Development of Foam Glass as a new Insulating Building Material
Muhammad Tariq Saeed*, Muhammad Saadet, Mustansir Billah Bhatty
Muhammad Afzal Khan & Ahmad Din (Late)
Abstract
Uniform quality of foam glass has been developed from local waste soda-lime-silica glass powder containing
SO3 contents about 0.3% by mixing various foaming agent such as carbon powder, graphite, cellulose material
or saw dust and firing the mixture at about 700-900oC. A study of important properties like density, thermal
conductivity, thermal expansion and moisture absorption has proved it to be a good insulating building
material. Useful applications in other fields have also been suggested.
Introduction
The purpose of the present study was to develop the
product from local raw materials and to introduce it
into the local market as cheaper and stronger a new
insulating material. It is planned to utilize the
waste of soda-lime-silica glass which is abundantly
available in Pakistan. About 600-700 tons of glass is
daily produced in Pakistan. About 70% of which is
packable material and 30% goes as a waste called
glass cullet. This broken glass can be used for the
production of foam glass. In Gujranwala, the broken
waste glass is pulverized to powder form for sale to
various factories. It usually has a mesh size of 40 to
60. Apart from its utilization in foam glass it is also
abundantly used for glazing the cheaper type of
pottery. Foam glass which is also called as cellular
glass is rigid, fire proof, odourless, light weight
enough to float on water and an excellent insulator.
Foam glass contains great number of tiny bubbles of
regular size packed closely together and separated
from each other by thin walls. Any glass powder can
be changed into foam glass by mixing in it a minor
percentage of foaming agents like carbon, graphite,
coal, saw dust, sodium sulphate, calcium sulphate
and calcium carbonates. The mixture after fine
grinding is heated slowly in a closed or covered
container to about 700-900oC and is maintained
there for about an hour to complete the reaction.
The mass swells to fill the container and is then
slowly cooled to room temperature. The product so
obtained is classified according to the uniformity of
the diameter of the pores of the product, small sized
pores have greater mechanical strength and high
density while medium and larger sized pores have
less strength and low density which are considered
as inferior in quality for commercial purposes [1].
Foam glass, because of cellular structure finds vast
use and an insulating material. The closed
boundary walls of the pores do not allow the
moisture to pass or absorb and also inhibit heat or
coolness, thereby making the foam glass as a best
insulating material for roofs, ceilings and walls. Its
substantial mechanical strength makes it useful for
the partitions in the halls, cold storages and in walls
facing insulation.
Glass & Ceramics Research Centre, PCSIR Labs. Complex, Lahore – Pakistan
Corresponding Author: M. Tariq Saeed. E-mail: [email protected]
13
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Journal of Pakistan Institute of Chemical Engineers
Experimental
It was planned to utilize cullet (waste glass ) of sodalime-silica glass which is abundantly available in
Pakistan. The most suitable glasses which can be
used for the production of foam glass are of
container glass and window glass. The waste glass
of the following composition is used for development
of foam glass [2].
SiO2
65-73%
Na2O
14-18%
CaO
6-10%
Al2O3
0.5-2.00%
MgO
0.2-3.00%
SO3
0.2-0.6%
Fe2O3
0.02-0.08%
The waste glass whose composition falls in the
range of above mentioned glass composition is
easily available from Gujranwala in powdered form.
This powdered glass has mesh size 40 to 60 mesh.
The powder was analyzed in the analytical
laboratory before experimentation. The analysis
results are as under:
Vol. XXXVIII
make the material castable in desired shape.
Usually tiles and bricks were fabricated in this case.
Slabs of 4″x8″x2″ were fabricated; these slabs were
dried in open atmosphere naturally or dried in a
drier. After drying, the samples were heated in an
electrical furnace. The samples in the furnace were
slowly and gradually heated. The temperature was
raised at a rate of 4oC per min upto the temperature
500oC. After 500oC it was raised at rate of
1.5oC/min. [3]. Slow heating causes more strength
due to uniform tiny pores while hazard firing causes
irregular large pores which produced foam glass of
less strength. Foaming of samples was occurred at
o
o
temperature from 750 C to 950 C depending upon
the composition and softening temperature of the
particular glass. The evolution of gas forms voids in
the material, which swells to fill a closed container.
