bitumen
Bitumen ( Latin pix tumens , " sweating pitch", "earth pitch", "grave pitch") EN 12597 is the name for the dark-colored, semi-solid to hard, sticky hydrocarbon mixtures obtained during the gentle processing of petroleum . It is also available in natural asphalt . Because of its health benefits, bitumen has replaced the coal tar previously used and is nowadays used for the same purpose, especially in road construction and for sealing work. Bitumen is a colloidal system made up of a dispersant, the maltenes, and the proportions of asphaltenes and petroleum resins dispersed in it.
Definition of terms
Residues that are left behind during the pyrolysis of carbon-rich substances cannot be described as bitumen, but as tar . Since tar is very similar to bitumen due to its black color and the viscous consistency when heated , both substances are often equated or confused with one another. It is often said that a road will be "tarred" when the road is given a new asphalt surface. However, tar differs significantly from bitumen in terms of its production and chemical composition. It is not obtained from crude oil, but mainly from lignite and hard coal and contains a high proportion of polycyclic aromatic hydrocarbons (PAH). Since these are very harmful to health , tar products may no longer be used as building materials in Germany . Mixtures of tar and bitumen have not been used in road construction since the 1980s .
The equation or confusion of tar and bitumen is due not least to the fact that until 1983 both bitumen and tar, pitch and asphalt were grouped under the umbrella term bituminous substances . Today, a clear distinction is made between bitumen and coal tar pitch , as they are fundamentally different groups of substances . According to EN 12597, the generic term for bitumen products is "Bitumen and bituminous binders". Only bituminous, ie tar-free, mixtures may also be referred to as “asphalt” .
history
Bitumen was used in ancient times . Archaeologists discovered bitumen remains in as-Sabiyah (Kuwait) as fragments of sealing material that are more than 3000 years older than those found in Ra's al-Jins in Oman (2400–2300 BC). In a Neolithic village on the edge of a lagoon , they found not only the Arab artifacts to be expected but also those of the Mesopotamian Obed culture . 3000 BC It was first verifiably mined in the city of Hīt at natural exit points. According to numerous descriptions, the place must have been a center of the asphalt industry at that time. In the 26th century BC A limestone plaque was created in Iraq , framed with shells and bitumen in Tell Asmar . In Assyria 2200 was v. Chr. The altar in the Mausoleum of Bur-sin coated with bitumen.
Bitumen objects are known almost exclusively from Susa , the capital of the Elam Empire (today's Iran ). Bitumen was heated and then formed a hard mastic- like mass into which scenes and figures were scratched.
The hanging gardens are said to have been sealed with bitumen. Herodotus describes 500 BC Methods of extracting “pitch” from oil wells on Zakynthos . Strabo writes 100 BC About the extraction of "earth pitch" at the Dead Sea . At the same time Diodorus mentions the ancient bitumen industry. After this heyday , natural asphalt was forgotten for centuries. The Greeks were not particularly interested in the material, the Romans had hardly any asphalt deposits. Up until the Middle Ages , bituminous substances practically only played a role in magic , medicine and the embalming of mummies . With the time of the Enlightenment and the voyages of discovery (15th century) natural asphalt was rediscovered. In the time of the Renaissance had roof gardens popular and these were sealed with bitumen.
In 1556 Georgius Agricola wrote in Germany about the properties of bitumen and its extraction in bituminous sources. In 1704 Michael Bernhard Valentini describes the properties of Juden-Glue, Juden-pitch or asphaltum . The distillation unit of the brothers Dubinin supplies in Russia in 1823 in addition to petroleum small amounts of bitumen.
The first great oil boom of the 19th century began with the successful oil drilling in the US state of Pennsylvania in 1859. Luminous oils for lamps were initially obtained from crude oil by distillation. A little later, further distillations were carried out and it was discovered that the distillation residues have various positive properties. In 1873, with the use of so-called bubble distillation, the continuous extraction of bitumen became possible on an industrial scale. In 1888, HC Bowen developed the first test method for bitumen with the penetration test
In 1906 a patent was applied for in Germany for the first "bitumen emulsion". Bitumen was found a few years later as insulation in electrical systems, for sealing fuses and house roofs. The bitumen was also used to seal dams in hydraulic engineering .
