Deterioration Processes of Travertine Monumental and Contemporary Stonestructures

Architectural decorative elements as well as monumental stone structures made of travertine are subject to complex deterioration processes, which cause morphoses and strength reduction depending on climatic conditions.
   Deterioration susceptibility was compared for travertine from boundaries of Mediterranean area (Hierapolis, Turkey) and from Lowland Polish area (Raciszyn, Poland). The comparison outcome is the observation that wall surface colours turn gradually to grey, become rough, and weather-exposed structure fragments crack irregularly and fall off.
   For both travertine varieties, macroscopic analysis, microscopic analysis, scanning (SEM) analysis, and strength and strain tests indicated that younger Hierapolis travertine were more porous and lighter than Raciszyn travertine. Besides, Hierapolis travertine featured a lower strength as a result of a significantly stronger leaching out of organic debris, and of a lower crystallization extent level for the carbonate skeleton structure.
   Comparative porosity tests made for new Hierapolis travertine (HO) and for ancient quarry Hierapolis travertine (HA) provided with a conclusion that since the ancient time until presently, the material porosity increased by range of 60%, while the strength decreased by range 50%. At the same time, accelerated deterioration tests under lab conditions proved that a further deterioration of this weathered and porous material gave reason for an entire decomposition of structure to irregular rubble chips.
   As determined in further tests, the reason for travertine deterioration was mainly the structure weakening due to the leaching of carbonate compounds, organic fragments in particular. Located in the voids created that way, the secondary material was removed at a later time by eolian action or by infiltration. This process developed dynamically because travertine featuring a low resistance to varying temperatures in both climatic environments was exposed to temperature imact. The frost action caused a strength reduction by approx. 20% of the fresh materials, and in case of advanced weathering (HA), material is decomposed very soon. Similarly, above-zero temperatures reduced the fresh material strength by range 20% and even more than 60% for advanced weathering (HA). In those case for the weathered material integrity factor IRc = 0.12% for the weathered material. Laboratory tests of deterioration processes with application of ultrasonic methods and strength tests indicated that thermal changes were the major factor for a slow destabilisation of travertine structure in both climate zones. Sunlight operating at daytime combined with cooling down at night for surfaces of ancient structures over centuries - that was the reason for a significant loosening of inter-grain bonds and the strong eolian erosion, which was made even more serious by biological weathering, and which led to falling apart to irregular pieces due to absence of any maintenance work.
   Travertine rocks feature a relatively significant resistance to salt solutions. In highly porous materials, salt can freely crystallize inside voids without any damage to the structure. This positive feature is significant, in particular under moderate climate conditions where travertine used as an elevation material is exposed to adverse winter weather factors.