EP1655410B1 - Method of constructing a base layer - Google Patents

Description

1. Technical area

The present invention relates to a method for producing a base course, in particular for road construction or as a stand space for buildings.

2. The state of the art

The increase in deserts is a known problem in many countries of the world. A re-use of desert areas to recultivation requires a corresponding infrastructure, in particular the construction of roads to develop the land.

In these areas, but also in areas with little precipitation, which are not yet (completely) deserts, so-called arid zones, predominantly gleichkömige, fine-grained sands occur in loose storage, which do not have sufficient capacity for road construction or other foundations. Due to their uniformity, they are not compressible. The shear strength is therefore very low. The cause of the low shear strength is the round grain shape and the uniformity of the sand.

Therefore, in a conventional approach to road construction in such areas, it is necessary to use large quantities of base course material such as crushed mineral mix, recycled materials or quarry stone of sufficient thickness as a base course. Another alternative is the mortaring of the sand layers. However, this requires a very high proportion of cement and is therefore uneconomical. Furthermore, this approach requires due to the low shear strength of the sand very powerful hydraulically bound support layers, as they break apart on the soft loose ground otherwise.

Another problem with making the milled base course in the hot climatic zone is keeping it moist until the final setting takes several days. The milled layers must be prepared with sufficient water content and kept moist until the final hydraulic binding with high water levels, so that these layers do not burn in the hot sun and bind only partially hydraulically, resulting in considerable loss of strength.

Such road construction or the production of support layers for foundations is therefore extremely expensive not only because of the lack of materials in these areas. It is therefore necessary to develop alternatives for the production of base courses for road and road works or foundations for the large-scale development of desert edge areas, as they are found everywhere in North Africa and Arabia. In this case, a construction process is only economical if the pending in the arid zones soil types are recycled and beyond suitable waste materials can be used for the treatment of base layers.

A technically related problem arises in the recycling of residues or residues of mechanically-biologically treated household waste, so-called MBA residues. These are mainly fibrous wood and plastic residues with peat-like residual waste of coarse fiber structure with different grain size and length in the dry state. These residues accumulate in large quantities in mechanical-biological treatment plants and are not landfillable. If these materials are deposited in a landfill and blended, no strength is achieved and it is given a high sensitivity to weathering, since the light materials are washed away in the rain. This also applies if waste incineration slag is added to the MBT residues.

• Profilierung der Einbaubereiche mit einem Gefalle zwischen 5 % und 10 % zur gezielten und kontrollierten Ableitung des Niederschlagswassers, wobei die Oberfläche geglättet und mit wasserundurchlässigen Materialien mit Verdichtung abgedeckt wird.
• Zur Gewährleistung eines gering durchlässigen Deponiekörpers ist der Abfall im Dünnschichtverfahren hochverdichtet einzubauen. Durch Einstellung eines optimalen Wassergehaltes der Abfälle ist eine höchst mögliche Verdichtbarkeit zu gewährleisten, so dass ein entsprechender Wassergehalt eingestellt werden muss.

Therefore, the following stringent requirements for the installation of these mechanically treated biological waste are placed in a landfill.

• Profiling the paving areas with a gradient of between 5% and 10% for the targeted and controlled discharge of rainwater, whereby the surface is smoothed and covered with impermeable materials with compaction.
• To ensure a low-permeability landfill the waste is to be installed in a highly compacted manner using the thin-film process. By setting an optimal water content of the waste a maximum possible compressibility is to be ensured, so that a corresponding water content must be set.

With these requirements, both an improvement in the quality of running off of the body waste surface water as well as a minimization of Sikkerwasseranfalls to be achieved at the landfill base. However, as the experiences of the first plant operators with large-scale industrial tests have shown, it is not possible, even if the material is adjusted with an optimized water content, in favor of an optimized compaction, the above-mentioned. Problem to solve, because despite good compaction, a high porosity of the material and thus a high permeability remains and the compacted material softens in rain and washed off, so that the drain water is heavily contaminated with these ingredients. In order to prevent this, elaborate covering measures are required at the landfill or else the MBT residues have to be costly incinerated.

