Cements and concretes which contain them

The invention is directed to a cement composition comprising (1) 10-30% of an alkaline-earth mineral substance such as a slag or cement having a base of calcium aluminate or a calcined alkaline-earth oxide, (b) 14-56% of a constituent of a grain size of 100 A to 0.1 micron selected from silica, chromium oxide, TiO.sub.2, ZrO.sub.2 and Al.sub.2 O.sub.3, and (c) 14-56% of an inert filler of a grain size from 1 to 100 microns, the sum of (b) + (c) representing from 70 to 90% of the cement. Concrete mixtures which employ the inventive cements display superior properties.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to new cement compositions as well as 
concretes which utilize these cements. 
2. Description of the Prior Art 
The cements employed at this present time are hydraulic cements which have 
a base of hydrated compounds of calcium silicate and aluminates of 
calcium. Amongst these cements, those poorest in lime are the aluminous 
cements of the "ciment fondu" type and the superaluminous cements such as 
SECAR 250, SUPER-SECAR, ALCOA CA-25, ASAHI AC.1, etc.. All of these 
cements nevertheless still assay more than 20% of CaO. Unfortunately in 
numerous cases lime is a baneful constituent (lowering of the refractory 
character, solubility in an acid medium, violent dehydration during a 
fire, and . . . ). Thus it is desirable to have available cements which 
are free of these disadvantages. 
U. S. Pat. No. 3,802,894 describes hydraulic-setting refractory 
compositions which comprise by weight 
(a) 5-8 parts of at least one aluminous hydraulic cement, 
(b) 2.5-4 parts of at least one powdery refractory material selected from 
clay, kaolin, micronized silica, micronized magnesia, micronized chromite 
and micronized forsterite, 
(c) 0.01 to 0.30 parts of at least one dispersing agent selected from the 
phosphates of alkali metals, the carbonates of alkali metals, the humates 
of alkali metals, and 
(d) 86-92 parts of at least one refractory aggregate. The constituent (b) 
must have a particle size less than 50 microns, preferably less than 1 
micron. The constituents (a), (b) and (c) constitute a cement or binder 
for the aggregate (d). 
U.S. Pat. No. 3,060,043 describes a refractory composition having improved 
mechanical strength and resistance to abrasion, which comprises by weight 
55-90% of a refractory aggregate (chromium ore, calcined alumina, etc.), 
9-40% of a cement having a base of calcium aluminate, and 1 to 5% of 
volatilized silica of a particle size less than 44 microns, with more than 
half the silica particles being smaller than 10 microns. 
The object of the invention is to provide new cements having remarkable 
properties, as well as concretes which contain these cements as a binders. 
SUMMARY OF THE INVENTION 
The cements of the present invention consist of a mixture of (1) 10 to 30% 
by weight of an alkaline earth mineral substance selected from steelworks 
slags having a base of calcium mono- or di-aluminate or of calcium 
silico-aluminates, aluminous cements of calcium mono-aluminate and calcium 
di-aluminate types silico-aluminous cements, calcium or barium silicate, 
and alkaline-earth oxides previously calcined at very high temperature 
from the group comprising magnesia, dolomite, calcium oxide and baryta; 
(2) 14 to 56% of a constituent having a particle size lying between 100 A 
and 0.1 micron selected from silica, chromium oxide, zirconia, titanium 
dioxide and alumina; and (3) 14 to 56% of an inert filler having a 
particle size lying between 1 and 100 microns, the sum of the constituents 
(2) and (3) representing from 70 to 90% of the weight of the cement. 
The invention likewise involves concrete mixtures which consist by weight 
of 10 to 30% of a cement in accordance with the invention as a binder, and 
70 to 90% of an aggregate. 
The invention is based upon the discovery that cements and concretes having 
exceptional properties can be prepared by incorporating into their 
compositions two mineral constituents, one in the range of grain size from 
1 to 100 microns and the other in the range of grain size from 100A to 0.1 
micron, these two constituents being capable of being easily dispersed in 
water, if necessary with the addition of a dispersing agent, without 
reacting with the water to form gels or various sols. 
