The determination of values of the specific heat capacity of the selected thermal insulation materials used in track bed structure

Transcription

1 The deterination of values of the specific heat capacity of the selected theral insulation aterials used in track bed structure Peter Dobeš 1,*, Libor Ižvolt 1, Martin Mečár 1, and Jana Malachová 2 1 University of Zilina, Faculty of Civil Engineering, Departent of Railway Engineering and Track Manageent (DRETM), Univerzitná 8215/1, Žilina, Slovakia 2 University of Žilina, Institute of Continuing Education, Univerzitná 8215/1, Žilina, Slovakia Abstract. The report concentrates on the deterination of the specific heat capacity of the selected theral insulation aterials (liapor, styrodur, foa concrete). The ai of the report is to gain the necessary input paraeters for the nuerical odelling of the changes of various track bed structures of the railway line where a part or, if appropriate, the whole protective layer is replaced by the aterial with better theral insulation properties. There are described the ethods for stating the specific heat capacity as well as the calibration of the calorieter for stating of the calorietric constant in the introduction of the report. The paraeters needed for calculation of the specific heat capacity of the selected theral insulation aterials are characterized in the second part of the report. There are also introduced the laboratory stated values of the paraeter in question. The coparison of the values stated by the laboratory easureents with the values introduced in the technical data sheets fro their producers (or if appropriate gained fro the foreign sources) is ade in the conclusion of the report. 1 Introduction The design and exaination of the trackbed structure on the non-traffic load, related to nuerical odelling of the frost penetration of the railway line structure (of the track bed), cannot be ade without the basic input thero-technical paraeters of the built- in aterials. Therefore, the ost iportant characteristics are the heat conductivity coefficient λ and the specific heat capacity c of the building aterials. The accepted EN STN do not introduce all the values of the theral conductivity coefficients λ and the specific heat capacity c of the aterials which are used in trackbed structure nowadays. The design and exaination of the trackbed structure of the railway lines is ade according to TNŽ [1]. There are introduced the theral conductivity coefficients λ of various building aterials used in the trackbed structure, in this legislative docuent. These coefficients are presented in the part concentrating on the design and exaination of * Corresponding author: dobes@fstav.uniza.sk The Authors, published by EDP Sciences. This is an open access article distributed under the ters of the Creative Coons Attribution License 4.0 (

2 Railways of Slovak Republic on the non-traffic load. With regard to the necessity of aendent to the legislation docuent [1] and the updating of chart with the proposed values of the theral conductivity coefficients λ of the used building aterials it is necessary to verify soe of the and for soe to deterine new aterials. Since 13 the Departent of Railway Engineering and Track Manageent (DRETM) has been specialising in the probleatics of the cliatic paraeters and the probleatics of the frost penetration of the railway line structure. A utual coparison of the results of frost penetration into the real odels of the railway line structure with different aterial coposition and the results obtained by nuerical odelling of the odels in question has been realised since 200. The DRETM has been focusing on the probleatics of the application of theral insulation aterials in the structure coposition of the trackbed (where the theral insulation aterial in question (structural eleent) replaces a part of protective layer) since There was proceeded an extension of the original experiental stand for onitoring the thero-technical properties and penetration of the zero isother of the railway line structure (of the trackbed) in There was copleted a easuring profile with the application of the theral insulation layer to the easuring profiles which constituted the standard track bed structures. This experiental workplace, in a workrelated context referred to as Experiental stand DRETM, consists of ore easuring profiles nowadays and it will be copleted within the year 2017.The first three easuring profiles represent the ost frequently used railway line structures for odernisation of the railway infrastructure of Slovak Republic nowadays. The first profile is created by an ebankent fro the crushed aggregate of size fraction 0/63 without any protective layer. The second easuring profile fors an ebankent with a protective layer fro the crushed aggregate of size fraction 0/31.5 and the structural thickness The third easuring profile is a cutting with the protective layer fro crushed aggregate of the sae size fraction and structural thickness as in the second easuring profile. In the fourth profile was a part of the protective layer, the crushed aggregate of size fraction 0/31.5 and of construction thickness 0.30, replaced by a layer of liapor of size fraction 0/16 and of construction thickness The application of liapor in the structure coposition of the track bed resulted fro the fact, that the aterial in question has been used in ebankents of traffic structures for several years. The use of liapor is relevant because of its sall bulk density (the lightenance of the ebankent in case of a poor supporting soil) and its excellent theral insulation properties. However, liapor is not the only theral insulation aterial which sees to be an appropriate structural eleent for the protection against the frost-susceptible subgrade in the track bed against the adverse frost effects. Therefore, there has been planned an extension of already existing Experiental stand DRETM to other two easuring profiles (5 th and 6 th easuring profile) this year. It is expected that there will be built-in and tested other theral insulation aterials in these easuring profiles. Specifically, there is expected to built-in slabs fro styrodur and liapor bound by ceent. Unfortunately, the thero-technical paraeters (especially the specific heat capacity c) of the building aterials in question are issing on the websites of producers or they are insufficiently introduced. Since these paraeters are inevitable for the nuerical odelling of the developent of railway line in the software Soilvision, it was necessary to deterine the by laboratory tests. The odification of the procedure for easuring, calibration of the apparatus, as well as the easured paraeters theselves, which are inevitable for deterination of the specific heat capacity, are introduced in the following text. 2

