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Influence of Silicon Carbide and Electrocorundum on the Thermal Resistance of Cement Binders with Granulated Blast-furnace Slag
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 172 (2017) 497 – 504
Modern Building Materials, Structures and Techniques, MBMST 2016
Influence of silicon carbide and electrocorundum on the thermal resistance of cement binders with granulated blast-furnace slag Teresa Kantela, Agnieszka Ślosarczyka* a
Poznan University of Technology, Faculty of Civil and Environmental Engineering, Institute of Structural Engineering, Street Piotrowo 5, Poznan, 60-965, Poland
Abstract The aim of this work was to compare the influence of the electrocorundum and silicon carbide on the strength and the microstructure of the cement composite with the addition of granulated blast-furnace slag, before and after exposition to higher and high temperature. Research proved that compressive strength of the cement composite with addition of Al 2O3 in the amount of at least 2 wt.% increased in comparison to the referential samples, regardless of the high temperature, by about 25%, and the best results in the whole temperature range were obtained in case of cement binder with 6 wt.% addition of electrocorundum. On the other hand, addition of silicon carbide resulted in a relevant increase of the sample resistance (by 20-30%) only when added in the amount of at least 10 wt.%. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MBMST 2016. Peer-review under responsibility of the organizing committee of MBMST 2016 Keywords:cement; silicon carbide; electrocorudnum; XRD analyses; laboratory experiments.
1. Introduction High temperatures cause changes in the cement mortar and in the aggregate, which results usually in deterioration of physical and mechanical properties of the cement composite. The resistance of the cement composites to short term exposition to temperature oscillates around 200 to 300oC. With gradual heating of the cement matrix, the water bound in it is gradually removed, which leads further to physical and mechanical changes in the structure of the cement
* Corresponding author. Tel.: +48-61-665-2168. E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MBMST 2016
doi:10.1016/j.proeng.2017.02.058
498
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
mortar and destruction of the structure created during the hydration of the cement. After crossing the 400 oC a degradation of the hydrated calcium silicate of the so-called C-S-H phase takes place, which is manifested in a sharp deterioration of the compressive strength of the matrix. In the temperature of 900 oC the C-S-H phase undergoes a total disintegration. Thus, the critical temperature range defining the mechanical durability of the matrix equals 400-800oC. The influence of the high temperatures on the cement matrix durability has been a subject of many publications of local and international range for years. The authors draw attention to the influence of the aggregate type, the cement and the additions on the thermal resistance of composites based on cement binders. The application of the additions used for production of fireproof materials, characterised by high mechanical strength, durability and exceptionally high thermal conductivity, may result in improvement of the resistance of the cement composite in high temperatures. However, most of the research on the influence of those additions on the properties of the cement matrix concentrated on defining its physico-mechanical properties [1,2]. For example, it was proved that concretes with addition of SiC were characterised by high wear resistance, thermal shock resistance, slag corrosion and low porosity and high thermal conductivity [3]. On the other hand, the research conducted by [4] proved, that the cement composites containing significant amount of alumina, or based on aluminium cements, were more resistant to high temperatures, than Portland cements. Reports on the impact of Al2O3 and SiC on cement composites with addition of granulated blast-furnace slag are a real rarity in the literature. Partial replacement of the clinker with the blast-furnace slag contributes to improvement of the cement binder resistance to higher temperatures, and addition of the fireproof materials enhances this effect even further. Therefore, the aim of this work was to compare the influence of the electrocorundum and silicon carbide on the strength and the microstructure of the cement composite with the addition of granulated blastfurnace slag, before and after exposition to higher and high temperature. 