Dégradation et origine des matériaux de construction des monuments historiques

Abstract

The Byzantine wall and the Roman basilica are the main representative examples of historical sites in Tébessa (North-eastern Algeria), which pink limestones of Middle Turonian and carbonate tufas are the most used construction materials. In-situ investigations have shown the most common weathering forms are flaking, alveolisation, efflorescence, fracturing, discoloration, white crust, dusting, powdering and granular disintegration. These weathering forms are produced by the salt action (Gypsum and Halite) which are related to the petrophysical and textural properties of pink limestones and carbonate tufas. Quantification of degrees of weathering using physico-mechanical properties revealed that degradation is characterized by a decrease in density and increased porosity for pink limestone, while carbonate tufas are characterized by a decrease in density with the decrease in porosity. Schmidt's hammer revealed that the damage is medium to severe in both monuments studied. The petrophysical properties and durability are measured for both stone types which extracted from quarries. Porosity, capillary absorption coefficient, ultrasonic waves and uniaxial compression are used to characterize the petrophysical properties, and the salt crystallisation tests is used to estimate their durability. These properties are closely linked to the microstructure of the stone. Carbonate tufas show excellent durability under salt crystallization and lower mechanical strength than limestone. Limestone, on the other hand, despite its lower porosity and better mechanical strength, show lower durability values. While micropores contribute to the relatively lower value of sustainability; in tufas, macropores reduce the saline action on the porous structure and increase its durability. Our investigations have shown that the Byzantine wall and the Roman basilica require urgent conservation measures. Finally, in the ancient constructions of Tébessa, the pink limestone will be the most degraded than the carbonate tufas.