12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

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1 THE COMBINATION OF CALCIUM HYDROXIDE-SOL AND SILICIC ACID ESTER AS NEW METHOD FOR THE STRUCTURAL CONSOLIDATION OF OBJECTS BUILT OF TUFF, LIME MARL, TRACHYTE LATEST FINDINGS Ewa Maryniak-Piaszczynski, 1 Verena Wolf 1 and Elisabeth Ghaffari 2 1 Company: Strotmann & Partner, Restorers, Hauptstr. 140, Siegburg, Germany 2 University of Applied Arts Vienna, Institute of Arts and Technology, Section of Conservation Sciences, Salzgries 14/1, A-1013 Wien, Austria Abstract Laboratory investigations concerning the consolidation of flaking and scaling stones (tuff, trachyte, marl and limestone) show that common testing methods do not give sufficient information s when utilised on not weathered materials. New methods had to be found. Therefore dummy samples (samples of powder, cubic samples, cylindric samples), which simulate deteriorated stone were developed in three years of investigations within the EU project STONECORE. These samples gave totally new insights to the structural consolidation of disintegrated stones. Three different consolidation methods were tested: - consolidation with silicic acid ester (Funcosil 100 and 300, Remmers, Germany) - consolidation with nanolime: calcium hydroxide nano-particles in different alcohols (CaLoSiL, IBZ Salzchemie, Germany) - consolidation with a combination of nanolime and silicic acid ester The efficacy of consolidation treatments was assessed through various methods of measurements: tensile bending strength, water absorption after 24h, porosity, peeling test, drilling resistance, X-ray-analyses and microscopic analyses. The best results gave dummy samples which were first treated with CaLoSiL to consolidate flakes and loose particles and additionally with silicic acid ethylester. Keywords: stone conservation, consolidation, scales, flakes, silicic acid ester, nanolime, CaLoSiL, combination of CaLoSiL and silicic acid ester 1. Introduction Heritage protected stone monuments show among deterioration patterns like sanding as well degradation in terms of scaling and flaking. Till this day common consolidation materials often show unsatisfying results when dealing with those decays. One example of the inorganic consolidation group is silicic acid ester based on tetraethoxysilane, which is a very popular material in the field of conservation of stones and mortars. CaLoSiL products can offer a new method of consolidation where traditional materials and techniques fail. Therefore the use of CaLoSiL compounds is desirable 1

2 especially where silicic acid ester is inappropriate. For example silicic acid ester is in some cases not able to bridge large spaces which make it unsuitable as consolidant for flaking and scaling stones. In this kind of deterioration phenomena fillers and adhesives for bridging are required. Nano-lime could be a possible solution. A further alternative might be a combination of both products (CaLoSiL and silicic acid ester) to utilise their particular advantages for a successful consolidation. Three years of investigations have been engaged in this topic. This paper presents the most important laboratory results. 2. Materials and sample preparation Former consolidation investigations on unweathered materials show insufficient significant results for praxis relevant application methods. Therefore different kinds of samples were prepared in laboratory which simulates a diversity of stone deterioration. Figure 1-3. Flaking and sanding stones: Limestone, Marl, Tuff. Table 1: Range of used materials Sample Crushed Consolidant Short name shape material of consolidant Dummy samples Marl Nano-lime: calcium hydroxide in ethanol CaLoSiL E25 Sandwich samples Limestone Nano-lime: calcium hydroxide in iso-propanol CaLoSiL IP25 Cylindrical samples Trachyte Nano-lime: calcium hydroxide in n- propanol CaLoSiL NP25 Cubic Tuff Silicic acid ester Funcosil 100 samples Silicic acid ester Funcosil 300 Figure 4. Dummy samples Figure 5. Cylindrical samples 2

