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Characterization of mortars used for the construction of Saithidai Heroon Podium (1st century AD) in ancient Messene, Peloponnesus, Greece
Materials Characterization 58 (2007) 1229 – 1239
Characterization of mortars used for the construction of Saithidai Heroon Podium (1st century AD) in ancient Messene, Peloponnesus, Greece I.C. Zamba a,⁎, M.G. Stamatakis a , F.A. Cooper b , P.G. Themelis c , C.G. Zambas d a
NKUA, Dept of Geology, Panepistimiopolis Ano Ilissia 157 84, Athens, Greece b Minessota University, USA c The University of Crete, 24100 Rethymno, Greece d 43Skiathou str, 11254, Athens, Greece Received 3 July 2007; accepted 6 July 2007
Abstract The Saithidai Heroon Podium is a Mausoleum dated to the Roman Period located in ancient Messene, Peloponnesus, Greece. Its outer walls were constructed with porous and massive limestone blocks with no mortar in the joints. The core of the podium was filled by rock chips to angular boulders of sandstone, limestone, sand, gravel and earthy groundmass material. The groundmass is mostly composed of quartz and calcite, with minor amounts of clay minerals. Small, irregular lime lumps also occur, composed of authigenic euhedral calcite crystal assemblages and rare sub-microscopic quartz fragments, or rod-like CaO/SiO2-rich mineral assemblages developed in pore spaces on fine-grained authigenic calcite crystals. The mortar used for the filling material of the Podium was poorly homogenized semi-hydraulic lime derived from the calcination of pure limestone and siliceous limestone fragments, possibly the waste material from the finishing of the building blocks of the Podium walls. © 2007 Elsevier Inc. All rights reserved. Keywords: Messene; Mortar; Lime lumps; SEM analysis
1. Introduction — archeological data The studied monument, Saithidai's Heroon-Mausoleum, dated from the Roman Period (1st Century AD), is located at the south end of the stadium of ancient Messene, western Pelloponesus, Greece. Of all the old ⁎ Corresponding author. Fax: +30 2102237167. E-mail addresses: [email protected] (I.C. Zamba), [email protected] (M.G. Stamatakis), [email protected] (F.A. Cooper), [email protected] (P.G. Themelis), [email protected] (C.G. Zambas). 1044-5803/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2007.07.004
cities in mainland Greece, Messene is known to have the largest number of grave monuments associated with public buildings such as the Asklepieion and the gymnasium-stadium complex [1]. Nowadays, we can observe the surviving Podium of the monument, forming a projection of the city walls as shown in Fig. 1, while Fig. 2 presents a view of the Heroon west side. The Heroon had the form of a Doric Temple with four columns in front and a cella. Herron Podium has dimensions of 16.70 × 10.60 m and it is up to 7.50 m high. Fig. 3 illustrates an architecture plan for the reconstruction of the monument [2].
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1.1. Podium walls The Podium's external walls were constructed by alternated courses of yellowish porous limestone and greyish massive limestone cut into well dressed blocks,
mined from nearby located quarries [4]. There is no mortar in the joints and the stone blocks are mostly wellpreserved. The architectural members, found scattered around the ruined podium during the recent excavations, were identified and a project of restoration is in progress
Fig. 1. Part of the archeological site of Messene [1,2]. The Saithidai Heroon is located in the southern side of the Stadium.
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Fig. 2. The Heroon viewed from the west.
[2,3,5,6]. However, there is an exception concerning the highest extant stone blocks, mainly the sandstone ones, which are highly damaged and removed from their original position. This is due to extensive stone-thievery, environmental factors and vegetation growth between the joints.
1.2. Podium core The interior (core) of the podium was filled by rock chips to angular boulders of sandstone and limestone, sand, gravel and earthy material bounded with a beige– off brown to white material that was originally
Fig. 3. An architecture reconstruction of the Heroon and the Podium [3].
