Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2022.34.0085 Acta Polytechnica CTU Proceedings 34:85–93, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague ADHESION TEST – TESTING OF SELECTED ADHESIVES ON FIRED CLAY Kristýna Richterová∗, Pavel Heinrich, Petr Bílý Czech Technical University in Prague, Faculty of Civil Engineering, Department of Concrete and Masonry Structures, Thákurova 7, 166 29 Prague 6, Czech Republic ∗ corresponding author: kristyna.richterova@fsv.cvut.cz Abstract. The following paper deals with the comparison of adhesion of specimens made of fired clay and selected adhesives. The adhesion was tested on specimens at the age of one, two and three days in order to determine the parameters of young masonry. Nine different adhesives (adhesives intended for masonry and adhesives for others material) were tested in total. The above mentioned test is not standardized. The obtained results from the adhesion test determine the tensile strength between the adhesive and the fired clay and the adhesion of selected adhesive to the fired clay. The small specimens were made of two ceramic plates and an adhesive. Selected adhesives were applied to ceramic plates according to the usual standards. Eighty-one small specimens were produced in total – twenty-seven specimens for the adhesion test at each defined age of the specimens (one day, two days, three days). The produced specimens were cured in the climatic chamber with set laboratory conditions until the time of the test. The specimens were tested in the laboratory of the Heluz brick plant in Dolní Bukovsko. This paper deals with the procedure of preparation of the specimens, the course of the test and the comparison of gained results. Keywords: Fired clay, adhesion test, adhesive. 1. Introduction The adhesion test determines the tensile strength be- tween the adhesive and the building material (in our case fired clay) and the adhesion of selected adhesive to the building material (fired clay). Although re- quirement for tensile strength between a fired clay and adhesive is not defined by any regulation, the obtained results of the measurement provide informa- tion, which is important for the design of innovative construction methods. The test was performed at the age of the samples of one, two and three days. The measured values of “young” samples give an idea of the behaviour of selected adhesives available on the Czech market and indicate, which adhesives reach the required strength in a short time. A similar adhesion test (the centric adhesion test on two-unit test sam- ples with 2C-PUR adhesive and thin-layer mortar) was performed in 2013 by the Institute of Building Materials Research (ibac) in Aachen. The performed tests were a necessary basis for the introduction of a new construction method in Germany – see [1]. Today´s trend is the construction of structures in the shortest possible time, using suitable and efficient construction methods in compliance with high quality implementation, so the adhesion test is a felicitous tool for determining the required properties of tensile stressed structures. 2. Materials and samples Eighty-one small samples were produced for the ad- hesion test – twenty-seven samples for adhesion test at each defined age of the samples. The samples were made of fired clay and selected adhesive. Nine adhe- sives were tested in total. The selected adhesives are listed in the following table. Sample Description A HELUZ SIDI B HELUZ SB mortar for a thin joint C HELUZ TYTAN PUR foam (thin-filmadhesive) E PU-contact two-component adhesive F Den Braven – MULTI KLEBER –masonry foam G Den Braven – low expansion – masonryfoam I Den Braven – MAMUT GLUE (HighTack) J Illbruck – universal chemical anchorOT120 K Den Braven – wood glue – WOODFIXD3 Table 1. List of used adhesives [2]. The fired clay in the form of plates used for the adhesion test – size 30×30 mm and thickness 15 mm – has the same properties as HELUZ bricks. Small samples for the adhesion test were made of two plates of fired clay and selected adhesive – Table 1. HELUZ SIDI is a silicate-dispersion masonry mortar for a thin joint, which is specified for masonry made of clay blocks HELUZ grinded. HELUZ SIDI was 85 https://doi.org/10.14311/APP.2022.34.0085 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en K. Richterová, P. Heinrich, P. Bílý Acta Polytechnica CTU Proceedings launched in the