Werner Sobek prefers light weight materials

logo_smallWerner Sobek is a German famous architect and structural engineer. I cite a part of the Wikipedia link.

Werner Sobek[1] was born 1953 in AalenGermany. From 1974 to 1980, he studied structural engineering and architecture at the University of Stuttgart. From 1980 to 1986, he was post-graduate fellow in the research project ‘Wide-Span Lightweight Structures’ at the University of Stuttgart and finished his PhD 1987 in structural engineering. In 1983, Sobek won the Fazlur Khan International Fellowship from the SOM Foundation.

220px-Portrait_Werner_SobekIn 1991, he became a professor at the University of Hanover (successor to Bernd Tokarz) and director of the Institute for Structural Design and Building Methods. In 1992 he founded his own company Werner Sobek which now has offices  in StuttgartFrankfurtLondonMoscowNew York, and Dubai. The company has over 200 employees and works with all types of structures and materials. Its core areas of expertise are lightweight construction, high-rise construction, façade design, special constructions made from steel, glass, titanium, fabric and wood, as well as the design of sustainable buildings.[2]

pentagonSince 1994, he has been a professor at the University of Stuttgart (successor to Frei Otto) and director of the Institute for Lightweight Structures and of the Central Laboratory for Structural Engineering. In 2000, he took over the chair of Jörg Schlaich, and fused the Institute for Lightweight Structures and the Institute for Construction and Design into the Institute for Lightweight Structures and Conceptual Design (ILEK). Both in its research and teaching, the ILEK at the University of Stuttgart unites the aspect of design that is dominant in architecture with the focus on analysis and construction from structural engineering as well as materials science. On the basis of a goal-oriented and interdisciplinary approach, the institute is concerned with the conceptual development of all types of construction and load-bearing structures, using all types of materials. The areas of focus span construction with textiles and glass all the way to new structures in reinforced and prestressed concrete. From the individual details to the whole structure, the approach focuses on the optimisation of form and construction with respect to material and energy use, durability and reliability, recyclability and environmental sustainability. The results of this work are published in the bilingual (German/English) serial from the institute (IL) or published individually in special research reports on particular topics.[3]   

layersI got a presentation  of his view on the future building world and was surprised by his preference for cellular materials where possible. These materials have to be by preference recycled materials. It is clear that cellular recycled glass, foamed with a minumum of energy in large boards is exactly what he is looking for. Indeed, a simple structure where this material is a structural element AND thermal insulation allows easy recycling later on. The figure on the right is exactly how we should NOT work.




Measuring the open / closed porosity of cellular glass

logo_smallFactory made standard cellular glass for thermal insulation is assumed to have 100% closed cells like described in the standard  EN 13167. Indeed, the mu-value is not allowed to be lower than 40000. Measurements on materials with such a high mu-value easily take 3 months, which means that this method cannot be used for daily quality control.

pycnometerOn the other hand, the gas – pycnometer is a nice and simple instrument to measure the volume of the closed cells. If this volume is in line with the geometric volume, we know that the cells are closed and that the mu-value will be above 40000. Because this method takes a few minutes, it is the ultimate instrument for QC in factories where open (acoustic ) and closed cell material (thermal insulation) is produced.

The following paper describes nicely the principle of the measurement.


An over pressure in the sample chamber is released into the (calibrated) reference chamber. The pressure before and after release, together with the known volume of the reference chamber allows to calculate the volume of the sample chamber. If this volume is also known, we can calculate the volume of the sample. From this sample volume, we can calculate the amount of closed / open cells.

The instrument can be quite simple like shown here under:


For about 2000€, this instrument can be built and connected to a PC. It is not clear why the above commercial instrument costs about 16000€. For larger samples, a pycnometer with compressor in situ is also available on the market like shown in this leaflet.

The battle for waste glass

logo_smallIn Europe, we are going from huge piles of waste glass to a higher demand than available. A long time ago, manufacturers were paid absorbing waste glass but today they have to pay.

But there is still one type of glass for which the demand is in fact not existing. Indeed, since the Cathode Ray Tube (CRT) televisions are replaced by LCD (Liquid Crystal Display), the CRT´s are not remelted anymore. And as a consequence, a huge pile of glass is available for other applications.

