Temperature rise and initial shrinkage of alkali-activated fly ash cement pastes

Shekhovtsova, Julia; Kovtun, Maxim; Kearsley, Elsabé P.

doi:10.1680/adcr.14.00079

Cited by 16 publications

(4 citation statements)

References 40 publications

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“…For instance, Rovnanik [28] reported that GP specimens stored between 40 and 80 • C exhibited higher early-age strengths, as compared to companion specimens cured at ambient temperature. Similar conclusions were drawn by Kuenzel et al [29] and Shekhovtsova et al [30], who found that the increased curing temperature favored the strength development at early and late ages.…”

Section: Introductionsupporting

confidence: 87%

“…The prisms were demolded after 24 h and stored side-by-side in a closet where ambient temperature and RH were 23 ± 3 • C and 90% ± 5% RH, respectively, until testing time after 7 and 28 days. Earlier studies showed that the complete immersion of GP specimens in water detrimentally alters the development of strengths [28][29][30].…”

Section: Testing Methods and Proceduresmentioning

confidence: 99%

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Use of Seashell and Limestone Fillers in Metakaolin-Based Geopolymers for Masonry Mortars

Assaad

Saba

2023

Minerals

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Mortars intended for plastering and masonry works normally comply to EN 413-1 and/or ASTM C91 specifications. This paper seeks to assess the suitability of geopolymers (GPs) composed of metakaolin and seashell wastes for masonry applications. The sodium hydroxide and sodium silicate activators contained air-entraining molecules to secure about 10% ± 2% air content. Just like the cement-based mortars, test results showed that the mechanical properties of GPs including the compressive strength, flexural strength, pull-off adhesion, and water sorptivity decreased when the seashell concentration increased in the mixture. This was mainly related to a dilution effect that reduces the aluminosilicate precursor content and formation of rigid bonds. The replacement of limestone filler by seashell powder slightly increased the mechanical properties, which was attributed to higher seashell hardness that densifies the microstructure and provides additional resistance to support the external stresses. Yet, the grinding of seashells into fine powder required higher energy than what is needed for the comminution of clinker or limestone. The use of GPs is particularly advantageous for masonry applications, as it speeds up the construction operations while eliminating the hassle of moist curing normally required with cement-based plasters.

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Section: Introductionsupporting

confidence: 87%

Section: Testing Methods and Proceduresmentioning

confidence: 99%

Use of Seashell and Limestone Fillers in Metakaolin-Based Geopolymers for Masonry Mortars

Assaad

Saba

2023

Minerals

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“…The production of hybrid cement requires less clinker than that for ordinary Portland cement, leading to a decrease in CO 2 emissions per tonne of hybrid cement manufactured. Hybrid alkaline cements is often preferred over their alkali activated counterparts because its hydration occurs at ambient temperature, and its production do not require the addition of highly alkaline chemicals, but rather rely on a safe source of alkali formed in situ (sodium hydroxide) to facilitate both the dissolution of any amorphous phases present in the source materials [5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Characterisation of the Hydration Products of a Chemically and Mechanically Activated High Coal Fly Ash Hybrid Cement

Toit¹,

Merwe

Kruger³

et al. 2022

Minerals

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Cement companies are significant contributors of the planet’s anthropogenic CO2 emissions. With increased awareness of the substantial volume of CO2 emissions from cement production, a variety of mitigation strategies are being considered and pursued globally. Hybrid cements are deemed to be technologically viable materials for contemporary construction. They require less clinker than that for ordinary Portland cement, leading to a decrease in CO2 emissions per tonne of hybrid cement manufactured. The hybrids produced in this study consist of 70% siliceous coal fly ash and 30% Portland cement, and combines chemical (sodium sulphate) and mechanical (milling) activation. The aim of this work was to develop a better understanding of the hydration products formed and the resulting effect of activation on these hydration products, of hybrid coal fly ash cement pastes over an extended curing period of up to one year. The results indicated that chemical activation increases the formation of stable, well crystallised ettringite. Chemical activation as well as mechanical activation increased the rate of the pozzolanic reaction between portlandite contained in cement and coal fly ash. The application of combined chemical and mechanical activation definitely resulted in the fastest rate of portlandite consumption, hence an increased rate of the pozzolanic reaction.

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“…The papers are concerned with early-age performance through to long-term durability, while covering both applied fields and fundamental studies.The first paper, by Shekhovtsova et al (2016), investigates the temperature rise and early-age performance of alkaliactivated fly ash geopolymeric systems; continuing the work of this group in the field of heat-cured alkali-activated systems (Shekhovtsova et al, 2015). They show that the exothermic alkali activation of fly ash geopolymers can affect curing temperatures, especially at high alkali contents or in large samples.…”

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confidence: 99%

Editorial

Black

2016

Advances in Cement Research

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This issue of Advances in Cement Research contains seven papers that span a broad range of topics within the field of cement science; from Portland cement to alkali-activated systems, composite cements and polymer-modified cements. The papers are concerned with early-age performance through to long-term durability, while covering both applied fields and fundamental studies.The first paper, by Shekhovtsova et al. (2016), investigates the temperature rise and early-age performance of alkaliactivated fly ash geopolymeric systems; continuing the work of this group in the field of heat-cured alkali-activated systems (Shekhovtsova et al., 2015). They show that the exothermic alkali activation of fly ash geopolymers can affect curing temperatures, especially at high alkali contents or in large samples. This may have implications for precast geopolymer quality control.The second paper (Santacruz et al., 2016) is a fundamental study into the structure of strätlingite. The work show that the hydration conditions in which strätlingite forms may affect its microstructure; mostly related to the occurrence of dehydration during hydration or sample preparation. Loss of water during certain high-temperature curing regimes is reflected in subtle changes in X-ray diffraction (XRD) patterns, a point of note for those wishing to perform quantitative XRD analysis on systems where strätlingite may be a key phase, such as belite calcium sulfoaluminate cements.The third paper (Zeng et al., 2016) is another fundamental study, this time concerned with accurate determination of the pore structure of cement matrices. The authors have used a combination of mercury intrusion porosimetry (MIP) and nitrogen adsorption to follow changes in the pore structure of cement pastes with age. A combination of the two techniques gave information on the specific surface area, pore volume and pore size distribution. As the authors say 'the hydrates filling process can be best captured by total MIP pore volume and the SSA values are more related to calcium-silicate-hydrate growth'.The next paper (Tasci and Yılmaz, 2016) shifts the focus from later-age properties to early-age performance. The authors have looked at the interparticle interactions between cement particles and pozzolans, performing chemical, physical, mineralogical and electrokinetic analyses of samples. This was coupled with determination of free surface energy components by Van Oss, Chaudry and Good equations.The two final papers look at more applied aspects of cement science, but considering very different timescales. The first of these (Liu et al., 2016) investigates the early-age properties of polymer-modified cements, specifically the effects of asphalt emulsions on cement hydration. In addition to studying asphalt emulsion-cement mixes, the authors also investigated how the individual components affected cement hydration. Overall, hydration was slowed, due primarily to the presence of a cationic lignin-amine emulsifier. The other phases present, non-ionic emulsifier and hydrochloric aci...

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Temperature rise and initial shrinkage of alkali-activated fly ash cement pastes

Cited by 16 publications

References 40 publications

Use of Seashell and Limestone Fillers in Metakaolin-Based Geopolymers for Masonry Mortars

Use of Seashell and Limestone Fillers in Metakaolin-Based Geopolymers for Masonry Mortars

Characterisation of the Hydration Products of a Chemically and Mechanically Activated High Coal Fly Ash Hybrid Cement

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