3 2 Methodology for the deterination of the specific heat capacity c of the selected theral insulation aterials of the trackbed The application of the theral insulation aterials in the construction of the trackbed ay see irrelevant according to the predictions of the odels concerning the cliatic conditions. As according to the cliatologists there is the assuption of the waring to continue, the annual average s to grow and the snow cover to decrease. However, these cliatic odels do not exclude extree winter periods - with longer and intense periods of frost and a reached high frost index-which can occur fro tie to tie. The use of the theral insulation aterials is also supported by the fact, that the odernisation of ain corridors of the railway lines in Slovakia approaches slowly the coldest areas of Slovakia (the regions of Low and High Tatras). Nowadays there have been reached the values of frost index close to the proposed values of the frost index which were defined for the territory of the Slovak Republic. The application of the heat insulation building aterials into the structure of the railway line or the track bed can bring any advantages with itself. To these belong in particular the total heat protections of the frostactive soil against the adverse effects of frost while saving natural aterials (crushed aggregate) because of the design with the lesser structural thickness of the frost protective layer. The experiental easureents of the specific heat capacity c and other paraeters, which are necessary for the final deterination of the theral conductivity coefficient λ, have been realised in the laboratory of DRETM since The initial easureents of the paraeters in question served especially to verify the paraeters introduced in [1] and [2]. As entioned above, nowadays the experiental easureents are concentrated on new building aterials which could be applied in the structural coposition of the railway line trackbed (e.g. liapor, styrodur, foa concrete, etc.). As the ost iportant thero-technical paraeter the theral conductivity coefficient λ is well identified for the building aterials in question, the experiental easureents were concentrated only on the deterination of the specific heat capacity c of the theral insulation aterials in question. This paraeter is either unknown or insufficiently introduced but it is needed for the nuerical odelling of the frost penetration of railway line structure (of the track bed). 2.1 The adaptation of the equipent for deterination of the specific heat capacity c The specific heat capacity c [J.kg -1.K -1 )] of the onitored building aterials is being deterined by a calorietric test. The precise deterination of the specific heat capacity c is represented by a coplex laboratory process of defining the partial paraeters which influence the overall results achieved. As the water, which surrounds the saple of the easured aterial, is the ain ediu for the calorietric test and the theral insulation aterials have a saller bulk density than water, it was necessary to adapt the structure of the calorieter. In contrast to the standard structure of the calorieter it was necessary to fix a nylon thread to the inner walls of the calorieter. The nylon thread not only keeps the saple under water during the entire process of easureent but it also prevents the test saple to be sucked into the stirrer. There were used plastic holders (plastic aterials consue iniu heat) for fixing the nylon tread to the inner walls of the calorieter. The further procedure reained unchanged where a polyethylene packaging was used to protect the saple against soaking. The saple was tepered to the of the roo (less than 20 C) and the calorietric test started at the of the + 50 ºC ± 2 ºC water. 3