Finally, load-bearing problems arise, as in the case of equidular desert sand with impending loose bulk fillings, as can be found on old industrial wastelands, for example in the Ruhr area. So far, it was necessary to remove such soil layers from old sites and by compactable to replace granular replacement building materials such as recycled materials, sand or gravel sand in favor of a flat foundation. For deep infiltration layers even pile foundations had to be carried out. Here, too, there is therefore a need for a meaningful use of such, for example in the Ruhr area widespread soil layers.

The discharges may be granular soil layers with too low a compactness such as e.g. Home burners or boiler ashes act. These soils are not sufficiently stable despite compaction because the grain breaks under load. Foundations of foundry sands, slag sand, blasting sand, etc. comparable to a uniform desert sand, due to their uniformity, do not have sufficient bearing capacity for foundations. Mixed-grained deposits, in which, however, also Feinstkom, silt occurs and are additionally wetted, can not be densified because of their high water content, as they soften during mechanical processing and even in the compressed state, assuming an optimum for the compaction water content is not sufficient capacity for Give birth to buildings.

By the BE-822838 A1 is a method for producing a support layer is known in which sewage sludge is mixed with extinguishing calf and fly ash.

The FR-1433508 A describes a method for producing a base course in which sand is mixed with slag, fly ash and lime. However, this document does not describe the mixing of the Sand with chippings of small grain size, nor the mixing of 20 to 30 vol.% Watery mud or silt.

The present invention is therefore based on the problem to provide a method in which open-pore low shear strength starting materials can be used in support layers for road construction or for other purposes, even under extreme climatic conditions by physical Komstützungen.

3. Summary, of the invention

The present invention solves this problem by a method for producing a supporting layer, in particular for road construction or as a stand space for buildings, with the steps specified in claim 1.

The method according to the invention provides the following basic prerequisites for solving the abovementioned problem: Replacing the open-pore sand, the MBT residues or the aforementioned fillings with substitute building materials which achieve good compaction capability and high shear strengths by filling the microporous structure of the starting material. Thus, the material mixture is brought directly into a state by already having a minimum level of load capacity, so that they can be applied and compacted even in damp weather as a support layer.

With the water-containing silt of the material mixture, if necessary, mixed with a water carrier so that the hydraulic setting in the preferably already solidified support layer can be done over several days without costly moisture retention. Optionally, the material mixture can additionally be treated with seawater without causing damage to the load bearing capacity due to resulting salt structures.

The starting material is first mixed with chippings of a grain size of on average ≤ 6 mm, the chippings being admixed with 20-30% by volume of the starting material. Chippings of this size are capable of filling the open pores of the stock, thereby providing grain support and hence higher shear strength. The materials named as substitute building materials have a free lime content of ≥ 20%. The grain size of the substitute building materials is preferably ≦ 2 mm, more preferably ≦ 1 mm. Substitute building materials with these properties contribute to grain support and, on the other hand, enable hydraulic bonding in the base course to further solidify it.

The water-containing silt optionally to be used preferably has a cohesive soil with grain sizes of ≦ 0.06 mm. For this purpose, the silt may be, for example, sewage sludge or sludge. The water content of the slurry is preferably 75% by weight - 85% by weight, preferably 70% by weight - 80% by weight.

Further advantageous developments of the claimed methods are defined in further dependent claims.

Finally, according to a further aspect, the present invention relates to a support layer, in particular for road construction or as a support layer for buildings, which has been produced by one of the methods explained above.

4. Detailed description of preferred embodiments

First, a presently preferred embodiment for the preparation of a support layer of desert sand as a starting material is explained in more detail:
For this purpose, the desert sand is mixed with broken and therefore preferably sharp-edged recycling materials such as building rubble or rock debris so that the pore volume of the sand is filled with sharp-edged chippings edge substantially. In order to achieve the highest possible material yield from demolition concrete, grit size 0 - 6 mm must be selected. A larger grain is not necessary, because it is important to substantially fill the open pores of the sand with chippings to obtain high shear strengths and thus to obtain a grain support.

