Investigation of the physico-chemical and microscopic properties of Ottoman mortars from Erzurum (Turkey)

Construction and Building Materials 24 (2010) 1995–2002

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Investigation of the physico-chemical and microscopic properties of Ottoman mortars from Erzurum (Turkey) Hanifi Binici a,*, Joselito Arocena b, Selim Kapur c, Orhan Aksogan d, Hasan Kaplan e a

Kahramanmaras Sutcu Imam University, Engineering and Architectural Faculty, Department of Civil Engineering, Kahramanmaras, Turkey Canada Research Chair-Soil and Environmental Sciences, Ecosystem Science and Management, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N 4Z9 c Cukurova University, Department of Soil Science and Archaeometry Adana, Turkey d Maltepe University, Department of Civil Engineering, Istanbul, Turkey e Pamukkale University, Department of Civil Engineering, Denizli, Turkey b

a r t i c l e

i n f o

Article history: Received 28 April 2008 Received in revised form 29 March 2010 Accepted 31 March 2010 Available online 22 April 2010 Keywords: Ottoman mortars Erzurum Chemical assessment Microscopic properties

a b s t r a c t Ottoman mortar is the long-established binding material used for centuries and there are many historical buildings as evidence of its use by Ottomans in Erzurum (Eastern Turkey). The physico-chemical and microscopic properties of the Ottoman mortars in Erzurum have been studied in detail as part of an investigation of the mineral raw materials present in the territory of Turkey. For this purpose, SEM, XRD and EDS analyses of six main types of mortars were carried out showing the presence of organic fibers and calcite, quartz and muscovite minerals. The chemical analyses of the specimens showed that higher SiO2 + Al2O3 + Fe2O3 contents yielded in higher values of hydraulicity and cementation indices. A significant result of this investigation was that mortars with higher hydraulicity and cementation indices had higher compressive strengths. Most probably this is the main reason why historical Ottoman buildings were resistant against serious earthquakes. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction The Ottomans were one of the greatest and most powerful civilizations of the modern period (1299–1923) (see Fig. 1). Their moment of glory in the 16th century represents one of the heights of human creativity, optimism, and artistry. The empire they built was the largest and most influential of the Muslim empires of the modern period and their culture and military expansion crossed over into Europe. One of the countries where the Ottoman cultural influence is the densest is Turkey. Looking from an historical perspective, it is known that many civilizations have lived in the country and consequently produced many different cultures and architectural products. For instance, a case point is Erzurum which is one of the oldest cities that boasts such historical examples surviving until the present. It is a historical city in the east of Turkey, which has been influenced by several cultures and civilisations (Fig. 1). To cite some examples, Ibrahim Pasa Mosque, Erzurum Castle, Lala Pasa Mosque, Pasinler Castle, Cifte Minerat and Pasinler Ulu Mosque

* Corresponding author. Tel.: +90 344 2191278; fax: +90 344 2191052. E-mail addresses: [email protected] (H. Binici), [email protected] (J. Arocena), [email protected] (S. Kapur), [email protected] (O. Aksogan), hkaplan@ pamukkale.edu.tr (H. Kaplan). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.03.013

are some of the historical masterpieces, most of which were probably designed by the famous Ottoman architect ‘Sinan’. The Romans are credited with a large number of innovations in construction, including hydraulic cement, a mixture of volcanic ash and lime. Mortars of different types and compositions were widely known and used in the ancient world and the lime mortar–putty was widespread throughout the Roman and Byzantine Empires. In many cases lime was used as a binder and for better plasticity [1,2]. Mortars with crushed ceramics as aggregates were used by the Ottomans. These mortars, besides being suitable for building purposes were also preferred as a watertight layer on building mortars or to enhance the watertight aspects of a building mortar. Adding limestone to the mix has been known to enhance the mortar strength. Mortars with volcanic aggregates, with or without limestone fragments, were used for most building components or on exterior surfaces in the Ottoman and Byzantine buildings, as was used in the unique dome structure mortars of the contemporary St. Sophia Museum in Istanbul [3]. The better freeze–thaw resistance of the mortars prepared with limestone and volcanic aggregates is probably due to an appropriate pore structure and sufficient mechanical strength. Furthermore, the better waterproofing behavior of the mortars with the addition of fine crushed ceramic is believed to result from a denser pore structure of the mortar binder [4].