In 1936 the test for the RuK softening point was developed for the first time , and in the following year that for the Fraass breaking point was developed. It was also used as an adhesive in the manufacture of briquettes and as a component of insulating tapes . In 1957 foamed bitumen was developed . Ten years later, "polymer-modified bitumen", which is very important for today's application, was developed and tested.
The most important application of bitumen is in road construction, in the 2000s the share of road construction bitumen was around 75%. Especially when the use of tar in asphalt was banned in West Germany in the 1970s and bitumen was used instead, the demand for road construction bitumen rose rapidly.
properties
Bitumen are colloidal systems made up of three different types of molecules. Oily, low molecular weight fractions, so-called Maltenes, with molar masses of 500 to 1500 g / mol form the dispersant. It contains, on the one hand, meltable, soluble petroleum resins with good adhesiveness and a particle mass of 1000 to 1500 u, and on the other hand so-called asphaltenes - infusible, insoluble constituents with particle masses of 5000 to 9000 u - dispersed.
Bitumen mainly consists of many different long-chain hydrocarbons (aliphatic as well as aromatic) and hydrocarbon derivatives. The mass fraction of carbon is 80-85%, of hydrogen 7-10%. Other constituents are small amounts of oxygen, sulfur, nitrogen and some traces of metals.
Bitumen is practically insoluble in water (hydrophobic) and also largely impermeable to water vapor. It is therefore used, for example, to protect sensitive materials and components against water. In practice, years of exposure to water can only be demonstrated on the surface.
The properties of bitumen are based on the colloidal system structure. The structure changes from a sol to a gel state when heated. Therefore most of the properties are temperature dependent. Bitumen, for example, is a thermoplastic substance, which means that its viscosity is also temperature-dependent: when it cools down, it becomes brittle, when heated, it passes through all states from solid (glass-like) to viscous and between 150 ° C and 200 ° C thin. When the temperature rises, it slowly begins to age, the oil components evaporate and the bitumen hardens. Bitumen does not have a fixed melting point such as B. water, but it has a melting range because the numerous components of the hydrocarbon mixture have different melting points.
Bitumen's behavior towards chemicals and chemical influences is also partly dependent on the temperature. At room temperature, bitumen is practically resistant to most chemicals. These include organic and inorganic salts, strongly polar solvents such as alcohol or aggressive water, as well as bases and weak acids such as. B. carbonic acid. However, some strong acids such as sulfuric acid and nitric acid can chemically attack bitumen at elevated temperatures. Bitumen is soluble in hydrocarbons of the same origin, i.e. gasoline, oil, diesel, and also in many other organic solvents such as benzene, carbon disulfide, trichloroethane, toluene, etc. Bitumen is considered flame-retardant. The flash point is generally above 220 ° C. In contrast to road pitch (tar), bitumen does not contain any carcinogenic, polycyclic hydrocarbons and is biologically harmless.
The properties of bituminous building materials are determined by the following typical characteristics:
- Hardly volatile , black, high-molecular hydrocarbon mixture
- Low density , i.e. H. 1.01 to 1.07 kg / dm 3 (like water, oxidized bitumen even less)
- Extreme temperature and time dependency ( visco-elasto- plastic), hence also low heat and fire resistance
- Good sealing properties against water and steam ( diffusion resistance μ = 50,000)
- Water repellent, low water solubility ( solubility of water in bitumen 0.001 to 0.1%)
- Good adhesion and adhesive properties on dry surfaces (with emulsions also conditionally on moist surfaces)
- Low thermal conductivity (0.16 W / (m K))
- Large thermal expansion (6 × 10 −4 / K)
- Specific heat capacity (1.7 kJ / (kg K))
- Low electrical conductivity at 30 ° C, it is only 10 −14 S / cm.
- Good weather resistance (hardly any oxidation in air)
- In contrast to coal tar pitch, bitumen contains very few PAHs
- Largely physiologically harmless
- Recyclable
The aging of bitumen can be divided into three groups that communicate with each other through oxygen , light and heat :
- Evaporation aging (distillative aging): More and more oil components evaporate through heat , which leads to an increase in the concentration of asphaltenes.
- Oxidative aging: atmospheric oxygen reacts with hydrocarbons or the CH bonds, which leads to a higher concentration of asphaltenes.
- Structural aging: Asphaltenes and resins are enlarged through agglomeration .
This causes the bitumen to lose its "adhesion", harden and crack .
