Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
Method for the production of a hydraulic binding agent, a
structural component, use thereof and device therefor
The invention relates to a method for the production of
an inorganic-based hydraulic binding agent according to
the preamble of Claim 1 and to a structural component and
an aerated concrete block. The invention furthermore
encompasses a device for carrying out the method and the
use of the binding agent on the one hand and of
polyelectrolytes on the other hand.
Concrete is one of the most important building materials
and usually consists of a mixture of mineral components -
such as sand, gravel or rubble - and cement as binding
agent; the latter sets when water is added and produces a
type of conglomerate stone.
The most important hydraulic binding agent for concrete
is Portland cement (PC), which consists of a finely
ground mixture of PC clinker and calcium sulphates - such
as gypsum or anhydrite. After mixing with water, it sets
both in air and under water and retains its strength even
under water. For its production, lime- and clay-
containing raw materials - such as limestone, clay, lime
marl and clay marl - are mixed with one another in such a
way that the mixture of raw materials contains between 75
and 79o by weight of lime (CaC03) in addition to silicic
acid (SiO~) , alumina (A1203) and iron oxide (Fe203) from
the clay part. Preferably, there are at least 1.7 parts
by weight of lime per part by weight of soluble silicic
acid, alumina and iron oxide. The mixture is finely
ground and then usually heated in rotary furnaces with an
upstream preheating system of different type until
sintering is achieved. The Portland cement clinker
resulting from this process is then finely ground and
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processed by adding aggregates such as gypsum or the like
to form Portland cement.
Other types of cement include, for example, slag cements
(iron Portland cement and blast furnace slag cement),
trass cement and oil shale cement, which contain various
aggregates other than the Portland cement clinker (DIN
1164). Special cements which are not standardized as
cement include, inter alia, aluminous cement, deep well
cement and expanding cement.
Cements are sold in three quality classes. The high-
quality cements CEM' 42.5 and CEM 52.5 differ from the
standard cement CEM 32.5 by a different composition and a
finer grain size, which gives rise to faster setting -
not binding - and on standardized test bodies after 28
days results in the compressive strengths denoted by the
numbers. The higher initial strengths of the high-quality
cements allow earlier removal of the formwork and thus
faster progress of the construction work.
In order to reduce the costs for the production of
binding agents, alternatives to the starting materials
used are increasingly being sought. For example, fly ash
is used as an aggregate in concrete production; fly ash
is a product which is removed by filter systems from the
waste gas of industrial furnaces or waste incineration
plants, which is carried along as combustion residue in
the combustion gases and mechanically removed or
condensed out of the vapour state upon cooling.
Also used are calcined ashes and fly ashes (for example
from industrial furnaces from the paper industry) or slag
sands. The latter are formed when the burning blast
furnace slag flowing from the slag hole of the blast
furnace is introduced into moving water.
CEM = international designation for cement
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These aforementioned aggregates which are used in cement
mean that the binding agent cures more slowly. For
example, a strength achieved after 28 days in the case of
conventional concrete will be achieved only after
approximately 90 days. These so-called latent hydraulic
binding agents can therefore be used only to a very
limited extent.
In view of these conditions, the object of the invention
is to improve the usability of latent hydraulic binding
agents - particularly those based on fly ash, calcined
ash or slag sand and combusted oil shale - for practical
use in the construction sector, and in particular to
permit faster setting.
The teaching of the independent claim aims to achieve
this object; the dependent claims provide advantageous
further developments. Moreover, all combinations of at
least two of the features disclosed in the description,
the drawing and/or the claims fall within the scope of
the invention. In respect of stated numerical ranges,
values which lie within the stated limits are also
intended to be disclosed as limit values and can be used
at will.
By means of suitable components which can be used to
balance out different fly ash compositions, on the one
hand and a treatment of the mixture in an activator on
the other hand, the materials in the latent hydraulic
state can be altered in terms of the lattice structure
and the geometry of the individual particles, in such a
way that active hydraulic effects are obtained which then
correspond to a high-quality Portland cement clinker.
By subjecting the mixture to high mechanical stress in an
activator, the product is ground and this results inter
alia in an increase in the surface area. Moreover, the
globular structures of a fly ash are altered in such a
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way that an amorphous structure is obtained. This
structure promotes the binding process by hooking the
individual particles together and increases the strength
values, in particular the compressive strength and the
bending tensile strength.
The newly created reactive surfaces of the mixture
consequently increase the total specific surface area of
the particles or grains - also referred to as the Blain
value. The increase in surface area as a result of the
fine grinding operation on the one hand and the
conversion of the particle structures into reactive
surfaces on the other hand result in an overall increase
in the Blain value by 8 to 29 times that of a Portland
cement.