4 The specific heat capacity of a dry saple c 0 was calculated fro the following relation on the basis of the experientally stated paraeters: c 0. cv K P - K. - v (1) K Where is: c 0 - specific heat capacity of a dry saple, [J/(kg. K)], v - water,, c v - specific heat capacity of the water, [J/(kg. K)], - test saple,, θ P - initial of the water, (ºC), θ K - final of the syste, (ºC), θ - of the saple before easureent, (ºC), K - heat capacity of the calorieter, (J.kg -1 ), The recalculation of the specific heat capacity of the saple fro the dry to the wet state was subsequently realised by eans of the relation: c c c v - c 0 w. 100 w 0 (2) Where is : c - specific heat capacity of a wet aterial, [J/(kg. K)], w - oisture content in the saple, (%) [3]. Since the equipent for deterination of the specific heat capacity c was suppleented by other coponents, there was necessary a calibration of calorieter what is introduced in the following part of the text. 2.2 Calibration of calorieter The experiental onitoring of the decrease of the theral insulation aterial (ediu) within the calibration was carried out in the identical working procedure as the for the standard building aterials of exceeding specific with the difference that there was used water as a saple (it has the biggest specific heat capacity fro the coon substances) with lower than the ediu has (less than 20 C). It should be ephasised that the saple of water was not inserted into the calorieter in the polyethylene packaging but it was poured freely and the tepering of it to the of the roo was realised by placing it into the container with water. The resulting value of the heat capacity of the calorieter was defined by deriving the paraeter K fro the relation (1). Overall, there were realised 5 calibration easureents for calibration of the calorieter where the water volue was about 10 litres in the calorieter, its was 50 C ± 2 C and the of the test saple was fro 500 to 700 g. The deterined values of the heat capacity K are presented in Table 1. Table 1. Deterined values of heat capacity K of the calorieter. Nuber of easureent θ θ p θ k v Heat capacity K (J.kg -1 )

5 Subsequently, there was calculated, as an arithetic average, the resulting value of the heat capacity K = 288 J.kg -1 fro the 5 deterined values of the heat capacity of the calorieter. This heat capacity was further used for the calculation of specific heat capacity c 0 of other tested building aterials. 2.3 Deterination of specific heat capacity of the selected aterials The specific heat capacity is a quantity characteristic for the substance and it has for various substances and various fors various values. In general, this quantity specifies what aount of heat is to be added to a substance with the of one kilogra to increase its in 1 C or 1 K. For all the substances reains the fact, that the specific heat capacity is being reduced by the decrease of the, however, the reduction is not very big so it is possible to consider the values of specific heat capacity as constant for a certain interval [4]. As entioned in the introduction of this article, there were tested 3 theral insulated building aterials altogether, naely liapor of size fraction 0/16, styrodur and foa concrete, which are assued to be built-in to other easuring profiles of the railway line odel of the Experiental stand DRETM Deterination of specific heat capacity of liapor of size fraction 0/16 Liapor is lightweight clay aggregate which is produced by burning and expanding clay in rotary kilns at s about 1200 C. There are created granules of pure natural aterial with excellent perforance that is transferred also to other aterials produced of it. Liapor, in the for of ceraic granules, is used in various grain sizes especially for different backfills and subbase where it perfors a theral insulation function. This aterial is used, because of its low specific weight, into the lightened ebankents of line constructions abroad. The value of the theral conductivity coefficient λ of liapor is fro 0.0 to 0.15 W. -1.K -1 depending on its specific weight. The basic properties of liapor are: low specific weight kg. - ³, heat conductivity fro 0.10 W. -1.K -1, high copressive strength, echanical resistance, cheical stability, fire-resistance, low absorptivity, high soundness, without organic particles and foreign bodies, wholesoeness [5]. The value of specific heat capacity c 0 of liapor was defined fro the easured paraeters presented in Table 2, where are presented also its specific values for the individual easureents. There was created a saple of about 500 g for deterination of the specific heat capacity c 0 of liapor. The saple was produced by ixing of size fraction 8/16 and 0/4 in a ratio 1:1 (the sae ratio was used also for the construction of the 4 th easuring profile of the Experiental stand DRETM. Table 2. Deterined values of the specific heat capacity c 0 of liapor of size fraction 0/16. Nuber of easureent θ θ p θ k v Spec. heat capacity c Subsequently, there was defined (as an arithetic average) the resulting value of the specific heat capacity c 0 of liapor of size fraction 0/16 fro the five easured values of the specific heat capacity. The resulting value is c 0 = 860 J.kg -1.K -1. 5