Manufacturing
Bitumen is mainly obtained as a residue from the vacuum distillation of petroleum. Only special crude oils are permitted, almost exclusively high-sulfur , "heavy" crude oils such as "Arab Heavy", "Kuwait", "Iran Heavy", "Urals", "Kirkuk". Low-sulfur , light crude oils such as B. Brent or Forties are completely unsuitable because the required low needle penetration of the vacuum residue cannot be achieved. The special vacuum distillation is either operated "on pen", which means that the bottom product already corresponds to the desired quality, or the needle penetration is set by mixing with heavy vacuum gas oil . Around 4,289,000 tons of bitumen were produced in Germany in 2017.
The bitumen is differentiated according to the manufacturing process.
- Distillation bitumen or road construction bitumen also referred to as penetration bitumen or primary bitumen. Distilled bitumen is obtained by distilling crude oil in two stages. In the first stage, gasoline, petroleum, diesel and heating oil are vaporized at atmospheric pressure. The distillation residue is then distilled in the second stage under reduced pressure (4 to 7 kPa) at temperatures of 350 ° C to 380 ° C. Other oils such as machine oil or gas oil evaporate. The residues that have not evaporated are bitumen. In this way, soft and medium-hard grades are obtained, which are mainly used in road construction (according to DIN EN 12591 and DIN EN 13924).
- Standard road construction bitumen (penetration between 20 and 330 [0.1 mm]).
- Hard road construction bitumen (penetration between 5 and 25 [0.1 mm]), used for asphalt with a high module.
- Soft road construction bitumen (penetration between 250 and 900 [0.1 mm] or kinematic viscosity at 60 ° C from 1000 mm² / s to 16,000 mm² / s), use at extremely low temperatures ( Scandinavia ).
Use for hot mixes in road construction and in special cases for surface treatments, also for electrical cables, emulsions, grouting compounds.
The rheological behavior of bitumen can be influenced in different ways:
- Polymer modified bitumen DIN EN 14023 / TL PmB
Polymer-modified bitumen (PmB) are bitumens that are produced by mixing distilled bitumen and polymers , whereby the thermo-viscous and elasto-viscous behavior changes. The designation for PmB is given with an additional letter in accordance with the "Technical delivery conditions for polymer-modified bitumen in asphalt layers in hot paving" (TL PmB). The letters A and B stand for modification with elastomers, the letter C for modification with thermoplastics and the letter H for more highly polymerized modification.
Polymer-modified bitumen show a higher cohesion, a larger plasticity range, less aging and a large elastic recovery after relief.
The most important areas of application for polymer-modified bitumen are particularly stressed traffic areas in road and airport construction and the production of high-quality roofing and sealing membranes.
Industrial bitumen: bitumen that is not used in road construction:
- Oxidized bitumen DIN EN 13304
Oxidation bitumen or blown asphalt (mineral rubber, mineral rubber, mineral rubber) may be in special reactors ( "blow moulder" Blasturm produced) by distillation soft bitumen at temperatures between 230 ° C and 290 ° C are further treated by blowing in air. When air is blown in, the structure of the dispersed parts changes and a coherent framework (gel state) is formed from them. This considerably reduces needle penetration, increases the plasticity range, and makes the bitumen more melting and stronger. Depending on the product used, temperature and blowing time, bitumen types with improved resistance to cold and heat are obtained.
Oxidized bitumen is used in the industrial sector at extreme temperatures. They are also used for the production of roofing and waterproofing membranes, adhesive compounds and for the insulation of pipelines. They are used in the rubber industry as plasticizers for rubber . When designating oxidized bitumen, the ring and ball softening point (RuK) and the maximum needle penetration are usually given.
- High vacuum and hard bitumen DIN EN 13305
High vacuum and hard bitumen, also known as spöd bitumen, arise in the further treatment of distilled bitumen in an additional processing stage, including cracking in special “ visbreaker systems”. They have a hard to hard to crack consistency. As Hartbitumina bitumens are generally having a needle penetration <10. The classification is done on the area between the upper and lower limit on the experimental ring and ball softening point determined.
These bitumens are used in the production of mastic asphalt for screeds in civil and industrial construction and in the production of paints , rubber products and insulation materials.