2. Materials and research methods In the research the metallurgical cement CEM III/A 52.5 N was applied, meeting the requirements of the norm PNEN 197-1. Its main ingredients are the Portland clinker (35÷64%), granulated blast-furnace slag (36÷65%) and a regulator of the binding time (calcium sulphate). As the additions that improve the temperature resistance of the cement binder a regular electrocorundum and silicon carbide were applied, both with granulation of 250-300 μm. Regular electrocorundum is a synthetic abrasive material consisting of crystalline aluminium oxide in the amount of 94.5 - 97% and a small admixtures of oxides: TiO2, SiO2, Fe2O3, CaO, MgO, that shows a relatively high thermal conductivity and low thermal expansion. It is the less brittle and the most tensile (elastic) electrocorundum. It finds application in metalworking of steel, cast steel, malleable iron and non-ferrous materials in cutting, as well as in the fireproof industry and ceramics. The silicon carbide consisting in 95 – 98% of silicon carbide and chemical admixtures of oxides such as Fe2O3, Al2O3, CaO, SiO2, MnO2 is an abrasive grain of the highest cutting properties, very high toughness and durability. It is characterised by high mechanical resistance and an exceptionally high thermal and electrical conductivity. It can be applied in the treatment of brittle and hard materials (such as glass), in the production of abrasive tools and bulk materials, as well as the fireproof materials. In order to test the influence of those additions on the physico-mechanical properties of the cement composites in different temperatures, three series of cement binders were prepared. Mixtures from the first series were prepared from the blast-furnace cement and water with the water-binder index of 0.48. In the two further series electrocorundum or silicon-carbide was added to the cement binder in the amounts of: 2%, 4%, 6% and 10% of the cement mass. Homogenization of the mixtures begun by stirring the binder with an addition for 1 minute, and then the water was added. Total time of stirring equalled 4 minutes. The binders were formed into cylinders, which were concentrated on a vibration table, and after 48 hours of maturation they were deformed and kept in 20°C water for 90 days. Samples prepared in this way underwent a treatment in higher and high temperature, within the range of 225°C to 900°C, where the temperature increased by 2.5°C every minute. The samples were kept in the given temperature for 30 minutes. Next, the cement mortars with and without modifying additions for given temperatures, respectively: 225, 450 and 900°C, underwent compressive strength tests in the air-dry state. Phase composition of the cement mortars, with and without modifying additions after the influence of 225°C and 900°C was described with the use of a Bruker X-ray diffractometer, model AXS D8 Advance; and the analysis of the microstructure was conducted with the use of scanning electron microscopy, with the Hitachi S-3400N microscope.
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
499
3. Results and discussion
Compressive Strength [MPa]
Figures 1 and 2 present compressive strength of the cement binders with and without modifying additions after exposition to high temperature. 60 50 40 30 20 10 0
CEM III 52,5
CEM III 52,5 + 2% Al2O3
CEM III 52,5 + 4% Al2O3
CEM III 52,5 + 6% Al2O3
CEM III 52,5 + 10% Al2O3
20 °C
39,97
52,07
42,19
50,15
51,05
225 °C
35,53
34,24
33,16
42,33
44,81
450 °C
25,24
35,91
34,03
35,09
29,63
900 °C
9,8
11,26
11,12
12,36
12,31
Fig. 1. Compressive strength of the cement binders with and without electrocorundum after exposition to high temperature.
Electrocorundum, as well as the silicon carbide, improve the mechanical properties of the cement binder in room temperature. Along with the rising amount of the addition, the increase of the compressive strength of the cement mortar was observed. It is the so-called filling effect; the presence of fine particles of the electrocorundum and the silicon carbide results in concentration of the structure of the cement binder and improvement of its mechanical properties. The presence of electrocorundum and silicon carbide also contributes to improving the resistance of the cement binder to higher and high temperature, but the significant effect was observed only when adding greater amount of the additions - 6% in case of electrocorundum and 10% in case of silicon carbide. Moreover, the analysis of the research results proved, that the addition of the electrocorundum, irregardless of the percentage in the sample and the temperature, improved the compressive strength of the cement binder by about 25% in comparison to referential samples. SiC, on the other hand, increases the resistance of the composites, irregardless of the temperature, but only in case of applying it in the amount of minimum 10% of the cement mass. In case of temperature of 450°C a 20-30%, even up to 40% increase of compressive strength is observed. In 900°C, for both additions, a considerable decrease of the compressive strength was observed, and those values were by about 25% higher than those obtained for an unmodified binder.
