Natural Cement in Portugal: Context in Cement Production and Architectural Use

Natural cement, also known as “Roman cement”, was used across Europe during a historic period, mainly in many building facades, due to its hydraulic properties and aesthetic qualities. In Portugal, the use of natural cement occurred in buildings from the second half of the 19th century to the beginning of the 20th century, a period during which the use of lime binders decreased and before the massive use of Portland cement. Recent conservation and rehabilitation actions resulting from necessary interventions in heritage buildings from this period have played an important role in revealing evidence of the use of natural cement and clarifying the lacunae of information about this material. Due to the inadequate use of reparation materials in previous conservation and rehabilitation interventions, this study summarizes the historical production, study, and use of natural cement in Portugal. Natural cement results from the calcination of clay-rich limestone (marlstone) without any compositional changes after extraction, distinguishing itself from hydraulic lime due to its higher clay content and allowing for the formation of higher quantities of hydraulic reactive phases without free lime. Although this topic has been approached at a European level, mainly focusing on the production and use of natural cement in Central Europe, in Portugal, it is still necessary to produce and disseminate information on this specific subject. Therefore, this study focuses on the evolution of cement production in Portugal and an analysis of the existing knowledge of the binders used in architectural heritage based on the scientific and historical bibliography.