Molasses, a by-product of sugar industry, increases the fluidity of fresh concrete, and also delays the hardening time of cement paste. In this study, the molasses were determined from three different sugar production factories. A normal water-reducing admixture, based on lignosulphonate, has been used in the control mixture. Setting times of cement pastes prepared with molasses at three different dosages (0.20, 0.40, and 0.70 wt.% of cement content) were determined and it was found that molasses addition causes considerable increase in both initial and final setting times. Workability tests, as well as bleeding tests, were carried out on fresh concretes prepared with three molasses and also with lignosulphonate-based admixture. Flexural and compressive strengths were determined on hardened concretes at both early ages (1, 3, and 7 days), and moderate and later ages (28, 90, 180, 365, and 900 days). The permeability and durability properties of concretes have been investigated by using sorptivity, drying shrinkage, freezing thawing, wetting and drying, carbonation, and sulfate attack tests. The strength of concretes with molasses showed slight increase at all ages, except early age, with respect to the control mix and no adverse effect has been experienced on the durability properties over a long period of time (900 days). (c) 2004 Elsevier Ltd. All rights reserved.