TY - JOUR
AU - Slížková,, Zuzana
AB - Abstract It is rather difficult to set up non-destructive or considerate in situ tests for assessing material characteristics and consolidation effects on historic stone and mortar. However, some simple methods have proved to be helpful when applied appropriately and this paper provides brief information about two such methods: peeling tests, also known as the ‘Scotch tape’ method, and surface water uptake measurements using a digitized microtube. Both methods have some history of development and use Mora and Torraca (1965 Bollettino Istituto Centrale del Restauro (Rome) pp 109–32), Giorgi et al (2000 Stud. Conserv.45 154–61), Tiano et al (2006 J. Cult. Heritage7 49–55), Lehmann (2004 Thesis, Hochschule für Bildende Künste, Dresden pp 33–34), Drdácký et al (2011 Proc. European Workshop on Cultural Heritage Preservation pp 126–30) and Zíma (2011 Proc. 49th Int. Scientific Conf. on Experimental Stress Analysis pp 441–8) without any standardized support. This lack of a validated procedure can lead to some deficiencies and misinterpretations for applying the peeling test. Also, in the case of the digitized micro-tube, there can be some difficulties when the device is applied, which could prevent its wider adoption or even lead to rejection of the micro-tube technique. The paper summarizes basic principles for the application of both methods and reports illustrative results for laboratory and historic building investigations. testing in situ, near surface cohesion, water uptake, peeling test, digitized micro-tube Peeling test procedure We will explain the procedure in a form that we recommend for practical applications (Drdácký et al2012). The procedure depends on the ability to measure the released material directly on site, or to transport the samples to a laboratory. In either case, the first step is to select an area without gross defects and imperfections, which is dry and representative of the tested material (i.e. reasonably clean) and place the Scotch tape on the measured surface. When a sample is transported to a laboratory for further processing, we recommend the use of double tape samplers, which have to be prepared in the laboratory before the in situ test is performed. These samplers can be rather small in size, about 20 × 40 mm. A plastic strip with an adhesive layer on one side only can also be used if it is long enough to be folded for transportation with the attached particles. The double tape sampler has to be taken out of the sampling bag, and then the cover sheet of the adhesive layer must be removed and kept for readjustments after the peeling has been done, see figure 1 (upper left). The tape or plastic strip is then stuck to the surface, see figure 1 (upper right). The tape is then smoothed into place using a finger and after approximately 60 s of application removed by taking the free end and pulling it off steadily, without jerking, at a rate of about 10 mm s–1 and at an angle of 90°, see figure 1 (lower left). Adjusting the protective sheet over the adhesive layer with the released material, it is then inserted back into the transportation sampling bag, and the zip closed, see figure 1 (lower right). When a single sided plastic strip is used, the problem of measuring the amount of the stuck material occurs, which can be done in situ by a portable balance. Because a sensitive device must be used, its field operation might be very impractical or even impossible, e.g. when working on scaffolding. Therefore, we suggest folding the tape after measurement carefully by simply bending it along the centre, fixing it into a transportation box which the authors designed specifically for this purpose and taking the sampler to a laboratory (figure 2). The weight is measured in the laboratory. When using a double tape sampler, it is advantageous to weigh the bags together with the samplers before the field measurements, and to do the same when returning to the lab with the samplers carrying the stuck, released material. Plastic strips are usually not weighed before application, because the differences in the thickness and weight of the plastic strip are more or less negligible in comparison with the mass of the released sand or stone material. The folded strips with the attached material between the two strips are only cut to a given length in the laboratory and weighed for a comparative evaluation. This technique simplifies and accelerates the measurement procedure, and makes the method more versatile in contrast to recommendations published previously. Instead of plastic strips, commercially available paper labels with adhesives may also be used if there is no danger that they will be wetted. On site, the test should be repeated ten times at the same place (ideally) and then repeated in other places on the investigated surface. Figure 1. Open in new tabDownload slide Double side tape sampler with the cover sheet of the adhesive layer removed (upper left), the tape or plastic strip stuck and gently smoothed to the surface, (upper right), tape sampler removal