EP0045026B1 - Method for soil stabilisation - Google Patents

Abstract

There is described a process for the consolidation of soil in which the moisture containing soil to be consolidated, rubbish or a soil/rubbish mixture is mixed with cement and then compacted. A fluidizing agent is added to the composition to be consolidated.

Description

The invention relates to a method for soil consolidation, in which the soil, overburden or a soil-overburden mixture to be consolidated, which contains moisture, is mixed with cement and then compacted.

From DE-C 895461 it is known to produce road surfaces from a construction material similar to the known cement concrete, the ground in an unprepared or physically specially prepared state with cement, water and chemically combining with the cement and the soil particles, improving the structural properties Additives are processed into a mixture. Suitable additives are the additives known from concrete technology, such as calcium chloride, sodium hydroxide, calcium oxyhydrate, silicon fluoride, silicic acid-containing additives, such as sodium or potassium silicate (water glass) and others, such as those used in cementitious concrete in particular as a sealant. Although in practice all of these additives have become irrelevant in soil stabilization or are no longer relevant today, the present invention starts from this patent as prior art.

In the construction of roads and railway lines, the substructure or substructure is usually fastened before the road surface (superstructure) or the ballast bed is applied in railway construction. Nowadays, this is done using a method known as soil consolidation, in which a wide variety of soils (loose masses), such as soils in accordance with DIN 18196, dusty mineral materials or mixtures thereof are mixed with water and cement, for example with soil milling machines or in mixing plants, and then mixed through Rolling action can be compressed, for example by means of rubber wheel rollers. By hardening the cement contained in the ground stabilization compound, the individual grains of the ground stabilization compound are connected to form a solid cemented framework. While the cement stone practically completely envelops the grains in concrete, it only putties the grains at individual points during ground consolidation. This stems from the fact that in general much higher compressive strengths are aimed for and, accordingly, more cement is added than is required for soil consolidation, where, depending on the soil, 80 to 220 kg cement per m ³ (corresponding to 4 to 16% cement ) gets along.

Among the aforementioned dusty mineral materials, which are referred to as overburden in the following and in the patent claims for brevity, are natural and artificial mineral materials such as fly ash, combustion residues, other dusty or fine sand residues from dry, wet and electro-dedusting plants, silt and clay-containing washing residues from gravel and quarry stone washing plants, waste material from grinding processes and other finely divided inorganic and organic residues of all types.

Due to the different objectives and the different materials used, there are fundamental technological differences between cement consolidation and concrete production. While concrete (cement concrete) always requires practically complete compaction, so that the cavities between the individual gravel and sand grains are almost completely filled with cement paste, practically complete compaction cannot be achieved during soil consolidation.

For concrete (except for cement quality), only the cement paste, i.e. the water cement value and the associated porosity of the hardened cement stone. In contrast, no special requirements can be imposed on soil consolidation, for example to achieve a minimum void. Even with good compaction, there are therefore more voids in the grain structure during ground consolidation than with concrete. While the concrete usually strives for a residual pore content of approximately 2.0 vol.% Or less and only in exceptional cases, such as for road concrete, a total pore content of approximately 4 vol.%, The proportion of pores in soil consolidation is 10 to 20 times larger, that is, the mineral cavity in the case of ground consolidation with cement, it varies between about 20 and 40% by volume.

Compared to concrete production, compositions for cementing the ground with cement are therefore made according to other principles, namely those of soil mechanics. This is based on a system of solids and water and air as pores. Basically, the aim is to achieve the densest possible storage of the minerals. Accordingly, the essential parameters for the quality of soil consolidation with cement are the water content, the cement content and the degree of compaction.

For soil consolidation with cement, any soil that occurs in nature can be used, which can be crushed to the required extent, contains no hardening substances and can be mixed with cement (hydrophobic or non-hydrophobic) and water as well as any suitable additives. Water and cement do not behave in a water-cement ratio that is similar to that of concrete technology. Accordingly, there is no possibility of "reliably" calculating certain strength properties in soil consolidation with cement.

As already mentioned above, soil consolidation can also be carried out with the addition of overburden or, as already carried out on a trial basis, with the exclusive use of overburden how fly ash are done. The above-mentioned points of view also apply here essentially.