The collision of the particles onto and against one
another and the reflections which occur on the tools give
rise to shock waves in the particles which lead to
splitting of the particles into amorphous structures and
to disruptions to the lattice structure within the
particles.
During the impact of the particles - or by the collision
of the particles with one another on the one hand and the
tools on the other hand - shock waves in interaction with
occurring pent-up energy as a result of the pulse
interruption propagate in the ultrasound range.
This energy - such as friction, kinetics and shear force
acting on the particles - is largely converted into
thermal energy which in turn is conducted away via the
newly created surfaces and given off to the process air.
The increase in temperature of up to more than 3000°C
which occurs repeatedly at the break points for a brief
time within a few milliseconds causes a thermoplastic
alteration of the interfaces. The particles involved are
briefly in a plasmoid state.
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The described mechanochemical and tribomechanical
reactions activate the latent hydraulic mineral
components . The mixture can then be used as a substitute
for a Portland cement.
Tests have shown that this novel hydraulic binding agent
- in addition to the conventional uses in structural
engineering and civil engineering - can also be used in
the production of porous concrete and refractory
applications on account of its excellent properties.
An activator is used as the device for the production of
this hydraulic binding agent. This device makes it
possible, at high speeds of the rotating tools of up to
250 m/sec, to achieve the parameters required for
activation. Control of the material supply, the air
supply, the process heat and the material discharge is of
great importance here.
The configuration of the tools for the mechanochemical
and also tribomechanical effects is of particular
importance.
The activator consists essentially of a rotor and a
stator, which are held by a machine platform. The axis is
arranged vertically. The drive is obtained via an
electric motor by means of a V-belt on the rotor shaft
assigned to the rotor. The rotational speed of the rotor
can be adjusted in a step-free manner via a frequency
converter. The tools can be exchanged and adjusted.
The products to be activated are fed in from a silo from
above by a dosing device by means of a cellular wheel
sluice into the interior of the activator. In an annular
chamber or gap left free by the rotor and stator the
mixture is conveyed downwards in a spiral, wherein the
residence time of the product in this annular chamber can
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be adjusted by means of air flowing in the opposite
direction. Moreover, this flow of air makes it possible
to dissipate excess heat. In this annular chamber, the
individual particles are thrown outwards against the
stator by a pulse - caused by the rotor tools.
The tools both of the rotor and of the stator are
permanently covered with a layer of the mixture so that
the particles collide with one another and primarily with
this layer. This mutual collision and the effects
achieved thereby - such as plastic deformation, restoring
behaviour, splitting, friction - give rise to a
fundamental alteration of the physical characteristics of
the particles.
Since layers of the mixture covering the tools are
supported by the bearing and resistance force of the
same, the mass of the tools substantially assists both
the pulse and the pulse interruption and the interactions
resulting therefrom, such as reflections between the
tools.
The activatable mixtures, in terms of their chemical
composition, are of similar orders of magnitude to that
of the cements. However, the product produced is based
mainly on silicic acid-containing fly ash, slag sand and
slag from waste incineration.
This main constituent is in each case passed into the
activator under oxidative conditions with the addition of
aggregates - such as calcium oxides, calcium hydroxides,
calcium carbonates and aluminium hydroxide for example.
The supply of oxygen is ensured by air fed into the
activator from below.
The required added amounts for a setting time comparable
to that of conventional concrete lie in the range from
0..2 to 30 percent by weight in the case of calcium
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aluminate. The added amounts in the case of sodium
aluminate or potassium aluminate are in each case 0.1 to
20 percent by weight. The specified percents by weight
relate here to the finished binding agent mixture.
Of course, it is also possible to use mixtures of calcium
aluminate, sodium aluminate or potassium aluminate, in
which the amount of the respective added components is
defined such that the abovementioned ranges of the added
components are not exceeded.
Typical formulas will now be discussed:
TABLE 1
Fly ash/ Slag sand Burnt oil Ca alum.
Steink. o by weight shale o by weight
o by weight % by weight
Type A 69 15 15 1
Type B 65 10 20 5
Type C 65 13 15 7
Types A to C are explained below:
Type A: (a) Characteristics
~ binds slowly in the form of strength class
32.5 N
(> 32.5 N/mm~ standard strength after 28
days);
~ compressive strength after 7 days
> 16 N/mm2;
~ modulus of elasticity is defined with the
strength class;
~ high bending tensile strength.
(b) Use
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Finished products various concrete components
(bricks, panels, angle plates or the like).
Type B: (a) Characteristics
~ binds fairly quickly in the form of
strength class 32.5 R
(> 32.5 N/mm2 standard strength after 28
days);
~ compressive strength after 2 days
> 10 N/mmz .
(b) Use
As type A and in civil engineering
(foundation of borders, foundation of
lampposts, substructure formwork or the
like).
