DE102007031418B3 - Dry mortar for a pressing material for pressing intermediate spaces between geothermal probes and the ground comprises cement, quartz sand and a clay mineral mixture - Google Patents

Abstract

Dry mortar comprises 15-40 wt.% cement, 30-60 wt.% quartz sand and 15-50 wt.% clay mineral mixture containing 10-30 wt.% mica, 25-30 wt.% free silica, more than 25 wt.% caolinite and less than 1 wt.% smectite.

Description

The The invention relates to a dry mortar mixed with water an injection material results, with the geothermal probes interspaces between the geothermal probes and the surrounding soil, and essentially from Cement, quartz sand and a clay mineral mixture is composed. The invention relates to the performance and stability of geothermal probes

In connection with modern and energy-saving building heating and cooling systems more and more geothermal probes are used in recent times. In this case, one or more holes are spent in the soil according to the requirements of the heating or cooling capacity. In these holes special pipes are set in U-shape. The spaces between the pipes and the soil are pressed with a grout. Through the U-shaped pipes, a heat transfer medium is pumped during operation. The heat transfer medium used is usually brine, for example, water-ethylene glycol solutions or water-salt solutions. As an alternative, CO ₂ and ammonia are also suitable as heat transfer media. During operation, heat is taken up from the ground via the surface of the pipelines or dissipated to this heat. The thermal conductivity of the soil and the pressing material, the qualitative design of the bore and the compression affect the thermal efficiency of the geothermal probe significantly, the long-term stability of the geothermal probe depends on it.

Of the Dry mortar, as an injection material for geothermal probes is being used, is currently predominantly as construction site mix on site from various individual components mixed together. There are different compositions for use. Occasionally also pre-mixed products are offered, but in the sum of their properties not optimal on the Application, d. H. the compression of geothermal probes are tailored.

To For example, Stüwatherm is one of these ready-to-use dry blends the company Stüwa Konrad Stükerjürgen GmbH. This dry mix has over other injection molding materials a high thermal conductivity resulting from the grain structure of the mixture and the addition of another natural Stoffes should result. The mixture has a share of one Clay mineral mixture between 25 and 30%, the clay mineral mixture is used the improvement of the thixotropic properties as well as the improvement the binding capacity under water.

Another product, which is suitable for pressing spaces in geothermal probes, and which also has a high thermal conductivity, is the mortar ThermoCem the company HeidelbergCement. The increased thermal conductivity is achieved by adding a natural substance. As such additive for admixture, for example, graphite, as well as in the EP 1 065 451 B1 described. Also ThermoCem is a mixture that contains as essential ingredients, inter alia, cement and a clay mineral mixture. The clay mineral mixture is used essentially to ensure tightness and plasticity of the injection molding material. This is achieved, as with the other known dry mortars used in geothermal, in that the clay mineral mixture has a high content of bentonite. Bentonite contains as an essential component montmorillonite, which is responsible for the water absorption and swelling capacity of the bentonite and significantly affects the plasticity.

In the DE 692 27 771 T1 describes a high-performance mortar with a high compressive strength of more than 40 MPa. In addition to cement, solid aggregates and quartz sand, this mortar or concrete has a share of diatomaceous earth. Their share is between 10 M% and 15 M%, but only the cement content. The kieselguhr can be kaolinhaltig, the kaolin content in the examples mentioned in the disclosure is a total of at most 1.4 M%.

In the DE 198 11 607 B4 a dry mortar for injection into cavities is described. The mortar is cement-free, because as binder no cement, but hydraulic lime is used, which has an advantageous effect on the suitability for cavity pressings.

In the DE 10 2004 039 107 A1 describes a highly heat-conductive building material for backfilling deep geothermal probes at depths of more than 100 m. That in the DE 10 2004 039 107 A1 described backfill material has a sound component or a clay mineral. Bentonite is mentioned in particular as a clay-containing material, its swelling capacity playing an essential role in order to obtain a plastic character of the hardened material.

A problem which hitherto adhered to all known dry mortar mixtures is the fact that the suspensions or the pressing material which is obtained from the mixture of dry mortar with water releases water again after the interstices have been pressed during drying. This can lead to the formation of voids in the hardened injection molding material, which on the one hand reduces the thermal conductivity, on the other hand but also reduces the stability of the entire geothermal probe. Another disadvantage of the known materials are the relatively long curing times of about 12-16 h. If a water vein is cut during the drilling, this can lead to the carryover of injection material, which in turn affects the stability of the probe. Finally, a third problem is air pockets in the injection material, which arise due to the flow behavior of the injection material in the borehole. These cavities also reduce stability and reduce the thermal conductivity.

task The invention is therefore to develop a dry mortar, which at the compression of gaps between geothermal probes and they can be used for surrounding soil, and the said Disadvantages of the prior art does not have.