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
Compressive Strength [MPa]
500
60 50 40 30 20 10 0 CEM III 52,5
CEM III 52,5 + 2% SiC
CEM III 52,5 + 4% SiC
CEM III 52,5 + 6% SiC
CEM III 52,5 + 10% SiC
20 °C
39,97
44,39
47,01
44,65
51,77
225 °C
35,53
39,28
32,55
33,83
39,42
450 °C
25,24
32,35
27,05
27,42
36,59
900 °C
9,8
9,82
6,95
8,17
12,13
Fig. 2. Compressive strength of the cement binders with and without silicon carbide after exposition to high temperature.
Analysis of the phase composition of the cement binders from blast-furnace cement with addition of 10% silicon carbide and 6% alumina in the temperature of 225°C and 900°C is presented in Figures 3-5. Analysis of pure binder in 225°C presented in Figure 3a shows typical phases present in the binder with slag, that is dicalcium phosphate, aluminosilicate, calcium carbonate in a polymorphic variety of vaterite and calcite, and calcium hydroxide.
(a)
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
(b) Fig. 3. XRD analysis for CEM III at 225°C (a) i 900°C (b).
(a)
(b) Fig. 4. XRD analysis for CEM III with 6 wt. % of electrocorrundum at 225°C (a) i 900°C (b).
In case of a binder with the addition of silicon carbide and electrocorundum, the X-ray structural analysis proved the presence of both oxides in the cement mortar, both in 225°C and in 900°C. A comparison of phases present in pure cement binder and in binders with additions of electrocorundum and silicon carbide in both tested temperatures implies a lack of chemical reaction between additions and cement binder. However, a clear change is visible in phases in cement binder after exposition to temperatures of 225°C and 900°C. After heating the cement binder in 900°C the silicate and aluminosilicate phases occur, with magnesium built-in in the structure, and dehydrated form of calcium sulfate in the form of anhydrite, and a more solid form of calcium carbonate – a calcite. Polymorphic forms of calcium carbonate, vaterite and aragonite, present in the temperature of 225°C, changed in 900°C into the most solid trigonal structure of calcite. Aluminosilicate and calcium silicate with a built-in magnesium cation, received in high
501
502
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
temperature, are the result of a reaction between the cement binder and a component of the blast-furnace slag, the magnesium oxide, and those phases significantly improve the high thermal resistance of the binder with the addition of blast-furnace slag. Those phases are not present in binders made of pure clinker cement (Figure 6).
(a)
(b) Fig. 5. XRD analysis for CEM III with 10 wt. % of silicon carbide at 225°C (a) i 900°C (b).
(a)
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
(b) Fig. 6. XRD analysis for CEM I at 225°C (a) i 900°C (b).
CEM III 225°C
CEM III 900°C
CEM III + Al2O3 225°C
CEM III + Al2O3 900°C
503
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
504
CEM III + SiC 225°C
CEM III + SiC 900°C
Fig. 7. SEM spectra of cement composites with and without additives.
