A long time ago, cellular glass was a thermal insulation which is vapor tight and has a large compressive strength. Later on, I realized that it is a thermal insulating material which can replace bricks, it is a construction material. But recently, I learned as suggested by Michael Ashby that cellular glass is the lightest material between the ones which can support there own weight.

The following table shows a list of all kind of materials. We consider a beam with a certain span and width and allow a certain deflection under its own weight. The thickness is a free parameter. We calculate weight and also embodied energy, which is the primary energy needed to produce the beam. We have rescaled the weight by dividing by the weight of the GLAPOR PG600 beam.

Like can be observed, GLAPOR cellular glass is the lightest material that support its own weight but it has also the smallest embodied energy like shown in the GLAPOR cellular glass EPD. And in a near future, it will also be the cheapest material in the list.

This means that cellular glass can replace concrete in unloaded situations, when non-combustibility and water tightness are an iussue. Besides light, ecologic and cheap, cellular glass can be produced in about 10 hours while concrete takes several days.

Although this application of cellular glass is straightforward, it became only realistic after GLAPOR developed the continuous foaming process, delivering large boards upto 2.8m x 1.2m based on direct foamed recycled glass with prices below 200€/m3. The mould process and the cellular glass based on a special composition can never compete in this discipline.

In this post, I like to put the attention on more academic / laboratory contributors. Indeed, cellular glass is born on the scale of a cup of coffee and later on further extended to larger dimensions, today up to 2.8m x 1.2m.

Bernard Long, a scientist working once for St Gobain Glass, filed in 1938  patent US2337672 about the foaming of glass. He used carbon as foaming agent and describes the reduction of an oxide as the gas evolution source. I guess this is the first closed cell cellular glass patent and this foam could be used as floating device for the curtains in the harbours against submarines.

Boris K. Demidovich,  has published in 1972 a book about the production and use of cellular glass. It is the perfect description of the knowledge at that time and is the advised work to study for each cellular glass starter. It was so important that the American Army translated the work in English. Personally I was impressed by the knowledge in Czecho-slovakia, with a plant in Usti nad Labem in 1947. Sixty years later, a cellular glass plant was built in 2007 at about 80 km from the first plant.

Prof. Dr. Bernardo Enrico, a professor at the University of Padua developed the cold foaming of glass like already described in a previous blog. This open cell foam can be made from bottom ash and fly ash from waste incinerators. Up to now, open cell foams were not popular but this will change in the near future.

Prof. Dr. Lorna Gibson is a cellular solids expert at MIT. By studying her work, people become aware of the opportunities of the cellular version of a material. Glass is already extraordinary  and the cellular version extend largely the importance of that product.

Prof. Dr. Michael F. Ashby is a material engineering expert at Cambridge Univerisity, which is already mentioned in a previous blog. He described cellular glass as the most efficient  material to support its own weight. Since GLAPOR is delivering large boards by 2.8m x 1.2m, this property can be applied everywhere to replace unloaded concrete beams.

Prof. Dr. Christian Maes, Physics department of the KU Leuven, Belgium discovered that cellular  glass fails under a compressive load in a diffusive way. This important statement is probably valid for all kind of fragile heterogeneous materials. This was already discussed in a previous post.

The previous heroes were all experts with the dry powder method. The following heroes have worked or are working with the wet method (or water glass method).

Recently there was a meeting of a group of people, who will change the cellular glass world thoroughly and even a large part of the mineral insulation world. It is a combination of knowlegde, huge ecology loving capital and direct communication without any hiearchical borders.

Dr. Oleg Sharykin (second from right) is an important investor in the Russian cement industry, who believes strongly that ecology is the future for this planet. A long time ago, he recognized the assets of the GLAPOR technology and invested in the further development of that company. Today, GLAPOR has the technology (and a booming market) to produce a product of excellent ecologic quality, like shown in a GLAPOR EPD (Environmental Product Declaration), certified by the world famous IBU (Institut Bauen and Umwelt, Germany). It will be a mistery forever whether two technologies, namely gluing sand particles with cement and sintering waste glass particles belonging to the same investor is a coincidence or not. Indeed, in a lot of applications, concrete boards can be replaced by cheaper and lighter cellular glass boards.