In the soil-cement mixtures to be consolidated, the water acts as a "lubricant". Accordingly, for each soil, spoil or soil / spoil mixture or for each soil-cement mixture, soil / spoil-cement mixture or spoil-cement mixture, there is a so-called “optimal water content” from the point of view of the above principles, which is determined in the so-called proctor test (see leaflet DIN 18127 for the proctor test, published by the Research Association for Roads).

The water demand in soil stabilization is based on the “optimal water content”, which - as described in the above-mentioned leaflet - can be determined according to the rules of soil mechanics. The dry space density (Proctor density) corresponding to this optimal water content is generally also to be aimed for in the construction, provided that the result of the Proctor test is confirmed in the subsequent manufacture of test cylinders to determine the required or suitable cement content to achieve the necessary compressive strength.

The test specimens formed in the Proctor test are examined for compressive strength on the 7th and / or 28th day after their manufacture (see TVV 74, Federal Minister of Transport, Dept. Road Construction). The increase in strength is roughly linearly related to the increase in cement content. Interpolation is used to infer the associated cement requirement from the compressive strength achieved [cf. «Concrete» 19 (1969), pages 19 to 24].

There is no relationship between strength properties and water cement value as with concrete in soil stabilization. So-called “optimal compaction” as with concrete does not exist in soil stabilization either, because the degree of compaction always depends on the “Proctor density” determined from the same mass.

Although the soil consolidation with cement and, if necessary, additives according to DE-C 895461 results in a considerable improvement in the properties of the sub-floor or substructure, in particular with regard to the frost resistance in road and railway construction, this procedure nevertheless has various disadvantages. The addition of extraneous water beyond the inherent water content of the hardening material in situ means that additional process steps and increased costs are required. Furthermore, so-called macro cracks occur in such solidified soils or frost protection layers when hardening as a result of shrinkage. These make it necessary, for example, to use relatively thick bituminous or cement-bound road surfaces in order to avoid the reflection of the macro cracks in the superstructure. There is a great need for a method for ground consolidation that can be carried out in a simpler and cheaper manner and leads to equally good and better results in terms of frost resistance, load-bearing capacity and crack structure. The avoidance of macro cracks is particularly desirable, since this would allow the use of thinner bituminous or cement-bound road surfaces in road construction, which in view of the scarcity and the rising price of petroleum will be an ever increasing necessity in the future.

Accordingly, the object of the invention is to propose a method for ground stabilization, in particular for road and railway construction, which can be carried out in a simpler manner and, if appropriate, using smaller amounts of cement and water than conventional ground stabilization with cement and, if appropriate, additives according to DE-C 895461 is. In addition, the method according to the invention should lead to reduced formation of macro cracks, so that, for example, thinner bituminous or cement-bound road surfaces can be used in road construction.

The invention therefore relates to a method for soil consolidation, in which the moisture-containing soil, spoil or a soil-spoil mixture to be solidified is mixed with cement and a concrete admixture and then compacted, characterized in that the concrete admixture, calculated as dry matter, is characterized , Concrete plasticizer and / or concrete plasticizer in an amount of 2.5 to 5% and preferably 3 to 4.5%, based on the cement weight used.

A preferred embodiment of the invention relates to a method as indicated above, which is characterized in that a soil containing natural moisture is used and the moisture content of which is not increased.

It is known to use additives such as concrete plasticizers, concrete flow agents, concrete accelerators, air-entraining agents, sealants, concrete retarders and injection aids as well as additives such as mineral substances, organic substances and colorants in the production of concrete. In the manufacture of road surfaces, some such additives are known in the context of DE-C 895461 mentioned above. However, the additives known from this patent have not gained any practical importance for soil stabilization and the other additives or additives mentioned with the exception of the mineral substances (overburden) have so far not been used in soil stabilization. It has now surprisingly been found that the use of concrete plasticizers and / or concrete plasticizers leads to advantageous results in soil consolidation, in spite of the completely different situation compared to concrete production. So can For example, with the cement content unchanged, the addition of extraneous water can be dispensed with, ie the inherent moisture of the material to be consolidated is sufficient. In addition, the addition of such agents leads to higher compressive strengths, so that it is possible to significantly reduce the proportion of cement. The reduction in the water and cement content in turn results in less cracking behavior of the solidified masses, so that, with the same or higher compressive strength, macro cracks no longer occur, as was customary hitherto. Rather, only a micro-crack behavior can be observed in the soil consolidation according to the invention. In contrast to the previous soil consolidation with cement, this also allows the use of thin bituminous or cement-bound road surfaces, which in addition to the savings in soil consolidation itself leads to a further reduction in the cost of road construction.

