The beauty of open cell cellular glass thermal insulation, even for building applications

logo_smallThe EN-standard 13167 is rather clear about cellular glass for building applications. The water vapor diffusion resistance µ should be larger than 40000. This property has to be measured according to the standard EN 12086, which has its last version in 2013. The reason for this large µ-value is rather clear. Cellular glass has the reputation to eliminate perfectly internal condensation thanks to this very large µ-value.

However, there are two reasons to doubt and review the above story in the building , namely two practical ones and a bureaucratic one.

  1. WVTThe bureaucratic one is that the standard EN-12086 from 2013 contains an error on page11.  Indeed, the mentioned gas constant of water vapor is a factor 100 too small, which means that a cellular glass with a real µ-value of 400 is allowed by the (erroneous) standard. A µ-value = 400 is an open cell cellular glass. This means that today open cell cellular glass is covered by the EN13167 standard.
  2. imagesThe practical one is that an open cell cellular glass has an improved acoustical absorption with thermal conductivity 0.056 W/mK. This material can be used between two thin sound reflecting materials to obtain a light sandwich with a small sound transmission. Another application is simply to use it to reduce echo (reverberation) without using combustible material.
  3. Another use op open cell cellular glass can be find in the hydro-culture world, like already mentioned in a previous post. But I can imagine it makes also sense to let grow plants against this material vertically installed inside and outside. The material serves as plant growth medium, thermal insulation and acoustic absorb-er.

280px-Conformité_Européenne_(logo).svgIn our opinion, it is clear that the EN-standard 13167 should be rewritten to allow non-combustible (cellular glass) thermal insulation with a high compressive strength and interesting acoustic properties. We should simply specify a minimum µ-value and maybe even a maximum µ-value. Today, it seems hard to sell cellular glass thermal insulation with important acoustic absorption within the EN- standards system because only cellular glass with µ-value > 40000 is allowed for building applications.



Cellular glass as a plant growth medium

logo_smallFor a long time, we were thinking that only closed cellular glass has a future. However, more and more, GLAPOR receives requests to deliver open celled material. In most cases, people are interested to consider this material as an acoustic absorber.

61gjV0LFxbL._SL1024_But last week, we got a request to use this material as a plant growth medium as an alternative to Growstone. But this case, there is interest for the gravel and the boards. At GLAPOR, this evolution was predicted and a one step foaming of 100% open cell cellular glass with a large water vapor transmission was developed. However, Growstone is more than only open cell cellular glass gravel like shown in their patent.

In this case, the cellular glass serves as support for the plants but is also able to keep the pH of the water stable in hydrophone applications. The patent gives such a nice introduction that I give here simply a citation:

Growstone-photo-Hydro-page-Top-Drip-set-up-2-1024x680Hydroponics is the science of growing plants in a nutrient solution with the mechanical support of an inert medium. Hydroponics is an old art, and a variety of inert
media are known as suitable for the germination, rooting and growth of plants. Such substrates include peat, vermiculite, perlite, fly ash, pumice, rock wool, glass wool,
organic and inorganic fibers, polymers such as polyurethane, polystyrene, polyethylene, and the like. These substrates have been used for true hydroponics or in quasi-hydroponic environments such as in admixtures with soil. Typically, the inert medium is either in the form of a contained loose particulate, such as sand, or as a rigid and self-supporting structure that can support growth of the plant. The rigid structure has some notable advantages over the loose particulates, in particular the ability to stand alone without a requisite container. However, the loose particulate media tend to offer better pathways for water and gasses to be delivered to and from the root systems.
One problem common to hydroponic gardening is under/overwatering. Some media offer limited porosity and/or limited means for circulating water into and out of
pores. As a result, vegetation growing hydroponically is often underwatered. Conversely, hydroponic techniques lend themselves to the provision of excessive water to the plant root system, often in response to the underwatering that is occurring. Overwatering can result in chlorosis, retarded growth, pallor, and, eventually death. In such situations, the water around the roots becomes stagnant and gasses dissolved therein are only urged to
and from the roots through diffusion. Moreover, vital gasses quickly become depleted and waste gasses saturated in the water proximate the roots, exacerbating the situation. Thus, it is desired to reduce the stagnant water around the roots by circulating the water.
Most of the substrates currently known are solids with limited porosity. Some known substrates have attempted to add or increase the porosity of the substrate
in order to better provide for gas exchange to the roots. One such substrate has been produced in the form of a sponge-like or foraminous foamed polymer body with
conduits 1-5 millimeter in nominal diameter, spaced about 1-8 mm apart and extending throughout the substrate. The conduits drain water from the substrate and provide reservoirs of oxygen for the plant roots and at the same time allow substrate to hold some water that may then be available to the roots. The porosity of this substrate ranges from between 6 and 53 percent. Soil or the like is deposited on top of the substrate and a seed, cutting or small plant is placed in the soil. With the substrate under the soil layer, over-watering induced problems are prevented, as excess water drains from the substrate, filling the conduits with air and oxygen will be readily
available to the roots. 

