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PREPARATION OF POZZOLANIC LIME MORTARS FOR REPAIRING LIMESTONES OF NEMRUT DAĞ MONUMENT

B. Alp Güney∗, Emine N. Caner Saltık

Materials Conservation Laboratory, Department of Architecture, Middle East Technical University,

06531, Ankara, Turkey Keywords: pozzolanic lime mortars, historic mortars, repair mortars, Nemrut Dağ Monument

ABSTRACT

The aim of this study is to prepare pozzolanic lime mortars to be used for stone repairs such as sticking large detached scales, filling gaps and large cracks in the deteriorated limestone objects of Nemrut Dağ Monument in Adıyaman Turkey. Mortar samples from rubble stone masonry of Kahta Castle, a medieval structure, in close vicinity of the Nemrut Dağ Monument, were investigated to set an example for the preparation of repair mortars. Repair mortar mixtures were prepared by using laboratory grade Ca(OH)2, local river sand and two types of pozzolans; metakaolin and natural trass. Basic physico-mechanical properties of historic mortars and repair mortar cubes after 60 day curing period were determined. Both historic and repair mortars were investigated by optical microscopy and SEM-EDX, XRD, FTIR. Pozzolanic activity of the pozzolans used in this study, fine aggregates of historic mortars and fine aggregates of local river sand were investigated. CSAH and CSH were detected by XRD and SEM-EDX in the repair mortars prepared with added metakolin. After 60 days, the bulk density and effective porosity values of prepared repair mortar cubes were observed to be slightly lower than that of historic mortars. The compressive strength of prepared mortars with added metakaolin were quite near to the compressive strength historic mortars, however their carbonation were not yet completed. The results were further evaluated in comparison with historic mortars and for the preparation of compatible and durable repair mortars. INTRODUCTION

Mortar is the material which holds the masonry units like stone and brick together as a bonding agent and thus enduring several structural inputs such as the gravity, movements due to soil settlements or seismic loads through the lifespan of historic buildings [1, 2]. For the preparation of repair mortars for conservation purposes, it is important to have detailed knowledge about the physical and mechanical properties, the raw materials and compositional characteristics of historic mortars in order to understand the technologies behind their use and utilize that information for the production of compatible and durable repair mortars. The use of lime mortars with pozzolanic additives was of special importance in the construction of historical structures therefore historic mortars from standing historical monuments were considered to be a source of information for the preparation of durable and compatible repair mortars for deteriorated limestone. Characterization of historic mortars which was primarily based on wet chemical analyses until 1980’s [3, 4, 5] has proved to be insufficient to have knowledge on the nature of the mortar components. Mortar characterization and identification studies later on focused on the optical

∗ To whom all correspondence should be addressed.

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microscopy and X-ray diffraction analyses as the initial step for the qualitative identification of mortar components. Afterwards the use of several analytical techniques like SEM-EDX, DTA/TGA, FTIR etc. to quantitatively and qualitatively determine the components of the mortar became quite common [6, 7, 8]. Characteristics of the lime used and the properties of aggregates play important roles on the final characteristics of the mortar [9, 10, 11, 12, 13, 14]. For the field of conservation characterization of historic mortars in relation to their raw material components are crucial to formulate compositions for compatible repair mortars [15, 16, 17]. For the design of compatible repair mortars the most critical information to be gathered are the type and hydraulicity of the binder, the aggregate binder ratio and the characteristic properties of the aggregates like their particle size distribution and pozzolanic activity of fine aggregates[18]. The use of lime mortars with pozzolanic additives was of special importance in the construction of medieval structures. Therefore historic mortars from standing medieval monuments were considered to be a source of information for the preparation of durable and compatible repair mortars for deteriorated limestones. To ensure a durable connection between the original stone and the repair mortar, the mechanical and physical properties of the mortar must be adapted to that of the stone [19]. Therefore it was very important to analyze the physical and mechanical properties, compatibility and durability properties of the repair mortars in relation to the original mortars and to have detailed information about the factors affecting the final properties of the mortars with regard to the raw materials used and their proportions. The aim of this study was to prepare pozzolanic lime mortars with metakaolin and natural trass additives to be used for the repairs such as sticking large detached scales, filling gaps and large cracks in the deteriorated limestone objects of Nemrut Dağ Monument in Adıyaman, Turkey. For that purpose mortar samples from the rubble stone masonry of Kahta Castle, a medieval structure, in close vicinity of the Nemrut Dağ Monument, were investigated as an example for the preparation of repair mortars since the rubble stone masonry of Kahta Castle contained limestone pebbles and cobbles having similar microstructural characteristics with the limestone used in the Nemrut Dağ Monument. EXPERIMENTAL

