Environmental impact on the Roman monuments of Tarragona, Spain

Abstract

The extant remains of the Roman monuments of Tarragona, Spain are made of different types of Miocenic rocks from the quarries surrounding the city, which vary from calcarenite to bioclastic limestones, showing different degrees of dolomitization, depending on their diagenetic evolution. The decay of these monuments is highly dependent on the mineralogy and the fabric of the stone as well as on the environmental conditions to which the monument subjected. As a consequence, different forms of decay are observed on these monuments, namely, granular disintegration, differential erosion between sparitic and micritic areas of the rock, and development of black crust and orange patinas, some of them attributed to a sulfation process. A number of processes have been established as being responsible for the decay forms observed: sulfation on sheltered areas of the building in the urban environment; differential dilatation because of the NaCl of the marine spray that crystallizes inside the porosity; hydric and thermal expansion of the stone, both related to the amount and crystallinity of the clay minerals forming the rock matrix; and biocolonization on the stone surface. An empirical model is proposed to explain the decay forms studied in relation to these factors (rock and environment).