12TH INTERNATIONAL

BRICK/BLOCK Masonry c O N F E R E N C E

CHARACTERISTICS OF BRICKS OF BYZANTINE PERIOD

loanna Papayianni* Professor A.U.TH Maria Stefanidou PhD student*

Ste

*Civil Engineering Department of Aristotle University of Thessaloniki, Greece

ABSTRACT

Byzantine monuments are widely spread in Greeee especially in North part of it and cover a historical period of more than one millennium. Brieks used during Byzantine period were mainly plates 30x30 or 35x35 or 30x40em and their thiekness varied from 2.5 up to 5em. In the frame of the NATO Sf5 Pro­gramme measurements of morphological, physical and meehanical properties were performed in order to eharaeterize the old brieks and proeeed to the manufaeture of compatible ones. Some pieees of information eoneerning the ancient teehnology sueh as the quality of c/ay and the manufaeture and baking teehnology, are also given in the paper.

Key words: Byzantine brieks/pathology / mierostruetural / meehanical properties/ compatible brieks.

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1730

INTRODUCTION

Typical elements of the masonry in Byzantine architecture are bricks and thick mortar joints. The manufacture techniques have passed from generation to ge­neration up to the period of industrialization at the end of 18th century.

The production of old bricks seems to have followed the stages (1):

1. Finding a suitable clay

2. Mature of the clay by exposition at open place

3. Mix clay with water in a pit

4. Knead by hand and shape them in wooden moulds

5. Burn in clamps or kilns

MORPHOLOGY

The bricks that were used for construction were mainly plates 30x30cm, 35x35 or 30x40cm. Their thickness varied from 2.5 up to 5cm. The surfaces (mainly the bottom) were rough, indicating the use of bottomless moulds while the upper surface texture is less rough but very anomalous with hollows and chips. Great variation in dimensions and distortion can also be met in bricks. Often, there we­re stamps indicating the manufacturer or religious markings (photo 7) (2) (3).

Indicators of the low temperature at which the bricks were produced, is the pre­sence of chips of wood and shells inside some of them (photo 2). The presence of

Photo 1. 5tamps in the upper surface of an old brick.

Photo 2. Pices of shel in the brickmass.

different coulored zones in thick bricks shows the unhomogeneity during burning (photo 3). Lime lumps could also be found as additives in old bricks (photo 4). Gra­vei or crushed brick of second use have often been used in the original mixture.

MECHANICAL! PHYSICAL CHARACTERISTICS

Testing the mechanical and physical characteristics of bricks from monuments from different periods of Byzantine era (considering the deterioration they suffer) it could be said that the remaining strength ranges between 1 00-180Kg/cm 2 (table 7). Po­rosity also ranges from 15% up to 35% and seems that there is a clear relationship between porosity value and strength value as it is shown in table 7. High porosity values correspond to low strength material. It is obvious that porosity is not only influenced by voids ar other discontinuities in the mass of the brick but also by the cracks which have been created secondarily by deterioration processo

Tab/e 7. Mechanico/ and physico/ characteristics af a/d bricks

Monument/ Code Nr Strength (Kg/cm')

Acheropoiitos !1 O 184

Acheropoiitos / 2 58.6

Acheropoiitos / 3 136

Acheropoiitos / 6 166

Acheropoiitos 14 156

Hagia Aikaterini 15 41 .3

Hagia Aikaterini 17 64

Hagios Panteleimonas !1 50.9

Hagios Panteleimonas 12 171

Hagios Panteleimonas 13 94.7

Panagia Chalkeon !1 94

Hagia Sophia/ 7 139

Hagia Sophial 8 109.6

Phata 3. Zane af different co/aur inside an a/d brick.

E". (Kg/ cm') 'Porosity % Spec. gravity

74686,8 18.38 1,80

62930,7 16.78 1,88

91281,9 16.72 1,81

82942,2 16.14 1,85

80723,0 16.25 1,88

91862,3 34.87 1,71

47942,6 33.27 1,38

29916,2 28.54 1,44

110444,2 25.93 1,59

26407,2 32 .21 1,41

39941,2 16.99 1,46

103205,8 16.66 1,86

89934,7 14.96 1,88

Phata 4. Grains af co/cite reacting with clay.

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1732

100

70-

250 250- 550- 1000- 15(J().

!XX) 1(0) 1500 :nxJ

d(im)

Dred

II bram

70- 250- 550- 1000- 15(J(). 2aX).

250 !XX) 1(0) 1500 2(l)J 3500

d(im)

Figure 1. Pore size distribution con­cerning bricks from diffe­rent monuments of Byzan­tine period

Figure 2. Pore size distribution in bricks made of different c/ay from Hagios Pantelei­monas

Measurements of pore distribution in Byzantine bricks were performed by using the

image analysis system technique. The results are refereed to stereoscopic observa­tion xl O. It is obvious that the main volume of pores are at the range of 70-250llm.

From the pore distribution analysis of two bricks (from Hagios Panteleimonas) ma­de of different day, we can see the different structure of the final product (figure 2).

PATHOLOGY OF OLO BRICKS

The common symptoms of bricks are:

• Cracks, usually vertical to the length, or inside the structure of the bricks (around coarse aggregates)

• Pulverization

• Chipping

• Biological deterioration

Photo 5. 50lt crystols inside o void in the brickmoss.