Products derived from bitumen:
- Bitumen solutions
- Flux bitumen: So-called flux bitumen (formerly blended bitumen) are produced from a mixture of certain flux oils (petroleum distillates) with soft road construction bitumen.
- Cold bitumen: Cold bitumen are bitumen solutions made from soft to medium-hard road construction bitumen with highly volatile solvents.
- Bitumen emulsions
- Anionic emulsions: Bitumen is broken up into droplets and dispersed in hot water with the addition of an alkaline emulsifier.
- Cationic emulsions: bitumen is broken up into droplets and dispersed in hot water with the addition of an acidic emulsifier
- Bitumen paints: Bitumen paints can be produced like bitumen solutions or emulsions. Usually, however, a harder road construction bitumen is used.
Natural occurrence
The largest share of bitumen is obtained from crude oil. However, bitumen also occurs naturally on earth. In principle, they are created there like oil: over hundreds of thousands of years they arise from the remains of organic material, such as microorganisms, at elevated temperatures and pressure under the upper layers of the earth.
Bitumen is found in the pore space of some sedimentary rocks (primarily, for example, in black clay stones such as copper slate). There are also natural asphalt lakes with a significant amount of bitumen. The largest natural asphalt lake is " Pitch Lake " in Trinidad and Tobago. Bitumen also occurs in so-called oil sands mixed with sand and water. The largest deposits of oil sands are in Canada, e.g. B. the Athabasca oil sands, and Venezuela.
Classification
| variety | EP RuK in ° C | Penetration into 1 / 10 mm | Outdated designation |
|---|---|---|---|
| 160/220 | 35-43 (37-43) | 160-220 | B 200 |
| 70/100 | 43-51 (43-49) | 70-100 | B 80 |
| 50/70 | 46-54 (48-54) | 50-70 | B 65 |
| 30/45 | 52-60 (53-59) | 30-45 | B 45 |
| 20/30 | 55-63 (57-63) | 20-30 | B 25 |
The properties of different types of bitumen are examined using special test methods. These are specified in the DIN standards for bitumen and bituminous binders.
The most important key figures are: the RuK softening point (EP RuK) DIN EN 1427, the breaking point according to Fraass DIN EN 12593 and the needle penetration values DIN EN 1426, these are used to denote the bitumen type (see table).
Further bitumen properties can be analyzed by:
- a thin-film test furnace DIN EN 12607-1 (RTFOT) to measure the air and temperature effect on bitumen
- a pressure aging tank (PAV) (DIN EN 14769) to investigate the long-term aging of bitumen after 5 to 10 years
- a dynamic shear rheometer (DSR) (DIN EN 14770) to determine the flow properties
- a bending bar rheometer to determine the cold behavior and the flexural creep stiffness (DIN EN 14771)
- a vacuum capillary viscometer to determine the dynamic viscosity (DIN EN 12 596)
- a method for determining the kinematic viscosity (DIN EN 12 595)
- a ductometer to determine the elastic recovery, especially of polymer-modified bitumen (DIN EN 13 398)
- a method for determining the stretch properties, especially of polymer-modified bitumen, with a force-ductility test (DIN EN 13 589)
According to DIN EN 12597, bitumen and bituminous binders are differentiated as follows:
- Road construction bitumen (distillation bitumen) DIN EN 12591
- Special road construction bitumen
- Hard road construction bitumen DIN EN 13924-1
- Multigrade road construction bitumen DIN EN 13924-2
- Polymer modified bitumen (PmB) DIN EN 14023
- Blended and fluxed bitumen DIN EN 15322
- Bitumen emulsions
- Industrial bitumen
- Oxidized bitumen (oxidation bitumen) DIN EN 13304
- Hard bitumen DIN EN 13305
- Special bitumen
| variety | 120 / 200-40A | 45 / 80-50A | 25 / 55-55A | 10 / 40-65A | 40 / 100-65A | 45 / 80-50C | 25 / 55-55C | 10 / 40-65C |
|---|---|---|---|---|---|---|---|---|
| Needle penetration in 1/10 mm | 120-200 | 45-80 | 25-55 | 10-40 | 40-100 | 45-80 | 25-55 | 10-40 |
| EP RuK in ° C | ≥ 40 | ≥ 50 | ≥ 55 | ≥ 65 | ≥ 65 | ≥ 50 | ≥ 55 | ≥ 65 |
| Break point in ° C | ≤ −20 | ≤ −15 | ≤ −10 | ≤ −5 | ≤ −15 | ≤ −10 | ≤ −5 | ≤ −15 |
| Force ductility in J / cm² | ≥ 2 | ≥ 2 | ≥ 3 | ≥ 2 | ≥ 3 | ≥ 2 | ≥ 3 | ≥ 2 |
| (at 0 ° C) | (at 5 ° C) | (at 5 ° C) | (at 10 ° C) | (at 5 ° C) | (at 5 ° C) | (at 5 ° C) | (at 10 ° C) | |
| Elastic recovery at 25 ° C in% | ≥ 50 | ≥ 50 | ≥ 50 | ≥50 | ≥ 70 | NO | NO | NO |
| Bending bar rheometer value at −16 ° C in MPa | 200 | 250 | 300 | 350 | 250 | 300 | 350 | 200 |
| old name (until 2007) | PmB 130 A | PmB 65 A | PmB 45 A | PmB 25 A | PmB 40 / 100-65 H. |
The area between cold brittleness (breaking point) and softening (softening point) is called the “plasticity range”. Road construction bitumen according to DIN EN 12591 usually has a "plasticity range" of around 60 ° C. Polymer-modified bitumen types according to DIN EN 14023, for example, offer larger ranges.