Type C: (a) Characteristics
~ binds rapidly in the form of strength
class 42.5 R
(> 42.5 N/mm' standard strength after 28
days);
~ compressive strength after 2 days
> 20 N/mm2.
(b) Use
Civil engineering, structural engineering
components and water engineering since it
binds rapidly!
If further additives are added, these binding agents can
be used in different sectors. The addition of cationic
surfactants means that the component produced is water-
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resistant approximately 28 days after the setting phase;
no more water is absorbed through the structure of the
component.
The use possibilities are to be seen inter alia in the
sectors of water engineering, waste engineering,
sanitation and the clearing of polluted areas, etc.
By adding refractory components and increasing the amount
of calcium aluminate to approximately 400, this binder
can be used in the sector of thermally stable building
materials, such as in the linings of furnaces,
converters, etc.
Also of particular interest is the use of the binder in
the production of porous concrete. It has been found here
that, when aluminium powder (less than 70 micrometres) is
added, a closed-pore structure is obtained which
corresponds to conventional products in terms of strength
values, densities, etc.
However, the main advantage is the fact that there is no
longer any need to use an autoclave, which is necessary
in conventional production methods.
Open moulding and the waterproof nature and leaktightness
that can be achieved when cationic surfactants are added
are further advantages that are obtained in combination
with the binding agent according to the invention.
The invention also encompasses a method for the
production of building components such as bricks, panels
or moulded parts for structural engineering and civil
engineering, which can be implemented in a cost-effective
manner; the building components thus produced have proven
to be resistant to tensile and compressive stress and to
weathering.
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In order to achieve this, according to the invention a
mixture of in each case equal amounts of clay with
particle sizes of less than 100 um, fine sand with
particle sizes of 100 um to 2 mm and sand with particle
sizes of more than 2 mm is mixed in a mixer with
polyelectrolytes - preferably polymers or copolymers
based on acrylamide - and a hydraulic binding agent,
placed in moulds and moulded at a pressure of at least
40 N/mmz. This method can be carried out in a particularly
simple manner since on the one hand only small demands
are placed on the apparatus and on the other hand the
required added components can be obtained easily and
inexpensively..Here, clay is understood to mean that part
of the soil with particle sizes of less than 100 um, fine
sand is understood to mean that part with particle sizes
of 100 um to 2 mm and sand is understood to mean that
part with particle sizes above 2 mm. These clay, fine
sand and sand components are widely available from soil,
even though the amounts of clay, fine sand and sand
obtained from the soil may differ in terms of their
quantities from the required composition. European soils
for example have a high content of loam and gravel, so
that in this case quantities of sand have to be added.
The required hydraulic binding agents, for example
cement, highly hydraulic lime, lime hydrate or fine lime,
are also widely and inexpensively available.
The mixture of clay, fine sand and sand which is required
to carry out this method can be obtained in a simple
manner since most soils contain these three constituents
in sufficient quantity. In practical use, only the top
layers of soil have to be removed in order to obtain the
mixture of clay, fine sand and sand and, after removing
gravel, stone and organic constituents, this is fed to
mixing systems in which it is mixed with the respective
binding agent and the polyelectrolytes. Only the
composition of clay, fine sand and sand must be checked
to ensure that these are present in equal amounts. A
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component may optionally be added if it is present in too
small a quantity. If clay, fine sand and sand are present
in essentially equal quantities, as defined above, this
mixture, which is hereinafter also referred to as the
"prepared mixture" can be passed to the further method
steps.
The choice of respective binding agent and the required
quantity to be added in each case depends in particular
on the precise particle size distribution and the
moisture content of the prepared mixture. In terms of the
particle size distribution of the prepared mixture, it is
not only the quantity distribution between clay, fine
sand and sand that is of interest, but also the particle
size distribution within each of these groups. Basic
properties of the prepared mixture, for example in terms
of its ability to be compacted, can already be derived
therefrom.
As discussed in more detail below, usually fine lime or
lime hydrate prove to be suitable as hydraulic binding
agent for carrying out the method according to the
invention, wherein in some cases it is also possible to
use highly hydraulic lime, cement and bituminous binding
agents.
The polyelectrolyte here in the conventional sense is a
water-soluble ionic polymer which results anionically
from polyacids - for example polycarboxylic acids -
cationically from polybases - e.g. polyvinyl ammonium
chloride - or is neutral (polyampholytes or polysalts).