Experiments were done for the analyses of historic mortars and preparation and analyses of pozzolanic lime mortars. Analyses of historic mortars Mortar samples from Kahta Castle in close vicinity of Nemrut Dağ Monument were investigated for their physico-mechanical properties. The bulk density, effective porosity of the mortar samples were determined according to the RILEM standards [20]. Measurements of ultrasonic pulse velocity values were performed. The acid soluble/insoluble parts of mortars were analyzed by treating the samples with 5% HCl solution. Particle size distribution of the acid insoluble parts were determined. Thin sections of the mortar samples were prepared for their minerological and petrographical analyses by optical microscopy. Determination of the mineralogical phases in the mortar mixtures were performed by XRD analyses of powdered samples. FTIR analyses were carried out and interpreted together with XRD analyses. Pozzolanic activity of the fine aggregates having particle sizes smaller than 125 µ were evaluated by their treatment with saturated Ca(OH)2 solution for 14 days and determining the amount of Ca2++ ion consumption by volumetric titration.

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Preparation and analyses of pozzolanic lime mortars For the preparation of pozzolanic lime mortars chemical Ca(OH)2 was used. Ca(OH)2 was mixed with water in a mass ratio of 1:1.7. Sand from a local river (Cendere river) were used as aggregate. Natural trass and metakaolin were used as pozzolanic materials. Metakaolin was prepared in the

laboratory by heating pure kaolinite at a temperature of 700 °C for 24 hours. Pozzolanic activity of the materials were assessed by determining the amount of Ca2+ ion consumption in a saturated solution of Ca(OH)2 by volumetric titration after 14 days [21]. Mortar mixtures were prepared by mixing aggregates, pozzolonic material and Ca(OH)2 in a ratio of 1:0.75:1. The mixtures were then casted in 5 cm cubic molds. Test mixtures were demolded after

3 days and stored in 20 °C and 85% relative humidity. After 60 days of curing period, bulk density, effective porosity of the mortar cubes were determined and ultrasonic velocity measurements were performed. Uniaxial compressive strength tests were carried out by point load measurements [22]. XRD analyses of the mortars were conducted after powdering 2 g samples from cubes. The mortar samples were analyzed with XRD, SEM-EDX and FTIR for the investigation of the mineral structure and formation of new phases. RESULTS AND DISCUSSION

Analyses of historic mortars XRD and FTIR analyses of powdered mortar samples from Kahta Castle showed the dominant presence of calcite indicating the use of lime as the binder (Fig 1, 2). Analyses of the thin sections revealed the existence of the white lumps. The occurrence of white lumps was most probably due to insufficient mixing of slaked lime with aggregates. They were identified as micritic calcite crystals which did not mix with the binder matrix. SEM-EDX analyses of those lumps showed the presence of calcium and relatively small amount of magnesium confirming the nature of the slaked lime used in the historical mortars as being fat lime (Fig 3)

Figure 1: XRD trace of mortar sample from Kahta Castle showing calcite binder and quartz aggregates. C: calcite, Q: quartz

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Figure 2: FTIR spectra of mortar sample from Kahta Castle showing the abundance of CaCO3.

Figure 3: EDX analyses of white lump in the matrix from Kahta Castle mortar sample.

Figure 4: SEM image of binder matrix of mortar sample from Kahta Castle (left). White lump in the mortar matrix showing the distinction between the particle sizes of the crystals in binder and white lump.

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Acid treatment of mortar samples showed that an average of 37% by mass of the samples were acid soluble indicating that the binder of the historic mortar could be about 37%. Average particle size distribution of the acid insoluble part of the Kahta Castle mortars was shown in Figure 5. Analyses showed that more than 50% of the acid insoluble aggregates had particle sizes greater than 1000 microns. Approximately 35% of the acid insoluble aggregates were in the range of 250-1000 microns and 15% was smaller than 250 micron. The aggregates of the latter were the ones that could react with lime to an extent to affect the final properties of the mortar because of their high surface area. To determine the pozzolanicty of the aggregates smaller than 125 microns, pozzolanic activity test was conducted. The results were shown in Table 2. The finer aggregates of the mortars showed relatively high pozzolanicity.

