Alternative stones and cleaning efficiencies for historical building stones used in İstanbul (Türkiye)

Historical buildings are important part of the common heritage of mankind. İstanbul comprises many historical buildings built by geo-materials. A limestone (named as Küfeki stone in the region) is one of the most widely used stone in and around the city since thousands of years. The durability, excavability and workability of the stone attract the usage of this stone. Besides the outcrops of the rock were very common. Unfortunately, nowadays quarries and outcrops of Küfeki stone are totally abandoned due to dense settlement. For this reason, replacement of damaged or polluted stone with the original stone is a hard task to overcome. There are some rock types around the city with similar physical properties but the durability of the stone may not match the appropriate values as a substitute. The study aims to define appropriate substitute stone and effect of cleaning on original and alternative stones. For this purpose, micro-textural, physical and mechanical studies and durability tests were conducted on each alternative and original stone regarding EN standards including at least five samples for each group. Same stones were then subjected to pollutant effects. The difference between non-polluted stones and polluted stones were compared regarding changes in mass and visual appearance. Additionally, two widely used cleaning techniques (i.e. sand blasting and laser cleaning) were applied on these stones. The results showed that the water absorption by capillarity and P-wave velocity tests provide useful data for quick decision to understand the durability of studied rocks. But it is clear that due to micro-textural variations durability tests must be conducted on each sampling level for substitute stone selection. Results also revealed that load bearing stones should be cleaned using laser cleaning or other non-destructive method. And sand blasting can be used in non-load bearing structural elements of historical buildings.