6 2.3.2 Deterination of specific heat capacity of styrodur Excellent theral insulation properties, variability of types, various copressive strength and edge perforance ake styrodur a very necessary and useable aterial in structural, underground and traffic building industry. Besides of the application for insulation of circuferential walls, roofs and ceilings it is possible to use it also as a frost protection in the road and railway construction. Styrodur is extreely hard extruded polystyrene produced fro polystyrene granules by a physical change of for called extrusion. It is characterised by its high copressive strength up to 700 kpa according to the type by 10 % copression. The heat conductivity coefficient of styrodur is λ = W. -1.K -1 [6]. The value of specific heat capacity of styrodur was defined fro the easured paraeters presented in Table 3, where are presented also its specific values for the individual easureents. There was created a saple of about 80 g and with diensions about 150x150x100 for deterination of the specific heat capacity of styrodur. The saple was cut out of a styrodur slab (STYRODUR 2800 C). Subsequently, there was defined (as an arithetic average) the resulting value of the specific heat capacity c 0 of styrodur fro the five easured values of the specific heat capacity. The resulting value is c 0 = 2051 J.kg -1.K -1. Table 3. Deterined values of the specific heat capacity c 0 of styrodur. Nuber of easureent θ θ p θ k v Spec. heat capacity c Deterination of specific heat capacity of foa concrete Foa concrete is a building aterial with a good echanical strength, low theral conductivity and siple but highly technological processing. It is produced by ixing of binder, water, ingredients and technical foa. Foa concrete contains closed air gaps by which is reached its low specific weight and saving of aterial inputs. The variability of properties and wet process of its production offer a wide range of uses of foa concrete for copensation layers, fillings of various deaf spaces and production of prefabricated panels and blocks. This aterial can have its application on the places with a low deforation resistance of subgrade as well as in the areas with great frost-penetration depth. There is used foa concrete of low bulk density in practice, however, generally it is possible to produce foa concrete with bulk density fro 350 to 1200 kg. -3. On the bulk density and also oisture of the foa concrete depends its value of the theral conductivity coefficient λ which reaches the values fro 0.1 to 0.4 W. -1.K -1 [7]. The value of specific heat capacity of foa concrete was defined fro the easured paraeters presented in Table 4, where are presented also its specific values for the individual easureents. There was created a saple of about 500 g for deterination of the specific heat capacity c 0 of foa concrete. The saple had diensions 100x100x100 and bulk density 500 kg. -3. Subsequently, there was defined (as an arithetic average) the resulting value of the specific heat capacity of foa concrete fro the five easured values of the specific heat capacity. The resulting value is c 0 = 1118 J.kg -1.K -1. 6

