In the context of long term CO2 sequestration, we present an original laboratory workflow which allows a multi scale analysis of the effect of chemical alteration on both petrophysical and mechanical properties of a carbonate. The relationship between the mechanical behavior and the micro-structural evolutions is investigated using digital image correlation methods. For this purpose we imaged intact and altered samples during uniaxial and triaxial mechanical tests using optical microscopy, scanning electron microscopy (SEM) and 3D X-ray micro-tomography. The porosity increase induced by homogeneous alteration leads to lower elastic moduli and critical stress at sample failure. Furthermore, at similar confining pressures we observed a transition from brittle to ductile failure mechanisms with the alteration level. These observations are verified by digital image correlation. Altered samples indicate early strain localization which was not observed in the intact ones. These early localization events induce more compaction at the macroscopic scale and tend to initiate early fracturing.