DE102009005610B3 - Process for the preparation of a hydraulic binder - Google Patents

Abstract

The present invention relates to a method for producing a hydraulic binder, consisting of a finely ground component limestone and at least one other silicate component, which is characterized in that is used as the siliceous component diatomaceous earth, depending on the purity of the raw material components limestone and diatomaceous earth the kiln is designed so that the molar ratio of calcium oxide (CaO) to silicon oxide (SiO 2) contained by the mixing of the two main components limestone and diatomaceous earth is 3: 1, whereby after the thermal decomposition of the calcium carbonate (CaCO 3) and the subsequent firing process an alite moiety of> = 90% in the kiln.

Description

Technical area

The The present invention relates to a novel process for the preparation a hydraulic binder from a kiln, consisting of fine limestone and at least one other silicate Component kieselguhr as main components.

State of the art

For the production of cement - in particular Portland cement - the raw materials limestone (CaCO ₃ ), clay (Al ₂ O ₃ -2SiO ₂ -2H ₂ O) with quartz sand (SiO ₂ ) and iron oxide (according to the known state of the process technology following pre-comminution Fe ₂ O ₃ ) are mixed in a precisely defined ratio to a so-called raw meal, where appropriate, correction substances such as bauxite, sand or iron ore are added. By milling the raw meal is further crushed, dried and then fed via a preheater a Drehrohofen dusty, in which the cement clinker is fired from the raw meal at temperatures between 1250 ° C to 1450 ° C, so that after the thermal decomposition of the calcium carbonate (CaCO ₃ ) (so-called calcination reaction) a certain composition of calcium oxide (CaO), silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ) and iron oxide (Fe ₂ O ₃ ) is present.

After grinding mixed with admixtures (calcium sulfate, blastfurnace slag, fly ash, limestone powder, burned oil shale, trass, etc.), the actual cement is produced. In this process, artificial mineral phases are formed, which are largely responsible for the hydraulic properties of the binding agent. The most important component of the cement clinker is the mineral phase alite (tricalcium silicate (3CaOxSiO ₂ )), which gives the cement the desired properties such as rapid hardening and high strength.

During the subsequent clinker burning, further clinker phases such as dicalcium silicate (C ₂ S -belite), calcium aluminate (C ₃ A) and calcium aluminate ferrite (C ₄ AF) as well as free calcium oxide (CaO) form in addition to the main constituent alite according to the method described above. Above a temperature of about 1250 ° C., a melt is formed with a decrease in the CaO content, with the formation of increased alite, which usually represents a proportion of about 40-80% by weight of the total binder.

The usual proportions of the individual phases in the cement clinker are shown in the following table: Mineralogical phase abbreviation Proportion of cement clinker (free calcium oxide) C (<2% by weight) tricalcium C ₃ S about 40-80% by weight dicalcium C ₂ S about 0-30% by weight calcium C ₃ A about 7-15% by weight calcium aluminate C ₄ AF about 4-15% by weight

Of the Disadvantage of this method used according to the prior art is that calcium aluminate reacts very quickly and without Addition of a sulfate carrier would lead to rapid solidification of the binder.

Out For this reason, Portland cements are predominantly calcium sulfate (gypsum and / or anhydrite) added during grinding. The calcium aluminate but make the hardened Concrete sensitive to a sulfate attack. The formation of ettringite or ettringike Phases due to a sulfate attack are known to lead to Expansion, cracking and finally loss of strength in concrete and cement-based structures. Moreover, from the cement chemistry It is known that belite and calcium aluminate ferrite react only slowly. These components, which in each Portland cement according to above Occur in different proportions but bind CaO, have to burned and ground. This means that through integration these two phases are unnecessary Energy is consumed, although the selective contribution of the phases to corroboration is very low.

Presentation of the invention

The present invention is based on the object to develop a binder that can set slowly even at elevated processing temperatures and is easily adjustable to appropriate processing conditions. Another object of the present invention is to provide a binder which is resistant to sulfate. For this purpose, it is necessary to keep the proportions of belite (C ₂ S), calcium aluminate (C ₃ A) and calcium aluminate ferrite (C ₄ AF) in the binder as low as possible or preferably completely exclude and the percentage of alite (3CaOxSiO ₂ ) by to make an optimal mixing ratio in the kiln as high as possible.