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characterised as a kind of “loose’ lime mortar. Figs. 4 and 5 show two stratigraphic columns drawn by Cooper in two sites (trench F and trench G) of the Heroon core [3]. Rock fragments of the Heroon core (western wall) bounded by an earthy unsorted sandy material are depicted in Figs. 6 7 8 and 9.
The Podium is based on natural bedrock, which is inclined from north to south and east to west, so that the higher part of the construction, corresponding to 20 courses, appears on the SW corner. The extant part of the external walls reaches up to the18th course in the eastside, the 8th in the south and the 14th in the west side.
Fig. 4. Stratigraphic column drawn by Cooper F. in Trench F of the Heroon core. Note that the original field descriptions [3], as “soil” and “mortar” samples, were precisely identified after SEM and XRD analyses.
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Fig. 5. Stratigraphic column drawn by Cooper F. in Trench G of the Heroon core [3].
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Fig. 6. Angular and partly finished rock fragments filling the Heroon core and bounded by an earthy unconsolidated and unsorted sandy material. Western wall of the Heroon.
The aim of the present study was to identify the nature of the filling material used for the construction of the core of the Saithidai Heroon Podium. 2. Materials characterization During archaeological excavations in the filling material during the late 1990's, 25 samples of about 100 g each were extracted from 5 trenches dug up to 3 m deep. During 2004, 10 additional samples from the core were obtained from the western side of the Podium. All samples were dried at temperatures of 70 °C for 24 h. To identify the nature of each component, earthy loose material, sand and gravel, rock fragments, and
lime lumps were separated. Each material was ground in an agate mill and the powders were mineralogically analysed using X-Ray Diffraction (SIEMENS D-5000, conditions 40 kV, 40 mA, 1 step/s). To identify the texture of the mineral aggregates the shape of the crystals and their chemistry, Scanning Electron Microcopy analytical techniques were applied on chipped rock fragments using the JEOL JSM-5600 instrument, equipped with Energy Dispersive X-ray Microanalysis (EDX) system OXFORD LINK™ ISIS™ 300 and software package of quantitative analysis, OXFORD SEMQuant™ with ZAF correction. The conditions of analysis were: 20 kV (accelerating voltage), 0.5 nA (beam current), 50 s (lifetime) and b2 μm (beam diameter).
Fig. 7. Enlarged detail of Fig. 6.
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Fig. 8. Earthy mortar containing rare and small lime lumps (white spots close to the coin). Note the chaotic appearance of the rock fragments and the unsorted binding matrix.
2.1. Earthy loose material — sand and gravel
2.2. Rock fragments
In general, the earthy material was inhomogeneous with weak to moderate cohesiveness and beige to white colour. It contained silica sand, angular limestone fragments of gravel size, and clayey material. Pozzolanic additives of volcanic origin were not detected. The X-Ray Diffraction analysis of the mixed material has shown that it is mostly composed of quartz and calcite, whereas chlorite and illite are present in subordinate amounts. Samples extracted from lower levels of the Podium have the same mineralogy, but they differ in the percentages of each of the three components (detrital quartz, clay minerals and calcite). The results are shown in Table 1.
Angular rock fragments predominate in the filling material varying in size from a few cm up to 40 cm in diameter. They were characterized as massive limestone that has the same nature as the Cretaceous limestone building blocks of the outer walls of the Podium [4]. Even though there are cherts in association with the limestone in the nearby slopes, fragments of a siliceous nature were not detected. Platy pottery fragments up to 2 cm in diameter were rarely found, hosted in the fine sand/clayey matrix. X-Ray Diffraction analysis was implemented to determine the exact mineralogy of the calcareous rock fragments. As seen in Table 1, the calcareous rock is an almost pure limestone composed of calcite with traces of quartz.
Fig. 9. Small lime lumps bounded by an earthy unsorted material in another site of the Podium core.
