New biopolymers as viscosity-modifying admixtures to improve the rheological properties of cement-based materials

The performance of various new biopolymers as viscosity-modifying admixtures (VMAs), including tragacanth, almond, and locust bean gums and giant kelp extract, in addition to two commercial biopolymer-VMAs, welan and guar gums in cement-based materials was evaluated. The effect of the preparation/addition method, type, and dosage of the investigated biopolymers on rheology, hydration kinetics, stability, and compressive strength of various cement paste mixtures was evaluated. The pre-dispersion and pre-dispersion/pre-hydration techniques showed greater influence on the rheology of the investigated mixtures compared to dry addition. Moreover, the investigated biopolymers led to a shear-thinning response with higher viscoplastic properties than the reference. The structural build-up of the mixtures was mainly influenced by the type and dosage of the biopolymers, observing higher performances in mixtures containing guar gum, giant kelp extract, and welan gum. The use of the investigated biopolymers enhanced the stability of the paste mixtures, while negatively influenced the earlyage strength development.