from the tested place (lower left), double side tape inserted back into the transportation sampling bag (lower right). Figure 1. Open in new tabDownload slide Double side tape sampler with the cover sheet of the adhesive layer removed (upper left), the tape or plastic strip stuck and gently smoothed to the surface, (upper right), tape sampler removal from the tested place (lower left), double side tape inserted back into the transportation sampling bag (lower right). Figure 2. Open in new tabDownload slide Plastic single tape folded and fixed in a transportation box (design Tomáš Fíla and Miloš Drdácký). Figure 2. Open in new tabDownload slide Plastic single tape folded and fixed in a transportation box (design Tomáš Fíla and Miloš Drdácký). Testing procedure background Why do the authors recommend repeating the measurement ten times? The main doubts about the method lie in the fact that the loosened particles on the tested surface do not represent the ‘near surface cohesion’ characteristics of the tested material. If we repeat the peeling in the same place we observe a decrease in the released material and thus an apparent, but false, consolidation effect. Obviously, the same problem exists when consolidation treatment effects are checked on degraded historic materials or on deteriorated materials of any other age. After sticking and peeling has been repeated several times, the amount of detached material starts to become almost constant and characterizes the cohesion of the material (figure 3). The illustrative figure clearly shows that the method is sufficiently sensitive to lime mortar quality variations caused by various mixture composition. Another measurable parameter may be the peeling force for which a special device has been developed by SINT (Regione Toscana) (Bertelli (2011)) or resistance against peeling. This is obviously less practical, but it also corresponds quite well with the material characteristics. Figure 3. Open in new tabDownload slide Weights of the released material particles at individual test repetitions on lime mortars of various lime to sand ratios (1:3, 1:4, 1:6 and 1:9). Figure 3. Open in new tabDownload slide Weights of the released material particles at individual test repetitions on lime mortars of various lime to sand ratios (1:3, 1:4, 1:6 and 1:9). For an evaluation of the weight measurements, a nonlinear approximation model is adopted. This is necessary if the data converges to some positive, i.e. non-zero value, see figure 4. The approximation function in the shape presented in figure 4 relates the amount of the released material (m(n)) in a peeling sequence to the number of the peeling sequence (n). The determined approximation asymptote is considered to be a surface cohesion characteristic. This method has been successfully applied to several historic objects and has provided data on the consolidation effects attained on degraded porous materials after various impregnations (Machačko et al2011). Figure 4. Open in new tabDownload slide Nonlinear approximation model for a sequence of measurements. Figure 4. Open in new tabDownload slide Nonlinear approximation model for a sequence of measurements. In situ water uptake measurements Another simple method that can be applied in situ has been suggested instead of the so-called Karsten tube for in situ water uptake measurements. The Karsten tube method was introduced into stone survey practice several years ago, although it was developed for a different purpose (Wendler and Snethlage 1991). This method is not very user-friendly and its application leads to many difficulties, namely problems with fixing a heavy glass tube on vertical surfaces. In addition, it cannot be used for measurements on inclined surfaces and ceilings, and the application requires two operators: one who observes the water movement in the scaled glass tube and operates the stop-watch, and another who records the readings. There can also be problems with sealing the contact ring area, and the sealing putty can soil the surface. Some other approaches have therefore been tested (Pleyers and Sasse 1999, Vandevoorde et al2011). Digitized micro-tube system This innovated micro-tube system for water uptake measurements is based on the ability to: make an electronic recording of the data, record the water sorption from the very beginning, make continuous measurements of water infusion into the surface, make measurements on arbitrarily inclined surfaces, and measure ‘point’ characteristics. No fixing to the surface and no special sealing are required. The mechanical part of this pistol-like device (figure 5) consists of a scaled capillary tube or any other scaled glass tube in a tube holder adjustable in horizontal or vertical position (swivel connected), a connecting plastic hose, an outlet hinged head with a three-point support, a switch for manual data recording, and a connection cable to the data storage unit. The electronics are housed in a sheet metal box which has an OFF/ON switch on the front panel. The upper panel has an illuminated LCD alpha-numerical