Walter Frank (right side on above picture) is the founder of GLAPOR and took beyond any doubt the largest risk. Therefore, I would rank him as the largest cellular glass hero of all times. Walter was a sales engineer and sold for Horn Glass Industries the first float glass line in Russia, without any reference. But he was also working in the old Coriglas plant where he met cellular glass for the first time. Walter has chosen the recipe of Millcell with glycerin / water glass. He extended the cellular glass gravel process with an annealing furnace and broadend the furnaces to what was standard in the float glass industry. He immideately realized that large cellular glass boards are the future and focused on direct foaming of recycled glass to improve ecology. He did not jump into the thermal conductivity rat race, started by the polymer Pied Piper of Hamelin to hide their own important weakness, which is combustibility. Today his dream is reality, which also means that his dream is gone (is not a dream anymore). His next dream is to jump beyond the typical thermal insulation jobs and to start an entirely new cellular glass market besides the existing one. For that reason, he can not retire during the first ten years.

Otto Anton Vieli is the inventor of the wet process with waterglass and glycerin like already discussed in a previous post. This recipe is applied in a large part of the cellular glass gravel production and for the boards by GLAPOR. This recipe has a huge potential because it foams a low density with rather coarse powder and allows to work in a furnace with efficient stochiometric combustion.

In Thuringen, Germany, there was once a small cellular glass factory, VEB Schaumglas Taubenbach, producing the product Coriglas. After  “Die Wende“, the factory was first owned by Heraklith and later on by an American multinational. The last owner shut down the production exactly 50 years after it was built. The shutdown induced a brain drain to Russia (STES), Ukrain (PINOSKLO) and GLAPOR and is one reason of the current price drop of cellular glass, making it economically available for more people.

In this series of blogs, I will remember the work of some previous cellular glass workers and thinkers. They all took once a big risk to fail and were in that way important in the evolution of cellular glass. For some legal reasons, I cannot mention people, still at work in cellular glass.

Louis Troussart was an expert in the annealing of (cellular) glass as an employee of St. Gobain Glass and a cellular glass manufacturer. Some years ago, he passed away as a well respected man. The reasons for that are obvious:

• Louis was the first to find out that glass has a thermal history. Indeed, by measuring carefully the thermal expansion for different cooling rates, he proved that the physical properties of glass are dependent on the cooling history.
• Later on, he moved to cellular glass and did important published work with finite elements. He optimized for example the guarded hot plate for the measurement of the thermal conductivity.
• Many other work cannot be mentioned because it is not public domain

Charles Beerten, an exponent of accuracy was a chemist working on the glass composition. Today, cellular glass with the best thermal conductivity is produced with “his” glass composition in Europe, China and the USA. Also in his case, most of his work is not public domain. Charles became retired against his will and lives in the “Ardennen” in the south of Belgium.

Pierre Gérard, a smart and fast mechanical civil engineer was also an efficient cost cutter. Pierre understood very fast that the most efficient cost cutting was improving the process. He was an enormous support for me, especially when the tunnel seemed endless long. His father, Paul Gérard was the collaborator of Louis Troussart during the discovery of the thermal history of glass. Pierre is retired and is spending his time with travelling with his wife.

Hugo Frederix, a typical self made man, checked in hardware mode the ideas of the above and also participated to a paper about the stability of cellular glass, like mentioned in a previous post. Hugo lives in Limburg in the east of Belgium.

Jos Bellens, a laboratory chemist passed away much too early. His important R&D work is not public domain but in his second career, he became an outstanding safety engineer. I will never forget him.