Overview-of-a-commercial-greenhouse-trialAnother issue with known substrates is pH control. Natural substrates tend to include soluble mineral residue that dissolves at uncontrolled rates, shifting water pH. Man-made substrates likewise may include materials that dissolve over time and at nonlinear rates, shifting pH as they do. Changes in pH can have a drastic and deleterious effects on plant growth. While useful in hydroponic and soil amendment applications, the above substrates are still hampered by a lower than optimal porosity, limited wicking capacity, low capacity for water infiltration and retention, and uncontrolled pH arising from mineral dissolution. [0006] The documents US 2007/0186467, US 2009/0056221 and US 2008/0034653 describe foamed glass substrates for use as plant growth medium and methods for its production. Thus, there remains a need for a highly porous substrate for supporting plant growth. There also remains a need for improves the aeration of soil and allows for better water filtration and irrigation. The present novel technology addresses these needs.

shoppingInformally, it was communicated that cellular glass is well suited to harvest marijuana for medical purposes. On Amazon, we found that Growstone costs about 16€ for 9 l while typical gravel for building costs 50€ for 1000 l.

GLAPOR enters the tankbase world

logo_smallGLAPOR put also his first steps into the industrial insulation world where a larger thickness is not an issue. Although this world is very well closed, GLAPOR is invited to offer for the thermal insulation of tank bottoms.

DownloadFor that reason, Fraunhofer IBP in Stuttgart has measured the thermal conductivity between -150°C and 250°C on a 1000 kPa foam. Comparison with classic cellular glass shows that about 25% more thickness is needed for the same mechanical stability.

DownloadTank bottom insulation refers to the thermal insulation under the steel tank, which has to carry the weight of the cold liquid. In the case of liquid natural gas, we speak about -162°C. The better the thermal insulation of the tank, the less liquid will evaporate. In most cases, the cellular glass under the ring of the tank has to carry the load of the moving liquid during an earth quake. For that reason, compressive strengths up to 2400 kPa are some times requested.

For your information, we add the technical report from Fraunhofer with the equation, which describes the thermal conductivity in function of the temperature.


Marketing for cellular glass starts at 18 years

logo_smallIt is still unbelievable that the oldest man made hard foam, cellular glass has still a limited market penetration. And the few who are familiar with cellular glass have the image of very expensive material, reserved for the happy few. BELGLAS is started 5 years ago with the following target: “It is our mission to lower the prices to make cellular glass available for a larger group of people“.

logo-university-of-bayreuthIn the mean time, the prices have lowered substantially but it is still not well known. For that reason, we have accepted an invitation for a seminar for students at the university of Bayreuth.


By that occasion, GLAPOR will also disclose its first steps on the acoustical market.


Open source software: Wikipedia

logo_smallWe all know Wikipedia and it is used a lot in this blog. Everybody is able to write a contribution to this on line encyclopdia and to consult it free of charge. There is a limited peer review to avoid that complete nonsense would be published. I consider it as the best contributing social medium 150px-Wikipedia-logo-v2.svgand I can “loose” a lot of time by just checking the main page.

