Lidé na fakultě
Ing. Michaela Petříková, Ph.D.

2023, International Conference of Numerical Analysis and Applied Mathematics ICNAAM 2021, Melville, NY, AIP Publishing), ISBN 978-0-7354-4589-5, ISSN 1551-7616

The basic premise of self-heating function of construction materials is favorable electrical properties, which is not fulfilled in the case of common geopolymers, cementitious or alkali-activated materials. To gain self-heating ability of such materials, an optimized amount of metal- or carbon-based admixtures is used to form electrically conductive paths which in case of higher amount of admixture results in a significant increase in electrical conductivity. It was reported at low voltage load an outstanding self-heating ability of cementitious composites with nickel powder. Nevertheless, such composites are of high environmental impact due to cement and nickel production. Therefore, it is beneficial to seek promising self-heating construction materials based on byproducts or wastes. The paper is focused on metallic 3D printing waste characterization and the determination of electrical and thermal properties of alkali-activated slag mortar with 3D printing waste. It was proved by measurements of electrical properties and confirmed by measurement of volt-ampere characteristics in the range of 40 to 100 V that even a high dosage of 3D printing waste admixture rich on nickel alloys, that the effective electrical conductivity of the composite is not sufficient to allow meaningful self-heating ability.

Stať ve sborníku z prestižní konf. (Scopus)

2021, AIP Conference Proceedings 2429, New York, AIP Conference Proceedings), ISBN 978-0-7354-4139-2, ISSN 1551-7616

The biodegradation of caffeine, theobromine and theophylline by wood destroying fungi Coniophora puteana were analyzed in the present study. Aquatic solution of caffeine (1 g.l-1) was performed and fungal hyphae were put into the solutions for 28 days. Vials with the fungi were stored in a biological incubator at 22 ±2 °C for 28 days. The same design was used for vials with the fungi without the tested substances and the pure distilled water as a reference. The results of biological tests were evaluated by a liquid chromatography-mass spectrometry method. The fungal samples were analyzed each 7 days. Caffeine concentration increased in the fungal mass during the first 14 days. After that its concentration decreased. Caffeine was also degraded to theophylline and theobromine. Theophylline and theobromine concentrations rapidly increased during the first 7 days and then rapidly decreased fast to zero. The decreasing levels of all substances in fungi indicated their biodegradation during time.

Stať ve sborníku z prestižní konf.

2021, AIP Conference Proceedings 2429, New York, AIP Conference Proceedings), p. 020033-1-020033-5), ISBN 978-0-7354-4139-2, ISSN 1551-7616

Whereas the hydration stoppage of cementitious materials has been widely studied and discussed, there is a lack of knowledge concerning water removal techniques/arresting of hardening processes of non-cementitious materials, such as environmentally friendly calcined gypsum. This article, therefore, aims to apply the commonly used water removal methods, namely direct drying and solvent replacement for arresting processes of gypsum paste, and compare their effects on its composition. The effects of drying methods were studied with the help of thermal analysis consisting of differential scanning calorimetry and thermogravimetry, and these results were complemented with X-ray powder diffraction analysis.

Stať ve sborníku z prestižní konf.

2021, Energies, 14 (23), ISSN 1996-1073

The negative environmental impact of cement production emphasizes the need to use alternative binders for construction materials. Alkali-activated slag is a more environmentally friendly candidate which can be utilized in the design of mortars with favorable material properties. However, the electrical properties of such materials are generally poor and need to be optimized by various metallic or carbon-based admixtures to gain new sophisticated material functions, such as self-sensing, self-heating, or energy harvesting. This paper investigates the influence of waste metal powder originating from the 3D printing process on the material properties of alkali-activated slag mortars. The untreated metal powder was characterized by means of XRD and SEM/EDS analyses revealing high nickel content, which was promising in terms of gaining self-heating function due to the high electrical conductivity and stability of nickel in a highly alkaline environment. The designed mortars with the waste metal admixture in the amount up to 250 wt.% to the slag and aggregates were then characterized in terms of basic physical, thermal, and electrical properties. Compared to the reference mortar, the designed mortars were of increased porosity of 17–32%. The thermal conductivity of ~1–1.1 W/m·K was at a favorable level for self-heating. However, the electrical conductivity of ~10−6 S/m was insufficient to allow the generation of the Joule heat. Even though a high amount of 3D printing waste could be used due to the good workability of mixtures, its additional treatment will be necessary to achieve reasonable, effective electrical conductivity of mortars resulting in self-heating function.

