Experimental study for the consolidation of stone of old fortifications

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1 Structural Studies, Repairs and Maintenance of Heritage Architecture IX 395 Experimental study for the consolidation of stone of old fortifications M. Stefanidou & I. Papayianni Department of Civil Engineering, Aristotle University, Greece Abstract For the construction of fortifications large amounts of stone pieces from nearby deposits have been used. Serpentines, gneiss, schist, limestones and marbles are the most commonly found stones. Most of them present decay which is not only surfacial but goes deeper to the interior of the stone. The problem is that their replacement is not always easy and there is a need for cleaning and consolidating them. Since fortifications are usually exposed to extreme climatic conditions because of their position, the question is which consolidant will be more effective in protecting the stones. In this paper the results of a study concerning the characteristics of serpentines, schist and gneiss are presented. Strength, porosity and pore size distribution as well as microscopic observations have been measured before and after the application of commercial consolidants on those stones. The methodologies followed for the determination of the above mentioned characteristics are the recommended ones by NORMAL 26/87 (Group M). Based on the measurements, it seems that ethyl silicate combined with methyl resin is more effective than the other consolidants used. Keywords: stones, physical properties, mechanical properties, consolidation, cleaning. 1 Introduction There are two ways to approach the problem of conservation of stones. The most pessimistic one considers that the conservation should be more effective as there is no progress in the way that stones are cured (C.A. Price, 1996 [1]) and it seems unavoidable to stop the deterioration (N. Belogiannis, 1987 [2]). On the other hand there is the option according to which many steps forward have WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

396 Structural Studies, Repairs and Maintenance of Heritage Architecture IX been made to the right direction (M.L. Tabasso [3]). Many products and technologies have been used since the 195s.

The effectiveness of the treatment can be judged in time and it is considered positive when: - it does not provoke any damage - it reduces the weathering rate To this direction many products of

2 396 Structural Studies, Repairs and Maintenance of Heritage Architecture IX been made to the right direction (M.L. Tabasso [3]). Many products and technologies have been used since the 195s. Experience has made clear that there are no miracle products and no treatment can last forever. The effectiveness of the treatment can be judged in time and it is considered positive when: - it does not provoke any damage - it reduces the weathering rate To this direction many products of different nature have been used from synthetic resins to micro silica. A large number of published papers are referred to the tests based on chemicals that have been performed to different type of stones (A. Moropoulou et al [4]) (A.C Inigo and Jiminez de Haro 1996 [5]). In the case of the stones used in fortifications the forms of pathology are mainly salts, biological growth, crumbling parts and weathering joints. The conservation products should be affective solving the above mentioned problems. In this paper different known products based in ethyl silicate have been used in silicic origin stones and the performed tests are discussed. 2 Materials The materials used for the construction of fortifications were selected according to their availability. A variety of natural stones from the local quarries or even second used stones are usually the constituents of these massive structures. In Greece the materials of fortifications are stones of different types and size, bricks (usually forming belts in the masonry, Castle of Thessaloniki) connected with mud mortars, lime mortars or in some cases (castle of Paros) with lime and pozzolan mortars. Brick pieces were also used in order to fill empty spaces between the stones or to form decorative motives (castle of Servia). In some castles blazons were used in order to determine the construction period (Rhodes). The stones were untreated or treated (usually those of second use). In some cases (castle of Nisiros) large blocks up to 6-7cm were used (A. Loupou-Rokou, 1999 [6]). Figure 1: Biological growth in the stone of the castle of Servia. Figure 2: Alveolization in stone. WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

3 Pathology Structural Studies, Repairs and Maintenance of Heritage Architecture IX 397 The most common problems found in the fortifications are: - Cracks - Loose parts of masonry due to lack of the

3 3 Pathology Structural Studies, Repairs and Maintenance of Heritage Architecture IX 397 The most common problems found in the fortifications are: - Cracks - Loose parts of masonry due to lack of the connected mortar - Biological growth on the stones and mortars (figure 1) - Bulking of masonry walls or declination from vertical position - Stabilization of the ground supporting the castle walls - Weathering of mortars and stones due to the combined action of the wind, rain and salt presence (figure 2) (I. Papayianni et al [7]) 4 Laboratory work This experimental work concerns the application of some commercial consolidants on stones taken from the castle. Three types of stones were used, serpentines, gneiss and schist. The study consists of two parts: - The first concerns the petrographic characterization of the stones and the determination of their mechanical and physical properties - The second part concerns the application of the consolidants on the crumbled stones, the cleaning of the biological growth on the stone s surface and the checking of their effectiveness. In order to fulfill the needs of the first phase microscopic analysis by optical microscopy and SEM had been performed in parallel to the determination of direct compressive strength on the stone samples. Furthermore, porosity analysis concerning the open and total porosity and the pore size distribution of those stones was made. In the case of the castle of Dioklitianoupoli the main stone is serpentines the structure of which is shown in figure 3. Figure 3: Thin section of serpentine from the castle of Dioklitianoupoli. WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

398 Structural Studies, Repairs and Maintenance of Heritage Architecture IX The porosity of this stone is 5,5-9,5 measured by microscopic observation (tab. 1).