The Task is in a dry mortar of Specially described in the beginning, made of cement, quartz sand and a Tonmineralgemisch is composed, achieved by the dry mortar one Cement content between 15 M% and 40 M%, a proportion of quartz sand between 30 M% and 69 M% and a proportion of the clay mineral mixture between 15M% and 50M%. The clay mineral mixture has a Proportion of mica between 10 M% and 30 M%, a share of free Silica between 25 M% and 30 M%, a share of more than 25 M% Kaolinite and a smectite content of less than 1 M%. As well as with the montmorillonite contained in the bentonite is in the case of kaolinite, a phyllosilicate. So far, this phyllosilicate is predominant used in the production of porcelain, as filler in colors and plastics, or as filling material and finish in papermaking. Furthermore finds it in brick making and as a refractory material Application. However, 60% of the degraded kaolinite is currently being used for the coating used by paper. One of the essential properties of kaolinite Is that it is becomes plastically deformable with the addition of water.

By the enclosure from kaolinite in the clay mineral mixture creates a dry mortar, the when mixed with water results in a molding material, its flow and curing properties particularly well suited to the geothermal requirements for geothermal probes customized are. Thus, the addition of kaolinite by the cavitation different sources excluded. It turned out that at the use of kaolinite the molding material substantially during drying releases less water, so that the Formation of cavities reduced during drying of the pressed material or completely is avoided.

by virtue of the set thixotropic property of the injection molding material, d. H. the suspension consisting of the dry mortar according to the invention Mixture is made with water, the suspension first stiffens after pressing in the probe quickly, if no shear forces through the pressing work more. Cavities can be affected by the very good flowability do not form when pressed. In this way, the Carryover of the suspension counteracted by groundwater. Due to the uniform compression without cavities becomes the thermal conductivity of the overall system improves efficiency.

at the production of the dry mortar has turned out to be a Proportion of more than 25 M% kaolinite in the clay mineral mixture advantageous is to significantly improve the properties of the injection molding material to reach. in principle the proportion may also be lower, but then u. U. the desired Properties are harder to reach. Instead of kaolinite can Dickit, too, Nakrit and other polytypes of kaolinite are used differ only in the crystal structure, but not in the chemical properties. Instead of kaolinite or in addition to it Illit can also be used. Basically, there are more, here not explicitly mentioned clay mineral components usable, provided these in the injection material to the desired ones lead thixotropic properties and above In addition, when mixed with water or only slightly swell or the water during curing difficult or impossible to give back.

By doing Care is taken that no or only slight traces of smectites, in particular of montmorillonite, appear in the clay mineral mixture and thus in the dry mortar, the mentioned properties in terms of flowability, curing and Reduction of water release on curing further improved. There by dehydration processes that usually used bentonite and there in particular the montmorillonite the Water is withdrawn, shrinks the volume of the molding material, it comes to air pockets and the demolition of the Contact between injection material and soil, indicating the thermal conductivity Overall deteriorated. By the proportion of smectites, the water store reversible, is kept as low as possible, can the additionally to counteract the addition of kaolinite. The kaolinite replaced the montmorillonite in this way almost completely, the dry mortar points a reduced swelling capacity on.

It has been found that the desired properties of the injection molding material are best achieved when the proportion of kaolinite in the clay mineral mixture, which is part of the dry mortar, between 30 M% and 50 M% lies.

In The above composition of the clay mineral mixture is obtained in Overall, the best features of the dry mortar and Water formed pressing material in relating to suspension formation, thixotropic properties, plasticity, frost resistance and swelling behavior.

For the dry mortar has the above composition is composed of cement, one share of quartz sand and a proportion of the clay mineral mixture as special proved advantageous. The admixture of cement provides strength and frost resistance, also for Sulphate resistance. Of the Carries quartz sand except to increase the thermal conductivity im pressed Condition also to increase the internal friction of the dry mortar at what, in a better miscibility and Aufschließbarkeit with respect to water results. Finally hardens due to the mixing ratio of kaolinite and cement, the injection material also much faster as conventional Pressing materials, what especially due to that kaolinite the few ingested water only slowly or not at all emits. Due to the composition of the dry mortar remains the injection molding material even after curing plastic and offers at normal geological activity - such as subsidence or displacements - static Security for the geothermal probe.