Concrete plasticizers (plasticizers) were mainly developed in Germany and Switzerland a few decades ago. Your task is to convert a stiff fresh concrete into a plastic fresh concrete without adding more water. Before using plasticizers, it was common to use a larger amount of cement paste, i.e. with a higher cement additive combined with a higher water content to obtain a more plastic concrete. For some years now, there have also been concrete superplasticizers that are super plasticizers.

The excavated materials that can also be used in soil stabilization increase the apparent cohesion in the fresh base layer after today's compaction in the fresh state of soil consolidation after compaction has been achieved. In addition, certain mineral fines are latent hydraulic, i.e. they participate to a certain extent in the hardening behavior as a result of the Portland cement clinker components, so that the cement can be reduced as a “crack-promoting” component of the system.

• 1. Präparate aus Sulfitablaugen (Ligninsulfonsäuren bzw. deren Salze),
• 2. Carbon- und Oxycarbonsäuren sowie deren Salze, Derivate dieser Verbindungen und Detergentien,
• 3. bestimmte Silikone,
• 4. sulfonierte Melamin-Formaldehyd-Kondensationsprodukte (Superverflüssiger),
• 5. Kondensationsprodukte aus Naphthalinsulfonsäure und Formaldehyd,
• 6. Präparate aus Zuckerarten, die wegen ihrer Verzögerung des Erhärtungsvorganges gelegentlich mit Calciumchlorid kombiniert werden,
• 7. Kondensationsprodukte von Anthracenen analog wie beim Naphthalin,
• 8. sulfoniertes Phenolformaldehydkondensat und
• 9. Kombinationen der unter 1. bis 8. aufgeführten Substanzen.

According to the prior art, the following substances essentially serve as liquefiers and flow agents in the production of concrete:

• 1. Preparations from spent liquor (lignin sulfonic acids or their salts),
• 2. carboxylic and oxycarboxylic acids and their salts, derivatives of these compounds and detergents,
• 3. certain silicones,
• 4. sulfonated melamine-formaldehyde condensation products (super liquefier),
• 5. condensation products of naphthalenesulfonic acid and formaldehyde,
• 6. preparations from types of sugar that are occasionally combined with calcium chloride due to their delay in the hardening process,
• 7. condensation products of anthracenes analogous to naphthalene,
• 8. sulfonated phenol formaldehyde condensate and
• 9. Combinations of the substances listed under 1 to 8.

(The sulfone group-containing compounds of the substances mentioned are usually commercially available in the form of their sodium salts and are also used in this form.) In practice, from 0.2 to a maximum of 1.5% of plasticizer solutions, based on the cement content, are used. Due to the limited solubility, these are generally 20 to 30% solutions. Larger amounts of these additives generally do not bring any additional advantages, but rather lead to excessive liquefaction, deaeration in the case of road concrete and to an undesirably long delay in hardening. In Germany, the use of plasticizers and concrete plasticizers in cement concrete is based on DIN 1045.

Although it can be assumed that the "clinker phases" of the cement interact with water during ground consolidation in a similar way to when producing concrete, there are some serious differences compared to concrete during ground consolidation. While the aggregate mixtures A, B, C according to DIN 1045 have surfaces of approximately 0.8 to 4.6 m ² / kg, the sieve lines of the sands and soils to be consolidated run at a great distance from the concrete sieve lines in the fine to medium grain range. A specific surface can only be roughly estimated at around 10.0 rub / kg. Due to the much smaller volume proportion of cement paste (cement + water + pores) in soil consolidation, the amount of cement paste present in soil consolidation is offset by a much larger surface area than in concrete. This results in the already mentioned high pore volume in soil stabilization compounds. Furthermore, the relatively small amount of cement used in soil consolidation means that the distribution in the entire soil system cannot be continuous. In the case of soil stabilization compounds, this leads to "punctiform cementing" of the soil particles with cement paste. Due to the lack of the dispersant water as the carrier substance for the cement as the disperse phase, cement grain aggregates form in numerous grain packing points. As a result of the aggregation of cement granules to form larger aggregates, the hydration of a larger cement package with gel formation and volume increase that is becoming increasingly dense is always slower, but always progressing. This is one of the reasons for the often criticized late strengths after longer periods.

