Determination of Optimum VMA Utilization Dosage in Cementitious Systems (2023-04)¶

In mixtures such as self-compacting concrete (SCC) and 3D printing concrete (3DPC) having a high amount of binder, utilization dosage of water-reducing admixture (WRA) is increased to provide the rheological requirements. In such a case, in addition to the increase in cost, the presence of a high dosage of WRA in the system can cause segregation in the SCC mixture and a decrease in the buildability capacity of the 3DPC mixture. However, the addition of viscosity-modifying admixture (VMA) to the mixture together with the WRA reduces the risk of bleeding and segregation in SCC mixtures and increases shape stability and buildability in 3DPCs. Nevertheless, it was emphasized that these properties were seriously affected by the VMA dosage. It was aimed to determine the optimum VMA utilization dosage by examining the effect of dosages of VMA on the rheological properties and flow performance of paste mixtures in this study. Paste mixtures containing 4 different dosages of VMA (0%, 0.2%, 0.4% and 0.6%) were prepared. In all mixtures, the w/c and the WRA dosage were 0.35 and 0.2%, respectively. The rheological properties of the mixtures were evaluated by measuring the dynamic yield stress (DYS), final viscosity value and structural build-up (Athix) parameters. In addition, flowability of mixtures was also examined. DYS value of all mixtures decreased with the increase in VMA utilization dosage. The highest viscosity and Athix values were measured in the mixture containing 0.4% VMA. However, the lowest DYS, viscosity and Athix values were determined in the 0.6% VMA-containing mixture. Flowability of the mixtures generally increased with the increase of VMA utilization dosage. The optimum VMA usage dosage was chosen to be 0.4% in terms of rheological properties.