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Table 1 XRD mineralogical analysis of filling material, Saithidai Heroon Material
Quartz
Illite
Chlorite
Calcite
Earthy loose Rock fragments Sand & gravel Lime lumps
Major Trace Major Trace
Medium – – –
Medium – – –
Major Major Major Major
SEM followed by microprobe analysis (SEM-EDS analysis). According to the analytical results, the lime lumps are diverse in nature. Hence, one group of lumps is composed of solely calcite and traces of quartz grains (non-hydraulic lime), and the other group contains additionally CaO–SiO2-rich compounds, typical of hydraulic lime. 2.4. Non-hydraulic lime lumps
2.3. Lime lumps Within the sandy–clayey incoherent matrix, small and rare whitish lime lumps are developed, sometimes exhibiting well-developed desiccation cracks. To determine the texture and composition of the lime lump five samples were examined by a binocular microscope and
SEM analysis revealed that several lime lumps of less than 2 cm in size extracted from the loose mortar of the Podium are solely composed of neoformed euhedral calcite crystal assemblages, mostly in rhombohedral form, and rare sub-microscopic quartz fragments (Figs. 10A, B, C, D).
Fig. 10. (A) Euhedral calcite growths as rhombohedral crystals in pores of small lime lumps, Heroon Podium. (B): Neoformed euhedral calcite crystal assemblages. (C): Rhombohedral calcite crystals composing the lime lumps extracted from the mortar of the Podium. (D): Euhedral calcite aggregates revealed by the SEM analysis of the lime lumps.
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crystals, indicating a late stage formation (Fig. 12A, B, C, D). Similar needle or rod-like forms had been described and detected during initial carbonation of hydraulic lime [7] and in microstructures in pozzolanic mortars [8]. In addition, in lime lumps located close to the Heroon walls, where humidity is high all year round due to hydrological reasons, algal filaments with diameter b 2 μm are present, grown on pre-existent calcite crystals, Fig. 13A, B. The organic matter of the algae filaments was diagenetically transformed to calcite by calcification. 3. Results and discussion
Fig. 11. (A): Original micritic lime crystals transformed to sparry calcite by aging. Within the lime lumps, secondary calcified spherulites, were rarely determined. (B): Sub-microscopic spherulites of CaCO3 composition grown as secondary microbial deposit on rhombohedral calcite in a non-hydraulic lime lump, Heroon Podium.
It is suggested that the original micritic lime crystals have been transformed to sparry calcite by aging (Fig. 11A, B). Within the lime lumps, secondary calcified spherulites, most likely representing bacteria replacements (because of the shape, texture and size of the microparticles) were also rarely determined (Fig. 11B). 2.5. Hydraulic lime lumps Another group of lime lumps of less than 2 cm in size that were extracted close to the walls at the SW part of the Podium, were examined by SEM. This indicated that they are composed of rod-like mineral assemblages that form thin to thick networks with CaO–SiO2 (plus minor amounts of Al2O3, Fe2O3, MgO and K2O) composition, possibly CSH. They are mostly developed as pore fillings and cover earlier formed euhedral calcite
The general view of the Podium filling material is that it represents a chaotic mixture of sharp-edged pieces of rocks consisting of either porous sandy limestone or most commonly non-graduated pieces of grey massive limestone that are actually rock chips produced by the curving of the building blocks of the monument. These pieces are bounded by siliceous earthy material and small lime lumps. Hughes and Leslie [9] and Leslie and Gibbons [10] have described as lime lumps the white, irregular to spherical particles of b 2 cm in diameter included in historic mortars that do not contain aggregate inclusions, visible with the naked eye. It is not clear if the lime lumps detected had a role as a component in the construction, or if they were a kind of aggregate in the construction. According to Leslie and Gibbons [10], who make a distinction between lime inclusions and “active” binder in historic mortars, the Podium mortar lime lumps can be classified as a form of aggregate, rather than a functional binder. Hughes and Leslie [9] demonstrated that the abundantly occurring lime lumps in historic mortars, can have a variety of textures that reflect the nature of the original limestone source rock. The results obtained by the microscopic examination of the Messene Podium mortar are consistent with that. Hence, it is suggested that the lime lumps that contain CaO–SiO2 (plus minor Al2O3, Fe2O3, MgO and K2O) rods in abundance, covering early formed calcite in pore spaces, represent a hydraulic lime, most likely originating from the calcination of impure limestone. It is plausible to suggest as a possible calcareous source in the place the sandy (siliceous) limestone fragments resulted from the fashioning of the building blocks used in the Podium walls. On the other hand, the massive (pure) limestone fragments in the fill of the Podium resulted from the fashioning of the building blocks that form alternate courses with the sandy limestone in the Podium walls.
