EP1871725A1

EP1871725A1 - Method for producing components

Info

Publication number: EP1871725A1
Application number: EP06723679A
Authority: EP
Inventors: Peter Stemmermann; Krassimir Garbev; Günter BEUCHLE; Uwe Schweike
Original assignee: Forschungszentrum Karlsruhe GmbH
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 2005-04-21
Filing date: 2006-03-24
Publication date: 2008-01-02
Also published as: JP5065245B2; JP2008536789A; WO2006111241A1; US7807078B2; US20080093774A1; DE102005018423A1

Abstract

The invention relates to a method for producing components based on calcium-silicate-hydrates (C-S-H-phases). Said method consists of the following steps: a) an aqueous suspension made of solids, which contains calcium oxide CaO and silicon dioxide SiO2, is produced, the molar ratio Ca: Si being a value selected from between 0.5:1.0 to 2.5:1.0, b) the aqueous suspension is ground without increasing the temperature to higher than 100 °C, thus forming nanocrystalline C-S-H-phases, c) the aqueous phase is separated, d) the residual, which contains the nanocrystalline C-S-H-phases, is extracted and dried and a powdery product is obtained, e) the dried powder is filled into a mould and impinged upon with pressure and then the powder is compressed into a structural component, f) the mould is removed. The inventive method is used to synthesise nanocrystalline cement hydrate phases having a specifically adapted surface charge, for producing completely hydrated C-S-H-phases having defined compositions and surface charges as base material for producing binding agents and for producing totally hydrated, dried cement hydrates as initial material for binding a structural component which is to be bound to cement.

Description

Process for the production of components

The invention relates to a process for the preparation of components based on calcium silicate hydrates, which are also referred to as C-S-H phases.

The production of components (Forrαteilen), in which Zementstein, the essential components of which also comprise C-S-H phases, takes over the function of a binder, usually takes place in three steps:

1. The starting materials cement, aggregates and water are mixed

(so-called make-up).

2. This mixture, which is referred to as cement paste, fresh mortar or fresh concrete, is poured into a mold and usually compressed mecha ^¬ nisch by shaking.

3. The component cures for a long time until the surrounding mold can be removed.

Here it is crucial that the mixture is composed so that a suitable consistency during processing and a sufficiently long processability are guaranteed. Likewise, the mixture must be so composed or post-treated so that after completion of the reaction with water, the required final strength is achieved.

The three steps mentioned are carried out in cementitious systems by coordinated reaction of the constituents of the cement. CEM I (portland cement) includes lien a mixture of two groups of Minera ^¬ each perform a function:

1. Calcium silicates whose hydration products are responsible for the final strength of the molding and

2. Calcium aluminates, calcium aluminate ferritates and calcium sulfates which control processability and early strength.

In addition, other inorganic and organic substances zugege ^¬ be added, the z. B. densify the structure, the processability improve or increase the strength.

The procedure described has the following disadvantages:

- The preparation of cementitious binders requires high temperatures (eg for CEM I 1450 ⁰ C), which requires high energy costs.

Only a part of the phases constituting the binder (for example for CEM I about 50%) contributes to the final strength of the component.

- About 50% of the calcium carbonate used for the production of CEM I are deacidified with high energy expenditure, without contributing later in the component to the strength. This pollutes the environment with C0 ₂ emissions.

- In order to achieve the required reactivity of the product, takes place after the burning of cement an energetic complex grinding process.

- Mixture design is a complex, experience-based process. Variable raw material qualities require a constant adaptation of the mixture design.

- Special additives used in mixtures are expensive.

- Only a well-defined period of time is available for processing. An interruption of processing is possible only to a very limited extent.

- The strength of the mixture increases after processing only over a long period.

- The chemical properties of the phases resulting from the mixture are different and can not be optimally adapted to the surcharges applied.

- The final strength is often reached only after months.

- The final strength is reduced by high porosity, small particle binding and reduced amount of the strength determ ^¬ Menden phases.

- The stability of the moldings against external chemical attack z. B. by acids, CO ₂ or sulfates is limited.