The analysis of the microstructure of the cement binders with and without addition of electrocorundum and silicon carbide in 225°C and 900°C is presented in Figure 7. In the pictures, in the temperature of 225°C we can see a well crystallised phase C-S-H, and precipitations of calcium hydroxide, and spaces after spherical slag. Microstructure is coherent, in case of pure cement binder, as well as in case of additions of electrocorundum and silicon carbide. Heating of the binder samples in 900°C resulted in an increased porosity of the cement mortar microstructure; in all the pictures we can see the pores in the structure, which is consistent with the obtained results in strength and the X-ray structural analysis. Loosening of the microstructure of the cement binder is related to the evaporation of water, and partial decomposition of the calcium silicate, creation of less coherent calcium silicates and aluminosilicates, and replacement of calcium cation with a magnesium cation, which result in lowering the mechanical parameters of the binder. 4. Conclusions Application of additions, characterised by high mechanical resistance, durability and exceptionally high thermal conductivity, that are used in production of fireproof materials, in cement composites has a crucial influence on the improvement of their resistance to high temperatures. Research proved that compressive strength of the cement composite with addition of Al2O3 in the amount of at least 2% increase in comparison to the referential samples, regardless of the high temperature, by about 25%, and the best results in the whole temperature range were obtained in case of cement mortar with 6% addition of electrocorundum. On the other hand, addition of silicon carbide resulted in a relevant increase of the sample resistance (by 20-30%) only when added in the amount of at least 10%. Moreover, research proved, that the higher thermal resistance of the cement binder resulted from the addition of electrocorundum and silicon carbide on one hand, and from creation in high temperatures of new calcium silicate and aluminosilicate phases, with a magnesium cation built-in in its structure, on the other. References [1] A. Nazari, G. Khalaj, S. Riahi, M. J. Khalaj, Wpływ Nano-Al2O3 na właściwości betonu z granulowanym żużlem wielkopiecowym, Cement Wapno Beton 6 (2011) 311-321 [2] E. Drygalska, T. R. Lipinski, C. Tontrup, Wpływ dodatku nanotlenków Al 2O3 i TiO2 na właściwości tworzyw wysokoglinowych, Materiały Ceramiczne/Ceramic Materials 62(2) (2010) 191-196. [3] I. Majchrowicz, J. Witek, J. Barański, M. Cholewa, Monolityczne materiały ogniotrwałe do zastosowań w odlewnictwie, XII Konferencja Odlewnicza Technical 2010. [4] P. Ogrodnik, B.Zegardło, A. Halicka, Wstępna analiza możliwości zastosowania odpadów ceramiki sanitarnej jako kruszywa do betonów pracujących w wysokich temperaturach, Bezpieczeństwo i Technika Pożarnicza 1 (2012) 49-56
ScienceDirect Procedia Engineering 172 (2017) 497 – 504
Modern Building Materials, Structures and Techniques, MBMST 2016
Influence of silicon carbide and electrocorundum on the thermal resistance of cement binders with granulated blast-furnace slag Teresa Kantela, Agnieszka Ślosarczyka* a
Poznan University of Technology, Faculty of Civil and Environmental Engineering, Institute of Structural Engineering, Street Piotrowo 5, Poznan, 60-965, Poland
Abstract The aim of this work was to compare the influence of the electrocorundum and silicon carbide on the strength and the microstructure of the cement composite with the addition of granulated blast-furnace slag, before and after exposition to higher and high temperature. Research proved that compressive strength of the cement composite with addition of Al 2O3 in the amount of at least 2 wt.% increased in comparison to the referential samples, regardless of the high temperature, by about 25%, and the best results in the whole temperature range were obtained in case of cement binder with 6 wt.% addition of electrocorundum. On the other hand, addition of silicon carbide resulted in a relevant increase of the sample resistance (by 20-30%) only when added in the amount of at least 10 wt.%. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MBMST 2016. Peer-review under responsibility of the organizing committee of MBMST 2016 Keywords:cement; silicon carbide; electrocorudnum; XRD analyses; laboratory experiments.