The voids amount to be more than 90% of total
volume. The samples at their foaming temperatures
were maintained for about one hour. After that the
furnace was switched off and samples were allowed
to cool gradually to the room temperature in the
furnace. After 24 hours, the samples were taken out
from the furnace. The samples were cut into
required dimensions. The properties like density,
coefficient of thermal expansion, thermal
conductivity and water absorption were studied.
The results are shown in Table -1.
SiO2
=
71.18%
Na2O
=
16.7%
CaO
=
10.2%
Effect of mesh size of raw materials:
Al2O3
=
1.34%
MgO
=
0.18%
SO3
=
0.35%
Fe 2O3
=
0.05%
Too coarse particle size of raw materials creates non
uniform foaming, irregular cell size and high
foaming temperature. While too much fine particle
size of raw materials resulted high density foam
glass, high crushing strength and the core of the
body remained unfoamed. Fine particles produced
tiny pores of foam glass which resulted less swelling
of the material [4].
Glass powder passed through mesh 40 and retained
on mesh 50 was taken for experimentation
.Foaming agent 2-4% was mixed in the glass
powder. Small addition of borax and boric acid
catalyses the reaction. The batch was prepared in a
plastic container. 1 to 2% solution of sodium silicate
is added as a binder. The function of binder is to
Effect of Foaming Agent:
Type of foaming agent plays a vital role in the
production of foam glass. Pore size, density and
strength depend upon the foaming agent used.
When fine carbon powder is used as a foaming
2010
M. Tariq Saeed, M. Saadet, Mustansir Billah Bhatty, M. Afzal Khan, Ahmad Din (Late)
agent, it produced grey coloured material having
tiny cells, high density and high crushing strength.
While saw dust produced light grey colour foam
glass having relatively large cells of diameter 1.5 to
2mm, light weight (less density) and less crushing
strength. As the product has light colour so many
coolurs can be produced in it. The properties of foam
glass also depend on the composition of glass
powder used. Soft glasses like container glass and
window sheet glass produce good quality foam
glass. For hard glass like borosilicate glass, foaming
occurs in the temperature range of 950-1150oC [5].
Addition of magnesite and dolomite in this
composition improve the mechanical and chemical
resistance of the foam glass [6].
Effect of Heat Treatment:
The samples after complete drying are slowly and
gradually heated in an electric furnace. Controlled
heating and cooling is very important. Temperature
should be raised at a rate of 4oC per min. upto the
temperature 500oC.After 500oC, it should be
increased at a rate of 1.5oC/min. Controlled heating
rate causes complete foaming of the samples. While
fast heating rate left behind some unfoamed
material in the core of the sample. Fast heating rate
also produces irregular pores. Some pores are very
large in size while others are small in size. After
foaming, cooling rate of the samples should also be
the same as heating rate otherwise fast cooling will
cause thermal shock i.e. damaging of samples.
Results and Discussion:
Cellular or foam glass can be developed on
industrial scale for insulation of roofs, side-walls
and erecting of partition walls. It is not only a very
good insulator but also a good barrier against sound
as well.
From the studies of properties as shown in Table-1.
It is concluded that satisfactory quality of foam
glass can be developed quite cheaply from
indigenous waste glass powder in our country. The
process does not involve huge economy and its
15
know-how is so simple that it requires little
involvements of unit operations. It can replace
fibre-glass which is an imported material in the
field of insulation of buildings, industrial pipings,
boilers and cold-storage godowns. A plant on
industrial scale can be designed easily to produce 5
to 6 tons of foam glass daily. The rough surface of
bricks and slabs provide good adherence of mortar
which may consist of bitumen coal mixed with some
silicate and Portland cement. The mechanical
strength gives the possibility of nailing through the
slab for tightening. Its easy cutting by simple tools
like hand saw can convert it to any shape and size.