From S. Goni, A. Guerrero, MP Luxan and A. Macias, Activation of The fly ash pozzolanic reaction by Cement and Concrete Research 33, pp. 1399-1405, 2003 discloses the production of fly ash-belit low-calcium fly ash by a two-stage process. For this purpose, first a hydrothermal treatment of flyashes under saturated water vapor partial pressure at 200 ⁰ C and then a roast at 700 ° C. After production, fly ash-belite cement is conventionally dressed and processed with water. Energy costs are significantly reduced compared to the production of Portland cement; However, a higher proportion of CaCO ₃ must be deacidified than is necessary for the preparation of the strength-determining phase, whereby the environment is additionally burdened with CO ₂ . Only part of the phases constituting the binder contribute to the final strength of the component, since fly ash-belite cement, like CEM I, contains calcium aluminates and aluminum ferrates. In contrast, the grinding costs are lower compared to conventional CEM I. Fly ash is limited and comparatively expensive. Since fly ash-belite cement is conventionally processed further, the remaining disadvantages mentioned above can not be overcome.

SC Mojumdar, B. Chowdhury, KG Varshnney and K. Mazanec, synthesis sis, Moisture Resistance, thermal _r Chemical and SEM Analysis of Mac ro-Defect-Free (MDF) Cements, Journal of Thermal Analysis and Calorimetry 78, Pp. 135-144, 2004, suggest the production of macro defect free cement (MDF) by blending various clinker materials such as SAFB, CEM I or Al ₂ O ₃ with other inorganic and organic additives. MDF cements are conventional, but dressed with greatly reduced water / solids ratio and tet proces ^¬.

From GR Gouda and DM Roy, Characterization of Hot-Pressed Cement Pastes, Journal of the American Ceramic Society 59, pp. 412-414, 1976 and AA Paschenko, VV Chistyakov, EA Myasnikova and LA Kulik, Formation of the Structure of Hot Pressed Cement Paste, Dopovidi Akademii Nauk Ukrainskoi RSR, Seriya B, Geologichni Khimichni ta Biologichni Nauki 9, p. 41 (abstract), 1990, is the production of

Hot-Pressed Cement Paste by hardening conventionally water-treated and processed cement pastes at elevated pressure (3-5 kbar) and elevated temperature (150-250 ⁰ C) known.

Both MDF cements and hot-pressed cement pastes have a denser structure without macropores compared to conventional CEM I. However, the primary porosity in the micrometer range is considerable. The final strength is reached only after storage in water and is multiplied compared to CEM I (up to 700 N / mm ² in hot-pressed cement pastes). The stability against an external chemical attack z. B. by acids, CO ₂ or sulfates is improved over CEM I due to the dense structure. However, there is the danger of so-called swelling due to unreacted clinker phases for these products. Neither MDF cements nor hot-pressed cement pastes can overcome the other disadvantages listed above.

From G. Wed, F. Saito and M. Hanada, Mechanochemical synthesis of to- bermorite by wet grinding in a planetary ball mill, Powder Technolo gy ^¬, Volume 93, pages 77-81, 1997, the production of the CSH phase tobermorite by means of the so-called mechanochemisehen treatment ei ^¬ ner aqueous suspension of CaO and SiO ₂ in an agate ball mill known.

DE 28 32 125 C2 describes a method in which CaO and SiO ₂ -containing materials with a synthetic calcium silicate, (CaO: SiO ₂ - ratio of 0.8 to 1.1) and fibers are mixed with water. After a waiting period of at least 5 hours ("pre-reaction"), since the sedimentation tendency is prevented by stirring, a pumpable slurry is formed, which is poured into plate-like molds and dehydrated under pressure After autoclave hardening and drying, "fire-resistant dimensionally accurate lightweight building boards" in front. The calcium silicate synthetic origin, which ^¬ by autoclave curing is made. DE 33 02 729 A1 discloses the reaction of aqueous-dispersed

Starting materials under heating and then filter presses (water shaping), followed by steam curing and subse- _^ ßender drying. The reaction (heating) is carried out at a temperature of 80 to 230 ⁰ C within 30 minutes to 10 hours.

Proceeding from this, it is the object of the present invention to provide a method for the production of molded parts, which does not have the disadvantages and limitations mentioned.

This object is achieved by the method steps of claim 1. The dependent claims describe advantageous Substituted each ^¬ refinements of the invention.

The present invention is based on the synthesis of calcium silicate hydrates (C-S-H phases) in aqueous solution or suspension with a layered structure. The fact that the method according to the invention actually produces such a layer structure can be observed by X-ray structure analysis, since such a structure, as soon as it has a regular spacing, leaves a so-called basal reflex in the X-ray diffractogram. In the case of the present C-S-H phases, a line in the range of 9 Ä to 20 Ä forms, which indicates the formation of this layer structure.

