ABSTRACT:

The coastal city of Rio de Janeiro has historical buildings dating from the Portuguese imperial period to the beginning of last century. A remarkable feature of this cultural heritage was the use of porphyroblastic gneiss as stone masonry. As a consequence of city location, soluble salt crystallization is one of the most destructive processes leading to rock degradation. The aim of this manuscript was to evaluate the seismic response of gneiss submitted to laboratory controlled cycles of immersion in a saturated salt solution of sodium chloride and subsequent drying at 100±5 °C. Salt crystallization has produced an increase of initial porosity of samples from a mean value of 1.19% (initial condition) to 2.91% after 30 cycles. Regarding compressional wave velocities the average value in the fresh gneiss is around 4530 m/s while in the salt weathered gneiss the average value is 1453 m/s. The seismic anisotropy has also presented a huge increase from 1.06 to 1.79. It can be concluded that rock seems to become a medium progressively more heterogeneous and anisotropic. It requires a greater number of in situ non-destructive ultrasonic pulse tests in order to adequately characterize the gneiss degradation caused by natural cycles of salt crystallization.

1. INTRODUCTION
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