Recycled bassanite for enhancing the stability of poor subgrades clay soil in road construction projects

This research investigates the use of recycled bassanite produced from gypsum waste plasterboards to enhance the compressive strength, splitting tensile strength and CBR of weak subgrade clay soils used in roads construction. For this purpose, two types of soils which represent weak subgrade soils located at two different sites were used. This research is preliminary investigations of utilizing recycled bassanite in road construction projects. Recycled bassanite was mixed with furnace slag cement with a ratio of 1:1 to prevent the solubility of bassanite when water introduced as bassanite is a soluble material. Four different amounts of this admixture were mixed with the tested soils and then examined for compressive strength, tensile strength, CBR, volume change and capillary rise. Results showed that the use of recycled bassanite resulted in a considerable increase in CBR and compressive strength for the two types of soils used. The addition of recycled bassanite lead to a small improvement in the tensile strength compared to the improvement in compressive strength and CBR. The induced volume change in term of swelling, when stabilized soil samples soaked in water, increases with the increase of bassanite content in soil mixture. While in the case of un-soaked samples, volume change in term of settlement reduces with the increase of bassanite content in soil mixture. The induced volume changes for the different investigated cases in both soaked and un-soaked conditions are insignificant. The unit weight increased and water content decreased with the increase of bassanite content in soil mixture. The amount of bassanite in soil mixture had a significant effect on the reduction of capillary rise in the case of silt soil while it had insignificant effect in the case of clay soil. The use of recycled bassanite enhanced the performance stability of weak clay subgrade soils. The enhanced stability would result in longer service life and smaller thickness sections for road construction. Besides, the environmental and economic benefits associated with the use of wastes in construction, the use of gypsum wastes in road construction is attractive and support sustainable development in construction. (C) 2013 Elsevier Ltd. All rights reserved.