It has now surprisingly been found that when using concrete plasticizers and / or concrete flow agents in soil stabilization compositions, the water content can be reduced to about 70 liters / m ³ and still be sufficient Compatible building material is obtained, although in the case of soil stabilization compounds, a much smaller amount of cement is available from the outset for a much larger surface (compared to concrete) and the low water content no longer guarantees the continuity of the liquid phase within the building material mixture.

The development work carried out has shown that water savings of up to 50%, based on the “optimal water content”, are possible. Surprisingly, however, useful results are only achieved at much higher concentrations of plasticizer and / or superplasticizer than is customary in concrete production. Based on the cement weight, amounts of 2.5 to 5% and preferably 3 to 4.5% dry substance in powder form have proven suitable.

The concrete plasticizers and concrete plasticizers suitable for soil consolidation can be used as dry matter, i.e. can be used in powder form. In contrast, only liquid concrete plasticizers may be used in the production of flow concrete according to DIN 1045. The liquefiers and flow agents can, however, also be used in liquid form, such quantities being used that the concentrations given above, based on dry matter, are observed. They can be sprayed or sprayed onto the formation in liquid form before the cement is added. filled into the mixer or in powder form together or separately by means of the scattering devices for cement, sprinkled onto the subgrade or added to the mixer or also intimately mixed with the cement before being applied to the ground to be solidified.

In experiments, sulfonated naphthalene formaldehyde condensate in particular has proven to be a suitable additive. The other means mentioned can only be used in practice if no previously determined impairments in the hardening process and no more changes in space (swelling) occur. In this connection, the often high sugar content of commercial plasticizers and concrete plasticizers has had a negative impact (see below).

The possibility of saving water of around 50% has great economic and technical advantages. The economic advantages are that most of the rough planes of roads and paths prepared for ground consolidation no longer require pre-wetting. The provision of irrigation facilities can thus be omitted. A major technical advantage is that due to the use of greatly reduced amounts of moisture, the shrinkage or cracking behavior is also greatly reduced. It is known from the relevant literature that the formation of cracks in soil consolidation layers is only influenced to a small extent by higher compressive strength. To a much greater extent, the cracks arise due to the shrinkage behavior due to the capillarity of fine-grained masses. In the soil stabilization according to the invention, the shrinkage crack formation is greatly reduced to a micro-crack formation or does not occur at all, since it is possible to reduce the water saturation value that is normally required technically.

Furthermore, higher compressive strengths are achieved through the use of concrete plasticizers and / or concrete flow agents according to the invention. The higher compressive strengths that can be achieved according to the invention in turn results in a further economic advantage in that, in comparison with the normal case, cement savings are possible without loss of strength.

Of the waste materials that can be used in soil stabilization, fly ash in particular is likely to be of great importance in the future, since it is produced in large quantities and has so far only been used to a reasonable extent. However, the investigations carried out within the scope of the invention have shown that the possible uses of fly ash in soil stabilization strongly depend on its properties. The size of the loss on ignition has proven to be a suitable assessment criterion in previous experiments.

Fly ash with the lowest loss on ignition (fly ash 1 with loss on ignition of not more than 5% by weight), which can be used alone or in any ratio mixed with soils, is most suitable for the method according to the invention. Suitable amounts of fly ash in mixtures with soils are 30 to 70% and in particular about 50%. Fly ash with higher loss on ignition (fly ash 2 with loss on ignition between 5 and 8% by weight) should only be used in ground stabilization in exceptional cases. Usually, however, such fly ash can be added to the soil to be consolidated in amounts of up to 60% and preferably 40 to 50%. Even fly ash with a high loss on ignition (fly ash 3 with a loss on ignition of more than 10% by weight, e.g. up to 40% by weight and more) is not only suitable for soil consolidation, but can be added to soil to be consolidated in quantities of up to 20%. In this context, however, it should be pointed out that the aforementioned proportions of the various fly ash are based on the fact that the soil stabilization to be produced meets the requirements of TVV 74. If higher or lower requirements are placed on soil consolidation, then in particular the possible quantities of fly ash with higher and higher loss on ignition change.

