Evaluating the Effects of Viscosity-Modifying Agent on the Flow Behavior, Segregation Resistance, and Strength of Self-Compacting Concrete

Abstract

One of the basic characteristics that self-compacting concrete (SCC) possesses is resistance to segregation; the mix is homogeneous through its placement and hardening. Poor resistance to segregation will be manifested by internal and external water leakage, accumulation of lighter components, a paste-rich layer forming at the top, and coarse aggregate settling at the bottom. Such imbalances may grossly compromise the long-term structural integrity of the concrete. A few of the key factors determining the potential for aggregate sedimentation include mix viscosity, size, and density of the aggregates, along with flow rate. To be effective, the SCC needs to retain homogeneity throughout the mix in retaining required mechanical properties. This paper presents the cylinder-column segregation test for monitoring static segregation with time in both fresh and hardened states of SCC. Concretes containing different amounts of viscosity modifying agent (VMA) were prepared to investigate the effectiveness of viscosity modifying agent (VMA) in enhancing the rheology and stability of SCC mixtures. In this respect, the study concerns the understanding of the aptitude of VMA to influence important parameters such as slump flow, flow time, and time of flow in a diameter of 500 mm and resistance to vertical segregation. Other issues related to the study include the determination of the long-term VMA effects on compressive strength and tensile strength by testing the cured concrete. The segregation test of the cylinder column is very important, as it determines and quantifies the static segregation within the mixtures of SCC. This test provides a direct and quantitative determination of stability in regard to the fresh state of concrete. More specifically, the experiment calculates the contents of coarse aggregate above 8 mm in a specimen that is 300 mm high in time lapses of 15, 30, and 45 minutes after casting. These sedimentation tests conducted provide a clear picture of segregation with regard to time through the cylindercolumn segregation test. Additions of VMA have shown immense improvements in the rheological properties of SCC, hence improving segregation resistance and thereby improving both compressive and tensile strengths compared to a reference mixture without VMA. This underlines the favorable role of VMAs for better overall performance in SCC.