Figure 5: Average particle size distribution of the acid insoluble part of Kahta Castle mortars. Petrographical analyses of thin sections showed that radiolarite and various types of schist (muscovite-quartz, biotit-quartz) and serpentinite were in abundance. Quartzite, limestone and dolomitic limestone were also observed (Fig 6). Those results were used to compare the characteristics of historic aggregates with the river sand from a local river (Cendere river). Sand from that river was used for the preparation of pozzolanic lime mortars in this study.

Figure 6. Thin section images of mortars from Kahta Castle ((cross nicols 2.5x). The results of physical and physicomechanical tests were shown in Table 1. The average bulk density of the mortar samples from Kahta castle was 1.70 g/cm3. Average porosity was 35%. Uniaxial compressive strength test results varied between 7.2 and 8.4 MPa. Those were approximate values due to the assumptions made for calculating the compressive strength data from irregular non-standard shaped historic mortar samples.

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Table 1. Physical and physicomechanical properties of mortar samples from Kahta Castle

Sample Bulk density

(g/cm3) Porosity

(%) USV

(m/s) Uniaxial comp. strength

(MPa) Emod (MPa)

MK1 1,71 35 1928 8,4 5872

MK2 1,72 34 1854 7,8 5434

MK3 1,68 36 1781 6,3 5010

MK4 1,65 36 1844 7,2 5376 Analyses of prepared pozzolanic lime mortars The river sand used for the preparation of the mortars was analyzed for the particle size distribution. The particles having sizes greater than 1000 micron constituted approximately 40% of total aggregate mass. Particle size distribution of aggregates resembled to that of acid insoluble part of mortars from Kahta Castle (Fig 7). Analyses of thin sections of mortars prepared with those aggregates showed that radiolarite, serpentinite and schist were the common aggregates similar to the mortar samples from Kahta Castle. Limestone and quartzite were also observed both in historic and prepared mortars with local sand (Fig 8). There was considerable similarity between the mineralogical components of aggregates in Kahta Castle mortars and local river sand. That showed that the aggregates of mortars from Kahta samples were probably from that local source, however some of the mineral fragments like muscovite and titanite in aggregates of Kahta Castle and plagioclase in the local river sand were different. That might indicate that the aggregates were coming from the same river but from different parts or branches of the river.

Figure 7: Particle size distribution of the aggregates used for preparing pozzolanic mortars.

Figure 8. Thin section view showing the aggregates used for the prepation of pozzolanic mortars (cross nicols 2.5x). Pozzolanic activity results of the pozzolans used and the fine acid-insoluble aggregates of mortars

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from Kahta Castle were shown in Table 2. Table 2. Pozzolanic activity of pozzolans and fine aggregates of mortars from Kahta Castle.

Sample Percent Ca(OH)2 consumed by 1 g

material (%)

Metakaolin 33

Trass 6

MK 15

CS - MK:acid insoluble fine aggregates of mortars from Kahta Castle. CS: fine aggregates of local river sand.

Metakaolin was observed to have the highest pozzolanic activity compared to the others. The fine acid insoluble aggregates of mortars from Kahta Castle also showed relatively high pozzolanic activity. The fine aggregates of local river sand used for the preparation of the pozzolanic mortars showed no pozzolanic activity. Results of physical and physicomechanical analyses were shown in Table 3. Compressive strength and modulus of elasticity values of metakaolin added mortars were greater than that of mortars with added natural trass. Porosity values of the metakolin added mortars were lower than mortars prepared with trass. Higher pozzolanic activity of the metakaolin contributed for these results as formation of CSH and CSAH phases formed a denser mortar with higher mechanical strength. Table 3. Physical and physicomechanical properties of pozzolanic lime mortars after 60 days.