One example of natural polyelectrolytes are
polysaccharides with ionic groups such as carrageen, but
also proteins and long-chain polyphosphates. According to
the invention, polyacrylamides are preferably used as
polyelectrolytes, that is to say compounds consisting of
monomers based on acrylamide. It is furthermore
conceivable also to use mixtures of monomeric and
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polymeric polyelectrolytes, optionally together with
solubilizers, emulsifiers and catalysts and with added
amounts of propylene diamine, dimethyl ammonium chloride
or isopropyl alcohol. Alternatively, mixtures of cationic
surfactants can also be incorporated. These
polyelectrolytes give rise to an agglomeration of the
fine-grained constituents which is not based on the
chemical conversion of water.
The blend consisting of clay, fine sand and sand mixture,
polyelectrolyte and hydraulic binding agent is then
placed in moulds and moulded at a pressure of at least
40 N/mm2. The choice of pressure influences the ultimate
strength of the building component, but it is usually
possible to work with a pressure of 40 - 120 N/mm2.
According to a further feature of the invention, the
polyelectrolyte is added in a preferred amount of 0.001
to 2o by weight with respect to the dry weight of the
mixture consisting of clay, fine sand and sand. Moreover,
before adding the hydraulic binding agent, a styrene
acrylic copolymer is added to the hydraulic binding
agent, which is particularly advantageous in the case of
wet and salty mixtures.
The objects of the invention are also achieved by the
characterizing features of Claim 22. This procedure is
particularly advantageous in the case of prepared
mixtures which have a low moisture content and a high
content of fine sand. It is provided here that a bitumen
emulsion and polyelectrolytes, preferably polymers or
copolymers based on acrylamide, are added to the prepared
mixture.
It has also proven to be advantageous to add the
polyelectrolyte in a preferred amount of 0.001 to 2o by
weight with respect to the dry weight of the mixture
consisting of clay, fine sand and sand. To this end,
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Claim 35 finally covers the use of polyelectrolytes,
preferably polymers or copolymers based on acrylamide,
for the production of building components such as bricks,
panels or moulded parts for structural engineering and
civil engineering.
Claim 36 discloses bricks and moulded parts for
structural engineering and civil engineering, which
contain polyelectrolytes, preferably polymers or
copolymers based on acrylamide.
This method according to the invention will be described
in more detail below:
Firstly, in order to obtain the mixture of clay, fine
sand and said, the top layers of soil are removed and,
after removing gravel, stone and organic constituents,
fed to mixing systems. No high demands are placed on the
composition of these layers of soil, since the clay, fine
sand and sand components required to carry out the method
are usually present in sufficient quantity. Only the
relative composition of clay, fine sand and sand must be
checked to ensure that these are present in each case in
equal amounts for further processing. Where necessary, a
component must be added if it is present in too small a
quantity.
Once clay, fine sand and sand components are present
essentially in equal amounts, as defined above, this
prepared mixture is mixed with polyelectrolyte in a mixer
in a subsequent method step. As already mentioned,
polyelectrolytes here means water-soluble ionic polymers
which result anionically from polyacids - for example
polycarboxylic acids - ca n onically from polybases - e.g.
polyvinyl ammonium chloride - or are neutral
(polyampholytes or polysalts). It is furthermore
conceivable also to use mixtures of monomeric and
polymeric polyelectrolytes, optionally together with
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solubilizers, emulsifiers and catalysts and with added
amounts of propylene diamine, dimethyl ammonium chloride
or isopropyl alcohol. These polymers have ionic
dissociable groups which may form part of the polymer
chain and the number of which is so large that the
polymers are water-soluble in dissociated form. Use is
preferably made of polyacrylamide in suspension form. In
aqueous solution, polyelectrolytes have reactive groups
which exhibit high affinity for the surfaces of the
colloids and extremely fine particles of the fine-grained
part of the soil. Depending on the ionogenicity of the
polyelectrolyte, the interactions with respect to the
solids particles are based on the formation of hydrogen
bridges, as is the case with non-ionic polymers, or on
electrostatic interactions and on charge exchange and the
resulting destabilization of the particle surface. The
anionic (= negatively charged) and cationic (= positively
charged) polyelectrolytes act in this way. The
destabilization and linking of a large number of
individual particles leads to irreversible agglomeration
of the fine particles in the clay, fine sand and sand
mixture, which gives rise to a higher density and thus a
higher strength of the building component ultimately
produced. The polyelectrolytes used according to the
invention can thus also be referred to as surface-active
substances.
An important factor for the optimal effect of the
polyelectrolyte is represented by the potentials active
at the particle surface. These depend both on the
particles themselves and on the ambient conditions, that
is to say on the ionic strength of the conglomeration and
the properties defined thereby, such as pH value,
electrical conductivity or hardness. By means of
relatively simple preliminary tests, the person skilled
in the art will determine the polyelectrolyte with the
appropriate ionogenicity that is suitable for the
respective application. However, it has been found that
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polyacrylamide for example is suitable in most cases and
exhibits good properties with respect to setting. The
polyelectrolyte is in this case used in a preferred
amount of 0.001 to 2o by weight with respect to the dry
weight of the conglomeration. The amount will depend in
particular on the ionogenicity of the polyelectrolyte
used and on the fine-grained part of the mixture. When
using polyacrylamide, usually 0.010 by weight has proven
to be sufficient. In the case of clay, fine sand and sand
mixtures with a low moisture content, any necessary
addition of water can be added via dilution with water.