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4. Conclusions The literature data, combined with field work, measurements and laboratory analysis lead to the following conclusions: • The Podium walls were constructed by alternated courses of massive and porous sandy limestone blocks, fitted without any mortar. • The core of the Podium is filled by unsorted large and small broken blocks, partially trimmed, angular rock fragments and lime mortar. • The aggregates of the mortar have a chaotic appearance, are poorly sorted and are mostly composed of massive and porous sandy limestone angular fragments.
• The fine sand and clay fraction of the mortar is composed of quartz that predominates and subordinate calcite, illite and chlorite. • Rounded brick fragments rarely occur as aggregates in the mortar. • The lime mortar contains visible whitish, porous and earthy lime lumps up to 2–3 cm in diameter. Microscopic examination of the lumps revealed that part of the lumps contains only fine-grained euhedral CaCO3 crystal assemblages, whereas the rest of the lumps contain, in addition, rod-like CaO–SiO2-rich compounds that cover early calcite crystals in pore spaces. • Because of the diversity of the original calcined limestone rocks used to produce the Podium lime, a mixed product resulted after calcining that can be
Fig. 12. (A): Rod-like forms of CaO–SiO2 (plus minor amounts of Al2O3, Fe2O3, MgO and K2O). (B): Needle-like mineral assemblages of CaO– SiO2 composition forming thin to thick networks. (C): Needle-like CaO–SiO2 aggregates developed as pore fillings. (D): Rod-like forms of CaO– SiO2 covering earlier formed euhedral calcite crystals.
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poorly homogenized semi-hydraulic lime derived from the calcinations of pure limestone and sandy (siliceous) limestone fragments, probably the waste material generated during the finishing of the building blocks of the Podium walls. Acknowledgments Thanks are expressed by the authors to the staff of the archaeological museum of Messene for their helping during field work. We also thank Mr. J. Mitsis and E. Michailidis, NKUA, for their assistance in XRD and SEM analysis, respectively. References
Fig. 13. (A): Calcified algal filaments developed along with the CaO– SiO2-rich rods on fine-grained calcite. (B): Algal filaments grown on pre-existent calcite crystals.
characterized as semi-hydraulic lime with unknown percentage of non- hydraulic and hydraulic lime in the final mixture. The diversity of the lime used to fill the core of Heroon Podium of Messene was “fossilized” in the lumps and reflects the diversity of the chemical/mineralogical composition of the original limestone source rock. • According to the present study, the mortar used for the filling material of the Podium of the Heroon was
[1] Themelis P. Heroes and hero shrines in Messene (in Greek with a summary in English). Athens; 2000. p. 2. [2] Themelis P. Heroes and hero shrines in Messene (in Greek with a summary in English). Athens; 2000. p. 102–13. [3] Zambas C. Structural study for the restoration of Saithidai's Heroon (in Greek). Athens; 2003. [4] Higgins MD, Higgins R. A geological companion to Greece and Aegean. London: Duckworth; 1996. p. 240. [5] Cooper F. Scamilli impares at the Heroon at Messene. Appearance and essence refinements of classical architecture — curvature. Philadelphia: L. Haselberger; 1997. p. 97–112. [6] Themelis P. The Ancient Messene. Athens: Ministry of Culture, TAP Publications; 1999. p. 155. [7] Radonjic M, Hallam KR, Allen GC, Hayward R. Mechanism of carbonation in lime-based mortars. Proc 8th Euroseminar on Microscopy Applied to Building Materials. Athens; September 4–7 2001. p. 465–75. [8] Stefanidou M. Study of microstructure and mechanical properties of traditional repair mortars. Unpublished Ph.D. Thesis, Civil Engineering Department, Aristotle University of Thessaloniki, Thessaloniki, Greece 2000; p. 345. [9] Hughes J, Leslie AB. The petrography of lime inclusions in historic lime based mortars. Proc 8th Euroseminar on Microscopy Applied to Building Materials. Athens; September 4–7 2001. p. 359–64. [10] Leslie AB, Gibbons P. Mortar analysis and repair specification in the conservation of Scottish historic buildings. In: Historic Mortars: Characteristics and Tests. Proc Int RILEM Workshop, Bartos, PJM, Groot CJW Hughes JJ editors. Paisley, May 1999. RILEM Publications; 2000, p. 273–280.
