Rheological properties of cement-based materials using a biopolymer viscosity modifying admixture (BVMA) under different dispersion conditions

Nowadays, concrete industry uses viscosity-modifying admixtures (VMA) for the production and placement of special construction applications such as underwater or self-consolidating concrete. VMAs can decrease the movement of water and fines, and maintain the underwater concrete's homogeneity. Self-consolidating concrete requires high stability since the material shows a high slump-flow, but high viscosity is also required to avoid aggregate segregation. Currently, the use of both superplasticizer admixtures (SP) and VMAs is very common, as they improve the stability of special cement-based materials. The combined influence of a biopolymer admixture (BVMA) and a commercial SP under different dispersion conditions on the rheological properties of cement pastes was analyzed. Results showed a delayed hydration of cement compounds when incorporating both SP and BVMA into the mixture; however, SP contents controlled the hydration rate, the setting times, and the specific heat. Although mechanical strength tests showed that an increase in SP dosages caused a decrease in this parameter, higher compressive-strength values were achieved with BVMA incorporation. Results also showed that BVMA increased cement pastes' viscosity; however, this effect is adequately compensated by the dispersion properties of the SP employed. The rheological parameters of the cement pastes analyzed were obtained by using the Herschel-Bulkley's model. Hence, it was concluded that the BVMA used in this study has a very interesting potential to be used as a viscosity modifier when it is properly dispersed using superplasticizers.