It seems in fact that the exceptional properties of the products of the 
invention result from the fact that the constituent of grain size from 100 
A to 0.1 micron acts to fill a considerable portion of the voids existing 
between the particles of the constituent of grain size from 1 to 100 
microns. 
At the present time cements are preferred in which the constituent (1) is a 
steelworks slag of calcium aluminate, an aluminous cement of the types 
defined or calcined magnesia, and the constituent (2) is vitreous silica 
or chromium oxide. Likewise preferably the constituent (3) has a particle 
size between 1 and 10 microns. Likewise preferred are cements consisting 
of a mixture of 25 to 30% by weight of aluminous cement, 35 to 40% by 
weight of vitreous silica, and 35 to 40% by weight of inert filler. 
The constituent (1) must have been calcined (preferably fused or sintered) 
at very high temperature in order to be sufficiently inert and to react 
only progressively with water and in any case solely when the cement or 
the concrete formed from this cement has been put into position, 
preferably by vibration. The cement of the present invention may be put 
into position by vibration after mixing with less than 20% of water, 
preferably less than 15% of water with respect to the weight of the 
cement. When an aluminous cement is employed of calcium mono-aluminate or 
calcium di-aluminate type as constituent (1), aluminous cements may be 
employed which are available in the trade such as "fused cement", SECAR 
250, ALCOA CA.25, ASAHI AC.1. When an aluminous steelworks slag is 
employed as constituent (1), it may be a recovery slag containing 
ferruginous or titaniferous impurities. The size of particles in 
constituent (1) is not very critical. It is, however, preferred to employ 
a constituent (1) having a particle size not exceeding 100 microns, and 
better still of not more than 50 microns. 
The constituent (2) must have a particle size lying between 100 A and 0.1 
micron. This constituent (2) may be vitreous silica such as the vitreous 
silica obtained as a by-product in certain industrial processes such as in 
the reduction of zirconium silicate into zirconia or in the production of 
ferro-silicon (the dust from electric furnaces contains suitable silica). 
The constituent (2) may also be silica, chromium oxide, titanium oxide or 
even aluminum oxide obtained by known techniques of precipitation, drying 
and calcination. These oxides might also be obtained by known techniques 
of dissociation or hydrolysis of certain metallic compounds (such as 
halides) in a hot flame, in a plasma or by simple firing in a furnace. 
Oxides of a particle size less than 0.1 micron are also called colloidal 
oxides. The method of preparation of the constituent (2) does not in fact 
appear to be critical. What matters is that this constituent have a 
particle size within the range from 100 A to 0.1 micron, can be easily 
dispersed in water (where necessary with the help of a dispersing agent) 
and does not form with water any gel or sol. Whilst an aluminous cement or 
a conventional Portland cement is mixed with water contents of 25 to 30%, 
the cements of the invention are normally mixed with a water content of 
less than 20%, preferably less than 15%, which after setting enables 
cements to be obtained which are of high density and low porosity. 
The constituent (3) may be any mineral matter insensitive to hydration, 
capable of being obtained in the natural state or by grinding, with an 
average grain size of 1 to 100 microns. Preferably an inert filler will be 
employed with particles of a size from 1 to 10 microns because a coarser 
(10 to 100 microns) inert filler (3) yields less advantageous results, in 
particular in the production of concretes (less advantageous mechanical 
properties and higher water content for working up). Suitable inert 
fillers are, for example, oxides such as silica, alumina (alternatively 
calcined), magnesia, zirconia, titanium dioxide, natural minerals such as 
bauxite (alternatively calcined), quartzite, dolomite, magnesite, 
chromite, zircon, granite, basalt, or pure quartzitic sands. One may also 
employ calcined clay or synthetic minerals such as silicon carbide, 
silicon nitride, silicon oxynitride, etc. In no case must there be 
employed as filler, clays, bentonites or other earths which can have a 
colloidal action upon contact with water. 