display, and in the upper right corner there is a two-position switch (with positions marked 0 and 1). This opens and closes the measured data group. The red switch has the same function as the trigger (4) on the pistol, and records an instantaneous time value in the memory. On the left side of the box there is a USB connector for transferring the data from the electronic unit to a PC or a Notebook (Drdácký et al2011). The device is commercially available and only a few prototypes have been produced. Figure 5. Open in new tabDownload slide Digital microtube device for water uptake measurements. Figure 5. Open in new tabDownload slide Digital microtube device for water uptake measurements. Water uptake measurement procedure This unit records time intervals corresponding to the defined volume of water absorbed by the tested material. The water uptake velocity is observed on the scaled microtube, which is kept in a holder fixed to the pistol with a magnet. The holder also enables other tubes to be fixed, for example a Mirowski tube or even a Karsten tube (when rotated into vertical position) and the holding fixtures are replaced by fixtures matching the applied tube. However, the horizontal capillary tube can be used for measurements on inclined surfaces e.g. vaults or ceilings. The pistol trigger is modified in the form of a microswitch, which manually controls the recording of the instantaneous real time value into a processor memory in the relevant set of the open group of measurement data. It is pushed when the water meniscus in the capillary tube crosses the scale line, corresponding to a value of 0.01 mL in a typical capillary tube. Of course, other scaled tubes can be used. The trigger is connected to the electronic unit through a cable with a connector. The device enables 40 measuring groups to be recorded, i.e. measurements can be recorded on 40 places. Then the records should be stored on a computer and the device memory erased for the device to be ready for another series of measurements. Data presentation In the case of a microtube, the acquired data covers a very short period of water absorption, due to the limited amount of water in the tube. The records are therefore approximated by a linear function, which is used as the measurement representation instead of the usual water uptake coefficient. Figure 6 is a graphical representation of the measured data from in situ water uptake measurements on a differently deteriorated ‘opuka’ (marl) stone wall—from a rather compact material (1), through slightly degraded rock (2) to seriously deteriorated and cracked material (3) and (4). Line (5) relates to a vertically cracked part of the relatively compact stone on which measurement no. 1 was made. It is apparent how cracks influence the measurements. Another illustrative example in figure 7 shows evaluated data from in situ water uptake measurements on differently treated historic plaster-–there is an untreated Romanesque/Gothic plaster (full line), then a family of measured characteristics of the same type of historic plaster treated with CaLoSiL nanolime (a suspension of calcium hydroxide in various alcohols—ethanol (E25, E50)) or isopropanol (Ip25), and the plaster treated with ethylsilicate Funcosil 500 (dashed line) (Bryscejn et al2010). Figure 6. Open in new tabDownload slide Graphical representation of the measured data from in situ water uptake measurements on a differently deteriorated ‘opuka’ (marl) stone wall. (The photograph covers a length of 1 m). Figure 6. Open in new tabDownload slide Graphical representation of the measured data from in situ water uptake measurements on a differently deteriorated ‘opuka’ (marl) stone wall. (The photograph covers a length of 1 m). Figure 7. Open in new tabDownload slide Water uptake characteristics of historic plasters—untreated and after impregnation by nanolime or ethylsilicate. Figure 7. Open in new tabDownload slide Water uptake characteristics of historic plasters—untreated and after impregnation by nanolime or ethylsilicate. Conclusion We can conclude this presentation of the peeling technique as follows: the method is quite sensitive to the condition of the surface, but, on the other hand, one measurement does not provide data for reproducible measurements of quantitative material (mechanical) characteristics describing the state of the material under the very near surface layer. It seems that the change in the amounts of material released from a surface, which has been repeatedly touched—by repeated peeling testing, by the application of consolidation treatment, or by cleaning—may render the peeling material characterization after any treatment non-objective, uncertain and not reproducible. After repeated peeling at an identical place, the amount of released material starts to become almost constant. The method is quite applicable for a relative assessment of material cohesion characteristics. In this paper we presented an innovative technique using single sided tape, which simplifies the procedure and spares labour time significantly. Similarly, the