1A series of laboratory tests mandated by the Ephorate of Antiquities of Cyclades were undertaken in 2017 to determine the characteristics and properties of four samples of earth‑based material from the joints of ancient walls at the archaeological site of Delos. Based on the experimental results, three variations of an earth‑based mortar were tested in order to select the most compatible one in terms of characteristics and properties, for the stabilization of said structures.
2Four samples were taken from the site in July 2017 by archaeologists J.‑Ch. Moretti and P. Karvonis. Samples ∆Πκ1 & ∆Πκ3 were taken from the area around the theatre, from residence VID (wall between c and d) and residence IIB (wall between m and i), respectively. Samples ∆Πκ2 & ∆Πκ4 were taken from the area of the coastal commercial district, from the commercial building with bathtub (room VII, east wall) and the commercial building with columns (north stairwell, east wall) respectively (fig. 1).
Fig. 1 — Location of sampling (a) samples ∆Πκ2 and ∆Πκ4 and (b) samples ∆Πκ1 and ∆Πκ3.
EFA, J.‑Ch. Moretti and P. Karvonis d’après Moretti et al., EAD XLIII (2015).
3The analysis of the authentic materials included:
- 1 Teutonico 1988, p. 73.
- 2 Houben, Guillaud 1989, p. 58.
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Mineralogical analysis by XRD Porosity measurement by mercury porosimeter Simple mortar analysis1 Granulometry Atterberg limit tests2 Microscopy Qualitative and semi-quantitative soluble salt analysis by conductivity measurement and spot tests Particle size analysis by laser diffraction for fine particles Ø<75 µm to determine the percentage of clay content (particle size Ø<6 µm). |
4It was not possible to conduct measurements of specific apparent weight, water absorption capacity at saturation, or tensile strength on any samples, as they were not cohesive enough.
5The design of compatible repair mortars was based on the experimental results of the authentic materials. The experimental program for the proposed stabilization mortar encompassed the following:
- 3 EN 1015‑11 (2005) Methods of test for mortar for masonry-Part 11: Determination of flexural and com (...)
- 4 BS EN 1936:1999 Natural stone test methods Determination of real density, apparent density and of t (...)
- 5 ΕΛΟΤ 747 Natural stones and aggregates-determination of water absorption at saturation.
- 6 Sodium sulphate immersion-drying cycles, Commission 25‑PEM, Test No V. 1b.
- 7 Pavia, Treacy 2006.
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Compressive and tensile strength at 28 days3 Porosity measurement by Mercury porosimeter Apparent specific weight measurement4 Water absorption at saturation5 Sodium sulphate resistance test6, Thermal cycling or wetting and drying cycles7. |
6XRD analysis was used to identify the crystalline phases of minerals, and in this case the content and type of alumnosilicates in order to determine their ability to expand and contract and therefore affect the behavior of the material when subjected to wetting-drying cycles. Clay minerals are hydrated aluminum silicates, which give plasticity to soil and earth-based materials. They are the weathering products of igneous rocks which contain minerals such as mica, feldspars, muscovite etc. which through ion exchange induce the formation of secondary clays. These can be broadly divided in three categories, smectites, kaolinites and illites, each category has different water absorption and expansion characteristics.
7Atterberg limits tests establish empirically the behavior of soils as correlated to moisture content as the material transitions from solid, semi-solid, plastic and liquid states with the concomitant differences in strength, consistency and behavior. Atterberg limit tests accurately define the boundaries between these states using moisture contents at the points where the physical changes occur. The Liquid limit (LL) is the boundary between fluid and soft soil, the plastic limit (PL) the boundary between soft and malleable soil at which stage the material can be rolled in rolls of Ø3 mm without breaking. The shrinkage limit lies at the end of the spectrum between malleable and rigid soil (Warren 1999). The plasticity index is calculated by subtracting the value of the LL from the PL and can qualify cohesiveness, expansion and activity.
8The most important parameters in assessing plasticity of a soil sample are (a) the mineralogy and (b) the percentage of clay in terms of particle size which is defined as Ø<6 µm which in turn affects water absorption and therefore expansion/contraction and cohesion.
9The analyses were undertaken both at collaborating laboratories and as well as on our premises. XRD analysis of the fine material (Ø<75 µm) following wet sieving and porosity measurements were done at the Research Development and Quality Department of Titan Cement Co. by K. Koutsodontis and C. Naoumi as well as measurements of mechanical strengths of proposed mortar by Dr N. Pistofides. The rest of the analyses (microscopy, simple mortar analysis by dry and wet sieving, aggregate granulometry and soluble salts analysis) as well as the casting of the proposed stabilization mortars were done on our premises.
