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Hardness Testing of Polymer Concrete Castings by Schmidt Hammer
Available online at www.sciencedirect.com
ScienceDirect www.materialstoday.com/proceedings Materials Today: Proceedings 22 (2020) 293–299
2018 2nd International Conference on Nanomaterials and Biomaterials, ICNB 2018, 10–12 December 2018, Barcelona, Spain
Hardness Testing of Polymer Concrete Castings by Schmidt Hammer ZAJAC Jozefa, PETRUSKA Ondreja, RADCHENKO Svetlanaa, DUPLAKOVA Darinaa* and GOLDYNIAK Davida a
Technical University of Kosice, Faculty of Manufacturing Technologies with a seat in Presov, Bayerova 1, 080 01 Presov, Slovakia
Abstract Presented paper is focused on testing the hardness of polymer concrete castings by Schmidt hammer. The first part of the paper describes the theoretical knowledge from the material area of the issue. The experimental part of the paper is devoted to the production process of the polymer concrete castings and to the materials, machines and tools used in the process. The third part of the paper contains the hardness test by Schmidt hammer and interprets the measured results of three samples. Obtained results are summarized in the conclusion part. © 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the 2018 2nd International Conference on Nanomaterials and Biomaterials. Keywords: polymer concrete; testing; Schmidt hammer;
1. Introduction The construction and material side of the supporting parts of lathes, milling machines, drills and other machine tools need to be improved in order to handle the increasingly dynamic and performance parameters of these machines [1, 2, 3]. Due to certain limitations of conventional materials such as steel and cast iron, has begun with their replacement by a suitable composite [4]. One of the solutions for the replacement can be to use polymers, whose properties can be influenced by the change of the composition. Polymer concrete is a new, modern composite material, that has application in various areas of industry. It consists of a matrix (binder), filler and suitable additives. Fig. 1 presents the example of polymer concrete castings. The main component of the polymers is the filler, which generally forms 70-85% of the total volume of the blend. In generally fillers can be divided into organic
* Corresponding author. Tel.:+4210556026358. E-mail address: [email protected] 1876-6102 © 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the 2018 2nd International Conference on Nanomaterials and Biomaterials.
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(natural) and inorganic (artificial). The most commonly used organic fillers are flours, sands and flakes of various fractions of the following rocks and minerals: andesite, quartz, dolomite, limestone, basalt, granite and the like. The properties of these fillers affect the resulting properties of the polymer concrete composite [5].
Fig. 1 Polymer concrete castings [6].
As inorganic (artificial) fillers are the most commonly used carbon, glass, metal and polymer fibres in the form of dispersed reinforcement. The purpose of the inorganic filler is to provide better distribution of the stresses and thus to increase the strength, in particular, the tensile strength and the bending strength. The matrix of polymer concrete consists of resin and hardener. For the production of the polymer, concrete castings are most commonly used epoxy resins because they have the lowest volume shrinkage. They also have good strength characteristics and chemical resistance. The role of additives or the agents added to the matrix is to influence the various properties of the mixture, such as thickening, reducing flammability, increasing toughness, casting colour change [7, 8]. 2. Materials, machines, tools and equipment The following materials (Table1) were used in the manufacture of test bodies: • Binders (hardener and epoxy resin) • Fillers (silica sands, danube gravels, limestones, and andesite) Table 1. Properties of binders. Epoxy resin 700-900
Viscosity at 25°C [mPa.s] Epoxide mass equivalent [g.mol-1]
166 – 182
Epoxide index [mol.1000-1]
0.55 – 0.60 Hardener
Amine number [mgKOH.g-1]
450 – 500
Density at 25°C [g.cm-3]
0.93 – 0.96
In the manufacturing of the test bodies, there were used: vibration table, electric stirrer and plastic moulds. The used equipment is presented in Fig. 2.