innovated micro-tube method provides easy and fast operation, easy storage, easy further elaboration of data, measurements on arbitrarily inclined surfaces and no surface soiling. It can be used for water uptake point-wise measurements on very complex shapes with a small radius of curvature. It is several times more efficient than the Karsten tube method in terms of demands on personnel and time for surface water uptake characterization. The presented prototype with a scaled glass tube is intended for measurement on surfaces with a medium rate of water uptake. For very high, as well as rather low, water absorption rates a prototype without a glass microtube has been developed—here the contact sponge (a ‘cigarette filter’) is fed from a water container connected by a flexible hose and the uptake velocity is measured by the position of a small float in the container. However, this method is under development, and more verification and correlation studies are needed. This paper has shown that rather simple techniques in combination with modern digital technologies and numerical methods, when used in a correct way, may provide the user with affordable instruments for an in situ assessment of important material characteristics which are difficult to measure by other means. Acknowledgments The authors acknowledge kind support from the Czech Science Foundation Project GAČR P105/12/G059 and from the institutional support RVO 68378297, and thank RN Dr Ivanka Frolíková for careful preparation of the figures. References Bertelli L . , 2011 , Sistema per I'Esecuzione di Test di Peeling su Materiali Lapidei—Relazione Technica Periodica (April 2011, SINT) report no. 2924 Bryscejn J , Drdácký M , Valach J , Zíma P . , 2010 Testing of CaLoSiL treatment effects on historic rendering at rosa coeli monastery in dolní kounice , Research Report FP 7 NMP STONECORE Project (Praha: ÚTAM AV ČR) p 44 Drdácký M , Černý M , Slížková Z , Zíma P . , 2011 Microtube device for innovative water uptake measurements Proc. European Workshop on Cultural Heritage Preservation 26–28 Sept. Berlin Krüger M . Stuttgart Fraunhofer IRB Verlag (pg. 126 - 130 ) ISBN 978-3-8167-8560-6 Drdácký M , Lesák J , Rescic S , Slížková Z , Tiano P , Valach J . , 2012 Standardization of peeling tests for assessing the cohesion and consolidation characteristics of historic stone surfaces , Mater. Struct. , vol. 45 (pg. 505 - 520 ) 10.1617/s11527-011-9778-x Google Scholar Crossref Search ADS PubMed WorldCat Crossref Giorgi R , Dei L , Baglioni P . , 2000 , Stud. Conserv. , vol. 45 (pg. 154 - 161 ) 10.2307/1506761 Crossref Lehmann M . , 2004 Die gewölbemalereien in der krypta der stiftskirche st. servatius in quedlinburg , Thesis Hochschule für Bildende Künste, Dresden (pg. 33 - 34 ) Machačko L , Kolinkeová B , Macounová D , Bayer K . , 2011 A few notes on research and restoration works carried out at the university of pardubice within the frame of the EU project STONECORE Proc. European Workshop on Cultural Heritage Preservation Berlin 26–28 Sept. Krüger M . Stuttgart Fraunhofer IRB Verlag (pg. 246 - 253 ) ISBN 978-3-8167-8560-6 Mora P , Torraca G . , 1965 Fissativi per dipinti murali , Bollettino Istituto Centrale del Restauro Rome (pg. 109 - 132 ) Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Pleyers G , Sasse H R . , 1999 Non-destructive determination of the penetration depth of impregnation materials , The Use of and Need for Preservation Standards in Architectural Conservation Sickles-Taves L B . Atlanta, GA ASTM International ISBN 0803126069 Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Tiano P , et al. , 2006 Biomediated reinforcement of weathered calcareous stones , J. Cult. Heritage , vol. 7 (pg. 49 - 55 ) 10.1016/j.culher.2005.10.003 Google Scholar Crossref Search ADS WorldCat Crossref Vandevoorde D , Cnudde V , Dewanckele J , Boone M N , Verhaeven E . , 2011 Contact-sponge method: performance compared with capillary rise, Karsten tube and Mirowski pipe Proc. European Workshop on Cultural Heritage Preservation Berlin 26–28 Sept. Krüger M . Stuttgart Fraunhofer IRB Verlag (pg. 117 - 125 ) ISBN 978-3-8167-8560-6 Wendler E , Snethlage R . , 1991 Der wassereindringprüfer nach karsten–anwendung and interpretation der messwerte, münchen, bayerisches landesamt für denkmalpflege , Forschungsbericht Nr. 3 (pg. 23 - 34 ) OpenURL Placeholder Text WorldCat Zíma P . , 2011 Measurement of water uptake of historic surfaces—state of the art review Proc. 49th Int. Scientific Conf. on Experimental Stress Analysis Návrat T , Fuis V , Houfek L , Vlk M . Brno Brno University of Technology (pg. 441 - 448 ) ISBN 978-80-214-4275-7 © 2013 Sinopec Geophysical Research Institute
TI - Enhanced affordable methods for assessing material characteristics and consolidation effects on stone and mortar
JF - Journal of Geophysics and Engineering
DO - 10.1088/1742-2132/10/6/064005
DA - 2013-12-01
UR - https://www.deepdyve.com/lp/oxford-university-press/enhanced-affordable-methods-for-assessing-material-characteristics-and-XNulT5mv2t
VL - 10
IS - 6
DP - DeepDyve
ER -