There are also other projects in the same format like wikibooks, wikispecies, wiktionary, … . They are all based on the same open source software of Mediawiki.

wikiThis software is written in PHP and works together with a (open source) database. But is less known that this software can run on your personal or company server where you can develop your own documentation system. Indeed, a PC under Linux can run this software for your private documentation system at home or in the company. BELGLAS can assist you in starting such a documentation system where each document gets its own comments in order to find it when you need it (when you already forgot you made it). The software is free of charge like all open source.


Bathtub´s and cellular glass

logo_smallThe bathtub curve is used for many subjects where an estimation of the remaining life is needed. It was used to estimate the best time to change an air conditioning or even to estimate the creep of steel. The last application was the motivation to try this concept on the creep of cellular glass. It was brought to my attention by G. Crevecoeur.

350px-Bathtub_curve.svgThe creep of cellular glass can be very sensitively monitored with the acoustic emission technique (AE) like shown in this paper. There we mentioned that creep on cellular glass can be described with a bathtub curve. We were combining Omori’s law (power law in time) with an exponential, which describes the damage already done in the foam due to the creep and so increasing the load. We found that if we fit the AE-signals with this simple bathtub curve, we can safely describe the mechanical stability of the cellular glass on the long term. Twenty years back, this statement was not really accepted.


godinBut recently, a book appeared on the market about estimating lifetime with AE, with a reference to our paper. Googling the authors brought me to a PhD thesis  about this subject, applied on composite materials. In this thesis, I found power laws and bathtub curves. The bathtub curve was also inspired on Omori´s law for earthquakes but the exponential is rather complicated.

aebath  aepower

220px-Didier_SornetteIn the references, I found also Prof. Didier Sornette. Didier became an expert in the prediction of catastrophes, like earth quakes and financial bubbles. I know him because he was the one who downgraded the above paper from Physical Review Letters to Physical Review. The reason was that we had written in the original paper title “self organized criticality”. Later on, he recognized that earthquakes are self organized critical due to the fractal nature of the tectonic plates like we had argued for the microscopic defects in cellular glass, showing exactly the same statistics.

bakDidier was not really a friend of Per Bak, the inventor of self organized criticality. In fact, Per had a lot of discussions with theoretical physicists like him but he loved experimental guys, which are testing (and hopefully) confirming his theory. When I informed Per about our results, he kindly asked me to publish the data in a high level magazine. Per passed away much too early but he left us a fantastic book: How Nature Works: The Science of Self-socOrganized Criticality. Like acoustics, you need a logaritmic scale to describe the intelligence of people. Per has a few octaves more than most other people.


weversI learned once the tool AE from Prof. Wevers, KU Leuven during a workshop, organized by my (ex-)father in law, Jules Heirman. We collaborated in a few papers about this technique on cellular glass. She was well informed about our interpretation of AE with bathtub curves. Great was my surprise when I discovered the following paper about AE on creep of masonry, interpreted by the bathtub curve, published ten years later than ours. The following picture says everything.


godinThere are generally two kind of bright scientists. The one who recognizes the work of less intelligent industrial scientists and the one who seems to have a blackout about this. Prof. Godin, AE expert in composite materials at Mateis, Lyon, does not know me but refers to our work twenty years later. I must be honnest, my ego got a boost.



Open source software: Python

logo_smallWe are still selecting the right replacement for FORTRAN, because we like to work with a graphical interface (GUI) and to develop new programs in an efficient way. The current speed of ordinary PC’s allow us to work with a script language. In this case, an interpreter reads, translates and executes line by line. Declarations of variables is not needed anymore and debugging is much easier.

pythonOne of the most popular languages today is beyond any doubt Python. It is a 27 years old language, which is object oriented and procedural. In our case, we just want a FORTRAN equivalent. Python is written by  Guido van Rossum, a mathematician from the Netherlands. The blocks in the programs are created with indentation to improve readability of the programs. But on top of that, the Python community has written a huge amount of external commands for mathematics, science, data-mining, etc … . The intelligent language, easy to learn, together with the large amount of external commands makes the language extremely attractive.

220px-Guido_van_Rossum_OSCON_2006The language runs on Windows, Linux, Unix, Android and probably more operating systems. The Internet is full of tutorials and examples with this language. It seems that almost every programmer is a fan.