DownloadOne function of CRT glass is to absorb the X-ray radiation, generated by the high velocity electrons bombarding the front panel with phosphor. For this important function, PbO and BaO are introduced in the glass. PbO is introducing a brown color into the screen after long use. For that reason, the PbO is replaced by SrO in the front panel of the color television CRT. This and more is well explained in the following paper about CRT´s.

The source of CRT-panel glass waste seems to be very large like found in the following reports:

  • The following  paper describes the worldwide situation and even mention cellular glass as a way to recycle CRT glass.

Foam glass is a lightweight and handy product that is especially used where heat and sound insulation is necessary [122]. Its use has increased in recent years due to it being nonflammable, waterproof, a good insulator and having a long
life. Foam glass is produced at temperatures of 700 °C and 900 °C [123]. In the production of these products, CRT glass components with a lower melting temperature can reduce the product’s melting temperature in some cases [12].
Although first applications were made entirely of pure glass, the rate of these industrial waste products being used has increased to 98% today [56]. In order to improve the mechanical properties of these products, different materials have
been used besides CRT [124]. Investigations have shown that the amounts of lead leaked through the glass foams are acceptable [125]. Foam glass is usually produced by adding a gas producing material to powdered glass and then baking it to trap the gas bubbles in the glass. These products are generally used as foaming agents, carbon-containing materials, organic compounds, and carbonates [126], [127]. Depending on the area to be used and the desired properties, other minerals can be added to the mixture and the mixture is then sintered. During sintering, the foaming agent content reacts to increase the volume and obtain the glass foam [128]. The foaming agent added to alter the properties of the produced glass foam varies depending on the grain size of the glass used and the cooking temperature [129].

  • Another paper gives the situation in the UK for CRT glass recycling and also mentions cellular glass:

Foam glass is an insulating material which can be made from post-consumer waste glass. Experience in Norway indicates that it is feasible to incorporate at least 20% CRT panel glass in foam glass. There are no known technical  barriers to using CRT glass and no adverse environmental impacts compared with using other types of waste glass. Demand for foam glass in the UK, however, is limited and there is currently no production capability. Production facilities
are being considered, but the projected demand for CRT glass in this application is low, starting at 3,000 tonnes per annum and rising to a maximum of 9,000 tonnes per annum.

  • separatorAnother  paper  mentions the recycling problems of Pb-glass from CRT and the different laws about this in Europe.
  • Further, we also found equipment to separate the panel and other parts of the CRT in the following leaflet.
  • A research paper  warns up for the eventual leach out of CRT-glass and so cellular glass based on this.
  • Last but not least, we found a another paper about the foaming of CRT-glass with SiC and TiN.



A nice introduction in vacuum technology

logo_smallVacuum cellular glass is still fascinating some people, like can be found on this link of the Technical University in Freiberg, Germany. I give a citation here under:


tu-freiberg-logoDas Ziel des Projektes liegt in der Entwicklung eines nachhaltigen, brandfesten und tragfähigen vakuum-isolierten Bauelementes (VIP), mit erheblich verbesserten Eigenschaften im Vergleich zum Stand der Technik. Dazu sollen die derzeitig für den Stützkern verwendeten Werkstoffe durch Schaumglasstrukturen substituiert werden.

Zwei Wege werden untersucht, um die Dämmeigenschaften konventioneller VIPs mit Schaumglas zu erreichen. Einerseits soll ein offenzelliges Schaumglas entwickelt werden, welches im Nachgang evakuiert wird. Andererseits ist ein geschlossenzelliges Schaumglas Ziel der Entwicklungen, welches bereits im Schäumungsprozess mit einem sehr geringen Poreninnendruck versehen wird.

imagesAlso in this case, it is mentioned to develop a recipe for open cell cellular glass, which will be evacuated later on. The evacuation has to be done to a very low pressure because the mean free path of the gas molecules must be larger than the cell size. A very nice introduction to vacuum technology, written by Leybold, can be found here.