In a further method step, in the case of a wet and/or
salty mixture and/or a mixture with a high content of
fine grains, a styrene acrylic copolymer is added, for
example an acrylic acid dispersion. In the case of a
prepared mixture with a low moisture content and a high
content of fine grains, a bitumen emulsion is preferably
added. However, it is not ruled out that a mixture of a
styrene acrylic copolymer and of a bitumen emulsion may
also prove to be advantageous.
The hydraulic binding agent is then added. Usually, fine
lime or lime hydrate prove to be suitable binding agents
for carrying out the method according to the invention,
wherein, in cases with a respectively high content of
relatively large particle sizes, highly hydraulic lime,
cement and bituminous binding agents may also prove to be
advantageous. The added amount of the respective binding
agent also depends in particular on the moisture content
of the prepared mixture, wherein it is desired to achieve
the so-called Proctor optimum at which the mixture
reaches the degree of saturation at which the optimal
compactability of the mixture is obtained. Soils and thus
the clay, fine sand and sand components obtained
therefrom often have too high a moisture content, with
water being drawn from the mixture when use is made of
fine lime, lime hydrate or highly hydraulic lime. This
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can be attributed on the one hand to the chemical
conversion of calcium oxide (Ca0) into calcium hydroxide
(Ca(OH)z) with binding of water, but on the other hand
also to the thermal energy released during this reaction,
which leads to the physical evaporation of water. The
water content of the mixture should be at the Proctor
optimum or slightly above for this method according to
the invention.
The blend consisting of clay, fine sand and sand mixture,
polyelectrolyte and hydraulic binding agent and any
required additives such as styrene acrylic copolymers is
then placed in moulds and moulded at a pressure of at
least 40 N/mm'. The choice of pressure influences the
ultimate strength of the building component, wherein it
is nevertheless usually possible to work with a pressure
of 40 to 120 N/mm2. After compression, the building
components can be subjected to stress after 50o drying.
These methods according to the invention thus firstly
give rise to an irreversible joining of the starting
components, namely clay, fine sand and sand. This is
achieved by agglomeration of the small-grained components
and alteration of the capillary water conveyance by
breaking up the adhering water film on the colloidal
constituents. This results in better compressibility of
the mixture and a high strength of the building component
produced by means of the method according to the
invention.
The scope of the invention also includes a method for the
production of an aerated concrete block, in which a
mixture of a hydraulic binding agent, a fine-grained
component, water and an aerating .agent is produced, cast
in moulds and dried.
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For the production of aerated concrete blocks, various
methods are known in which use is made in each case of a
mixture consisting of
~ a fine-grained component, such as quartz sand for
example,
~ lime,
~ a hydraulic binding agent, such as cement for
example,
~ water
~ and an aerating agent as pore former.
To this end, lime and cement are used in approximately
equal parts, and the aerating agent used is usually
aluminium powder. The amount of aerating agent is in this
case less than 0.050 by weight of the overall mixture.
The reaction of the calcium hydroxide with the aluminium
releases hydrogen, which is responsible for the high
number of pores. The mixture is cast in moulds, wherein
it is also possible to cut different formats and
profilings in the semi-solid state. The high strength of
the porous concrete is achieved after approximately four
to eight hours by steam-curing in autoclaves at
approximately 160 to 220°C and approximately 12 to 15 bar
pressure. During this, the hydrogen escapes and the pores
that are formed are filled with air. The effect of the
pressure and the hot steam gives off silicic acid from
the surface of the sand grains, which together with the
binding agent lime (lime hydrate) forms crystalline
binding agent phases - so-called CSH phases. These
crystalline binding agents bind to the sand grains and
create a solid structure of the individual additives. The
aerated concrete blocks thus produced have relatively low
densities of up to 400 kg/m3 and have good heat insulation
properties on account of the pore structure and the air
inclusions thereof.
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However, on account of the machines and systems to be
used, methods of this type are expensive and use a lot of
power. For example, high pressures have to be maintained
in the autoclave over a number of hours, wherein the high
power consumption can be attributed primarily to the
required heat treatment with steam. It is also
disadvantageous that for example groove and springs must
be milled into the blocks subsequently; complicated
shapes are often not possible on account of the necessary
steam curing. The quartz sands usually used to produce
aerated concrete blocks must moreover be of high quality
and may sometimes only be provided to the production
works after relatively long transport. When aluminium is
used in a production environment, there is also a risk of
explosion.
