COMPOSITION CONTENANT DU CIMENT ET COMPRENANT DES PARTICULES DE SILICE

CEMENTITIOUS COMPOSITION COMPRISING PARTICULATE SILICA

Abrégé anglais

ABSTRACT
A cementitious composition and, by extension, an
article of manufacture and a curable composition of
particulate or comminuted silica, an alkali-metal silicate
and, optionally, an alkyl silicate and/or ester catalyst is
disclosed. The silica, (80-75%, 80-95%, 80-92.5%), is
preferably sand, either pure silica sand for a white effect,
or naturally/artificially coloured for colour effects. The
alkali metal silicate, (20-25%, 20-5%, 20-7.5%), may be
either sodium and/or potassium. The alkyl silicate is
preferably ethyl silicate and the ester catalysts are
generally esters of long chain organic, (preferably
unsaturated aliphatic), carboxylic acids. Ester catalysts
usually employed in foundry sand moulding may also be used.
The addition of an alkyl silicate and/or ester catalyst
(5-15%) appear(s) to give added strength to the product over
that by the alkali-metal silicate alone. The alkali-metal
and alkyl silicate combination, moreover, is useful for the
prevention of rough surface texture. The preferred
compositions shown in parentheses above for silica and
alkali-metal silicate indicate the amounts used in the
absence of an additive and in the presence of the alkyl
silicate and/or ester catalyst(s) respectively. The curable
composition/article of manufacture is prepared by mixing an
amount of 5-20% of finely ground or comminuted "flour" of
silica with the balance of the mix to exclude
voids, occlusions or rough surface texture. The alkali-metal
silicate may be added or prepared in situ by mixing the sand
with caustic alkali. After mixing all the constituents
together and reaction, if any, has ceased, the mixture is
then allowed to cure for several hours at temperatures up to
200°C. to stabilise and increase the strength of the
composition. Cementitious compositions of the above type
have particular advantages, as they are resistant to the
acid constituents in the urban atmosphere, finding
applications in the manufacture of building units, such as
various tiles, paving materials and special plastering
compounds.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A curable composition for the manufacture of
building blocks, structural units and preformed concrete-
like materials suitable for internal or external use, said
composition comprising 80-95% by weight silica and
correspondingly 5-20% by weight of sodium or potassium
silicate, and including also ethyl silicate present in a
proportion of from 5-15% by weight of the total weight of
silica and sodium or potassium silicate.
2. A composition according to claim 1 wherein said
silica comprises a mixture of silicas, from 5-20% by weight
of the mixture being comminuted silica flour.
3. A method for preparing a building product suitable
for use as a building block, structural unit or pre-formed
concrete-like material for either internal or external use,
said product being long term resistant to rainwater and
atmospheric gases, comprising the following steps:
(a) preparing a water-glass composition comprising
80-95% by weight silica and correspondingly 5-20% by weight
of either sodium or potassium silicate, and including also
ethyl silicate present in a proportion of from 5-15% by weight
of the total weight of silica and sodium or potassium
silicate, and
(b) forming an article from said composition in a
mold and allowing said composition to set thereby producing
said article.
4. A method according to claim 3 wherein said
silica comprises a mixture of silicas, from 5-20% by weight
of the mixture being comminuted silica flour.

