WO2014179847A1

WO2014179847A1 - Building material and method to produce it

Info

Publication number: WO2014179847A1
Application number: PCT/BE2014/000019
Authority: WO
Inventors: Krist Paul DEGEZELLE
Original assignee: Devarec-Eco2 Beton, Besloten Vennootschap Met Beperkte Aansprakelijkheid
Priority date: 2013-05-08
Filing date: 2014-05-06
Publication date: 2014-11-13
Also published as: BE1021721B1

Abstract

Ecological cement characterised in that it is formed by the combination of two components: on the one hand an additive in gel form with strong acidic and strong alkaline components and on the other hand a metal oxide and silicon oxide containing binder, whereby an ecological cement is formed from low CO₂ raw materials that replace traditional Portland cement in building materials with the formation of ecological concrete that causes far fewer CO2 emissions, and provides greater compression strength, higher acid resistance, can harden much faster even at temperatures down to freezing point, and whose properties can be controlled by the composition of metal oxide and silicon oxide containing material in order to obtain the desired elemental composition.

Description

Building material and method to produce it.

The present invention relates to a building material and a method to produce it .

More specifically, the invention is intended for producing mortar and concrete without traditional Portland cement, but with similar or better properties such as compression strength and acid resistance.

Portland cement is an essential ingredient for producing traditional concrete, as a binder for sand and pebbles. However, the production of Portland cement is a highly energy-consuming process, which leads to substantial emissions of C0₂ in the atmosphere as a result of the use of carbon-containing fuels. The production of 1 tonne of Portland cement results in the emission of 1 tonne of (Χ½. The production of Portland cement is responsible for 8% of global CO2 emissions. On the other hand, the increase of greenhouse gases such as C(¾ in the atmosphere must be prevented due to the resulting climate change. The climate organisation of the United Nations announced in June 2013 that the critical threshold of 400 ppm C02 in the atmosphere had been exceeded, such that warming of three to four degrees worldwide can be expected.

The European Community is aiming for an economy that requires as little carbon as possible and issues directives whereby in the long term up to 90% of building materials will have to consist of recycled materials.

However, these recycled materials such as rubble granulates must also be held together by a binder in order to make concrete for example. The traditional binder is Portland cement, but for the reasons set out above this is not CO2 neutral, such that it is not suitable for achieving the intended objective.

The switch to rubble granulates yields as good as no C0₂ emission reductions, as these rubble granulates are also bound with Portland cement. Only if the cement is replaced will the impact of the granulates be many times greater, and if we then switch to rubble granulates this will lead to the lowest possible CO2 emissions.

DE 2.237.460 describes a cement in the form of a sodium and/or calcium aluminosilicate network of the zeolite type, that is formed at a temperature of 140 to 500 °C with increased water vapour pressure in a closed vessel to obtain a porous body.

A disadvantage of this cement is that it is only obtained at an increased pressure and temperature and is not suitable for producing non-porous concrete.

EP 1.401.783 AO (extension of WO 02/18290) describes an additive in gel form for building materials for the purpose of homogeneously distributing dyes or pigments in an ion- containing building material, including in mortars, cement materials, Portland cement or covering materials. The additive contains polyacrylic acid, EDTA, and ethanolamine or triethanolamine as an alkaline electrolyte. A disadvantage of this additive in gel form is that it only ensures the homogeneous distribution of dyes or pigments for the purpose of obtaining an even colour distribution in the building material, but does not replace the Portland cement .

The purpose of the present invention is to provide a solution to the aforementioned and other disadvantages, by providing an ecological cement with which concrete with the desired properties can be produced, but without using traditional Portland cement, so that an ecological concrete is obtained.

Hence the present invention concerns an ecological cement that consists of carefully selected oxides of silicon and metal oxides, mixed in a specific ratio, from the group of aluminium, titanium, iron, magnesium, manganese, chromium and calcium oxides, which together form a low COj raw material, whereby the selected oxide ratio is attuned to the compression strength that must be obtained with the concrete formed and to which an additive is added with strong acidic and strong alkaline components that form anionogenic groups that react with the oxide mixture to form ecological cement that can replace traditional Portland cement. The present invention also concerns an ecological concrete that is formed from the ecological cement and filler materials . An advantage of this ecological cement is that much less C0₂ is generated during the production of the components present in it, than during the production of Portland cement. For the total lifecycle of concrete,, calculations show that CO2 emissions are reduced by 75% if ecological concrete is used instead of blast furnace slag cement- concrete, and the emissions are reduced by 90% if ecological concrete is used instead of Portland cement- concrete, while the primary use of non-renewable energy is reduced by 50%. For the production process itself, the reduction is 104% for C0₂ emissions and 72% for nonrenewable energy used.

An additional advantage of this ecological cement is that the ecological concrete produced with it will absorb some of the CO2 from the atmosphere while setting such that this ecological concrete is practically climate neutral.

Another advantage of this ecological cement is that waste products that contain aluminium and aluminium silicates, such as glass or certain stones, can be worked into the concrete as filler materials.

Another advantage of the ecological concrete is that it is salt, acid, chloride, sulphate and base resistant. An additional advantage is that the ecological concrete is not polluting as a result of metals leaching out, but on the contrary can be recycled and used again to make concrete, which is demonstrated experimentally further.

An additional advantage is that the ecological liquid concrete mixture has a much lower water content than traditional Portland cement and during hardening presents a much lower heat generation.