7 Table 4. Deterined values of the specific heat capacity c 0 of foa concrete. Nuber of easureent θ θ p θ k v Spec. heat capacity c Conclusion Theral insulation building aterials find their usage not only in the building industry but also in other various parts of industry. Theral insulation aterials are often used also in the structure coposition of layers of linear traffic structures abroad. Also our legislative docuents, involved in the design of structure coposition of traffic structures, consider these aterials. The ai is to increase the heat resistance of paveent structure or track bed. Nowadays an aendent to the legislative docuent shall be taken [1] which has been in force since 188. There are not presented the theral conductivity coefficients of all building aterials which are (or can) be used in the trackbed layers in the part of diensioning of the track bed structure on the non-traffic load. It is desirable to verify in this connection not only the theral conductivity coefficients λ of standard aterials, but also of the ones which have a perspective to be used. The Experiental stand DRETM, which is represented by a odel of a railway line on a scale 1:1, serves to verify this paraeter within our research. There already is (4 th easuring profile) or is intended to be built-in (5 th and 6 th easuring profile) a theral insulation layer in soe parts of the track bed. In particular, there is assued to use styrodur and liapor bound by ceent. The verification of the developent and penetration of zero isother into the railway line structure (of the track bed) happens in two ways by an experiental easureent of the relevant thero-technical paraeters on the real railway line structure, but also by a nuerical odelling of the developent of the railway line structure in software SoilVision. It was essential to obtain the necessary input paraeters, to which belongs also the special heat capacity of the individual aterials, for the realisation of the experiental onitoring and also the nuerical odelling. The value of the specific heat capacity c of the theral insulation building aterials is not as iportant to the final custoers as the theral conductivity coefficient λ. Because of this reason, it is often uch ore difficult or absolutely ipossible to obtain these values. At DRETM (in response to the necessary aendent to the legislation docuent [1]) is paid attention to the verification of the theral conductivity coefficients λ of the aterials used in the track bed layers of the railway line. For this verification and their calculation is necessary a partial paraeter what is a specific heat capacity. The values of the specific heat capacity c 0 of the individual theral insulation building aterials and their coparison with the values fro their producers or fro foreign sources are presented in Table 5. As is evident fro Table 5, the difference between the laboratory defined specific heat capacity of the tested theral insulation building aterials and the specific heat capacity declared by producer or gained fro foreign sources (foa concrete) is inial. The biggest difference was identified in case of liapor. However, it is necessary to ephasise that the value defined by producer is allocated to the size fraction 8/16 but the tested saple in laboratory DRETM was of size fraction 0/16 (it was created by ixing of two fractions). 7

8 Table 5. Measured values of the specific heat capacity c and their coparison with the values fro producer. Building aterial Specific heat capacity c 0 (deterined in the laboratory KŽSTH) Specific heat capacity c 0 (technical data sheet of the producer or foreign source) Liapor fr. 0/ [8] Styrodur 2800 C [] Foa concrete [10] The application of the theral insulation aterials in the structure coposition of the railway line appears as undesirable based on the cliatic odels forecasting constant waring of cliate and increase of the average annual s. But at the sae tie the cliatologists do not exclude winter seasons with intense and longer frost periods. In this connection, we have to respect the fact that we have regions in Slovakia where were and are likely to be reached high values of frost index (Podtatranský region, Orava, Kysuce). In response to the necessary odernisation of the railway infrastructure of Railways of the Slovak Republic, the building aterials with better theral insulation properties can find a real application in the track bed structure related to the odernisation of railway lines. The presented results are the results of solving the VEGA grant project 1/0275/16 Optiization design of sleeper subgrade due to non-traffic load aspect. References 1. TNŽ , Design of subgrade construction layers, Standard of Slovak Railway (2005) 2. STN EN ISO , Construction aterials and products. Hygrotheral properties. Tabulated design (calculated) values and procedures for the deterination of declared and design values of theral quantities (2007) 3. P. Dobeš, Optiization of the subgrade design for non-traffic load (Dissertation thesis), ). University of Žilina, Faculty of Civil Engineering, Departent of Railway Engineering and Track Manageent (2015) _list.pdf