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Fig. 2. Equipment used in the manufacture of the test bodies. (Lievers LTT 40/40 – left, Makita UT1200 – in the middle, mould – right)
3. Production of the polymer concrete castings Polymer concrete castings were manufactured at the Faculty of Manufacturing Technologies, on October 8th 2018, at the temperature of 21.7°C and relative air humidity 64%. Firstly, the moulds were prepared, after that were their inside sides cleared from impurities formed after the previous casting and subsequently coated with silicone oil, which served as separating agent. Subsequently, all components of filler and binder were dosed. For each type of polymer, the concrete casting was used three types of filling and the binder consisting of hardener and resin. • Polymer concrete casting No.1: o Type of filling: 8 – 16 mm fraction of danube gravel, o Type of filling: 4 – 8 mm fraction of danube gravel, o Type of filling: 0.3 – 0.8 mm fraction of silica sand. • Polymer concrete casting No.2: o Type of filling: 8 – 16 mm fraction of dolomitic limestone, o Type of filling: 4 – 8 mm fraction of dolomitic limestone, o Type of filling: 0.3 – 0.8 mm fraction of silica sand. • Polymer concrete casting No.3: o Type of filling: 4 – 8 mm fraction of andesite, o Type of filling: 0.3 – 1 mm fraction of silica sand, o Type of filling: 0.1 – 0.3 mm fraction of silica sand. Precise ratios of the used filling and binder for each polymer concrete casting are shown in Table 2. Table 2. Ratios of the binders and filling used. Polymer concrete casting No.1 1. type of filling (35%) Filling 85%
2. type of filling (35%) 3. type of filling (30%)
Binder 15%
50 parts of hardener 100 parts of resin Polymer concrete casting No.2 1. type of filling (35%)
Filling 85%
2. type of filling (35%) 3. type of filling (30%)
Binder 15%
50 parts of hardener 100 parts of resin
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Z. Jozef et al. / Materials Today: Proceedings 22 (2020) 293–299 Polymer concrete casting No.3 1. type of filling (35%) Filling 70%
2. type of filling (35%) 3. type of filling (30%)
Binder 30%
50 parts of hardener 100 parts of resin
All three types of the filling of each casting were manually mixed right before adding them to the matrix, to ensure the most uniform distribution. Matrix was prepared by mixing hardener and resin using electric stirrer. The electrical stirring of the mixture is presented in Fig. 3. To ensure the exothermic reaction, the mixture was stirred for 3 minutes. After that, the filler was sequentially added. The mixture was electrically stirred for another 3 minutes to ensure that the resin has uniformly coated the whole filler.
Fig. 3. Electrical stirring of the mixture.
The precisely stirred mixture was subsequently added to the prepared mould and they were placed on the vibration table (Fig. 4). The process of vibration lasted two minutes, during which little air bubbles were occurring on the surface, which led to the lowering of the porosity. The surface of the mixture was covered in a binder, it was smooth and glossy. After the vibration process moulds with mixtures were placed on the horizontal surface for 24 hours. Afterwards were castings removed from moulds and left for another 15 days to additional hardening.
Fig. 4. Vibration process.
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4. Testing of hardness by schmidt hammer The Schmidt hammer is used for non-destructive testing of hardened polymers and concrete. Counter to destructive testing on presses, it is a quick and inexpensive version of testing. However, the accuracy of the measurement is lower, roughly within ± 10%. The principle of testing by Schmidt hammer is pressing the surface of the test body against the hammer, which leads to the ejecting the spring inside the Schmidt hammer perpendicularly to the surface. The hardness of the test body is subtracted from the scale. After the impact, the measured value indicator must be locked. The hardness measurement is based on the size of the hammer's reflection from the test surface. The hardness testing was performed by the Schmidt N-34 Retroreflector. This device is presented in. Fig. 5.
Fig. 5. Schmidt N-34 Retroreflector.
Tested polymer concrete castings were placed on the concrete floor during testing to avoid distortion of the results by damping. Testing was always done from the top of the sample. The castings were gradually turned to every side to measure the hardness of each surface from the top. On each side of the cube (top, bottom and side), four measurements were made. The values of the hardness of all three polymer concrete castings are shown in Table 3. Table 3. Measured values of the hardness.
Polymer concrete casting no.1
Measurement no.
The hardness of the top [N/mm2]
The hardness of the side [N/mm2]
The hardness of the bottom [N/mm2]
1. 2. 3. 4.
50 48 49 46
42 36 46 45
38 37 38 36
48.25
42.25
37.25
52 50 49 52
48 47 44 46
38 36 39 38
50.75
46.25
37.75
58 64 64 63 62.25
48 51 52 51 50.5
42 41 43 41 41.75
Average value Polymer concrete casting no.2
1. 2. 2. 4.
Average value Polymer concrete casting no.3 Average value
1. 2. 2. 4.