A very good resistance can be achieved by using as cement a blast-furnace cement, CEM III, used. This may cause the occurrence of heat-related Stress cracks in the injection material, which can occur when using normal cement, reduced become. Furthermore blast furnace cement is more resistant against salts and carbonic acid. Cement type CEM III / B, for example, is particularly suitable 32.5 NW, HS, NA.

In a particularly preferred embodiment of dry mortar this has a composition of 30 M% cement, 45 M% quartz sand and 25 M% clay mineral mixture. When using this composition for the dry mortar are all desired Balanced properties. To the injection material To obtain, mix one ton of dry mortar with 600 liters of water. The Stirring time is about three minutes, then that must grouting be processed within four hours, the curing time is less than ten hours.

In In a further embodiment of the invention, the dry mortar additionally contains limestone flour. When mixed with water, this serves to stabilize the suspension, Furthermore a gradation of the grain band is achieved. Thus, a higher packing density of the injection material achieved and the porosity reduced. This proves to be advantageous for heat conduction, as less air pockets in the injection molding available.

Of the Proportion of limestone powder in the dry mortar is preferably between 5 M% and 15 M%. In this area come the advantageous properties of limestone flour well without the properties of others Components that are added at least partially reduced accordingly are going to affect.

A typical composition of dry mortar when using Limestone flour with high balance of properties has a Cement content of 28 M%, a quartz sand content of 45 M%, a Tonmineralgemischanteil of 20 M% and a limestone content of 7 M%.

Mixing ratios, mixing times and lifetime are identical to those already for the limestone-free mixture specified values.

Mixed with the dry mortar according to the invention Water, so receives you have an injection material, which is especially good for the compression of gaps between geothermal probes and the surrounding soil is suitable. The spaces will be pressed permanently and cavity-free, water-bearing layers are permanently separated.

Of the dry mortar and its use will be described below with reference to an embodiment be explained in more detail. In the accompanying drawing shows

1 a schematic representation of a geothermal probe, which was pressed with a conventional suspension, as known from the prior art, and

2 schematically a geothermal probe, which was pressed with injection molding material, which was obtained from the dry mortar.

Based on 1 will first be explained the basic structure of a geothermal probe. The geothermal probe consists of one or more U-shaped tubes 1 , Through the pipe 1 During operation, a heat transfer medium, for example a water-ethylene glycol or a water-salt solution is pumped. Alternatively, carbon dioxide and ammonia can be used. About the outer surface of the pipe 1 Heat is taken up from the surrounding soil or given into this. The soil consists in the shown case play of several layers. The topmost layer is topsoil 2 , This is followed by a weathering horizon of sandstone down 3 at. It follows a water gate 4 , This can be, for example, a water vein through which groundwater is transported. Below the water tap 4 is again a layer of sandstone 3 , which, however, has no weathering effects. Underneath is again a water gate 4 , finally, a layer of Rotliegendes follows 5 ,

To bring the geothermal probe into the ground, first has a hole 6 be brought into the soil, whose diameter is large enough to the U-shaped tubes 1 to be able to record. After the U-shaped tube 1 into the hole 6 was introduced, the spaces between the pipe 1 and the surrounding soil with a suspension 7 pressed from bottom to top. For suspensions 7 As used in the prior art, the clay mineral mixture used usually contains a high proportion of bentonite, which absorbs a great deal when mixed with water and swells it. By dehydration processes such as capillary dehydration or drying, the bentonite is added after the drilling 6 with the suspension 7 is pressed, a portion of the water withdrawn - the water absorption is therefore reversible. This leads to a shrinkage of the volume, resulting in the formation of cavities 8th can lead. In this way arise large areas filled with air areas. These are now no longer available for the heat exchange between the geothermal probe and the ground, because air is an extremely poor conductor of heat. As a result, the efficiency of the geothermal probe decreases. Due to the flow behavior of the injection molding material, as used in the prior art, it also leads to air pockets 9 , which also reduce the stability of the probe and adversely affect the thermal conductivity. The long curing time of more than 12 hours also leads to the fact that when passing through several groundwater leading layers, the water gates 4 , Suspension 7 can be removed and the groundwater horizons can mix with each other, which is also referred to as a hydraulic short circuit. The long curing time can thus contribute to the formation of cavities and to the undesirable mixing of groundwater horizons. In particular, however, the long-term stability of the geothermal probe is adversely affected. The required permanent separation of groundwater floors can not be guaranteed.

