Influence of Mixing Time on Fresh and Hardened Cast-in-place Concrete

Abstract

An adequate mixing time in concrete casting allows to achieve a homogeneous mass and improve compressive strength and durability. However, the lack of standards for cast-in-place concrete causes that the builders use different mixing times according to the locality usages and customs, which results in a high variability of the expected quality. In this paper, fresh and hardened cast-in-place concrete was evaluated. Seven samples were tested with different mixing time using portable rotary drum mixer. The used materials were ordinary portland cement, water and high absorption aggregates, fine and coarse, coming from a limestone crushing process. The results of the research showed that the mixing time and environmental temperature had no apparent influence on the slump of the mixtures, and trapped air and compressive strength increased slightly with increasing mixing time. Finally, it was found that the recommended mixing time, with rotation speed of 28 RPM, is 2.5 minutes, which differs from the common practice in the study area.