (pozzolanic reaction), which is formed during hydration of cement or it may be introduced as an additional component of mixture.…”

Section: Early Hydration Of Non-activated Mixtures Containing High Anmentioning

confidence: 99%

“…Research concerning influence of Na 2 SO 4 on fly ash-lime paste showed that early pozzolanic reaction is accelerated and ettringite may be formed. The presence of Na 2 SO 4 accelerates consumption of Ca(OH) 2 , and hydration products such as C-S-H and hydrated aluminosilicate phases are formed faster [44,60,117]. Li et al [44] reported that in case of fly ash activated by Ca(OH) 2 , CaSO 4 and Na 2 SO 4 (blended together) and temperature 60°C, ettringite is formed.…”

Section: Moderate Alkali Activationmentioning

confidence: 99%

“…The presence of Na 2 SO 4 accelerates consumption of Ca(OH) 2 , and hydration products such as C-S-H and hydrated aluminosilicate phases are formed faster [44,60,117]. Li et al [44] reported that in case of fly ash activated by Ca(OH) 2 , CaSO 4 and Na 2 SO 4 (blended together) and temperature 60°C, ettringite is formed. It confirms that sulfoaluminate phases type of ettringite may be formed not only in reaction of C 3 A (constituent of cement) but also with the aluminate ions coming from breaking of glass in grains of fly ash.…”

Section: Moderate Alkali Activationmentioning

confidence: 99%

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Influence of selected activating methods on hydration processes of mixtures containing high and very high amount of fly ash

Wilińska

Pacewska

2018

J Therm Anal Calorim

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Binders containing fly ash as cement substitute have been used for many years. Typical amount of fly ash in cement composite does not exceed 35% of mass of binder. Replacement of substantial amount of cement mass by fly ash results in retardation of hydration of binder and deterioration of some concrete properties, e.g. delay in setting time and reduction in early compressive strength. These inconveniences may be reduced using proper method of activation. In this paper, possibilities to activate binding mixtures containing high and very high amount of fly ash and low amount of Portland cement were discussed basing on the literature reports as well as on our own research results. Several activating methods were described, such as mechanical activation, exchanging of part of components of binder (cement, fly ash or both of them) by more reactive fine-grained material, chemical activation by the use of alkaline activators as well as combined methods. Possibilities of using these methods were discussed in relation to amount of fly ash introduced as replacement of cement and kind of fly ash used. Usefulness of calorimetry and thermal analysis methods was also presented.

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Section: Early Hydration Of Non-activated Mixtures Containing High Anmentioning

confidence: 99%

Section: Moderate Alkali Activationmentioning

confidence: 99%

Section: Moderate Alkali Activationmentioning

confidence: 99%

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Influence of selected activating methods on hydration processes of mixtures containing high and very high amount of fly ash

Wilińska

Pacewska

2018

J Therm Anal Calorim

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“…Comparing the two systems, it is obvious that the Ca(OH) 2 content in coal gangue-CaO-4%NaOH system is lower than that in coal gangue-CaO-2%NaOH system at the same age, indicating a faster consumption of lime for coal gangue-CaO-4%NaOH system [7] . It means that addition of 4% NaOH is more propitious to accelerating hydration reaction [8,9] .…”

Section: Resultsmentioning

confidence: 96%

Activity and structure of calcined coal gangue

Gong

Wang

et al. 2007

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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Coal gangue was activated by means of calcination in seven temperature ranges. Systematic research was made about activation mechanism and structural evolution. Glycerin-ethanol method, SEM, MIP and XRD were used to determine the variation of structure and activation of coal gangue during the calcination. The experimental results show that because of heat treatment in the range of calcination temperature, mineral composition and microstructure of coal gangue are changed. In addition, its activity is improved evidently. The amount of lime absorbed by the sample calcined at 700 ℃ is 2-4 times that by uncalcined coal gangue in the course of hydration. When NaOH is added to coal gangue-lime system, hydration reaction of the system is sped up and the microstructure of hydrating samples of coal gangue is improved.

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“…Meanwhile, little lime (CaO) (10% of cement mass) was used in all concrete specimens to obtain the appropriate strength of concrete. Because CaO is an effective activator to improve the production of Ca(OH) 2 in the low calcium FAC [13], from here, the emphasis of the study focuses on the effect of Na 2 SiO 3 , CaCl 2 and Na 2 SO 4 . The ACs in the present paper mean the three main activators.…”

Section: Proportion Detailsmentioning

confidence: 99%

Hydration, Setting and Crack-Resistance Properties of Activated HVFACs at Early Stages

et al. 2016

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Abstract:In order to develop a simple and effective activation method of low calcium fly ash concrete (FAC) and to understand their basic properties, the present paper experimentally investigates the influences of the volume of fly ash (FA), the dosage of the activator (AC) and the water to binder ratio (w/b) on the hydration, setting times and the crack-resistance properties of activated FACs. Results verify that increasing FA can effectively reduce the hydration heat of the FA-cement system and increase the setting time of FACs, as well as indicate that FA can delay the occurrence of the initial crack and reduce the maximum width and total area of cracks in these concretes through a new quantitative test. The curing time of concrete affects the hydration heat of FA paste with/without AC. When the curing time of FAC increases, the decrease in amplitude of hydration heat reduces gradually. Additionally, it was found that the used ACs can effectively stimulate the activity of FA in Portland cement (PC) systems, which reduces their setting time slightly. However, high dosages of ACs also accelerate the development of early cracks in the FACs, as well. According to the study, the combined activator (10% CaO + 1.5% Na 2 SO 4 ) was suggested as the most effective way to promote FA-PC concrete for obtaining acceptable properties at early stages. Besides, the existing calculation model for predicting the setting times of FACs was examined and modified to be more suitable to FACs activated by 10% CaO + 1.5% Na 2 SO 4 . The proposed model was verified and can evaluate the experimental results well.

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The influence of alkalinity on activation and microstructure of fly ash

Cited by 81 publications

References 7 publications

Influence of selected activating methods on hydration processes of mixtures containing high and very high amount of fly ash

Influence of selected activating methods on hydration processes of mixtures containing high and very high amount of fly ash

Activity and structure of calcined coal gangue

Hydration, Setting and Crack-Resistance Properties of Activated HVFACs at Early Stages

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