DE19853196A1 - Hydraulic binder with reduced shrinkage and its use - Google Patents

Abstract

The invention relates to a hydraulic binder with reduced shrinkage and its use for the production of cement-bound structures, the binder in a standard formulation at least containing: burnt oil shale, cement clinker, calcium sulfate, silicon dioxide, alkali sulfate and flow agent.

Description

The present invention relates to a binder, which because of its Low-shrinkage or slightly swelling hydraulic hardening used very versatile and can be used.

Shrinkage is the reduction in the volume of cement stone or cement-bound masses. The shrinkage can e.g. B. easily the formation of network like spider webs causing shrinkage cracks that cause the cracks of similar to drying clay or mud. In both cases the drying solid-water mixture can reduce the volume by Loss of water no longer follow through plastic deformation and tears. at hydraulically hardening binders, such as. B. cement according to DIN 1164, that comes chemical shrinkage without water loss, which is explained by the fact that the Cement-added liquid mixing water in the grid of the resulting Hydration products take up less space than before.

Fig. 1 shows the change in length of a normal normal concrete under controlled conditions.

Cracks that arise are often not only visual defects, but also favor this Penetration of water and pollutants into the building materials or components, and put thus direct and indirect damage and thus ultimately an enormous people economic burden. To reduce the formation of shrinkage cracks technological (1), physical (2) and / or chemical for many decades (3) ways of influencing applied.

1) Technologically, z. B. in the case of concrete, a suitable after-treatment for a long time Keep it moist so that the large free surfaces from sun, wind and drafts, z. B. protected with suitable foils, mats or irrigation by spray and so that there is little or no risk of drying out.

Such post-treatment measures are e.g. B. also with cement screeds Wundt. Especially in the production of floating screed as well as Screed on separating layer are made by another technological measure, namely the division of larger screed areas by expansion joints or dummy joints in as compact as possible, the formation of free shrinkage cracks compensated. Indeed  it is very much a matter of the craftsman's experience of the processors, because Incorrectly inserted dummy joints, it can still lead to the formation of shrinkage cracks the screed surfaces come. In addition, such post-treatment is very time-consuming. and therefore very expensive.

2) A proven form of physical manipulation to reduce shrinkage Cracking is the selection of suitable raw materials and the composition of the manufactured hydraulically hardening building materials. The aim of these measures is always that Reduction of the mixing water and thus the direct reduction of the Dehydration risk. Type and form of aggregate, grain distribution, aggregate size, Share of Abschlämmbares etc. allow z. B., screed mortar with possible to produce a low water cement value or the lowest possible cement paste content.

The fineness of grinding of the binder used is also a physical influence. For the production of cement screed z. B. all cements according to DIN 1164 and building authority-approved cements are used, but preference is given to cements with an average grinding fineness, for example between 2800 cm ² / g and 3500 cm ² / g. The length change behavior of hydraulically hardening building materials can also be influenced with the duration and intensity of the mixing or with the processing temperature, see "Rendchen K .: Technology, manufacture and application of cement screed, TAE course documents screed in construction 1995".

Another possibility of influencing is the addition of physically active additives, such as B. plasticizers, plasticizers, air entraining agents, etc. or fine additives. In the publication "Rendchen K .: composition and properties of cement bound floating screed, Beton 39 (1989) H. 3, p. 111 ff ", are detailed Effect of additives such. B. limestone flour or fly ash and various Superplasticizer is described and explained in detail. Reduction is essential the mixing water and thus the tendency to shrink; a low shrinkage or even however, free hardening cannot be achieved in this way.

Since the cracking u. a. also by the hindrance of those occurring in the component Tension is caused by improving elastic behavior the building material, d. H. can be suppressed by reducing the modulus of elasticity. Practical is z. B. the addition of so-called polymer or plastic dispersions; in the publication "Alexanderson J .: Self-Smoothing Floors Based on Polymer Cement Concrete, Concrete International, January 1990, p. 49 ff ", is about such  Application reported. This is possible due to the necessary additional quantities the influence however very expensive.

In the publication "Engstrand J .: Shringkage Reducing Admixture for Cementitious Compositions, ConChem-Journal, 5th year 5/97, p. 149 ff ", becomes the possibility shrinkage compensation by using volatile alcohols in powder form, e.g. B. hexanediols described. The effective water / binder value reduced because the water required to achieve processing consistency the hydraulic component and the volatile component. It is reported that the shrinkage due to dehydration decreases by approximately 40% 21 days could be reduced - from 0.8 mm / m to 0.47 mm / m. The effect is however very much dependent on the type of cement used; this variant is also too expensive for practical use.