Albert Van der Heyden, production engineer and self made man, was an expert in tuning a foaming furnace for the carbon black process with the necessary reducing atmosphere. Albert made once an important experiment, which ignited the continuous foaming process project. Albert is retired and lives in Meldert, Lummen as the very best grandfather.

Marc Kolenberg was about everything: electronic, electrical and mechanical engineer, software developer and most of all production manager for cellular glass. Marc did not know any limit to reach what he considered as possible. Without him, my largest project should never run. Marc is retired and lives close to Diest with his family and dogs.

Robert Havel started as a worker and became production manager of the cellular glass factory, producing the highest quality ever. After having done the startup of a cellular glass factory in China, Robert´s ambition drove him in another direction. He lives in Klasterec Nad Ohri in the Czech Republic with the lovely Jitka Havlova and their child.

Jean Melchior, a civil engineer from Luxemburg is known as an extremely strong marketeer for cellular glass. He understood very early the importance of ecology for the thermal insulation world. Not cost cutting but ecology was his drive to support me for my largest project. From him, I got the nice title “free electron”, although that property let him explode many times. Jean is retired against his will and lives in the center of Belgium, studying Machiavelli.

This sounds like energy by cold fusion, but in this case it is real.  Prof. Enrico Bernardo from the Engineering University of Padua invented a new process to foam glass below 80°C. The motivation for this invention is quite clear.

Enrico does not want to limit him self to the foaming of “easy” soda lime glass but he wants also foam glasses which are eager to crystallize. Such glasses are already crystallizing during sintering and does not foam due to the crystallization. Glasses obtained from waste incinerators (bottom ash, fly ash) are a typical example. In fact, all the efforts are based on the philosophy to recycle any waste.

The full process is described in a paper. The alkali-activation method (geopolymers) is used to create a gel. Air is introduced in this gel (foaming) by mechanical stirring. The resulting foams are hardened at 75°C. After this step, the foam has already all its properties like compressive strength, thermal conductivity, ….. To eliminate leaching out or to make the foam chemically stable, a temperature step at 700°C (firing) is needed. Because the foam is formed, crystallization in this last step is not a problem anymore.

The foams are open celled, which opens a new market for cellular glass, based on “real” waste and as a consequence at very low cost. I think now on a cheap alternative of low and high density gas concrete. But if the foam can be evacuated to low pressures (0.1 Torr) and packed, a low thermal conductivity of the order of 0.025 W/mK can be reached.

Michael F. Ashby is a Cambridge University professor about new (and old) materials. By accident, I found his textbook about engineering materials Vol. 1  on research gate.

The textbook describes the important physical properties and physcis behind these properties. But also the availability and price are given some attention.

The book is of course illustrated with case studies. Hereunder we cite the case study about the support of a large telescope mirror.

Introduction
The worlds largest single-mirror reflecting-telescope is sited on Mount Semivodrike,
near Zelenchukskaya in the Caucasus Mountains. The mirror is 6m (236 inches) in
diameter, but it has never worked very well. The largest satisfactory single-mirror
reflector is that at Mount Palomar in California; it is 5.08 m (200 inches) in diameter. To
be sufficiently rigid, the mirror (which is made of glass) is about 1 m thick and weighs
70 tonnes.*
The cost of a 5m telescope is, like the telescope itself, astronomical – about UKE120 m or US$180 m. This cost varies roughly with the square of the weight of the mirror so it rises very steeply as the diameter of the mirror increases. The mirror itself accounts for about 5% of the total cost of the telescope. The rest goes on the mechanism which holds, positions and moves the mirror as it tracks across the sky
(Fig. 7.1). This must be so stiff that it can position the mirror relative to the collecting system with a precision about equal to that of the wavelength of light. At first sight, if you double the mass M of the mirror, you need only double the sections of the
structure which holds it in order to keep the stresses (and hence the strains and deflections) the same, but this is incorrect because the heavier structure deflects under its own weight. In practice, you have to add more section to allow for this so
that the volume (and thus the cost) of the structure goes as M2. The main obstacle
to building such large telescopes is the cost. Before the turn of the century, mirrors were made of speculum metal, a copper-tin alloy (the Earl of Rosse (1800-18671, who lived in Ireland, used one to discover spiral galaxies) but they never got bigger than 1 m because of the weight. Since then, mirrors have been made of glass, silvered on the front surface, so none of the optical properties of the glass are used. Glass is chosen for its mechanical properties only; the 70 tonnes of glass is just a very elaborate support for 100 nm (about 30 g) of silver. Could one, by taking a radically new look at mirror design, suggest possible routes to the construction of larger mirrors which are much lighter (and therefore cheaper) than the present ones?

