Opal-A rich additives used in ancient lime mortars

Abstract

Ancient stone and brick masonry mortars from three monuments in Konya, Central Anatolia dated to the Anatolian Selçuk Period (12th and 13th centuries AD) were examined for their raw material composition and durability characteristics to understand some characteristics of medieval mortar technology. Optical microscopy, XRD, SEM, EDX, FTIR and TGA analyses revealed that the mortars contained high percentage of lime binder totally carbonated into micritic calcite. Coarse and medium aggregates were mainly composed of sandstone and metamorphic rock fragments, quartz, feldspar and mica minerals. Opal-A was found in considerable amounts in the fine aggregates, likely not derived from the coarser ones but added separately. Pozzolanic activity of the fine aggregates was determined by conductometric measurements. Their ability to form C-S-H was observed by treating them with saturated Ca(OH)2 solution. Bulk density and total porosity measurements showed that the mortars were highly porous due to the use of high amount of lime. On the other hand, they possessed sufficient mechanical strength. Mechanical properties were determined by point load tests and ultrasonic pulse velocity measurements. They were expressed as uniaxial compressive strength (UCS) and modulus of elasticity (Emod) in MPa. The results were also discussed in terms of durability characteristics of the mortars. They were expressed with the use of uniaxial compressive strengths in dry and wet states, and total porosity values. The mortars were considered to have high durability to wetting and drying cycles but had poor durability to the crystallization of water-soluble salts.