DE-GM 295 03 540.4 uses a combination of the additives mentioned position of a self-leveling screed on the basis of cement self-leveling mortar with a closed surface. It acts it is a dry mortar, d. H. a finished product from binder, surcharge substances and additives, preferably a cement mixture of Portland cement and quick cement is provided so that the necessary for processing Water - already reduced in quantity - through the composition of the liquid screed mixtures predominantly chemically bound and shrinking due to drying out is reduced. A disadvantage is the high material costs, which one Use in normal residential construction as a floating cement screed or on Exclude separation layer. Investigations by the applicant have also shown that despite all measures to reduce shrinkage, a crack formation in floating Screeds, especially for screed thicknesses <35 mm, in connection with Auf keying occurs. In addition, the quick setting is a normal Ver work is not possible with a correspondingly long processing time.

It is state of the art, not only due to dry mortar the risk of shrinkage to reduce cracking, but also by producing so-called fresh mortar. According to DE-GM 295 18 306 there is a mixture of washed Sand in the grain size 0 to 8 mm, cement, filler, a stabilizer and water for Use that is mixed at the factory using a compulsory mixer, with concrete mixing vehicles transported to the construction site and after adding highly concentrated superplasticizer is then conveyed to the installation site using a concrete pump.  

The disadvantage here is mainly ecological, since the primary energy consumption due to the transportation of all components is very high and material not installed must be transported back and disposed of.

3) In particular, the influence of chemical reactions of the hydraulically hardening binders used with the Mixing water understood. This includes the addition of special active ingredients and additives, z. B. accelerators, retarders etc. and especially the chemical and mineralogical composition of the binder used. The development Low-shrinkage or even slightly swelling binders were therefore early on of great importance for practice.

In the publication "Keil F .: cement - production and properties, Springer-Verlag 1971 ", it is reported that as early as 1940 with those that are fundamentally similar until today Mixtures of standard Portland cement clinker and a clinker made of calcium Aluminate sulfate with the addition of blast furnace slag as moderator or stabilizer was started. In DE 44 10 850 z. B. a binder for hydraulic setting self-leveling screeds or industrial floors, which consists of a mixture of Calcium sulfate, slag sand and reactive aluminates exist and so in addition to high early strength and sufficient surface strength such a low shrinkage when drying out and final setting shows that there is no tearing or unraveling.

A disadvantage of using the components mentioned is that they are relatively expensive are and are not available everywhere.

For the production of crack-free cement screeds in particular, it is state of the art to mix reactive CaSO ₄ compounds and cement with one another in such a way that the greatest possible formation of ettringite takes place, as a result of which the cement screed cures quickly, free of cracks and without shrinkage. This z. B. reported in DE 44 10 130. After part of this invention is that the product is mixed with limestone aggregates and thus cannot be used on regionally suitable sands. In addition, only Portland cement, iron Portland cement or blast furnace cement can be used as cement, but not e.g. B. Portland oil shale cement.

EP 427 064 also describes a hydraulic binder and its many possible uses. Here too, α-calcium sulfate hemihydrate and cement and other additives are mixed with one another, the cement being characterized in that a low-aluminate Portland cement HS to DIN 1164, C ₃ A <3% is used. The use of normal cement, i.e. not highly sulfate-resistant, with a higher C ₃ A content is not intended.

In addition, it is state of the art, the tendency to shrinkage through so-called To reduce expansion or swelling cements. In DE 195 01 074 such a Binder described, the Portland cement, alumina cement, plaster and in particular Contains citric acid or tartaric acid or its salts. One such binder is for the filling of cavities, preferably in the manufacture of soil anchor or rock anchors. However, the volume expansion is 10 to 20%, with stable water storage and processing times of 20 to 40 minutes. The low processing time and high volume expansion therefore make one Use in building materials such as screeds, grouting concrete, stucco, etc. impossible Lich.

In the publication "Kikas et al .: Portland oil shale cement as swelling cement, Wiss. Journal of the Bauhaus-Universität Weimar 42 (1996), 4/5, p. 165 ff ", the Ein swelling up to 40 mm / m, especially for the production of special swelling and tension cements. However, it is the so-called Kukersit oil shale, which is used in dust furnaces at temperatures of 1300 to 1400 ° C is burned and thus a free lime content of up to 14% and a calcium sulfate Contains up to 15%. The compressive strengths that can be achieved and the observed ones Swelling dimensions can be used to produce low-shrinkage binders based on Oil shale cannot be used.

