Methodology of identification of natural and historic Portland cements. Application and study in mortars of Madrid and Barcelona

Abstract

Natural cement was patented in England in 1796, but did not arrive in Spain until 1835. Its arrival supposed a natural coexistence with the rest of traditional mortars that had been used (lime, hydraulic limes and gypsum). However, its use was not extended in time, and soon it was replaced by the use of artificial Portland cements. Although in Spain the natural cement came later, it was massively used in the decorations of historicist and modernist facades during the 19th and 20th century. Nowadays, after more than 100 years since its construction, it’s necessary to conserve all this heritage. In order to achieve a good restoration, it is essential to correctly identify the binders originally used. The restoration of these mortars with incompatible materials can cause irreparable damage to the original elements of the buildings. The aim of this research is the development of a simple, practical and economical method for the identification of natural cements and historic Portland cements mortars. We have use petrographic microscopy techniques in laboratory samples to establish the identification patterns of these cements. Then, this methodology has been applied in samples of buildings of Madrid and Barcelona where it is documented the use of historical cement mortars. The differences in the formation of alite and belite crystals between Portland and natural cements have been analyzed, as well as the differences in the petrographic textures between the cements of Madrid and Barcelona.