In 2 the result is shown when the spaces between the geothermal probe and the surrounding soil with pressing material 10 be pressed, wherein the injection molding material 10 is obtained from the mixture of water and dry mortar, and wherein the dry mortar is composed essentially of cement, quartz sand and a clay mineral mixture, wherein the clay mineral mixture has a content of more than 25 M% kaolinite. The high kaolin content improves the flow properties. In addition, while kaolinite absorbs water to a much lesser extent than montmorillonite, it gives it more difficulty to dehydrate upon desiccation and ensures that the compression material has some plasticity which stabilizes the geothermal probe against normal geological activity. In addition, the clay mineral mixture with kaolinite advantageous thixotropic properties, which ensure that no cavities can form during the compression. In this way, the carryover of the injection material 10 counteracted by the groundwater and hydraulic short circuits are avoided.

To the properties of the injection molding material 10 To further improve and in particular to prevent shrinkage, the clay mineral mixture in the dry mortar on a proportion of smectites, which is less than 1 M%. The hitherto used bentonite or montmorillonite is essentially replaced in this way by the kaolinite, which leads to the improved properties. For this purpose, the proportion of kaolinite in the clay mineral mixture is advantageously selected between 30 M% and 50 M%. Further constituents of the clay mineral mixture are mica in a proportion between 10 M% and 30 M% and free silica in a proportion between 25 M% and 30 M%. When dry mortar, with water to the injection material 10 is mixed, the proportion of cement, preferably blastfurnace cement, for example, CEM III / B 32.5 NW, HS, NA - between 15 M% and 40 M%, the proportion of quartz sand between 30 M% and 60 M% and the proportion of the clay mineral mixture between 15 M% and 50 M%. A balanced mixture is obtained, for example, when using dry mortar with the composition 30 M% cement, 40 M% quartz sand and 25 M% clay mineral mixture. 1000 kg of this mixture are mixed with 600 l of water. The stirring time is three minutes, the curing time is less than ten hours and is thus significantly below the curing time of known in the art materials.

In addition, can the dry mortar also cold stone flour, preferably with a share between 5 M% and 15 M% be added. In this case results in a balanced Dry mortar mix with a share of 28 M% cement, 45 M% quartz sand, 20 M% clay mineral mixture, as well as 7 M% limestone flour.

The dry mortar is usually in advance mixed and then packed in sacks, so that at the construction site with respect to the mixture of the individual components - except water - no dosing errors can occur.

1

pipe

2

topsoil

3

sandstone

4

water gate

5

Rotliegendes

6

drilling

7

suspension

8th

grouting

9

air pocket

10

grouting

Claims (8)

Dry mortar, composed of cement, quartz sand and a clay mineral mixture is with - one Proportion of cement between 15 M% and 40 M%, - one Proportion of quartz sand between 30 M% and 60 M%, - and one Proportion of a clay mineral mixture between 15 M% and 50 M%, - in which the clay mineral mixture • one Proportion of mica between 10 M% and 30 M%, • a part of free silica between 25 M% and 30 M%, • a part of more than 25 M% kaolinite and • smectite content of less than 1 M%. dry mortar according to claim 1, characterized in that the proportion of kaolinite in Clay mineral mixture is between 30 M% and 50 M%. dry mortar according to one of the claims 1 or 2, characterized in that the cement is a blast furnace cement is. dry mortar according to one of the claims 1 to 3, characterized in that the proportion of cement 30th M%, of quartz sand 45 M% and of the clay mineral mixture 25 M%. dry mortar according to one of the claims 1 to 4, characterized in that the dry mortar additionally limestone flour contains. dry mortar according to claim 5, characterized in that the proportion of limestone flour between 5% and 15% by mass. dry mortar according to claim 5 or 6, characterized in that the proportion of cement 28 M%, of quartz sand 45 M%, of the clay mineral mixture 20 M% and of the limestone powder is 7 M%. Use of injection molding material, which consists of dry mortar one of the claims 1 to 7 and water is mixed, for pressing in between spaces geothermal probes and the surrounding soil.