The aggregate of the concretes of the invention may consist of hard and 
dense rocks (for example, basalts, quartzites, granites, pebbles, etc...), 
electrically fused or sintered oxides (corundum, for example), 
premanufactured or synthetic matter (for example, calcined clay, calcined 
bauxite, etc.), as well as carbonaceous matter (coke, coal, anthracite, 
for example). The grain size of the aggregate is not very critical and 
will generally lie within the range normally employed in conventional 
concretes (less than 30 mm, preferably not more than 10 mm, the majority 
of the components forming the aggregate being more than 0.2 mm). 
The cements and concretes of the invention may be worked up with a 
proportion of water distinctly less than that necessary with conventional 
concretes. The reduction in water content for one and the same workability 
is at least of the order of 25% and may reach in certain cases 50% and 
over. 
The concretes of the invention exhibit high density, an open porosity in 
the raw state of less than 15%, preferably less than 10%, and a 
compressive strength in the raw state higher than 400 kg/cm.sup.2, 
preferably higher than 700 kg/cm.sup.2 and better still higher than 1000 
kg/cm.sup.2. After complete dehydration of the cement at a temperature 
from 800.degree. to 1000.degree. C. (firing), the open porosity of the 
concretes remains less than 15%, preferably less than 10%, and the 
compressive strength remains higher than 400 kg/cm.sup.2, preferably 
higher than 700 kg/cm.sup.2, and better still higher than 1000 
kg/cm.sup.2. 
The concretes of the invention exhibit in addition after hardening, 
excellent resistance to fierce heating in the event of fire. Setting of 
the concretes is rapid. Removal of forms from the concretes obtained is 
possible after 24 hours. About 80% of complete setting is reached 48 hours 
after working up. 
Apart from the essential constituents indicated above, the cements and 
concretes of the invention may contain one or more mineral or organic 
dispersant additives in order to facilitate dispersion of the various 
constituents and the wetting of them, in a manner in itself known. A very 
effective dispersant additive is sodium tripolyphosphate in the ratio from 
0.01 to 0.05% by weight with respect to the weight of the concrete. The 
concretes of the invention are useful in both civil engineering and 
refractory applications, for example, for the achievement of highway 
surfacings which are resistant to erosion and to frost, containers for 
radioactive waste, light-weight reinforced concrete structures, 
prefabricated parts, undersea works and fire-resistant structures.

The following non-restrictive examples are given with a view to 
illustrating the present invention. 
EXAMPLE 1 
A cement is prepared in accordance with the invention, which is useful for 
the preparation of civil engineering concretes, by carefully mixing the 
following constituents: 
______________________________________ 
aluminous slag of a 
particle size from 5 to 50 microns 
25% by 
weight 
vitreous silica of a 
particle size from 100 A to 0.1.mu. 
38% by 
weight 
Fontainebleau sand of a 
particle size of 5.mu. 37% by 
weight 
______________________________________ 
The chemical compositions according to the fired product of the different 
constituents are the following in % by weight: 
______________________________________ 
Aluminous Vitreous Fontaine- 
slag silica bleau sand 
______________________________________ 
SiO.sub.2 0.10 94.70 98.75 
Al.sub.2 O.sub.3 
57.90 3.65 1.25 
Fe.sub.2 O.sub.3 
0.05 0.15 traces 
TiO.sub.2 2.60 traces traces 
CaO 35.5 traces 0 
MgO 1.13 traces 0 
Na.sub.2 O 
0.01 0.15 traces 
K.sub.2 O 0.01 0.05 traces 
ZrO.sub.2 -- 1.30 -- 
SO.sub.3 2.70 -- -- 
100.00 100.00 100.00 
______________________________________ 
The CaO content in the final cement is 8.87%. 
In Examples 3 and 4 this cement will be called "inv.1". 
