Europe goes for natural and mineral thermal insulation

I was very nice surprised about how architects in Europe are looking into the future of thermal insulation. The enquiry was done  by BauInfoConsult with 1600 architects in 8 countries in Europe. 

The tendency is clear:polymer (plastic) thermal insulation like EPS, XPS, PIR and PUR are decreasing while natural  and mineral insulation will increase. Of course the last tendency is interesting. We further have to explain the customer that in case a certain mechanical stability is needed, a cellular structure is more appropiate than a fibrous structure. And if humidity and air tightness are a issue, cellular glass is the only option. 

Once cellular glass is choosen, we have to explain that direct foaming of recycled glass in a continuous system is the cheapest and most ecologic solution. This technology is invented and developed by GLAPOR. After a life in cellular glass, I feel that the future is great without limits. 


Popular post: Mineral wool versus foam

Some years ago, we wrote a post about a comparison between mineral wool and cellular glass. And suddenly during the last months, this post became popular like shown hereunder. 

It is not clear which (GOOGLE or WORDPRESS) mechanisms are eventual repsonsible and I assume that some people are just interested. Like explained in this previous post, it is not clear why engineers should choose for fibrous structures when mechanical stability is involved. A cellular glass structure is obviously better for this kind of applications. On top of that, cellular glass with closed cells cannot have any issue with humidity due to internal condensation and water absorption. In that case, you think that the price is the reason to choose for mineral wool. 

As an example, we have taken the data from FLUMROC in Switzerland, a company producing mineral wool since 1950. We consider the three types with a mechanical stability. FLUMROC PRIMA , 341 and MEGA are mineral wool boards with different densities and allowabel loads. The properties and price are listed hereunder. 

For comparison, GLAPOR cellular glass PG600 has an allowable load of more than 250 kPa at 130 kg/m³ and can be bought for 280€/m³ without negociation. This is 6 times the one of FLUMROC MEGA ,160 kg/m³ density priced 438€/m³. After correction for the thermal conductivity (0.045 W/mK) to be compared with 0.054 W/mK for GLAPOR PG600, we arrive at 365€/m³ to be compared with 280€/m³ for GLAPOR cellular glass with 6 times higher stability. 

GLAPOR PG600 involves grinding and foaming at 800°C of 170kg recycled glass while FLUMROC MEGA needs minimum 160 kg basalt and recycled glass, melted at 1600°C and again reheated at 200°C for the binder. It is logic that mineral wool with a 6 times lower stability is more expensive than cellular glass. But is is not logic that people prefer mineral wool with a lower stability, humidity risks and even more expensive unless the acoustic absorption is needed. It seems that some types of cellular glass have a serious marketing problem.

Open source: Latex, a document preparation system

logo_smallIn 1987, I have written my PhD-thesis and Word Perfect was the only text processor available on a PC. In that time, the university was giving some financial support for a PhD-thesis, printed in two colums in landscape. However, with LATEX and a laserprinter, this became very easy and a year later, the financial support was removed. Also Internet was not available in that time and “Open source” was something we did not know and we believed was impossible.

imagesI remember that LATEX was really more difficult to use compared to Word Perfect but it was easy to include formula in your text. After the introduction of Word and Windows, I used Word or an open source version like Libreoffice, because I was to lazy to work with the difficult LATEX.

But times have changed. A LATEX editor like Texmaker and a latex2pdf converter like Miktex under Windows is a good team, which helps to remember all the commands in LATEX. On top of that, GOOGLE helps you with all possible problems by simply copying the error message in the editor.

DownloadToday an excel-table is easily incorporated by using the (LATEX) table generator or by including a CSV-file. Also figures are easily included and absorbed in the text in a professional way. Every symbol you can imagine is available if you search in this document. Citations and footnotes are easily included and all kind of accents and fonts are available with any keyboard. I write in Dutch, English, German, French and Czech and in Word you need a lot of keyboards or a very good memory. For tables, figures, formula, citations and footnotes, an automatic numbering system is available. A table of content, list of figures and tables is generated with only one command. There are packages for each style: an article, a letter, a book, a presentation, an invoice, a report, …. . In fact, your hard intellectual work will be presented in the best way possible.

I challenge everybody to find something about typesetting which does not exist with LATEX. In the unexpected case you should succeed, it is possible to program your own package and to upload it in the LATEX society.

unnamedBut in fact you don´t need to install software on your PC. Overleaf is the best place to start with your document in Latex. And in case you are working under Linux, Latex is probably already preinstalled. Also on Android LATEX editors are available included the converter to pdf. I tried already VerbTeX.

Light weight cellular glass most popular post

logo_smallIt can be interesting to find out how people arrive at your blog. The blog  “And the lightest beam is … cellular glass “, published in January 2018 is getting a lot of attention with an exponential growth.

Michael Ashby has already mentioned that a glass foam would be the most interesting self supporting material but this statement had less value with monolithic boards measuring maximum 60 x 45 cm. However, since GLAPOR introduced the large monolithic cellular glass boards 280 x 120 cm, produced with the modern continuous foaming method, this statement became very important.