1. Introduction High temperatures cause changes in the cement mortar and in the aggregate, which results usually in deterioration of physical and mechanical properties of the cement composite. The resistance of the cement composites to short term exposition to temperature oscillates around 200 to 300oC. With gradual heating of the cement matrix, the water bound in it is gradually removed, which leads further to physical and mechanical changes in the structure of the cement
* Corresponding author. Tel.: +48-61-665-2168. E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MBMST 2016
doi:10.1016/j.proeng.2017.02.058
498
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
mortar and destruction of the structure created during the hydration of the cement. After crossing the 400 oC a degradation of the hydrated calcium silicate of the so-called C-S-H phase takes place, which is manifested in a sharp deterioration of the compressive strength of the matrix. In the temperature of 900 oC the C-S-H phase undergoes a total disintegration. Thus, the critical temperature range defining the mechanical durability of the matrix equals 400-800oC. The influence of the high temperatures on the cement matrix durability has been a subject of many publications of local and international range for years. The authors draw attention to the influence of the aggregate type, the cement and the additions on the thermal resistance of composites based on cement binders. The application of the additions used for production of fireproof materials, characterised by high mechanical strength, durability and exceptionally high thermal conductivity, may result in improvement of the resistance of the cement composite in high temperatures. However, most of the research on the influence of those additions on the properties of the cement matrix concentrated on defining its physico-mechanical properties [1,2]. For example, it was proved that concretes with addition of SiC were characterised by high wear resistance, thermal shock resistance, slag corrosion and low porosity and high thermal conductivity [3]. On the other hand, the research conducted by [4] proved, that the cement composites containing significant amount of alumina, or based on aluminium cements, were more resistant to high temperatures, than Portland cements. Reports on the impact of Al2O3 and SiC on cement composites with addition of granulated blast-furnace slag are a real rarity in the literature. Partial replacement of the clinker with the blast-furnace slag contributes to improvement of the cement binder resistance to higher temperatures, and addition of the fireproof materials enhances this effect even further. Therefore, the aim of this work was to compare the influence of the electrocorundum and silicon carbide on the strength and the microstructure of the cement composite with the addition of granulated blastfurnace slag, before and after exposition to higher and high temperature. 2. Materials and research methods In the research the metallurgical cement CEM III/A 52.5 N was applied, meeting the requirements of the norm PNEN 197-1. Its main ingredients are the Portland clinker (35÷64%), granulated blast-furnace slag (36÷65%) and a regulator of the binding time (calcium sulphate). As the additions that improve the temperature resistance of the cement binder a regular electrocorundum and silicon carbide were applied, both with granulation of 250-300 μm. Regular electrocorundum is a synthetic abrasive material consisting of crystalline aluminium oxide in the amount of 94.5 - 97% and a small admixtures of oxides: TiO2, SiO2, Fe2O3, CaO, MgO, that shows a relatively high thermal conductivity and low thermal expansion. It is the less brittle and the most tensile (elastic) electrocorundum. It finds application in metalworking of steel, cast steel, malleable iron and non-ferrous materials in cutting, as well as in the fireproof industry and ceramics. The silicon carbide consisting in 95 – 98% of silicon carbide and chemical admixtures of oxides such as Fe2O3, Al2O3, CaO, SiO2, MnO2 is an abrasive grain of the highest cutting properties, very high toughness and durability. It is characterised by high mechanical resistance and an exceptionally high thermal and electrical conductivity. It can be applied in the treatment of brittle and hard materials (such as glass), in the production of abrasive tools and bulk materials, as well as the fireproof materials. In order to test the influence of those additions on the physico-mechanical properties of the cement composites in different temperatures, three series of cement binders were prepared. Mixtures from the first series were prepared from the blast-furnace cement and water with the water-binder index of 0.48. In the two further series electrocorundum or silicon-carbide was added to the cement binder in the amounts of: 2%, 4%, 6% and 10% of the cement mass. Homogenization of the mixtures begun by stirring the binder with an addition for 1 minute, and then the water was added. Total time of stirring equalled 4 minutes. The binders were formed into cylinders, which were concentrated on a vibration table, and after 48 hours of maturation they were deformed and kept in 20°C water for 90 days. Samples prepared in this way underwent a treatment in higher and high temperature, within the range of 225°C to 900°C, where the temperature increased by 2.5°C every minute. The samples were kept in the given temperature for 30 minutes. Next, the cement mortars with and without modifying additions for given temperatures, respectively: 225, 450 and 900°C, underwent compressive strength tests in the air-dry state. Phase composition of the cement mortars, with and without modifying additions after the influence of 225°C and 900°C was described with the use of a Bruker X-ray diffractometer, model AXS D8 Advance; and the analysis of the microstructure was conducted with the use of scanning electron microscopy, with the Hitachi S-3400N microscope.
