The microcrack distribution in a low porous granite exposed to weathering after quarrying
was investigated in order to detect its microstructural evolution. Two blocks (A and B) were taken in
the same granite body from two quarry faces respectively exposed during a few weeks and twenty
years. Porosimetry by injection of carbon-14-methylmethacrylate (14C-MMA) was used for
analysing the porous medium. Measurements of optical densities of autoradiographs provided data
for the localization and the quantification of porosity. Results are compared with those obtained by
mercury porosimetry. Average porosity of sample A was found to be 0.37 ± 0.03% whereas average
porosity in sample B reaches 1.07 ± 0.45%. Most of the porosity increase may be explained by the
opening of grain boundaries.