Článek v periodiku excerpovaném SCI Expanded

2021, AIP Conference Proceedings 2429, New York, AIP Conference Proceedings), ISBN 978-0-7354-4139-2, ISSN 1551-7616

Self-heating construction materials belong to the group of multifunctional materials with high potential in the construction industry. Maximization of the self-heating potential of geopolymers / alkali-activated aluminosilicates / cementitious materials is mainly dependent on two factors. The first is optimization of the effective electrical conductivity of the material, which is crucially dependent on the amount of a chosen electrically conductive admixture. The second is the selection and way of fitting/embedment of a particular type of electrode on samples. Even a sufficient increase in the amount of electrically conductive admixture, which is directly proportional to the number of formed conductive paths within the solid matrix accompanied by an increase in the effective electrical conductivity corresponding to the amount of evolved Joule’s resistance heat, does not guarantee a good heating potential without an appropriate attachment of electrodes. In this paper, several types of electrode embedment were tested within self-heating experiments carried out on optimized multifunctional geopolymers with carbon black and graphite powder. Examples of errors observed during self-heating experiments due to failure of particular types of electrode embedment are presented. With respect to the observed failures, the electrode embedment was stepwise optimized

Stať ve sborníku z prestižní konf.

2020, AIP Conference Proceedings 2275, Melville, NY, AIP Publishing, APL, the American Institute of Physics), ISBN 978-0-7354-4005-0, ISSN 1551-7616

Construction materials are required to exhibit good mechanical properties, sufficient durability, and resistance to the negative influence of the environment, such as resistance of the moistened material to freeze-thaw cycles, resistance to intake and crystallization of salts or significant changes in temperature. Besides, it exists the requirement for the design of materials with additional properties, so-called multifunctional materials. Optimization of electrical properties of mostly electrically non-conductive construction materials opens up a wide range of their new applicability, such as in self-heating or self-sensing applications. In the case of self-heating, sufficiently high electrical conductivity of the optimized construction material must be achieved. Determination of electrical properties is the first crucial step for the estimation of self-heating ability. This paper is focused on experimental determination of basic physical and electrical properties in DC/AC regime of the composite based on alkali-activated slag with graphite admixture in the amount of 6.25 wt.%. Basic physical properties were determined by gravimetric method and helium pycnometry. DC parameters were identified by measurements of the resistance and calculations of the electrical conductivity. AC parameters were identified by LCR bridge. It was observed that electrical properties of geopoymer enhanced by graphite powder in amount of 6.25 wt.% ensure self-heating ability of such composite which can be classified as multifunctional.

Stať ve sborníku z prestižní konf. (Scopus)

2020, MATEC Web of Conferences, Les Ulis Cedex A, EDP Sciences - Web of Conferences), ISSN 2261-236X

In this study, the different proportions of co-fired fly ash and ground granulated blast-furnace slag were used to fully replace the cement as non-cement blended materials in a fixed water-cement ratio. The recycled fine aggregates were replaced with natural fine aggregates as 10%, 20%, 30%, 40% and 50%. The flowability, compressive strength, water absorption and scanning electron microscope observations were used as the engineered indices by adding different proportions of recycled fine aggregates. The test results indicated that the fluidity cannot be measured normally due to the increase in the proportion of recycled fine aggregates due to its higher absorbability. In the compressive strength test, the compressive strength decreased accordingly as the recycled fine aggregates increased due to the interface structure and the performance of recycled aggregates. The fine aggregates and other blended materials had poor cementation properties, resulting in a tendency for their compressive strength to decrease. However, the compressive strength can be controlled above 35 MPa of the green non-cement blended materials containing 20% recycled aggregates.

Stať ve sborníku z mezinár. konf.