According to the invention the above objects with the features of the claim 1 solved. Advantageous embodiments of the method according to the invention are specified in subclaims.

In contrast to the usual Portlandzenentklinker be instead of limestone marl as a component with high CaO content and clay / slate as a carrier of SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ höherwertigerer, so calzcarbonatreicherer limestone as a carrier for CaO and diatomaceous earth as a carrier SiO _{2 is} used.

It is already known from the prior art that alite can be produced by firing a mixture of limestone and a silicon source, such as kieselguhr (diatomite) (cf., inter alia US 4,274,881A , Lines 20 to 23, column 5). Diatomaceous earth (also known as mountain flour, diatomaceous earth, diatomaceous earth, diatomite, infusorial earth, pebble, novaculite, novaculite, tripel, tripolite, tripolite, celite) is a whitish powdery substance consisting mainly of the silica shells of fossil diatoms. The peculiarity of kieselguhr is its mineralogical and physical nature. The shells of the diatomaceous earth consist mainly of amorphous (non-crystalline) silicon dioxide (SiO ₂ ) and have a very porous structure. Due to the amorphous state, the silica is much more reactive than the crystalline SiO _{2 formed} in the quartz sand. Also, kieselguhr is much easier to grind up than quartz sand. The reaction of the silica (SiO ₂ ) from the kieselguhr and CaO, which forms during the deacidification of the calcium carbonate, also starts much earlier.

Around According to the task, the shares in belite in the alit kiln to be produced are so high as possible to keep it, it is necessary to create the mixture to be burned so that a molar ratio from calcium oxide to silica of (at least) 3: 1. The binder according to the invention is designed so that the composition of the Kiln good an Alitanteil of> = 90 wt .-% can form.

production method

For the production of cement clinker by the method according to the invention, the raw material batch is intensively mixed together according to generally well-known in the prior art method with the addition of water and other additives and pressed into moldings. The additives used are special substances which, on the one hand, cause the formation of the glass phase as sintering aids and thereby favor the solid-state reaction between the reactive calcium oxide (CaO) formed after the deacidification of the calcium carbonate (CaCO ₃ ) and the amorphous silica (SiO ₂ ) from the diatomaceous earth contribute to the formation of alite as mineralizers. The pressing method used is the usual shaping method or the roll press technology used in the sand-lime brick production.

The moldings be in a subsequent Process dried and fired. As firing units are used tunnel kilns, shaft kilns or Rotary kilns. The litigation is preferably to be chosen so that a complete one Sales of CaO is achieved in the kiln (free lime content CaO-free less than 1.5% by weight). To stabilize the alite formed in the kiln, will the kiln - like when burning Portland cement clinker common - cooled quickly. The cooling air is used to dry the moldings used.

embodiments

On the basis of the fact that other oxides such as MgO, Al ₂ O ₃ , Fe ₂ O ₃ , ZnO, CaF ₂ , Mn ₂ O ₃ , BaO, P ₂ O ₅ can be incorporated in the alite lattice and stabilize the alite formation, such components become incorporated as impurities in the fuel mixture over the main components limestone and diatomaceous earth as impurities, or added as additives over up to 2 wt .-%, alone or in combination. Taking into account the impurities present in the diatomaceous earth, the composition of the burning material changes only insignificantly.

Depending on the application, the binder is ground to different grinding finenesses. The grinding finenesses are in the range of 3000 cm ² / g to 6500 cm ² / g. For the grinding of products with a high fineness of grinding, it is expedient to add grinding aids which allow a reduction in the grinding energy costs. The grinding fineness is determined by the usual method in cement technology (Blaine measurement). The grinding process used are grinding units which are suitable for the grinding of hard materials, but preferably those which permit a steep particle size distribution of the material to be ground.

In advantageous embodiment gets over it In addition, another, not previously mentioned in the literature sintering aid added, namely Recycled glass, in a correspondingly finely ground amount of up added to 5 wt .-%. Recycled glass stands out for its health compatibility and ecological safety out.

