Slump Loss of Concrete Based on RCA and Prepared by Specific Mixing Approach

Concrete is a dynamic material and its consistency changes with time, having impact on technological processes at working site. It is expressed due to slump loss - the reduction in slump from the time of original batching to the point when concrete is discharged from a truck mixer. Two kinds of additives (fly ash and recycled concrete powder) were tested to find their potential to improve the performance of recycled concrete aggregate in concrete, while the principle of triple-mixing method was adopted. Slump loss was evaluated based on measurements taken at 0, 45, and 90 minutes after mixing. The kind of aggregate, as well as kind of powdery material for coating the coarse fractions play significant role for the slump loss. Mixtures with fly ash as coating material achieved the biggest slump loss for both types of aggregate. The recycled concrete powder is well acceptable having similar impact on the slump loss as the cement has. When the NA is changed to RCA, the slump loss is higher and depends on material used for coating.