spring of 2020, it is a prepared mix- ture and is applied evenly crosswise with a structured roller [3]. HELUZ SB mortar for a thin joint is applied to the ribs of the grinded clay blocks and is applied with HELUZ applicator roller SB or by direct dipping of the bed joint in a pre-prepared mixture. The mixture is prepared from HELUZ SB and water – in a ratio of 0.45 liters of water per 1 kg HELUZ SB. HELUZ SB was applied to small samples on the whole surface of the bed joint using a spatula [4]. HELUZ TYTAN PUR foam was applied with the ap- plication gun on the whole surface of the bed joint [5]. PU-contact two-component adhesive is composed of two components – adhesive and accelerator – and it was applied on the whole surface of the bed joint of both parts of the sample. The adhesive was applied by a pneumatic spray gun. The application of PU- contact two-component adhesive has to be fast due to the presence of the accelerator. The increase of adhesion and application of the adhesive are very fast. Den Braven masonry foams were selected to com- pare the results with HELUZ TYTAN PUR foam and were also applied by application gun [6, 7]. All sam- ples with masonry foam were not loaded fast enough – the foam has swelled up, and the thickness of bed joint was greater than stated in the technical datasheets of adhesives. Swelling of the foam negatively affects its declared values, the probability of failure at the site of adhesive increases and therefore the values obtained from the adhesion test are on the side of safety. MAMUT GLUE is a one-component adhesive MS polymer-based. This adhesive has a declared high ini- tial adhesion (up to 500 kg/m2) and has been applied by application gun [8]. Illbruck – universal chemical anchor OT120 is a two-component resin without styrene. This chemi- cal anchor is intended for anchoring rods, bolts and bushings to concrete and common building materials. This chemical anchor is also suitable for anchoring in hollow masonry. The chemical anchor is applied by an application gun for silicone sealants [9]. The wood glue – WOODFIX D3 – is an aqueous dispersion glue and is intended for gluing wood [10]. Figure 1. The fired clay in the form of plates and the produced samples. The produced samples (9×3×3) for the adhesion test were cured in the climatic chamber until the time of the test. The climatic chamber was set to Figure 2. The selected adhesives: B – HELUZ SB mortar for a thin joint, A – HELUZ SIDI, C – HELUZ TYTAN PUR foam (thin-film adhesive), E – PU-contact two-component adhesive. Figure 3. The selected adhesives: F – MULTI KLE- BER – masonry foam, G – Low expansion – masonry foam, I – MAMUT GLUE (High Tack), J – Illbruck – universal chemical anchor OT120, K – Wood glue – WOODFIX D3. laboratory conditions – constant temperature 23 ◦C, constant relative humidity 50 %. The test samples were loaded by steel plate (m = 280 g) in the cham- ber. The steel plate is a component for the adhesion test. Each sample from a series of test samples was equipped with steel plates with hitches for attachment to the test apparatus before the adhesion test. Steel plates measuring 50×50 mm were glued by epoxy glue (Sikadur®-31 CF Rapid) to the lower and upper surface of the test sample. A small number of samples with the selected adhe- sive at each defined age (three test samples) were se- lected due to the total number of test samples (eighty- one test samples).The adhesion test was performed mainly for the selection of unsuitable adhesives. Ad- hesives with satisfactory results from this test will be subjected to further testing in the future. 86 vol. 34/2022 Adhesion test – testing of selected adhesives on fired clay Figure 4. Application of epoxy to samples for fixing steel plates. 