Taiwanese cellular glass

logo_smallEverywhere in the world, small cellular glass companies are popping up. Most of them are based on direct foaming of recycled glass. Taiwan is another example with Taiwan Material Development Co., Ltd.

This company describes themselves in the following way:

TWMD-v2-1-1Innovation, Green energy, Quality, and Service are the purpose of Taiwan Material Development Co., LTD, and become the greatest sustainable operation green material industry is our goal. We provide high quality construction and guarantee in building material, construction, techniques, and after-sales service, and also reduce the waste of energy resources. We provide a healthy, environment friendly, convenience and high quality functional material. TWMD introduce AH lightweight solid wall to market, and provide users the internal wall partition with all function. On the other hand, we keep developing related green building materials. Look forward to developing a complete production system. To build a green building material brand. Hope to satisfied architects, interior designers, businesses of related industries and ordinary people by doing one-stop shopping.

icon1-300x300They describe their product as a Lightweight Insulation block, foamed from LCD glass, obtained from Spring Pool Glass. This means that they are foaming a borosilicate glass. This kind of glass has a lower thermal expansion coefficient and higher chemical resistance, which means that this product can withstand more than standard cellular glass. It is not clear how this glass is foamed because LCD glass does not contain sulphate because it is sodium free. I guess it will be carbon black and Antimonytrioxide.

The product is nevertheless promoted as a typcial building material and not an industrial one. The boron in the glass gives other perspectives. As end of this post, I give you also the link to some movies about this product:  1, 2 , 3, 4  and 5.  The last one seems to be the best one. In this movie, the use of cellular glass as an acoustic screen is mentioned.

 

 

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Foamed glass by Walter Lovett

logo_smallWalter Lovett was a professor of Civil Engineering at the University of Pittsburgh and made the following contribution on a conference about structural foams in 1960.

The first foamed glass was developed in this country in 1938 and was first placed on the market in 1942. Several factors contributed to the production of this material, but the most important were:

  • An idea that there was a need for a waterproof, noncombustible, inorganic ma­terial of low density and low thermal conductivity to serve industry as an insulant.
  • The Navy’s need for a material which would stand up well in salt water, be buoy­ant enough to float anti-submarine nets, and also withstand the action of enemy

2019_05_23_10_37_22_Structural_Foams_Google_BooksSince the United States was at war during 1942, the larger part of the development of foamed glass was pointed toward the production of a buoyant item. From foamed glass, cubes were formed approximately 8′ on a side, protected on the outside by heavy plank­ing. They were floated out into the mouths of harbors and rivers by the thousands, and there used to hold up steel anti-submarine nets. During the war years, the vast quan­tity of foamed glass produced was used for this purpose; however, some was also made available for use as an insulant for roofs, and as cold storage and wall insulation for humidity-controlled buildings such as exist in the textile industry.

The material is made by grinding a bora-silica type glass to about the consistency of portland cement. This fine glass powder, with a small addition of other ingredients, is placed in stainless steel pans and heated to about 17500F, which causes the material to foam. The material is then put through an annealing lehr (oven) to relieve any in­ternal stresses, and then is cut into blocks of various thicknesses.

The primary use of foamed glass is for insulation, but it has been and is being used as a structural load-bearing material. For example, when the Central Mortgage and Housing Corporation of Canada was studying the need for low-cost housing, they first made a study of materials other than the conventional wood frame and the prefabricated wall system, which both involve numerous, time-consuming operations to fabricate and erect,

Central Mortgage and Housing’s requirements for an acceptable wall material were that the material must be strong, rigid and possess resistance to heat transfer, moisture transfer and fire, and preferably that it be homogeneous and easily mass-produced, After studying various materials, it was decided that foamed glass was the closest ap­proach to the desired material. Having chosen the wall material, it was decided to build an experimental house in the industrial community of Ajax, Ontario. A basement-less house was chosen for this investigation consisting of two bedrooms, bathroom, combination dining and living room, kitchen and utility room.

The house was erected in the spring of 1949. The wall and interior partitions were pre­fabricated using 2″ x 12″ x 18″ thick foamed glass blocks bonded together with hot asphalt to form a 4″ thick panel. The joints between the blocks were staggered to assure an overlap. Window and door openings were made in the panels as they were fabricated. The edges of the panels were vertical construction joints to be made during erection and were coated with a thermoplastic adhesive which can be reactivated after it has hardened by applying heat.