Another advantage of ecological concrete is that it has a much higher fire resistance than traditional concrete and is even fire retardant, Preferably the additive contains strong acidic and strong alkaline components that form anionogenic groups such as silicic acid, resins with free acids and lactates (pH 2.2} and also strong basic components and alkaline-metal activators, such as alkaline hydroxides or similar organic salts (pH 12-14) and metal carbonates (pH 11.6). In its simplest form the additive only contains sodium or potassium hydroxide, but rubidium hydroxide or trialkylcarboniura compounds can also be used. Lithium hydroxide can also be used but this metal is much more expensive and has environmental polluting properties.

Preferably the additive is added in gel form, so that it adheres well to the materials to be wetted. An advantage of the addition of the additive in gel form to the mixture of oxides is that the metal and silicon atoms are released as ions from their fixed compound. The active ionogenic groups of the additive in gel form change the oxidation level of the metal and silicon atoms in the oxides such that they go into solution as cations and repel one another and move further in the mixture separately.

The splitting of these oxides proceeds very quickly in the alkaline environment and this forms a supersaturated turbid mixture. In concentrated solutions this results in the formation of a gel in which an increasingly extensive network of metal and silicon-containing particles forms, that form new solid compounds with one another by sharing their oxygen atoms through the contribution of positively charged metal ions (M⁺ such that the compound again reaches equilibrium.

After this gel formation the mixture continues to constantly reorganise itself such that the bond is strengthened and the ecological cement with the added filler materials finally forms a hard ecological concrete, whereby compression strengths of less than 30 MPa to more than 60 MPa after one month of curing are not exceptional.

The ecological cement contains silicon oxides (Si0₂) and metal oxides that are converted into Si¹⁺Oit- and metal oxide tetrahedra by changing their oxidation state. These tetrahedra link together via a common oxygen atom, whereby the central atom surrounded by four oxygen atoms in each linked tetrahedron can be a silicon atom but also a metal such as aluminium, titanium, magnesium, iron, manganese or chromium, so that networks of tetrahedra occur with different elements in the centre, but always bound by oxygen atoms .

The SiOj and AI2O3 oxides are converted into Si^C and Al³⁺0- tetrahedra by the anionogenic groups such as OH^" of the additive in gel form at room temperature or even lower temperatures down to 1°C, without forming C0₂ in contrast to the environmentally polluting heating of CaC0₃ to 1400 °C to form Portland cement that the traditional cement industry uses.

The anionogenic groups oxidise the silicon atom in S1O2 to a tetravalent positively charged silicon ion, while the two oxygen atoms each capture two electrons that were previously shared with the silicon atom. The ions formed are now very reactive due to the positive charge of silicon and the negative charge of oxygen and as a result have also become mobile. The silicon cation will bind with oxygen again as quickly as possible and this can be by binding with four oxygen atoms that each transfer one electron to the central silicon atom, which thereby has no further net charge and is stably bound to the oxygen atoms that are each at a vertex of a tetrahedron with the silicon atom in its centre.

The oxygen atoms at the vertices each have one negative charge or electron left over, such that they can also bind with an adjacent silicon or metal ion, such that a network of tetrahedra occurs, filled with silicon or metal atoms that are linked to one another by means of a common oxygen atom.

Some metal ions can take the place of the central silicon atom in the tetrahedra that present an oxygen atom at each vertex .

An example is the aluminium atom that is bound to oxygen in the AI₂O₃ molecule, but due to the action of anionogenic groups from the additive it is converted into trivalent Al³⁺ anions, with the formation of three bivalent oxygen O^2" cations that have become chemically highly reactive and have become very mobile. The Al³⁺ anion is able to take the place of silicon in a tetrahedral structure with four oxygen atoms at the vertices of the tetrahedron with the formation of an Al^O^4" tetrahedron. These aluminium-containing tetrahedra can form a network with other silicon-containing tetrahedra that are all bound by oxygen atoms.

The ecological concrete formed consists of a network of different silicon-containing and metal-containing oxides that are each bound together by sharing their oxygen atoms.

Our experiments have shown that the properties of the ecological concrete formed by these silicon-containing and aluminium-containing tetrahedra is predictably influenced by the ratio of silicon to aluminium. For example, by adding more silicon cations the concrete can be made more compression resistant, or by adding aluminium oxides is made more acid resistant.

The degree of coverage of the aluminium oxide and silicon oxide particles by the additive in gel form is important. With a complete coverage of the surface by the additive in gel form, higher compression strengths are obtained.

The general chemical formula of the ecological concrete formed can be presented as: x t (~Si0₂)_y - A10₂]_x . z H₂0

Where M is a positively charged metal cation and x the level of multiple condensation. For each quadruple bond that the aluminium atom makes, a cation is needed for compensation.

Depending on whether Si~Al Si-Al-Si or Si-Al-Si-Si is formed, y is equal to 1, 2 or 3, Z is the degree of hydration and is a maximum of 3 depending on the reaction product .

Experiments show that the measured compression strength of the ecological concrete obtained is determined by the value of y. The following table shows this relationship:

Y Formula Compression

strength

1 Si-Al 0 - 30 MPa

2 Si-Al-Si 30 - 45 MPa Si-Al-Si-Si 45 - 65 MPa

Table I: Relationship between the ratio of silicon atoms to aluminium atoms and the compression strength of the ecological concrete.

The ecological concrete consists of fillers and a binding cement with an amorphous network of tetrahedra that are bonded together by shared oxygen atoms. Due to the quadruple bond of aluminium to oxygen atoms there is a surplus of one negatively charged electron per aluminium atom, as the aluminium cation is only trivalent positive and not tetravalent.

This surplus negative charge must be offset by the pres< of positive metal ions (M*) or cations that enable additional structuring.