In order to avoid these disadvantages and provide a
relatively inexpensive method, in order to produce the
hydraulic binding agent used for this method according to
the invention, domestic waste is comminuted, homogenized
and mixed with calcium-containing additives such as
dolomite, calcite, lime marl or marl and with aluminium
oxide-containing aggregates such as corundum abrasives,
clay marl or clinker, and burnt; then up to 40o by weight
of tectosilicates, for example tuff, are added and the
resulting product is ground to an average particle size
of less than 0.063 mm. Furthermore, the fine-grained
component used is a fine slag from waste incineration
plants or slag from smelting works or steelworks, and the
aerating agent is a surface-active agent. These
constituents will be explained in more detail below.
Typical domestic waste contains, in percent by weight,
usually 59 to 69o silicon oxide, 4.9 to 7.8o iron oxide,
5.1 to 6.3o aluminium oxide and 8.3 to 10.30 lime, and is
therefore suitable for the production of an inorganic
binding agent for concrete-type setting compounds.
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The production of the binding agent may take place in
waste incineration plants operated by special fuel from
waste. This gives, in o by weight, 18 to 26o silicon
oxide, 2 to 5o iron oxide, 4 to 12o aluminium oxide and
58 to 660 lime and 2 to 5o magnesium oxide.
The combustion bed temperature is at least 950°C and the
calorific value of the waste is at least 13 MJ/kg. This
ensures that practically no additional primary energy has
to be used for combustion purposes.
The additives used may be calcium-containing waste from
industry or calcium-containing stone, such as dolomite,
calcite, lime marl and the like, which are easily
available.
The aggregates used may likewise be industrial waste,
such as corundum abrasives, but also clay marl, clinker
and the like.
This generally gives an ignition loss of approximately
50, a sulphate content of 4%, a chloride content of
approximately 30, a Blair value of 5000 cmz/g and a total
base content of p > 2, wherein the total base content is
calculated via p = (Ca0+Mg0+A1203+Fe203) SiO~.
By virtue of the ion exchange occurring during the
process and by virtue of sorbtion, any harmful substances
possibly contained in the domestic waste are bound and
can therefore be leached out of the binding agent and the
concrete produced therewith, and thus do not represent
any appreciable risk to the environment. It is largely
possible to omit the need for raw materials which can be
obtained only with considerable outlay. At the same time,
the problem concerning storage and treatment of houshold
waste is substantially alleviated. Since the energy is
essentially provided by the domestic waste itself, very
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consdierable energy savings are also made during
production of the binding agent.
According to the invnetion, the fine-grained component
used is fine slag from waste incineration plants or slag
from smelting works or steelworks. This is the solid,
non-combustible residues which arise during the course of
incineration in industrial furnaces or waste incineration
plants.
In waste incineration, slag amounts to approximately 350
of the original weight of the waste. Beside iron-
containing components, waste incineration slag also
contains significantly smaller amounts of non-ferrous
metals such as copper, nickel, lead, zinc or tin in
varying quantities.
Ironworks slag can be broken down into blast furnace slag
and steelworks slag, wherein blast furnace slag arises
during the production of crude iron in the blast furnace
and steelworks slag arises during the production of steel
in converters, in electric furnaces and in Siemens-Martin
furnaces.
Metal smelting slag is formed during the production of
non-ferrous metals. According to the current state of the
art, approximately 250 kg of blast furnace slag is
produced per ton of crude iron and approximately 120 kg
of steelworks slag is produced per ton of crude steel.
Large amounts of slag are thus produced, which can be
reused.
Blast furnace slag and steelworks slag differ in terms of
their chemical composition, but on account of their main
constituents of calcium oxide, silicon dioxide, aluminium
oxide and iron oxide they are both also suitable for use
with the method according to the invention.
CA 02538056 2006-03-07
21
It has been found that, due to the chemical composition
of the binding agent obtained from domestic waste and of
the fine slag from waste incineration plants or
industrial furnaces, there is no need to use aluminium
powder. Instead, use can be made of a relatively
inexpensive aerating agent, such as a surface-active
agent for example. This is understood to mean compounds
which become greatly enriched from their solution at
interfaces (e.g. water/oil) and as a result lower the
interfacial tension - the surface tension in the case of
liquid/gaseous systems. Although even polar solvents such
as alcohols, ethers, pyridines, alkyl formamides, etc.
are surface-active, within the scope of the invention the
surface-active substances used are preferably those
compounds which have a lipophilic hydrocarbon radical and
a hydrophilic functional group or possibly even a number
of hydrophilic functional groups - -COONa, -S03Na,
-O-SO~Na and the liked such substances are also referred
to as surfactants or detergents.