1996

H. Binici et al. / Construction and Building Materials 24 (2010) 1995–2002

Fig. 1. Map of Ottoman Empire and location of Erzurum.

Some recent research is conducted on pilot applications with compatible restoration mortars, avoiding the common practice of cement mortar mixtures. These applications are sought to be evaluated not only by their performance during the recent earthquakes in Turkey and Greece, but also by their examination in situ with non-destructive tests [5]. A selected set of specimens from excavations from the Cathedral at Tournai in Belgium has been characterized using a combination of chemical and microscopical techniques [6]. The results of the characterization of these specimens clearly indicate the importance of an optical microscopic study using thin sections as a first step in the chemical–mineralogical characterization of historic mortars because of the complexity and heterogeneity of such composite materials. It was concluded that microprobe analysis results on mortars have proved to be useful in helping the interpretation of the hydraulic character of ancient mortars.

The compactness of the studied mortar groups confirms that there were, in the past, traditional mortar technologies that remained unaltered for large historical periods. The properties of crushed brick mortars, for example, do not show appreciable changes from the early Byzantine to the late Ottoman period [1]. Roman mortars have been highly appreciated for their durability. Hence, their physico-chemical and microstructural characteristics have been widely investigated [7]. However, the main technological properties of the Ottoman mortars, such as the mechanical strength, durability, and permeability, are not sufficiently well known to enable correlations to be established with their microstructure. The concrete manufacturing process consists of, the development of macro-porosity of a micro-mortar matrix made of cement, lime, sand and water, by the addition of an expansive agent, which reacts with the water and the lime liberated by the hydration of

H. Binici et al. / Construction and Building Materials 24 (2010) 1995–2002

the binder [8]. The gaseous release generated by this chemical reaction causes the fresh mortar to expand and leads to the development of pores, which give the aerated concrete its well known characteristics, i.e., the low weight and high thermal performances [9]. Moreover, the high porosity of aerated concretes, essential to their main function, which is thermal insulation, leads to very poor mechanical strengths compared to normal concrete. The quantity of pores and the pore distribution mainly influence the mechanical properties [10]. An experimental study has shown that an increase in the cement dosage increases the introduced porosity, whereas an increase in the sand or lime dosages decreases it [11]. The aim of the present study is to draw attention to the general resistance of the Ottoman buildings, by studying the chemical, strength, porosity and microscopic properties of the Ottoman mortars from Erzurum (Turkey). The performance of Ottoman buildings against earthquake damage is dependent, to a large extent, on the physical characteristics of their mortars. Hence, compressive strength is a crucial parameter regarding the load capacity of the structures and was therefore included in the assessment programmed. 2. Materials and methods

1997

Specimens were taken from minaret walls and leftovers from castle restoration works. The main elemental contents in the Ottoman mortars are given in Table 3. Depending on the colors and the types of aggregates, the specimens were separated into three groups. Samples from each group were used for chemical and microscopic analyses and for the compressive strength tests. The major elements Ca, Mg, Fe, and Al were measured by Atomic Absorption Spectrometry after HCl (1 N) treatment. The amount of soluble SiO2 (not equal to the total amount), was estimated by the dissolution of the specimens in HCl (3 N) and analysis by Atomic Emission Spectrometry. The amounts of the elements are related to the degree of hydraulicity of the mortars as suggested by EN TS 3624 with higher indices indicating higher hydraulicities. Hydraulicity and cementation indices are defined, respectively, as follows [12]:

Al2 O3 % þ Fe2 O3 % þ SiO2 % CaO% þ MgO% 1:1Al2 O3 þ 0:7Fe2 O3 % þ 2:8SiO2 % CI ¼ CaO% þ 1:4MgO%

HI ¼

ð1Þ ð2Þ

This paper discusses six different groups of mortars from six different buildings as shown in Fig. 2 in Erzurum, Turkey (see selected buildings in Figs. 2a–2d). The specimens were taken from the walls of the minarets and walls of the castles, left behind after restoration works. The cross-section of the studied historical building (S1) is given in Fig. 3. Samples varied in size from thumbnail to hand specimen, weighing between 100 and 150 g, and containing coarse aggregate grains up to 10 mm.