Indeed, the following graph shows the number of the specific blog visits since publication in 2018.


It is also clear that besides the large dimensions GLAPOR cellular glass has the most interesting recipe for this application. Indeed, GLAPOR foams directly recycled glass without melting a special composition. This recipe is interesting from the ecologic and economic point of view.

Float glass technology in the cellular glass world?

logo_smallFloat glass technology is quite attractive for cellular glass and writing a blog is good method to think about the advantages and disadvantages. I spent already a blog on a patent and on a paper, which showed that the powder method could be history. One major question is why the flat glass world converted to float glass technology?

StHelensPilkingtonsTheHottiesBefore the float glass process became developed, quality glass needed to be ground and polished to get a smooth surface. Like described in this patent of Pilkington, introducing the hot glass on a molten metal bath with temperature treatment delivered a plan parallel glass pane, which could be used without grinding and polishing. The non-interaction between 100% flat molten metal and molten glass is the main reason for this huge development. However, a fire finished glass surface is not needed for cellular glass.

patentLike shown in the previous blogs, the tin bath is suggested only to be used as transport carrier during the foaming of the glass. This is a much more expensive solution than the a belt which turns around within the furnace without leaving and so reheating. A glass fleece can be used to avoid sticking of the foam on the steel belt.

VliesstationThe more I think about using a tin bath, I see a lot of  advantages evaporating if compared with a steel belt, turning around strictly inside the furnace. Especially the previous paper, which gives an an alternative to the powder method, could be much easier executed by putting the ribbon on a belt,  instead on a tin bath. But on the other hand, the float process could become a 100% non-waste process because the ribbon should be perfectly flat and plan parallel. If the non-powder method on a belt would be the second generation, on a tin bath would it become the third generation process. I have the feeling that after almost 90 years cellular glass, we are just at the beginning.


In honor of Sir Alistair Pilkington: float foam glass

logo_small2018 was indeed a fruitful year for the development of cellular glass.  In a previous post, I already declared the Aalborg – Ljubljana team as the one who made the largest progress during the last year with consequences on the market the next years.

But yesterday, I found a new paper, published in 2018 with an extremely important experimental fact. This paper proves that it is possible to produce a glass foam with an homogeneous and CLOSED cell structure with only a melting step at 1100°C without grinding and sintering process. I give here under the abstract:

Glass foams are being widely used as constructional materials due to their unique properties in thermal insulation, fire retardation, and shockwave absorption. However, the cost of energy consumption and processes in a conventional glass foam production limited the use of glass foams as sustainable materials. In this study,
for the very first time, thermally tunable CaO−SnO2−P2O5−SiO2 glass foams with controllable pore size were presented as a novel category of melt-casting and float-manufacturable glasses. It was found that the pore size and thermal properties become tunable by manipulating the glass network, i.e., connecting linear chained Sn−P
network with [SiO4] units. In addition, the unique combination of thermal properties and porous structure of CaO−SnO2−P2O5−SiO2 glasses shows potential in float glass foam production, which can produce glass foams sheet-by-sheet with less complexity in
manufacturing processes.

float foam

1575-004-FB2133B6This means that this glass foam can be formed with the floating method on a tin bath, generally know as the float glass process, invented by Sir Alistair Pilkington.

This foam should have NOX gases in the cells but density, thermal conductivity and compressive strength are not given. The authors claims that this will be the route to low cost cellular glass. I see the following positive and negative points.

  • By working with top rollers like for float glass, it could be possible to flatten the cells and to tune the couple thermal conductivity / compressive strength. 
  • There are no belts or molds which have to be replaced, molten tin is doing this. 
  • There is one heating step to 1100°C to be compared with a heating to 800°C after energy intensive grinding. 
  • The glass composition with phosphates and tin oxide is probably costly.
  • It is not clear that replacing tin is less costly than replacing a steel belt or molds.
  • A lot of (expensive) heat has to be extracted at the bottom of the tin bath to avoid that molten tin hits the steel casing. 
  • It is not clear how we keep the same temperature under and above the foam because heating the molten tin is not needed for float glass. 
  • A typical float glass line costs typically 130 000 000€ while a low cost cellular glass production line, based on direct foaming of waste glass costs less than 20 000 000€.

alistairNevertheless, this invention is of major importance especially when the waste glass becomes less available and in that way more expensive. In fact, we could speak about the continuous foaming second generation and it will be a major challenge to develop this new process. Alistair is dead, long live Alistair.

In a very short time, I see that phosphates are introduced in the cellular glass world. The first time as a crystallization inhibitor, the second time now for a “grinding-sintering free” cellular glass process.

Pyrobubbles from the Genius group

logo_smallIn this blog, we have written about boards, gravel and boards made of foamed glass granulate. But up to now, we never discussed the foamed glass granulate itself. Foamed glass granulate is produced in a rotary furnace. I guess that white granulates  are foamed by using white sodalime glass with Calciumcarbonate as foaming agent. The following picture shows a rotary furnace from Liaver.


