Abstract
Viscosity enhancing admixtures are widely used to improve properties of concrete and ready-mix mortars. Guar gum derivatives and chitosan ethers are reported to have water-retaining effect, which is beneficial for the adhesion of the mixture as well as for the hydratation of hydraulic particles in the binder phase of concrete or natural hydraulic lime (NHL) mortars. Influence of addition of admixtures in doses of 1, 5, and 10‰ of the binder weight has been studied on NHL based pastes with constant water:binder ratio. The measurements were carried out on the Discovery HR-1 rheometer with DIN concentric cylinders geometry. The flow properties and viscoelastic properties were studied on the specified mixtures. Pastes expressed shear-thinning behaviour with thixotropic character of flow curves. Admixture addition caused increase of yield stress, fluidity index and consistency coefficient varying on the amount and type of the admixture. Differences in the effectivity of admixtures were observed, the dosage-dependency of the admixtures varied.
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