The explanations in the description and in the following examples are essentially based on the requirements specified by TVV 74. However, the method according to the invention is of course not limited to the fulfillment of these requirements, but it is at the discretion of the average expert to adapt the method according to the invention in the event of differing requirements.

example 1

Certain soils with a cement content of 7% were initially examined normally according to Proctor. For this purpose, the removed soils were air-dried over several days. The Proctor investigation then started from a water content of around 1.0 to 1.5%. The water content was increased in steps of 1.5% and led to the optimal point. The final water content was 10.5%. The Proctor examination, which was carried out over 7 moisture levels, showed a Proctor value of 1.87 g / cm ³ and an optimal water content of 9.0% for the representative floor (frost-proof sand SE according to DIN 18196 and ZTVE-StB 76).

Proctor examinations were then carried out with the same soil material with the same moisture levels, but with the addition of concrete plasticizers and plasticizers in powder form in the dosages between 2.5% and 5.0%, based on the cement content of the sample. It was found that water contents between 3.0 and 4.5% dry room densities were already close to 100% Proctor density (normal case). With water contents of over 4.5%, these substances even showed Proctor densities of well over 100%.

Subsequent compressive strength tests on Proctor cylinders showed higher strengths than normal ground consolidation compounds, i.e. Soil stabilizers produced without the addition of concrete liquefier and plasticizer.

Example 2

A sand (sand removal from Moorfleet; frost protection sand SE according to DIN 18196, floor F1) with the addition of 7% cement and 2.5% plasticizer, based on the cement content, was examined according to Proctor. The Proctor curves shown in FIG. 1 were obtained.

The liquefiers used were lignin sulfonates. The manufacturer's dosage recommendation (intended for concrete) was exceeded ten times. As can be seen from the Proctor curves shown in FIG. 1, a clear increase in dry density was observed.

A good liquefaction effect was also observed in samples with 5% plasticizer, based on the cement. Due to the very high sugar content of the lignin sulfonate used and the associated delay in hardening, however, no usable compressive strength values were determined after 7 days:

Example 3

The experiment according to Example 2 was repeated using two further additives. Veflüssiger B consisted of a combination of lignin sulfonates and melamine formaldehyde condensates. The condenser C consisted of a combination of lignin sulfonates and naphthalene sulfonate formaldehyde condensates. The two plasticizers were used in an amount of 2.5 and 5%, based on the amount of cement. The Proctor dry densities obtained are shown in FIGS. 2 and 3.

The observed liquefaction effect was very good (see Fig. And 3). Due to the high sugar content of the lignin sulfonates, the compressive strength results obtained were only partially satisfactory.

Example 4

The experiment according to Example 2 was repeated using a commercially available sulfonated naphthalene formaldehyde condensate in the form of the sodium salt (liquefier A). The plasticizer was used in an amount of 1.5, 2.5 and 5.0%, based on the cement. The Proctor curves obtained are shown in FIG. 4.

The results show that with a water content of around 3 to 4.5%, the minimum compaction required for soil stabilization of 98% of the normal Proctor density is obtained.

The examination of samples with a water content of 4.5% showed compressive strength values that were about ½ higher (after 7 days) than for corresponding samples without the addition of a condenser. This shows that when using plasticizers, the cement content can be reduced by about '/ ₃ compared to «normal» soil consolidation with cement (see example 6).

Example 5

In the preceding description, it has been emphasized several times that concrete is produced with a very small proportion of residual pores, while the pore proportion is 10 to 20 times that of the concrete pores when the soil is consolidated. From the literature and our own investigations it follows that soil consolidation can be considered frost-proof if a compressive strength of 2.5 N / mm ^{2 has been reached} in the component. This significantly lower minimum compressive strength, in contrast to concrete, is due to the fact that even when stored in water, a test specimen made of soil stabilization material does not absorb the amount of water that it could absorb due to its pore volume. This means that ice formation has enough pore space for the volume change from water to ice (plus 9%).

The influence of frost in the freeze-thaw alternation process on test specimens with the dosages described in Examples 3 and 4 of the plasticizers and plasticizers, Proctor test cylinders were made with 7% pectacrete cement. When, after 7 days, the test cylinders had a compressive strength of approx. 5 N / mm ² , the investigations began in accordance with the information sheet for suitability tests for soil consolidation with cement, Research Association for Roads, Working Group for Underground Structures, Edition 1975, Section 4.4.3-Frost test . In amendment to paragraph 4.4.3, not only was the measured value of the change in length between the first and after the twelfth frost effect specified, but the change in length was determined after each frost effect, in order to make the development of frost elevations more visible. After completion of the 12 freeze-thaw changes, the tests were stopped and the measured values were evaluated in a graphic representation (see FIG. 5).

