Note: Descriptions are shown in the official language in which they were submitted.
107~181
This invention relates to compositions of matter com-
prising a cellular aggregate distributed in a hardenable or
hardened binder or matrix material.
It is known to use cellular bodies, e.~., bodies of
expanded clay, clinker or glass, as an aggregate in mouldable
compositions for reducing the weight of products formed there-
from or for modifying their thermally insulating properties.
Problems arise in formulating such compositions to
achieve the required combination of properties. This is due
in part to a conflict between different demands. For example
a problem is involved in achieving light weight products without
too great a sacrifice of mechanical strength, and this is
particularly so if at the same time it is desired to form moulded
products having good thermally insulating properties.
Such problems have been encountered, inter alia, in the
production of light-weight concretes.
Due to the incompatibility of various ideal properties
a compromise necessarily has to be made.
The object of the present invention is to provide a
composition having a favourable combination of properties
which is not attainable by known compositions.
According to the present invention there is provided
a composition of matter comprising a cellular aggregate distri-
buted in a hardenable or hardened binder or matrix material,
characterised in that the aggregate consists of or includes (i)
a fraction of cellular glass beads (hereafter called "fine
fraction beads") of mesh sizes up to 3 mm, individually con-
taining one or more interior cells with a maximum cross-sectional
dimension at least 0.3 times the mesh size of the bead and
having a non-cellular or micro-cellular surface skin, and
~ii) a fraction of cellular glass beads (called "coarse fraction
beads") of mesh sizes above 3 mm, individually having a multi-
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: . .
1077~81
cellular core with a cell population per unit volume substantially
higher than the population of said interior cells in said fine
fraction beads and likewise having a non-cellular or micro-
cellular surface skin.
It has been found that by employing as an aggregate
cellular glass beads of a size range distribution extending
above and below 3 mm, and using for the fine and coarse frac-
tion beads which have different structural features as above
specified, it is possible to make compositions which in the
hardened state have remarkably high strength in relation to
their specific gravity and their thermal conductivity. In
addition, the fine and coarse fraction beads together confer
advantageous sound insulating properties on products formed
from the compositions.
It is another advantage of the invention that a
good distribution of the glass beads in any required volume
of binder or matrix material can be easily achieved. The facil-
ity with which the beads can be mixed with a hardenable binder
or matrix material is due to their composition and physical
form and tends to increase the closer the beads approximate
to a truly spherical shape. It is preferable for the glass
beads employed in carrying out the invention to be of substan-
tially spherical form but that is not essential. Beads of
any rounded form, e.q., ellipsoidal beads, can be used.
In the preferred embodiments of the invention the ;~
fine and coarse fraction beads have substantially water-
impermeable surface skins. This feature affords the advantage
that mouldable compositions, e.~., cement, can be made up
without having to reckon with water absorption by the beads
and water will not be trapped in the beads when the product
dries. In addition the thermally insulating properties of the
product are not likely to be impaired by moisture absorption
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1~771~3~
by the beads. Cellular glass beads can be considered to have
substantially watcr-impermeable skins if the water absorption
after immersion of the beads in water for 24 hours is less than
20% by weight.
For any given type of composition, the best volume
ratio between the cellular glass beads and the binder or matrix
material will depend of course on numerous factors including
the properties of the binder or matrix material and the strength,
thermal conductivity and other properties of the product to
be formed.
Preferably the coarse fraction beads cover a size
range extending up to at least 8 mm. Generally speaking it is
preferred not to use beads above 30 mm in size and in most
cases it is advisable to observe a maximum size much below 30
mm. The use of coarse fraction beads up to at least 8 mm in
size promotes a very favourable strength/density ratio for
products formed from the composition. In certain compositions
according to the invention the said coarse fraction beads
cover a size range extending up to at least 16 mm.