EXAMPLE 2 
A cement is prepared in accordance with the invention, which is useful for 
the preparation of refractory concretes, by carefully mixing the following 
constituents: 
- aluminous cement of a particle size of 5 to 50 microns . . . 28% by 
weight 
- vitreous silica of a particle size from 100 A to 0.1.mu. . . . 36% by 
weight 
- calcined alumina, ground to a particle size of 5.mu. . . . 36% by weight 
The chemical composition according to the fired product of the different 
constituents is the following, in % by weight: 
______________________________________ 
Aluminous Vitreous Calcined 
cement silica Al.sub.2 O.sub.3 
______________________________________ 
SiO.sub.2 0.25 94.70 0.05 
Al.sub.2 O.sub.3 
71.50 3.65 99.50 
Fe.sub.2 O.sub.3 
0.06 0.15 traces 
TiO.sub.2 traces traces traces 
CaO 27.74 traces traces 
MgO 0.10 traces 0 
Na.sub.2 O 0.35 0.15 0.45 
K.sub.2 O traces 0.05 traces 
ZrO.sub.2 -- 1.30 -- 
100.00 100.00 100.00 
______________________________________ 
The CaO content of the final cement is 7.76%. 
In Example 5 this cement will be called "INV.2". 
EXAMPLE 3 
a concrete is prepared in accordance with the invention, which is useful 
for civil engineering purposes by mixing carefully in the usual fashion 
the constituents indicated in the table below, which likewise gives by way 
of comparison the composition of a conventional concrete. The properties 
of the concretes obtained are likewise indicated. 
______________________________________ 
Conventional 
Concrete with 
Composition in % by weight 
concrete INV.1 cement 
______________________________________ 
Finely crystalline granite, grain 
size 4/2mm 46.5 46.5 
Granite, ungraded 2mm 
18.6 18.6 
Sand, grain size 0.15/0.05 mm 
15 15 
Portland cement 400 HTS 
20 -- 
INV.1 cement -- 20 
Water, % added with respect to 
the composition of dry concrete 
9.6 3.5 
Dispersing agent (sodium 
-- 0.1 
tripolyphosphate) 
Properties 
Density in the rough, dry 
2.21 2.49 
Open porosity, % 11.1 4.1 
Compressive strength after 20 
days, Kg/cm.sup.2 400 1200 
Content of CaO capable of being 
hydrated, % 13 1.73 
______________________________________ 
EXAMPLE 4 
A concrete is prepared in accordance with the invention, which is useful 
for civil engineering purposes by mixing carefully in the usual fashion 
the constituents indicated in the table below, which likewise gives by way 
of comparison the composition of a conventional concrete. The properties 
of the concretes obtained are likewise indicated. 
______________________________________ 
Convent- Concrete 
ional with 
Composition in % by weight 
concrete INV.1 cement 
______________________________________ 
Black corundum, grain size 5/10 mm 
23 23 
Black corundum, grain size 2/4 mm 
23 23 
Black corundum, grain size 0.2/2 mm 
20 20 
Black corundum, grain size 0./0.2 mm 
20 20 
Portland cement 400 HTS 
14 -- 
INV.1 cement -- 14' 
Water, % added with respect to 
the compositon of dry concrete 
5 2.5 
Properties 
Density in the rough, dry 
3.10 3.46 
Open porosity, % 16.80 7.1 
Compressive strength after 20 days, 
kg/cm.sup.2 445 1050 
Content of CaO capable of being 
hydrated, % 9.1 1.23 
______________________________________ 
EXAMPLE 5 
A refractory concrete is prepared in accordance with the invention by 
mixing carefully in the usual fashion the constituents indicated in the 
table below, which likewise gives by way of comparison the composition of 
a conventional concrete. The properties of the concretes obtained are 
likewise indicated. 
______________________________________ 
Convent- Concrete 
ional with 
Composition by weight 
concrete INV.2 cement 
______________________________________ 
Calcined bauxite, grain size 4/2 mm 
30 30 
Calcined bauxite, ungraded 2 mm 
50 50 
Calcined bauxite, grain size 0/0.2 mm 
10 11 
SECAR 250 cement 15 -- 
INV.2 cement -- 14 
Water, % added with respect to the 
composition of dry concrete 
12.5 5 
Properties 
Density in the rough, dry 
2.50 3.00 
Open porosity % 19 11 
Compressive strength after 3 days, 
kg/cm.sup.2 600 1050 
After firing at 1200.degree. C 
Density in the rough 2.35 2.90 
Open porosity % 24 12 
Compressive strength, kg/cm.sup.2 
300 1100 
Content of CaO capable of being 
hydrated, % 4.15 1.09 
______________________________________ 
EXAMPLE VI 
A cement is prepared in accordance with the invention, which is useful for 
the preparation of a concrete, by mixing carefully the following 
constituents: 
- 14% by weight of an aluminous slag ground to a particle size less than 20 
microns, 
- 43% by weight of a vitreous silica of a particle size from 0.1 micron to 
100 A, and 
- 43% by weight of calcined alumina of a particle size from 1 to 10 
microns. 