Characterization of mortars used for the construction of Saithidai Heroon Podium (1st century AD) in ancient Messene, Peloponnesus, Greece I.C. Zamba a,⁎, M.G. Stamatakis a , F.A. Cooper b , P.G. Themelis c , C.G. Zambas d a
NKUA, Dept of Geology, Panepistimiopolis Ano Ilissia 157 84, Athens, Greece b Minessota University, USA c The University of Crete, 24100 Rethymno, Greece d 43Skiathou str, 11254, Athens, Greece Received 3 July 2007; accepted 6 July 2007
Abstract The Saithidai Heroon Podium is a Mausoleum dated to the Roman Period located in ancient Messene, Peloponnesus, Greece. Its outer walls were constructed with porous and massive limestone blocks with no mortar in the joints. The core of the podium was filled by rock chips to angular boulders of sandstone, limestone, sand, gravel and earthy groundmass material. The groundmass is mostly composed of quartz and calcite, with minor amounts of clay minerals. Small, irregular lime lumps also occur, composed of authigenic euhedral calcite crystal assemblages and rare sub-microscopic quartz fragments, or rod-like CaO/SiO2-rich mineral assemblages developed in pore spaces on fine-grained authigenic calcite crystals. The mortar used for the filling material of the Podium was poorly homogenized semi-hydraulic lime derived from the calcination of pure limestone and siliceous limestone fragments, possibly the waste material from the finishing of the building blocks of the Podium walls. © 2007 Elsevier Inc. All rights reserved. Keywords: Messene; Mortar; Lime lumps; SEM analysis
1. Introduction — archeological data The studied monument, Saithidai's Heroon-Mausoleum, dated from the Roman Period (1st Century AD), is located at the south end of the stadium of ancient Messene, western Pelloponesus, Greece. Of all the old ⁎ Corresponding author. Fax: +30 2102237167. E-mail addresses: [email protected] (I.C. Zamba), [email protected] (M.G. Stamatakis), [email protected] (F.A. Cooper), [email protected] (P.G. Themelis), [email protected] (C.G. Zambas). 1044-5803/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2007.07.004
cities in mainland Greece, Messene is known to have the largest number of grave monuments associated with public buildings such as the Asklepieion and the gymnasium-stadium complex [1]. Nowadays, we can observe the surviving Podium of the monument, forming a projection of the city walls as shown in Fig. 1, while Fig. 2 presents a view of the Heroon west side. The Heroon had the form of a Doric Temple with four columns in front and a cella. Herron Podium has dimensions of 16.70 × 10.60 m and it is up to 7.50 m high. Fig. 3 illustrates an architecture plan for the reconstruction of the monument [2].
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1.1. Podium walls The Podium's external walls were constructed by alternated courses of yellowish porous limestone and greyish massive limestone cut into well dressed blocks,
mined from nearby located quarries [4]. There is no mortar in the joints and the stone blocks are mostly wellpreserved. The architectural members, found scattered around the ruined podium during the recent excavations, were identified and a project of restoration is in progress
Fig. 1. Part of the archeological site of Messene [1,2]. The Saithidai Heroon is located in the southern side of the Stadium.