Breathing walls, does it make sense?

logo_smallBreathing walls are requested due to the “sick building syndrome“. This illness is attributed (without real proof) to air conditioning, out-gassing of some materials (VOC), too small intake of fresh air, mold and ozone. We may assume that depending on the person some of these products are indeed not positive for the health. Generally, there are two solutions:

  • The passive housing system with air tight walls and forced ventilation
  • The breathing wall system

passive-house-illustrated-simplicityThe passive housing system is the well known. Air tight walls with a very large thermal resistance (U=0.1 W/m2K) where all the fresh air comes from forced ventilation. The intake air is heated by the air leaving the building with a heat exchanger between both flows. Due to the low heat flow, the wall may be a source of interstitial condensation, generating mold while also the heat exchanger needs regular cleaning to avoid mold. On top of that, the limited diameter of the ventilation channels is the reason of high air speed regions in the house, which is not comfortable. It is clear that passive housing is not the favorite for people suffering from the sick building syndrome.

1-s2.0-S2212609013000046-gr1On the other hand, the breathing wall system is solving all the above problems. In a previous post, we used another definition: Dynamic insulation. In this case, cold outside air is sucked through the wall and heated with (low value) heat, which tries to leave the building. This sucking happens with a fan and the heat is stripped of the (warm) air by a heat exchanger and returned into the building. In this way, we have a low energy building with a very low air velocity ventilation and no possibilities for interstitial condensation in the wall, while the cleaning of the heat exchanger remains. A serious disadvantage is that wind on the building creates pressure differences in the building and also outside odor comes into the building.

An Hungarian paper lists the advantages of breathing walls (or dynamic insulation) while a more technical paper treats the dynamic insulation as a heat exchanger. Theory and experiments are given to know the real efficiency of dynamic insulation.

7f6d2b30dc77e32e369d51a258707ec3-Alma_22It is clear that open cell cellular glass can play a role in this dynamic insulation but I do not believe in breathing (dynamic insulation) walls due to wind problems. However, a breathing ceiling would be a nice application. Fresh air is pumped through a ceiling, constructed with open cell cellular glass, generating a ventilation over a large surface with extremely low air velocity. Besides ventilation, the open cell cellular glass serves also as acoustic absorber. I can imagine that this a perfect system for a student restaurant at the university. Ventilation and acoustic absorption, besides food are there the main issues.


Russia goes for the glycerin / water glass system

logo_smallWe found a nice recent paper paper about the foaming of glass, sponsored by the Russian federation, cited as follows:

This research work is carried out with the financial support of the Scholarship of the President of the Russian Federation for young scientists and postgraduates (2016-2018, #SP-1074.2016.1).

Maybe, that is the most important fact. For many years, the development was only in the hands of private capital but now governments are aware of the importance of cellular glass for the society. Today Russia and Slovenia, yesterday Denmark and it is clear, more will come. That gives a good feeling: many brains and huge piles of money are increasing the knowledge about this wonderful product. Today it is only available for the happy few but that will clearly change.

The paper focuses on foaming of waste glass and selects the glycerin / water glass because in this system, a furnace with neutral atmosphere will perform well contrary to carbon (black) foaming. The water glass protects the glycerin for oxidation while the glycerin delivers the carbon by decomposition.

More in detail, the paper selects the best ratio glass / water glass and glycerin. Some experiments are shown here under:


B3 at 825°C seems the best candidate.

Vaporglass ETIZ, a completely new type of cellular glass

logo_smallRussia has always been a home of cellular glass but Russia failed to exploit their knowledge in time. Recently, Russians developed a new type of cellular glass and it seems that this time there is also a marketing machine working.

Parosteklo_120_100_4Vaporglass ETIZ is based on water glass (liquid glass, sodium silicate solution) and is produced by the evaporation of the water at rather low temperatures. The material is a 100% open cell material, which is claimed to be a fiber free acoustic absorber and thermal insulation (0.045 W/mK) at the same time with a very low vapor diffusion resistance.

image-paroglassBut more important, this material is sold at 190 €/m³ for the 120 kg/m³ density version. Larger densities up to 180 kg/m³ are available. Dimensions are 600 x 600 mm, which is rather small. The low density version has a compressive strength of 240 kPa with a thermal conductivity of 0.045 W/mK. It is not mentioned how the thermal conductivity is measured.