This cement may be put into a form by vibration with 13 to 15% of water 
with respect to the weight of the cement. This cement will be called 
INV.III cement. 
The chemical compositions according to the fired product of the different 
constituents are the following, in % by weight: 
______________________________________ 
Aluminous Vitreous Calcined 
slag silica alumina 
______________________________________ 
SiO.sub.2 0.10 94.70 0.05 
Al.sub.2 O.sub.3 
57.90 3.65 99.5 
Fe.sub.2 O.sub.3 
0.05 0.15 traces 
TiO.sub.2 2.60 traces traces 
CaO 35.5 traces traces 
MgO 1.13 traces 0 
Na.sub.2 O 0.01 0.15 0.45 
K.sub.2 O 0.01 0.05 traces 
ZrO.sub.2 -- 1.30 -- 
SO.sub.3 2.70 -- -- 
TOTAL 100.00 100.00 100.00 
______________________________________ 
With this cement a concrete is prepared which is of high density, low 
porosity and good compressive strength by mixing carefully in the usual 
fashion the constituents indicated below in the proportions by weight as 
mentioned: 
______________________________________ 
23% of black corundum of grain size 5/10 mm, 
23% of black corundum of grain size 2/5 mm, 
20% of black corundum of grain size 0.2/2 mm, 
20% of black corundum of grain size 0.05/0.2 mm, 
14% of INV.III cement 
100 
______________________________________ 
-Water, % added with respect to the composition of the dry concrete: 2.9. 
______________________________________ 
Properties 
Density in the rough dry state: 
3.42 
Open porosity: 4.2% 
Compressive strength: 
1500 kg/cm.sup.2 after 8 days 
After firing at 800.degree. C: 
Apparent density: 3.40 
Open porosity: 5.6% 
Compressive strength: 
1400 kg/cm.sup.2 
After firing at 1200.degree. C: 
Apparent density: 3.40 
Open porosity: 5.4% 
Compressive strength: 
1450 kg/cm.sup.2 
______________________________________ 
EXAMPLE VII 
A cement is prepared in accordance with the invention, which is useful for 
the preparation of a concrete, by mixing carefully the following 
constituents: 
- 28% by weight of MgO calcined at 1650.degree. C., of a grain size less 
than 50 microns, 
- 36% by weight of a vitreous silica of a particle size from 0.1 micron to 
100 A, 
- 36% by weight of a calcined alumina of a particle size from 1 to 10 
microns. 
This cement may be put into a form by vibration with 13 to 15% of water 
with respect to the dry weight of cement. This cement will be called 
INV.IV cement. 
The chemical compositions according to the fired product of the different 
constituents are the following, in % by weight: 
______________________________________ 
Calcined 
Calcined MgO 
Vitreous silica 
alumina 
______________________________________ 
SiO.sub.2 
1.80 94.70 0.5 
Al.sub.2 O.sub.3 
0.40 3.65 99.50 
Fe.sub.2 O.sub.3 
0.70 0.15 traces 
TiO.sub.2 
0.05 traces traces 
CaO 1.25 traces traces 
MgO 95.60 traces 0 
Na.sub.2 O 
0.07 0.15 0.45 
K.sub.2 O 
0.03 0.05 traces 
ZrO.sub.2 
-- 1.30 -- 
Total 100.00 100.00 100.00 
______________________________________ 
With this cement a concrete is prepared which is of high density, low 
porosity and good compressive strength by mixing carefully in the usual 
fashion the constituents indicated below in the proportions by weight as 
mentioned: 
______________________________________ 
23% of black corundum of grain size 5/10 mm, 
23% of black corundum of grain size 2/5 mm, 
20% of black corundum of grain size 0.2/2 mm, 
20% of black corundum of grain size 0.05/0.2 mm, 
14% of INV.IV cement 
100 
______________________________________ 
-Water, % added with respect to the composition of the dry concrete: 3.1. 