The aluminium ions have a larger radius (45 pm) than the silicon ions (42 pm) but still just fit in the lattice to make replacement possible and are thereby isoelectronic with the silicon ions, but cause a surplus negative charge in the lattice.

If only one silicon atom is replaced by an aluminium atom it is sufficient to add one monovalent positively charged metal ion to the lattice in order to preserve the balance. The monovalent charged metal ion can be H⁺, Li⁺, Rb⁺, K^'1', or Na⁺ _f or also a carbonium ion ₃C⁺. If two silicon atoms have been replaced by an aluminium atom, this must be counterbalanced by one bivalent positively charged metal ion (M²⁺) in order to bring the lattice back to equilibrium whereby this bivalent charged metal iron can be Fe²⁺, Mg²⁺, Ba²⁺, Ti²⁺ or Ca^2h.

The monovalent charged metal ions and the bivalent charged metal ions are electrostatically bound by Van der Waals forces in the three dimensional network of the crystal lattice and ensure a greater density and lower compressibility.

If more of the cheaper aluminium oxide is used to make the lattice more acid resistant, this can be counterbalanced by bivalent metal ions such as Ca²⁺ that are present in abundance in recycled bricks for example.

In addition to an amorphous network of tetrahedra it is possible for three dimensional sheet structures to emerge due to the counterbalancing bivalent charged metal ions occupying a position surrounded by six oxygen atoms, four of which are in a horizontal plane around the metal ion and one above and one below the metal ion. This position is called an octahedral coordination and is possible for Fe²⁺, Mg²⁺ Mn²⁺ and Ca²⁺ ions.

Such sheet structures have a surplus negative charge on their surface, that can be counterbalanced by interstitial positively charged metal ions that can be monovalent or bivalent and which ensure the fixing of the sheet structures with respect to one another, and prevent them sliding away, which influences the properties of the ecological concrete formed.

In the ecological cement the positive metal cations <Fe²⁺, g²⁺, Ba²⁺, Ca²⁺ , Fe³⁺, or Ti⁴⁺) or R₃C⁺ occur as strong acids and they react with the strong bases present {0^2", Η₂0, OH^", CO3^2", SO ^") . Aluminium oxide will react as a base with the formation of an Al^3'h ion. The force of attraction between strong acids and bases is mainly of an ionic nature and they form strong compounds based on coulomb forces such that they react more quickly.

These strong acids and bases present:

- a small ion radius;

- a high oxidation number;

- a low polarisability;

- a high energy level of the lowest unoccupied atomic orbital for the strong acids;

- a low energy level of the highest occupied atomic orbital for the hard bases.

The energy difference between the aforementioned energy levels is of great importance for the properties of the ecological cement that forms the basis of the ecological concrete .

The attraction between the opposite charges leads to an orientation effect that occurs more quickly in a liquid concrete mixture than in a dry mixture and is further accelerated if the liquid concrete mixture is vibrated.

This means that faster bonding and hardening occurs because the molecules can arrange themselves more quickly to form ionic bonds.

As a result of this chemical bond new compounds emerge and a lattice is formed. The more strongly. the ions attract one another the greater the energy released upon lattice formation, and this energy is at a maximum when the ion charges are greater and the ion radii are smaller, whereby the magnitude of the charge has a more relevant effect on the lattice energy than the ion radius.

The following table shows the ion radius for a number of cations, as well as their coordination number with oxygen and the polyhedron formed with oxygen.

Table II: Ion radius, coordination number with oxygen and polyhedron formed for a number of cations,

The surplus energy from the lattice formation can be used again to extract electrons with the ionisation of the adjacent metal-containing oxides. With this ecological concrete much less energy is released during the lattice formation than with traditional concrete with Portland cement because the magnitude of the ion charges is smaller as we work with different ratios. This means that much less heat is generated (up to only one quarter) in the formation of the ecological concrete, which enables the ecological concrete to be used for massive constructions whereby preferably less heat must be emitted and less shrinkage occurs.

To ionise Si to Si⁴⁺, 9948 KJ/Mol of energy is required. To ionise Al to Al³⁺, 5133 KJ/Mol of energy is required. To ionise Mg to Mg²⁺, 2180 KJ/Mol of energy is required.

This means that the aluminium and magnesium oxides will dissociate more quickly because they require less energy, which in practice manifests itself by faster bonding with the addition of more aluminium oxides or magnesium oxides to the ecological concrete.

It was already stated above how the compression strength of the ecological concrete formed can be controlled by varying the ratio of aluminium oxide to silicon oxide, such that the compression strength of the ecological concrete formed can be raised to 60 MPa.

Even higher compression strengths can be achieved through the addition of Fe²⁺ and Ca²⁺ cations in the form of ferrous salts and calcium salts, whereby a composition with the following percentages for example yields a compression strength of more than 65 MPa after curing:

21% Al³⁺ : 26%

Fe²⁺ : 17%

Si"⁺ : 30%

0 : 4.<

H⁺ : 1.'

In order to obtain these properties the percentages of cations have to remain within the follovjing ranges :

Ca²⁺ ; 19 - 21%

Al³⁺ : 26 - 28%

Fe²⁺ : 17 - 19%

Si«⁺ ·, 30 - 32%

0 : 1.4 - 4.<

H^÷ : 0.4 - 1.'

In addition to pure calcium salts , recycled rubble granulates can also be used with a suitable Caⁱ⁺ content that has been measured by atomic spectrometry.

