A Comprehensive Review of Plant-Based Biopolymers as Viscosity-Modifying Admixtures in Cement-Based Materials  
[PERSON]  
1 Department of Civil and Building Engineering, Universite de Sherbrooke, 2500 Blvd. de l'Universite, Sherbrooke, QC J1K 2R1, Canada; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (A.Y.) 2 Department of Biology, Universite de Sherbrooke, 2500 Blvd. de l'Universite, Sherbrooke, QC J1K 2R1, Canada; [EMAIL_ADDRESS]  
3 Department of Civil Engineering, Canadian University Dubai, 675C+C33 Al Satwa, Dubai F.O. Box 117781, United Arab Emirates  
4 Correspondence: [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Civil and Building Engineering, Universite de Sherbrooke, 2500 Blvd. de l'Universite, Sherbrooke, QC J1K 2R1, Canada; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (A.Y.) 2 Department of Biology, Universite de Sherbrooke, 2500 Blvd. de l'Universite, Sherbrooke, QC J1K 2R1, Canada; [EMAIL_ADDRESS]  
3 Department of Civil Engineering, Canadian University Dubai, 675C+C33 Al Satwa, Dubai F.O. Box 117781, United Arab Emirates  
4 Correspondence: [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Biology, Universite de Sherbrooke, QC J1K 2R1, Canada; kamal.bouarabwater-reducer (HRWR) to enhance fluidity without increasing the water-cement ratio (W/C) [4]. Flowable concrete, owing to its high fluidity and low yield stress, poses a significant risk of bleeding and segregation, potentially compromising its stability in the fresh state and affecting its hardened properties. Contrary to Newtonian fluids, where the shear stress, \(\tau\), is proportional to the shear rate, \(\gamma\) (Equation (1)), cement suspensions are typically described by the Bingham model (Equation (2)) or the Herschel-Bulkley model (Equation (3)). In these cases, the materials require a minimum shear stress, referred to as yield stress, to initiate flow. Additionally, these materials can exhibit shear-thinning behavior, characterized by a decrease in apparent viscosity with shear rate [5]. \[\tau=\mu_{0}\;\gamma^{\cdot} \tag{1}\]  
\[\tau=\tau_{0}+\mu_{\mathrm{p}}\;\gamma^{\cdot} \tag{2}\]  
\[\tau=\tau_{0}+\mathrm{k}\;\gamma^{\cdot\mathrm{n}} \tag{3}\]  
Here, \(\tau\) is the shear stress (Pa), \(\gamma^{\cdot}\) is the shear rate (s\({}^{-1}\)), \(\mu_{0}\) is the material viscosity (Pa s), \(\tau_{0}\) is the yield stress (Pa), \(\mu_{\mathrm{p}}\) is the plastic viscosity (Pa s), k is the consistency, and n is the power index representing the deviation from the Newtonian behavior. To mitigate these issues, viscosity-modifying admixtures (VMAs) are incorporated to minimize segregation and enhance concrete's stability during transport, placement, and consolidation [6]. VMAs, also known as viscosity-enhancing admixtures (VEAs) or antiwashout admixtures, primarily consist of water-soluble polysaccharides. When properly used in cement-based materials, VMAs enhance rheology, stability, cohesion, and water retention capacity of concrete [4]. Initially adopted in Germany during the mid-1970s, followed by Japan in the 1980s, and eventually integrated into North American practices by the late 1980s, VMAs are available in both powder-based and liquid-based forms [6]. VMAs have diverse applications in various types of concrete, fulfilling specific purposes such as in tremie concrete used in constructing curtain walls and deep foundation walls, the underwater repairing of marine and hydraulic structures, and shotcrete for repairing deteriorated structures [6]. Additionally, in applications where exceptional sedimentation and bleeding resistances are essential for effective corrosion protection for stressed tendons, VMAs are used to fill post-tensioning ducts [4]. VMAs are thus used to enhance the stability of the fluid system by increasing the viscosity and promoting the homogeneous dispersion of solid particles while also retaining water until hardening. Moreover, VMAs play a crucial role in enhancing the thixotropy of cement-based materials.