『Abstract
　The Orval Abbey, a major monument of southern Wallonia, Belgium, was partly destroyed and rebuilt several times between the Middle Ages and the present time. The oldest parts are made of natural stones of local origin (Bajocian and Sinemurian limestones) and the most recent parts are mostly made of reconstituted stone. The process of reconstituted stone making is not known. Although confronting the same environmental conditions, the reconstituted stone is much more susceptible to weathering than the natural limestones, especially to salt crystallisation. The present study compared the mineralogical and petrophysical properties of these building materials to gather information on the making of the reconstituted stone and to understand the difference in salt susceptibility between natural and reconstituted stones. Microscopic observations and petrophysical measurements showed that the reconstituted atone is composed of debris of Simenurian and Bajocian limestone and cement, and the salt efflorescences were thenardite. Within the cement, amorphous grains were found that may correspond to grains of clinker, which have not reacted during stone making. Although its porosity and water transfer properties were close to that of the Bajocian limestone, its pore access distribution was centred around 0.1μm. Furthermore, the details of the pore size distribution allowed calculating salt susceptibility indices that were very high in the case of the reconstituted stone. Thus, the composition of the cement and the pore size distribution are likely the two factors explaining a high susceptibility of the reconstituted stone to salt weathering.

Keywords: Reconstituted stone; Bajocian and sinemurian limestone; Salt weathering; Thenardite; Heritage conservation』

Introduction
Materials and methods
　Climate in Orval
　Building materials of Orval
　Petrography
　　Colorimetry
　　Coloured thin sections
　　SEM images
　　XRD and XRF
　Petrophysics
　　Porosity
　　Capillary kinetics
Results
　Petrography
　　Colorimetry
　　Coloured thin sections
　　　(Sinumurian limestone from the Luxembourg formation in Orval)
　　　　Elements
　　　　Binding phase
　　　　Porosity
　　　(Bajocian limestones from the Longwy formation originally used in Orval)
　　　　Elements
　　　　Binding phase
　　　　Porosity
　　　(Reconstituted stone made in Orval in the early twentieth century)
　　　　Elements
　　　　Binding phase
　　　　Porosity
　　SEM images
　　XRD and XRF
　Petrophysics
　　Sinemurian limestone from the Luxembourg formation
　　Bajocian limestones from the Longwy formation
　　Reconstituted stone
Discussion
Conclusion
Acknowledgments
References