Description

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SILICATE-BONDED SILICA MATERIALS
This invention relates to silicate-bonded
silica materials, and more particularly to structural
and masonry units and building components produced from
such materials including wall, floor, roof and ceiling
tiles~ p~ving materials and special plastering (in situ
and masonry unit application) compounds
"Artificial" and "reconstituted" stone has long
been made by man, many buildings dating from the
`10 Imperial Rome epoch being mainly constructed of a kind
of concrete which was faced with marble. However, in
this latter half of the twentieth century, concrete has
proved to be less attractive as a building material
because of the high atmospheric pollution obtaining in
today's towns and cities, which conditions can destroy
concrete, and even such natural materials as marble and
sandstone, in the course of time.
AU-B-155,386 describes fast-setting acid-proof
mortars which contain i) sodium silicate, ii) finely
ground silica, sand, or diorite dust and iii) partly
condensed organic silicates (e.g. hydrolysed ethyl
silicate). The weight ratios of these components is
such that the mortars have very short setting times,
typically a matter of minutes, and produce l'granite-
like masses." GB-A-256,258 discloses hardenable
mixtures of various silicates and a water-glass
solution.
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It is an object of the present invention to
overcome the above and other disadvantages of
conventional building materials by the provision of
"artificial stone" which is extremely resistant to
acidic and other atmospheric pollutants, and which has
the physical strength and other mechanical
characteristics to enable it to be used in buiIding
construction.
It is a further object of the present invention
to utilise, for the above purpose, one of the Earth's
most abundant elements, that is to say, silicon, to
produce silicate-bonded silica materials.
According to one aspect of the present
invention there is provided a curable composition for
the manufacture of building blocks, structural units
and preformed concrete-like materials suitable for
internal or external use, said composition comprising
80-95% by weight silica and correspondingly 5-20% by
weight of sodium or potassium silicate, and including
also ethyl silicate present in a proportion of from
5-15qo by weight of the total weight of silica and
sodium or potassium silicate.
The invention also provides a method for
preparing a building product suitable for use as a
; 25 building block, structural unit or similar material for
either internal or external use, said product being
long term resistant to rainwater and atmospheric gases,
comprising the following steps:
(a) preparing d water-glass composition
comprising 80-95% by weight silica and correspondingly
5-20% by weight of either sodium or pot~ssium silicate,
and including also ethyl silicate present in a proportion
o~ from 5-15% by weight of the total weight of silica
and sodium or potassium silicate, and
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(b) forming an article from said composition
in a mold and allowing said composition to set thereby
producing said article.
The silica may be any suitable readily
available silica sand or mixture of sands. A
preferred silica sand is a pure white silica sand, very
large deposits of which have been ascertained to exist,
particularly in Australia. One such deposit which has
been identified is of very high purity, having a Fe203
content of less than 0.008%; the virtually iron-free
nature of this raw material being of great natural
advantage in avoidance of discolouration, streaking,
etc, due~ to weathering; and producing pristine white
units, or combined with additives e.g. pigments, to
give subtle shading effects. However, other sands of
various colours can also be employed to give different
shades of colour or different surface effects to the
final moulded product.
In some embodiments of the invention, a
predetermined percentage of silica sand is firstly
ground to a smaller particle size (e.g. 100~300 mesh),
and in some cases finely comminuted silica "flour" is
employed in the sand mix. Usually, no more than about
S-20% by weight of the fine sand is used in the sand
mix. This flour tends to prevent any voids or
occlusions occurring in the finished blocks, and may
also reduce the quantity of binder required in the
manufacturing process. It has been found that when no
fine sand is included in the sand mix the surface of
3 the moulded product has a rough texture. However,
incorporation of even 10% fine silica material is
sufficient to substantially eliminate most of this
surface roughness. The presence of ethyl silicate and
an alkali metal silicate al 50 9 i ves quite a smooth
surface texture.
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The alkali metal silicate is selected from
sodium silicate or potassium silicate, preferably the
latter (preferred SiO2:K20 ratio in the range of 1.7:1
to 1.4:1). In some cases, it may be of advantage to
use mixtures of sodium silicate and potassium silicate.
Sodium silicate has for many years been
extensively used in the field of metal-founding as a
binder. Spray-on protective coatings have also been
proposed, composed of curable silicate compositions
containing a phosphate hardener coated with a reaction
product of a metal aluminate and/or metal borate.
It is envisaged, however, that a sodium
' silicate binder may lack the necessary strength
characteristics, particularly for the manufacture of
pre-cast units, and in consequence potassium silicate
binders are highly preferred.
Various proposals for the production of
potassium silicate binders and "waterproof" protective
coatings have been made; for instance Weiand et al.
have worked on cold hardening refractory binders
