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

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 M w 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.

Impact of sand and filler materials on the hydration behavior of calcium aluminate cement

“…The set behavior of cements such as ordinary Portland cement (OPC) or calcium aluminate cement (CAC) in the presence of various admixtures like superplasticizers, [1][2][3] latex polymers, 4,5 retarders, 6,7 or accelerators including nano C-S-H 8,9 or biopolymers, for example, alginate [10][11][12] has been investigated extensively. Most often, heat flow calorimetry in cement paste and mortar strength tests are applied to study the impact of admixtures on the hydration reaction of the binder.…”

“…In previous works, we have investigated the accelerating effect of alginate and similarly structured biopolymers on CAC. 10,11 As working mechanism for these unusual accelerators, we proposed a heterogeneous surface crystallization process facilitated by alternating layers of Ca 2+ und [Al(OH) 4 ] − ions deposited along the molecular chain of the biopolymers. 12 Furthermore, in this study a discrepancy between heat flow calorimetry using paste and strength data collected from mortar was observed.…”