Alternatively Mg⁺ cations can also be added such that lower lattice energies are obtained and such that lower compression strengths are obtained. The oxides that are used in the ecological cement have 4 electrons or less in the valence band such that they are free to move and such that they contribute to the electrical conductivity. After the liquid ecological concrete mixture has been prepared from the ecological cement with the additive in gel form mixed with rubble granulates as a filler material for example, the progress of the curing can be measured amperometrically. The electrical resistance through the mixture falls at the start of the bonding when electrons are transferred and ions become mobile, but rises again at the end of the curing because all ion lattices have been formed and the bonding is complete.

The measurement of the conductivity of the liquid concrete mixture consequently enables the processor or customer of the concrete to know what the expected bonding and finishing time is, and thus when is the right time for casting and finishing, such that the implementation can be better planned in advance.

An advantage of the ecological concrete is that the curing time for a concrete with low compression strength can proceed just as quickly as for a concrete with a high compression strength,

For example, foundation concrete with a low compression strength (C16/20) can be walked on after one hour.

During curing, chains and ring structures with Si^4'1- and Al³⁺ atoms are formed, each time bonded to four oxygen atoms and their structure varies from amorphous to semi-crystalline.

The chemical reaction that leads to an ecological concrete due to the action of alkaline components in the additive in gel form can be presented as follows: 1) For concrete with a low compression strength (30 MPa or less) :

(Si0_2f Al₂0₃)_n + 3n ¾0 plus additive in gel form ->

n M\ n[ (OH)₃ -Si-0-Al^~- {OH} ₃]

By adding more amorphous silicic acid to the reaction mixture the following is obtained: 25 For concrete with medium compression strength (45-65 MPa) :

(Si0₂, Al₂0₃)_n + n Si0₂ + 4n H₂0 plus additive -> n M*. n[(OH)₃ -Si-0-Al^~-0-Si-{OH)₃]

(OH) ₂

And by adding more amorphous silicic acid to the reaction mixture the following is obtained:

3) Concrete with high compression strength ( > 65 MPa) n M*. n[ (OH) ^Si-0-Al^~-0~Si-O~Si- (OH) ₃]

1¹

(0H>₂ (OH) a

By further increasing the silicic acid content in the reaction mixture the following is obtained:

4) Concrete with very high compression strength {> 70 MPa) This ecological concrete can be compared to a natural rock and has the same hardness, chemical stability and erosion resistance .

Due to the chemical stability, this type of concrete is resistant to temperatures of more than 1000°C, whereby the material will sinter and form a denser more stable whole whereby first the water evaporates.

Upon further research it turns out that this type of concrete heats up to a temperature of only 300 ^DC over half an hour in temperatures of more than 1100°C, such that this type of concrete has fire retardant properties.

5) Concrete with ultrahigh compression strength (> 200 MPa) :

Even higher compression strengths are achieved by increasing the specific area of the silicon oxide particles used, such as is possible in certain forms of nanoparticles that are provided with outgrowing surface fibres so that a greater area can come into contact with the additive in gel form. As a result, the bond is strengthened to such an extent that the quantity of silicon oxide particles used can be reduced by half and the intended compression strength nevertheless stays within range.

The bonding and hardening of the ecological concrete can be presented schematically in the following six consecutive steps : 1 - Formation of metal and silicon oxide cement:

Dissociation of the oxides by the addition of the additive in gel form and water at room temperature or lower temperatures down to 1°C.

2- Formation of an aluminium/silicon monophase:

The aluminium and silicon oxides form one mixture, to which optionally a hardening accelerator (lactic acid salts) or a hardening retardant (boric acid) can be added.

3- Formation of a viscous mixture:

The monophase mixture becomes a viscous gel, whereby optionally the mixture can be vibrated to accelerate the hardening,

4- First extraction of water:

Formation of ecological concrete with low compression strength {< 30 Pa) ,

5- Second extraction of water:

Formation of ecological concrete with medium compression strength (30-45 MPa), with the formation of amorphous structures .

6- Third extraction of water:

Formation of concrete with high compression strength (45-60 MPa) , with the formation of a three dimensional network, The greatest compression strength is obtained with an optimum Si/Al ratio. With a low Si/Al ratio a crystalline structure is formed that is rather weak, while with a greater Si/Al ratio a gel phase forms that sets into an amorphous structure. With too high a Si/Al ratio the compression strength decreases again because then the reaction does not continue through to completion.

The curing time is influenced by the temperature of the mixture and the stoichiometr , The curing time can be reduced by increasing the temperature, increasing the cation content or reducing the Si/Al content.

The microstructure is strongly influenced by the Si/Al ratio. With a low ratio an open, porous, weak and crystalline structure is formed, Higher ratios lead to a less porous and amorphous material that is stronger due to the formation of more gel phase in the chemical reaction.

An increase of the anionogenic groups in the additive in gel form only leads to an increase in the tensile strength and compression strength of the concrete formed if there is also a sufficient quantity of cations and water molecules to allow the reaction to be fully completed. The processing time decreases as the concentration of anions increases. The increase of metal cations also ensures faster bonding between Si, Al and the anionogenic groups because more of them are present. Kith a smaller quantity of cations there are consequently also fewer anions, which first have to correctly orient themselves in order to make a bond. More such groups ensure that a there is a greater probability of a good orientation quickly. For the modulus of elasticity there is an increasing trend with the increase of the number of cations. Indeed they ensure an arrangement of the polar water molecules such that the -water no longer flows. With a larger number of ions the ordering of these molecules is stronger and the ordered water reacts more viscously.