These may be water-soluble sodium or potassium salts of
saturated and unsaturated higher fatty acids (also
referred to as lye soap), or water-soluble sodium or
potassium salts of resin acids of colophonium (also
referred to as colophonium soap), or water-soluble sodium
or potassium salts of naphthenic acids - for example
casein-based enriched alkyl naphthalene sulphonic acid.
Moreover, the surface-active agent should be added in an
amount of 0.03 to O.OOlo by weight with respect to the
mixture prior to drying.
By way of a non-limiting example of embodiment, it is
possible to produce, stated in absolute amounts, a
mixture consisting of 780 kg of the hydraulic binding
agent according to Claim l, 290 kg of fine slag, 250 kg
of water and 0.25 kg of the surface-active agent, which
after air drying results in an aerated concrete block
having a density of approximately 600 kg/m3.
CA 02538056 2006-03-07
22
The drying may also take place without steam curing and
without creating high pressures; instead, air drying
proves to be sufficient. The maturation process up to
processability of the aerated concrete blocks is in this
case approximately 3 to 7 days, with the final strength
increasing as the drying time increases. Not only does
this result in a high energy saving, but it also makes it
possible to produce complicated shapes on account of
there being no need for steam autoclaving. The risk of
explosion associated with the use of aluminium powder is
omitted.
It has furthermore been found that, during the inflation
process, a lower expansion pressure is produced than in
the case of conventional production methods. As a result,
it is also possible to use less expensive materials as
formwork material for the casting of moulded parts. The
use of inexpensive raw materials such as domestic waste
or fine slag from waste incineration plants or industrial
furnaces ensures an additional cost reduction of the
method according to the invention.
During practical testing of the aerated concrete blocks
produced by means of this method according to the
invention, it has also been found that less water is
absorbed on account of the closed-cell structure of the
aerated concrete blocks and no shrinkage occurs, but
rather, on the contrary, there is a slight swelling. This
counteracts the risk of crack formation in the impact
area.
The density of the aerated concrete blocks produced
according to the invention is between 650.and 1200 kg/cm3.
The compressive strengths and the bending tensile
strengths are dependent on the density, with the ratio
between compressive strength and bending tensile strength
being considerably greater than in the case of concrete,
CA 02538056 2006-03-07
23
that is to say the bending tensile strength is relatively
high with respect to the compressive strength. This
ensures that heat-insulating panels produced from this
material have excellent stability for example. However,
by means of this method according to the invention, it is
also possible to reinforce the resulting aerated concrete
block with fibres, for example based on coconut or
synthetic material, as a result of which the bending
tensile strength can be further considerably increased.
It has been found that in particular the use of fine slag
instead of the conventionally used fine sand has
advantageous effects on the strength of the aerated
concrete block produced by means of the method according
to the invention.
In order to achieve lower densities of down to 300 kg/m~,
it is possible to use, in addition to the surface-active
agent, also powdered aluminium, this being aluminium from
recycling materials according to Claim 6. In this case,
too, it is possible to omit the energy-intensive and
complicated steam autoclaving operation.
According to a further feature, the powdered aluminium is
added in an amount of 0.05 to O.OOlo by weight with
respect to the mixture prior to drying. The amount of
aluminium powder used will depend on the one hand on the
amount of surface-active agent used and on the other hand
on the desired properties, in particular the density, of
the aerated concrete block ultimately produced.
Additional amounts of aluminium powder ensure in
principle that the pore structure after drying is
coarser, as a result of which the density of the aerated
concrete block is reduced. In particular, the average
pore size is dependent on the average particle size of
the aluminium powder used. It is thus obvious that,
depending on the mixing ratio and particle sizes of the
aluminium powder used and of the aerating agent,
CA 02538056 2006-03-07
29
different properties of the final aerated concrete block
can be obtained.
Particularly when using aluminium powder from recycling
materials, it has proven to be advantageous to mix the
powdered aluminium with an alcohol solution before adding
it to the overall mixture. This is because aluminium
tends to become covered with an oxide layer which makes
the aluminium non-reactive. The coating with alcohol
prevents oxidation of the surface of the aluminium
powder, as a result of which the effect of the aluminium
powder during the method according to the invention is
optimized.