At the end, it is summarized in a material index, which is calculated for a few materials.

The following conclusions are taken:

The optimum material is CF’RP. The next best is polyurethane foam. Wood is obviously
impractical, but beryllium is good. Glass is better than steel, aluminium or concrete
(that is why most mirrors are made of glass), but a lot less good than beryllium, which
is used for mirrors when cost is not a concern.

But at the end, we find the inventive step:

The most obvious obstacle is the lack of stability of polymers – they change dimensions with age, humidity, temperature and so on. But glass itself can be foamed to give a material with a density not much larger than polyurethane foam, and the same stability as solid glass, so a study of this sort can suggest radically new solutions to design problems by showing how new classes of materials might be used.

Indeed, with low density cellular glass, we arrive at a material index = 0.1, which is the best value. However, with the usable dimensions of cellular glass (60 x 40 cm), the idea of building a large mirror cannot be realized with cellular glass. But the continous glass foaming technique as developed by GLAPOR allows dimensions up to 3.2 m. Even wider up to 6m (like for float glass) is possible in case there should  a market for this large product. Indeed, light structures built from foamed recycled glass have a certain future.

Also Engineering Materials vol2 is available in pdf on nanotech. This book contains a nice chapter about glass and the production of glass articles. Also ceramics and more particular concrete are mentioned with a lot of data to be used for the calculation of an order of magnitude.

Generating an Environmental Product Declaration involves a lot of work about the transport. Like already mentioned in this blog, transport is indeed an issue but transport over water seems to be more likely. Indeed, the following map shows what is possible in Europe.

The standard cellular glass like GLAPOR is a floating material, which is nevertheless 100% transported by trucks. In case more waterways should be used, transloading from truck to ship and ship to truck  is the big and expensive problem. In the past, this involves always an important structure along the river or canal.

But recently I learned that GRIFF drones are able to load and transport 200 kg, which is more than one typical pallet GLAPOR cellular glass. The drone can operate 30 minutes with one full battery. And now I dream about  barges, floating around Europe, each loaded with the equivalent of many trucks cellular glass. Trucks are waiting along the canal or river on a simple parking place and the barge captain unloads the barge with the help of drone. In principle, the barge does not even have to moor and an intelligent program calculates the best route for truck, ship and transloading.

A typical M8 ship measures 11 x 110 m  or more than 1000 m² loading surface. It can be easily loaded 6m high or about 6000m³ cellular glass, weighing 800 ton while the minimum load is 900 ton (we need to add extra load). Each barge can be seen as a warehouse, guarded by a typical barge crew, transporting ware the equivalent of about 100 trucks. The actual truck transport can be reduced from waterway to job site.

If transloading is indeed possible with the wild idea of drones, this option needs more attention for the transport of all thermal insulation.

Assume you have a large pile of sand, sodaash, limestone and clay. What should we choose to produce with these materials? Cellular glass, a closed cell structure or cellular concrete, an open cell structure. Cellular glass has a higher chemical resistance against water than cellular concrete, is vapour tight and is expected to be stronger in tension and so also in compression than concrete. In the case of cellular concrete, the sand particles are bound with cement while in the cellular glass case, the glass particles are fused into each other, creating a better bond.