3 Figure 6. Sandwich samples Figure 7. Cubic samples On the one hand samples were sole treated with CaLoSiL or Funcosil, on the other hand combinations of both consolidants were tested. Subsequent a set of analysis were conducted to approve the results. 3. Measurements and analyses on selected samples The most important investigations and their results are given in the following section. This includes only a selection of laboratory made samples. However, applications on real objects and their examinations are not included in this paper. 3.1 X-ray-analyses and mineralogical composition Scanning electron microscopy and EDAX investigation (Investigations by D. Kirchner, Deutsches Bergbau-Museum Bochum with Pananlytical X Pert Pro Data Collector X-Celerator) Investigation after two weeks of storage at RH 75% X-ray examinations of samples, which were treated with different combinations of CaLoSiL and Funcosil show a lot of amorphous structures which cannot be clearly identified. The following crystals can be detected: calcites, portlandites and vaterites. The lower the concentration of Funcosil the higher is the concentration of calcites, vaterites and calcium hydroxide. EDAX analyses always present chemical structures of silicon and calcium but the structure changes in each composition. Investigations show that CaLoSiL IP25 with heptane, CaLoSiL E25, CaLoSiL IP25 and CaLoSiL NP25 build the biggest amount of calcites, vaterites and portlandites. Figure 8. X-ray examination of all compounds 3

4 12th International Congress on the Deterioration and Conservation of Stone X-ray examinations on samples which were treated with CaLoSiL NP25, Funcosil 100 and 300 in different variations: Figure 9. CaLoSiL NP25, after 24 hrs: Funcosil 100 Figure 10. CaLoSiL NP25, after 24 hrs: Funcosil 300 Figure 11. All methods (Grey: Mixture of CaLoSiL NP25 and Funcosil 100) EDAX investigations and SEM-analyses on samples which were treated with CaLoSiL NP25, Funcosil 100 and 300 in different variations: Figure CaLoSiL NP25, after 24 hrs: Funcosil 100 Figure CaLoSiL NP25, after 24 hrs: Funcosil 300 Figure Mixture of CaLoSiL NP25 and Funcosil 100 4

5 Treatments with pure CaLoSiL form Ca- minerals: vaterites, calcites and portlandites. In combination with silicic acid ester amorphous structures are built as well. The lower the concentration of silicic acid ester (Funcosil 100 ) in combination with CaLoSiL the more portlandites, calcites and vaterites can be analysed. The bigger the amount of silicic acid ester (Funcosil 300 ) the less Ca-minerals are formed. In that case, the amount of amorphous structures decreases. 3.2 Physical and mechanical properties dependant on the used consolidant The change of physical and mechanical properties is shown on examples of marble samples (fraction of 0 2 mm) which were treated with CaLoSiL and Funcosil 100 and 300 in different combinations F u n c o s i l F u n c o s i l , 2 0, 1 5 0, 1 0, F u n c o s i l F u n c o s i l Funcosil 100 Funcosil 300 Figure 21. Porosity (vol. %) Figure 22. Tensile bending strength N/mm 2 Figure 23. Water absorption after 24h (w. %) 0,3 0,25 0,2 0,15 0,1 0,05 0 Funcosil 100 Funcosil 300 Figure 24. Compressive strength N/mm² Control: marble without consolidation : : : Control: CaLoSiL 25g/l with ethanol, after 6 treatments Control: only silicic acid ester 1 x CaLoSiL 25g/l with ethanol after 2 h silicic acid ester 6 x CaLoSiL 25g/l with ethanol after 1 day silicic acid ester 8 x CaLoSiL 25g/l with ethanol after 1 day silicic acid ester 6 x CaLoSiL 25g/l with ethanol after 6 days silicic acid ester 6 x CaLoSiL 25g/l in ethanol, first wetted with water (16%) Following changes compared to the control sample occur by a treatment with CaLoSiL and silicic acid ester in combination: - the water absorption decreases - the porosity and the mechanical properties increase - best results show samples with a treatment of CaLoSiL (six times) and after 24 hrs Funcosil 100 and Funcosil the mechanical properties improve 5

