PHYSICAL, MECHANICAL AND MICROSTRUCTURAL CHARACTERIZATION OF BASILICA PLASTERS AND BOULEUTERION MORTARS IN SMYRNA AGORA

Abstract

Lime based plaster and mortar specimens from three different locations of Smyrna Agora excavations have been investigated within the scope of this study. A two-layer graffito plaster from Basilica (P1 inner layer, P2 outer layer) and two distinctive mortars from Bouleuterion were collected from the site. While one of the Bouleuterion mortars was masonry mortar from walls (BWM), other one was from the floor blockade (BBM – porous mortar). Physical and mechanical properties of plaster and mortar specimens such as water absorption, density and surface hardness and compressive strength have been determined. Thin section analyses were performed for mineralogical investigations. Aggregate particle size distribution of both plaster and mortar specimens were determined by sieve analysis. The fraction passing through 0.063 mm sieve was considered as the binder. Powder fractions of 0-0.063 mm and 0.063-0.125 mm were used in X-ray Diffraction (XRD) analysis for the comparison and characterization of binder and aggregate crystal structure respectively. The chemical composition of polished sections of plaster and mortar specimens were also investigated by Scanning Electron Microscope equipped with an Energy Dispersive Spectrometer (SEM-EDS). Test results showed that outer plaster layer (P2) is denser, harder and exhibited higher strength compared to inner plaster layer P1. This strength difference can be attributed to the possibly low water/lime ratio of P2 plaster in order to finish the outer surface of plaster by pressurized troweling. By this way, it is possible to obtain a smooth surface suitable for graffito applications. High compressive strength and surface hardness of Bouleuterion wall mortars (BWM) is due to the presence of crushed brick particles as aggregates which provides a good aggregate-matrix bonding. This improved bonding can be attributed to the pozzolanic activity of crushed brick particles with lime mortar. Dense matrix structure is also responsible for the relatively high mechanical performance of BWM. On the other hand, porous structure of floor blockade mortar located between stones results with low strength and hardness.