It is therefore the object of the present invention, a binder mixture and To create ways of using the same with which a low shrinkage or shrinkage-compensated binder can be produced that a reduced Water demand with good rheological behavior, moisture resistance, Crack resistance and temperature independence guaranteed and a light reliable and economical production of building materials from it, using local, suitable sands of different grain distributions and grain sizes and thus creates additional ecological advantages.

This object is achieved by the binder mixture characterized in claim 1 solved. Advantageous further developments of the mixture and possible uses are identified in the subclaims.

According to the invention, low-shrink binders can be produced with a binding medium mixtures, the burnt oil shale, cement clinker, calcium sulfate, silicon  contain dioxide, alkali sulfate and eluent. Other useful additives are Defoamers, retarders and plastic dispersions.

The following dry mixes are advantageous:

• - 10 to 20 wt .-%, in particular 12 to 16 wt .-% of burnt oil shale according to DIN 1164, Part 1, Section 4.5 and ENV 197,
• 20 to 50% by weight, in particular 30 to 45% by weight of Portland cement clinker,
• 15 to 30% by weight, in particular 20 to 25% by weight, of fly ash from coal,
• 15 to 30% by weight, in particular 20 to 25% by weight, of anhydrite,
• 0 to 3% by weight, in particular 2 to 2.5% by weight, of superplasticizer,
• 0 to 2% by weight, in particular 0.4 to 0.8% by weight, of alkali metal sulfate,
• 0 to 1% by weight, in particular 0.2 to 0.4% by weight, of defoamers,
• 0 to 1% by weight, in particular 0.3 to 0.6% by weight, of retarder,
• - 0 to 3 wt .-%, in particular 1 to 2 wt .-% plastic dispersions.

The oil shale used is low-bitumen Posidonia shale with an average organic matter content of 10 to 13%.

After appropriate processing, the oil shale is burned in a fluidized bed furnace at approx. 810 ° C and then ground very finely. The fired oil shale is preferably brought to a fineness of grinding according to DIN EN 196-6 according to the air permeability method (Blaine) of 6,000 to 10,000 cm ² / g.

The chemical composition of the burnt oil shale depends on the geology of the deposit and the burning process. The average analysis shows about 32% CaO, 36% SiO ₂ , 11% Al ₂ O ₃ , 10% SO ₃ , 7% Fe ₂ O ₃ and small amounts of MgO, K ₂ O and Na ₂ O (values with loss on ignition). The mineralogical composition is described, inter alia, in "Rohrbach R .: Production of oil shale cement and extraction of electrical energy from oil shale according to the Rohrbach-Lurgi process; ZKG 7 (1989, Issue 7, p. 293 ff)". The reaction in a fluidized bed in the solid state produces calcium silicates (primarily C ₂ S), various calcium aluminates and calcium sulfate. In addition to approx. 4 to 5% free lime, the burnt oil shale contains even larger amounts of reactive silica.

The burnt oil shale is itself hydraulically hardening and can partially through latent hydraulic substances are replaced. It is also possible to part of the baked oil shale through stone powder, especially from limestone or lime  marl, to be replaced, provided this does not result in the mentioned important requirements hydraulic binders with reduced shrinkage are impaired.

The Portland cement clinker used has a customary clinker phase composition according to "VDZ Cement Paperback 1984 (Bauverlag)" and is characterized by a much lower fineness. It is preferably ground to a fineness of 2,700 to 4,500 cm ² / g according to Blaine.

Burnt oil shale and Portland cement clinker are common according to the invention ground sam or separately. With separate grinding, both components mixed dry homogeneously in a suitable binder mixing plant.

The hard coal fly ash is fly ash for concrete in accordance with EN 450. Coal fly ash with test marks has long been used as a concrete additive fabric or used as a component of fly ash-containing cements. You improve that Concrete properties through physical and pozzolanic effects. The middle grain diameter of the glassy, predominantly spherical particles should preferably be between 1 to 100, preferably 5 to 20 microns.

Natural anhydrite, synthetic anhydrite or REA anhydrite can be used as the anhydrite be set. This means that the properties of a hydraulic bandage required at the outset can be achieved with reduced tendency to shrink, become uniform and the purity of the anhydrite used made great demands. Therefore preferably very homogeneous, pure REA anhydrite with purities <85% used.

The alkali sulfate used serves as an influencing component for the Reaction. Alkali sulfates are known and serve e.g. B. as a stimulator in conventional calcium sulphate flowing screeds. A targeted use in hydraulic bound building materials is not yet known.

