Mechanical and Microstructural Study of Raw Earth Stabilised by Alkali-Activated Slag

Ground blast furnace slag (GBFS) activated by two different sodium hydroxide solutions was used in this study to stabilise a natural raw earth material with the aim of formulating an earth-based concrete with high hygrothermal properties. Indentation tests were carried out to measure the effect of alkaline conditions and the amount of GBFS on the cohesion and mechanical properties of the stabilised raw earth. Measurements show that the hardness of the material increases with the amount of slag added and reveal the existence of a percolation point when the slag content is greater than 10%. However, this improvement depends on the alkaline conditions used for slag activation. The improved properties are related to a good integration of the hydrates into the earth matrix, as observed by scanning electron microscopy (SEM). In addition, microstructural modifications have been investigated to control the behaviour of earth compounds under alkaline conditions. Fourier transform infrared (FTIR) analysis shows that the global chemical structure of the crude earth compounds is conserved, despite a slight modification of the structural order at the microscale, observable by X-ray diffraction (XRD).