Testing of the hardness of the polymer concrete castings by Schmidt hammer showed that the hardness of the casting No.3 is greater than the hardness of the castings No.1 and No.2. The compression strength values obtained from casting No.3 are higher than casting No.2 by 13 N/mm2 and from casting No.1 by 19 N mm2. The highest hardness values were measured at the top of the castings. This was due to the fact that after the vibration a clean binder appeared on the surface and the filler dropped to the lower part of the casting. Since the filler hardness is lower than the binder hardness, testing by Schmidt hammer exhibited the highest values on the top surface.
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Fig. 6. Polymer concrete casting No.1 (left), No.2 (middle), No.3 (right).
In Fig. 6, it can be seen that castings No.1 and No.2 contain air cavities that are not filled by the binder. This porosity leads to a decrease in the physical properties of castings. In this case, they are caused by a high filler ratio (85%) to the binder (15%). Casting No.3 with a ratio of 70% filler and 30% binder does not contain any cavities because the mixture was more ductile, lighter in the corners and filled with air gaps. 4. Conclusion Materials can be tested in a non-destructive and destructive manner [9, 10, 11]. In the polymer concrete, the nondestructive test by Schmidt Hammer is popular because it is quick and cheap. However, the measured results can only be considered as indicative because they do not measure the strength of the polymer casting as a whole, but only the hardness values at the measured points. Destructive tests such as compression strength, flexural tension, etc. are much more accurate. They measure in particular, the strength of the cast as a whole (synergistic effect on composites). These tests are carried out in the Slovak Republic in particular by the Technical and Testing Institute (TSUS) in accredited testing laboratories. Presented samples together with other products produced within the project will be tested in these accredited testing laboratories and measured results will be published in the following publications. Acknowledgements This work was supported by the Slovak Research and Development Agency under the contract No. APVV-150700 and by the grand KEGA 025TUKE-4/2018 of The Ministry of Education, Science, Research and Sport of the Slovak Republic. References [1] Dobransky, J., and Hatala, M. "Influence of selected technological parameter to quality parameters by injection molding." 18th International Symposium of the Danube Adria Association for Automation and Manufacturing (2007): 223-224. [2] Čep, R., Malotová, Š., Lichovník, J., Hatala, M., and Legutko, S. "The influence of cutting conditions on the selected parameters of the surface integrity." Acta Polytechnica 58 (6), 334-338. [3] Botko, F., Hatala, M., Kormoš, M., Ungureanu, N., and Šoltés P. "Using Edgecam for creating CNC programs in education process." In 2015 IEEE 13th International Symposium on Applied Machine Intelligence and Informatics (2015): 255-259. [4] Knapcikova, L. Herzog, M., and Oravec P. "Material characterization of composite materials from used tires." Výrobné inžinierstvo (4) (2010): 31-34. [5] Trofimov, A., Mishurova, T., Lanzoni, L., Radi, E., Bruno, G., and Sevostianov, I. "Microstructural analysis and mechanical properties of concrete reinforced with polymer short fibers." International Journal of Engineering Science 133 (2018): 210-218. [6] Yemam, D. M., Kim, B. J., Moon, J. Y., and Yi Ch. "Mechanical Properties of Epoxy Resin Mortar with Sand Washing Waste as Filler." Materials. 10 (3) (2017): 246. [7] Hu, B., Zhang, N., Liao, Y., Pan, Z., Liu, Y., and Jiang, Z. "Enhanced flexural performance of epoxy polymer concrete with short natural fibers." Science China Technological Sciences 61 (8) (2018): 1107-1113.
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[8] Jafari, K., Tabatabaeian, M., Joshaghani, A., and Ozbakkaloglu, T. "Optimizing the mixture design of polymer concrete: An experimental investigation." Construction and Building Materials 167 (2018): 185-196. [9] Orlovský, I., Hatala, M., and Duplák, J. "Balance equation-an essential element of the definition of the drying process." Advanced Materials Research 849 (2014): 310-315. [10] Schmidova, E., Hlavaty, I., and Hanus, P. "The Weldability of the Steel with High Manganese." Technical Gazette 23 (4) (2016): 749-752. [11] Sadílek, M., Fojtík, F., Sadílková, Z., Kolařík, K., and Petrů, J. "A Study of Effects of Changing the Position of the Tool Axis to the Machined Surface." Transaction of FAMENA 39 (2) (2015): 33-46.