2.2. Electron microscopy and EDS analyses

2.1. Materials Ottoman mortar specimens were taken using hammer and chisel. With respect to their function, the specimens can be divided into three main groups. The first group consists of broken brick and limestone masonry mortars, the second group consists of crushed ceramic and broken bricks and the last group has only limestone. Sample locations and appearance of Ottoman mortar specimens from Erzurum, Turkey, are given in Table 1. Color of the patina and interiors are observed to be very different. This may be depending on the mineral binder and the additional constituents. The main mineral constituents of these specimens are given in Table 2. The proportion of the lightweight particles in the aggregate material was determined according to the Turkish Standard Specification EN TS 3528.

The hydration–dehydration products were identified by means of a Scanning Electron Microscope. Selected mortar prisms were cut into cubes of approximately 10 mm3 size, one side of which was polished flat. The samples were then placed in a vacuum dessicator for a minimum period of three days. Polished surfaces were coated with gold using a BIO-RAD polar Division SEM coating system. The microstructure of the specimens was studied in a Philips XLS 30 scanning electron microscope equipped with an energy dispersion spectrometer (EDS) detector. The SEM-EDAX study was carried out at low vacuum and acceleration voltages of 20 keV, beam current of 36 lA, vacuum pressure (in the electron gun) of 8.3  108 mbar, sample pressure of 4.5  106 mbar, 400 s of counting–integration time for EDS and beam size of 1 lm. The submicroscopic pore and aggregate characterizations of the mortars, namely as size, shape and orientation was carried by the micromorphological approach developed by FitzPatrick and Kelling et al. [13,14].

Table 1 Locations and colors of the mortars. Specimens

Location

Year completed

Patina color

Interior color

S1

Ibrahim Pasa Mosque Erzurum Castle Lala Pasa Mosque Pasinler Castle Cifte Minerat Pasinler Ulu Mosque

1748

White

White

1771 1571 1336 1294 1564

White White Black Gray Gray

Gray Gray Gray White White

S2 S3 S4 S5 S6

Table 2 Additives and mineral constituents of the mortars. Specimens

Additives–coarse materials

Binder

Additions

Light substance (wt.%)

S1

0.27

–

0.44

S6

Limestone

Calcite, muscovite Muscovite, calcite Calcite, quartz Calcite, quartz, muscovite Calcite, muscovite, quartz Calcite, muscovite, quartz

Organic fragments Organic fragments Organic fibers Organic fibers

S5

Broken bricks (200 mm) + limestone Broken bricks + limestone Broken bricks + limestone Broken bricks + crushed ceramics Limestone

–

0.41

S2 S3 S4

0.35

2.3. X-ray powder diffraction analysis X-ray diffraction analysis was conducted using a Bruker D8 diffractometer with general area diffraction detector and an 800 mm collimator with a pinhole from 2.2° to 90° 2h using Co Ka radiation with wavelength k = 1.79026 Å, generated at 40 keV and 20 mA. Diffraction patterns were compared with ICDD PDF card files to identify mineral species and were obtained using a laser-focusing system that allows nondestructive spot XRD analysis of the mineral of interest on the rock samples.

2.4. Chemical assessment methods The chemical composition of the Ottoman mortars was determined by a number of complementary methods, according to the Turkish Standard EN TS 196-2 presented in weight percentage. Sample material was pulverized and subsequently digested in excess concentrated hydrochloric acid (1 N HCl). Na and K were measured separately in a Jenway PFP 7 flame photometer. Main elements Ca, Mg, Fe, and Al were measured by atomic absorption spectrometry (AAS). Analysis of Mn2O5 and P2O5 was done by XRF. Loss on ignition was determined at 1000 °C. The amount of soluble SiO2 (as different from SiO2-total!) was estimated by dissolution in excess 3 N HCl and subsequent analysis by AES. Furthermore, analysis of SiO2 was conducted by gravimetric method by determining the insoluble residue by weight and the remaining components were determined by EDTA titration. Hydraulicity and cementation indices were recalculated using Eqs. (1) and (2).