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Fig. 2. The Heroon viewed from the west.
[2,3,5,6]. However, there is an exception concerning the highest extant stone blocks, mainly the sandstone ones, which are highly damaged and removed from their original position. This is due to extensive stone-thievery, environmental factors and vegetation growth between the joints.
1.2. Podium core The interior (core) of the podium was filled by rock chips to angular boulders of sandstone and limestone, sand, gravel and earthy material bounded with a beige– off brown to white material that was originally
Fig. 3. An architecture reconstruction of the Heroon and the Podium [3].
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characterised as a kind of “loose’ lime mortar. Figs. 4 and 5 show two stratigraphic columns drawn by Cooper in two sites (trench F and trench G) of the Heroon core [3]. Rock fragments of the Heroon core (western wall) bounded by an earthy unsorted sandy material are depicted in Figs. 6 7 8 and 9.
The Podium is based on natural bedrock, which is inclined from north to south and east to west, so that the higher part of the construction, corresponding to 20 courses, appears on the SW corner. The extant part of the external walls reaches up to the18th course in the eastside, the 8th in the south and the 14th in the west side.
Fig. 4. Stratigraphic column drawn by Cooper F. in Trench F of the Heroon core. Note that the original field descriptions [3], as “soil” and “mortar” samples, were precisely identified after SEM and XRD analyses.
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Fig. 5. Stratigraphic column drawn by Cooper F. in Trench G of the Heroon core [3].
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Fig. 6. Angular and partly finished rock fragments filling the Heroon core and bounded by an earthy unconsolidated and unsorted sandy material. Western wall of the Heroon.
The aim of the present study was to identify the nature of the filling material used for the construction of the core of the Saithidai Heroon Podium. 2. Materials characterization During archaeological excavations in the filling material during the late 1990's, 25 samples of about 100 g each were extracted from 5 trenches dug up to 3 m deep. During 2004, 10 additional samples from the core were obtained from the western side of the Podium. All samples were dried at temperatures of 70 °C for 24 h. To identify the nature of each component, earthy loose material, sand and gravel, rock fragments, and
lime lumps were separated. Each material was ground in an agate mill and the powders were mineralogically analysed using X-Ray Diffraction (SIEMENS D-5000, conditions 40 kV, 40 mA, 1 step/s). To identify the texture of the mineral aggregates the shape of the crystals and their chemistry, Scanning Electron Microcopy analytical techniques were applied on chipped rock fragments using the JEOL JSM-5600 instrument, equipped with Energy Dispersive X-ray Microanalysis (EDX) system OXFORD LINK™ ISIS™ 300 and software package of quantitative analysis, OXFORD SEMQuant™ with ZAF correction. The conditions of analysis were: 20 kV (accelerating voltage), 0.5 nA (beam current), 50 s (lifetime) and b2 μm (beam diameter).
Fig. 7. Enlarged detail of Fig. 6.
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Fig. 8. Earthy mortar containing rare and small lime lumps (white spots close to the coin). Note the chaotic appearance of the rock fragments and the unsorted binding matrix.
2.1. Earthy loose material — sand and gravel
2.2. Rock fragments
In general, the earthy material was inhomogeneous with weak to moderate cohesiveness and beige to white colour. It contained silica sand, angular limestone fragments of gravel size, and clayey material. Pozzolanic additives of volcanic origin were not detected. The X-Ray Diffraction analysis of the mixed material has shown that it is mostly composed of quartz and calcite, whereas chlorite and illite are present in subordinate amounts. Samples extracted from lower levels of the Podium have the same mineralogy, but they differ in the percentages of each of the three components (detrital quartz, clay minerals and calcite). The results are shown in Table 1.