Before erection, the surfaces of all partitions and exterior panels were covered with cloth set in ordinary oil base paint, over which one coat of paint was applied. Second coats of paint were added on the inside and outside walls for aesthetic reasons, and a decorative finish was applied to the interior walls.

The exposed edges of the panels were protected by wooden crating during transportation and stock piling.

The panels were erected by setting them on the concrete slab in a slow-setting adhesive compound. Aligning the vertical edges close together, a specially designed heater was inserted between the edges In order to reactivate the thermoplastic coating. To prevent heat from escaping, a vertical wood strip was placed over the joint. When the adhesive was reactivated, the heater and wood backing strip were removed, and the one panel was shoved manually against the other.

After all the wall panels were in place, the prefabricated plywood roof sections were hoisted into place and adhered to the top edges of the exterior and interior walls.

A look at the performance record of this foamed glass house reveals that it has been economical to heat since the 4″ wall has a 0.09 coefficient of thermal transmission. Also, the homogeneous foamed glass reduced the air infiltration to a minimum. In the coldest months, the tenant uses slightly over 80 gallons of oil. The greatest heat loss is at the perimeter of the concrete slab.

In addition to its resistance to heat transfer, this material has very good resistance to moisture penetration. Some small penetration occurred at the joints of panels. At these points, caulking compounds were applied which remedied the situation.

The house has weathered the elements for ten years and has proven structurally sound against high wind, including “Hurricane Hazel.” The cost of the experimental unit was $14, 117, This included all material, labor, trial installations and development work. It was estimated that the potential cost of the same unit produced on a mass-production basis and erected by an experienced crew would run about $7,600 using 1949 costs.

figure 1The newest use of foamed glass is in the acoustical absorption field. Foamed glass, as originally manufactured, is a completely closed-cell material. In order to give the material sound-absorbing properties, foamed glass with open cells has been develop­ed. A unit is now being produced which measures 13-1/2″ x 13-1/2″ x 2-1/2″ having four 2.1/2″ square x 1/2″ thick pads on the back for mounting, to leave a 1/2″ air space behind each unit. This unit is designed to be used as a “patch absorber,”

figure 2These foamed glass units (Fig. 1) are incombustible, rigid, and dimensionally stable. They will not shrink, warp or change dimension with changes of temperature or humid­ity. The units are especially designed as a sound-conditioning material to provide the architect or designer with a product whose prime function is sound absorption, diffusion and control. By the proper placement and spacing of these units in a room, the reverberation time and diffusion of the sound waves may be closely controlled.

figure 3Let us look at how the foamed glass sound absorbers are adapted in a room to provide good listening conditions. For example, if we decided that a particular room is to have a certain desired reverberation time, and calculated that “x” amount of Sabina of ab­sorption is required, knowing the number of Sabina required, we divide this figure by two which gives the number of absorbers required, since each foamed glass unit absorbs an average of 2.0 Sabina over the speech frequency range.

figure 4For good acoustics, the sound reflection must be diffused and must not give a direc­tional impression. To accomplish this, the absorbing units should be distributed on the surfaces of a room and not concentrated on one surface or in large areas. This can be done by the “spot-and-patch” technique. This consists of spacing absorbers to provide contrasting reflection and absorption surfaces. With foamed glass unit absorbers, this is easily done because of the independent unit design that allows spaced or cluster mounting on wall and ceiling areas.

In general, the upper areas of the wall and perimeter areas of ceilings in from the wall are used for mounting the units. In classrooms or auditoriums, the units are placed in larger numbers around and toward the listening (audience) end. At the speaking  end, the units are few or nonexistent, for reflective reinforcement. In areas of general noise (cafeterias, swimming pools, etc.) the units are placed uniformly around wall and ceiling areas. Figure 2 shows foamed glass absorbers being placed on the wall. Figure 3 shows a classroom treatment, and Figure 4 shows the units on the walls and ceiling of a swimming pool.

figure 5Another use of foamed glass has been in the construction of cold storage warehouses. Blocks of foamed glass have been erected and fastened to the steel framework forming the outside wall where they also serve as insulation. Foamed glass blocks have also been placed between or over bulb purling to form the structural roof deck. Figure 5 shows foamed glass being erected against the outside framework of a large freezer.