2020, 20th International Multidisciplinary Scientific GeoConference SGEM 2020, Sofia, International Multidisciplinary Scientific GeoConference SGEM), p. 359-366), ISBN 978-619-7603-12-5, ISSN 1314-2704

Alkali-activated aluminosilicates and geopolymers in the dry-state are typical dielectrics which is a limiting factor for their utilization in new sophisticated ways in construction industry. Nevertheless, such an issue can be solved by using various electrically conductive admixtures to attain reasonable electrical properties that ensure new functional properties, such as self-heating or self-sensing. Self-heating ability is attained by the addition of electrically conductive aggregates or sufficient amount of metallic or carbon-based powders or fibers ensuring a significant increase in electrical conductivity. However, the self-heating was studied mainly for cementitious materials. Taking into consideration good materials properties of alkali-activated aluminosilicates and geopolymers, such as good mechanical properties, chemical resistance, and durability together with the lack of research concerning electrically enhanced multifunctional materials, it is obvious the necessity of new studies. In this paper, alkali-activated ground-granulated blast-furnace slag composite with graphite admixture was studied in terms of basic physical and electrical properties together with the experimental verification of self-heating ability. It was proved that the designed composite with 35 wt. % of graphite powder can be classified as multifunctional material that could be utilized in special applications, such as snow-melting pavements, snow-melting roads or self-heating construction elements.

Stať ve sborníku z prestižní konf. (Scopus)

2020, Journal of Cleaner Production, 260, ISSN 0959-6526

Recently, materials with enhanced electrical properties appeared as very good candidates for self-heating applications. When exploited for icing prevention or deicing of roads, pavements, or runways, they may bring environmental benefits as they do not load the environment with chemicals, salts in particular. Utilization of waste products instead of traditional materials, such as Portland cement, makes these materials even friendlier to the environment. In this paper, three alkali-activated materials composed of slag, water glass, aggregates, water, and carbon black as an electrically conductive admixture are analyzed and compared to a reference one without any conductive admixture. Experimental results show that the designed materials have a very favorable combination of mechanical- (compressive strength up to 44 MPa and flexural strength up to 9 MPa) and electrical (electrical conductivity up to ∼55 × 10-3 S/m) properties. Satisfactory self-heating properties in a low-voltage range are exhibited as well; 45 V DC heating of the samples can increase their temperature by up to 39 °C. The environmental assessment indicates that the designed alkali-activated materials can be considered as promising alternatives to cement-based composites with similar properties, reducing the carbon dioxide production by up to 44%.

Článek v periodiku excerpovaném SCI Expanded

2020, AIP Conference Proceedings 2275, Melville, NY, AIP Publishing, APL, the American Institute of Physics), ISBN 978-0-7354-4005-0, ISSN 1551-7616

Building materials have been comprehensively explored and optimized mainly to achieve appropriate mechanical properties, sufficient durability, resistance to aggressive chemicals or high temperatures. Various new abilities of mainly cementitious materials were already studied and optimized, e.g. self-compacting, self-expanding, self-curing, self-healing, anti-spalling, light-transmitting, light-emitting or photocatalytic activity. Some abilities, such as self-heating, self-sensing, energy harvesting or electromagnetic wave shielding/absorbing, are crucially dependent on electrical properties which are in the case of conventional building materials very poor. This deficiency can be solved by using various electrically conductive admixtures in an appropriate amount close to the percolation threshold. In this paper, experimental investigation of self-heating ability of an aluminosilicate composite based on ground-granulated blast-furnace slag activated by water glass is presented. Electrical properties of the studied composite were enhanced by graphite powder in the amount of 6.25 wt.%. Experimental results show good self-heating performance at 40 V voltage load. The temperature increase after 30 min of heating was about 24 °C, and the maximal temperature increase of 37 °C was achieved after 2 h of heating.

Stať ve sborníku z prestižní konf. (Scopus)

2019, CONSTRUMAT 2019 - XXV International Conference and Meeting of Departments, London, IOP Publishing), ISSN 1757-8981

Geopolymers as competitors to the cement-based construction materials are intensively studied in the present. Their competitiveness mainly arises from their high strength, favourable development of hydration heat at early age, good chemical resistance and thermal stability. Further qualitative improvement of functional properties can be achieved by adding electrically conductive admixtures. In an appropriate amount (called percolation threshold), mechanical properties remain reasonable and electrical properties become sufficient to ensure evolution of heat by acting of an external power source (self-heating), to detect material damage (self-sensing) or to harvest thermoelectric energy (energy harvesting). In this paper three geopolymers with different dosages of carbon black (CB) admixture (0 wt. %, 4 wt. %, 10 wt. %) were studied by means of LCR bridge AC measurements. It was observed significant difference in electrical behavior of the studied geopolymers. 0 wt. % geopolymer exhibited highly capacitive character, 4 wt. % geopolymer was slightly shifted to resistive behavior and 10 wt. % geopolymer behaved like resistor even to high frequencies with reasonable resistance which indicates its possible self-heating ability.