Angular rock fragments predominate in the filling material varying in size from a few cm up to 40 cm in diameter. They were characterized as massive limestone that has the same nature as the Cretaceous limestone building blocks of the outer walls of the Podium [4]. Even though there are cherts in association with the limestone in the nearby slopes, fragments of a siliceous nature were not detected. Platy pottery fragments up to 2 cm in diameter were rarely found, hosted in the fine sand/clayey matrix. X-Ray Diffraction analysis was implemented to determine the exact mineralogy of the calcareous rock fragments. As seen in Table 1, the calcareous rock is an almost pure limestone composed of calcite with traces of quartz.
Fig. 9. Small lime lumps bounded by an earthy unsorted material in another site of the Podium core.
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Table 1 XRD mineralogical analysis of filling material, Saithidai Heroon Material
Quartz
Illite
Chlorite
Calcite
Earthy loose Rock fragments Sand & gravel Lime lumps
Major Trace Major Trace
Medium – – –
Medium – – –
Major Major Major Major
SEM followed by microprobe analysis (SEM-EDS analysis). According to the analytical results, the lime lumps are diverse in nature. Hence, one group of lumps is composed of solely calcite and traces of quartz grains (non-hydraulic lime), and the other group contains additionally CaO–SiO2-rich compounds, typical of hydraulic lime. 2.4. Non-hydraulic lime lumps
2.3. Lime lumps Within the sandy–clayey incoherent matrix, small and rare whitish lime lumps are developed, sometimes exhibiting well-developed desiccation cracks. To determine the texture and composition of the lime lump five samples were examined by a binocular microscope and
SEM analysis revealed that several lime lumps of less than 2 cm in size extracted from the loose mortar of the Podium are solely composed of neoformed euhedral calcite crystal assemblages, mostly in rhombohedral form, and rare sub-microscopic quartz fragments (Figs. 10A, B, C, D).
Fig. 10. (A) Euhedral calcite growths as rhombohedral crystals in pores of small lime lumps, Heroon Podium. (B): Neoformed euhedral calcite crystal assemblages. (C): Rhombohedral calcite crystals composing the lime lumps extracted from the mortar of the Podium. (D): Euhedral calcite aggregates revealed by the SEM analysis of the lime lumps.
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crystals, indicating a late stage formation (Fig. 12A, B, C, D). Similar needle or rod-like forms had been described and detected during initial carbonation of hydraulic lime [7] and in microstructures in pozzolanic mortars [8]. In addition, in lime lumps located close to the Heroon walls, where humidity is high all year round due to hydrological reasons, algal filaments with diameter b 2 μm are present, grown on pre-existent calcite crystals, Fig. 13A, B. The organic matter of the algae filaments was diagenetically transformed to calcite by calcification. 3. Results and discussion
Fig. 11. (A): Original micritic lime crystals transformed to sparry calcite by aging. Within the lime lumps, secondary calcified spherulites, were rarely determined. (B): Sub-microscopic spherulites of CaCO3 composition grown as secondary microbial deposit on rhombohedral calcite in a non-hydraulic lime lump, Heroon Podium.
