The influence of calcium nitrate on the plasticizing effect of cement paste

Abstract

The rheological properties of the cement pastes have been determined using a rotational viscometer under a special testing routine by increasing and retaining a steady rotation speed of the viscometer cylinder up to certain values and for a certain time. These tests, using rotational viscometer, have been conducted by making the assessment of ce­ment paste flow curves, using Bingham rheological model. Rheological properties of cement pastes were tested at dif­ferent times after pastes mixing: 0 min, 30 min, 60 min, 90 min, 120 min and 180 min. Cement pastes with same W/C ratio equal to 0.35 were tested. The content of admixture was used 0%, 0.5%, 1%, 2%, 3% and 5%. The admixture of Ca(NO₃)₂ can be used in cement pastes and concretes without a reduction in consistency during 120 min in the dosage of up to 2%. Dosages of Ca(NO₃)₂ from 3% are not recommended for cement pastes and concrete, they significantly increase the viscosity of mixtures immediately after mixing The admixture of calcium nitrate changes thixotropy of ce­ment pastes. In this case, a bigger dosage of calcium nitrate increases the thixotropy of pastes.

Keyword : cement pastes, calcium nitrate, admixture, shear stress, viscosity, thixotropy