Stať ve sborníku z prestižní konf. (Scopus)

2019, Central European Symposium on Thermophysics 2019 (CEST), New York, AIP Conference Proceedings), ISBN 978-0-7354-1876-9

Geopolymers can be considered as competitive construction materials to cement-based materials. It is mainly due to their high strength, good chemical resistance, thermal stability and favorable development of hydration heat at early age. A reasonable amount of electrically conductive admixtures close to the percolation threshold enhances electrical properties of geopolymers which leads to their potential utilization in self-heating applications. In general, electrical and thermal conductivity is essential for an effective heat evolution and distribution through the material. Sufficiently high electrical conductivity ensures evolution of Joule’s heat initiated by acting of a power supply, whereas sufficiently high thermal conductivity ensures effective spreading of the generated heat. To assess the self-heating ability of such materials and effectiveness of their self-heating, it is necessary to experimentally determine electrical and thermal properties. In this paper, basic physical, electrical and thermal properties of geopolymers with different dosages of electrically conductive carbon black admixture are measured. Basic physical properties are determined by the gravimetric method, DC electrical properties by the 4-probes method and thermal properties by the pulse method. Addition of 10 wt. % of CB to the reference geopolymer is found to lead to a significant increase of electrical conductivity at the cost of a decrease of thermal conductivity. Nevertheless, geopolymer enhanced in such a way can be considered as a promising self-heating material.

Stať ve sborníku z prestižní konf.

2019, PROCEEDINGS of the 7th International Conference on Chemical Technology, Prague, Czech Society of Industrial Chemistry), p. 42-45), ISBN 978-80-88307-00-6, ISSN 2336-811X

Tenebrio molitor belong to the cosmopolitan pests of human dwelling and various agriculture or food stores. Larvae can eat almost anything and food attacked by T. molitor is more susceptible to mold, which can adversely affect human health. The aim of this study was to compare the effect of two methylxanthines (caffeine and theobromine) occurring, e.g., in tea, coffee and cacao beans, on larvae of Tenebrio molitor in avoidance- and feeding bioassays. Methylxanthines uptakes were determined in glass Petri dishes after 1 to 7 days of exposure. The results showed that larvae avoided the contaminated part of filter paper after only a several-seconds contact with caffeine. The mortality of larvae after caffeine and theobromine feeding was not observed. Theobromine caused larvae eclampsia and then paralysis for several days but their behavior was not different from the control group after 96 hours.

Stať ve sborníku z prestižní konf.

2019, 19th International Multidisciplinary Scientific Geoconference SGEM 2019, Sofia, STEF92 Technology Ltd.), p. 107-114), ISBN 978-619-7408-89-8, ISSN 1314-2704

Cement-based composites belong to the most frequently used construction materials in the world for their good mechanical properties and durability. However, production of cement exhibit significant impact on environment due to high amount of consumed energy and CO2 emissions. Therefore, alternative environmental-friendly construction materials with comparable materials properties are currently intensively studied. Geopolymers are materials based on alkali activation of various precursors that exhibit lower impact on environment. Innovative approach lies in design of multifunctional construction materials that can together with good mechanical properties and durability e.g. evolve heat, detect the current material condition or harvest energy from various ambient energy sources. Such desired capabilities can be ensured by geopolymers doped by electrically conductive admixtures in an appropriate amount. In this paper, self-heating geopolymer mix based on ground granulated blast furnace slag and carbon black is designed and characterized in terms of basic physical, mechanical, thermal and electrical properties. Electrical properties that are crucial for self-heating ability involve experimental determination of the electrical conductivity and volt-ampere characteristics. Finally, the self-heating experiment is conducted by acting of an external power source. The obtained results showed that self-heating ability of the designed geopolymers is promising and such materials can be classified as multifunctional. Taking into account materials properties comparable with cement-based materials and the fact that ground granulated blast furnace slag is a waste product, the designed geopolymer can be considered as environment friendly compared to the materials based on Portland cement.