It is suggested that the original micritic lime crystals have been transformed to sparry calcite by aging (Fig. 11A, B). Within the lime lumps, secondary calcified spherulites, most likely representing bacteria replacements (because of the shape, texture and size of the microparticles) were also rarely determined (Fig. 11B). 2.5. Hydraulic lime lumps Another group of lime lumps of less than 2 cm in size that were extracted close to the walls at the SW part of the Podium, were examined by SEM. This indicated that they are composed of rod-like mineral assemblages that form thin to thick networks with CaO–SiO2 (plus minor amounts of Al2O3, Fe2O3, MgO and K2O) composition, possibly CSH. They are mostly developed as pore fillings and cover earlier formed euhedral calcite
The general view of the Podium filling material is that it represents a chaotic mixture of sharp-edged pieces of rocks consisting of either porous sandy limestone or most commonly non-graduated pieces of grey massive limestone that are actually rock chips produced by the curving of the building blocks of the monument. These pieces are bounded by siliceous earthy material and small lime lumps. Hughes and Leslie [9] and Leslie and Gibbons [10] have described as lime lumps the white, irregular to spherical particles of b 2 cm in diameter included in historic mortars that do not contain aggregate inclusions, visible with the naked eye. It is not clear if the lime lumps detected had a role as a component in the construction, or if they were a kind of aggregate in the construction. According to Leslie and Gibbons [10], who make a distinction between lime inclusions and “active” binder in historic mortars, the Podium mortar lime lumps can be classified as a form of aggregate, rather than a functional binder. Hughes and Leslie [9] demonstrated that the abundantly occurring lime lumps in historic mortars, can have a variety of textures that reflect the nature of the original limestone source rock. The results obtained by the microscopic examination of the Messene Podium mortar are consistent with that. Hence, it is suggested that the lime lumps that contain CaO–SiO2 (plus minor Al2O3, Fe2O3, MgO and K2O) rods in abundance, covering early formed calcite in pore spaces, represent a hydraulic lime, most likely originating from the calcination of impure limestone. It is plausible to suggest as a possible calcareous source in the place the sandy (siliceous) limestone fragments resulted from the fashioning of the building blocks used in the Podium walls. On the other hand, the massive (pure) limestone fragments in the fill of the Podium resulted from the fashioning of the building blocks that form alternate courses with the sandy limestone in the Podium walls.
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4. Conclusions The literature data, combined with field work, measurements and laboratory analysis lead to the following conclusions: • The Podium walls were constructed by alternated courses of massive and porous sandy limestone blocks, fitted without any mortar. • The core of the Podium is filled by unsorted large and small broken blocks, partially trimmed, angular rock fragments and lime mortar. • The aggregates of the mortar have a chaotic appearance, are poorly sorted and are mostly composed of massive and porous sandy limestone angular fragments.
• The fine sand and clay fraction of the mortar is composed of quartz that predominates and subordinate calcite, illite and chlorite. • Rounded brick fragments rarely occur as aggregates in the mortar. • The lime mortar contains visible whitish, porous and earthy lime lumps up to 2–3 cm in diameter. Microscopic examination of the lumps revealed that part of the lumps contains only fine-grained euhedral CaCO3 crystal assemblages, whereas the rest of the lumps contain, in addition, rod-like CaO–SiO2-rich compounds that cover early calcite crystals in pore spaces. • Because of the diversity of the original calcined limestone rocks used to produce the Podium lime, a mixed product resulted after calcining that can be
Fig. 12. (A): Rod-like forms of CaO–SiO2 (plus minor amounts of Al2O3, Fe2O3, MgO and K2O). (B): Needle-like mineral assemblages of CaO– SiO2 composition forming thin to thick networks. (C): Needle-like CaO–SiO2 aggregates developed as pore fillings. (D): Rod-like forms of CaO– SiO2 covering earlier formed euhedral calcite crystals.
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poorly homogenized semi-hydraulic lime derived from the calcinations of pure limestone and sandy (siliceous) limestone fragments, probably the waste material generated during the finishing of the building blocks of the Podium walls. Acknowledgments Thanks are expressed by the authors to the staff of the archaeological museum of Messene for their helping during field work. We also thank Mr. J. Mitsis and E. Michailidis, NKUA, for their assistance in XRD and SEM analysis, respectively. References
Fig. 13. (A): Calcified algal filaments developed along with the CaO– SiO2-rich rods on fine-grained calcite. (B): Algal filaments grown on pre-existent calcite crystals.
characterized as semi-hydraulic lime with unknown percentage of non- hydraulic and hydraulic lime in the final mixture. The diversity of the lime used to fill the core of Heroon Podium of Messene was “fossilized” in the lumps and reflects the diversity of the chemical/mineralogical composition of the original limestone source rock. • According to the present study, the mortar used for the filling material of the Podium of the Heroon was
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