3. Adhesion measurement The adhesion test was performed at the age of the samples one day, two and three days – each series of 27 samples at a defined age. The series of samples at a defined age was transferred from the climatic chamber to the testing laboratory in Dolní Bukovsko on the day of the test. At first the cross-sectional area Ai of each test sample was measured using caliper. Then the samples were placed in a test apparatus and after that loaded with a tensile force. The used test apparatus was apparatus named TIRAtest 2803, which can exert a force of up to 3 kN. this force is sufficient for the purpose of the adhesion test. Figure 5. The sample preparation in a test apparatus. At first the sample in a test apparatus was fixed manually. After that the sample was loaded with tensile force – the value of increase of tensile force was set to 10 N/s – until the sample failed. The measured tensile force Fti,max and the type of failure of the test sample were recorded in the prepared measurement table. The possible types of failure of the sample are failure in the adhesive, in the fired clay, in a combination of fired clay and adhesive or in the epoxy between the fired clay and the steel plate. The named failure types and scheme of adhesion test are depicted in the following figures. From the tensile force Fti,max and from the cross- sectional area Ai the tensile stress σti, the average stress σtm and finally the characteristic stress σtk were calculated. The characteristic stress σtk was Figure 6. The scheme of adhesion test. Figure 7. The possible types of failure of the sample in the adhesion test. calculated using the standard deviation s, the coef- ficient of variation V and the uncertainty coefficient kn (2.01 (n=2), resp. 1.89 (n=3)). The individual parameters were calculated according to the following formulas. Ai = A · B [mm2] (1) σti = Fti,max A [MPa] (2) σtm = 1 n · ∑ σti [MPa] (3) σtk = σtm · (1 − kn · V ) (4) s = √ 1 n − 1 · ∑ (σti − σtm)2 (5) V = s σtm (6) 87 K. Richterová, P. Heinrich, P. Bílý Acta Polytechnica CTU Proceedings 4. Results and discussion The values and the information obtained from the adhesion test in the following tables state which ad- hesives performed the best in the adhesion test. The assessment of the adhesion test depends mainly on the measured values of the tensile force at the failure of the sample, but the variance of the results and the character of the failure of the sample are also impor- tant. The type of sample failure gives us an idea of what limits the measured value of tensile stress and whether the used adhesive can resist greater tensile stress then was measured. The failure of the sample in the fired clay says that the used adhesive is likely to resist greater tensile stress than the fired clay used to production of the samples; however, this type of failure did not prevail in any set of samples. The samples that demonstrated satisfactory results in the adhesion test are the samples made of adhesives Den Braven – MAMUT GLUE (High Tack), HELUZ SIDI, PU-contact two-component adhesive and Den Braven – wood glue – WOODFIX D3. MAMUT GLUE (High Tack) performed the best in the adhesion test and the samples with this adhesive failed in the adhesive or in a combination of fired clay and the adhesive – it can be assumed that the adhesive is limited by tensile stress values close to the values measured by us. The negative factors of MAMUT GLUE (High Tack) are the unpredictability of sample failure and its price. A typical failure of PU-contact two-component adhesive is failure in the adhesive at different deformation. This adhesive is very malleable, with reduced adhesion when applied unprofessionally and is applied in a thin layer. Very surprising results were measured on samples with applied wood glue – WOODFIX D3. The mea- sured values of tensille stress were higher for wood glue than for some samples with aplicated adhesives intended for masonry. The low expansion foam (Den Braven) was the worst of the tested masonry foams. The worst of all the samples were those with the adhesive Illbruck – universal chemical anchor OT120 and HELUZ SB mortar for a thin joint. The principle of the chemical anchor consists in its expansion into the borehole; this was not possible in the case of application to the contact area of small samples. The samples with the chemical anchor were broken in the adhesive in all cases, which did not adhere sufficiently and reached low resistance to tensile stress. The performed adhesion test is not completely valid, because the number of test samples for series at a de- fined age was small (three samples for every adhesive at a defined age). Relatively high standard deviations in individual series of measurements (small number of test samples) caused a significant decrease of the characteristic stress of some samples aged two days and three days, respectively. The large variance of the measured values is also the reason for the nega- tive value of the characteristic stress of samples with adhesive named HELUZ SB mortar for a thin joint at the age of one day. It would be necessary to produce and test more small samples to obtain valid values of the characteristic stress. 