0.33 2.5. Physical and mechanical assessment methods 0.26 The specimens used for the compressive strength test were 40 ± 5 mm cubes. The density, specific porosity and water absorption of the specimens were calculated using the Archimedes principle on the same size cubes [12]. Aggregate types and lightweight particle contents of the mortars were tested according to the EN TS 196-1. The compressive strength tests were carried out using a 20,000 kN capacity automatic compression machine according to EN TS 24 by taking the average strength of the three parallel measurements of each specimen. The total porosity was determined according to the water saturation test with a hydrostatic balance [15].

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Table 3 EDS-Spot analysis of mortars. Energy level (keV)

Intensity (csp)

0–0.8 and 08–1.6 2.6–4.0 4.2–6.4 7.2–8.0

Medium High High Low

Specimens S1

S2

S3

S4

S5

S6

Ca, Cu, Si Si, Ca Ca Fe

Ca, Cu, Si Ca Ca Fe

Ca, Cu, Si Ca Ca Fe

O, Mg Si, Cl, Ca – Fe

Si Ca – –

Si Ca – –

The SEM images reveal the presence of calcite and amorphous CSH phases (Fig. 4) determined as the major component of the mortar admixtures commonly known as the ‘lime mortars’ (Table 2). However, XRD analysis revealed the presence of fine muscovite and quartz that were masked by the abundant calcite binder and the amorphous hydraulic formations determined in the SEM

images (Table 2). Frequent organic fibers and fragments were identified in the matrices of the S1, S2, S3 and S4 specimens respectively (Figs. 5–8). Some were partly decomposed organic fibers (most probably straw fragments) (Fig. 5) and plant epidermal tissues (Fig. 6). The images, furthermore, reveal an open pore (continuous pores) structure with pore sizes of about 20–100 lm complemented by about an equal distribution of smaller closed pores (discontinuous pores) of 5–50 lm size embedded in a very fine grained granular matrix, i.e., matrix composed of irregular to elongated micro-aggre-

Fig. 2a. Ibrahim Pasa Mosque.

Fig. 2c. Lala Pasa Mosque.

Fig. 2b. Erzurum Castle.

Fig. 2d. Pasinler Castle.

3. Results 3.1. Electron microscopy and X-ray diffraction (XRD)

H. Binici et al. / Construction and Building Materials 24 (2010) 1995–2002

Fig. 3. Cross-section of the studied historical building (S1).

1999

Fig. 6. SEM image of specimen S4.

Fig. 7. SEM image of specimen S1. Fig. 4. SEM image of specimen S5.

Fig. 8. SEM image of specimen S2. Fig. 5. SEM image of specimen S3.

gates (varying sizes from 10 lm to 200 lm) and reinforced by the frequent organic fragments and fibers observed in some of the specimens. The average grain size of the abundant calcite crystals aggregated with the CSH structures was 5–10 lm, with minor differences between mortars from different structures (Fig. 4).

The oxide composition analysis of the Ottoman mortars used in the historical buildings conducted by the EDS of the selected specimens (Table 3), revealed the presence of the dominant elements of calcium, magnesium, silica and iron. Other elements were below the lower detection limits of the EDS system. Table 3 illustrates

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Table 4 Chemical compositions of the mortars by wt.%. Element species

LLD

Na2O K2O CaO MgO MnO Fe2O3-total Al2O3 SiO2 P2O5 LOI Total HI (hydraulic index) CI (cementation index)

0.1 0.1 0.1 0.1 0.01 0.1 0.1 0.1 0.1 0.1 99.9 – –

Specimen S1

S2

S3

S4

S5

S6

0.7 1.3 29.8 0.8 0.03 5.3 7.4 40.1 0.4 14.1 100.0 1.7 4.0

0.7 1.3 29.2 0.9 0.02 5.6 7.5 40.3 0.5 14.0 99.2 1.8 4.1

0.6 1.2 29.6 0.9 0.03 5.3 7.9 41.0 0.5 12.2 99.1 1.8 4.1

0.7 1.3 29.1 0.9 0.03 5.8 8.2 41.9 0.4 10.8 99.7 1.9 4.3

0.7 1.3 29.3 0.8 0.03 5.4 7.5 41.6 0.5 12.6 99.6 1.8 4.2

0.6 1.2 29.3 0.9 0.03 5.5 7.9 40.8 0.5 13.9 1.8 4.1

peaks near 0.80 keV for copper (Cu), a rather unusual constituent of mortar, especially in quantities detectable by SEM-EDS and two peaks near 2.6 keV for chlorine (Cl), which is another rather unusual mortar constituent.

