Identification of Specific Structural Motifs in Biopolymers That Effectively Accelerate Calcium Alumina Cement

Alexander Engbert, Johann Plank

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Abstract

Following a previous study where we presented on the surprising accelerating effect of alginates on calcium aluminate cement (CAC), we now systematically screened specific groups of biopolymers, hoping to identify other polysaccharides that also can accelerate CAC. Testing of pure, noncompounded alginates from different species/genera of algae revealed comparable strong acceleration, while chemical modification via esterification, decarboxylation, or sulfatation reduced the accelerating effect, thus highlighting the importance of high anionic charge and the presence of carboxylate groups as key structural features. Furthermore, biopolymers possessing a "cavity"that effectively can chelate and capture Ca2+, such as alginate, were found as another key structural unit; hence, pectin and ι- as well as κ-carrageenan were identified as biopolymers that possess a similar accelerating effect to alginate. Among other natural, synthetic, or semisynthetic biopolymers, karaya, gellan, and xanthan gum as well as agarose produced a slight accelerating effect, whereas konjac gum, hydroxypropyl guar, and methyl hydroxyethyl cellulose ether either perform neutral or retard CAC hydration. A preliminary mechanistic study revealed that effective accelerators reduce the concentration of free Ca2+ present in the cement pore solution and that a combination of high anionic charge, presence of a Ca2+ capturing cavity, and a high Mw is required for a biopolymer to act as an accelerator in CAC. Our concept of using biopolymers such as alginate allows us to replace at least partially lithium salts (e.g., Li2CO3), which are currently applied to accelerate CAC but are much needed for the production of Li-ion batteries that are necessary for widespread electromobility.

Original languageEnglish
Pages (from-to)11930-11939
Number of pages10
JournalIndustrial and Engineering Chemistry Research
Volume59
Issue number26
DOIs
StatePublished - 1 Jul 2020
Externally publishedYes

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