The present invention utilizes the formation of an electric double layer at the interface between a solid and a liquid phase. On the surface of the solid, a star ^¬ re layer of ions, behind which a diffuse charge cloud of ions accumulates. The electric potential is referred to as zeta potential or electron-trokinetisches, falls of its magnitude by first strongly within the rigid layer from to fall in the liquid thereto at ^¬ closing phase either slightly further (positive zeta potential) or slightly higher (negative zeta potential)

Potential). The zeta potential, its amount by the relationship

ζ = 4πηv / ε _r E

where η is the viscosity of the liquid, v its velocity, ε _r its relative permittivity and E the electric field, is a measure of the mobility of the ions.

The ratios described are for the case of calcium silicate hydrates (CSH phases) with a ratio of CaO / SiO ₂ > 1 and positive zeta potential in Fig. Ia).

The surface of the solid preferably consists of negatively charged 0 ^{2 ~} ions, so that a rigid layer of Ca ²⁺ ions is formed in the solution adjacent thereto. Here, a diffused layer of 0H ^~ and Ca ²⁺ ions is deposited. The surface-distant solution is electrically neutral.

By taking advantage of these charge layers, as shown in FIG. 1b), similar solids or surfaces, in particular promoted by external pressure, can approach one another. The diffused charge layers are displaced toward the off-surface solution as the rigid layers reform into a connecting layer between the approaching surfaces. The required charge compensation takes place via easily movable protons according to the equation

Suitable additives modify the interfaces or layers, especially by acting as nuclei for self-assembly of aggregates in the size range up to 1 micron with controllable properties. This process was detected by surface analyzes.

For the process for the production of components according to the invention If appropriate, an aqueous solution of calcium oxide CaO and silicon dioxide SiO _{2 is} provided in accordance with method step a). Here, the molar ratio of calcium to silicon (Ca: Si) takes a value in the range between 0.5: 1.0 to 2.5: 1.0, preferably from 0.5: 1.0 to 1.0: 1, 0, with the boundaries included. At a value above 1.3: 1.0, calcium hydroxide Ca (OH) _{2 forms} simultaneously in the system CaO-SiO ₂ -H ₂ O, as a result of which an otherwise inventively produced component no longer has sufficient strength.

The water to solid ratio in the preparation of the C-S-H phases is freely selectable within wide limits. Preferably, the proportion of water is 4-20 times, more preferably approximately 10 times the total weight of the solids.

For the preparation of calcium silicate hydrates, the raw material used is preferably lime CaO or calcium hydroxide-containing sludges. The silicate source used is preferably Aerosil, silicic acid (pyrogenic or precipitated), kieselguhr, waterglass solutions, technical by-products such as microsilica from the production of ferrosilicum, slags from waste incineration or blast furnace processes, granulated blastfurnace or fly ash.

The solution thus provided is then mixed after process step b) and reacted. It is crucial that no increase in temperature above 100 ⁰ C, preferably not more than 80 ⁰ C. To improve the conversion or to achieve a better homogeneity, grinding assistants or processes for better mixing (so-called mechanochemical treatment) are used during the synthesis. A measurement of the temperature is difficult because it is local, occurring in the contact area Mahlbecher Mahlhilfsmittel- suspension temperatures and considerable tempera ^¬ turgradienten to be expected. In carrying out the Mahlvor ^¬ is periodically interrupted gear, to enable temperature compensation or gege ^¬ appropriate, a cool down. The synthesis is carried out before ^¬ preferably at room temperature. To shorten the synthesis time, so to accelerate the reaction is carried out at slightly elevated temperatures or pressures. The reaction is then terminated when nanocrystalline material has formed, which has fertil at the training _Λ shows an X-ray Basalreflexes in.

Subsequently, the remaining aqueous phase according to process step c) is separated off (eg filtered off), leaving behind nanocrystalline material which is removed according to process step d) and dried to a powder. The solid product is thus separated from the suspension water and dried, resulting in a free-flowing, storage-resistant powder, which is not subjected to any further temperature or steam pressure treatment.