The texture of fine pored foam glass approximates it
like that of pumice stone. Therefore it can be used as
mild scrubbing material in laundry washing and for
other purposes.
Properties and uses:
Foam glass has entirely different properties from
those of ordinary glass. It could be sawn, chiseled,
filed and drilled. It has light in weight and had a
high heat insulation capacity. By reason of these
properties, it is superior to other insulting materials
for construction purposes. The comparison of gross
weight and heat conductivity of foam glass with
other materials is shown in Table-2 [7].
Cold Insulation:
This classification comprises insulation of walls,
ceilings, and floors of cold-storage rooms or
buildings, as well as refrigerated equipment and
piping in the temperature range of – 196 to 16oC
o
(-320 to 60 F). The lowest temperatures in this
range are encountered in tanks for liquid air
storage. Because cellular glass is imperious to gases
and vapors, it is protected against internal
condensation of moisture. It is necessary, however,
to vapour-seal all joints and seams with a suitable
mastic material to prevent water vapour from
penetrating through these spaces and condensing
on the chilled inner surfaces. Table-3. Lists
insulation thicknesses ordinarily recommended for
cold-storage rooms and buildings. Local conditions
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Journal of Pakistan Institute of Chemical Engineers
may modify these values in individual cases. When
used for floor insulation, the cellular glass must be
covered with a layer of material, such as cement, to
distribute concentrated loads over a large area of
the insulation [8].
Hot Insulation:
This classification describes the temperature range
100 to 482oC (212 to 900oF). The glass can be used in
contact with metal surfaces upto the high end of this
range. It is installed by conventional methods used
for block or pipe-cover insulations. Metal bands
secure the insulation in place, although on large
surfaces welded steel pins are also used. Provisions
should be made for differential expansion between
the insulation and metal surface, by designing
appropriately spaced expansion joints. Above
200oC, some provision for thermal stress relief
Vol. XXXVIII
should also be made. A variety of reinforced mastic
coatings or metal jacketing is available for finishing
outer surfaces [9].
Thermal conductivity:
Cellular glass has a low value of thermal
conductivity. It is non-combustible, and each cell is
enclosed with its own barrier against convection
currents and moisture diffusion. Because it is
impervious to water vapour, condensation cannot
occur within the body of the material and,
consequently, it is particularly suitable for lowtemperature applications below 32oF. It retains its
rigidity and mechanical properties at temperatures
upto 800oF [10].
2010
M. Tariq Saeed, M. Saadet, Mustansir Billah Bhatty, M. Afzal Khan, Ahmad Din (Late)
Table 1: Properties of Cellular Glass
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Journal of Pakistan Institute of Chemical Engineers
Vol. XXXVIII
Table 2: Comparison of density and heat conductivity of foam glass with other materials
Table 3: Thickness of Cellular Glass Insulation Recommended for Cold Rooms and Buildings
Conclusions:
Uniform quality of foam glass has been develop from local waste soda-line-silica glass powder by mixing
with foaming agents and characterised. It is foam that formulation 3 & 11 in table 1 are excellent for the
development of foam glass.
2010
M. Tariq Saeed, M. Saadet, Mustansir Billah Bhatty, M. Afzal Khan, Ahmad Din (Late)
Acknowledgement
The help of M/s. Muhammad Amin, PT,
Muhammad Hussain Sr. Tech., Abdul Ghafoor, Sr.
Tech. and Muhammad Ali, Furnace Builder in
fabrication of clay crucibles, glass melting and in
mechanical work is acknowledged.
References
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[4] Yatova, R and S.A. Monenko. High melting
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[5] Buran, N.Y and M. Sander. Properties of foam
glass. Ceram Ind., 12; 161-164 (2004).
19
[6] Seki, m and R.T. Uneno. Foaming of borosilicate
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