Generally we have commercially today three foaming recipes for closed cell cellular  glass. First there was the carbon system, which works under a reducing atmosphere. This system is still dominant in the production of boards. Later on, there was the SiC foaming agent and the organic foaming agent, dissolved in water glass. SiC is only used for the production of foamed glass gravel while the organic foaming agent in water glass shows up in gravel and boards.

The SiC system involves rather high foaming temperatures above 900°C, which shortens the life of the expensive belt on which the foaming happens. The carbon system involves a strong reducing atmosphere, which includes a rather low combustion efficiency. Both are dry methods, which generate a lot of dust during production.

The glycerin / water glass foaming agent is an alternative, which foams in a neutral atmosphere (high combustion efficiency) below 800°C, without generating any dust thanks to the water glass. This foam can be cut or broken after foaming without inducing any decoloring or other damage, which is important for gravel and board production. For board production from a continuous ribbon, annealing becomes a lot easier due to this cutting after foaming because temperature gradients only acts on the sawed stroke and not on the full ribbon. On top of that, the water glass improves the sintering behaviour of the glass powder, which is translated in a reduced grinding of the glass cullet.

From the above, it is clear that the glycerin / water glass foaming system is the future and this foaming system is indeed booming with boards and gravel. Reduced production cost, reduced investment and improved ecology are the main reasons.

Therefore, we came interested to find the brilliant inventor of this process. We found a patent from Millcell AG in Switzerland with Otto Anton Vieli as inventor and also a US-patent version. The patent was filed in 1978 and was expired in 1998. Today, this process is booming without any royalties in Germany, Austria, Switzerland and Russia with at least 1000000 m³ cellular glass yearly.

The patent mentions that the organic foaming agent has to be dissolved in the water glass which is basically the reason why it can be used in a neutral atmosphere and sawing / cutting is possible at higher temperature without burning out of the foaming agent causing decoloring of the foam. Glycerin is the typical example of an organic foaming agent.

Diest is an old city in Belgium with for example a church built in 1253. As a consequence, old buildings with some history are renovated instead of demolished to keep the typical warm culture of Diest alive.

In the Koning Albertstraat, an old building (1880) was bought for renovation by Pieter Wellens. The main building is kept while the extension is completely renovated from scratch.

For the floor insulation of the extension, GLAPOR RDS has been chosen due to its sustainability at a good price.

It was decided to insulate also the foundations of the old part, constructed with bricks and a lime mortar. Newly developed high density GLAPOR cellular glass will be installed with a Unilit TD 1320 mortar between foundation and wall.

This high density cellular glass (160 kg/m³, about 300€/m³) is installed without (bitumen) coating and for that reason a lime mortar is needed. Compressive strength of cellular glass and mortar exceeds largely 2000 kPa. All the cellular glass, used in this project is manufactured for 100% from waste glass, unsuited for the production of new bottles or windows.

Although GLAPOR made a large effort to deliver at an attractive price, the major challenge is for Pieter Wellens, who decided to renovate in the city instead of building from scratch outside the city. Renovating old buildings is ecology at the best.

Above we see how the floor insulation of the extension has been done. Special GLAPOR boards (RDS system) are enclosing the gravel and will serve later as form work for the concrete slab on top of the foamed glass gravel. Due to the lack of space in the city, the gravel is unloaded from big bags.

On top of the GLAPOR structure with the concrete slab, a passive housing construction of ISOVARIANT will be build. ISOVARIANT is based on EPS and contains the concrete wall. It serves as form work for the concrete and as thermal insulation. The load of the walls and rest of the building  is distributed over the vibrated GLAPOR gravel system by the concrete slab.

GLAPOR system sustaining the concrete slab

ISOVARIANT system on the thermally insulated concrete slab

Cellular glass is known as a thermal insulation in two shapes: boards and gravel. It is used in the building industry and for industrial applications. The first sold production was based on a special glass composition and recycled glass was careful introduced with remelting at temperatures around 1500°C. The final high quality product was never adapted to the availability of recycled glass.

At the other side, R&D was performed to find more direct applications of recycled glass and cellular glass gravel was developed. First SiC was used as a foaming agent for gravel but this process involves higher foaming temperature above 900°C and has a tendency to induce open cells (crystallisation) when a too low density was the target. Gravel is continuously foamed on a steel belt which has a short life at 900°C and higher energy consumption. In my opinion, this SiC process will disappear due to the high energy cost and short belt life as a consequence of the high foaming temperature.

A smart (Bulgarian?) individual developed the glycerin / sodium silicate process for gravel, which was already reported in a post. GLAPOR introduced first the large width foaming with this recipe to cut the production cost. Later on the cellular glass market was expanded from floor insulation to road works and other civil engineering work. A Finnish company FOAMIT is showing the way to these alternative applications.

The following files can be downloaded from their site.

• Foamed glass applications
• Foamit brochure
• Innovative use of foamed glass as light weight material of approach embankment

The last file is a paper about an embankment with cellular glass gravel. I give the following citation, which says everything about the advantages and cost saving thanks to cellular glass gravel.

Normal gravel filling was not an option, since it would have caused stability problems, lateral stresses to the piles and increased the strength demands on piles and sheet pile wall anchors. Organizing the temporary traffic over piled structures would have been a costly solution. For these reasons foamed glass was chosen to lighten the embankment load. Foamed glass was also chosen because of its technical and structural qualities, usability and recyclability. Foamed glass’s low unit weight lightened the loads on the subsoil and high friction angle together with low unit weight minimized the lateral stresses against the sheet pile walls. Because of the high friction angle, it was even possible to construct steep embankments without support levels and structures beside foamed glass embankment. Up to 10 000 m3 of foamed glass was delivered to four different embankments on the construction site. The foamed glass will be reused, after the construction of the new bridge abutments, for example in backfills of the market
building and the surrounding roads. Lack of work space near the abutments required a narrower structure, which was achieved by placing the foamed glass between two sheet pile walls.

The stardard method for a well insulated flat roof is to put the thermal insulation on a concrete, steel or even wooden deck. In the case of cellular glass, the most popular method is still to push the boards into liquid hot bitumen. The hot bitumen rises in the joints and a certain overflow has to be present for a vapor tight roof. As a consequence, the weather conditions are rather stringent to construct a quality roof.

However, recently in Norway another method is used due to the availability of large monolithic cellular glass boards 2.8m x 1.5m x 0.18m from GLAPOR. The boards are assembled to large panels up to 8m x 2.5m x 0.25m thickness. Afterwards, the panels are coated with a reinforcing product. This work is done inside independent of the weather conditions.

Later on, the large assembled GLAPOR cellular glass panels are put on the roof with a crane and a final coating is performed on the top surface as waterproofing. These panels are self supporting which means that only beams are needed to support the roof. In principle, steel, concrete or wood deck are not necessary anymore in the roof structure, reducing significantly the cost.

The construction of the 25cm thick insulating roof panel is shown in the pictures. In our opinion, the future of cellular glass is to be used for large self supporting panels instead of only insulating structures. For the last option, plenty of low stiffness alternatives like XPS, EPS, MW, … are available. This future for cellular glass was born when Walter Frank at GLAPOR has built the first continuous foaming production line for larger sizes.