The open pore volume of the sand is preferably 30 vol.% To max. 35 vol.%. It has been found that the highest shear values are achieved if there is no overmixing when adding the split sand, i. H. no maximum filling of the pores takes place. The amounts added should therefore be 15% by volume, preferably 20% by volume, max. Vol. 30%. This takes into account that even more materials must be mixed into the sand pores.

While with the starting material, i. in the present case, even-grained desert sand, only shear values of ρ = 30 ° are determined, is achieved by a grain support with chippings a shear value of 38 ° to 42 °, depending on the rock strength of recycled materials. These shear values correspond to the shear strength of mineral mixtures, as used in Europe for road construction as minimum values.

With the explained interference of the grain size with a diameter between 0 and 6 mm and a volume fraction of 20-30% by volume alone, load carrying capacities, such as those required for road construction materials for heavy goods traffic (E _v2 ≥ 150 MN / m ² ) achieve. With such However, mixtures are already achieved carrying capacity values of E _v2 ~ 80 MN / m ² .

For this reason, it is advantageous for many purposes to further increase the starting material of the support layer by filling also the finest grain structures to increase the load capacity values and by an additional hydraulic bond. Due to the high granularity of the named substitute building materials, a further addition of granules to the fine grain, i. a grain size ø ≤ 0.06 mm, which already leads to an increase in strength after compaction with homogeneous mixing. For this purpose dry coal fly ash, fluidized bed ash, ladle slag or lignite ashes and also paper ashes are suitable. These substitute building materials are characterized in particular by the fact that they have a free lime content of ≥ 25%. The grain size of these replacement building materials is 0.01 to 1.0 mm, sometimes up to 2.0 mm. It is important that the substitute building materials are available in large quantities in substantially completely dry form similar to cement for such tasks. Moistened deleted replacement building materials of this type are less suitable for this purpose.

The addition of said substitute building materials in the soil-moist above-mentioned support layer mixture in the order of 15 to 25 vol.% And a subsequent compaction revealed after 4 to 5 days a stabilized and hydraulically bonded support layer. The support layer produced in this way should be installed in layers in thicknesses of preferably 30-40 cm and compacted with heavy vibratory shell smoothing rollers weighing 10 - 15 t , preferably to 100% of the Proctor density.

The hydraulic binding, finally, takes place over several days. If the mixture is kept moist for hydraulic setting, optimal values are achieved after one week. The longer period of time is explained by the CO ₂ absorption from the air required for the hydraulic setting, when the lime, which has been cleared by the water, changes to hardened lime. This requires CO ₂ first penetrate into the layer so that the required chemical reaction can take place. Due to the comparatively high strength, even before the hydraulic binding, the base course can already be exposed to medium loads during this time, whereby a rational implementation of further processing measures with machine assistance is to a certain extent possible.

In order to enable the described slow hydraulic setting in desert regions, a slurry is preferably added to the base course mixture which corresponds approximately to the grain size of a mixed soil of clay, silt and sand of a loess clay with grain sizes of 0.001 to 0.06 mm and up to 2 mm natural Schluffen has a very high water content. This is ideal for sewage sludges and / or aquatic sludges, such as those found in harbor pits. It is known that sewage sludge is used as an additive for surface waterproofing. This is preferably sewage sludge with a dry matter of TS = 30% by weight and 70% by weight of water. The preferred use of sewage sludge having a water content of W = 70% by weight was chosen because of the workability in earthworks. Wet sewage sludge can, however, be pre-dried in the sun and then mixed into the base layer, so that even very soft sludges with a dry matter of TS = 20% by weight and water of W = 80% by weight can be utilized.

The incorporation of such sludges in the desert sand split mixture with added amounts of 20 to 25 vol.% And substitute building materials 15-20 vol.%, Gives a good earth-moist, compactable soil mixture that remains moist despite intense sunlight, is well-supported in a compacted state and additionally sets hydraulically , After a week, such mixtures yield load-bearing capacity values of E _v2 ≥ 150 MN / m ² and compressive strengths of 7 N / mm ² , as required by the state guidelines for the standardization of the superstructure of traffic areas of the Federal Republic of Germany for heavy goods traffic under asphalt pavement calls. Even buildings can be founded on such prepared with desert sand base courses.