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
499
3. Results and discussion
Compressive Strength [MPa]
Figures 1 and 2 present compressive strength of the cement binders with and without modifying additions after exposition to high temperature. 60 50 40 30 20 10 0
CEM III 52,5
CEM III 52,5 + 2% Al2O3
CEM III 52,5 + 4% Al2O3
CEM III 52,5 + 6% Al2O3
CEM III 52,5 + 10% Al2O3
20 °C
39,97
52,07
42,19
50,15
51,05
225 °C
35,53
34,24
33,16
42,33
44,81
450 °C
25,24
35,91
34,03
35,09
29,63
900 °C
9,8
11,26
11,12
12,36
12,31
Fig. 1. Compressive strength of the cement binders with and without electrocorundum after exposition to high temperature.
Electrocorundum, as well as the silicon carbide, improve the mechanical properties of the cement binder in room temperature. Along with the rising amount of the addition, the increase of the compressive strength of the cement mortar was observed. It is the so-called filling effect; the presence of fine particles of the electrocorundum and the silicon carbide results in concentration of the structure of the cement binder and improvement of its mechanical properties. The presence of electrocorundum and silicon carbide also contributes to improving the resistance of the cement binder to higher and high temperature, but the significant effect was observed only when adding greater amount of the additions - 6% in case of electrocorundum and 10% in case of silicon carbide. Moreover, the analysis of the research results proved, that the addition of the electrocorundum, irregardless of the percentage in the sample and the temperature, improved the compressive strength of the cement binder by about 25% in comparison to referential samples. SiC, on the other hand, increases the resistance of the composites, irregardless of the temperature, but only in case of applying it in the amount of minimum 10% of the cement mass. In case of temperature of 450°C a 20-30%, even up to 40% increase of compressive strength is observed. In 900°C, for both additions, a considerable decrease of the compressive strength was observed, and those values were by about 25% higher than those obtained for an unmodified binder.
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
Compressive Strength [MPa]
500
60 50 40 30 20 10 0 CEM III 52,5
CEM III 52,5 + 2% SiC
CEM III 52,5 + 4% SiC
CEM III 52,5 + 6% SiC
CEM III 52,5 + 10% SiC
20 °C
39,97
44,39
47,01
44,65
51,77
225 °C
35,53
39,28
32,55
33,83
39,42
450 °C
25,24
32,35
27,05
27,42
36,59
900 °C
9,8
9,82
6,95
8,17
12,13
Fig. 2. Compressive strength of the cement binders with and without silicon carbide after exposition to high temperature.
Analysis of the phase composition of the cement binders from blast-furnace cement with addition of 10% silicon carbide and 6% alumina in the temperature of 225°C and 900°C is presented in Figures 3-5. Analysis of pure binder in 225°C presented in Figure 3a shows typical phases present in the binder with slag, that is dicalcium phosphate, aluminosilicate, calcium carbonate in a polymorphic variety of vaterite and calcite, and calcium hydroxide.
(a)
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
(b) Fig. 3. XRD analysis for CEM III at 225°C (a) i 900°C (b).
(a)
(b) Fig. 4. XRD analysis for CEM III with 6 wt. % of electrocorrundum at 225°C (a) i 900°C (b).
In case of a binder with the addition of silicon carbide and electrocorundum, the X-ray structural analysis proved the presence of both oxides in the cement mortar, both in 225°C and in 900°C. A comparison of phases present in pure cement binder and in binders with additions of electrocorundum and silicon carbide in both tested temperatures implies a lack of chemical reaction between additions and cement binder. However, a clear change is visible in phases in cement binder after exposition to temperatures of 225°C and 900°C. After heating the cement binder in 900°C the silicate and aluminosilicate phases occur, with magnesium built-in in the structure, and dehydrated form of calcium sulfate in the form of anhydrite, and a more solid form of calcium carbonate – a calcite. Polymorphic forms of calcium carbonate, vaterite and aragonite, present in the temperature of 225°C, changed in 900°C into the most solid trigonal structure of calcite. Aluminosilicate and calcium silicate with a built-in magnesium cation, received in high
501
502
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
temperature, are the result of a reaction between the cement binder and a component of the blast-furnace slag, the magnesium oxide, and those phases significantly improve the high thermal resistance of the binder with the addition of blast-furnace slag. Those phases are not present in binders made of pure clinker cement (Figure 6).