Stať ve sborníku z prestižní konf. (Scopus)

2019, 4th Central European Symposium on Building Physics 2019 (CESBP), Les Ulis Cedex A, EDP Sciences - Web of Conferences), ISSN 2261-236X

Molds on buildings can cause health- and aesthetic problems. Looking for suitable cheap and non-toxic substances to eliminate them is therefore an actual task. In the present study, effect of three selected methylxanthines (1,3,7-trimethylpurine-2,6-dione, 3,7-dihydro-3,7-dimethyl-1H-purine-2,6-dione and 1,3-dimethylxanthine) on growth of non-specific species of molds occurring on building materials were tested on agar medium under laboratory conditions. The chemical substances were dissolved in distilled water and applied into agar. Solid agar has been exposed to air molds for 24 hours. Agar plates were then covered with lids and placed for 5 days in a laboratory thermostat at stable test conditions (dark place, 25 0C). After that, the mycelium was observed. The results showed that 3,7-dihydro-3,7-dimethyl-1H-purine-2,6-dione and 1,3- dimethylxanthine were not effective against the molds growth. On the other hand, 1,3,7-trimethylpurine-2,6-dione was able to eliminate mold growth on agar medium at a concentration of 1 g∙l-1 or higher.

Stať ve sborníku z prestižní konf.

2019, Energies, 12 (21), ISSN 1996-1073

Sustainable development in the construction industry can be achieved by the design of multifunctional materials with good mechanical properties, durability, and reasonable environmental impacts. New functional properties, such as self-sensing, self-heating, or energy harvesting, are crucially dependent on electrical properties, which are very poor for common building materials. Therefore, various electrically conductive admixtures are used to enhance their electrical properties. Geopolymers based on waste or byproduct precursors are promising materials that can gain new functional properties by adding a reasonable amount of electrically conductive admixtures. The main aim of this paper lies in the design of multifunctional geopolymers with self-heating abilities. Designed geopolymer mortars based on blast-furnace slag activated by water glass and 6 dosages of carbon black (CB) admixture up to 2.25 wt. % were studied in terms of basic physical, mechanical, thermal, and electrical properties (DC). The self-heating ability of the designed mortars was experimentally determined at 40 and 100 V loads. The percolation threshold for self-heating was observed at 1.5 wt. % of carbon black with an increasing self-heating performance for higher CB dosages. The highest power of 26 W and the highest temperature increase of about 110 °C were observed for geopolymers with 2.25 wt. % of carbon black admixture at 100 V.

Článek v periodiku excerpovaném SCI Expanded

2019, International Conference on Numerical Analysis and Applied Mathematics (ICNAAM-2018), American Institute of Physics Inc.), ISBN 978-0-7354-1854-7, ISSN 0094-243X

In the present, traditional building materials with an adjusted composition are widely studied in terms of sophisticated applications. Self-heating ability of cement-based materials and geopolymers is based on supplementing the originally non-conductive material by electrically conductive admixtures. Addition of electrically conductive metal-based or carbon-based admixtures results in a significant increase in the electrical conductivity of such composites which is a crucial assumption for generation of heat by the action of an external electric source. Such materials can be then practically used in self-heating constructions, such as in pavements, bridges or self-heating elements used in interiors and exteriors of the buildings. Within the research, alkali-activated aluminosilicate with 11.1 wt% of carbon black (CB) admixture was designed, material parameters necessary for the successive calculations were experimentally determined, self-heating experiment was carried out and FEM calculations were conducted in order to validate the proposed heat model. It was observed good agreement of the modeled data with the experimentally determined data.

Stať ve sborníku z prestižní konf.

2019, PROCEEDINGS of the 7th International Conference on Chemical Technology, Prague, Czech Society of Industrial Chemistry), p. 310-313), ISBN 978-80-88307-00-6, ISSN 2336-811X

Titration (volumetry, volumetric analysis) is a common laboratory method of quantitative analysis. It belongs to the robust but relatively precise determination methods of measuring various inorganic and organic substances. It can be used for analysis of high concentrations unsuitable for measuring by very sensitive instrumental analyses as GC/MS or HPLC. In the present study, we used titration for measuring of wood leachate containing methylxanthines caffeine, theobromine and theophyline. Concentrations corresponding to the highest solubility of studied substances in water were analyzed. Theobromine and theophyline were titrated by verified methods by adding of 0.1 M AgNO3 solution. Titration of caffeine was modified and verified spectrometrically in the present study. The results indicated suitability of used methods for methylxanthines analyses of wood leachates.