The test specimens each contained 2.5% of liquefier A, B or C based on cement. The height of the Proctor test cylinders was 12 cm. The permissible length change should be a maximum of 1% o after the 12th freeze-thaw change. 1% o of 12cm is 0.12mm.

Furthermore, the compressive strength of the test cylinders was determined after 7 and 28 days and after the freeze-thaw cycle had ended. The results are summarized in the following table.

Compressive strength in N / mm ²

The results obtained show that usable compressive strength values were obtained using all three condensers. With regard to the change in length after 12 freeze-thaw changes, only condenser A gave the required change in length of less than 1% ₀ , namely a change in length of less than 0.1 mm. As can also be seen from the compressive strength values when using condensers B and C, the high sugar content in condensers B and C also has a negative impact on the frost-thaw cycle tests.

Example 6

In example 4, it was pointed out that the addition of plasticizers leads to approximately% higher compressive strength values, so that the cement content can be reduced by approximately V3 when using plasticizers compared to the «normal» soil consolidation with cement. To show this, a flushing sand «SE» according to DIN 18196 and ZTV StB 76 according to Proctor was examined. The cement content was initially changed at a constant water content of 4.5%. With a cement content of 4.6%, a dry density according to Proctor of 1.840 and a compressive strength after seven days of 2.4 N / mm ² were found, while with a cement content of 7.0% the dry density according to Proctor 1.871 and the compressive strength after seven Days were 4.5 N / mm ² . These results confirm the above finding that the increase in strength is approximately linearly related to the increase in cement content.

Furthermore, samples with a content of 4.5% water, 4.6% cement and - based on the cement content - 3% of plasticizer A were examined. A dry room density of 1.898 and a compressive strength after seven days of 4.4 N / mm ² were found. This shows that the addition of plasticizer actually allows savings of about% of the cement without the compressive strength deteriorating.

In the course of the tests carried out, samples were also examined which, with a water content of 4.5%, contained only the stated amount of plasticizer A but no cement. It was shown that the addition of condenser A alone improves compression, i.e. results in a higher drying room density in the Proctor test.

Example 7

Several test series were carried out with unwashed sand 0 / 8mm (sand SE according to DIN 18196) with the addition of fly ash 1 and 3, which have been explained in the description. Fly ash 1 with a low loss of ignition came from the Kiel-Ost coal-fired power plant, fly ash 2 with a higher loss of ignition from the Wedel coal-fired power station and fly ash 3 with a high loss of ignition from the Tiefstaak and Neuhof coal-fired power plants, Hamburg. The Proctor curves were determined for different compositions.

Experiment A: The Proctor curve for sand was determined by adding 4 parts by weight of cement to 100 parts by weight of sand. The maximum dry density was 1.919.

Experiment B: The Proctor curves for compositions of 100 parts by weight of sand, 2 parts by weight of cement and 4 parts by weight of fly ash were determined. Tests were carried out in each case without the addition of a plasticizer and with a plasticizer (3% based on the cement). The maximum dry densities obtained are shown in the table below.

Trial C: Trial B was repeated with the difference that 4 parts by weight of cement were used. The maximum dry densities obtained are also shown in the table below.

Experiment D: Experiment C was repeated with the difference that the proportion of fly ash was increased to 15 parts by weight. The result These are also shown in the table below.

Test E: Test D was repeated with the difference that the proportion of fly ash was increased to 30 parts by weight. The results are also in the table below

The mixtures with fly ash 1 have the highest dry space densities when using the powdered liquefier. Without the use of powder plasticizers, the densities are clearly lower. The mixtures with fly ash 2 show essentially the same dry density differences, but the dry densities generally move somewhat below the dry densities of the mixtures with fly ash 1. The fly ash 3 behaves in a greatly changed manner compared to the two fly ash mentioned above, in that the dry densities of the mixtures with one economically interesting fly ash content of more than 15 parts by weight will drop sharply. Lower dry densities are associated with a high proportion of pores and generally also with weaker strength properties. Proctor tests carried out with the use of steel plates showed that the grain crushing was greatest at fly ash 3. It was found that in general the grain breakdown seems to decrease as the dry density decreases while the proportion of fly ash increases.