ScienceDirect www.materialstoday.com/proceedings Materials Today: Proceedings 22 (2020) 293–299
2018 2nd International Conference on Nanomaterials and Biomaterials, ICNB 2018, 10–12 December 2018, Barcelona, Spain
Hardness Testing of Polymer Concrete Castings by Schmidt Hammer ZAJAC Jozefa, PETRUSKA Ondreja, RADCHENKO Svetlanaa, DUPLAKOVA Darinaa* and GOLDYNIAK Davida a
Technical University of Kosice, Faculty of Manufacturing Technologies with a seat in Presov, Bayerova 1, 080 01 Presov, Slovakia
Abstract Presented paper is focused on testing the hardness of polymer concrete castings by Schmidt hammer. The first part of the paper describes the theoretical knowledge from the material area of the issue. The experimental part of the paper is devoted to the production process of the polymer concrete castings and to the materials, machines and tools used in the process. The third part of the paper contains the hardness test by Schmidt hammer and interprets the measured results of three samples. Obtained results are summarized in the conclusion part. © 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the 2018 2nd International Conference on Nanomaterials and Biomaterials. Keywords: polymer concrete; testing; Schmidt hammer;
1. Introduction The construction and material side of the supporting parts of lathes, milling machines, drills and other machine tools need to be improved in order to handle the increasingly dynamic and performance parameters of these machines [1, 2, 3]. Due to certain limitations of conventional materials such as steel and cast iron, has begun with their replacement by a suitable composite [4]. One of the solutions for the replacement can be to use polymers, whose properties can be influenced by the change of the composition. Polymer concrete is a new, modern composite material, that has application in various areas of industry. It consists of a matrix (binder), filler and suitable additives. Fig. 1 presents the example of polymer concrete castings. The main component of the polymers is the filler, which generally forms 70-85% of the total volume of the blend. In generally fillers can be divided into organic
* Corresponding author. Tel.:+4210556026358. E-mail address: [email protected] 1876-6102 © 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the 2018 2nd International Conference on Nanomaterials and Biomaterials.
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Z. Jozef et al. / Materials Today: Proceedings 22 (2020) 293–299
(natural) and inorganic (artificial). The most commonly used organic fillers are flours, sands and flakes of various fractions of the following rocks and minerals: andesite, quartz, dolomite, limestone, basalt, granite and the like. The properties of these fillers affect the resulting properties of the polymer concrete composite [5].
Fig. 1 Polymer concrete castings [6].
As inorganic (artificial) fillers are the most commonly used carbon, glass, metal and polymer fibres in the form of dispersed reinforcement. The purpose of the inorganic filler is to provide better distribution of the stresses and thus to increase the strength, in particular, the tensile strength and the bending strength. The matrix of polymer concrete consists of resin and hardener. For the production of the polymer, concrete castings are most commonly used epoxy resins because they have the lowest volume shrinkage. They also have good strength characteristics and chemical resistance. The role of additives or the agents added to the matrix is to influence the various properties of the mixture, such as thickening, reducing flammability, increasing toughness, casting colour change [7, 8]. 2. Materials, machines, tools and equipment The following materials (Table1) were used in the manufacture of test bodies: • Binders (hardener and epoxy resin) • Fillers (silica sands, danube gravels, limestones, and andesite) Table 1. Properties of binders. Epoxy resin 700-900
Viscosity at 25°C [mPa.s] Epoxide mass equivalent [g.mol-1]
166 – 182
Epoxide index [mol.1000-1]
0.55 – 0.60 Hardener
Amine number [mgKOH.g-1]
450 – 500
Density at 25°C [g.cm-3]
0.93 – 0.96
In the manufacturing of the test bodies, there were used: vibration table, electric stirrer and plastic moulds. The used equipment is presented in Fig. 2.