______________________________________ 
Properties 
Density in the rough, dry: 
3.35 
Open porosity: 8.80% 
Compressive strength: 
770 kg/cm.sup.2 after 8 days 
After firing at 800.degree. C 
Apparent density: 3.35 
Open porosity: 10% 
Compressive strength: 
700 kg/cm.sup.2. 
After firing at 1200.degree. C 
Apparent density: 3.35 
Open porosity: 9.5% 
Compressive strength: 
900 kg/cm.sup.2 
______________________________________ 
EXAMPLE VIII 
A cement is prepared in accordance with the invention, which is useful for 
the preparation of a concrete, by mixing carefully the following 
constituents: 
- 24% by weight of an aluminous cement of a particle size from 5 to 50 
microns, 
- 47% by weight of chromium oxide of a particle size from 500 A to 2500 A, 
- 29% by weight of calcined alumina ground to a particle size from 1 to 10 
microns. 
This cement may put into a form by vibration with 11 to 14% of water with 
respect to the weight of cement. 
This cement will be called INV.V cement. 
The chemical compositions according to the fired product of the different 
constituents are the following, in % by weight 
______________________________________ 
Aluminous Chromium Calcined 
cement oxide alumina 
______________________________________ 
SiO.sub.2 0.25 0.22 0.05 
Al.sub.2 O.sub.3 
71.50 0.18 99.5 
Cr.sub.2 O.sub.3 
0 98.90 0 
Fe.sub.2 O.sub.3 
0.06 0.30 traces 
TiO.sub.2 traces 0.10 traces 
CaO 27.74 0.14 traces 
MgO 0.10 0.16 0 
Na.sub.2 O 
0.35 traces 0.45 
K.sub.2 O traces traces traces 
Total 100.00 100.00 100.00 
______________________________________ 
With this cement a concrete is prepared which is of high density, low 
porosity and good cold compressive strength by mixing carefully in the 
usual fashion the constituents indicated in the table below in the 
proportions by weight indicated: 
______________________________________ 
23% of black corundum of grain size 5/10 mm, 
23% of black corundum of grain size 2/5 mm, 
20% of black corundum of grain size 0.2/2 mm, 
15% of black corundum of grain size 0.05/0.2 mm, 
19% of INV.V cement 
100 
______________________________________ 
- Water % added with respect to the composition of the dry concrete: 3.3. 
______________________________________ 
Properties 
Density in the rough, dry: 
3.55 
Open porosity: 6% 
Compressive strength: 
800 kg/cm.sup.2 
After firing at 800.degree. C 
Apparent density: 3.53 
Open porosity: 6.9% 
Compressive strength: 
750 kg/cm.sup.2 
After firing at 1200.degree. C 
Apparent density: 3.49 
Open porosity: 11.0% 
Compressive strength: 
1050 kg/cm.sup.2 
______________________________________ 
EXAMPLE IX 
A concrete is prepared in accordance with the invention, having the 
following composition by weight: 
______________________________________ 
23% of black corundum of grain size 5/10 mm 
23% of black corundum of grain size 2/5 mm 
20% of black corundum of grain size 2/0.2 mm 
aggre- 
20% of black corundum of grain size 0.2/0.01 mm 
gate 
6% of calcined Al.sub.2 O.sub.3 of a particle size 
from 5 to 20 microns 
6% of vitreous silica of a particle size 
binder 
from 100 A to 0.1 micron cement 
2% of Portland cement 
100 
______________________________________ 
The chemical analysis of the constituents is the following: 
______________________________________ 
Black Calcined Vitreous Portland 
corundum Al.sub.2 O.sub.3 
silica cement 
______________________________________ 
SiO.sub.2 
0.50 0.05 94.70 22.0 
Al.sub.2 O.sub.3 
6.5 99.5 3.65 4.5 
Fe.sub.2 O.sub.3 
0.1 traces 0.15 1.5 
TiO.sub.2 
2.7 traces traces 0.2 
CaO traces traces traces 70.8 
MgO 0.2 traces traces 0.8 
Na.sub.2 O 
traces 0.45 0.15 0.1 
K.sub.2 O 
traces traces 0.05 0.1 
ZrO.sub.2 
-- -- 1.30 -- 
Total 100.00 100.00 100.00 100.00 
______________________________________ 
The composition so defined may be put into a form by vibration with 3.8% of 
water. 