The fine fraction beads may and preferably do cover
a size range extending substantially below 3 mm. For a given
weight of fine beads, a reduction in their size tends to result
in a reduction in the thermal conductivity of the product and
makes it easier uniformly to distribute a substantial proportion
of such beads in the composition. Taking these considerations
into account, certain compositions according to the invention
contain fine fraction beads which cover a size range extending
down to below 1 mm in size.
me fine fraction beads preferably have a bulk density
of not more than 350 kg/m3. The observance of this condition
makes it easier to make up compositions having a low thermal
conductivity and a reasonably high compression resistance.
)77181
In certain compositions according to the invention the said
fine fraction beads have a bulk density between 250 and 350
kg/m3.
The coarse fraction beads preferably have a bulk
density lower than the fine fraction beads. In certain compo-
sitions according to the invention the coarse fraction beads
have a bulk density of not more than 200 kg/m3 and most pref-
erably a bulk density between 80 and 200 kg/m3. The use of
coarse fraction beads in such categories is conducive to
achieving products of low density.
The binder or matrix material is preferably cement,
e.~., Portland cement. It is in this field that the invention
affords the most important advantages. The need for concretes
which combine lightness of weight with good mechanical strength
and low thermal conductivity has stimulated considerable
research in recent years and the invention makes an important
contribution in this field. In particular, concretes incor-
porating fine and coarse cellular glass beads with the charac-
teristics required according to the present invention can be `
formed into monolithic structures combining load-bearing and
thermally insulating properties. Such concretes can be used,
for example, for forming walls, floors, flat roofs, cladding
layers, blocks and other prefabricated components for struc-
tural or other purposes.
Reference has already been made herein to preferred
values for the size range covered by the cellular glass beads.
The values which have been given are applicable to compositions
containing various kinds of binder or matrix material. Exper-
iments have shown that when applying the invention to the
production of light weight concrete, l.e., when using cement
as the binder or matrix material, the most useful results can
be achieved when adopting one or more of the following condi-
: :
77181
tions (a3 to (f):
(a) the volume of the combined fine and coarse frac-
tions of beads is at least 50% of the dry volume
of the composition,
(b) the coarse fraction beads are wholly or predomi-
nantly in the size range 8 to 16 mm,
(c) the coarse fraction beads are classifiable into
two sub-fractions respectively containing beads
above and below 8 mm in size and the bulk volume
of the 3 to 8 mm sub-fraction beads is less than
the bulk volume of the beads of the other of said
sub-fractions but greater than the bulk volume
of the fine fraction beads,
(d) the ratio between the bulk volumes of the coarse
fraction beads and the fine fraction beads is be-
tween 6:1 and 1:1,
(e) the proportions by volume of the fine and coarse
fractions of beads in the composition is such
that the dry composition has a thermal conductiv-
ity below 0.25 kcal/mhC,
(f) the proportions by volumes of the fine and coarse
fractions in the composition and their size dis-
tribution are such that the dry composition 28
days after setting has a density below 950 kg/m3
and a compression resistance of more than 60
kg/cm2 (preferably 70 to 120 kg/cm2).
Compositions according to the invention (not only
those wherein cement is used as binder or matrix material) may
incorporate one or more other aggregate components additional
to the specified fine and coarse fractions of cellular glass
beads. For example the aggregate may incorporate other cellu-
lar glass beads which do not fall in the specified categories,
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-- ~077~81
As another example, in a light-weight concrete the aggregate
/ may incorporate sand in addition to the specified fine and
coarse fractions of cellular glass beads. The presence of
sand tends to increase the compression resistance of the
concrete when set and is therefore a useful addition in cases
where very high compression resistance is required and the
maximum permissible product density is not very low.
The invention can be employed in the formation of
compositions comprising synthetic polymeric material as binder
or matrix material. By applying the invention compositions
can be prepared which combine to a very advantageous degree,
good mechanical strength with good thermally insulating and
sound insulating properties. Such compositions are very use-
ful, e.q., in making prefabricated panels or other components
for use in buildings or other structures or for application
to form insulating layers or coatings in situ.
