Changes in engineering properties of natural stone

It has long been known that some stone types show significant loss in strength, both in compression and bending during the service life of a building. These differences can include changes as a result of long-term changes in physical structure, for example as a result of thermal and moisture cycles, but there can also be shorter term changes between the wet and dry states. The European Standards that are now in place in the UK and the rest of the CEN countries require stones to be tested under ambient conditions and, if required to declare these values as part of the CE marking process. This has led to some concerns that the data available for structural calculations may not reflect the actual performance during use, and as the demands for more slender stone units increase so the margins for error become smaller. The present paper begins by examining a number of reported examples of changes in properties with time as a result of changes in structure in some marbles as well as changes in appearance and strength in limestone and sandstone as a result of salt damage and freeze-thaw action.