We 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 and 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.

This 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.

The 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.

The 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.

But 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.

In 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.

Didier 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-Organized Criticality. Like acoustics, you need a logaritmic scale to describe the intelligence of people. Per has a few octaves more than most other people.

I 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.

There 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.

We 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.

One 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.

The 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.

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

Open 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.

Both 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.

Developing 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 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.

This 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 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.

Glass 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.

AeroAggregates 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.

We already have written a post about Permafrost. Although this Permafrost is unknown in our regions, a lot of people have to make their lifes on such an underground. In the Northern Hemisphere, 24% of the ice-free land area, equivalent to 19 million square kilometers,^[9]is more or less influenced by permafrost. Most of this area is found in Siberia, northern Canada, Alaska and Greenland. 

The basic problem to live on Permafrost is the stability because there is an active layer, which is melting every summer. Building on this layer makes that the building is continuous sinking into the underground.

Above on the left, a standard building is “sinking” into the underground while at the right, the building is put on concrete pillars, deep into the permafrost with a concrete slab on top of this pillars to support all bending forces of the building. The havier the building (more concrete), the deeper the pillars are put into the permafrost (more concrete). Between the ground and the building, we have an airlayer, which avoids that building heat is penetrating into the permafrost, creating even more instability.

The new system replaces the active layer (about 1.5m) by cellular glass. Cellular glass is weight light, can support the building and 1.5m cellular glass avoids perfectly that building heat penetrates into the permafrost. Another advantage is that a climate change hardly influences the permafrost under the building. In that way a lot of concrete has been avoided.

For this application, we don´t need cellular glass with the lowest thermal conductivity, which means that cellular glass, directly foamed from recycled glass will satisfy. This cellular glass can be prefabricated from large boards of 2.8 x 1.2m, today only produced by GLAPOR cellular glass. This can be done with the help of polyurea, like already done for flat roofs. Cellular glass gravel is less suited because it absorbs water, which freezes and increases the weight. I guess that the new construction is a better approach (more stable) and price competitive.

We found an interesting article, wriiten by an Airbus collaborator about energy absorbing barriers in air planes. Especially the impact of birds is dangerous and for that reason, the air plane needs protection with all kind of energy absorbing barriers. These barries should be lightweight but still efficient.

The article also shows the load deformation curve of the perfect kinetic energy absorber. This curve is typcial for foams and indeed also for cellular glass when the compressive strength measurement is done without capping. Indeed, the typical peak at the beginning of the flat part is absent for foams but not for honeycumbs.

The article shows also a graph with the specific kinetic absorption of foams, which do and do not comply with what is needed. The typical foams of polyurethane, polyisocianate and polyethylene do not comply, even at densities of 100 kg/m³. But on the other hand, GLAPOR cellular glass reaches 2000 kPa compressive strength with 140 kg/m³ density. In that case, we have a specific kinetic energy absorption of at least 8 kJ/kg, which is close below the well known (combustible) foams for these applications. Today, PVC-foam and PMI foams have taken this market but when non-combustibility becomes an issue, GLAPOR cellular glass is a good candidate.

Cellular glass is a perfect thermal insulation for outside walls after rendering with natural hydraulic lime mortars. These kind of systems are known in Europe as ETICS (External Thermal Insulation Composite System). For each system, the building company needs to find an ETA to be able to deliver the normal guarantee.

The ETA (European Technical Assessment) was requested by Arte Constructo, Belgium and can be applied on all kind of cellular glass boards equivalent with GLAPOR cellular glass. The rendering products are Unilit 15P2, Unilit 65M and Unilit 65F. The mineral adhesive to adhere the cellular glass boards on the wall is Unilit K/2. These mortars are produced at Tassullo, Italy.

After the hygro-thermal testing, the system did not show:

• blistering or peeling of any finishing
• failure or cracking associated with joints between insulation product boards or profiles fitted with the ETICS,
• detachment of render,
• cracking allowing water penetration to the insulation layer.

As a consequence, this system became approved and is now used for several years without important complaints.

Recently, we got a leaflet from the Welsch company Ty Mawr about the use of cellular glass gravel in Birmingham Paradise. The cellular glass for this project was delivered by GLAPOR.

Also in this case, the relation strength – weight was the main reason to use cellular glas instead of ordinary soil. BELGLAS was delighted to assist in this wonderful project with a large ecologic respect.