A well documented paper about foamed glass gravel

Cellular Glass Aggregate Serving as Thermal Insulation and a Drainage Layer is a nice logo_small
article written by Andreas Zegowitz. It handles generally about the production, use and opportunities of foamed glass gravel (or cellular glass aggregate).The paper is rather objective because it mentions the leaching out of certain heavy metals,

Factory-made aggregates of cellular glass with a typical lump size of 10 to 75 mm represent a new type of thermal insulation with drainage properties being applied in Switzerland, Germany, and other European countries. Cellular glass aggregates are used as insulating filling material at the perimeter of buildings as well as under load-bearing foundations. They can serve as insulation drainage layers of garden roofs. The insulation material is manufactured from recycled glass and mineral additives in a thermal process. The aggregates form when slabs of cellular glass crack while cooling down. In order to obtain the required hygrothermal properties, the manufacturing process must be carefully controlled. Despite its low density of approximately 120 to 250 kg/m³, cellular glass aggregate has a high pressure resistance, absorbs hardly any water, and is fireproof. The expected service life is at least 50 years. Since its first appearance on the market, this insulation material has been thoroughly tested and the effect of water clinging
to the aggregate has been investigated in the laboratory. To confirm the assumptions, the average moisture content and the thermal conductivity of the material in service was also determined by material sampling on existing buildings. This paper gives an overview of the different tests that must be performed in order to obtain a German and European Technical Approval. It summarizes the aggregate properties of different manufacturers and reports the practical experience gained by in-situ investigations.


Living on water with cellular glass

logo_smallMost people prefer to live on stable ground but other are born with sea legs and only sleep well on water. Personally, I remember I had the best sleep of my life on a cruise ship. Living spacely on a permanent place on water involves a floating home with a ponton. Therefore, we need to build a floating structure like shown hereunder.


This floating structure can be made with steel or other tubes but closed cell cellular glass could also be used. Indeed, cellular glass can have density below 120 kg/m³ and a full house can be taken with only 50 cm thickness.

On top of that, the floor has to be thermally insulated from the cold water. With a cellular glass ponton, this function is automatically included.

GLAPOR® cellular glass can be used. They are able to deliver dimensions up to 3.2m by 1.2m and 14 cm thickness. The different plates can be glued together and covered with a mortar based on natural hydraulic lime, which remains hard under and above water. This cellular glass material is today available for 200€/m³ or about 10000€ for a safe insulating ponton of 10x10m.

Living relaxed and ecological on water, enjoying nature at your feets is another possible application of cellular glass.

The mechanical stability of cellular structures

logo_smallIn a previous post we already reported about acoustic emission experiments on cellular glass. The experiments are described in a public scientific paper.  This paper was in the mean time 96 times cited, which is a nice result. Indeed, people found the same phenomena in the crumbling of paper, in bundles of glass fibres, in theoretical simulations and in earthquakes. The citations can be found here with GOOGLE SCHOLAR. This service is invented to satisfy the ego of scientists, also mine. Like can be observed, even in 2014 after more than 15 years, the paper is still cited and this year, an important paper was found by the system.

The paper describes tensile experiments monitored with acoustic emission on polyurethane foams. They found the following similarities:

  • power law distribution for the magnitudes of the events
  • Power law distribution for the time between events
  • almost no dependence on the density

The second power law is not present at lower temperatures, which is unexpected. At lower temperature where the foam is brittle, I would expect even more similarities.

But the paper focuses on the fact that cellular structures fail in a different way than the base material, explaining why a seriously reduced safety factor can be used. In cellular glass, this is an important property when we think about cellular glass under buildings, under large tanks with liquid gasdgc new anhydrous ammonia tank c5648-00051 and the intelligent GLAPOR® solution under buildings with boards and gravel. PeriBo RDS-SD GLAPOR PICT Button

Building with foamed glass gravel and boards

logo_smallFor years and years, I worked on the annealing of cellular glass to avoid breakage and producing foamed glass gravel is totally the opposite. But since 15 months, I daily watch the production of gravel and the product started to become very interesting to me. Indeed, in floor insulation is vapor tightness not an issue and the much more expensive horizontal boards are not necessary. Foamed glass gravel is also a durable solution for floor insulation and a nice method to use waste glass which became difficult to reuse as bottles or flat glass. On top of that, the waste glass can be foamed with healthy foaming agents, used in any house man or wife. The product does not absorb water, is 100% ecological and healthy and has a very long life time, compared to EPS and XPS. The last property is much more important under the floor (impossible to replace) than on a roof. Many companies are producing this material, which became rather cheap due to the market competition.