Cellular concrete or AAC (Autoclaved Aerated Concrete) can today produced in higher densities (Ytong) and lower densities (Multipor). I found two Environmental Product Declarations, which are describing the process. The Xella Multipor EPD describes the low density (115 kg/m³) process while AKG GAZBETON describes the process for higher densities (385 kg/m³).

For the high density, we read:

The autoclaved aerated concrete products are made of quartzite (40-50%), Portland cement (20-30%), lime (6-12%), gypsum (5-10%), aluminium (0.1-0.2%) and finally recycled waste slurry (closed-loop) (15-20%). In addition, water content of the mix is about 40-50% of the total mixture.

For the low density, we observe:

In all cases, sand, lime (CaO)  and gypsum (CaSO4) are bound with cement. The lime is produced by burning limestone at 800°C. Cement is produced from burning a mixture of limestone and clay at 1400°C and fine grinding the residue to a very fine powder. The foaming is done with Al powder and afterwards, autoclaving happens at 180°C and 12 bar to give the foam its strength. In both cases, a lot of water  (more than 50%) is heated and evaporated. It is clear that the complete process, including the preparation of the “raw materials” is very energy intensive for the production of AAC.

On the other hand, we could melt a soda lime glass at 1600°C with sand, sodaash, calcium sulphate and limestone. This glass can be ground to a fine powder and foamed above 800°C with carbon black or glycerin to a closed cell structure or with (fine) limestone to an open cell foam. However, the melting and foaming process is more energy intensive than the AAC process and also the investments are a lot larger due to the high temperatures used. At the end, cellular glass based on fresh raw materials is more expensive. It makes only sense to use this type of cellular glass instead of AAC in case closed cells are a must. This is typically the case in flat roofs and industrial insulation.

But if a large pile of waste glass is ready to be recycled, it is clear that this glass has to be  foamed to cellular glass with closed or open cells with only one temperature step at 800°C instead of producing cellular glass or cellular concrete with fresh raw materials like sand and limestone with multiple temperature steps. This third option is introduced by GLAPOR in the market and it is easily understood that this option is growing with two digits for ecologic and economic reasons. Especially the current possibility of boards up to 3.2 x 1.5m with compressive strength up to 3000 kPa is responsible for the succes.

We found a nice presentation from the FIW Munchen about “Nachhaltig bauen” which I translate as “sustainable building. In this presentation, cellular glass is compared with XPS, PIR, EPS and other thermal insulation materials. However, it is not clear whether this cellular glass is produced with the mold or continuous foaming process.

GLAPOR cellular glass is produced with the ecologic continuous foaming process and is based on recycled waste glass without remelting at 1600°C but directly foamed. Therefore I added the results for GLAPOR PG600 cellular glass in some figures of the presentation.

The primary energy per kg is one method to describe the different thermal insulations like done in the this graph. We observe that almost all thermal insulations have a higher primary energy content, even after correction for density and thermal conductivity. These corrections are done in the following graph.

Another method is the payback in J (energy) and not in €. Indeed, how much years do you have to use the thermal insulation to save the energy which is used for the production. In this method, we observe that cellulose, low density mineral wool and low density EPS are performing better. But in fact, we are comparing products without mechanical stability (mineral wool, cellulose) and with a poor stability ( EPS 15kg/m³ density )  = 60 kPa at 10% deformation with GLAPOR PG600, which is stable for eternity at 200 kPa without deformation. On top of that, GLAPOR cellular glass is absolutely resistant to rodents, which is also a point of sustainability, which is for unknown reasons never discussed in Europe.

From the above graph, I guess that XPS and PU (and so PIR) have only a short future anymore. The long term future is reserved for the mineral thermal insulations. In fact, the world needs more of this kind of work.