Formation of CSAH and CSH phases in the mortar matrix was investigated by XRD, SEM and EDX. In the XRD of mortars prepared with metakaolin, stratlingite peaks were detected showing the formation of CSAH crystals after the initial setting period. CSH peaks were also detected in the XRD traces of the same metakaolin added mortars (Fig 9). Unreacted portlandite were observed in XRD traces (Fig 9, 10) and FTIR spectra (Fig 11) of both mortars as confirmed by the free Ca(OH)2 test of mortar samples by EDTA titration. The free Ca(OH)2 percent with respect to the total mass of mortars with metakaolin and trass was 15% and 28% respectively. Calcite peaks were present in both mortars. The presence of portlandite peaks showed that the carbonation and pozzolanic reactions did not consume all of the Ca(OH)2 and reactions were continuing

Sample Bulk density

(g/cm3) Porosity

(%) USV

(m/s) Uniaxial comp. strength

(MPa) Emod (MPa)

Metakaolin added

1.37 29 1706 6.4 6780

Trass added 1.34 36 1421 3.5 4604

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Figure 9. XRD spectra of pozzolanic lime mortar with added metakaolin. Q: quartz, S: stratlingite (CSAH), P: portlandite, C: calcite

Figure 10. XRD spectra of pozzolanic lime mortar with added trass showing calcite and unused Ca(OH)2. C: calcite, Q:quartz, P: portlandite In the SEM analyses of the mortars with added metakolin needle like structures, possibly crystal phases from pozzolanic reactions were detected (Fig 12). Result of spot EDX analyses of the needle like structure was shown in Figure 13. In mortars prepared with added natural trass the crystal structure was granular and no fiber like structures was observed (Fig 12).

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Figure 11: FTIR spectra showing the presence of Ca(CO)3 and unreacted Ca(OH)2. Mortar with added metakaolin (left) and mortar with added trass (right).

Figure 12. SEM image of possible needle like CASH formation from mortar prepared with added metakaolin (left). Crystal structure of the binder of trass added mortars (right).

Figure 13. EDX analyses of needle like CASH structure

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CONCLUSIONS

Historic mortars investigated gave important information about the properties of a durable mortar that was used with limestones. Bulk densities of the investigated mortars were between 1.65-1.72 g/cm3, with an average porosity value of 35%. The compressive strength values were in the range of 6.3-8.4 MPa and modulus of elasticity 5010-5872 MPa. White lumps in the mortar matrix were determined to be unmixed slaked lime in the mortar matrix. They were formed by the carbonation of fat lime, used as binder in historic mortars as revealed by SEM-EDX. XRD analyses and free calcium hydroxide test showed that there was unused lime in mortars at the end of 60 days. Petrographical analyses showed that the aggregates of mortars from Kahta Castle was likely from the same local river (Cendere river) as the river sand used for the preparation of pozzolanic lime mortars in this study. But it should be emphasized that they were probably from a different part or branch of the river. The average bulk densities of mortars prepared by using metakaolin and trass were in the same range varying between 1.34-1.37 g/cm3. Average porosity of the mortars with added metakaolin were slightly higher. Repair mortars prepared with added metakaolin had higher strength values after 60 days of curing time. The uniaxial compressive strength values were 6.4 MPa on average for mortars with added metakaolin. Mortars with added trass had an average compressive strength value of 3.5 MPa after 60 days. Those results showed that metakoin added mortars reached the range of compressive strength of historic mortars at end of curing time but mortars with added trass had compressive strengths much lower than historic mortars. Presence of unreacted Ca(OH)2 in both pozzolanic mortars showed that the carbonation and pozzolanic reactions were not completed yet. So the physicomechanical values would probably continue to increase. The initial studies on pozzolanic lime mortars showed promising results. The effect of different pozzolan/lime ratios will be studied in the continuation of this study. The compatibility and durability of pozzolanic lime mortars and limestone will also be investigated. Acknowledgment This work is supported in part by a grant in the context of “Kommegene Nemrut Conservation and Development Project” by Ministry of Culture and Tourism, Turkey. REFERENCES [1] Salvadori M., 1982, Why Buildings Stand Up, The Strength of Architecture), McGraw Hil, 311 p. [2] Holmes S., Wingate M., 1997, Building with Lime, A Practical Introduction, Intermediate Technology Publications, London , 306 p [3] Jedrzejewska H., 1960, Old Mortars in Poland: A New Method of Investigation, Studies in Conservation, V 5, 132-138 [4] Frizot M., 1981, L’analyse des mortiers et enduits des peintures murales et des batiments anciens, Proceedings of the ICCROM Symposium “Mortars, Cements and Grouts Used in the Conservation of Historic Buildings, Rome, ICCROM, pp 281-295 [5] Cliver E.B., 1972, Tests for Analyses of mortar Samples, Bulletin-Association for Preservation Technology, V6, pp 68-73

