## 3 Plant-Based Biopolymers
### Pettin-Based VMAs
Firstly, pectin has been found to accelerate setting [71; 74] by forming three-dimensional gels with Ca\({}^{2+}\), a result that is contrary to that obtained with organic admixtures, which retard the setting [71]. On the other hand, conflicting results have been reported in other studies, where pectin was shown to delay the setting [31; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102; 103; 104; 1  
the Rhodophyceae class [79], including Solieriaceae, Rhabdoniaceae, Hypeneaceae, Phylolophoraceae, Gigartinaceae, Furellariaceae, and Rhodophyllidaceae [80; 81]. In fact, the cell walls of marine algae consist of a two-phase system, including a crystalline phase (skeleton) and a more amorphous phase (matrix) [82]. Moreover, examples like _Chondrus crispus_ and _Kappadhycus_ sp. are notable for their high carrageenan contents, reaching up to 71% and 88%, respectively. Moreover, carrageenan finds extensive applications in the food industry (bakery fillings, ice cream, pet food) [83], making it the third most important polysaccharide in the food industry [84]. Additionally, since the 1830s, carrageenan has also been employed in various medical applications, such as in pharmaceutical lotions and medicinal creams, as an anti-coagulant in blood products, and for treating gastrointestinal issues like diarrhea, constipation, and dysentery, due to its stabilizing properties [83]. Moreover, carrageenan are a type of sulfated galactans characterized by their structural composition consisting of alternating disaccharide repeating units. These repeating units consist of three-linked \(\beta\)-D-galactopyranose (G-units) and either four-linked \(\alpha\)-D-galactopyranose (D-units) or four-linked 3,6-anhydro-\(\alpha\)-D-galactopyranose (DA-units) [79; 85; 86]. There are several categories of carrageenan, based on the presence of 3,6-anhydrogalactose on the four-linked residue and the position and quantity of sulfate groups [85], with the most well-known being kappa (k-), iota (i)-, (Figure 11), and lambda (\(\lambda\))-carrageenan. Other categories include mu (\(\mu\))-, nu (\(\
u\))-, and theta (\(\theta\))-carrageenan, with mu- and nu-carrageenan being the biological precursors of kappa- and iota-carrageenan and theta the successor of lambda [80]. Indeed, the difference in their molecular structures contributes to variations in their functionalities and applications. For example, kappa- and iota-carrageenan, both containing the 3,6-anhydro unit, exhibit gel-forming properties. In contrast, lambda-carrageenan, composed solely of galactose groups, functions primarily as a thickening agent [85]. Indeed, as the applications of carrageenan expand across various industrial domains, they are proving to be valuable components in concrete formulations, providing unique characteristics. On one hand, they enhance the fresh properties of cement-based materials, particularly rheological and viscoelastic properties, build-up kinetics, and stability [78; 87]. In addition, kappa-carrageenan, when used as a VMA in cement-based materials, leads to a significant improvement of the shear-thinning behavior, accompanied by an increase in plastic viscosity at both low and high shear rates. In addition, an elastic network is formed, and stiffness and stability are improved by absorbing water and enhancing dispersion [4; 88]. Furthermore, the combination of kappa- and iota-carrageenan incorporated in cementitious suspensions has resulted in an increase in the elasticity of kappa-carrageenan gels under shear. As a result, thixotropic gels suitable for specialized applications (3D printing, the casting of high structures by reducing lateral pressure on the formwork) are formed. Consequently, the combination of the two polymers affected the thixotropic behavior, pseudoplasticity, plastic viscosity, bond strengths and build-up kinetics in one study [88].