As a result, it has been found that sewage sludge may be added as a hydrous soil to the hydraulic sealant mixture on the order of the open pore mixture of the base layer, that is about 20-30%, preferably 25%, without the base layer losing its load bearing capacity. In addition, it was found that in this state, the hydraulic setting retains its function under extreme climatic conditions of the hot sun and does not burn. Only on the surface of the Erdplanum the support layer is preferably to keep moist with enough water, which is why conveniently this base layers with a wear or cover layer, such as a road surface, overbuilt. Large volumes of water to moisturize the base course in the interior are not needed because the properties of the sludge are used as "dry water".

In order to test whether the method described above is also suitable for the production of base courses from old industrial sites, test fields from soil mixes, foundry sands, other ashes with building waste residues were leached to 20% - 30% and test fields from pure loess clay with increased water contents w = 20 - 24% created. The soil materials were not compressible due to their high water content. In the compacted state after re-drying in the sun, these soil materials achieved only low load-bearing capacity values of 10 to 20 MN / m ² .

However, by incorporating 20% fluidised bed ash or ladle slag into the wet, non-compactible soil, a good compaction capability was achieved so that the soils could be optimally compacted. After the hydraulic setting within one week, load-carrying values of E _v2 ≥ 120 to 180 MM / m ^{2 were} determined on the same materials. The amazing thing here is that uniform grained loam very high load capacity of E _v2 ≥ 120 MN / m ² achieved, which has not been achieved in conventional lime stabilization with added amounts of quicklime of 4 - 7%. The values are at E _v2 ≥ 45, max. 60 MN / m ² .

Even after a year, the layers showed no negative changes in carrying capacity. Rather, an increase in the values was found to be about 10%, so that such improvements are considered to be durable. This also applies if e.g. Sewage sludge was mixed in with 20%. This is probably due to the sealing effect of such composite support layer materials and the effective pH in the basic range.

Another example confirms the stabilizing effect of silt in the soil mixture:

In the forties to the fifties deposited house fire pockets in several meters of thickness initially yielded load capacities of E _v2 = 1 - 10 MN / m ² , compacting values of just E _v2 = 5 - 15 MN / m ² . The stabilized ash with addition of fluidized bed ash of 25% yielded values of E _v2 ≤ 30 MN / m ² .

If, on the other hand, the house-fire bag with stabilized silt is stabilized at 20% and then treated with fluidized-bed ash or ladle slag at 25%, carrying capacity values were measured after 1 week of E _v2 = 120-150 MN / m ² . As already described above, these surprisingly high load capacity values are due to addition material and the physical grain support caused thereby, in particular in the case of equal-grained soils. The hydraulic setting is only relevant secondarily, but with the addition of 20% of the above substitute building materials less hydraulic binding lime is available than with the addition of 7% quicklime. This once again indicates that the increase in load capacity is essentially due to the grain support, ie the physical properties.

With the method described, it is therefore possible to improve old soil deposits by mixing the above-mentioned substitute building materials with further addition of silt, if not present, in their carrying capacity so that it can be founded new structures with soil pressures. In this context, it should be noted that granular deposits such as rubble, slags, etc., which are sufficiently grain stable and compactable, do not require such improvement. The relationship between the load capacity and the foundation width is as follows: Width [m] 0.5 1.0 1.5 Load [kN / m2] 250 350 400

These soil pressures correspond to load capacities of compacted gritty sand and gravel sand layers or building rubble materials with a grain size of on average between 0 and 45 mm, on which is usually established with equal soil pressures.

Due to the very high achievable load-bearing capacity with the addition of the above substitute building materials, even in cohesive wet soils, it is now possible to have high-quality base layers of infill soils of sufficient thickness (2 to 4 m, depending on the total thickness of the infills up to ≥ 10 m) ) and to set up commercial or office buildings with the above ground pressures. This treatment represents a very economical solution for the revegetation of the above mentioned old sites.