As a liquefying component to reduce the water demand of the binder have become plasticizers or plasticizers based on lignin sulfonate, one Melamine, naphthalene, acrylic acid or maleic acid copolymers have proven their worth. A sodium sulfonate-based melamine polycondensate is preferably used.

A is used to adjust the elastic properties of the hardening solid mortar redispersible plastic dispersion powder used. Acrylate Dispersions and homopolymers or copolymers based on vinyl acetate or styrene or  so-called print polymer dispersions. A redispersible is preferred Dispersion powder of a vinyl acetate-ethylene copolymer with good saponification resistance used.

Polyglycols or combinations of liquid hydrocarbons are used as defoamers substances, polyglycol and amorphous silica. To be favoured Polyethylene glycols used in powder form.

Inorganic compounds, preferably complex phosphates, are used as retarders or alkali pyrophosphates used.

In view of the choice according to the invention of the solid components and their amounts or the composition of the dry mixture surprisingly succeeds in Binder with reduced shrinkage and the corresponding building materials places that have all the properties required at the outset, such as reduced water consumption, reduced porosity, use of locally suitable sands, ecological advantages etc. fulfill.

Essential to the invention is the increase in the proportion of SO ₄ and the proportion of SiO ₂ in the form of the additives mentioned, which is set in accordance with the composition of the fired oil shale mentioned at the outset, and the setting and control of the amount of alkali sulfate. This enables the exact course of the reaction of an ettringite formation and a corresponding breakdown in the solution phase and in the solidifying / hardening phase.

The previously known damage patterns in the solid phase - Ettringitzer fall through Humidity and temperature fluctuations and the associated loss of strength, Volume reduction and shrinkage or ettringite formation and thus Driver symptoms - are thus avoided according to the invention.

The added retarder regulates the setting and solidification of the one used Portland cement clinker, especially the typical reactions of aluminate and Silicate phases, so that the resulting strength-building CSH phases are the same as above do not interfere with the reactions described.

The binder according to the invention can expediently additionally contain suitable fibers, such as z. B. contain polypropylene, glass or polyacrylonitrile fibers. Have attempts shown that the inclination by adding fibers, especially alkali-resistant fibers  for the cracking of building materials, made with the low-shrink binder can be reduced.

When using the binder according to the invention for the production Shrinkage-optimized cement screeds are there to improve the Shrinkage reduction is advisable, the screeds on dry fill as a substructure apply. These are fillings made of expanded clay or expanded glass, which are used for Part were stabilized with cement. In measurements by the applicant, depending on Initial consistency thus reducing the effective W / Z value by up to 20% (measured after 6 h).

In the examples below, binder formulations according to the invention and some uses explained:

example 1

binder formulations

The components are mixed together homogeneously. These mixtures were in Various applications are used as binders and those described above Benefits examined. The measurements were made on so-called shrinkage channels (length 1 m) and mainly when stored in climates according to DIN 18557 (20 ° C / 65% r.F.) performed.  

Fig. 2 shows the different screening lines of the limestone aggregates used in the applications.

With 57.65% by weight of the grain size 0/8 B / C and 42.35% by weight of the binder fine concrete was prepared according to Example 1a and 1b to the influence of Examine binder composition.

Fig. 3 shows the measured changes in length with different binder composition. A good shrinkage reduction can already be achieved with the standard recipe according to Example 1a. For increased requirements, the other additives for the preparation of the binder according to Example 1b can be used.

Fig. 4 shows the influence of the binder preparation to the length change behavior, in particular the use of a milled binder compared to a mixed binder, as measured by the fine concrete after the above described mixture with the binder according to Example 1a. It can be seen that both production processes are possible, but the production of the low-shrinkage binder by mixing obviously results in better shrinkage compensation even to the extent of slight swelling (similar to calcium sulfate screeds).

Example 2 casting mortar

Grouting concretes are suitable for backfilling certain masonry formers, e.g. B. Soundproofing bricks, suitable hollow blocks with heat applied on the outside insulation, etc. Especially in the case of stones with continuous webs conventional grouting stresses risk of shrinkage and cracking.

The use of different particle size distributions was an advantage according to the invention at different processing consistencies. These two influencing factors were examined. For this purpose, 57.65 wt .-% surcharges of the respective Grain distribution and 42.35 wt .-% binder according to Example 1b to one workable plastic fine concrete mixed in a free fall mixer.

Fig. 5 shows the influence of the particle size distribution on the length change behavior when processing stiff consistency.

Fig. 6 shows the influence of the grain distribution on the length change behavior with plastic consistency.