Suitable synthetic polymeric materials for use as
binder material include thermoplastic and thermosetting resins.
Examples of particularly satisfactory binder or matrix materials
are polyurethane (e.~., reaction product of toluene diisocyanate
and hydroxyl terminated propylene adipate), and phenolic (e.q.,
phenol-formaldehyde), epoxy (e.~., bisphenol A-epichlorhydrin)
and polyester (e.q., styrene modified ethylene glycol-diethyl-
ene glycol-maleate-phthalate) resins. Other suitable binder or
matrix materials include plaster and bitumens.
The glass beads can be beads of natural glass, for
example obsidian, basalt, rhyolite or perlite. Preferably
however the glass beads are made of manufactured glass, e.~.,
soda-lime glass or sodium borosilicate glass.
Compositions according to the invention can be set
in a mould or trowelled or otherwise spread, e.~., as is done
in conventional plastering or when using concrete to form
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` 1077181
concrete floors or other structures in situ.
Preparation of Fine Fraction Beads
Beads having the characteristics required for the
fine fraction beads can be produced, for example, by spraying-
drying a feedstock comprising a liquid medium containing glass
particles, and if necessary a cellulating agent, thereby to
form "green" beads in which glass particles are held together
by the binder and which contain a cellulating agent or gas
derived therefrom, and then firing such green beads to trans-
form them into cellular glass beads. In such a method the
size and form of the fired beads are related to the size and
form of the green beads resulting from the spray-drying step
and can be predetermined within close limits. When preparing
cellular glass beads by such a method it is recommended to
make up the feedstock, i.e., the slip containing the glass
particles, to a viscosity within the range 200 to 10,000 cps.
The liquid medium is preferably water in a proportion of less
than 50%, most preferably 20 to 40% by weight based on the
total weight of the slip. In the spray-drying step sufficient
evaporation of water from the individual drops can then occur
in very short heating periods. It is very satisfactory for
the glass particles in the slip to be particles of crushed
glass in the size range 10 to 250 microns, but this is not
critical. The binder may be dissolved in the continuous liquid
phase of the medium or in a liquid disperse phase and is pref-
erably a substance which becomes chemically integrated with
the glass during the firing of the green beads to glass-forming
temperature. Sodium silicate is a particularly satisfactory
binder. Other categories of binder which can be used include ~,
synthetic polymeric substances, e.~., phenolic (e.q., phenol- i
formaldehyde) and epoxy (e.~., bisphenol A- epichlorhydrin)
resins, polyester (e.a., propylene glycol-adipate-maleate
~77181
modified by styrene) and polyamides (e.q., a copolymer of hexa-
methylenediamine-adipic acid and hexamethylenediamine sebacic
acid). The cellulating agent may be a gaseous substance or a
substance or combination of substances which give rise to the
evolution of gas causing cellulation during the spray-drying
step or during subsequent firing of the green beads. Examples
of suitable cellulating agents are carbonates, e.q., sodium
bicarbonate, calcium carbonate, nitrates, e.g., sodium nitrate,
urea, and combustible substances such as carbon and sawdust.
In most cases the vaporization of the liquid vehicle of the ini-
tial slip will give rise to some cellulating effect and it is
possible to rely upon this vehicle as sole cellulating agent.
If the binder is suitably selected, cellulation can be brought
about by evolution of gas from thé binder.
The following is an example of such a method of pre-
paring beads suitable for forming the fine fraction or part of
the fine fraction of the aggregate of a composition according to
the invention:
Bead Preparation Method 1 (Fine Fraction):
An aqueous solution of sodium silicate (38 Baumé) was
mixed with powdered urea and glass particles in the size range 20-
100 microns. The glass particles were particles of an ordinary
soda-lime glass having the following composition in percentages
by weight: 70.4% SiO2, 12.78% Na2O, 12.14% CaO, 1.77% MgO, 1.92%
A1203, the remainder being impurities. 10.5 litres of sodium
silicate solution were used per 20 kg of the glass. The amount
of urea was equal to 2% by weight based on the weight of the glass.