• Salt crystals diffused in the structure (photo 5)

• Efflorescence

The content in soluble salts depends on the place, orientation and the contami­nants they include. From the salt analysis of old bricks seems that sulfuric salts are commonly found and in considerable concentration but also chlorides and nitra­tes could be included (table 2).

RESUl TS FROM THE ANAL YSIS OF OlD BRICKS

Old bricks of Byzantine period were characterized by:

• low strength

• low modulus of elasticity

• high porosity

• low specific gravity (1.52-1.6)

• high degree of deterioration

Toble 2. 50luble solts in old bricks

Monument/ Code CI- NO,· 50.'·

Hagia Sophia/ 7 0.002 0.01 0.01

Hagia Sophia /8 0.02 0.06 0.23

Hagios Panteleimonas/l 0.15 0.28 1.11

Xalkeon/l 0.13 0.20 0.11

Axeropiitos / 5 0.07 0.08 0.04

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Photo 60. Structure of old brick (Axeropiitos). Photo 6b. Structure of o new brick.

• high content in soluble salts

• rough texture

• variation in dimensions

OESIGN OF BRICKS COMPATIBlE TO OlO ONES

Modern bricks produced by large industries are oriented to modern construction . By testing their physical and mechanical characteristics is obvious that they have high levei of strength (>200Kg/cm2

) and modulus of elasticity, low porosity «10%), high specific gravity (1.85-2.05) and they are baked at high temperatu­re (1200 0c) . The final product is very dense, strong and smooth (photo 6).

An effort was made to produce compatible and low cost bricks in order to be ap­plied in repairing old masonries. The main parameters which were taken into con­si der were:

• The quality of clay. From the analysis of new bricks made of clay rich in argi­lIaceous material (plylosilicates) seems that they absorb higher quantity of wa­ter than bricks made of clay poor in such material (table 3). The selection of the raw material is the first step for the production of bricks of good quality (con­cerning colour and physical requirements)

• The procedure during manufacture. Inadequate mixing and compaction can cause the formation of "nests" inside the brick structure with consequences

Table 3. Physical characteristics of bricks made of red and braun c/?y

Description

red clay without many phylosillicates

Braun clay rich in phylosillicates

Figure 3. Water elevation th­rough capil/aries in a new and old brick

'" ~ 1::

'"

Figure 4. Pore size distribution in new bricks made of red and braun c/ay.

4.00

3.50

3,00

2,50

2,00

,50

,(X)

0,50

0.00

°

~

Porosity %

18.1

19.32

sp. gravity

1.813

1.788

--+- axerpOlOlt0s6 ___ neN

200 400 600 !!lO txJO 1200 1400 f300

100 00 80 70 60 50 40 30 20 10 O

o o o o o o N ... <O 6 6 6 ..... o o

N ...

min

o o o o IX> o 6 6 o <O o

IX>

d(im)

Ored

.braun

o o o o N '"

6 o o

6 o N

upon the mechanical behaviour as well as the deterioration of the brick. On the other hand, strong mechanical compaction results in very dense and high stiff­ness material which is not compatible with the soft old bricks.

• The porosity of the new bricks was designed in order to be in the same range with old ones . The use of air-training agents helped to this direction. In coope­ration with a small scale industry, an experimental production of bricks of desi­red morthology, mechanical strength and porosity by using air entraining agents was made. Brick samples were tested to see if they have met the requirements.

- The comparison between the capillary suction between an old and a new brick proves the same behaviour (figure 3).

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1736

- The pore size distribution of new bricks made with different clays, shows that the main volume of pores (75-85%) are in the range 70-200lm (figure 4) simi­lar to old ones.

- The levei of strength was determined 1 00-120Kg/cm2 and the specific gravity 1.52- 1.6.

- Also, the variation in the shape and dimensions of the modern "traditional " bricks was acceptable.

RESULTS AND DISCUSSION

Bricks of Byzantine period were produced following different technology from the one that is used today. They are characterized by low strength (below 200Kg/cm 2

), relatively high porosity (15-20%), low modulus of elasticity and low specific gravity.

Modern bricks are not suitable for restoration works.Proporly designed mixtures can help in producing compatible (in aesthetic and functional way) bricks. The main principies in designing are: morphology, suitability of the raw materiais, me­chanical and physical properties that these bricks should fulfill in order to be com­patible with the old structure and be resistant to weathering.

REFERENCES

1. Theocharidou K. " A contribution to the study of brick and tile production in the Byzantine and Post -Byzantine period" Deltion Christianikis Archeologikis Eterias Athens, 1988

2. Papayianni 1., Stefanidou M. " Characteristics of bricks of old masonries" Workshop on Mate­riais for Consolidation and Restoration of Monuments and Historical Buildings: Reading, In­terpreting and Recovering the Knowledge of Traditional Materiais, Edited by I.Papayianni, P. Astrinidou, Thessaloniki, September 1995 pp 35-48

3. Papayianni I. Hatzitrifonos E. "A survey of the Pazar Hamam in Thessaloniki" Proceedings of Int. Conference on Studies in Ancient Structures July 14-18, 1997, Istanbul, Turkey