6 - the capillarity does not change much In general a pre-wetting with water prior to the consolidation shows a positive influence on the capillary and mechanical properties. 3.3 Physical properties dependant on the type of stone After a pre-consolidation with CaLoSiL E25 (six times) dummy samples of various kind of stones were treated 24 hrs later eighter with Funcosil 100 or with Funcosil 300 until saturation (storage for 4 weeks: T 18 C, RH 60%). 0,18 0,16 0,14 0,12 0,1 0,0 8 0,0 6 0,0 4 0,0 2 0 Control: only CaLoSiL : : : Tuff Römer Tuff Nordhessen Marl Gotland sandstone Baumberger limestone Carrara marble Figure 25. Tensile bending strength N/mm² Left: Funcosil 100, right: Funcosil 300 Tuff and marl only show a little increase of the tensile bending strength. A distinct increase show samples of calcareous stone. The best results achieve calcareous stones like marble and limestone. In general all samples treated with the combination of CaLoSiL and Funcosil feature an increase of the tensile bending strength instead of a pure silicic acid ester treatment. 3.4 Drilling resistance on sandwich samples Sandwich samples of marble which simulate weathered and unweathered stone were treated with different combinations of CaLoSiL and Funcosil and were stored for six weeks (T 18 C, RH 60%) before drilling resistance tests were investigated. 1 Funcosil applications of CaLoSiL E25 3 Funcosil applications of CaLoSiL E25 and Funcosil applications of CaLoSiL E25 and Funcosil 300 Figure 26. Drilling resistance measurement [atn] 6

7 Drilling resistance measurements show that the combination of CaLoSiL and silicic acid ester stabilizes sanding stone. The samples are harder than those which were consolidated with pure Funcosil 100 and 300 or only with pure CaLoSiL. The best results achieve calcareous stones. Low hardness show samples of tuff, marl and trachyte. Those results are especially practically important in case of scaling or flaking stones because the consolidant is able to build bridges between weathered and unweathered stones. 3.5 Peeling tests (Investigations by ITAM, Czech Republic) Peeling tests dependant on the consolidation method were made on dummy samples of marble (fraction of 0 2 mm) four months after the treatment. Figure 27. CaLoSiL E25, Figure 28. CaLoSil E25, after 24 h: Funcosil 300 after 24h, Funcosil 300 Figures 27 and 28 clearly show better results of a treatment with CaLoSiL E25 and after 24 hrs with Funcosil 300. Dependant on the different stone types a treatment with CaLoSiL E25 and Funcosil 300 achieve the best results: Carrara marble, tuff and Baumberger Limestone. Worse results show marl and trachyte. Figure 29. Marl Figure 30. Baumberger Limestone Figure 31. Tuff 7

8 Figure 32. Trachyte Figure 33. Carrara marble 3.6 Cubic samples: samples of stone powder. Distribution of the consolidants inside the material During laboratory tests it was found out that the distribution of the consolidants, inside a deteriorated stone is one of the most important facts. Therefore special samples which simulate weathered material were prepared (Idea: Malgorzata Musiela, Company Restauro). Cubic samples (2 x 4 cm) of different kind of stones with a drill hole in the middle were produced. The holes (6 mm width and 2 cm length) were filled with the particular stone powder (fraction of 0 2 mm) of each stone to simulate deterioration in practice. The powder was consolidated with different combinations of CaLoSiL and Funcosil. The consolidants were applied up to three times with a syringe until the powder was saturated. Afterwards the samples were put into a humid environment at RH 75% for three weeks. The whole compounds including the natural stone were vacuum-embedded in epoxy resin (Araldite 2020). Polished sections were produced perpendicular to the surface of treatment. The polished cross sections were coated with carbon and studied by SEM (Philips XL 30 ESEM, 20 KV, high vacuum, back-scattered electron detector-bse) fitted with an energy-dispersive X-ray analyser (Link-ISIS). The SEM-micrographs taken at low magnification had to be fitted together by use of Photoshop in order to cover the whole sample diameter. Pores were edited in pseudo colour (blue, in Figure white) in order to ease their visibility and to allow a comparison of the different treatment methods. Most important goal of the experiment is the verification of the penetration behaviour of the consolidant. That fact correlates in a penetration of the consolidant in the deteriorated part of the sample (which is simulated by the powder), a good bonding between weathered and unweathered area of the stone and nearly no penetration into the intact part of the sample. The best effect of consolidation (defined as the recovery of cohesion of loose grains of disintegrated material) was achieved in most cases if both preparations were used: CaLoSiL and then Funcosil. In case of consolidations with pure Funcosil further investigations are necessary because silicic acid ester is not visible in the whole sample although the material was treated until saturation. Especially in the case of Baumberger Limestone (Figure 34) Funcosil penetrates in the intact stone but is not able to bond the loose aggregates. The combination of the 8