The bond strength of the concrete is reduced by the presence of chlorides. Indeed, the chlorine ions ensure crystallisation and the formation of gel precipitates, which leads to a reduced attachment of the gel to the oxides . The shrinkage of the ecological concrete is less than with a traditional concrete v/ith Portland cement because the heat of hydration is lower {only 25%) , but also because the water molecules arrange themselves around the positive and negative ions over time. On account of this bonding, part of the water will no longer evaporate, which also limits the shrinkage by drying. The lower shrinkage of ecological concrete provides the advantage that no further shrinkage reinforcement has to be provided but a lighter reinforcement is sufficient.

Another contribution to the shrinkage, the chemical shrinkage, cannot be avoided by preventing the evaporation of water. This chemical shrinkage occurs due to the molecular chains entangling during curing, such that they dens fy. The difference in shrinkage behaviour with different anion/cation concentrations is thus not only the result of chemical reactions, but also of the evaporation of water. For a concrete with a higher anion/cation concentration, the reaction proceeds faster and is thus more exothermic, whereby the heat of reaction will evaporate the water more quickly.

This ensures a somewhat greater drying shrinkage, but which is still less than for traditional concrete with Portland cement. A good post-treatment by covering the surface with curing for example can be useful to this end.

An advantage of this method for producing an ecological concrete is that the quantity of water needed to maintain the same liquidity can be reduced by adding a certain quantity of additive in gel form. This results in a water content [liquid/solid material ratio of 1/4) that is a great deal lower than with a traditional concrete with Portland cement.

After curing, this lower water content results in a very fine and dense pore structure because the bonding of the ecological concrete does not come into being through the hydration of the binder as in traditional concrete, but due to the additive in gel form creating an alkaline environment that makes the oxides change form, irrespective of the temperature at which the curing occurs. This leads to a compact pore structure that is optimum when the areas of the aluminium/silicon particles are completely covered by the additive in gel form. Subject to the ratios in the formulation of the ecological concrete being within the ranges shown in the following table III, the compression strength of the resulting concrete can be read off from a graph shown in figure 7 ,

Table III: Ranges of the ratio between components of the ecological concrete required to be able to predict the compression strength.

Preferably the additive in gel form contains an activator based on lactic acid salts or lactates that act as a reaction accelerator.

An advantage of this reaction accelerator is that the concrete formed hardens more quickly and the formwork can be removed more quickly, which enables a faster delivery of prefabricated concrete or concrete for roadworks, for example.

Preferably the additive contains boron compounds in gel form as a reaction retardant. An advantage of a reaction retardant is that the hardening can be delayed, which can be useful for some applications such as transport over long distances or pumping up concrete .

Acid corrosion tests with acetic acid and lactic acid, whereby the concrete is cyclically immersed in an acid solution, shows the weight loss to be only 2.3% for the ecological concrete, while for traditional Portland concrete it is 11. 7 % in the same time span. The greater acid resistance of the ecological concrete can also be seen well on the surface of the repeatedly immersed material, while with Portland concrete the cement layer between the filler material is partly dissolved, while the surface of the ecological concrete remains smooth on the outside.

This difference in acid resistance arises from the fact that the ecological concrete emulates metal-containing sandstone, which is the most durable sandstone in nature, while traditional Portland concrete emulates a pure limestone by first breaking it down at 1400°C and then composing it again by adding water.

Diffusion tests on the ecological concrete have shown that the leaching out of components is much lower than the allowed limits imposed by the authorities. The following table shows the measured quantity of leached metal over a period of 100 years and this for a number of metals due to leaching out by rainwater and other solvents, and the measured immission value compared to the limit of the government standard for each metal, expressed in mg/m2 of the metal that gets in the soil.

Metal Rainwater Other Limit in solvent mg/m2

Arsenic 4.03 12.74 285

Cadmium 0.13 0.42 12

Chromium 2.66 8.43 555

Copper 10.66 33.70 255

Mercury 0.49 1.56 8,2

Lead 0.13 0.42 609

Nickel 1.34 4.24 136

Zinc 6.66 21.06 924

Table IV: Immission values after 100 years for metals in ecological concrete due to leaching out by rainwater or another solvent, compared to the limit values of the government standard.

These measurements show that the ecological concrete does not cause any inadmissible soil pollution due to metal ions washing out. Even better, the ecological concrete used can be recovered and recycled in new concrete mixtures.

It goes without saying that the higher compression strength that is obtained with the ecological concrete enables the dimensions of concrete constructions to be reduced, while maintaining the required strength. For example, a pillar of traditional Portland concrete can be replaced by a pillar of ecological concrete whose cross-section is 25% smaller, or a floor slab of traditional Portland concrete can be replaced by a slab that is 16% thinner while preserving the same load bearing capacity.

For glass concrete, whereby glass is bound in the concrete as a filler, ecological concrete provides the advantage that up to 2 tonnes of glass can be worked in per m³, while with Portland concrete it is only one quarter of this quantity of glass. It is thereby possible to produce concrete with ecological concrete that lets light pass through whose load bearing capacity is high enough to realise a skylight in a building, for example, that can be walked on.