After setting for 15 days and stoving at 110.degree. C, the following 
properties were obtained: 
______________________________________ 
Properties: 
Apparent density: 3.31 
Open porosity: 9.3% 
Compressive strength: 510 kg/cm.sup.2 
After firing at 800.degree. C: 
Apparent density: 3.28 
Open porosity: 12.6% 
Compressive strength: 695 kg/cm.sup.2 
After firing at 1200.degree. C: 
Apparent density: 3.27 
Open porosity: 13.1% 
Compressive strength: 740 kg/cm.sup.2 
______________________________________ 
By way of comparison, if the vitreous silica as defined is replaced by a 
micronized silica of a particle size from 1 micron to 10 microns, the 
amount of water necessary for putting into a form by vibration is 6%. 
After setting for 15 days and stoving at 100.degree. C., the following 
properties are obtained: 
______________________________________ 
Properties: 
Apparent density: 3.17 
Open porosity: 16.5% 
Compressive strength: 80 kg/cm.sup.2 
After firing at 1200.degree. C: 
Apparent density: 3.23 
Open porosity: 15.2% 
Compressive strength: 260 kg/cm.sup.2 
______________________________________ 
The results show well the critical importance of the use of a constituent 
(2) exhibiting a particle size within the range defined. 
EXAMPLE X 
A concrete is prepared in accordance with the invention, having the 
following composition by weight: 
______________________________________ 
41% of calcined anthracite of grain size 2/4 mm 
16% of calcined anthracite, ungraded 2 mm 
aggregate 
13% of calcined anthracite of grain size 0.5/ 
0.1 mm 
11% of Fontainebleau sand of a particle 
size of 5 microns 
11% of vitreous silica, of a particle size from 
binder 
100 A to 0.1 microns cement 
8% of aluminous slag of a particle size from 
5 to 50 microns 
100 
______________________________________ 
The characteristics of the calcined anthracite are the following: 
______________________________________ 
Carbon content &gt;94% 
Ash content: 5.1% 
Apparent density: 1.68 
Open porosity: 4.42% 
______________________________________ 
The chemical analysis of the other constituents is the following: 
______________________________________ 
Fontainebleau 
Aluminous slag Vitreous silica 
sand 
______________________________________ 
SiO.sub.2 
0.10 94.70 98.75 
Al.sub.2 O.sub.3 
57.90 3.65 1.25 
Fe.sub.2 O.sub.3 
0.05 0.15 traces 
TiO.sub.2 
2.60 traces traces 
CaO 35.5 traces 0 
MgO 1.13 traces 0 
Na.sub.2 O 
0.01 0.15 traces 
K.sub.2 O 
0.01 0.05 traces 
ZrO.sub.2 
-- 1.30 -- 
SO.sub.3 
2.70 -- -- 
Total 100.00 100.00 100.00 
______________________________________ 
The composition so defined may be put into a form by vibration with 5.8% of 
water. 
After setting for 8 days and stoving at 110.degree. C., the following 
properties were obtained: 
______________________________________ 
Apparent density: 1.77 
Open porosity: 7.3% 
Compressive strength: 620 kg/cm.sup.2 
Permeability: &lt;0.2 np 
After firing at 800.degree. C: 
Apparent density: 1.75 
Open porosity: 9.0% 
Compressive strength: 650 kg/cm.sup.2 
Permeability: &lt;0.2 np 
After firing at 1200.degree. C: 
Apparent density: 1.75 
Open porosity: 10.5% 
Compressive strength: 780 kg/cm.sup.2 
Permeability: &gt;0.2 np 
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It goes without saying that the embodiments described are only examples and 
that it would be possible to modify them, especially by substitution of 
equivalent techniques, without thereby departing from the scope of the 
invention.