Further water was added to adjust the viscosity of the slip to
substantially 3000 cps. With the aid of compressed air this slip
was sprayed into a drying column containing an ascending stream of
hot combustion gases coming from a glass firing furnace, and having
on entry into such column a temperature in the range of 200 to
400C. - 8 -
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1~77181
The drops leaving the spray head were of various sizes in the
range of 100 to 1000 microns. In the drying column the drops
were carried upwardly by the ascending hot gases and water
evaporated from the drops so that they became converted into
self sustaining beads individually containing glass particles
held together by sodium silicate as binder. At the same time
some decomposition of the urea took place with the evolution
of gases so that some expansion of the green beads took place.
These beads discharged continuously from the top of the drying
column and were collected preparatory to their delivery to the
glass firing furnace which was maintained at an operating
temperature in the range of 800 to 1200C. In this furnace
the green beads were carried upwardly by ascending hot gases
and the glass grains in the individual green beads softened and
sodium silicate became chemically integrated with the glass.
The beads expanded due to further decomposition of the urea
and increase of gas pressure within the beads. The green
beads fed into the furnace were thus converted into cellular
glass beads. These beads were discharged from the top of the
furnace and then cooled in a gas stream to below the softening
range of the glass before the beads were allowed to come together
in bulk. The cooled cellular glass beads were of more or less
spherical form and of sizes distributed over the range 150
microns to 2.5 millimetres. The beads were of cellular form
and had a bulk density of the order of 250 kg/m3. Most of the
beads at the lower end of the size range contained a single large
cell, the glass being confined to a thin surface skin. Most
of the beads at the upper end of the said size range contained
a plurality of large cells. All of the beads had substantially
water-impermeable surface skins. The surface skins of most of
the beads at the upper end of the size range contained micro-
cells. The presence of microcells were less in evidence in the
1077181
surface skins of the smaller beads. The small hollow beads
containing a single large cell and those larger beads which
contained a plurality of cells of which at least one had a
maximum dimension at least one third of the mesh size of the
bead could together be used as the fine fraction beads of a
composition according to the invention. By increasing the
amount of cellulating agent and/or by increasing the firing
temperature above the values given above, the average cell
sizes in the larger beads could be increased.
Preparation of Coarse Fraction Beads
Beads having the characteristics required for the
coarse fraction beads can be produced, for example, by forming
nodules of an aqueous pasty medium comprising glass particles
and a cellulating agent and subjecting such nodules to heating
and subsequent annealing stages. Provided the ingredients of
the mixture and the heating and cooling schedule are appro-
priate, the nodules become converted to beads of the required
structure. The mixture should contain only a small proportion
of cellulating agent, preferably less than 5% by weight based
on the weight of the glass. During the heating the glass
particles cohere and then coalesce, starting at the surface
of the nodules. Surface to surface cohesion of such glass
particles should occur before evolution of gas from the cellu-
lating agent. The nodules must be heated sufficiently to
allow expansion of the embryonic beads to take place under
the gas pressure but not to such an extent that such beads
collapse or that all of the molten glass becomes displaced
outwardly to the periphery of the beads.
The following is an example of a method of preparing
beads suitable for forming the coarse fraction or part of the
coarse fraction of the aggregate of a composition according to
the invention:
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~Cl 771~1
Bead Preparation Method 2 (Coarse Fraction)
Crushed soda-lime glass with a mean grain size of 6
microns and a specific surface of 3500 cm2/g was mixed with
crushed limestone having a mean grain size of 4 microns in an
amount of 2.25% based on the weight of the glass, plus water
in a quantity of approximately 10% by weight based on the
aggregate weight of the glass and limestone.
