Cellular 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 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.
Foam 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.
UBP is the German abbreviation of Umweltbelastungspunkte, which is a result of “Methode der ökologischen Knappheit”. The method is invented in Switzerland , which explains the use of the German language. In English, we speak about the Ecological Scarcity Method (which has no Wikipedia page).
An EPD gives you for the production of each product how much CO2 is generated, how much fossil energy is used, etc. These 8 numbers don´t say a lot to the common consumer. The UPB combines the impact of all these emissions and material-energy use on the environment, the future of the raw materials and our health in only ONE number. The method is defined in a paper by the Swiss government and also Volkswagen has sponsored a publication. But for the standard consumer, I have the following table with the quantity of products for 1000 UBP.
This method is also applied for thermal insulations on the Swiss market which can be found in this spreadsheet.
GLAPOR communicates 509 UBP per kg cellular glass board, which is lower than any thermal insulation except foamed glass gravel (also a GLAPOR product) like shown in the following figure. The improved value compared with “Schaumglas” is due to the fact that GLAPOR foams directly recycled glass without melting a special composition.
For a fair comparison of thermal insulations, we have to work with UBP/m² for a certain thermal resistance (R=5 m²K/W) to be obtained. This table is given in the following.
It is clear that according to the UBP system in Switzerland, GLAPOR cellular glass boards are the most ecologic thermal insulation which can take a compressive load of 600 kPa with a safety factor = 2.5. This is a consequence of the direct foaming of recycled glass. Standard cellular glass is made from a special glass composition involving an energy intensive melting step.
Clean Tech Block is a project from Gråsten Teglværk, the University of Aalborg and the University of Ljubljana. A few posts were already written about Aalborg and in fact, they collaborate with Ljubljana. I had the occasion to met very interesting people: Y. Yue and Martin B. Østergaard in Aalborg and Jakob König in Ljubljana.
Prof. Y. Yue
Martin B. Ostergaard
The complete team proud about their invention
This team did what I believed for a long time was impossible. They managed to foam directly waste glass (without melting) with closed cells, filled with CO2 with a minor content of H2. In my opinion, this is the best progress in cellular glass land in the last five years. In this way, cellular glass with 0.040 W/mK and 600 kPa compressive strength based on waste glass without remelting becomes possible at prices of about 150€/m³. They want to use this cellular glass between bricks to able to build houses like explained here under. It is a Google translation from Danish to English.
In a previous post, we mentioned already PhD work on cellular glass and also one on foaming of CRT-glass. However, the thesis in this post has a lot of attention for the methodology of searching for a new glass foaming system. Hereunder the abstract of the thesis is given.
Exponential growth of papers on cellular glass
Foam glass has been used for over 70 years in construction and industry for thermal insulation. Foam glass is mainly made of recycle glass. Strict energy policy motivates foam glass manufactures to improve the thermal insulation of foam glass. The effort to understand the making of foam glass with good insulation ability is scarcely reported. The goal of this Ph.D. thesis is to reveal the underlying mechanism of foaming reaction, foam growth and the heat transport of solid foam glass. In this thesis, the panel glass from cathode ray tubes (CRT) will serve as a key material to reveal the mechanisms.
Foaming is commonly achieved by adding metal oxides or metal carbonates (foaming agents) to glass powder. At elevated temperature, the glass melt becomes viscous and the foaming agents decompose or react to form gas, resulting in foamy glass melt. Subsequent cooling to room temperature, lead to solid foam glass. Metal carbonates decompose due to surface reaction. Based on Na2CO3, we show the reaction is fast and the glass transition is changed considerably. We propose the reaction rate is dependent on contact area between glass melt and Na2CO3, melt viscosity and Na+ diffusion.
A method is developed for optimising process parameters. Characteristic temperatures are derived from a deformation curve and the deformation rate curve. Maximum expansion rate was linked to closed porosity. Using this knowledge the method is applied to literature data to analyse for optimal conditions. The resulting conditions were in agreement with industrial conditions. Since no foam glass properties are necessary to measure, the method allows fast investigation of process parameters.
The melt viscosity is an important parameter for foam growth. We compared bubble- and crystal free melt viscosity with foam density and show in order to minimise the foam density, the heat-treatment should be performed in the viscosity regime of 103.7-106 Pa s.
The thermal conductivity of foam glass made is often reported to be linear dependent on porosity or foam density. Foam glasses made from CRT panel glass and different foaming agents confirm this trend at high porosity level (85-97%). The experimental data suggests the solid conductivity is dependent on the foaming agent applied.
The research is part of a project to build “passive houses” where the cellular glass is a structural element and not only thermal insulation. In fact, the cellular glass takes all the load while thin bricks are just creating a standard house look. Houses built from cellular glass was already mentioned in a previous post.
Werner Sobek is a German famous architect and structural engineer. I cite a part of the Wikipedia link.
Werner Sobek was born 1953 in Aalen, Germany. 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.
In 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 Stuttgart, Frankfurt, London, Moscow, New 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.
Since 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.
I 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.