The special properties of the innovative binder, which can be specifically optimized for the specific requirements of the intended application areas by adding concrete admixtures customary in construction chemicals such as retarders, accelerators, liquefiers and stabilizers, are achieved by the following features:
The binder is characterized by a high proportion of reactive alite, whereby high early and final strengths can be achieved. Tricalciumaluminat is not or only as extremely low component contained in the binder. There is no need to delay the rapid hydration of the C ₃ A in the early range of solidification by addition of dihydrate or other sulfate carriers. The absence of C ₃ A opens up possibilities for the production of cements with long processing times even at higher temperatures, eg. B. borehole cements for oil production. The cement produced by the method according to the invention is resistant to sulphate; the absence of C ₃ A does not produce sulphate rubbing due to sulphate attack from sulphate-containing solutions.

It Furthermore, there are no or not significant shares in Belit. Due to the absence of the slow reacting component belit in the clinker produced by the innovative process results a higher one Strength potential through high Alitanteile. Under normal site conditions comes the hardening potential of the Belits, which is well known only when stored under water for a long time reacts, not at all. Under normal site conditions For example, the proportion of belit present in Portland cements may be considered inert become.

In addition, there are no or not significant shares in the aluminate-ferrite phase C ₄ AF. Also the strength contribution resulting from the C ₄ AF when hardening of usual Portland cements should be neglected.

Cements with special properties are produced from the alumina-rich cement clinker obtained by fine grinding and the addition of additives such as gypsum and / or anhydrite, blastfurnace slag, limestone and kieselguhr or other pozzolanic materials. The process according to the invention makes it possible to produce innovative and high-performance hydraulic binders having the following properties of the mortars and concretes to be produced therefrom:
The cements have favorable processing properties which can be adjusted to the respective field of application, have high early and final strength, are impermeable to water, are resistant to carbonation and ultimately provide high protection of the steel reinforcement against corrosion.

The areas of application for such binders are in the areas of construction chemical products such as tile adhesive, grout, thin-bed mortar, adhesive and reinforcing mortar for thermal insulation systems, fillers, top plasters (precious plasters), concretes with high demands on against attack by aggressive sulfate and cloridhaltigen solutions, deep well cements for Used in drilling projects for the exploration and production of oil, gas, water or heat as well as CO ₂ - resistant well cement for the sealing of CO ₂ reservoirs.

The inventive method for producing a hydraulic binder is limited in its execution not to the preferred embodiments given above. Rather, a variety of design variations are conceivable which of the illustrated solution also in principle different type of execution Make use.

Claims (5)

A method for producing a hydraulic binder from a kiln, consisting of - as main components present finely ground limestone and at least diatomaceous earth as silicate component, - and sintering aids, wherein the kiln is designed depending on the purity of the limestone and the diatomaceous earth so that by mixing the two main components a molar ratio of CaO to SiO ₂ of 3: 1 sets, and the kiln is then subjected to a firing process in which the CaCO _{3 of} the limestone is thermally decomposed and forms an Alitanteil of ≥ 90 wt .-% in the kiln , wherein the sintering aids - on the one hand cause the formation of a glass phase, which promotes a solid state reaction between the resulting after the thermal decomposition of the CaCO ₃ reactive calcium oxide and amorphous silica from the diatomaceous earth, - and on the other hand, as mineralizers promote the formation of alite. Method according to claim 1, characterized in that that led the burning process so is that the calcium oxide is so completely converted to alite, that a free lime content of <1.5 Wt .-% is achieved in the kiln. Process according to Claim 1 or 2, characterized in that one or more of the components MgO, Al ₂ O ₃ , Fe ₂ O ₃ , ZnO, CaF ₂ , Mn ₂ O ₃ , BaO, P ₂ O have up to 2 wt .-% are introduced as a sintering aid in the kiln to stabilize the Alitbildung. Method according to one or more of the preceding claims, characterized in that the binder is ground to finenesses in the range between 3000 cm ² / g and 6500 cm ² / g. Method according to claim 3 or 4, characterized that as another sintering aid recycled glass in a corresponding finely ground amount of up to 5 wt .-% is added.