The mixture was thoroughly mixed to form a paste on
a tray or disc from which nodules of the paste were discharged
and gently distributed as a single nodule layer on a metal
screen belt by which the nodules of approximately 5 to 10 mm
in size were transported through a tunnel furnace maintained
at a temperature of 600 to 650C. The nodules remained in
the furnace for about 13 minutes. During an initial period of
about 10 minutes the nodules became dried and by that time the
nodules had been brought to the furnace temperature. The nodules
accordingly remained at that temperature for about 2 to 3
minutes. This was sufficient to cause the glass particles in
superficial surface layers of the individual nodules to become
sintered together. me quality of this surface sintering is
important because it has an important influence on the proper-
ties of the final product.
These surface-sintered nodules were fed into a rotary
drum furnace maintained at a temperature of 800C. The nodules
remained in this furnace for between 3 and 4 minutes. During
this period of time the continuous rotation of the drum kept
the nodules in mutual rolling contact. The glass particles
softened and the limestone decomposed with evolution of C02,
causing cellulation. The nodules became converted to cellular
glass beads in sizes approximately double the sizes of the
initial nodules, the beads being characterised by a foamed
glass core structure and an enveloping skin which was non-
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is cellular or only slightly cellulated. These beads were deposited
on a metal belt conveyor by which they were transported through
an annealing tunnel in which the beads were reduced to annealing
temperature (about 500C3 and were kept at that temperature for
10 to 15 minutes. The beads were subsequently rapidly cooled
to ambient temperature. The formed beads had a bulk density
of between 0.12 and 0.18 g/cm3.
The beads had a very low water permeability as is
evident from that fact that after immersion in water at room
temperature for a period of 24 hours the beads were found to
have absorbed less than 7% by volume of water. The water
; absorption after exposure of the beads for 24 hours in an
atmosphere of 99% relative humidity at 20C was less than 0.25%
by weight.
The water absorption tends to be lower for beads
having a bulk density at the upper end of the aforesaid bulk
density range and can be as low as 3% by volume and less than
0.1% by weight respectively under the specified conditions.
The beads had a crushing strength in excess of 15
kg/cm2 even for the beads having the lowest bulk density.
The manufacture of compositions according to the
invention requires merely the thorough mixing of the aggregate
with the selected binder or matrix material and water or other
liquid vehicle (if required). When making a light weight
concrete, it is preferred to mix the cement and the cellu-
lated glass beads dry and then to add water and continue
mixing until the beads are perfectly enveloped. As an alterna-
tive the beads could be added to previously prepared mortar.
A part of a structure formed of a particular compo-
sition according to the invention, selected by way of example, I
is represented in the accompanying diagrammatic drawing which
will now be referred to.
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The composition forming -the structure comprises a
cement matrix or binder 1 in which is distributed a coarse
fraction of glass beads such as 2 (above 3 mm in size) and a
fine fraction of glass beads such as 3 and 4 which are below 3
mm in size. The coarse fraction beads 2 have a multicellular
core enveloped by a substantially non-cellular surface skin
which is substantially water-impermeable. The fine fraction
beads 3 are hollow beads comprising a shell which is of micro-
cellular structure and is also substantially water-impermeable.
The fine fraction beads 4, which are of smaller size than the
fine fraction beads 3, are hollow beads having a substantially
non-cellular surface skin which is likewise substantially water-
impermeable. In the drawing, in order to clarify the illustra-
tion, the beads of the different fractions have not been drawn
to the same scale.