prepared from alkali metal (with particular reference
to potassium) silicate with various solutions. Weather
resistant coatings prepared by employing potassium
water glass have been proposed by Strobonov et al.,
modified potassium silicate binder in potassium
aluminosilicate-bonded material by Korneev et al.,
while optimal values for the potassium/silica ratio of
potassium silicate protective coatings have been
investigated by Perlin et al., and potassium silica
3 solutions by Murashkevick.
The sodium or potassium silicate is employed in
amounts of from 5-20% by weight of the moldable
composition, but usually requires thermal curing at
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temperatures of up to about 200C for several hours.
Ideally, the amount of sodium or potassium silicate is
kept to a minimum in the moldable mix to prevent
staining caused by alkali leaching.
The sodium or potassium silicate can be added
to the moldable composition or can be formed in situ by
mixing the sand with an alkali, such as sodium or
potassium hydroxide, whereby the corresponding alkali
metal silicate is precipitated and apparently functions
as a binder for the particulate silica sand, and is
allowed to cure at ambient temperature. Thermal curing
, up to 200C tends to strengthen the product and to
reduce the amount of free alkali present, presumably
due to reaction with the silica present.
The ethyl silicate is used in amounts of about
5-15% by weight of the moldable composition (e.g. 5-10%
potassium silicate and 5-15% ethyl silicate). The
addition of ethyl silicate appears to provide added
strength to the product when compared with potassium
silicate alone.
Thermal curing at temperatures of up to 200C
; for several hours increases the strength.
Other compounds may be included in the moldable
composition as required e.g. ester catalysts (typically
esters of long chain organic carboxylic acids),
additional binders, plasticizers and fillers. As
; fillers there are used the usual inert substances,
which may be incorporated for special purposes such as
colour or because it is a readily available local
;~ 3 material, e.g. bauxite, lime, kaolin and other clays.
According to the present invention the
~components of the moldable composition are admixed
together to form an homogeneous mixture, with water
added to the degree necessary to assist moldability to
the desired shape.
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If desired, the molded shape may be cured
entirely at ambient temperatures, since elevated
temperature curing is not required to provide a product
with excellent mechanical properties. However, thermal
curing at temperatures of up to 200C for several hours
may increase the strength of the product and reduce the
possibility of water slumping or the leaching of alkali
from the final product
The moldable compositions of the present
invention can be molded into a variety of shapes,
including blocks, panels, sheets, tiles and the like.
The final product is densely compacted and non-porous,
and resistant to acid and alkali corrosion (e.g. from
"acid rain"). Suitable pigments can be added during
the manufacture to produce a range of coloured
finishes. The surfaces of the product may be glazed or
given any desired surface finish treatment.
Although conventional mortars may be employed in
; the laying of blocks manufactured according to the
invention, suitable mortars and the like may also be
produced from the moldable mixtures of khe present
invention, with or without plasticizers or other
additives.
It will be seen that a particular advantage of
the invention lies in the fact that the materials can
be cured at ambient temperature just as are the much-
inferior concretes. Thus, masonry blocks, panels,
tiles, etc., can be pre-cast cheaply and easily and
then transported to a buiIding site; on the other hand,
large slabs, structural units and the like may just as
cheaply and rapidly be produced in situ (with or
without reinforcing).
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Molded products were prepared from a moldable
composition prepared by weighing out the necessary
quantities of material, mixing them, and molding the
resultant composition to the desired shape and curing
the molded shape at either ambient or elevated
temperature. The final products presented a good
finish and a pleasing appearance and had good strength
(15-40 MPa compressive strength), and were stable to
rain, sunlight and general weathering conditions.
Resistance to water slumping was tested by placing the
molded product in boiling water for at least four (4)
hours. Resistance to acid corrosion was tested by
placing the molded product in concentrated (4M)
hydrochloric acid for at least several hours.
The following non-limiting examples are
intended to illustrate the invention.
EXAMPLE 1
A mixture was prepared comprising 90% by weight
of silica (80% sand, 10%-100 mesh silica, 10%-300 mesh
silica), 10~ by weight of K60 potassium silicate and
7.5% by weight of ethyl silicate (based on total
weight); with sufficient added water to assist
moldability.
The mixture was cured at room temperature for
twenty-four (2~) hours. The cured samples exhibited
good strength and were not affected by hot water or 4M
hydrochloric acid.
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Example 1 was repeated, except that samples
were cured at 100C and 200C. The products exhibited
an increase both in hardness and in strength.
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EXAMPLE 3
95/0 silica (80% sand, 10%-lO0 mesh silica, 10%-
300 mesh silica), 5% K60 potassium silicate and 7.510
ethyl silicate (based on total weight).
The mixture was cured at room temperature for
twenty-four (24) hours. The cured samples exhibited
good strength and were not affected by hot water or 4M
hydrochloric acid.
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