Setting, Strength, and Autogenous Shrinkage of Alkali-Activated Fly Ash and Slag Pastes: Effect of Slag Content

Nedeljković, Marija; Li, Zhenming; Ye, Guang

doi:10.3390/ma11112121

Cited by 103 publications

(57 citation statements)

References 66 publications

(93 reference statements)

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“…This indicates that the Ca from fly ash was not/partially leached, but the Ca from the GGBS source leached completely; as a result, the setting time increased with increasing fly ash. The GGBS is more reactive than is fly ash, which was also observed in the previous studies [20,34]. Furthermore, the reactivity of fly ash accelerated when activated in NaOH + Na 2 SiO 3 solution.…”

Section: Compressive Strengthsupporting

confidence: 82%

“…Table 2 shows the ratio of water to alkali added paste (W/Mix), added in each mixture, it can be clearly seen that, with the increasing amount of GGBS, the demand of water increased. The increased water requirement with increasing GGBS was due to its chemical reactivity, and specific gravity which was comparatively higher than FA [34,35]. Comparatively, the water demand for all…”

Section: Sample Preparationmentioning

confidence: 95%

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Strength and Microstructure of Class-C Fly Ash and GGBS Blend Geopolymer Activated in NaOH & NaOH + Na2SiO3

et al. 2019

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In this paper, class-C fly ash (FA) and ground granulated blast-furnace slag (GGBS)-based geopolymer activated in NaOH and NaOH + Na 2 SiO 3 was studied regarding setting time, compressive strength, porosity, microstructure, and formation of crystalline phases. When comparing the effects of alkali type on the FA and GGBS geopolymer composites, results revealed that NaOH has a lesser effect in developing strength and denser microstructure than does NaOH + Na 2 SiO 3, since the addition of Na 2 SiO 3 provides the silica source to develop more compact structure. Incorporation of Na 2 SiO 3 reduced the crystallinity and the paste was more amorphous compared to NaOH activated pastes. The class-C FA and GGBS blends resulted in prolonged setting time, reduced strength, and loose matrix with the increase in fly ash content. The un-reactivity of calcium in blends was observed with increasing fly ash content, leading to strength loss. It is evident from XRD patterns that calcium in fly ash did not contribute in forming C-S-H bond, but formation of crystalline calcite was observed. Furthermore, XRD analyses revealed that the reduction in fly ash leads to the reduction in crystallinity, and SEM micrographs showed the unreactive fly ash particles, which hinder the formation of a denser matrix.Materials 2020, 13, 59 2 of 15 is also formed in Portland cement. Its formation leads to short setting time, reduced porosity, and increased compressive strength [9,10].Fly ash has been investigated as a precursor material in geopolymer mortar. The mechanical properties of fly ash-based geopolymer depends on the chemical composition of fly ash. As explored by Davidovits, Izquierdo [11] in their study, the fly ash containing low calcium (class-F) produced a workable geopolymer; however, the high calcium in fly ash did not contribute in producing the suitable geopolymer due to flash setting time. The flash setting time in the high-calcium fly ash was confirmed in studies [12,13] where they used borax in the mixture to delay the setting time. However, regardless of this problem, the class-C fly ash has been found to help improve the strength properties due the presence of adequate calcium content, which may forms C-S-H gel in the matrix [14].Ground granulated blast-furnace slag (GGBS) is another by-product material rich in amorphous calcium, silica, and alumina, which makes it suitable to be used as a binder in the construction industry [15]. Formerly, GGBS as a precursor material in geopolymer has been investigated. It is worth mentioning that the GGBS activated in alkali solution possess a high strength and good resistance to the chemicals compared to Portland cement. However, the reduced setting time makes it susceptible to high shrinkage and develops micro cracks, which increases the porosity leading to the strength loss [16]. Since the GGBS is rich in calcium, the main reaction product is C-S-H gel, which may coexist with the geopolymer gel depending on the chemical composition of the GGBS, alkali type, and alkali amount [4,17,18].The ...