The language allows to export (import) data to (of) other programs with all kind of file formats. For the physicsts, there are the following exceptional possibilities:

  • SciPy, a package for scientist with plotting possibilities
  • SfePy, a package to solve differntial equations with finite elements.
  • and much more … . We think the best way to start as a scientist is Anaconda.

anacondaWe wish you a nice adventure with Python. And it is true, the writer Guido answers all emails.

Open source software: octave

logo_smallOpen source software was always a point of interest for BELGLAS. Semi professionals work together and generate an equivalent of commercial software. In this case, we discuss GNU Octave, which is an alternative of MATLAB.

100px-Gnu-octave-logo.svgBoth products are used to solve mathematical problems with numerical methods. Everything is based on matrices but standard programming, like done with C and FORTRAN is also included. It is a script language, which means that every command is first interpreted and then executed , contrary to FORTRAN or C, where compiled programs are executed.

downloadDeveloping a solution for a problem goes much faster with this software but execution is slower than with FORTRAN. If a certain solution works well with Octave but execution is too slow, reprogramming partially or completely is an option. The plotting software is also very easy to use and writing or reading data to/from a file is straightforward. A lot of Octave programs are already available in all kind of technical disciplines.

For the interest reader, there is the official website, where you can download the program and I found a tutorial on the internet. Even a more complete handbook could be found next to the official octave manual.

Acoustic absorption with cellular glass

logo_smallAcoustic absorption is a typical open cell foam application like nicely explained in this handbook for acoustics or in this wikibook. In some cases, fibrous materials like mineral wool are not allowed and an open cell foam is chosen. But if also combustibility is an issue, we have to work with a mineral foam. A typical example (and maybe the only one today on the market) is Reapor.

In the datasheet, I found the following absorption spectrum.


absorberThis means that 1m² of this material is equivalent with an open window of 1m² for the noise in a room, which is almost perfect. In another post, we found what was already possible in 1963. In this case, we reach 70% to compare with 100% for the Reapor product.  This means we the 1963 product, you have to install 30% more to obtain the same result. The composition on the Reapor datasheet discloses that the material is in fact foamed bottle glass.

Both products are two steps process. Reapor starts from foamed glass granules, which are sinterd to obtain a irregular structure of small and larger pores. The 1961 process starts from closed cell cellular glass. The cells are opened with hydro-static pressure and the holes are introduced on both sides to improve the absorption.

If a material could be foamed in large boards with 100% open cells and an irregular hole pattern could be introduced during the finishing, we have a one step process, which should be competitive. But today, such a process is still not public domain. Typical (one step) open cell foams have about 70% open cells.


A new cellular glass gravel plant in the USA

logo_smallA new cellular glass gravel production line was built in Eddystone PA, USA by SGGC, Germany for the company Aeroaggregates. A second line will be built in the near future. They use SiC as foaming agent, which means they are using the dry process.

I found some remarkable facts on their website.

logotmlowresGlass is a fully recyclable material that can be recovered in a closed loop over and over again. This is particularly true for glass bottles which, on average, have a recycling rate of only 34% in the United States in 2013 (according to the U.S. Environmental Protection Agency).  Today, there is a limited number of glass processors to accommodate the entire glass stream that is generated in the United States.

awardAeroAggregates LLC is the first vertically-integrated, U.S.-based company to produce lightweight aggregates from 100% recycled glass. Our manufacturing capabilities include the ability to make several types of foamed glass including both open and closed cell aggregates.


The founders of AeroAggregates realized the need for a sustainable solution for lightweight construction materials due to increased design or constructability requirements. Today’s civil engineering challenges include construction on soft soils, lateral load reduction behind retaining walls and structures, insulating subgrade and backfill, and the protection of underground utilities. AeroAggregates provides an answer to most of these challenges by supplying a lightweight material with a high friction angle that is also insulating, free-draining, non-absorbent, rot-, acid-, and chemical-resistant, noncombustible, and a beneficial reuse for glass containers.

It is clear that the founders are aware about the opportunity to recycle and also understand that foamed glass is much more than thermal insulation. They also consider open cells besides closed ones. I wonder when they start to produce boards.