This study aims to characterize mechanical behaviour of light concrete under very high stress levels of the order of the Giga Pascal. The studied light concrete, called S800, has low density (800 kg/m 3) and high measured porosity accessible to water (47%). This paper presents the development of a radial strain measurement device and first tests results obtained on light concrete, using a large capacity triaxial press. These tests results show that the concrete volumetric strain reaches more than 150% at maximum mean stress of 700 MPa. Triaxial tests with confinements ranging from 50 MPa to 400 MPa, carried out on the studied concrete, highlight the evolution of light concrete behaviour with confinement. The increase of confinement strongly increases both the ductility and the loading capacity of light concrete. © 2010 Taylor & Francis Group, London.