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[6] Middendorf B., Baronio G., Callebaut K., Hughes, 2000, Chemical-Mineralogical and Physical-Mechanical Investigations of Old Mortars, Proceedings of the International RILEM Workshop: Historic Mortars: Characteristics and Tests, Paisley, pp 53-61 [7] Martinet G., Quenee B., 2000, Proposal for a Useful Methodology for the study of ancient mortars, Proceedings of the international RILEM Workshop, Historic Mortars: Characteristics and Tests”, Paisley, pp 81-91 [8] Van Balen K., Toumbakari E.E., Blanco-Verela M.T., Aguilera J., Puertas F., Palomo A., Sabbioni C., Riontioni C., Zappia G., 2003, Environmental Deterioration of Ancient and Modern Hydraulic Mortar, Protection and Conservation of European Culturalk Heritage, Research Report European Commission, No 15, EUR 19863 [9] Sanches-Moral S., Luque L., Canaveras J.C., Soler V., Garcia-Guinea J., Aparicio A., 2005, Lime Pozzolana Mortars in Roman Catacomns: Composition, Structures and Restoration, Cement and Concrete Research, V 35, pp 1555-1565 [10] Moropoulou A., Bakolas A., Bisbikou K., 1999, Investigation of the Technology of Historic Mortars, Journal of Cultural Heritage, V 1, pp 45-58 [11] Moropoulou A., Bakolas A., Anagnostopoulou, 2005, Composite Materials in Ancient Structures, Cement & Concrete Composites, V 27, pp 295-297 [12] Papayianni I., 2005, Design and Manufacure of Repair Mortars for Interventions on Monuments and Historical Buildings, Proceedings of the International RILEM Workshop: Repair Mortars for Historic Masonry, Delft, 2005 [13] Genestar C., Pons C., Mas A., 2006, Analytical Characterisation of Ancient Mortars from the Archaeological Roman City of Pollentia (Baleric Islands, Spain), Analytica Chimica Acta, 557, 372-379 [14] Lanas, J. and José Alvarez-Galindo, I., 2003, Masonry repair lime-based mortars: factors affecting the mechanical behavior, Cement and Concrete Research, Volume 33, Issue 11, Pages 1867-1876 [15] Elert K., Rodriquez-Navarro C., Sebastian Pardo E., Hansen E., Cazallo O., 2002, Lime Mortars for the Conservation of Historic Buildings, Studies in Conservation, V 47, pp 62-75 [16] Henriques, F.A., 2004, Replacement Mortars in Conservation: An Overview, Proceedings of the 10th International Congress on Deterioration and Conservation of Stone, ICOMOS, Stockholm, pp 1-11 [17] Papayianni I., 2005, Design and Manufacure of Repair Mortars for Interventions on Monuments and Historical Buildings, Proceedings of the International RILEM Workshop: Repair Mortars for Historic Masonry, Delft, 2005 [18] Leslie A.B., Gibbson P., 2000, Mortar Analysis and Repair Specification in the Conservation of Scottish Historic Buildings, Proceedings of the International RILEM Workshop: Historic Mortars: Characteristics and Tests, Paisley, pp 273-280 [19] Sasse, H.R. and Snethlage, R., 1997, Methods fort he Evaluation of Stone Conservation Treatments, Saving our Architectural Heritage, ed. By N.R. Baer and R. Snethlage, John Wiley&Sons, Berlin, pp 223-243 [20] RILEM, 1980, Tentative Recommendations, Comission-25-PEM, Recommended Tests to Measure the Deterioration of Stone and Assess the Effectiveness of Treatment methods, Materiaux and Construction, V 13, pp 173-253

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[21] Frias M., Villar-Cocina E., Sanches de Rojas M.I., Valencia-Maroles E., 2005, The Effect that Different Pozzolanic Activity Methods has on the Kinetic Constants of hte Pozzolnaic Reaction in Sugar Cane Straw-ash/Lime Systems : Application of a Kinetic-diffusive Model, Cement and Concrete Research, V 35, pp 2137-2142 [22] ISRM, 1985, Suggested Method for Determining Point Load Strength, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, V 22, pp 51-70