This dry powder is then filled immediately or after intermediate storage according to process step e) in a prepared form. By applying pressure, preferably between 50 MPa and 500 MPa, more preferably between 100 MPa and 200 MPa, the dry powder compacts into a solid component without subsequent temperature treatment. The nanocrystalline C-S-H phases are connected by a self-healing process. At the same time, the pores, which are larger than about Iμm, are closed.

To produce a larger component, this method step can also be carried out several times. For this purpose, it is advantageous to dry powder z. B. fill in layers in the provided form.

After the entire component has been completely created, the mold is removed according to method step f). The component remains either locally or if applicable, for its use elsewhere entnom ^¬ men.

In a preferred embodiment, the solution during or after process step a) or the powder according to process step d) with blended and homogenized with various additives and / or additives. Additives are on the one hand minerals such as calcite, wollastontite or corundum and fiber materials. This possible addition of fillers serves to optimize the mechanical properties or, in the case of heat-insulating materials, to influence the insulating properties of the component. On the other hand, it is also possible to use organic and inorganic additives which change the surface charge of the phases involved, in particular of the CSH phases. A particularly suitable additive is aluminum hydroxide Al (OH) ₃ , which can be added in excess and leads to the self-assembly of CSH phases with negative zeta potential and Al (OH) ₃ (positive zeta potential). Further suitable additives are sulfur-containing compounds such as CaSO ₄ modifications (gypsum) or ettringite, and hydroxides such as brucite or portlandite.

The binder produced by the process according to the invention from C-S-H phases or C-S-H phases with additives includes the additives firmly. By choosing the chemical properties of the nanocrystalline C-S-H phases and the additions, a firm bond of the binder to the aggregates is achieved. The bond between binder and aggregates can be adjusted by adjusting the surface charge of the aggregates, e.g. by prior chemical treatment e.g. improve with acid. This process step can be supplemented by a temperature application.

The process according to the invention has the following advantages:

- Simple raw material composition.

- The process already starts at room temperature; higher temperatures are optional.

- The entire material and not just a part of the binder building phases contributes to the strength.

- The shaping is done simply by applying an external pressure.

- The components made with it are immediately fixed and allow immediate stripping. - The density of the material according to the invention can be adjusted by selecting the substances according to process step a), the drying conditions according to process step d) and the amount of pressure applied to the powder during process step e).

The splitting tensile strength of the product produced by the process according to the invention corresponds already at a density of 1.2 g / cm ^{3 to} the splitting tensile strength of self-compacting concrete which has a density of 2.3 g / cm ³ .

- The conditions in the preparation of the powder (composition, conditions of synthesis) may be due to requirements for the component such. As to its chemical resistance and need not be determined due to the required reaction conditions. This advantage causes a considerable saving of material.

- The component shape is determined by its function and the requirements of its strength and not by flow and reaction conditions.

- The design of mixtures is much easier due to the manageable chemical processes.

- The density of the material can also be adjusted by selecting suitable additives and / or additives, so that values between 0.5 and 3.0 g / cm ^{3 are} achieved. Thus, the material can also be used as a lightweight construction material.

The inventive method is used for the synthesis of nanocrystalline Cementhydratphasen or mixtures of nanocrystalline Zementhydratphasen with tuned surface charge, in particular with a positive zeta potential. Furthermore, this method is used for the preparation and use of fully hydrated CSH phases with a defined composition and surface charge as a raw material for binder production. Finally, this Ver ^¬ will go to the production and use of fully hydratisier ^¬ th, dried cement hydrates used as starting material for bonding a cementitious component. The invention will be explained below with reference to exemplary embodiments.

Production of the powdery product

Served as starting materials for the basic system C-S-H

SiO ₂ in the form of Aerosil,

CaO, freshly fired from CaCO ₃ , cooled under inert gas,

- H ₂ O boiled, double-distilled.

Some were also used as additives:

Al ₂ O ₃ in the form of aluminum hydroxide Al (OH) ₃ ,

- CaSO ₄ .

In each case, 15 g of nanocrystalline CSH phases having compositions corresponding to molar ratios CaO / SiO ₂ = 0.5, 0.66, 0.75, 1.0 or 1.5 were prepared. The synthesis was carried out by mecha- the further treatment of an aqueous suspension of CaO and SiO ₂ in an agate ball mill. The stoichiometrically weighed oxides were mixed in deionized water in the ratio water / solid = 10, for which values between about 4 and 12 are also suitable, and milled for 48 hours at 600 revolutions per minute. After each 30 minutes of milling, the mill was stopped for 15 minutes to avoid overheating the sample. HERGÉ in this way ^¬ introduced substance (slurry) was 4 days at 60 ⁰ C dried. If necessary, drying may be preceded by a filtration step. All process steps, ie weighing, mixing, loading and Entla ^¬ the mills and drying, carried out under N ₂ atmosphere in a so-called. "Glove box" to create controlled environmental conditions and in particular to exclude CO ₂ .

