Workability and strength attributes of RCC: Effects of different chemical admixtures and resulting paste
Roller compacted concrete (RCC) is a drier consistency concrete proportioned with dense graded aggregates and has lesser paste content. Primarily owing to its drier consistency, the fresh and mechanical performances of RCC are distinctly different from conventional concretes. The objectives of this work were three fold. The first objective was to explain the anomalous behavior of fresh RCC in terms of different components of workability. The second objective was to explain the mechanisms of strength development in terms of paste quality and quantity. The final objective was to explain the roles of different chemical admixtures (water reducers, retarders, rheology modifiers, air entraining agents, dry cast products, etc.) in influencing the workability and strength performances of RCC.
It is observed that the relative volume and quality of the paste, in addition to combined aggregate grading, affect the overall workability of mixtures. The workability of concrete is characterized in terms of cohesion, angle of internal friction, air content, compactibility, and consistency retention over time. Air content plays a decisive role in influencing the performances of concrete. The resulting mobility of the paste influences the compactibility, which in-turn decides the strength as well. RCC shows anomalous behavior in terms of mechanical strength as shown by deviations in the Abrams' law. It is argued that water-binder ratio is not a comprehensive parameter to explain the overall concrete behavior and trends.
A significant body of knowledge is added in terms of the use of chemical admixtures in RCC. Atypical behaviors in influencing the fresh and hardened properties are explained by offering plausible mechanisms in terms of binder-admixture interactions. Irrespective of the admixture type, higher than normal dosages are required for RCC.