figure 6Figure 6 shows foamed glass being used on a large brewery. Foamed glass walls built in this manner are usually 7″ to 8″ thick and are erected in two layers, with horizontal and vertical joints staggered to prevent any thermal short circuit. The outside of the wall Is usually finished with stucco or metal siding. If metal siding is used, horizontal wood sleepers are im­bedded in the outer layer of foamed glass to facilitate fastening of the metal.

figure 7One might question how this construction stands up structurally. Wind load tests have been run on a ICV -0″ x Z01-0″ x 8″ thick foamed glass wall panel. Before excessive deflection took place, the wind velocity exceeded 78 mph. The panel tested did not have an out­side finish, which would add to the structural strength. Also, the foamed glass is rigid, having an ultimate compressive strength of 100 lbs. per sq. in., and the material is not affected by moisture or changes of humidity, which insures against sagging or buckling of the wall.

Walter Lovett was a visionary in 1960. We discussed the above in a few blogs about 55 years later: floating , Acoustic absorption with cellular glass and  Houses with cellular glass walls. 

Measuring thermal conductivity is not so easy …

logo_smallMeasuring the thermal conductivity seems to be easy. A stable temperature gradient is generated over a sample and the heat flow through this sample is measured . The thermal conductivity is this heat flow divided by the temperature gradient, section and multiplied with the thickness. But it seems not that easy. A recent  publication  on the website of Aalborg shows that at least measuring the thermal conductivity of cellular glass is not straigthforward. Indeed, in four cases, the declared value of the maufacturers is lower than the measured value. In the case of GLAPOR, I selected and transported the samples myselves, which reduces the risk of wrong sampling to almost zero.

All measurements are done with the Guarded Hot Plate EP500 from  Lambda Meßtechnik.  This is a one sample Guarded Hot Plate, which is described in the standard EN12667, where we find the following setup.

GHPoneplate

Samples can be easiliy loaded in this system and it should be perfect for students to be used. Nevertheless, it is impossible that 4 products from two manufactures are not in line with the published declared value with 10% exceedance. For that reason, we think that misuse or a defect of the equipment is the reason of the high measured thermal conductivities.

 

 

 

Magazine Haller Kreisblatt reports about EPS and XPS thermal insulation

logo_smallHaller Kreisblatt is a German local news paper in the Altkreis Halle region. It came with the following contribution. In the following, we give a Google translation of this contribution:

Never again polystyrene for urban buildings? UWG wants to do without the insulating material

190507-1820-211606285

Umstritten: Das Dämmen von Gebäuden mit Styropor. Foto: Fotolia (© www.ingo-bartussek.de)

Thermal insulation of urban buildings: The Group of Independent Voters will table an application for the future waiver of the material in the Building Committee Hall . “This topic has been occupying me for years. I just can not understand how you can stick such a Sch … to the house. “Lack of understanding and a trace of annoyance resonate when Jürgen drawl on the topic of polystyrene as insulation material speaks:” If you consider what there in the future when we come to waste disposal and what we leave behind for our children? “, the civil engineer asks a rhetorical question that no-one can yet conclusively answer.

That the insulation of buildings with styrofoam, as polystyrene commonly referred to, is anything but unproblematic, has been criticized by experts for years (see criticisms below). This has now induced the UWG Group to propose in the Committee on Construction and Transport that in the future, urban buildings should no longer be styrofoam-insulated. The explanatory statement states: “The production of styrofoam from fossil petroleum consumes vast amounts of energy. It emits a lot of CO 2 (climate-damaging greenhouse gas). “

Different views on the subject of mold

In addition, the UWG points out that Styrofoam despite fire protection class B in the event of fire releases strong smoke and toxic gases. In addition, it could come through the insulation with Styrofoam to increased mildew. In its report to the committee, the administration explains that in the course of the renovation of City Hall II on Graebestrasse rock wool and, alternatively, polystyrene as insulation were already tendered. The statement that Styrofoam promotes mold growth, however, does not want to leave the city’s building administration in such a position: “In a technically correct installation, the risk of mold formation is always reduced and not increased.