GLAPOR® is the only company, who is producing gravel and boards and has developed the best of two worlds. Indeed, in the GLAPOR® solution, the gravel is enclosed between walls, built from GLAPOR® cellular glass boards. In this way, rain water, falling aside the house, can not flow into the gravel, which is protected by the boards. In this way, the system has a perfect frost protection and other advantages. A schematic drawing and picture explain the above. The GLAPOR® mantra   “Fascination by glass bubbles” is well applied in this case.

Today, the gravel is sold at about 40€/m³ and the cellular glass boards at 150€/m³, making this system really competitive with the classic EPS and XPS solutions.


Gravel between upstanding boards


Actual building site with gravel between boards

The inverted roof reinvented

logo_smallThe inverted roof has its water proofing membrane under the thermal insulation. On the contrary, a cellular glass roof has in principle this membrane on top of the thermal insulation. For example GLAPOR cellular glass blocks are “swimmed” in hot bitumen to get a vapor (and water) tight system. This is nicely shown in the following YOU TUBE movie.

And indeed, the water proofing membrane is the weak point in the construction. UV-light and large temperature variations are causing the rather short life time of the membrane. In case of a leak, not visible inside, freeze and thaw on the cellular glass will damage irreversibly the roof in a few months over a large thickness.

On top of that, some cellular glass insulation becomes rather expensive when a large thermal resistance is requested, which is the standard today.

The inverted roof with XPS does not know these problems. Current producers are DOW, BASF and KINGSPAN. But this roof has another possible problem. During rain fall in the winter, cold water may reach the water proofing membrane, cooling the structure under the water membrane proofing. This may induce condensation inside if the structure is not very heavy. For this reason, BASF, synonym for German quality, requests to have a minimum thermal resistance  of 0.15 m²K/W.

This thermal resistance is already availbale with 1cm GLAPOR PG700 cellular glass but 4cm is needed to have enough mechanical strength for installing. For just 6€/m² extra material cost, you have the best of both worlds.

  1. An absolute protection against humidity problems inside
  2. A very well protected water proofing membrane
  3. A huge thermal insulation with cheap XPS without any problem possible

6€/m² or less than 600€/m² for a 200m² house (one stock) is giving you absolute protection against humidity with a cheap very well insulating inverted roof, with its never to replace water proofing membrane.

Indeed, this is the inverted roof reinvented or the best of two worlds: CG + XPS (CG = cellular glass; XPS = extruded polystyrene). It is the conviction of BELGLASCZ that the combination of different thermal insulations is giving you the best systems.

Russia goes (foamed glass) gravel

logo_smallI found a nice message in my mailbox. Indeed, Schaumglas Global Consulting managed to install a plant for the production of 300 000 m³ foamed glass gravel annually in Russia. Recycled glass can not be used in the regular glass industry if it contains all kind of contamination. In case there is a large request for foamed glass gravel, it is economic wise to use this waste glass without too much cleaning directly into foamed glass gravel.

Today, the further we go to the East, the larger is the growth of foamed glass, gravel and boards, while in West Europe, a foamed glass plant was recently closed. What should be the reason for this? More than 80 years ago, foamed glass was invented in Russia but that can’t be hardly the reason for this sudden growth and interest.

Kinetic energy absorption by cellular glass in the Formule 1 racing world

logo_smallMay 1, is the day we all think on the tragedy of this very skilled and friendly F1 driver Ayrton Senna. And that is probably the reason kinetic energy absorption crossed my mind in my previous post, although the idea was already published in a US2981317 patent about safety seats in 1961. In this post, I want to show my point with real numbers with a calculation in an Excel spreadsheet.

The following example could be tested. I assume a car at 300 km/h and a total weight of 1000 kg. I guess that this car hits a cellular glass wall and a cross section of 2 by 0.2 is really hitting the cellular glass wall. The used cellular glass has a compressive strength of 3 N/mm². The car will stop completely after crushing 3 m cellular glass and the deceleration will be about 250 g. A Head Injury Criterion (HIC) of 250 g should be the limit for concussions. An internal recoil of the brains will not be present because the cellular glass is entirely non-elastic, the kinetic energy is converted in breakage energy for the cellular glass.