GeniusThe Genius group, an organization which focuses on innovation, uses foamed glass granulate for fire protection and to absorb liquids. I give hereunder a citation from their website

  • PyroBubbles® have been positively tested by the MPA Dresden (in compliance with DIN EN 3-7) as an extinguishing agent for solid and liquid flammable materials (Fire Classes A, B, D and F).
  • PyroBubbles® are the ideal filler for storing and transporting lithium-ion batteries (UN3480, UN3090) and are lighter than sand (approximately 235 kg/m³).
    PyroBubbles® consist mainly of silicon dioxide with an average grain size of 0.5 to 5 mm.
  • PyroBubbles® absorb electrolytes (BAM tested).
  • PyroBubbles® have a low thermal conductivity and electrical conductivity and are electrically insulating.
  • PyroBubbles® are heat resistant to approx. 1050°C. At higher temperatures they begin to melt and form a closed and thermally insulating layer around the source of the fire.
  • PyroBubbles® float on the surface of the liquid and are particularly well suited for fighting flammable liquid fires, independent of polarity.
  • PyroBubbles® can be collected and to a large extent be reused after every application.
  • PyroBubbles® are hydrophobic and resistant to aging.
  • PyroBubbles® comprise porous hollow glass granules and are classified as Class A1 building materials (DIN 4102 and EN13501); they feature excellent processing capabilities.
  • PyroBubbles® require no maintenance and thus generate low maintenance costs.

This is clearly a new approach to clean up (industrial) disasters with waste glass and it can be recovered to be used again. In the datasheet, they mention a thermal conductivity and acoustic absorption. These properties are important for boards produced with these granulates like already mentioned in a previous post.



On the mechanical stability of cellular glass

logo_smallIn a previous post, we have already written about the mechanical stability of cellular glass. We even have discussed the static fatigue limit of glass and so cellular glass. These posts, based on acoustic emission experiments and self organized criticality (1988) take into account the interaction between the different cells. In case a cell breaks, the load is redistributed over the neighbor cells.

In a 1981 paper of the NASA, the mechanical stability of cellular glass is experimentally and theoretically studied. I give the abstract in the following:

DownloadCellular glasses are prime candidate materials for the structural substrate of mirrored glass for solar concentrator reflecting panels. These materials possess properties desirable for this application such as high stiffness to weight ratio, dimensional stability, projected low cost in mass production and, importantly, a close match in thermal expansion coefficient with that of the mirror glass. These materials are brittle, however, and susceptible to mechanical failure from slow crack growth caused by a stress corrosion mechanism.
This report details the results of one part of a program established to develop improved cellular glasses and to characterize the behavior of these and commercially available materials. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials are developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tin of the moving crack. The existence of a
static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region I may be slower, by orders of magnitude, than that found in dense glasses.

The motivation of NASA was already described in a previous post and it even already applied to replace concrete. On top of that, cellular glass and glass have the same thermal expansion coefficient if the foam is made from the same glass. This makes cellular glass as the preferred support for mirrors.

The mechanical stability was measured by measuring the velocity of a single crack under a load. In a previous post, we described how the acoustic emisson detects the interaction of many micro cracks. In fact, these microcracks are a complex system inducing small and large events. We prefer this method and not the study of a single macroscopic crack. The acoustic emission technique allows to measure the static fatigue limit of cellular glass.



On the water vapour transmission of cellular glass

logo_smallCellular glass according to EN 13167 “Thermal insulation products for buildings – Factory made cellular glass (CG) products – Specification” needs to have a water vapor diffusion resistance factor µ of at least 40000. This property has to be measured according to EN 12086:2013 “Determination of water vapour transmission properties”. This is a difficult way to state that cellular glass according to EN13167 has to have 100% closed cells.

The µ-value is expressed as the ratio to the water vapor transport properties in air. µ=40000 for a material means that the water vapour is diffusing 40000 times slower in the material than in air. Like shown in the following, this is hard to measure for two reasons:

  • The seal between the cup has to “vapor tight” but not one flexibe material has a µ-value like cellular glass. This induces always an error.
  • The weight changes of the samples are extremely low, which means that the weight balance has to be stable and reproducible.
  • The EN standard also request that the system is in a stationary state.

Indeed, for a sample of 40 mm thickness and a diameter of 100 mm we get a transmission of 0.004 mg/h if the dry cup is placed in 50% humidity. To have a certain accuracy (10%), the total weight difference needs to be about 10mg (we measure with 1mg error) which means we need to wait 10/0.004 = 2500 hours or about 100 days. It is clear that this test takes a long time and cannot be used for daily quality control.

Therefore, we suggest to measure daily the amount of closed cells with a pycnometer, like described in a previous post.



Glavel, a new American cellular glass producer

logo_smallGLAVEL as a name for cellular glass gravel is already genial, it says everything in one word. The mission of this company is surprising, contrary to what I am used in the USA.

1721349_originalFoam glass gravel is a highly stable and versatile product that has been successfully used in building and infrastructure construction in Europe for over twenty-five years. Our mission is to bring this product to the construction industry in North America.

Although a lot of American companies import European technology, most of them never state this explicit. But the Glavel management is different and also clearly ecologic minded about the climate change.