In his practice as a civil engineer, Jürgen Deichsel has, however, according to his own data, often experienced that work was not carried out properly, and after a few years, defects in the insulation were visible: “Styrofoam often does not last longer than 30 years and then has already been revised In addition, the expert criticizes that, according to his observation in the past, the necessary fire bars have not been sufficiently installed in many buildings, in order to prevent the fire from jumping from one floor to the other in the event of a fire, as a presbyter Tiller had to report that there is a condition of the state church, which prohibits the use of polystyrene in church buildings:”Steinwolle was used for the cultivation of the kindergarten in Künsebeck and also with the new building of the device at the Neustädter Straße no polystyrene is used.”

In its draft resolution for the committee meeting on Thursday evening from 17.15 clock in the town hall hall, the administration accepts the request of the UWG and advises to renounce in the future, in principle, the use of polystyrene in urban buildings. Exceptions should be made to the committee on a case-by-case basis. The decision on the application, however, the policy.

 INFO
Many criticisms
  • For many years, lobbyists and politicians have been campaigning to keep houses airtight with polystyrene, better known as styrofoam. Meanwhile, the critical voices are multiplying, stating reasons against the use of the insulating material made of petroleum.

Toxic HBCD

  • Older insulation boards contain the bromine compound HBCD (hexabromocyclododecane). In the event of a fire, it should prevent the fire from spreading over the entire façade. Already in 2008 it was included in the list of toxic substances and banned worldwide. However, it has only been possible to use insulation materials in Germany since 2015. Despite the ban, plates treated with HBCD were allowed to be sold until August 2017.

Hazardous waste?

  • Meanwhile, styrofoam plates treated with HBCD were classified as toxic waste and had to be disposed of as hazardous waste. Because there were massive disposal bottlenecks, the classification of the policy was withdrawn. Since August 2017, styrofoam treated with HBCD has therefore only to be disposed of separately.

Use of biocides

  • Styrofoam is also criticized because it often adds chemicals (biocides) to the material to prevent algae and mold on insulated house walls.

energy balance

  • Controversial is the energy balance of Styrofoam. Critics note that she turns negative when her lifetime is 50 years old

GLAPORlogo

The life time of EPS/XPS should be only 30 years while 50 years is given in the Environmental Product Declarations. Also flame retarders are (have to be ) used, which are problematic for disposal. On top of that, biocides are present to avoid mold and algae. All these large problems are NOT present in GLAPOR cellular glass and its life time is a lot larger than 50 years, like every bottle and window can tell you. Indeed, GLAPOR is foamed from bottles and windows.

Magazine “Das Haus” about Radon and cellular glass

logo_small“Das Haus” is a German magazine about building and decorating houses. In a recent number, they have a contribution about the risks of Radon. In this contribution, they advice to use cellular glass as a seal against the radon gas.  Hereunder, you will find a Google translation of the German article, which can be understood.

dashaus

Radon is a radioactive noble gas naturally occurring in granitic soils. Especially in regions in Baden-Württemberg, Bavaria and Saxony, the gas is pouring out of the ground. In unsealed basements and ground floors, it can collect and affect the health of residents. Radiation experts warn of this danger: After smoking, radon is one of the leading causes of lung cancer.

You can not smell, feel, see or taste it. Nevertheless, radon is a serious health hazard. Barely noticed by the public, it is the second leading cause of lung cancer. In the Federal Republic of Germany, 2,000 people suffer from this cancer each year due to radon. In the EU, according to recent studies, 20,000 people per year are affected. Radon is still a source of danger asbestos or diesel soot.

Radon is a big radioactive strain on humans

But what is Radon anyway? Radon-222 is a naturally occurring noble gas produced from uranium disintegration processes. It is itself radioactive and (according to information video of the Federal Office for Radiation Protection) “the largest radioactive pollution for humanity”. Like uranium, it occurs in all soils and rocks – whether it poses a threat depends on the uranium content and the permeability of the soil. Typical areas with high radon concentrations in this country are parts of the Erzgebirge and the Bavarian Forest, the Vogtland and the Eifel. Particularly affected are areas with granite and volcanic rock or black slate.

One in ten households is exposed to too much radon

As a gas, radon spreads easily in the pores in the soil, from where it then enters the atmosphere. “Depending on the region, the air at a height of 1.5 m contains between 5 and 30 becquerels per cubic meter (Bq / m³) of radon a year,” explains Jan Henrik Lauer of the BfS Press Office. That alone is not a cause for concern, because the gas is quickly distributed in the outside air. The situation is different in buildings: leaking foundations, even along pipelines, can cause the gas to reach basement rooms and accumulate in the room air. The radon finds its way to the upper floors via cable ducts, stairs and leaking ceilings. According to the BfS, every tenth household is exposed to such an increased radon load of 100 Bq / m³.

