Flue gas desulfurization (FGD) gypsum is a by-product created when sulfur is removed from flue gases in power plants. The utilization of FGD gypsum as a road sub-base for construction purposes is unsatisfactory when compared with other by-products such as fly ash and steel slag. As a result, FGD gypsum has generally been treated as a waste product and landfill. A new type of semi-rigid road sub-base is proposed, which is a mixture of FGD gypsum, water glass and slaked lime. Laboratory studies of moulded samples of this new material were investigated using different curing methods and measuring unconfined compressive strength, soundness and water stability. The experimental results showed that the road sub-base material reflects excellent mechanical properties and soundness durability. This contributes not only to improved road performance, but also represents a new and improved beneficial use of FGD gypsum. (C) 2009 Elsevier Ltd. All rights reserved.