10Three repair mortar mixes with slight variations in the binder composition were tested in order to select the most compatible with the authentic material in term of appearance, texture and composition as well durability, hydric behavior and resistance to soluble salt deterioration.
11All four reddish-brown samples of earth mortars (figs. 2 and 3) were similar both in appearance and characteristics, they were quite friable materials with a clay/silt content of 20‑33% w/w. Sample ∆Πκ1 was less plastic (table 1) and contained lighter colored aggregates.
Table 1 — Porosity, granulometry and Atterberg test results of authentic materials.
Sample |
Total porosity (%) & med pore Ø (µm) |
Granulometry |
Atterberg limits |
Clay 0‑6µm (%) |
Silt 6‑75µm (%)
|
Sand 75µm‑ 2mm (%) |
Gravel 2‑10mm (%) |
PL (%) |
LL (%) |
PI (%) |
∆ΠΚ1 |
25,63 34,24 |
3,3 |
10,4 |
72,2 |
14,1 |
- |
- |
- |
∆ΠΚ2 |
22,72 8,8 |
3,6 |
11,2 |
70,9 |
14,3 |
20 |
36 |
16 |
∆ΠΚ3 |
21,56 11,9 |
2,1 |
9,8 |
70,7 |
17,4 |
19,5 |
35 |
16 |
∆ΠΚ4 |
23,55 9 |
4,1 |
11,4 |
67 |
17,5 |
20,5 |
36 |
15 |
Note: The percentage of constituents was obtained by the combination of sieving for the particles >75 µm and laser grain size analysis for particles < 75 µm.
Fig. 2 — Sample ∆ΠΚ2.
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Fig. 3 — Sample ∆ΠΚ3.
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12All samples contain aggregates from the dissolution of granites and schist (figs. 4 and 5) which comprise the subsoil of the island (Higgins M., Higgins R. 1996). XRD analysis of the four samples (table 2) yielded quartz (~23‑30%), calcite (7,4‑31%) and clay minerals (~23%) mostly illite and albite which are moderately expansive. The presence of sanidine, anorthite and microcline (mica) present in relatively high quantities (~15‑28%), are attributed to the aggregates, the erosion products of igneous and metamorphic rocks. The maximum grain size was Ø10 mm, the median ranged from Ø 0,23-0,44 mm (fig. 6) and all samples contained larger fragments of said rocks (dimensions 1,5‑2 cm). Examination under the microscope revealed the presence of charcoal (fig. 7) and lime clumps (fig. 8) in all samples while in sample ∆ΠΚ3 sea‑shell fragments and straw were identified. The amount of binder (lime) which ranged from 6‑10% w/w can be approximated by the weight loss during wet sieving, with a mild acid, while the ratio of fines (clay and silt) to aggregate ranged from 1:1,5 to 1:3 w/w.
Table 2 — XRD analysis of the four samples.
|
∆ΠΚ1 |
∆ΠΚ2 |
∆ΠΚ3 |
∆ΠΚ4 |
Minerals |
% Rietveld |
Quartz |
23,1 |
31,3 |
31,6 |
28,9 |
Calcite |
31,0 |
11,5 |
7,4 |
12,3 |
Aragonite |
8,9 |
2,0 |
0,5 |
1,0 |
Dolomite |
0,0 |
0,1 |
0,1 |
0,2 |
Albite |
14,0 |
11,5 |
14,5 |
14,6 |
Illite |
7,4 |
9,5 |
7,8 |
12,3 |
Muscovite |
0,1 |
2,8 |
2,1 |
3,9 |
Kaolinite |
1,6 |
0,9 |
0,5 |
1,7 |
Magnesite |
0,1 |
0,0 |
0,1 |
0,1 |
Hemaite |
0,3 |
0,3 |
0,4 |
0,2 |
Sanidine |
2,3 |
8,1 |
8,4 |
5,1 |
Goethite |
0,3 |
0,2 |
0,2 |
0,6 |
Microcline intermediate |
4,5 |
7,4 |
11,0 |
7,2 |
Anorthite |
6,4 |
14,5 |
15,5 |
11,7 |
Fig. 4 — Sample ∆ΠΚ2 aggregates after dry and wet sieving.
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Fig. 5 — Sample ∆ΠΚ3 aggregates after dry and wet sieving.
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Fig. 6 — Granulometry curves for samples ∆ΠΚ1‑4.