Clues as to how high the burden of radon in a region is, call authorities such as environmental and health offices and the radon card of the BfS. But that does not say anything about the actual burden on your own home. Thus, the brochure “Radonschutz measures” (a planning aid for new and existing buildings of the state of Saxony) states: “Large differences are even within a plot … not uncommon”.

A soil survey can show the radon load

GLAPORlogoCertainty brings a Bodegutachten before buying a property. Based on this, it is already possible to prevent a radon load during the construction phase, eg with a foam glass seal or a radon drainage. Even in existing buildings, the danger is not helpless: already consequent airing, especially in the cellar area, is an important step to prevent the enrichment. Likewise, a sealing of the cellar door can be helpful. But if you also use the basement as a living space, larger steps are required. A general overview of such measures is provided by the Radonhandbuch Deutschland.

A Radon standard is currently being prepared to provide planners and contractors instructions. This will also be necessary because in 2018 a new Radiation Protection Act will come into force, which will also be dedicated to protection against radon. However, it incorporated the Radon reference value of 300 Bq / m³ from the EU. The Ministry of the Environment and the BfS already see a need for action for recreation rooms at radon concentrations above 100 Bq / m³ (annual mean). According to Jan Hendrik Lauer, it should be examined here “whether these can be reduced below 100 Bq / m³ with reasonable effort. In rarely or only temporarily used rooms, higher concentrations can be tolerated “. Whoever picks up a beer or potatoes from the cellar, does not need to be active.

Tenants are not entitled to protection against radon

However, while under the new law on workplaces there is an obligation not to permanently exceed the reference value of 100 Bq / m³, tenants in living spaces are not entitled to measures by the homeowner. Here you should look for the conversation with the landlord: Often, any necessary rehabilitation measures can be so connected to the Radonschutz that no excessive extra costs are caused. However, it is only possible to determine how high the values ​​are by means of a professional on-site measurement over a longer period of time.

The most important measures against radon

You can hardly escape the radon. Most important measure: a professional long-term measurement. And then: ventilate consistently, seal off creeping paths, vacuum the gas.

Who informs about radon?

  • The radon map with values ​​from more than 2,300 measuring points nationwide shows how high the regional exposure to radon is. These can be found online at the BfS at  https://www.bfs.de/DE/themen/ion/umwelt/radon/boden/radon-karte.html
  • The environmental ministries of individual federal states also provide overview maps.
  • The Radon manual with practical information from the BfS can be downloaded here:  www.raumanalytik.de/media/radonhandbuchdeutschland.pdf
  • The brochure “Radon-protective measures – planning aid for new and existing buildings” of the state of Saxony.
  • Measuring instruments are available from specialist companies.

The original article can be found in pdf1 and pdf2. In case cellular glass is chosen to seal the house, it makes sense to use the large GLAPOR boards to reduce the number of joints.

 

Cellular glass is radon tight … so what?

logo_smallToday there are too much lawyers on this world and they are boring themselves to death. And as a consequence, they become politican and find out laws, which we do not need. One such a thing is the radon tightness of closed cell cellular glass.

Gavel in courtroom working office of lawer legislation.If cellular glass is vapour tight, we can expect that it is also Radon tight. But this logic is not accepted by our lawyer world. For that reason, GLAPOR has ordered a RADON diffusion experiment with is described in this report.

radonexp

What-is-Radon920x426_menuIndeed, a layer of 50 mm cellular glass is 250 times the diffusion length, which means that Radon cannot diffuse through the cellular glass without decaying in the cellular glass. In that way, it is impossible that Radon decays in the lungs of humans and animals behind the cellular glass.

01_06_04It is needed to install the boards with hot bitumen (which is also Radon tight) but pinholes in the bitumen remain a small risk in the joints. For that reason, it is advised to work with large boards (GLAPOR cellular glass: 2800 mm x 1200 mm) to reduce the number of joints as much as possible. Dry installation of the boards will only minimally protect against Radon.