All Ottoman mortars do fulfill compressive strength requirements of ASTM C 140-05a and EN TS 3114 and 6433.

3.2. Chemical compositions

4.1. Microscopy, mineral content and chemical composition

Chemical composition data in wt.% oxides for all six sample locations are shown in Table 4. The results reveal remarkably uniform compositions for mortars from very different structures, almost spanning 500 years through history. Many authors have tried to determine the hydraulicity of ancient mortars on the basis of the combined results of chemical and microscopical analyses [16–22]. Concerning the results of the chemical analyses are given in Table 4, Hydraulic properties of mortars were determined by calculating hydraulic (HI) and cementation (CI) indices considering the chemical compositions of white lumps according to Boynton formula (Eqs. (1) and (2)), the highest values for the hydraulicity and cementation indices correspond to a higher SiO2, Al2O3 and Fe2O3 content. Table 4 illustrates that the above values are highest for specimen S4.

The oxide composition analysis of the Ottoman mortars used in the historical buildings by EDS indicated that all the mortars were mainly composed of high amounts of Si, Ca and moderate amounts of Fe, Na and K (Table 3). However, the amounts of Fe in all mortars used in the historical buildings were found to be more or less the same (see Tables 3 and 4). Abundant calcite crystal-amorphous hydraulic formations (CSH) clusters-aggregates were determined in the matrix of the mortars, especially in specimens S1, S3 and S5 (Figs. 4, 5 and 7). This reflected the use of finely ground abundant limestone fragments as the main ingredient of the mortars, which was most likely recrystallised as fine calcite and CSH aggregates and oriented as clusters following the hydration process. The well to moderately uniform distribution of the porosity observed in the SEM images is probably due to the homogeneous distribution of the hydration products, i.e., indicating most likely a uniformly proceeding hydration process, and mainly composed of calcite and CSH in specimen S1 of lowest density as also determined in the earlier studies [24,25]. The source of the detrital muscovite was most probably one of the sources of the mineral constituents, namely the brick, ceramic and limestone fragments added to the mortar mixtures (Table 2). Despite the limited sample sizes of the mortars obtained for the study, the above mentioned minerals and the amorphous CSH phase were most probably responsible for the development of the strong adhesion bonds and the durability of the lime mortars. The absorbant properties of the CSH amorphous phases, that have formed in the matrix of the mortars, was most likely one of the primary reasons of the earthquake resistance of the structures as earlier stated by Moropoulou et al. [26] to be valid for other Byzantine buildings. The presence of the frequent organic fragments and fibers may also indicate an incremental increase in mortar durability in specimens S3 and S4. The source of copper may be the infiltrated meteoric water containing dissolved Cu from the copper of bronze or brass rain pipes, roofing, cladding, or other copper-containing parts on the structure (scarecrow of the minaret). The presence of Cl may be due to the contamination during the restoration or cleaning of the facades of the building by dilute hydrochloric acid. Formation of the hydraulic compounds, such as calcium silicate hydrates and calcium aluminate hydrates at the interface were most probably due to the reactions between the broken bricks, crushed ceramics and aggregates, Similar to the highly cementi-

3.3. Physical properties Data on the physical properties are shown in Table 5. The content of lightweight particles in modern mortars is limited according to Turkish standard EN-TS 3528. Thus, mortars are considered durable when the content of lightweight particles is less than 0.5 vol.%, whereas content higher than 0.5 vol.% is considered poorly durable [23]. Specimen S4 contains brick fragments and crushed ceramics (Table 5) and is observed to have the highest compressive strength. Other specimens containing limestone fragments along with other ingredients mentioned show lower compressive strength. According to water absorption data, specimen S4 also has the lowest porosity value, whereas S2 containing brick and limestone fragments attained the highest porosity. Table 5 Some physical and mechanical properties of the mortars. Specimens