Stať ve sborníku z prestižní konf.

2018, Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2018 (ICCMSE-2018), New York, AIP Conference Proceedings), ISBN 978-0-7354-1766-3

Alkali-activated aluminosilicates (AAA) are promising materials alternative to the cement-based ones due to high strength, very good chemical resistance and durability. As well as for cement-based materials, enhancement of electric properties of AAA allows to classify such materials not just as smart materials. AAA with enhanced electric properties by means of addition of sufficiently high amount of electrically conductive admixtures are promising in terms of self-heating or self-sensing ability. In case of self-heating composites, sufficient electrical conductivity is needed to increase ability to generate heat. Besides, thermal conductivity must be sufficiently high in order to effectively spread generated heat. However, the effective electrical conductivity and the effective thermal conductivity of AAA is significantly affected by amount of water present in pores. It is therefore important to experimentally determine heat, water and water vapour transport and accumulation properties. In this paper, thermal properties represented by the thermal conductivity and the specific heat capacity, hygric properties represented by the water absorption coefficient, the apparent moisture diffusivity, the water vapour diffusion coefficient, the water vapour resistance factor and sorption isotherm were investigated for the reference AAA and AAA electrically enhanced by carbon black (CB) in amount of 5.56 %.

Stať ve sborníku z prestižní konf.

2018, Proceedings of International Conference on Numerical Analysis and Applied Mathematics 2017 (ICNAAM-2017), New York, AIP Conference Proceedings), ISBN 978-0-7354-1690-1, ISSN 0094-243X

Alkali-activated building materials with sufficiently high electrical conductivity are able to generate Joule heat which can be utilized in practical applications, e.g. for construction of heating elements incorporated to pavements, roads or bridges. Convenient electric properties of such materials are usually achieved by addition of a sufficient amount of electrically conductive admixtures to the reference material. Situation is relatively simple in case of dry materials: electrical conductivity and therefore heating ability is influenced just by electron charge carriers. However, thermal and electric properties of porous materials partially or fully saturated are significantly affected by water present in porous structure. With increasing amount of water, the effective electrical conductivity and the effective thermal conductivity increases with increasing amount of water due to substitution of air present in pores in dry state by water in partially or fully saturated state. Therefore, model taking into consideration coupled transport of mass, heat and electric charge needs to be used to assess heating ability of wet porous materials influenced by external electric voltage. In this paper, such model is outlined in theoretical way.

Stať ve sborníku z prestižní konf.

2018, CONSTRUMAT 2018, London, Institute of Physics Publishing), ISSN 1757-899X

Generally, the crack propagation is a problem of equilibrium and stability of silicate structures. The critical crack length depends on fracture toughness. The relationships between fracture toughness, bulk density, modulus of elasticity, and compressive strength are depicted in silicate material diagrams. Those diagrams have numerous application in engineering structural design.

Stať ve sborníku z prestižní konf. (Scopus)

2018, Special Concrete and Composites 2017, Zürich, Transtech Publications), p. 108-113), ISBN 978-3-0357-1240-7, ISSN 1013-9826

In this paper, the effect of elevated temperatures on the mechanical and basic properties of two different newly-designed high-strength concretes is studied. The studied materials were prepared from Portland cement, steel fibers, reactive finely milled quartz powder and quartz sand, silica fume, plasticizer, and with a relatively low water/cement ratio of 0.24. The samples were stored in water environment for the first 28 days of hydration to achieve better mechanical properties. Then, after pre-drying at 105 °C to constant mass, the materials were exposed to elevated temperatures of 600 °C and 1000 °C where they were kept for 2 hours. The basic physical properties, such as matrix density, bulk density and open porosity were determined as a function of temperature. Mechanical properties (compressive and flexural strength) were also studied. The measured parameters exhibited a high dependence on temperature and the obtained results pointed to the structural changes of the studied materials. Spalling was not observed because of the pre-drying treatment.

Stať ve sborníku z prestižní konf. (Scopus)

2017

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