(a)
(b) Fig. 5. XRD analysis for CEM III with 10 wt. % of silicon carbide at 225°C (a) i 900°C (b).
(a)
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
(b) Fig. 6. XRD analysis for CEM I at 225°C (a) i 900°C (b).
CEM III 225°C
CEM III 900°C
CEM III + Al2O3 225°C
CEM III + Al2O3 900°C
503
Teresa Kantel and Agnieszka Ślosarczyk / Procedia Engineering 172 (2017) 497 – 504
504
CEM III + SiC 225°C
CEM III + SiC 900°C
Fig. 7. SEM spectra of cement composites with and without additives.
The analysis of the microstructure of the cement binders with and without addition of electrocorundum and silicon carbide in 225°C and 900°C is presented in Figure 7. In the pictures, in the temperature of 225°C we can see a well crystallised phase C-S-H, and precipitations of calcium hydroxide, and spaces after spherical slag. Microstructure is coherent, in case of pure cement binder, as well as in case of additions of electrocorundum and silicon carbide. Heating of the binder samples in 900°C resulted in an increased porosity of the cement mortar microstructure; in all the pictures we can see the pores in the structure, which is consistent with the obtained results in strength and the X-ray structural analysis. Loosening of the microstructure of the cement binder is related to the evaporation of water, and partial decomposition of the calcium silicate, creation of less coherent calcium silicates and aluminosilicates, and replacement of calcium cation with a magnesium cation, which result in lowering the mechanical parameters of the binder. 4. Conclusions Application of additions, characterised by high mechanical resistance, durability and exceptionally high thermal conductivity, that are used in production of fireproof materials, in cement composites has a crucial influence on the improvement of their resistance to high temperatures. Research proved that compressive strength of the cement composite with addition of Al2O3 in the amount of at least 2% increase in comparison to the referential samples, regardless of the high temperature, by about 25%, and the best results in the whole temperature range were obtained in case of cement mortar with 6% addition of electrocorundum. On the other hand, addition of silicon carbide resulted in a relevant increase of the sample resistance (by 20-30%) only when added in the amount of at least 10%. Moreover, research proved, that the higher thermal resistance of the cement binder resulted from the addition of electrocorundum and silicon carbide on one hand, and from creation in high temperatures of new calcium silicate and aluminosilicate phases, with a magnesium cation built-in in its structure, on the other. References [1] A. Nazari, G. Khalaj, S. Riahi, M. J. Khalaj, Wpływ Nano-Al2O3 na właściwości betonu z granulowanym żużlem wielkopiecowym, Cement Wapno Beton 6 (2011) 311-321 [2] E. Drygalska, T. R. Lipinski, C. Tontrup, Wpływ dodatku nanotlenków Al 2O3 i TiO2 na właściwości tworzyw wysokoglinowych, Materiały Ceramiczne/Ceramic Materials 62(2) (2010) 191-196. [3] I. Majchrowicz, J. Witek, J. Barański, M. Cholewa, Monolityczne materiały ogniotrwałe do zastosowań w odlewnictwie, XII Konferencja Odlewnicza Technical 2010. [4] P. Ogrodnik, B.Zegardło, A. Halicka, Wstępna analiza możliwości zastosowania odpadów ceramiki sanitarnej jako kruszywa do betonów pracujących w wysokich temperaturach, Bezpieczeństwo i Technika Pożarnicza 1 (2012) 49-56