Good workability at construction site is essential for high quality concrete since concretes of bad workability are prone to yield low strength and poor durability properties since placement and consolidation procedures cannot be performed properly. Nevertheless, this is what usually encountered in practice because slump loss is indispensable particularly when long delivery times are the case. This would be more pronounced when mineral additives are incorporated into the concretes. In this study, concretes of C25/30 class with fly ash and silica fume were produced and slumps were measured with time elapsed. At the end of each agitating period, the slumps of the mixtures were restored to the initial slumps using a superplasticizer and specimens were thereafter prepared for strength measurement. The effectiveness of using fly ash and silica fume in concrete in relation with slump loss was sought by determining the amount of superplasticizer used. Regardless of the mixture recipe, it can be concluded that as the total amount of cementitious materials increases in the concrete mix of the same initial slump, the slump loss with the elapsed time decreases. (C) 2010 Elsevier Ltd. All rights reserved.