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Fig. 7 — Sample ∆ΠΚ1. Microscopy 20Χ. Medium grained aggregates and a piece of charcoal are embedded in the earth-based material.
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Fig. 8 — Sample ∆ΠΚ2. Microscopy 20Χ. Lime clumps and medium-grained aggregates are present in the earth-based mortar.
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13Plasticity measurements for the three samples ∆ΠΚ2, ∆ΠΚ3 and ∆ΠΚ4 showed medium to low cohesion (fig. 9) and medium expansion (fig. 10), with the exception of sample ∆ΠΚ1 which qualified as sandy, as rolling it into strands was not possible. All three samples contain ~2‑4% clay (as measured by size Ø<6 µm) and ~10‑11,5% silt (Ø 6‑75 µm) qualifying borderline between sand and sandy loam (table 1), which are characterized as minimally expansive. Cohesion is high when water content is below the PL. Activity is defined by the percentage of clay with grains below <Ø2 µm (Houben and Guillaud 1994) but is not always related to performance which is affected by the type of clay. Generally speaking, a clay content >25% leads to extreme plasticity and a high moisture absorption with the concomitant expansion of the material (Warren 1999). Porosity measurements ranged from 21‑25% with a median pore size (volume) of Ø8‑11 µm with the exception of sample ∆Πκ1 whose median pore size is much larger – Ø34,24 µm (fig. 11).
Fig. 9 — Soil cohesion diagram ∆ΠΚ2 ∆ΠΚ3 ∆ΠΚ4.
Houben, Guillaud 1994, p. 59.
Fig. 10 — Soil expansion diagram ∆ΠΚ2 ∆ΠΚ3 ∆ΠΚ4.
Houben, Guillaud 1994, p. 59.
Fig. 11 — Pore size distribution graphs for samples ∆ΠΚ1‑4.
14The soluble salts quantities in samples ∆ΠΚ1‑3 were not deemed significant enough to affect weathering and conductivity measurements showed a content of 0,4‑0,6%, (table 3) although sample ∆ΠΚ4 had a content of 1,1% and a high amount of chlorides which is attributed to orientation and the effects of salt spray.
Table 3 — Soluble salt analysis.
Sample |
Conductivity measurement |
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|
|
µS/cm |
% |
Sulfate SO42- mg/l (200‑1600 mg/l) |
Chlorine Cl‑ mg/l (2‑200 mg/l) |
Nitrates NO3‑ mg/l (10‑150 mg/l) |
∆ΠΚ1 |
124,8 |
0,5 |
>400 |
8 |
0 |
∆ΠΚ2 |
87,36 |
0,3 |
>400 |
18 |
0 |
∆ΠΚ3 |
118,08 |
0,4 |
>400 |
10 |
0 |
∆ΠΚ4 |
293,76 |
1,1 |
>400 |
58 |
10 |
15Three mixes were designed with slight variations in the binder. A well‑graded mix of siliceous and calcitic aggregates of maximum grain size of Ø6 mm and median grain size of Ø1,2 mm, was used in a binder to aggregate ratio of 1:2 w/w (table 4). The binder in each composition consisted of clay and natural hydraulic lime NHL5 (mix ΣΠ3,1α) and clay and natural hydraulic lime NHL5 part of which was replaced with pozzolan Ø<75µm (mixes ΣΠ3,1β & ΣΠ3,1γ). The ratio of water to binder was 0,45. A plasticizer/waterproofing admixture (A603, Bostik) 1% w/w was added to mixes ΣΠ3,1α και ΣΠ3,1γ.
Table 4 — Repair mortar mixes.