The following Table 1 summarizes five approaches for the basic system CSH (ratio water / solid = 10):

The following Table 2 shows in summary three approaches for the system CASH with Al ₂ O ₃ as additive (ratio SiO ₂ / Al ₂ O ₃ = 5.93, ratio water / solid = 10):

Starting substances CaO SiO ₂ Al ₂ O ₃

(M = 56, 08) (M = 60, 09) (M = 101, 96)

molar ratio

Mol% wt% mol% wt% mol% wt% CaO / [SiO ₂ + Al ₂ O ₃ ] Φ

1.50 62, 3 58, 3 32, 3 32, 4 5,4 9,2

1, 00 52, 4 48, 3 40, 8 40, 2 6,9 11,5

0, 66, 42, 38, 49, 48, 0, 8.3, 13.7

In addition, the ratios CaO / SiO _{2 /}

SiO ₂ / Al ₂ O ₃ and water / solid change. Likewise, other additives such. As Mg (OH) ₂ or CaSO _{4 are} added.

The phase composition of the samples was characterized by the consistency of the powder material, by X-ray diffraction to determine the qualitative and quantitative composition of the samples, and by thermogravimetry to determine the water content of the samples. Production of the component

For test purposes, components (specimens) in the form of tablets with a diameter of about 1.3 cm were subsequently produced from the powders. For the tablets, masses of 300 to 500 mg were weighed. The powder was applied in each case in a vacuum pressing tool with a force of 20 kN (values between 10 kN and 120 kN are possible), which corresponds to a pressure of about 140 MPa for said diameter.

Table 3 below shows the data of series of pressed tablets of pure CSH phases with different CaO / SiO ₂ ratio or after additional addition of Al (OH) ₃ , which significantly increases the strength:

The splitting tensile strength was measured by means of the so-called Brazilian Disk TestSr, ie on a disk. If the material is exceeded As a result, failure is caused by cracking. The

Splitting tensile strength of concretes is 4 to 5 MPa (see eg self-compacting concrete at 3.98 MPa according to Taschenbuch für den Zementindustrie 2002, page 307) and thus significantly lower than the values for compacts from CSH phases with C / S at 0.66 to 1.0.

Claims

claims

1. A process for the production of components, comprising the process steps: a) preparing an aqueous suspension of solids containing calcium oxide CaO and silicon dioxide SiO ₂ , wherein for the molar ratio Ca: Si a value of 0.5: 1.0 to 2, B) milling the aqueous suspension without increasing the temperature above 100 ° C to form nanocrystalline CS-H phases, c) separating the aqueous phase, d) removing and drying the residue, containing nanocrystalline C-SH phases, thereby obtaining a powdery product; e) filling the dry powder into a mold and pressurizing it, whereby the powder compacts to the component, f) removing the mold.

2. The method according to claim 1, characterized in that a value of 0.5: 1.0 to 1.0: 1.0 is selected for the molar ratio Ca: Si.

3. The method according to claim 1 or 2, characterized in that lime or calcium hydroxide-containing sludge are added as solids containing calcium oxide.

4. The method according to claim 3, characterized in that aerosil, silica, diatomaceous earth, water glass solutions, microsilica, granulated slag or slags from waste incineration or blast furnace processes as solids containing silica, are added.

5. The method according to any one of claims 1 to 4, characterized in that during or after process step a) or after Process step d) a supplement or another solid or liquid additive is added.

6. The method according to claim 5, characterized in that aluminum-containing compounds are added.

7. The method according to claim 5 or β, characterized in that sulfur-containing compounds are added.

8. The method according to any one of claims 1 to 7, characterized in that the application takes place at a pressure between 50 MPa and 500 MPa.

9. The method according to claim 8, characterized in that the Be ^¬ aufschlagung with a pressure between 100 MPa and 200 MPa he follows ^¬ .

10. The method according to any one of claims 1 to 9, characterized in that the component has a density between 0.5 g / cm ³ and 3.0 g / cm ³ .