4 398 Structural Studies, Repairs and Maintenance of Heritage Architecture IX The porosity of this stone is 5,5-9,5 measured by microscopic observation (tab. 1). Thin section analysis reveals the presence of open cracks (length >2µm and width 2-3µm) (figure 3). The pore size distribution (figure 4) shows that the stone is characterized by small pores with diameter up to 5µm by image analysis. Two main pore categories are shown by BET analysis. Pores with diameter 4A and pores with diameter larger than 24A. δvp/δrp Pore size distribution of untreated Serpentinite (des), ,1 15 1, r(ε) δvp Pore size distribution in serpentinite diameter (µm) Figure 4: Pore size distribution in untreated serpentinite by BET and image analysis. The main mineral is serpentine and also pyroxenes, olivine and calcite are present (I. Papayianni and M. Stefanidou, 23[8]). In figure 5 SEM analysis reveals the microstructure of the stone. As it can be seen the crystals of serpentine are well connected. Figure 5: Well-connected crystals of serpentine (SEM). The mechanical strength of the serpentine is about 1Kg/cm 2 and was determined by crashing cubes 5x5x5cm in compression. In the castle of Servia a various types of stones have been used as schist, marbles, gneiss and quartzite. From the above stones schist and gneiss suffer from various types of pathology mainly due to their nature. Thin section analysis in schist shows the presence of quartz, pyroxenes, biotite and feldspars. Not oriented micro-cracks and cracked crystals of pyroxenes are observed (figure 6). WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

Structural Studies, Repairs and Maintenance of Heritage Architecture IX 399 The porosity measured by image analysis is 4,5-8,5 and the open porosity is 4-5 (tab. 1).

5 Structural Studies, Repairs and Maintenance of Heritage Architecture IX 399 The porosity measured by image analysis is 4,5-8,5 and the open porosity is 4-5 (tab. 1). BET analysis indicates the presence of pores with diameter 4A and pores with diameter larger than 12A. The pore distribution assisted by image analysis shows that pores up to 5µm predominate in the structure and also pores with diameter up to 2µm are present (figure 7). Figure 6: Not-oriented microcracks in the structure of schist (polarized microscope, x65). Schist Pore size distribution (des) Pore size distribution in Schist v p / r p,34,32,3,28,26,24,22,2,18,16,14,12,1,8,6,4, ( v p ) , ,26 1,17 1->2 2 r( ) diameter (µm) Figure 7: Pore size distribution in schist by BET and image analysis. Gneiss on the other hand presents compact structure with microcracks (length 6-65µm, width 1-15µm) (figure 8). Also, the presence of feldspars, quartz, biotite, moscobite and pyroxenes can be seen. The total porosity is 1,73 and the open one is 2-3. The pore size distribution (by BET) shows the presence of pores with diameter 4A and large pores of diameter larger than 12A (figure 9). In order to fulfill the second phase of the study, four consolidation products under the following commercial names were applied to the serpentinite and gneiss and their physical properties were measured as well as their durability to deteriorating agents. WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

4 Structural Studies, Repairs and Maintenance of Heritage Architecture IX - Silex H(of Keim based on esters of ethyl silicate and siloxane) - Trapco Mineralisant (of Weber & broutin based on silic

6 4 Structural Studies, Repairs and Maintenance of Heritage Architecture IX - Silex H(of Keim based on esters of ethyl silicate and siloxane) - Trapco Mineralisant (of Weber & broutin based on silic salts) - RC-9 (of Rhodorsil based on ethyl silicate and methyl resin) - Strengthener H (based on silicon which provides water proof action and ethyl silicate) Figure 8: Open crack in the structure of gneiss (polarized microscope, x65). Gneiss. Pore size distribution (des) δv p /δr p,34,32,3,28,26,24,22,2,18,16,14,12,1,8,6,4, r(ε) (δv p ) Figure 9: Pore size distribution in untreated gneiss by BET. Table 1: Compressive strength and porosity measurements of untreated stones. Stones Comp. strength Kg/cm^2 Open porosity Total porosity O.M B.E.T. Serpentinite 1 5,5 5,5-9,5 4,3 Schist 8 4,65 4,5-8,5 1,53 Gneiss 2 2-3,2-1,2 1,73 WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