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Composition |
% w/w |
Ratio B:A1 |
Ratio W:B2 |
ΣΠ3,1α |
Siliceous sand 0,3‑1,2 mm River sand 0‑2 mm Black aggregate 2‑4 mm Black aggregate 4‑6 mm Quartz sand 2‑5 mm Clay Hydraulic lime NHL 5 Waterproofing admixture A603 |
17 33 7 7 3 23 10 1% of B |
1:2 |
0,44 |
ΣΠ3,1β |
Siliceous sand 0,3‑1,2 mm River sand 0‑2 mm Black aggregate 2‑4 mm Black aggregate 4‑6 mm Quartz sand 2‑5 mm Clay Pozzolan <75 µm Hydraulic lime NHL 5 |
17 33 7 7 3 19 4 10 |
1:2 |
0,47 |
ΣΠ3,1γ |
Siliceous sand 0,3‑1,2 mm River sand 0‑2 mm Black aggregate 2‑4 mm Black aggregate 4‑6 mm Quartz sand 2‑5 mm Clay Pozzolan <75 µm Hydraulic lime NHL 5 Waterproofing admixture A603 |
17 33 7 7 3 19 4 10 1%B |
1:2 |
0,47 |
1 Binder to aggregate ratio w/w 2 Water to binder ratio w/w. |
16The comparative assessment of all three mixes was overall satisfactory and their characteristics and properties were quite similar. Mixes ΣΠ3,1β & γ which contain a small quantity of fine-grained pozzolan had a slightly greater water to binder ratio (0,47) to mix ΣΠ3,1α (0,44). The specific apparent weight of all mixes ranged from 1,79-2,15 g/cm3 and water absorption at saturation ranged from 11‑13%. Total porosity of all samples was quite low and ranges from 13‑14,5% with a median pore Ø of 0,75‑1,27 µm with the exception of mix ΣΠ3,1α which has a larger median pore Ø of 8,55 µm. The mechanical strengths at 28 days are similar for ΣΠ3,1β & γ: compressive strength of 3,83 and 3,32 MPa and flexural strength 0,91 and 0,99 MPa respectively. Mix ΣΠ3,1α has slightly lower values, a compressive strength of 3,02 MPa and a flexural strength of 0,81 MPa.
Table 5 — Characteristics and properties of variations of mix ΣΠ3,1.
Mix |
S.A.W.1 (g/cm3) |
W.A.S.2 (%) |
Porosity |
Granulo- metry Range & median Ø (µm/mm) |
Ratio B:A3 |
Mechanical strengths |
Total (%) |
Med. Pore Ø (µm) |
C4 28/90 d (MPa) |
F5 28/90 d (MPa) |
ΣΠ3,1α |
2,07 |
11,37 |
14,01 |
1,27 |
75µm‑16mm 1,2 mm |
1:2 |
3,05/ 5,33 |
0,81/ 1,07 |
ΣΠ3,1β |
1,79 |
13,38 |
13,29 |
0,75 |
75µm‑16mm 1,2 mm |
1:2 |
3,83/ 6,98 |
0,91/ 2,33 |
ΣΠ3,1γ |
2,15 |
13,01 |
14,51 |
8,55 |
75µm‑16mm 1,2 mm |
1:2 |
3,32/ 6,13 |
0,99/ 2,03 |
1 Specific apparent weight 2 Water absorption at saturation 3 Binder to aggregate ratio by weight 4 Compressive strength 5 Flexural strength. |
17In the durability tests (soluble salt weathering) the mixes with the waterproofing admixture were slightly more resistant (ΣΠ3,1α & ΣΠ3,1γ). For approximately nine test cycles all three mixes showed a weight increase due to the initial absorption of solution (fig. 13). Following cycle 9, the erosion of the binder and concomitant loss of aggregates began to translate not only into weight loss but also in the rounding of the edges and microcracking of the specimens. No significant changes in any of the three mixes were noted in the wetting and drying cycles (max 20 cycles) either in weight loss or change in dimensions and shape.
Fig. 12 — Granulometric curve of mix ΣΠ3,1.
Fig. 13 — Sulphate immersion test, weight change (%) plotted by cycle.
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Fig. 14 — Samples of mix ΣΠ3,1α before the sulphate immersion test.
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Fig. 15 — Samples of mix ΣΠ3,1α on cycle 11 of the sulphate immersion test.
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Fig. 16 — Samples of mix ΣΠ3,1β before the sulphate immersion test.
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Fig. 17 — Samples of mix ΣΠ3,1β on cycle 11 of the sulphate immersion test.
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Fig. 18 — Samples of mix ΣΠ3,1γ before the sulphate immersion test.
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Fig. 19 — Samples of mix ΣΠ3,1γ on cycle 11 of the sulphate immersion test.
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18Based on the above, mix ΣΠ3,1γ was selected as it performed comparatively better in both the wetting-drying cycles and the sulphate immersion test showing minimal weight loss in the latter which factor was prioritized as these constructions are exposed to salt spray. This mix was prepared with the addition of a waterproofing agent which as expected showed a lower water absorption at saturation and porosity distribution (Fitzner 1996) which a larger median pore size. Both compressive and flexural strengths are higher than those of the other two mixes. In order to obtain an aesthetic match, inorganic pigments such as burnt umber and sienna should be added in powder form in a quantity of ~5% of the binder w/w. Optimum application and curing on site should ensure that the earth-based mortars obtain similar characteristics and properties as those obtained in the laboratory.