Control of effective water in recycled aggregate concrete using power curves of the mixer

Abstract

Composed of several components (natural aggregates and attached cement paste), crushed concrete aggregates (CCA) are not widely recommended in new concrete formulations. Their properties considerably complicate the determination of effective water in fresh concrete. The evolution of effective water in fresh concrete during mixing was studied using an original method based on the power evolution of the mixer. The presented experiments analyzed the water migration kinetics during mixing and the level of stabilization of the effective water at the end of the mixing. This analysis was established according to the initial moisture of the CCA and of the type of pores filled with water in these aggregate, and, of the total water in the new concrete mixture. It was shown that the exchange of water between recycled aggregate and the new concrete mixture during the mixing is more complex than generally considered. The water can get into or get out from the CCA, depending on the history of their initial moisture. The direction of water migration can also change at different stages of concrete mixing. Therefore, the amount of effective water decreases or increases during mixing and tends to stabilize once the uniform new concrete is obtained.