5. Conclusion This article introduces the results of the adhesion test performed on the small samples, which were made of fired clay in the form of plates and selected adhesive. The obtained results are not completely valid (a small number of test samples), but the results give an idea of the tensile properties of selected adhesives applied to the fired clay. Therefore they are useful for the selection of adhesives for a future, more detailed study. The adhesion test was performed at an early age of the samples to determine the adhesion and tensile strength between the fired clay and the selected adhe- sive. These ascertained properties are important for the progress of innovative construction methods – not only for the construction of brick buildings. Surprising results were measured on samples with applied adhesives that are not intended for masonry. We must be careful about these results because we do not know the development of their properties in contact with masonry over a longer period of time. The research will continue by deeper examination of several selected adhesives. List of symbols A,B Horizontal dimension of the sample Ai Cross-sectional area Fti,max Tensile force n Number of measurements σti Tensile stress σtm Average stress σtk Characteristic stress s Standard deviation V Coefficient of variation kn Uncertainty coefficient Acknowledgements The acknowledgement belongs to Assoc. Prof. Petr Bílý, who was the supervisor of my master thesis and to the company HELUZ, which helped to perform the adhesion test. The preparation of this paper was financially supported by student grant of the Czech Technical University in Prague SGS19/149/OHK1/3T/11. 88 vol. 34/2022 Adhesion test – testing of selected adhesives on fired clay A – HELUZ SIDI Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 A1 961.61 543.22 0.565 adhesive 2 0.583 0.025 0.532A2 959.31 575.86 0.600 adhesive A3 951.04 - - adhesive(when clamping) 2 A1 956.97 958.41 1.002 3/4 adhesive + 1/4 fired clay 3 0.954 0.171 0.630 A2 945.87 1036.55 1.002 fired clay A3 944.93 721.25 0.763 fired clay 3 A1 945.55 779.50 0.824 fired clay 3 0.687 0.219 0.273A2 965.87 773.15 0.801 fired clay A3 960.64 417.10 0.434 4/5 adhesive + 1/5 fired clay B – HELUZ SB mortar for a thin joint Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 B1 953.53 270.47 0.284 adhesive 2 0.341 0.224 -0.082B2 952.96 144.19 0.151 adhesive B3 945.78 555.59 0.587 adhesive 2 B1 951.72 219.49 0.231 adhesive 3 0.347 0.131 0.099B2 942.94 302.15 0.320 adhesive B3 946.13 462.38 0.489 adhesive 3 B1 946.79 - - when clamping 2 0.275 0.050 0.175B2 966.27 300.20 0.311 adhesive B3 956.36 229.42 0.240 adhesive C – HELUZ TYTAN PUR foam (thin-film adhesive) Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 C1 956.04 325.55 0.341 adhesive 3 0.338 0.163 0.031C2 956.31 477.45 0.499 adhesive C3 935.68 162.82 0.174 adhesive 2 C1 958.21 177.41 0.185 adhesive 3 0.192 0.006 0.180C2 954.40 183.67 0.192 adhesive C3 952.93 188.39 0.198 adhesive 3 C1 955.73 308.77 0.323 adhesive 3 0.297 0.034 0.233C2 956.85 296.97 0.310 adhesive C3 942.39 243.62 0.259 adhesive 89 K. Richterová, P. Heinrich, P. Bílý Acta Polytechnica CTU Proceedings E – PU-contact two-component adhesive Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 E1 944.30 - - adhesive(when clamping) 2 0.724 0.078 0.568E2 964.10 644.85 0.669 adhesive E3 964.41 750.96 0.779 adhesive 2 E1 939.39 526.22 0.560 adhesive 3 0.443 0.103 0.248E2 947.68 382.27 0.403 3/4 adhesive + 1/4 fired clay E3 926.90 338.60 0.365 adhesive 3 E1 980.25 27.68 0.028 adhesive(did not adhere) 2 0.534 0.038 0.457E2 946.78 530.87 0.561 adhesive E3 946.88 479.58 0.506 adhesive F – Den Braven – MULTIKLEBER – mansory foam Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 F1 991.60 211.40 0.213 adhesive 3 0.211 0.048 0.121F2 968.45 157.38 0.163 adhesive F3 962.23 248.28 0.258 adhesive 2 F1 723.23 368.26 0.509 adhesive 3 0.393 0.137 0.133F2 730.33 176.21 0.241 adhesive F3 948.33 406.53 0.429 adhesive 3 F1 859.60 253.21 0.295 adhesive 3 0.426 0.167 0.110F2 744.07 457.25 0.615 adhesive F3 948.64 350.27 0.369 adhesive G – Den Braven – low expansion – masonry foam Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 G1 969.70 182.85 0.189 adhesive 3 0.165 0.044 0.082G2 956.29 