Working mechanism of biobased rheology-modifying admixtures in cementitious and limestone calcined clay systems

Four types of biobased polymers were tested as rheology modifying admixtures in OPC and LC3 systems. Gum Arabic and water hyacinth polymers demonstrated strong plasticizing effect in OPC systems, while in LC3 systems the plasticizing effect was less pronounced. Unlike water hyacinth gum and gum Arabic, xanthan gum and alginate had increasing viscosity effects. In OPC systems, xanthan gum outperformed alginate and remarkably increased the yield stress at all tested dosages, while plastic viscosity was less affected and only amplified at higher dosages. In the LC3 system alginate and xanthan gum exhibited a nearly similar stabilizing effect. Alginate and xanthan gum work by means of strong adsorption and polymer-ion interaction which turn the pore solutions into non-Newtonian fluids between the particles. Alginate binds Ca 2+ and stabilizes the pore solution, while the presence of other monovalent ions, however, weakens the stabilizing effect, which is why it could be observed stronger in OPC systems. Xanthan gum forms a gel-like structure in water, while in the presence of Ca 2+ , K + , Na + and SO 4 2− ions the stabilizing effect becomes even stronger. All investigated polymers extend the induction period of the hydration of OPC and LC3 binders. Already at low dosages, water hyacinth and gum Arabic retarded the hydration significantly stronger than the other polymers, and water hyacinth in addition also significantly shifted the hydration peaks at later stages.