The present invention also includes, any and all composi-
tions within the following definition: A light weight moulded
composition, e.~., concrete of plain structure, formed from a
binder, water (optional) and coarse and fine aggregates, charac-
terised in that the fine aggregates have a granulometry from justabove 0 to 3 (or 4) mm, these aggregates being composed, at least
in part, of granules of an expanded product, the granules having
very small water absorbency and an apparent volume mass of not
more than 350 kg/m3, and in that the coarse aggregates have a
granulometry between 3 and 30 mm, these aggregates being com-
posed, at least in part, of granules of an expanded product, the
granules having small water absorbency and an apparent volume mass
of not more than 200 kg/m3. In addition to having such character-
istics, the moulded composition is preferably characterised in that
the apparent volume mass of the fine aggregates decreases as the
diameter of the aggregates increases. The present invention also
includes mouldable compositions (e.~., compositions in which cement
1(~771~3~
present as binder, together with water) for moulding into a
moulded composition as hereinbefore defined.
Certain specific embodiments of the invention will
now be described by way of example.
Example 1 to 4
The following Table I gives the compositions of four
different light-weight concrete mixes according to the invention:
Table I
Example Nos:
Inqredients of composition 1 2 3 4
Cellular glass beads
(bulk volume in litres):
0 - 3 mm 200 450 350 200
. .
3 - 8 mm 350 - - _
8 - 16 mm 700 800 900 1070
Water (in litres):
Theoretical amount
(water/cement ratio=0.4) 120 140 160 140
Amount in practice
(water/cement ratio=0.45)135 157 180 157
Artificial Portland
cement 400 (in kg) 300 350 400 350
River sand (in kg) - - - 255
Properties of the product:
Density of the freshly dried
composition (kg/m3) 639 692 793 962
Density of dried composition
after 28 days (kg/m3) 630 680 782 948
Compression re2sistance after
28 days (kg/cm ) 61 72 85 105
Thermal conductivity (kcal/
m/h/C) 0.12 0.15 0.17 0.22
Compatibility with cement
(tested according to ASTM
C 227.71) excellent excellent
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1~7'7181
In the above four compositions the cellular glass
beads of the fine aggregate fraction (0-3 mm) and of the
coarse aggregate fraction (3-16 mm) had the structures required
for such fractions by the present invention. All of such
beads absorbed less than 6% by weight of water during 2~ hours
immersion in water. The beads of the size range 0-3 mm were
produced by a method of preparation of fine beads as herein
described. They had a bulk density of 250 kg/m3. The beads
of the size range 3-8 mm, which had a bulk density of 160 kg/m3,
and the beads of the size range 8-16 mm, which had a bulk
density of 140 kg/m3, were produced by methods of preparation
of coarse fractlon beads as herein described.
Light weight concretes formed from compositions
according to the above Examples 1 to 4 show very small shrink-
age (little greater than ordinary concrete). They are incombus-
tible and remarkably resistant to high temperatures. For
example, on heating to 500C the crushing strength of such
light-weight concretes decreases by no more than 10%. The
corresponding value for ordinary concretes is 60 to 70%.
Light weight concretes according to the invention
afford excellent thermal insulation. The following Table II
illust`rates this advantage by comparing a light weight concrete
according to the foregoing Example I with other concretes of
conventional types. For each concrete the table gives the
total wall thickness necessary for obtaining a thermal transfer
coefficient of a wall, equal to 0.60 kcal/m2/h/C.
Table II
Total wall
Material Density (in kq/m3) thickness (in cm)
Conventional concrete 2,200(1) 23 cm(2)
Expanded clay concrete 1,300 86 cm
Autoclaved cellular concrete(3) 650 22 cm
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~ 77181
Table II - continued
Material Density (in kq/m3) Total wall thick-
ness (in cm)
Light-weight concrete 650 17 cm
according to Example 1
(1) apparent volume mass of the concrete alone
(2) comprising two layers of concrete 10 cm and 8
cm in thickness with an intervening 5 cm
space filled with an insulator
(3) cellular concrete commercially available under
the Trademark SIPROREX, YTONG or DYROX
The composition can comprise, consist essentially
of or consist of the materials set forth.
In addition to Portland cement, there can also be
employed as the binder other cements, e.~., other hydraulic
cements or gypsum cements (plaster).
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