Both with strongly fluctuating grain distribution and with very different ones Consistencies are achieved in all cases, slight swelling dimensions and thus one Shrinkage of the building materials avoided.

Example 3 Flowable cement screed

An advantage according to the invention is the use of suitable local sands such as this z. B. is possible in a ready-mixed concrete plant. There can be different Grains are used. This influencing factor was examined. To do this an average of 55% by weight of the respective additive with 45% by weight of binder Example for a homogeneous fine concrete or mortar with almost the same Mixed and processed water requirements.

Fig. 7 shows the influence of the aggregate maximum grain on the length change behavior of this mortar. The setting of a slight swelling is clearly shown, regardless of the largest grain used; no shrinkage of the building material is observed.

Another advantage according to the invention is the use in different climates. For this purpose, the change in length behavior of a flowable cement screed with a grain size of 0/4 mm, made from 54.65 wt Practice in a constant climate of 12 ° C - 80% RH, examined. In this case, according to Fig. 8 shows no climate-dependent deterioration of the length change behavior, so that the binder according to the invention works perfectly even with different climates with reduced shrinkage.

Example 4 Highly insulating building materials

On lightweight wall mortar LM21 according to DIN 1053, but also on thermal insulation plasters, Exterior stucco, etc., i.e. building materials that are applied in such thicknesses that free shrinkage is possible in practice, high demands are placed on reduced shrinkage properties. For this reason, two mortars produced, each from 57.65 wt .-% addition (expanded glass granules or broken Limestone sand) and 42.35 wt .-% binder according to Example 1b and to homogeneous Mortar mixed. Due to the much higher W / B value in the high thermal insulation building material, there is a slight shrinkage. Compared  to the usual highly heat-insulating building materials, where normal cement according to DIN 1164 are used, this shrinkage is very low.

Fig. 9 shows the influence of the type of surcharge on the length change behavior of the mortar described.

Example 5 Light wall mortar LM21 according to DIN 1053

Due to the., Lightweight wall mortar, made with cements according to DIN 1164 often very absorbent light aggregates and that to achieve a suitable Processing consistency necessary high water requirements also a corresponding high shrinkage. In many cases, this can lead to cracking on the Guide the plaster shell to the light masonry. The use of the Binder according to the invention for this application therefore brings considerable technical and economic advantages.

For this reason, LM21 was used for a conventional lightweight mortar DIN 1053 the binder used (CEM II / B-T 42.5 R) against the binder exchanged according to example 1a in the same mass ratio.

Fig. 10 shows the measured changes in length of the mortars. When using the binder according to the invention, the shrinkage can be reduced by over 75%.

Claims (6)

1. Binder for cement-bound compositions, which contains:

• 1. burnt oil shale
• 2. Cement clinker
• 3. Calcium sulfate
• 4. Silicon dioxide
• 5. Alkali sulfate
• 6. Superplasticizer.

2. Binder according to claim 1, which additionally contains:

• 1. Defoamer
• 2. Delayers
• 3. Polymer dispersion

3. Binder according to claim 2, which contains:

• 1. 10 to 20% by weight, in particular 12 to 16% by weight, of burnt oil shale in accordance with DIN 1164, Part 1, Section 4.5 and ENV 197,
• 2. 20 to 50% by weight, in particular 30 to 45% by weight of Portland cement clinker,
• 3. 15 to 30% by weight, in particular 20 to 25% by weight, fly ash,
• 4. 15 to 30% by weight, in particular 20 to 25% by weight, of anhydrite,
• 5. 0 to 3% by weight, in particular 2 to 2.5% by weight, of superplasticizer,
• 6. 0 to 2% by weight alkali sulfate, in particular 0.4 to 0.8% by weight sodium sulfate,
• 7. 0 to 1% by weight, in particular 0.2 to 0.4% by weight, defoamer,
• 8. 0 to 1% by weight, in particular 0.3 to 0.6% by weight, of retarder,
• 9. 0 to 3% by weight, in particular 1 to 2% by weight, of plastic dispersions.

4. A binder according to claim 3, wherein the fly ash coal fly ash for Is concrete in accordance with EN 450 and where the average grain diameter of the glassy, predominantly spherical particles is between 5 and 20 µm. 5. Binder according to one of the preceding claims, which additionally fibers, especially alkali-resistant fibers such as polypropylene, glass or Contains polyacrylonitrile fibers.   6. Building part with a cement screed, which is a binder according to one of the Contains previous claims and covers a substructure, the substructure Expanded clay or expanded glass, optionally at least partially with cement stabilized, includes.