With the intention of better showing the characteristics of the invention, a preferred embodiment of an ecological cement and ecological concrete element according to the invention is described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein:

Figure 1 schematically shows the electron structure of Si02 before and after dissociation by anionogenic groups ;

figure 2 shows a silicon-containing S1O4- tetrahedron; figure 3 shows a network of silicon-containing and aluminium-containing tetrahedra;

figure 4 presents the concentration of released Si^<3+ ions as a function of time for different concentrations of anionogens;

figure 5 shows figure 4 but now for the concentration of released Al³⁺ ions; figure 6 schematically shows the surface of an aluminate particle of 35 microns diameter after treatment according to the invention with the additive in gel form at different concentrations of the additive;

figure 7 shows the relationship between the compression strength obtained in the ecological concrete and the ratio of binder/additive in gel form in the ecological concrete;

figure 8 shows the relationship between the compression strength obtained in the ecological concrete and the ratio of oxide cement/additive in gel form, and this for four different concentrations of the additive in gel form;

figure 9 shows two sheet-like crystal lattices of oxide octahedra with 3 Si^4÷ ions per Al³⁺ ion in which Si⁴⁺ ions can be replaced by Mg²⁺ _f Fe²⁺ or Mn²⁺ ions; figure 10 shows figure 9 but in which Si ⁺ ions can now be replaced by Al³⁺, Fe³⁺ or Cr³⁺;

Figure 11 shows figure 10 but in which two trivalent cations are now replaced by one tetravalent Ti⁴⁺ and one bivalent cation Mg²⁺, Fe²⁺, Ca²⁺ or to a limited extent Mn²* ions;

figure 12 shows figure 9 but now with 1 Si⁴⁺ ion per Al³⁺ ion;

Figure 14 shows figure 13 but in which two trivalent cations are replaced by one tetravalent Ti^ and one bivalent cation Mg²⁺ _f Fe^2÷, Ca²⁺ or to a limited extent Mn²⁺ ions; figure 15 shows a spreadsheet with which a batch of ecological concrete with the desired properties can be composed. Figure 1 shows the electron structure of Si02, before and after dissociation by anionogenic groups (OH-) whereby silicon is surrounded by eight electrons and each oxygen also by eight electrons, but whereby due to the action of anionogenic groups, silicon loses its electrons in the outermost shell and forms a tetravalent positive cation, and whereby both oxygen atoms now form negatively charged bivalent O^z~ ions, such that the ions become mobile and reactive. Figure 2 shows the molecular structure of SiO^, after the tetravalent Si^15"1- ion has bonded to four oxygen ions whereby each oxygen atom transfers one electron (charge -1) to the central silicon atom so that a tetrahedron is formed whereby the net charge is zero for the central silicon atom, but each oxygen atom still has a negative charge left over to form a bond with another silicon or metal ion.

Figure 3 shows a network of silicon-containing and aluminium-containing tetrahedra that are linked together by means of a common oxygen atom. The network consists of tetrahedra of Si0₄ with one silicon atom in the centre of the tetrahedron and one oxygen atom per vertex, and of tetrahedra of A104, with one aluminium atom in the centre and one oxygen atom at each vertex. Figure 4 shows a curve that presents the concentration of silicon ions (Si^44'} that are released as a function of time as a result of the contact with the anionogenic groups of the additive in gel form, and this for three concentrations of the additive (5M, 10M and 15M) , where M stands for the molar concentration of the anionogenic components present in the additive.

Figure 5 shows a curve that presents the concentration of aluminium ions (Al³⁺) that are released as a function of time as a result of the contact with the anionogenic groups in the additive in gel form, and this for three concentrations of the anionogenic components of the additive (5M, 10M and 15M) .

Figure 6 shows the surface of a spherical aluminate particle of 35 microns diameter after the action of the additive in gel form according to the invention, and this for three concentrations of the additive (5M, 10M and 15M) as observed under a microscope.

Figure 7 shows the relationship of the compression strength of the ecological concrete obtained as a function of the binder/additive in gel form ratio in the ecological cement, and this for four different concentrations of active ingredients of the additive in gel form. With a 1/1 ratio of binder/additive, a compression strength is obtained of more than 60 MPa at the highest concentration of anionogenic components of the additive (15 M) . Figure 8 shows the relationship of the compression strength of the ecological concrete obtained as a function of the ratio of oxide cement/additive in gel form, and this for four different concentrations of anionogenic components such as hydroxides of lithium, sodium, potassium, rubidium trialkylcarbonium in the additive in gel form. With the highest concentration of anionogenic components in the additive (8M) a compression strength of more than 90 Mpa is obtained for a ratio of oxide cement/additive in gel form of 1.25.

Figure 9 shows the crystal lattice of two sheet-like structures formed of oxide tetrahedra consisting of SI⁴⁺ and Al^3'1" ions and whereby these tetrahedral structures are bonded together by the octahedral structures that consist of metal cations with charge 2+, 3+ and 4+ (Ti) that were shown in table II according to their ion radius ratio.

The two sheet-like structures are held together by monovalent positively .charged metal ions such as Na⁺, K⁺, Li^4" or Rb⁺, or also R₃C⁺ or H⁺ that counterbalance the surplus negative charge in the sheet-like structure that occurs due to the lower positive charge of aluminium ions in the structure with respect to the charge of silicon ions. The ions in the lattice can be replaced by Mg2÷, Fe2+ or to a limited extent by Mn2+ ions that form an octahedral structure.

Figure 10 shows the crystal lattice of two sheet-like structures formed of oxide octahedra with 3ϊ^ΐ÷ and Al³⁺ ions in the centre, whereby the ratio of tetravalent Si^ ions/trivalent Al ions is equal to 3/1. The two sheetlike structures are held together by monovalent positively charged metal ions, such as Na⁺ or K⁺ that counterbalance the surplus negative charge in the sheet-like structure that occurs due to the lower positive charge of aluminium ions in the structure with respect to the charge of silicon ions. The ions in the lattice can be replaced by Mg2+, Fe2+ or to a limited extent by Mn2+ ions that form an octahedral structure.

