Laboratory tests on swelling due to crystal growth in sulphate bearing rocks

Abstract

Precipitation of sulphate crystals in discontinuities due to evaporation of sulphate solutions is an important contribution to the degradation and swelling behavior of sulphate bearing argillaceous rocks. Although the phenomenon has been studied in laboratory during decades linked to the expansive behavior in tunnels, tests do not adequately reproduce field conditions and all variables involved in the swelling mechanism. Size effect problems and the difficulty in correctly applying hydraulic boundary conditions are the main aspects behind these experimental difficulties. To this aim, a new experimental setup has been designed to allow applying relative humidity control on the top cap of the sample, while the bottom cap is in permanent contact with a saturated sulphate solution. This way, controlled solvent evaporation conditions are applied, which control the rate of sulphate precipitation on the sample. The crystals are deposited along preferential discontinuities of the sample, as well as on fissures generated by the hydraulically induced degradation of the material. A sulphate bearing claystone of the Lower Ebro Basin (Catalonia, Spain) has been tested. Selected swelling tests are presented at different relative humidity values. Microstructural and DRX analyses are also included to complement the information of the mineralogical phases deposited during these processes. © 2014 Taylor & Francis Group, London.