However, according to the invention, it is also
conceivable that, instead of fine slag, the fine-grained
component that is used is fly ash from waste incineration
plants or slag from smelting works or steelworks. Of
course, it is also possible to replace amounts of the
above-described hydraulic binding agent with conventional
cement or amounts of the fine slag with conventional fine
sand, if this means that certain properties of the
resulting aerated concrete block can be optimized. By way
of non-limiting examples of embodiments, the following
formulas can thus be mentioned for aerated concrete
blocks having a density of 500 to 600 kg/cm3 and strengths
of 25 to 40 kg/cm2 (after drying for 28 days):
~ 330 kg of hydraulic binding agent according to
Claim 25, 165 kg of fine sand, 230 kg of water and
0.5 kg of a mixture of the surface-active agent
and aluminium powder;
~ 330 kg of hydraulic binding agent according to
Claim 25, 165 kg of fly ash, 300 kg of water and
0.5 kg of a mixture of the surface-active agent
and aluminium powder;
~ 165 kg of hydraulic binding agent according to
Claim 25, 165 kg of cement, 165 kg of fly ash,
CA 02538056 2006-03-07
300 kg of water and 0.5 kg of a mixture of the
surface-active agent and aluminium powder.
By virtue of precisely adapted formulas, it is thus
possible to achieve different properties of the aerated
concrete blocks produced by means of the method according
to the invention. The usability even in the case of
complicated shapes is also made much simpler by omitting
the steam curing operation.
This invention thus provides an extremely inexpensive
method for the production of an aerated concrete block
which is highly suitable for use as a high-quality, heat-
insulating light building material.
Other advantages, features and details of the invention
emerge from the following description of preferred
examples of embodiments and with reference to the
schematic drawing, in which
Fig. 1 shows an oblique view of a product to be
crushed;
Fig. 2 shows an oblique view of the crushed product;
Fig. 3 shows an oblique view of a device for treating
the product;
Fig. 4 shows an enlarged partial cross section through
the device;
Fig. 5 shows an enlarged detail from Fig. 4;
Fig. 6 shows the side view of a tool part.
Fig. 1 shows a heap of debris 10 consisting of spherical
constituents 12. By subjecting this mixture to high
mechanical stress in an activator (described below), the
CA 02538056 2006-03-07
26
product is crushed, as a result of which inter alia an
increase in surface area is achieved. Moreover, the
globular structures of a fly ash are altered such that an
amorphous structure is produced. This structure promotes
the binding process by hooking together the individual
particles 14 formed by the comminution process, and
increases the strength values, in particular the
compressive strength and bending tensile strength.
As a result of the particles 12 colliding onto and
against one another and the reflections occurring on the
activator, shock waves propagate in the particles 12 and
lead to splitting thereof into amorphous structures and
to disruptions in the lattice structure within the
particles, as shown in Fig. 2.
The comminution takes place in a so-called activator 20,
which has a machine platform 22, a rotor 24 and a stator
30, the cover plate 32 of which is passed through by a
rotor shaft 26. The latter runs coaxially with respect to
the vertical axis A of the rotor 24.
The rotor 24 is driven via an electric motor 36 (visible
outside the stator wall 34) by means of a V-belt 38 on
the rotor shaft 26. The rotational speed of the rotor 24
can be adjusted in a step-free manner via a frequency
converter (not shown).
Reference 40 denotes a cylindrical silo from which the
debris 10 is fed to a dosing device 42. Running below the
latter is a floor-level horizontal arm 45 of a conveyor
44 which is in this case Z-shaped when seen in
longitudinal section; the inclined central section 46 of
said conveyor merges into a front arm 47 above the cover
plate 32 of the stator 30. Arranged downstream of said
front arm is a cellular wheel sluice 50, through which
the conveyed goods 10 are fed to the interior of the
activator 20.
CA 02538056 2006-03-07
27
Figs. 4, 5 illustrate an annular chamber 52 of radial
width a between the outer face 28 of the rotor 24 and the
inner face 29 of the stator 30. Tools 54 and 54r,
respectively, protrude radially from both faces 28, 29.
Said tools have a channel-like recess 58 on either side,
close to their front end 56, as shown in Fig. 6.
In the annular chamber or annular gap 52, the mixture 10
is conveyed downwards in a spiral manner, wherein the
residence time thereof can be adjusted by means of air
flowing in the opposite direction. This stream of air
also dissipates excess heat. In this annular chamber 52,
the individual particles 14 are thrown outwards against
the stator 30 by a pulse, which is caused by the rotor
tools 54r.
The tools 54 and 54r both of the stator 20 and of the
rotor 29 are permanently covered with a layer of the
mixture 10 so that the particles collide with one another
and primarily with this layer. This mutual collision and
the effects achieved thereby - such as plastic
deformation, restoring behaviour, splitting, friction -
give rise to a fundamental alteration of the physical
properties of the particles 14.
Since layers of the mixture covering the tools 54, 54r are
supported by the bearing and resistance force of the
same, the mass of the tools 54, 54r substantially assists
both the pulse and the pulse interruption and the
interactions resulting therefrom, such as reflections
between the tools 54, 54r.
