Mortar samples saturated with different solutions (deionised water, 0.5 M NaCl and I M NaCl) are studied 10 quantify microstructural changes induced by weathering of concrete in near-neutral solutions containing chlorides. The Study is based on physical and electrochemical techniques. Mercury intrusion porosimetry is employed to quantify porosity and pore size distribution, and impedance spectroscopy as a non-destructive technique able to give information on structural Changes. SEM imaging, XRD. and EDX characterisation allow elucidating the Causes of the observed structural changes. Portlandite leaching tends to increase porosity. Nevertheless, the leaching process towards near-neutral Solutions makes resistivity to increase. The presence of chlorides induces Friedel's salt formation, a slow process associated to the development of small size pores (around 10nm). Impedance spectroscopy in the frequency range 10(-2) to 10(2) MHz is successfully employed to follow Friedel's salt formation and pore network-development in mortars. (c) 2007 Elsevier Ltd. All rights reserved.