processing
_ENI_4402090_on_the_Rhine_near_Sankt_Goar_pic1.JPG)
Most bitumen products cannot be processed or pumped at normal ambient temperature, since bitumen is normally solid at ambient temperature. Aids are therefore required to process bitumen into an end product. The best-known option is heating bitumen to a liquid state. With asphalt, the main application of bitumen, workability plays a major role. Therefore there is a processing time. This is the period in which the mix cools down until perfect processing is just possible. It depends on the weather, the type of bitumen and the thickness of the paving.
Other options include processing as a bitumen emulsion (bitumen emulsified in water), adding water and ambient air ( foamed bitumen ) or adding solvents, so-called flux agents. The "flux agents" are low-volatility oils ( flux oils ). The resulting fluxed bitumen (flux bitumen ) must still be heated for further processing. Since 2003, the petroleum-derived "flux agents" have been increasingly being replaced by oils from renewable raw materials .
use
The material properties of bitumen allow a multitude of possible uses. Bitumen is used particularly because of its sealing character and its adhesive properties. Road construction accounts for the largest share of bitumen production with around 80%. Bitumen also plays an important role in hydraulic engineering and in the roofing and waterproofing membrane industry. In building construction, for example, bitumen is used to protect sensitive parts of buildings against water. Bitumen paints are used or various bitumen materials, e.g. B. Bitumen welding membrane as roof waterproofing . They are available as bitumen sheeting (carrier inserts with bitumen layers on both sides) or as polymer bitumen sheeting (elastomer (PYE) and plastomer (PYP) bitumen sheeting). A bitumen thick coating is used for the external sealing of basement floors . Various bitumen or butyl rubber- coated foils ( aluminum or plastic ) and non- woven tapes are used for bonding, sealing or soundproofing in construction, craft and automotive engineering.
A so-called bituminous adhesive layer is also used in building construction. It connects z. B. a bridge covering with the steel substructure and protects the steel at the same time against corrosion . Bitumen is used in another form as the backing of carpet tiles .
If bitumen is permanently exposed to the weather , it becomes brittle and cracked due to oxidation processes . Surface protection systems or the addition of plastics can significantly extend the effectiveness of the seal. Bitumen waterproofing should normally be carried out with a gradient of at least 2% so that the water can drain off. At lower gradient water can standing remain. Water accelerates the biological and chemical degradation of bitumen. The remaining water is physically damaging due to wet and dry zones in summer and ice formation in winter.
In road construction, the bitumen, as a binding agent , forms the asphalt together with the aggregates . Along with bitumen, this role was played by tar , which today is banned for road construction due to its carcinogenic ( carcinogenic ) effect.
For the production of asphalt, "bitumens" that are modified with polymers are used more and more frequently . These are called polymer-modified bitumen or PmB for short . The bitumen properties can be significantly influenced by adding natural rubber , synthetic polymers or sulfur . Depending on the amount and type of addition, the stability and adhesion to the aggregate are improved . This type of bitumen is therefore used in particular for road surfaces with high traffic loads.