Styrene is probably cancerogenic for humans

logo_smallI was surprised when I found the following in the Lancet, a medical magazine. It states that: ” The Working Group classified styrene in Group 2A, “probably carcinogenic to humans” based on limited evidence in humans and sufficient evidence in experimental animals for carcinogenicity.”  This is a new classification since March 2018 because the older one gives a less dramatic one.

whale1Like described in this recent paper and this older paper, styrene is used to produce polystyrene and the latter one is foamed to expanded (EPS) or extruded (XPS) polystyrene. I don´t believe that XPS or EPS or cancerogenic during the use as thermal insulation but disposal is not straightforward.

Indeed, the landfill method is not a good method because these products are reduced spontaneously to small particles, which are not biogredable and end up in all kind of organisms and also later on in humans. Combustion has to be done above 1000°C to avoid all kind of flue gases while standard incinerators are working at 850°C.

For that reason, a lot of American cities have already banned the use of polytsyrene  for the following reasons:

  • It does not biodegrade. It may break into small pieces, even minuscule pieces. But the smaller EPS gets, the harder it is to clean up.
  • It is made of fossil fuels and synthetic chemicals. Those chemicals may leach if they come in contact with hot, greasy or acidic food. Yes, they keep your coffee hot – but they may also add an unwanted dose of toxins to your drink.
  • Animals sometimes eat it. Turtles and fish seem to mistake EPS for food, and that can kill them. Not only can they not digest it, but the foam could be full of poisons that it has absorbed from contaminants floating in the water.
  • It can’t be recycled. Some commercial mailing houses may accept packing peanuts, but for the most part community recycling centers do not accept throwaway foam food containers

To me it is clear. EPS and XPS are not needed in the building industry and can be replaced by cellular glass. GLAPOR cellular glass is in that case the most ecologic alternative.

Protecting against radon with cellular glass boards

logo_smallRadon is a natural radioactive gas that causes cancer when it is present in the lungs. In regions with a lot of Uranium and Thorium in the soil, this Radon gas is present in higher concentrations. When accumulated in a building, a real health problem is present being the second cause of lung cancer. The situation in Europe is shown in the following picture. Everything more tha yellow deserves measures against radiation.

radon_europe

radonThe American government educates its citizen how to build houses to avoid Radon accumulation like shown in this leaflet. The standard method is to use a ventilated space under the floor.

The need of this ventilated space is clear if cellular glass is not taken into account. A German paper of Keller shows how Radon diffuison is measured in building materials and gives a tabel (see hereunder) with the diffusion length for Radon. This is the length Radon diffuses before it decays with harmfull radiation. A Radon barrier should have a thickness three times this diffusion length to withstand 95% of the Radon.

table

It is clear that a concrete beam of 200mm thickness is on the limit and that for polymer materials the joints are uppermost important. Indeed, not using a ventilated space under these systems is a risk.

radonBut like already mentionned in a previous post, cellular glass boards are a perfect light barrier against radon. A compact layer of cellular glass boards in bitumen is a perfect screen (100 mm cellular glass is 100 times the diffusion limit of Radon) serving also as thermal insulation and avoiding expensive radon ventilation systems. The bitumen joints are the only risk but using large GLAPOR cellular glass boards  280 x 120 cm reduces this risk for radon leaks with a factor 12  compared with 59.9 x 44.9 cm boards.

On top of that, if for passive housing these GLAPOR boards are installed on a thick layer of (implicit ventilated) GLAPOR cellular glass gravel with the RDS system, even the presence of negligible concentrations of Radon in the house is eliminated and a passive housing standard thermal insulation is installed under the floor at a very good price.

The contributions of Elena Yatsenko for cellular glass

logo_smallProf. Elena Yatsenko has a chair at the Platov South-Russian State Polytechnic University (NPI) in Russia. While the universities of Aalborg, Ljubljana and St. Petersburg are recycling glass, prof. Yatsenko is converting slag into cellular glass.

str-12-13

I found the following publications:

yatsenko

Today, most of the recycled glass is used for the standard glass industry and a minor part, which cannot be recycled for bottles and windows is today used for cellular glass. However, reusing slag waste for cellular glass is a new step in the recycling industry. Today, slag is used in the cement industry and also slag wool can be produced for thermal insulation. But it seems that a new future, namely cellular slag is arriving. Indeed, glass powder for foaming should be at least 10 times more expensive than slag powder.