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Fig. 2. Equipment used in the manufacture of the test bodies. (Lievers LTT 40/40 – left, Makita UT1200 – in the middle, mould – right)
3. Production of the polymer concrete castings Polymer concrete castings were manufactured at the Faculty of Manufacturing Technologies, on October 8th 2018, at the temperature of 21.7°C and relative air humidity 64%. Firstly, the moulds were prepared, after that were their inside sides cleared from impurities formed after the previous casting and subsequently coated with silicone oil, which served as separating agent. Subsequently, all components of filler and binder were dosed. For each type of polymer, the concrete casting was used three types of filling and the binder consisting of hardener and resin. • Polymer concrete casting No.1: o Type of filling: 8 – 16 mm fraction of danube gravel, o Type of filling: 4 – 8 mm fraction of danube gravel, o Type of filling: 0.3 – 0.8 mm fraction of silica sand. • Polymer concrete casting No.2: o Type of filling: 8 – 16 mm fraction of dolomitic limestone, o Type of filling: 4 – 8 mm fraction of dolomitic limestone, o Type of filling: 0.3 – 0.8 mm fraction of silica sand. • Polymer concrete casting No.3: o Type of filling: 4 – 8 mm fraction of andesite, o Type of filling: 0.3 – 1 mm fraction of silica sand, o Type of filling: 0.1 – 0.3 mm fraction of silica sand. Precise ratios of the used filling and binder for each polymer concrete casting are shown in Table 2. Table 2. Ratios of the binders and filling used. Polymer concrete casting No.1 1. type of filling (35%) Filling 85%
2. type of filling (35%) 3. type of filling (30%)
Binder 15%
50 parts of hardener 100 parts of resin Polymer concrete casting No.2 1. type of filling (35%)
Filling 85%
2. type of filling (35%) 3. type of filling (30%)
Binder 15%
50 parts of hardener 100 parts of resin
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Z. Jozef et al. / Materials Today: Proceedings 22 (2020) 293–299 Polymer concrete casting No.3 1. type of filling (35%) Filling 70%
2. type of filling (35%) 3. type of filling (30%)
Binder 30%
50 parts of hardener 100 parts of resin
All three types of the filling of each casting were manually mixed right before adding them to the matrix, to ensure the most uniform distribution. Matrix was prepared by mixing hardener and resin using electric stirrer. The electrical stirring of the mixture is presented in Fig. 3. To ensure the exothermic reaction, the mixture was stirred for 3 minutes. After that, the filler was sequentially added. The mixture was electrically stirred for another 3 minutes to ensure that the resin has uniformly coated the whole filler.
Fig. 3. Electrical stirring of the mixture.
The precisely stirred mixture was subsequently added to the prepared mould and they were placed on the vibration table (Fig. 4). The process of vibration lasted two minutes, during which little air bubbles were occurring on the surface, which led to the lowering of the porosity. The surface of the mixture was covered in a binder, it was smooth and glossy. After the vibration process moulds with mixtures were placed on the horizontal surface for 24 hours. Afterwards were castings removed from moulds and left for another 15 days to additional hardening.
Fig. 4. Vibration process.
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4. Testing of hardness by schmidt hammer The Schmidt hammer is used for non-destructive testing of hardened polymers and concrete. Counter to destructive testing on presses, it is a quick and inexpensive version of testing. However, the accuracy of the measurement is lower, roughly within ± 10%. The principle of testing by Schmidt hammer is pressing the surface of the test body against the hammer, which leads to the ejecting the spring inside the Schmidt hammer perpendicularly to the surface. The hardness of the test body is subtracted from the scale. After the impact, the measured value indicator must be locked. The hardness measurement is based on the size of the hammer's reflection from the test surface. The hardness testing was performed by the Schmidt N-34 Retroreflector. This device is presented in. Fig. 5.
Fig. 5. Schmidt N-34 Retroreflector.
Tested polymer concrete castings were placed on the concrete floor during testing to avoid distortion of the results by damping. Testing was always done from the top of the sample. The castings were gradually turned to every side to measure the hardness of each surface from the top. On each side of the cube (top, bottom and side), four measurements were made. The values of the hardness of all three polymer concrete castings are shown in Table 3. Table 3. Measured values of the hardness.
Polymer concrete casting no.1
Measurement no.
The hardness of the top [N/mm2]
The hardness of the side [N/mm2]
The hardness of the bottom [N/mm2]
1. 2. 3. 4.
50 48 49 46
42 36 46 45
38 37 38 36
48.25
42.25
37.25
52 50 49 52
48 47 44 46
38 36 39 38
50.75
46.25
37.75
58 64 64 63 62.25
48 51 52 51 50.5
42 41 43 41 41.75
Average value Polymer concrete casting no.2
1. 2. 2. 4.
Average value Polymer concrete casting no.3 Average value
1. 2. 2. 4.