7 Structural Studies, Repairs and Maintenance of Heritage Architecture IX 41 The application of the consolidants was performed by brushing in two layers according to the instructions of each product. In tab. 2 and 3 the results of the porosity measurements on serpentinite and gneiss after treatment are shown. Table 2: SERPENTINITE 4.1 Untreated Porosity measurements for the serpentine. Total porosity Pore surface Open porosity m^2/gr 4,3 2,37 5,5 RC-9 6,8 27,53 5,49 Silex H 8,3 24,93 2,66 Strengthener 7,3 23,23 4,35 Table 3: Porosity measurements for the gneiss. GNEISS Total porosity Pore surface m^2/gr Open porosity Untreated 1,81 2,586 2,196 RC-9,83 3,46 1,682 Trapco 1,38 2,95 2,92 Silex H,31,822 1,12 In gneiss it seems that the consolidants have penetrated through the cracks and have reduced both total and open porosity. Serpentine on the other hand, presents higher total porosity after the treatment, which can be attributed to the formation of new open spaces during the BET measurements. BET measurements highlights that the porosity reduction to gneiss is due to the reduction of large pore (radius 6-17A). On serpentine, there seems to be a formation of large pores (>12A)(figure 1) after the measurement. Serpentinite treated with RC 9 Gneiss treated with RC9 δv p /δr p (δv p ) δvp/δrp,2 3,15 2,1 1, δvp r(ε) r(ε) Figure 1: Pore size distribution in treated serpentinite (left) and gneiss (right) with RC9. Comparing the behaviour of the consolidants under deteriorating agents the treated and untreated specimens were subjected to humidity and salt tests (1 WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

42 Structural Studies, Repairs and Maintenance of Heritage Architecture IX w/w Na 2 SO 4 ).

6-RC9 6 Figure 11: Influence of humidity of treated-untreated stones.

test than the untreated ones (figure 12). Figure 12: Biological cleaning by keim-algicid.

8 42 Structural Studies, Repairs and Maintenance of Heritage Architecture IX w/w Na 2 SO 4 ). Indicatively it is mentioned that there was not weight loss for the different samples (nr 3,4,6) of serpentine treated with RC-9 (figure 11). WEIGHT (gr) CASTLE OF SERVIA - STONES INFLUENCE OF HUMIDITY W W 1 W 3 W 5 W 7 W 1 TIME: No of cycles 3-RC9 3 4-RC9 4 6-RC9 6 Figure 11: Influence of humidity of treated-untreated stones. In the case of salt testing it seems that the treated samples of serpentinite showed better resistance to the hard conditions of the test than the untreated ones (figure 12). Figure 12: Biological cleaning by keim-algicid. 5 Conclusions Stones of different petrologic type with various mechanical and physical properties have been used for the construction of walls of fortifications according to the area and the local deposits. They often suffer from deterioration and must be concerned by cleaning and consolidating. WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

9 Structural Studies, Repairs and Maintenance of Heritage Architecture IX 43 Comparing the effectiveness of commercial consolidants it seems that in the case of silicic origin stones (serpentinite, gneiss and schist) the most effective products are those based on ethyl silicate and methyl resin. References [1] C.A. Price Stone Conservation- An overview of current research The Getty Conservation Institute, Santa Monica, CA, [2] N. Belogiannis The deterioration of Stone and how you Will (Not) Avoid it Archeologia Magazine Vol. 22 March 1987, p.p [3] M. L. Tabasso Stone conservation in the last few decades: conceptual and technical developments, scientific investigation and training of professionals. [4] A. Moropoulou et al. Evaluation of consolidation treatments of porous stones-application on the Medieval City of Rhodes 4 th International Symposium on the Conservation of Monuments in the Mediterranean Rhodes 6-11 May 1997 p.p [5] A.C. Inigo and M.C. Jimenez de Haro Study of the porous network of granites from Avila and its modifications by ethyl silicate treatment Proceedings of the EC workshop Sntiago de Compostela, Spain 28-3 November 1994 p.p [6] A. Loupou-Rokou Aegean Castle- and small castle Editions ADAMS, [7] I. Papayianni et al. The FORTMED EC Project A holistic Approach for the Restoration of Castles and their reuse for the Socioeconomic Development of the around Area. The castle of Servia [8] I. Papayianni, M. Stefanidou Study of the behaviour of Serpentine stone used for the construction of ancient Dioklitianoupoli in northern Greece ASMOSIA VII Thassos, Greece 15-2 September 23 (under publication). WIT Transactions on The Built Environment, Vol 83, 25 WIT Press ISSN (on-line)

FINAL REPORT. PROJECT COORDINATOR : Z. AHUNBAY, Dept. of Architectural Conservation and Restoration, Faculty of Architecture, I.T.U.

FINAL REPORT. PROJECT COORDINATOR : Z. AHUNBAY, Dept. of Architectural Conservation and Restoration, Faculty of Architecture, I.T.U. RESEARCH ON THE CHARACTERISATION AND THE DETERIORATION OF THE STONES, THE BRICKS AND THE KHORASAN MORTARS OF THE TOWER 4 (T4), OF THE LAND WALLS OF ISTANBUL (CONSTANTINOPLE) FINAL REPORT PROJECT COORDINATOR