Effect of iron and organic matter on mineralogy and texture of replacement bricks for heritage conservation: The case of the Alhambra Formation soil (Granada, Spain)

Abstract

Throughout history, bricks have been an important part of monumental and vernacular architecture but often suffer alteration due to physico-chemical weathering and require replacement. Local soil could be used to fabricate compatible replacement bricks with similar physico-chemical characteristics as historic ceramics. Here the mineralogical and textural evolution of bricks prepared with local soil containing iron-oxyhydroxides and organic matter and fired between 800–1100 ºC are evaluated. The study provides direct evidence for solid state formation of anorthite in contact with carbonate grains and sheds light on the fate of iron compounds under oxidizing and reducing conditions (induced by the presence of organic matter) and their influence on the textural evolution of fired bricks. Brick durability and compatibility are discussed based on their hydric and mechanical performance. The findings of this study further the understanding of temperature-induced soil mineral changes and have practical implications for the design of compatible bricks for heritage conservation and new construction.