Figure 11 shows the crystal lattice of figure 10 whereby two trivalent cations are now replaced by one tetravalent and one bivalent Mg²⁺ _f Fe²⁺ ₇ Ca²⁺ or to a limited extent Mn²⁺ cation so that their combined positive charge (6+) is counterbalanced by six OH^" ions (6-) in the lattice. In this way material originating from titanium production is used in the ecological cement whereby the higher charge of titanium results in a greater attraction between the ions and the lattice formed resulting in stronger lattices and a greater hardness. Here too the two sheet-like structures are held together by monovalent positively charged metal ions such as Na^÷, K⁺ _f Li⁺, Rb⁺, or also R₃C⁺ or H⁺.

Figure 12 shows the crystal lattice of two sheet-like structures formed of oxide octahedra with Si⁴⁺ and Al³⁺ ions in the centre whereby the ratio of tetravalent Si⁴⁺ ions/trivalent Al³⁺ ions is equal to 2/2. The two sheet- like structures are held together by two bivalent positively charged metal ions that counterbalance the surplus negative charge in the sheet-like structure due to the double less positive charge of aluminium ions in the structure with respect to the charge of silicon ions. The silicon ions in the lattice can be replaced by A13+, Fe3+ or Cr3+ ions. Figure 13 shows the crystal lattice of two sheet-like structures formed of oxide octahedra with Si^4÷ and Al³⁺ ions in the centre, whereby the ratio of tetravalent Si⁴⁺ ions/trivalent Al³⁺ ions is equal to 1, The two sheet-like structures are held together by bivalent positively charged metal ions that counterbalance the surplus negative charge in the sheet-like structure that occurs due to the lower positive charge of aluminium ions in the structure with respect to the charge of silicon ions. The silicon ions in the lattice can be replaced by A13+, Fe3+ or Cr3+ ions.

Figure 14 shows the crystal lattice of figure 13 but whereby two trivalent cations are now replaced by one tetravalent Ti⁴* and one bivalent cation Mg²⁺, Fe²⁺, Ca²⁺ or to a limited extent Mn²⁺ ion, so that their combined positive charge (6+) is counterbalanced by six OH^" ions

(6-) in the lattice. The bivalent positive cations that hold the two sheet-like lattices together consist of Ca²⁺ or Ba^2i' ions and whereby the higher charge of titanium leads to a greater hardness of the ecological concrete formed with it .

Figure 15 shows a spreadsheet by which a batch of ecological concrete with the desired properties can be composed. In the columns of the spreadsheet, column A shows the percentage share and column B the weight of each participating fraction of, in this case, four different mixtures of oxides whereby each mixture occupies its own row. Column C shows the volume in litres for each participating fraction. Columns D, E and F show the percentage of silicon dioxide, aluminium oxide and titanium dioxide for each fraction, that provide tetravalent and trivalent cations, while columns G, H, I and J show the percentage of iron oxide, calcium oxide, sodium oxide and magnesium oxide, which form a group of bivalent and monovalent cations. These percentages were measured beforehand for each participating fraction by elemental analysis with a spectrometric technique such as flame ionisation spectrometry or atomic absorption.

The lower rows take the elemental composition of the inert fillers into account, whereby the spreadsheet calculates the total percentage of cations that can be absorbed in the tetrahedra, and takes account of the total percentage of cations that can be put into the octahedra. The lower rows of the A and B columns take account of the percentage and the quantity of gel with ionogenic components, and optionally added resins with acid, accelerators or retardants, For the specified composition, the spreadsheet calculates the expected compression strength, and this for the intended formula, and also for the increase or decrease of the water content such that the ratio of water/solid material changes and the expected compression strength can be predictably influenced by changing the water content. The spreadsheet checks whether the mole ratios that were given in table III above fall within the ranges in which they have to be in order to ensure the predictability of the properties of the concrete formed,

The spreadsheet also shows a graphic presentation of curves, as described in Fig. 8, from which the expected compression strength of the ecological concrete can be read as a function of the oxide cement/additive in gel form ratio, and this for four different concentrations of anionogenic components of the additive in gel form. It can be read from these curves what changes to the concentration of the additive and to the ratio of oxide cement/additive are wanted in order to achieve the target compression strength.

These changes can then be entered in the set parameters of the spreadsheet, after which it calculates the new compression strength to be expected,

The curves of Fig. 8 were determined experimentally and can be replaced by other curves that have also been determined experimentally, as described in Fig. 7, in which the compression strength is given as a function of the binder/additive ratio and this for different concentrations of the ionogenic components in the additive.

Other parameters than the compression strength can also be predicted on the basis of experimentally determined curves, such as for example the acid resistance, resistance to high temperatures, curing time, pore size, liquidity of the concrete and the duration within which the concrete must be worked and other measurable properties of the ecological concrete . Depending on the objective, the composition of the concrete mixture can be adapted in the spreadsheet by means of these other parameters, and the new predicted parameters can be compared to the objective. These tools enable a method to be developed for producing ecological concrete, which forms part of this invention and this method can be described with the following steps.

- First silicon oxides and metal oxides are collected from recycled material or other sources, whereby each batch is pulverised or granulated and homogenised;

- Then for each batch the elemental composition is measured concerning the silicon and metal elements, that can be converted into cations, by means of an elemental analysis technique;

- Then a mixture is composed of different batches to obtain the desired elemental composition for the ecological cement that is required to obtain a set compression strength or another property of the ecological concrete, and this on the basis of the elemental analyses of each batch of raw materials and the known graphs that show the relationship between the composition and properties of the ecological concrete and whereby the composition is calculated for the mixture on the basis of the contributions of each batch of silicon oxides and metal oxides to the ecological cement;

- - Then an additive in gel form with ionogenic groups and water are added to the composition that contains metal oxides and silicon oxides, while the additive in gel form contains strong acids and bases such as ionogens that ensure that the silicon ions and metal ions in the composition go into solution and can further react to form ecological cement and this at room temperature or lower down to 1°C;