9 two consolidants remains in the deteriorated part of the stone, it does not penetrate the intact part. It bonds big and small grains together. This method is suitable for stones that show deteriorated areas like flaking and scaling up to several centimetres, especially on tuff, Baumberger limestone and calcareous stones. These results relate to specific types of stones and mortars. It must be pointed out that each new case requires a preliminary consolidation trial. Figure Baumberger Limestone Left: Funcosil 300 Centre: CaLoSiL E25 and E50 Right: CaLoSiL E25 and Funcosil Results and conclusions The results show that a treatment with CaLoSiL or with a combination of Funcosil is much more successful than a treatment with pure silicic acid ester. CaLoSiL is able to bond flakes and scales and to fill the small spaces between these particles. A following application of silicic acid ethyl ester gives further stability. The formation of stable bridges between the particles and the good distribution inside the stone are absolute advantages of the combination of CaLoSiL and silicic acid ester. The consolidation with CaLoSiL was successful, especially on tuff and limestone. It distributes evenly and bonds large and small grains together. This method can also be modified to match the special requirements of each object. All laboratory and in situ investigations show that a consolidation with CaLoSiL or with a combination of CaLoSiL and silicic acid ethyl ester allows a stabilization of deteriorated stones. CaLoSiL products show good adhesion forces and are able to bridge comparatively large spaces. CaLoSiL forms bridges between the grains and the silicic acid ester adheres to these bridges and to fine grains. The alkaline milieu causes a fast hydrolysis so that the gel is more stable. Beside calcite, vaterite and portlandite, amorphous calcium silicate is formed. Stones with high mechanical properties such as trachyte, marl or calcareous stones should additionally be treated with silicic acid ethyl ester. All investigations as well as the method of sample production cause in a better understanding of structural consolidation processes. In this paper introduced results 9

10 were already applied on following objects: rectory from XVIII century, cloister (1530): cathedral of Xanten, citadel Mainz: coat of arms. Figure Cathedral of Xanten, cloister: conservation on masonry Acknowledgments This article is part of the large research project EU-Project: Stonecore , Contract No STONE COnservation for the REfurbishment of buildings, SEVENTH FRAMEWORK PROGRAMME NMP-Nanosciences, Nanotechnologies, Materials and new Production Technologies. References Busse, H.-B., Egloffstein, P., Gerrecht, H. et al Model intentions: Effect of protective constructions (preventive measures) on the weathering of sandstones due to ecological damage using the example of the north portal of the Benediktinerabtei Tholey (Saarland), Project DBU Az Mainz, Germany : Institut für Steinkonservierung. Maryniak-Piaszczynski, E., Ziegenbalg, G The portal in Tholey- unconventional method for the preservation of scaling and shelled sandstone (Rotliegendsandstone), Proceedings of the 11 th International Congress on Deterioration and Conservation of Stone, Torun, Poland. Piaszczynski, E., Wolf, V The combination of nano-lime and silicic acid ester for stone conservation, Proceedings of the European Workshop on Cultural Heritage Preservation, Berlin 2011, Fraunhofer IRB:Verlag, 254. Piaszczynski, E., Ziegenbalg, G Nanolime as a binder for injection grouts and repair mortars, Historic Mortars-HMC and RILRM TC 203-RHM final workshop. 10