Testing of the hardness of the polymer concrete castings by Schmidt hammer showed that the hardness of the casting No.3 is greater than the hardness of the castings No.1 and No.2. The compression strength values obtained from casting No.3 are higher than casting No.2 by 13 N/mm2 and from casting No.1 by 19 N mm2. The highest hardness values were measured at the top of the castings. This was due to the fact that after the vibration a clean binder appeared on the surface and the filler dropped to the lower part of the casting. Since the filler hardness is lower than the binder hardness, testing by Schmidt hammer exhibited the highest values on the top surface.
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Fig. 6. Polymer concrete casting No.1 (left), No.2 (middle), No.3 (right).
In Fig. 6, it can be seen that castings No.1 and No.2 contain air cavities that are not filled by the binder. This porosity leads to a decrease in the physical properties of castings. In this case, they are caused by a high filler ratio (85%) to the binder (15%). Casting No.3 with a ratio of 70% filler and 30% binder does not contain any cavities because the mixture was more ductile, lighter in the corners and filled with air gaps. 4. Conclusion Materials can be tested in a non-destructive and destructive manner [9, 10, 11]. In the polymer concrete, the nondestructive test by Schmidt Hammer is popular because it is quick and cheap. However, the measured results can only be considered as indicative because they do not measure the strength of the polymer casting as a whole, but only the hardness values at the measured points. Destructive tests such as compression strength, flexural tension, etc. are much more accurate. They measure in particular, the strength of the cast as a whole (synergistic effect on composites). These tests are carried out in the Slovak Republic in particular by the Technical and Testing Institute (TSUS) in accredited testing laboratories. Presented samples together with other products produced within the project will be tested in these accredited testing laboratories and measured results will be published in the following publications. Acknowledgements This work was supported by the Slovak Research and Development Agency under the contract No. APVV-150700 and by the grand KEGA 025TUKE-4/2018 of The Ministry of Education, Science, Research and Sport of the Slovak Republic. References [1] Dobransky, J., and Hatala, M. "Influence of selected technological parameter to quality parameters by injection molding." 18th International Symposium of the Danube Adria Association for Automation and Manufacturing (2007): 223-224. [2] Čep, R., Malotová, Š., Lichovník, J., Hatala, M., and Legutko, S. "The influence of cutting conditions on the selected parameters of the surface integrity." Acta Polytechnica 58 (6), 334-338. [3] Botko, F., Hatala, M., Kormoš, M., Ungureanu, N., and Šoltés P. "Using Edgecam for creating CNC programs in education process." In 2015 IEEE 13th International Symposium on Applied Machine Intelligence and Informatics (2015): 255-259. [4] Knapcikova, L. Herzog, M., and Oravec P. "Material characterization of composite materials from used tires." Výrobné inžinierstvo (4) (2010): 31-34. [5] Trofimov, A., Mishurova, T., Lanzoni, L., Radi, E., Bruno, G., and Sevostianov, I. "Microstructural analysis and mechanical properties of concrete reinforced with polymer short fibers." International Journal of Engineering Science 133 (2018): 210-218. [6] Yemam, D. M., Kim, B. J., Moon, J. Y., and Yi Ch. "Mechanical Properties of Epoxy Resin Mortar with Sand Washing Waste as Filler." Materials. 10 (3) (2017): 246. [7] Hu, B., Zhang, N., Liao, Y., Pan, Z., Liu, Y., and Jiang, Z. "Enhanced flexural performance of epoxy polymer concrete with short natural fibers." Science China Technological Sciences 61 (8) (2018): 1107-1113.
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[8] Jafari, K., Tabatabaeian, M., Joshaghani, A., and Ozbakkaloglu, T. "Optimizing the mixture design of polymer concrete: An experimental investigation." Construction and Building Materials 167 (2018): 185-196. [9] Orlovský, I., Hatala, M., and Duplák, J. "Balance equation-an essential element of the definition of the drying process." Advanced Materials Research 849 (2014): 310-315. [10] Schmidova, E., Hlavaty, I., and Hanus, P. "The Weldability of the Steel with High Manganese." Technical Gazette 23 (4) (2016): 749-752. [11] Sadílek, M., Fojtík, F., Sadílková, Z., Kolařík, K., and Petrů, J. "A Study of Effects of Changing the Position of the Tool Axis to the Machined Surface." Transaction of FAMENA 39 (2) (2015): 33-46.