- Then water and filler materials are added to the mixture and optionally process accelerators such as lactic acids or retardants such as boric acid to control the curing rate of the ecological concrete;

- Then the electrical resistance of the liquid concrete mixture is measured continuously to be able to predict the start of the bonding and the end of the hardening;

- Then the liquid concrete is transported and cast at the right time in formwork intended for this purpose; - Then the cast ecological concrete is taken out of its formwork or mould when it has set sufficiently;

- Finally the surfaces of the ecological concrete exposed to air are optionally covered with a curing layer to make the surface watertight and to prevent the loss of hydration water from the ecological concrete, or these surfaces are covered with a layer of water to prevent evaporation of water from the concrete shortly after placement;

The cast ecological concrete is C(¾ neutral because less energy is required to make the ecological cement and because CO2 is absorbed from the air during curing.

During curing heat of hydration occurs, but the quantity of heat is only one quarter of the quantity of heat for traditional concrete with Portland cement and with the same dimensions. This is especially so because with the hydration of CaO, formed from the pyrolysis of CaC03 in the formation of Portland cement, much more heat is released than with the hydration of silicates and aluminates in the ecological concrete.

These properties enable the ecological concrete to be used for massive constructions, such as a concrete dam, whereby the whole can be finished more quickly because the ecological concrete produces less heat (only 25%) than a traditional concrete with Portland cement, such that there is less of a temperature difference between the interior and exterior of the construction. These properties are also useful for the application of ecological concrete in prefabricated concrete. With accelerated curing, the ecological concrete can be taken out of the mould or formwork more quickly than with traditional concrete with Portland cement, so that a signi icantly higher production per unit time can be achieved with the same mould or reusable formwork. The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but the ecological cement and the method for obtaining ecological cement according to the invention can be realised in all kinds of forms, dimensions and variants, without departing from the scope of the invention as described in the claims.

Claims

Claims .

1. - Ecological cement characterised in that it consists of carefully selected oxides of silicon and metal oxides, mixed in a specific ratio, from the group of aluminium, titanium, iron, magnesium, manganese, chromium and calcium oxides, which together form a low C0₂ raw material, whereby the specified ratio is attuned to the compression strength that must be obtained with the concrete formed, and to which an additive in gel form is added with anionogenic groups formed from at least strong alkaline components and optionally also strong acidic components and that replaces traditional Portland cement.

2. ~ Ecological cement according to claim 1, characterised in that the additive in gel form contains at least strong alkaline components and alkali-metal activators, i.e. an alkaline hydroxide or similar organic salts (pH 12-14) and metal carbonates (pH 11-6) , and optionally also strong acidic components, i.e. silicic acid, resins with free acids and lactates (pH 2.2).

3. - Ecological cement according to claim 1, characterised in that S1O2 and AI2O3 oxides are converted into S1O4 and AIO4 tetrahedra by the anionogenic groups in the additive in gel form without forming CO2.

4. - Ecological cement according to claim 3, characterised in that these tetrahedra can link themselves together via a common oxygen atom, whereby the central atom that is surrounded by four oxygen atoms in each linked tetrahedron can be a silicon atom but also a metal such as an aluminium, titanium, magnesium, iron, manganese, or calcium atom,

5. - Ecological concrete characterised in that it is formed from a mixture of ecological cement according to claim 1 and added fillers such as stones, sand or glass residues whereby the ecological concrete presents compression strengths of less than 30 MPa ranging to more than 60 MPa.

6.- Ecological concrete according to claim 5, characterised in that the properties of the concrete, which is formed with silicon-containing and aluminium-containing tetrahedra, are predictably influenced by changing the silicon to aluminium ratio whereby the addition of more silicon oxides makes the concrete stronger, of whereby the addition of more aluminium oxides makes the concrete more acid resistant.

7 . - Ecological cement according to claim 2 , characterised in that the additive in gel form contains an activator based on lactic acid salts that act as a reaction accelerator ,

8. - Ecological cement according to claim 2, characterised in that the additive in gel form contains boron compounds that act as a reaction retardant.

9.- Method for producing ecological concrete characterised in that it comprises the following steps:

- First silicon oxides and metal oxides are collected from recycled material or other sources, whereby each batch is pulverised or granulated and homogenised; - Then for each batch the elemental composition is measured concerning the silicon and metal elements, that can be converted into cations by means of the ionogenic groups in the additive still to be added; - Then a mixture is composed of different batches to obtain the desired elemental composition for the ecological cement that is required to obtain a set compression strength or another property of the ecological concrete, and this on the basis of the elemental analyses of each batch of raw materials and the known graphs that show the relationship between the composition and properties of the ecological concrete and whereby the composition is calculated for the mixture on the basis of the contributions of each batch of silicon oxides and metal oxides to the ecological cement;

- Then an additive in gel form with ionogenic groups and water are added to the composition that contains metal oxides and silicon oxides, while the additive in gel form contains strong acids and bases such as ionogens that ensure that the silicon ions and metal ions in the composition go into solution and can further react to form ecological cement and this at room temperature or lower down to 1°C;

~ Then the electrical resistance of the liquid concrete mixture is measured continuously to be able to predict the start of the bonding and the end of the hardening;

- Then the liquid concrete is transported and cast at the right time in formwork intended for this purpose;

~ Then the cast ecological concrete is taken out of its formwork or mould when it has set sufficiently;

- Finally the surfaces of the ecological concrete exposed to air are optionally covered with a curing layer or a layer of water to make the surface watertight and to prevent the loss of hydration water from the ecological concrete;