Cellular glass, produced from only recycled glass (without remelting) by for example GLAPOR can be used for this application, costing less than 450 € for one running meter. The cellular glass is non combustible, can always be recycled and is water proof. Having an idea is always easy but only the F1 organization can bring it into real life. Bernie, please wake up.

Other applications for cellular glass

logo_smallThe first application of cellular glass was a floating device. During the war, harbors must be protected with curtains against submarines. The Germans had occupied Portugal, the major source of cork and closed cell cellular glass was the best alternative.

Later on, cellular glass became popular as a thermal insulation and this is today the real market. But it can also used as an acoustic absorber, today sold under the name REAPOR®. An acoustic absorber avoids echo, which is for example always a problem in open offices.

A less known application is to use it as kinetic energy absorber. Kafka, the famous Czech writer invented the principle of a helmet during his work for an insurance company. But a helmet can not avoid that the brains have an internal recoil, although your head is well protected. This recoil is a consequence of the elastic behavior of the helmet.

But if this helmet should have been constructed from cellular glass, your head will crush the cellular glass but there will be no internal  recoil and brain damage would be less likely. The use of cellular glass as a kinetic energy absorber was already published in  US2981317 patent of 1961 about safety seats at line 49. The specification non-elastic crushable is clearly given on line 46.  The same is needed when a Formule 1 car looses control and hits the tires along the road. The recoil of the brains of the pilot can be the reason of medical problems afterwards although the outside damage can be relatively small. I am curious to know   what density the cellular glass needs to have and which thickness is requested to let stop a car at 120 km/h without even a headache  for the driver. I guess we will find reasonable values. The calculation can not be difficult: the kinetic energy of the car is used to crush the cellular glass = thickness * compressive strength * cross section of the car.  The maximum allowed deceleration gives the compressive strength you need. Solution will be given in a next post.

The dimensions of cellular glass

logo_smallRecently, I was in a small glass company. These people make small but old fashioned hand made glass plates as window and for other applications. Since 5 years, I regularly visit float glass plants for CNUD EFCO, where glass plates up to several meters width and height can be produced.

And suddenly a question came up? Why did this not happen with cellular glass? Cellular glass started (in the metric system) from about 45 cm by 30 cm, scaled up to 45 cm by 60 cm and recently 120 cm by 80 cm became available. I can imagine that the thickness is limited because annealing time goes linear with inverse of the thermal conductivity and with the square of the thickness. But I do not see a reason why several meters length and width are not available if I watch the cold end of a float glass line as installed for example by Grenzebach or Lisec.

But this week I visited a plant and the owner was proud to show me what he could produce. The actual dimensions are still secret but they are huge. And suddenly, I had a very nice application in mind for the world of tomorrow.

2014-04-17 09.20.48

Mineral rendering on cellular glass

Cellular glass is in the first place known as the best  thermal insulation in the roof but is  less popular on (in) facades. And within the facade world, it was for a long time not supported as thermal insulation under a rendering. The reason for this is quite clear:

Most (if not 99%) rendering products for application on walls and thermal insulation contain cement as bonding agent. Cement based products hardens in a totally not flexible way and have a tendency to let shear off the cellular glass. During drying, the rendering shrinks and induces an enormous tensile stress on the cellular glass. In case the layer is thicker than a few millimeter, the cellular glass shears off because the tensile strength of the cellular glass is exceeded. In reality, a rendering must be at least 1 cm thick to get a long life and cellular glass became obsolete in this application.

(Portland) cement changed our life with its great strength and short settling time and let us create strong but still elegant constructions. But there was a time before Portland cement where almost pure hydraulic lime was used as bonding agent. Buildings made with this bonding agent were able to deform without creating a crack, they were (are) in a certain way flexible. Foundations were much smaller or non-existent while today a house without proper foundations will show important cracks when the masonry is performed with ordinary Portland cement.

Rendering, properly based on this old recipe, don’t shear off from cellular glass, even if the layer has a few cm thickness. A thick  layer with coarse grained sand is put on the cellular glass and the finishing is done with fine grained layer. The fine grained layer will dry the wet thick base layer by the difference in surface tension.

Both systems are a perfect solution for those customers who want a rendering on thermal insulation which resists a foot ball, feels like a real wall and does not burn. Both solutions are guaranteed by an ETA and are insured.


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