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Section: Compressive Strengthsupporting

confidence: 82%

Section: Sample Preparationmentioning

confidence: 95%

Strength and Microstructure of Class-C Fly Ash and GGBS Blend Geopolymer Activated in NaOH & NaOH + Na2SiO3

et al. 2019

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“…For 0 EA without EA, the initial setting time (IST) was 101 min and the final setting time (FST) was 292 min. As for paste (w/c = 0.5) using ordinary Portland cement (OPC), the initial setting is within 6 to 7 h according to the literature [ 58 ]. Under the same mixing conditions, the AAM mortar exhibited a faster setting compared to mortar that used cement as a binder.…”

Section: Resultsmentioning

confidence: 99%

A Study on Initial Setting and Modulus of Elasticity of AAM Mortar Mixed with CSA Expansive Additive Using Ultrasonic Pulse Velocity

et al. 2020

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This study investigated the hardening process of alkali-activated material (AAM) mortar using calcium sulfoalumiante (CSA) expansive additive (CSA EA), which accelerates the initial reactivity of AAMs, and subsequent changes in ultrasonic pulse velocity (UPV). After the AAM mortar was mixed with three different contents of CSA EA, the setting and modulus of elasticity of the mortar at one day of age, which represent curing steps, were measured. In addition, UPV was used to analyze each curing step. The initial and final setting times of the AAM mortar could be predicted by analyzing the UPV results measured for 14 h. In addition, the dynamic modulus of elasticity calculated using the UPV results for 24 h showed a tendency similar to that of the static modulus of elasticity. The test results showed that the use of CSA EA accelerated the setting of the AAM mortar and increased the modulus of elasticity, and these results could be inferred using UPV. The proposed measurement method can be effective in evaluating the properties of a material that accelerates the initial reactivity.

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“…The literature has illustrated that alkali-activated slag and fly ash (AASF) shows superior strength, excellent durability and good fire resistance compared to OPC systems [2][3][4]. However, a wider application of this material has not been reached yet, partly due to the large autogenous shrinkage and the potential risk of cracking of this material, especially when NaOH and Na 2 SiO 3 are used as activators [5,6].…”

Section: Introductionmentioning

confidence: 99%

A Low-Autogenous-Shrinkage Alkali-Activated Slag and Fly Ash Concrete

Yao

Chen

et al. 2020

Applied Sciences

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Alkali-activated slag and fly ash (AASF) materials are emerging as promising alternatives to conventional Portland cement. Despite the superior mechanical properties of AASF materials, they are known to show large autogenous shrinkage, which hinders the wide application of these eco-friendly materials in infrastructure. To mitigate the autogenous shrinkage of AASF, two innovative autogenous-shrinkage-mitigating admixtures, superabsorbent polymers (SAPs) and metakaolin (MK), are applied in this study. The results show that the incorporation of SAPs and MK significantly mitigates autogenous shrinkage and cracking potential of AASF paste and concrete. Moreover, the AASF concrete with SAPs and MK shows enhanced workability and tensile strength-to-compressive strength ratios. These results indicate that SAPs and MK are promising admixtures to make AASF concrete a high-performance alternative to Portland cement concrete in structural engineering.

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Setting, Strength, and Autogenous Shrinkage of Alkali-Activated Fly Ash and Slag Pastes: Effect of Slag Content

Cited by 103 publications

References 66 publications

Strength and Microstructure of Class-C Fly Ash and GGBS Blend Geopolymer Activated in NaOH & NaOH + Na2SiO3

Strength and Microstructure of Class-C Fly Ash and GGBS Blend Geopolymer Activated in NaOH & NaOH + Na2SiO3

A Study on Initial Setting and Modulus of Elasticity of AAM Mortar Mixed with CSA Expansive Additive Using Ultrasonic Pulse Velocity

A Low-Autogenous-Shrinkage Alkali-Activated Slag and Fly Ash Concrete

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