Compressive strength (MPa)

Water absorption after 24 h (%)

Density (g/cm3)

Porosity (%)

S1 S2 S3 S4 S5 S6

13.2 12.4 13.6 15.3 14.5 14.1

12.4 12.1 12.3 9.6 10.4 11.6

1.96 2.24 2.15 2.23 2.18 2.16

34.3 39.1 36.6 31.3 35.1 36.4

4. Discussion

H. Binici et al. / Construction and Building Materials 24 (2010) 1995–2002

tious nature of the crushed brick–lime mortars of the dome of Hagia Sophia, which explains the fact that the monument still stands by absorbing the energy derived from the earthquakes without affecting the material properties [3]. The results indicated that the increase in the use of the additive type and content caused a significant increase in the durability of the Ottoman mortars in contrast to the lime mortars of the Noto Cathedral in Milan, Italy, with low cohesion and adhesion to the stones that were also friable and undurable [27,28]. 4.2. Physical and mechanical properties As physical properties, compressive strength is a prime property reflecting the quality of the mortars. It depends on the type of additives used and the density–porosity of the mortars. Specimen 4 has the highest compressive strength, which may be due to high hydraulicity and cementation indices. The compressive strength characteristics of the mortars were affected not only by the additive types, but in some cases, also by the organic fibers and probably muscovite flakes behaving as short fibers. The fibers oriented in longitudinal and transverse directions, prevent the deformations in the matrix and preserve the shape of the mortars by their stress-resistance. The fibers also prevent the mortar, near the surface, from being crushed and from falling off. Where there are fibers in the mortar, the transverse expansion due to Poisson’s effect is prevented by the fibers. The existence of these fibers increased the elasticity of the mortar. It is evident that some ancient mortars have been durable for centuries, depending on the fact that they contained hydraulic components, i.e. the binder. A significant result of our investigation was that the mortars with higher hydraulicity and cementation indices had higher compressive strengths. 4.3. The resistance to earthquakes Up to now, there have been many earthquakes of various intensities in Erzurum, e.g. the 1458 earthquake with an intensity of 10 (calculated according to Richter scale simulation) in which 32,000 lives were lost, the 1584 and 1859 earthquakes with an intensity of 9 in which 15,000 lives were lost, the 1901 earthquake with an intensity of 6.1 and the 1983 earthquake of 6.7 intensity [29]. The survival of the studied Ottoman buildings until today with the severe damages of the other buildings may be due to the materials used in their construction. The ductility capacity is important only in its relation to the ductility demand and this can be expressed equivalently in terms of the displacement capacity and demand [25]. The compressive strength of the Ottoman mortars fulfill the ASTM and TS standards requirements, hence, being more resistant to earthquakes. Moreover, the presence of fibers and muscovite minerals in the mortars provides flexibility to the structures thus enhancing their earthquake resistance. Thus, Ottoman mortars can store more elastic energy, which renders a higher resistance to earthquakes. 5. Conclusions The following conclusions can be drawn from the study: 1. The broken bricks, as appropriate puzzolanic materials, together with the organic fibers and fragments, the muscovite mineral content, the uniformly recrystallized calcite, the CSH amorphous phases (calcite + CSH aggregates) and the consistent open–closed pore distributions of the mortar matrices were most probably responsible for the high compressive strength of the mortars.

2001

2. EDS indicated that the oxide composition of the Ottoman mortars were mainly composed of high amounts of Si, Ca and subordinate amounts of Fe, Na and K. 3. The higher SiO2 + Al2O3 + Fe2 O3 content resulted in higher values of hydraulicity and cementation indices. Moreover, a significant result of this investigation was that the mortars with higher hydraulicity and cementation indices had higher compressive strengths. 4. Specimen S4 with the highest durability and lowest water absorption and porosity was used in the most intact building of the region. 5. The exceptional compressive strength obtained from the mortars of this study is primarily responsible for the survival of the Ottoman buildings, despite the periodic and severe earthquakes of Eastern Turkey.

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