In summary, it can be seen from the above Proctor investigations that fly ash with a combustible residue (loss of ignition) of approx. 3% (fly ash 1) has good properties even in a higher proportion of the mixture, fly ash with loss of ignition up to approx. 8% has somewhat less favorable properties and Fly ash with loss on ignition over 10% and more have unfavorable properties on the development of dry density.

Proctor test cylinders to determine the compressive strength after 7 and 28 days were manufactured with a few basic formulations. For all basic formulations, the sand content was 100 parts by weight and the water content was 4.5 parts by weight. The amount of powder plasticizer was a constant 3%, based on the cement content. Test cylinders with 3, 5 and 7 parts by weight of cement, based on sand and fly ash, were produced. From the graphical representation of the compressive strength values obtained as a function of the proportion of cement, that cement requirement which corresponds to the requirements of the was determined.

Experiment F: Experiment E was repeated with the difference that the proportion of fly ash was increased to 50 parts by weight. The results are also shown in the table below.

• GrundrezepturA: 4 Gewichtsteile Flugasche 1
• Grundrezeptur B: 4 Gewichtsteile Flugasche 2
• Grundrezeptur C: 15 Gewichtsteile Flugasche 1
• Grundrezeptur D: 30 Gewichtsteile Flugasche 1
• Grundrezeptur E: 30 Gewichtsteile Flugasche 3
• Grundrezeptur F: 15 Gewichtsteile Flugasche 3
  
  

TVV 74 gives sufficient compressive strength. The basic recipes used contained the following amounts of fly ash:

• Basic recipe A: 4 parts by weight of fly ash 1
• Basic recipe B: 4 parts by weight of fly ash 2
• Basic formulation C: 15 parts by weight of fly ash 1
• Basic formulation D: 30 parts by weight of fly ash 1
• Basic formulation E: 30 parts by weight of fly ash 3
• Basic formulation F: 15 parts by weight of fly ash 3
  
  

The results shown in the table above show that, based on the 7- or 28-day compressive strength measured against the requirements of the TVV 74, there is a considerable difference in the amount of cement required with an increasing proportion of fly ash. This makes it clear that the latent hydraulic properties of fly ash can lead to high post-hardening. The fly ash 1 requires a mixture proportion of 30 parts by weight to 100 parts by weight of sand when using a powder liquefier only 3 parts by weight of cement, ie less than about 50% of the proportion of cement customary in the prior art. However, if fly ash 1 is used only in a proportion of 4 parts by weight per 100 parts by weight of sand, the cement requirement only increases to 3.5 to 3.7 parts by weight.

Mixtures with 4 parts by weight of fly ash 2 only slightly increase the cement requirement to 3.8 to 3.9 parts by weight. Even the worst-quality fly ash, namely fly ash 3, can still be used in a proportion of 15 parts by weight, the cement requirement increasing to about 4.5 parts by weight. In contrast, mixtures with proportions of 30 parts by weight of fly ash 3 behave unfavorably, since they show inadequate strength properties.

It is worth noting that all cement requirements are derived from strength properties based on 4.5 parts by weight of water in the ground stabilization compound. This is an extremely important requirement, together with a relatively low cement requirement, for a largely crack-free ground consolidation covering construction.

Example 8

In order to investigate the influence of limestone powder as a dusty product of a basic composition in a soil consolidation mixture, first proctor tests were carried out to determine the influence of the mineral substances on one another, as well as tests with and without using the powder plasticizer. As before, different Proctor curves were shown, i.e. that with the same recipes, the Proctor curve with powder plasticizer was above the Proctor curve without powder plasticizer. Experiments carried out with a basic formulation to determine the compressive strength of test specimens after 7 and 28 days (cf. Example 7) gave results similar to those in Example 7, the cement requirement, based on the compressive strength required by TVV 74, being 3.80 parts by weight after 7 days to the compressive strength required by TVV 74 after 28 days was 4.14 parts by weight. The basic recipe consisted of 100 parts by weight of sand and 15 parts by weight of limestone powder. The powder plasticizer proportion was constant 3%, based on the cement. Here, too, there was a significantly lower cement requirement, namely with a water content of approximately 50% of the optimal water content. This enormous water saving must always be taken into account when assessing all reported results.

