Potential of Calcined Mixed Layer Clays as Pozzolans in Concrete

Beuntner, Nancy; Sposito, Ricarda; Thienel, Karl‐Christian

doi:10.14359/51716677

Cited by 16 publications

(15 citation statements)

References 49 publications

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“…7 Several studies have proven that alumina from metakaolin can contribute to ettringite formation. 4,8 Hence, in blends of cement and calcined clay there is a risk of undersulfation. An enhanced ettringite formation during the dormant period 9 as well as an acceleration of the sulfate depletion 7 is often observed.…”

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confidence: 99%

“…4 AS̅ x H 14 ) forms. The major part of the monosulfate formation still falls into the stadium, where the reaction kinetic is defined by the C 3 A dissolution.…”

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confidence: 99%

“…While some studies refer to the additional aluminum ions 10,11 to explain aforementioned effects, a recent work suggests the high specific surface area (SSA) of calcined clays as the driving force: 12 The faster aluminate reaction was correlated to the acceleration of the silicate reaction, which is driven by the filler effect. As SO 4 2− ions adsorb on the newly formed calcium silicate hydrate phase (C-S-H), [13][14][15] an accelerated C-S-H formation speeds up the adsorption of sulfate and thus the sulfate depletion peak. The role of ion adsorption during early cement hydration has gained increasing significance in recent research, especially regarding the aluminate reaction.…”

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confidence: 99%

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Hydration of cubic tricalcium aluminate in the presence of calcined clays

et al. 2021

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Calcium sulfates take an important role in the reaction of pozzolanic materials by forming ettringite with aluminum ions from the pozzolan. 1 Sulfate carriers like gypsum, bassanite, or anhydrite are used to retard the tricalcium aluminate (C 3 A) reaction in ordinary portland cement (OPC). 2 The latter mechanism is used to avoid flash set and to optimize strength development by preventing a superposition of the silicate and aluminate clinker reaction. 3 As calcined clay blended cements 4 or limestone calcined clay cements (LC 3 ) 5 are currently among the most promising solutions to address CO 2 emissions in cement industry 6 , their influence on cement hydration in general and on the aluminate reaction in particular is gaining attention. In calcined clay blended cements, where additional aluminum sources are present, awareness has been raised for extra sulfate demand, as the

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“…4 AS̅ x H 14 ) forms. The major part of the monosulfate formation still falls into the stadium, where the reaction kinetic is defined by the C 3 A dissolution.…”

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confidence: 99%

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confidence: 99%

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Hydration of cubic tricalcium aluminate in the presence of calcined clays

et al. 2021

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“…For instance, a bentonite from the Westerwald area calcined at 900 °C was found to exhibit an activity index measured by compressive strength in mortars close to 100 % after 28 days [78]. Also a clay from Southern Germany, referred to as Amaltheen clay, with a kaolinite content of 20-25 wt.% and around 40 wt.% 2:1 clay minerals exceeded a strength activity index of 100 % after 28 days at a replacement level of 25 wt.%, if calcined at the optimum temperature [30]. Common clays with a kaolinite content below 30 wt.% but with a high amount of other 2:1 clay minerals such as illite or chlorite may reach a pozzolanic reactivity similar to conventional SCMs[…”

Section: Performance Of 2:1 Clays As Scmmentioning

confidence: 93%

“…By using a lower level of clinker replacement, clays with even lower contents of kaolinite (25-40 wt. %) could still be used [30]. Given that the goal of the cement industry is to develop cements with a high level of clinker replacement for sustainable development and a performance similar to Portland cement even at early ages [31], a minimum content of clay minerals from the kaolinite group of 40 wt.…”

Section: Kaolin and Kaolinitic Claysmentioning

confidence: 99%

Properties and occurrence of clay resources for use as supplementary cementitious materials: a paper of RILEM TC 282-CCL

Díaz

Reyes²,

Hanein

et al. 2022

Mater Struct

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The use of clays as resource of supplementary cementitious materials (SCMs) for a new generation of low-carbon cements and concretes is currently the subject of intense research efforts. To this purpose, a large number of clay resources have been explored, characterized and evaluated. This paper introduces the basic knowledge and concepts on clay occurrence and clay mineralogy, before presenting up-to-date knowledge on properties and occurrence of clay resources suitable for use as SCMs. Occurrence, distribution and chemical and mineralogical selection criteria are discussed for kaolinitic clays, which often show superior reactivity and performance. 2:1 clay mineral resources have received somewhat less attention as SCMs resources, however recent developments indicate significant potential for calcined impure common clays, and are reviewed. An overview of ubiquitous clay mineral-bearing waste materials also identifies important opportunities for alternative clay sourcing in mining or extraction residues, and dredged or excavated sediments.

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