A m³ of this 120 kg/m³ material involves 300 kg water glass, which costs 50€. The evaporation of the water to induce the foaming takes minimum another 23€. There is also a stabilizer involved and industrial equipment. A price of 190€/m³ is reasonable. However, I have no idea about the chemical resistance of the product against water and else.

More interesting news from Aalborg

logo_smallLike already mentioned in a previous post, the chemical department of the technical university of Aalborg is performing very interesting work.

In a  paper about CRT-panel foaming with Manganese oxide, they study the foaming of the glass with a high temperature microscope and made important conclusions about the transition from closed to open cells. By using the percolation limit, they define a temperature window for closed cells.


lambdaIn the last paper, they foam CRT panel glass, soda lime glass and mixtures of these glasses with Fe2O3. CRT panel glass has the advantage to have a lower thermal conductivity (0.97 W/mK) than soda lime glass (1.1 W/mK) and on top of that, it should be rather cheap because there is no other use possible and the cellular glass manufacturer is paid to absorb the glass.

crystalBut in some cases, the glass in contact with Fe2O3 is prone to crystallization, which induces open cells. According to the paper, calcium phosphate is a crystallization inhibitor in this case and the cells remain closed. imagesIn our opinion, the use of a crystallization inhibitor to avoid open cells with a mineral foaming agent is the major contribution of this paper. It opens the door to 0.045 W/mK cellular glass at mineral wool prices with equivalent densities.


Water tank on GLAPOR cellular glass gravel and RDS. An approach for liquid gas tanks?

logo_smallSome time ago, I have already mentioned in a post that for tank bottom thermal insulation, more expensive boards could be replaced by gravel and the famous GLAPOR RDS system. The cost of the thermal insulation of the tank bottom should be reduced by about 80% and the installation (time) also of the same order.

RDSIn this system, the ring (walls of the tank) are supported by the GLAPOR RDS-composite while the bottom of the tank is insulated with cellular glass gravel. Today, GLAPOR RDS is used in Germany, Austria, Switzerland, Italy and Belgium for private houses. In that case, the load bearing walls are put on the GLAPOR RDS composites, while the actual floor is insulated and supported by cellular glass gravel.

But today, this system is already also used for water tanks. Concrete walls are supported by the RDS-composites while the actual bottom of the tank rests on cellular glass gravel. The following pictures are clear. In case of a bitumen of an ammonium tank, the cellular glass gravel layer has just to to be thicker. The price of cellular glass gravel is less than 50€/m³ while boards for tanks costs easily up to 400€/m³. The installation time of gravel is very short compared to boards.





Czech cellular glass Spumavit

logo_smallIt is not well known that the Czechs were the first in Europe to produce a commercial glass foam, Spumavit. I could find some information about the history of this product but I have to give it in graphical form from the “Legend of the Bohemian glass”, written by Antonín Langhamer.



Two names are mentioned, Vaclav Novak and Frantisek Schill. The last one has written a famous book about cellular glass in the Czech language. There is no English translation available but BELGLAS is searching for sponsors for a decent translation. After that, this site will have a download available.

The Spumavit glass foam was used on the Expo 58 in Brussels in the very successful Czecho-slovak pavilion, winning the first price. I am surprised that thermal insulation was used in 1958 for a temporary building. Production started in 1957 and ended 30 years later in 1988. The combustible polystyrene became a too large and cheaper concurrent.



Everything is pure coincidence but my story is nice. According to my parents, I am conceived in a hotel close to the Expo 58 (it was their honeymoon) and probably they visited (with me in situ) this Czech pavilion with Spumavit cellular glass. Later on, after my PhD, I started to work for Pittsburgh Corning in cellular glass in 1988 when Spumavit ended. After the development of the continuous process (endless foam), I end up in Klášterec nad Ohří in the Czech Republic to start up my dream at about 200 km from the old Spumavit plant. This factory is today the best performing cellular glass plant in the world. Today, I am a consultant for cellular glass and I live together with a Czech goddess. It is clear that cellular glass and Czech have a lot in common, they both make my life extremely interesting. In the mean time, I try to understand the book of Schill by studying the Czech language.