Corresponding experiments were carried out using quartz stone powder. Corresponding results were obtained, e.g. using 15 parts by weight of quartz stone powder per 100 parts by weight of sand (Sand SE according to DIN 18196) resulted in a cement requirement of 3.85 parts by weight after 7 days according to the requirements of TVV 74.

Example 9

As described in Example 5, test specimens from the compositions according to Examples 7 and 8 were examined using the freeze-thaw cycle. Only the sand-fly ash mixtures, whose proctor cylinders had compressive strengths of less than 2.0 to 2.5 N / mm ² after 7 days, show changes in length exceeding 1%. All other compositions, including those with the highest admixtures of stone powder, resulted in changes in length within the permissible range.

As a phenomenon, however, there are the studies with quartz stone flour, which, in contrast to all other results, did not result in a slight increase in length, but rather a slight reduction in length. However, these reductions in length were all below 1% ₀ (0.12 mm).

In summary, it can be stated that only the initial strength of the soil stabilization, but not the proportion of the finest minerals, can be the cause of frost damage.

In order to check the influence of the freeze-thaw changes, the test specimens were then examined for their compressive strength. It was found that no test specimen showed a drop in compressive strength, which would indicate that a strength-damaging influence had occurred due to frost. Rather, the test specimens tested according to the influence of frost showed differently higher compressive strength results compared to the normal 28-day compressive strength results. This proves that increasing the fine particles <0.06mm in soil stabilization compounds does not have a frost-damaging effect on the soil stabilization component.

Example 10

In addition to the previous examples 7 to 9, fly ash was subjected to proctor examinations without the addition of sand alone. Experiments were carried out with and without the addition of plasticizer powder. While fly ash 3 gave practically unusable results when using 6 or 10 parts by weight of cement per 100 parts by weight of fly ash with and without a plasticizer, the addition of plasticizer powder in fly ash 2 led to a significant increase in dry density and compressive strength. The dry densities of fly ash 1 were even higher than for fly ash 2. Here too, the addition of liquefiers led to a sharp increase in the compressive strengths.

It appears that soil consolidation compounds consisting only of fly ash and cement do not reveal a clear Proctor value. The increase in the curve of the dry. density leads to a maximum value which is related to the leakage of water during the test. The comparison of all three fly ashes suggests that the higher the loss on ignition, the higher the water requirement.

The experiments with fly ash 1, in which cement with and without powder plasticizer was mixed into the fly ash and then the water was added, showed that with a water content of 50% of the maximum water requirement, the use of plasticizers to reduce the cement requirement by about 35 to 40 % led. Increasing the water content to the maximum water content of about 16 parts by weight resulted in an increase in the compressive strength. This in turn makes it possible to use much smaller amounts of cement. It should be noted, however, that the likelihood of cracking increases with the possibility of high levels of moisture release from the ground consolidation layer. As in the previous examples, the cement requirement was determined using the criteria of TVV74.

In all of the examples described, hydrophobized cement (pectacrete cement, see DE-PS 1 300 856, 1 303 934, 1642380 and 1 646502) was used. In Examples 7 to 10, commercially available sulfonated naphthalene formaldehyde condensate was used as the powdery plasticizer.

Claims (4)

1. Method of soil stabilization, in which the moisture-containing soil, rubble, or soil/rubble mixture to be stabilized is mixed with cement and a concrete additive and then compacted, characterised in that a concrete thinner and/or a concrete flow promoting agent is used as the concrete additive, in an amount from 2.5 to 5wt.% and preferably 3 to 4.5 wt.%, relative to the weight of cement and calculated as dry material.

2. Method according to claim 1, characterised in that a soil which naturally contains moisture is used, and the moisture content thereof is not increased.

3. Method according to claim 1 or 2, characterised in that lignin sulphonates, sulphonated-melamine formaldehyde condensates, sulphonated naphthalene-formaldehyde condensates, thinning silicones, sulphonated anthracene-formaldehyde condensates, sulphonated phenylformalde- hyde condensates, carboxylic and oxycarboxylic acids, salts thereof and derivatives of these compounds, surfactants, or mixtures of two or more of these substances are used as concrete thinners or flow promoting agents.

4. Method according to any of claims 1 to 3, characterised in that one third less cement is used than would be necessary to achieve the same stability under pressure of the soil stabilizing material without the addition of concrete thinners and/or flow promoting agents.

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