109.63 0.115 adhesive G3 855.50 164.46 0.192 adhesive 2 G1 885.25 94.46 0.107 adhesive 3 0.198 0.084 0.040G2 989.78 267.68 0.270 adhesive G3 755.55 164.08 0.217 adhesive 3 G1 969.96 328.94 0.339 adhesive 3 0.417 0.190 0.058G2 915.55 255.04 0.279 5/6 adhesive + 1/6 fired clay G3 822.25 521.58 0.634 5/6 adhesive + 1/6 fired clay 90 vol. 34/2022 Adhesion test – testing of selected adhesives on fired clay I – Den Braven – MAMUT GLUE (Hight Tack) Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 I1 937.27 1098.71 1.172 adhesive 2 1.042 0.118 0.819I2 979.38 922.21 0.942 adhesive I3 980.92 992.69 1.012 adhesive 2 I1 938.44 1076.41 1.147 3/4 adhesive + 1/4 fired clay 3 1.004 0.176 0.672 I2 980.00 791.50 0.808 2/3 adhesive + 1/3 fired clay I3 965.33 1022.11 1.059 adhesive 3 I1 957.52 560.67 0.586 fired clay 3 0.769 0.159 0.468I2 974.93 841.90 0.864 adhesive I3 958.48 823.55 0.859 1/3 adhesive + 2/3 fired clay J – Illbruck – universal chemical anchor OT120 Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 J1 959.45 158.83 0.166 adhesive 2 0.244 0.110 0.022J2 974.06 - - adhesive(when clamping) J3 1005.73 323.34 0.321 adhesive 2 J1 1003.29 214.63 0.214 adhesive 3 0.248 0.029 0.192J2 667.99 176.98 0.265 adhesive J3 970.94 256.95 0.265 adhesive 3 J1 942.78 265.29 0.281 adhesive 2 0.317 0.050 0.217J2 962.20 338.38 0.352 adhesive J3 962.54 - - adhesive(when clamping) 91 K. Richterová, P. Heinrich, P. Bílý Acta Polytechnica CTU Proceedings K – Den Braven – wood glue – WOODFIX D3 Day Name Cross- sectional area Tensile force Tensile stress Type of failure Nr. of measure- ments Avg. stress Std. deviation Char. stress Ai [mm2] Fti,max [N] σti [MPa] n σtm [MPa] s [MPa] σtk [MPa] 1 K1 947.99 344.52 0.363 adhesive 2 0.449 0.121 0.206K2 955.68 2.84 0.003 fired clay(when clamping) K3 981.25 524.34 0.534 adhesive 2 K1 974.64 980.99 1.007 adhesive 3 0.878 0.179 0.540K2 961.84 647.83 0.674 fired clay K3 956.02 912.48 0.954 adhesive 3 K1 981.08 440.06 0.449 adhesive 3 0.659 0.210 0.263K2 992.86 656.44 0.661 fired clay K3 946.76 822.06 0.868 3/4 adhesive + 1/4 fired clay Table 2. The values and the information obtained from the adhesion test [1]. Figure 8. Summary of results from the adhesion test at the age of the samples one, two and three days [1]. 92 vol. 34/2022 Adhesion test – testing of selected adhesives on fired clay References [1] W. Brameshuber, M. Graubohm. Prefabricated masonry panel system with two-component polyurethane adhesive / vorgefertigte mauertafeln mit zweikomponenten-polyurethanklebstoff. Cement and Concrete Composites 19:3–26, 2015. https://doi.org/10.1002/dama.201500644. [2] K. Richterová. Precast masonry wall panels. Master thesis 2021. [3] Heluz. Heluz sidi. https://www.heluz.cz/sidi/. [4] Heluz. Heluz sb malta pro tenkou spáru. https://www.heluz.cz/files/sb_sbc.pdf. [5] Heluz. Heluz pĚna (tenkovrstvé lepidlo). https://www.heluz.cz/files/HELUZ-TREND_M5_P_NA_ technicky-list_CZ.pdf. [6] D. Braven. Multi kleber. https://www.denbraven.cz/produkt/multi-kleber/. [7] D. Braven. Nízkoexpanzní pěna. https: //www.denbraven.cz/produkt/nizkoexpanzni-pena/. [8] D. Braven. Mamut glue high tack. den braven. https://www.denbraven.cz/produkt/ mamut-glue-high-tack/. [9] Illbruck. Ot120 univerzální chemická kotva. https://www.illbruck.com/cs_CZ/produkt/ ot120-univerzalni-chemicka-kotva/. [10] D. Braven. Lepidlo na dřevo woodfix d3. den braven. https://www.denbraven.cz/produkt/ lepidlo-na-drevo-woodfix-d3/. 93 https://doi.org/10.1002/dama.201500644 https://www.heluz.cz/sidi/ https://www.heluz.cz/files/sb_sbc.pdf https://www.heluz.cz/files/HELUZ-TREND_M5_P_NA_technicky-list_CZ.pdf https://www.heluz.cz/files/HELUZ-TREND_M5_P_NA_technicky-list_CZ.pdf https://www.denbraven.cz/produkt/multi-kleber/ https://www.denbraven.cz/produkt/nizkoexpanzni-pena/ https://www.denbraven.cz/produkt/nizkoexpanzni-pena/ https://www.denbraven.cz/produkt/mamut-glue-high-tack/ https://www.denbraven.cz/produkt/mamut-glue-high-tack/ https://www.illbruck.com/cs_CZ/produkt/ot120-univerzalni-chemicka-kotva/ https://www.illbruck.com/cs_CZ/produkt/ot120-univerzalni-chemicka-kotva/ https://www.denbraven.cz/produkt/lepidlo-na-drevo-woodfix-d3/ https://www.denbraven.cz/produkt/lepidlo-na-drevo-woodfix-d3/ Acta Polytechnica CTU Proceedings 34:85–93, 2022 1 Introduction 2 Materials and samples 3 Adhesion measurement 4 Results and discussion 5 Conclusion List of symbols Acknowledgements References