1. Introduction

The stress generation on pore walls due to the growth of a sodium chloride crystal in a confined aqueous solution is studied from evaporation experiments in microfluidic channels in conjunction with numerical computations of crystal growth. The study indicates that the stress build-up on the pore walls as the result of the crystal growth is a highly transient process taking place over a very short period of time (in less than 1s in our experiments). The analysis makes clear that what matters for the stress generation is not the maximum supersaturation at the onset of the crystal growth but the supersaturation at the interface between the solution and the crystal when the latter is about to be confined between the pore walls. It is shown that the stress generation can be characterized with a simple stress diagram involving the pore aspect ratio and the Damkhöler number characterizing the competition between the precipitation reaction kinetics and the ion transport towards the growing crystal. This opens up the route for a better understanding of the damage of porous materials induced by salt crystallization, an important issue in earth sciences, reservoir engineering and civil engineering. PACS numbers: 47.56.+r, 61.05.cp Salt crystallization in pores causes damage in porous materials, a major issue in relation with building durability and cultural heritage conservation [1-4], underground structures [5], road [6] and geotechnical engineering [7]. A better understanding of the associated stress is also important in relation with geomorphology [8], concrete science [9] or the surface heave phenomenon of granular materials [10]. The fact that a growing crystal can generate stress has been known for more than a century [11], [12]. The key concept for the analysis of the stress generation is the crystallization pressure Pc [13-15]. Corrections to the original expression [14] taking account the water activities and the crystal size have been developed, e.g. [16], [17], so that the current expression for sufficiently large crystals of sodium chloride (>1μm) reads,