In hydraulic engineering, bitumen z. B. used for coastal protection to hold groynes (breakwaters) made of stones together, so to stabilize. But bitumen materials are also used in dams and pump storage basins, where the waterproof property of the material is used.
Due to their high weight and toughness , bitumen sheets are also used as a noise-dampening coating in motor vehicles , room partition systems , on showers and bathtubs , dishwashers and steel sinks . With a self - adhesive coating on one side, bitumen sheets can be bought as an anti-droning mat for retrofitting. Bitumen wood fiber boards are also produced, these have good water-resistant properties.
Another area of application for bitumen is the cable and electrical industry. It uses the low electrical conductivity of bitumen as an insulating medium. There are also many other uses of bitumen, for example in the paper industry.
In 2017, around 2,146,000 tons of bitumen were used in Germany; 2,020,000 tons were exported.
literature
- Georg Hansen: juice that sweats out of the mountain. In: The cut . Magazine for art and culture in mining. Vol. 20 (1966), No. 6, p. 26 ff.
- Cinzia dal Maso: The black ships of Magan . In: Spectrum of Science Special. 2003, No. 2, p. 34 ff.
- Edeltraud Straube, Klaus Krass: Road construction and road maintenance. A manual for study and practice. Erich Schmidt Verlag, Berlin 2005, ISBN 3-503-09067-3 .
- Asphalt and bitumen (PDF; 4.4 MB), from ifb.ethz.ch, accessed on August 31, 2016.
- Bitumen (PDF; 2.3 MB), on unibw.de, accessed on September 24, 2016.
See also
Web links
- Bitumen article Professional association research institute for occupational medicine
- Arbeitsgemeinschaft der Bitumen-Industrie e. V.
- the current scientific magazine on bitumen.
- The density building info page of the vdd Industrieverband Bitumen-Dach- und Dichtungsbahnen e. V.
- bga - Advice center for mastic asphalt application e. V.
Individual evidence
- ^ Daniel T. Potts, in: Touraj Daryaee (Ed.): The Oxford Handbook of Iranian History. Oxford, New York 2012, ISBN 978-0-19-973215-9 , p. 49.
- ^ Manfred Hegger, Volker Auch-Schwelk, Matthias Fuchs, Thorsten Rosenkranz: Construction Materials Manual. Birkhäuser, 2006, ISBN 978-3-7643-7570-6 , p. 62.
- ↑ Wendehorst building materials science . 2011, doi : 10.1007 / 978-3-8348-9919-4 .
- ↑ Roland Benedix: Construction chemistry for the bachelor's degree: Springer Vieweg, 2014, ISBN 978-3-658-05423-6 .
- ^ Konrad Zilch, Claus Jürgen Diederichs, Rolf Katzenbach, Klaus J. Beckmann (eds.): Structural engineering and building construction. Springer, 2013, ISBN 978-3-642-41839-6 , p. 1031.
- ↑ Ekkehard Richter, Richard Jenisch, Hanns Freymuth, Martin Stohrer: Textbook of Building Physics: 6th Edition, Vieweg & Teuber, 2008, ISBN 978-3-519-55014-3 , p. 235.
- ↑ Nabil A. Fouad: Building Physics Calendar 2016: Focus: Building waterproofing. Ernst & Sohn, 2016, ISBN 978-3-433-03128-5 , p. 641.
- ↑ John Read, David Whiteoak: The Shell Bitumen Handbook. Fifth Edition, Thomas Telford Publishing, 2003, ISBN 978-0-7277-3220-0 , p. 435.
- ↑ Norbert Welsch, Jürgen Schwab, Claus Liebmann: Matter: Earth, Water, Air and Fire. Springer, 2013, ISBN 978-3-8274-1888-3 , p. 251.
- ↑ a b Annual Report 2018 (PDF; 7.44 MB) Mineralölwirtschaftsverband , July 2018, accessed on April 7, 2019 .
- ↑ Straube, p. 94.
- ↑ DIN standards bitumen on arbit.de, accessed on August 19, 2016.
- ↑ Straube, p. 96.
- ↑ U. Musanke, R. Rühl, D. Höber, R. Mansfeld. Use of bitumen in road construction. Special issue bitumen for hazardous substances - keeping the air clean. 2010, 7/8.
- ↑ Bitumen wood fiber boards at materialarchiv.ch, accessed on August 18, 2016.