• Dem Material werden gebrochene Müllverbrennungsschlacke oder gleichwertige scharfkantige Kornfeste, Abfälle zur Scherfestigkeitserhöhung und der Verdichtungsfähigkeit zuzugeben.
• Dem Material wird ein Wasserträger in Form von Schlamm, Klär- oder Gewässerschlamm zum Porenschluss für eine langanhaltende Feuchtigkeit zur hydraulischen Abbindung und dem Porenschluss zugemischt.
• Es sind bis zum Feinkorn ≤ 0,06 mm kornstützende und hydraulisch abbindende Ersatzbaustoffe aus den oben genannten Materialien in ausreichender Menge zuzugeben.
• Die Materialien werden homogen in Zwangsmischanlagen aufbereitet und anschließend nach dem Einbau mit schweren Walzen ca. 10t verdichtet.

The described method can also be used to produce base layers of so-called MBA residues, so that these poorly disposable materials thus be recycled. For this purpose, these wastes are preferably treated as follows:

• Broken waste incineration slag or equivalent sharp-edged grain harvests, waste for shear strength enhancement and compaction capability are added to the material.
• The material is a water carrier in the form of sludge, sewage sludge or sludge for pore closure for a long-lasting moisture for hydraulic setting and pore closure mixed.
• Grain-supporting and hydraulically setting substitute building materials from the above-mentioned materials must be added in sufficient quantity up to the fine grain ≤ 0.06 mm.
• The materials are homogenously processed in compulsory mixing plants and then compacted with heavy rollers after installation approx. 10t.

In particular, it has been shown that with the load-bearing improvement measures by the addition of broken waste incineration slags of grain size 0 - 32 mm and 0 - 45 mm in a proportion of 25 vol.% - 30 vol.%, The shear strength of the mixture of φ = 20 ° - 24 ° increased to φ = 30 ° - 33 °. By adding suitable sludge, such as. As sewage or sludge, in an amount of 15 vol.% - 25 vol.% To the above mixture, the pore structure of this mixture is further filled and by adding said substitute building materials in an amount of 20 vol.% - 33 vol.% The Buildability, compaction capability, the necessary load-bearing capacity and erosion-like deflation resistance of mixtures with MBA materials achieved. The carrying capacity values are 20 - 30 MN / m ² after 14 days of service life; on the other hand, only values of 5-10 MN / m ^{2 were} achieved with the garbage slag alone, which corresponds to a soft clay. When it rained, no more abrasion was produced on the surface conditioned with the abovementioned substitute building materials and sludge.

Due to the pore closure, the load-bearing capacity and the good compactability, base courses with a water-repellent character and in particular with sufficient erosion resistance are formed, so that on embankments, the starting material is not washed out by precipitation.

Furthermore, because of the sufficient shear strength, the base courses have sufficient stability on embankments and sufficient strength, be it for further use or for driving over the materials for further proper layering with conventional earth-moving equipment, even in wet weather conditions. Due to the water-repellent properties of the MBT residues, the leachate recharge in the base area of the landfill is significantly reduced. Only by such a procedure, the above-mentioned governmental requirements for landfill deposition can be met.

Claims (8)

1. A method for fabricating a base layer, in particular for road construction or as a footprint for buildings with the steps in the following sequential arrangement:

   a. providing a base material having an open pore void volume between 25 % and 40 %, the base material comprising:

   i) sand, and / or

   ii) residual materials of mechanical biological waste treatment plants for municipal solid waste and waste which can be disposed like municipal solid waste, and / or

   iii) fill of an abandoned industrial site;

   b. mixing the base material with crushed stone sand having an averaged corn size ≤ 6 mm;

   c. mixing with replacement construction materials which have a volume portion in the mixture between 15 % and 25 %, the replacement construction materials comprising the following materials:

   i) dry coal flue ash, and / or

   ii) fluidized bed ash, and / or

   iii) brown coal ash from a power plant, or

   iv) collapsed ladle slags, and / or

   v) paper ashes,
   wherein these replacement construction materials have a free lime portion ≥ 20 %; and

   d. admixing a water containing mud or a silt if the water content of the base material is too low to enable a hydraulic binding in the mixture, wherein after the method step d. the base layer comprises 20 vol.-% to 30 vol.-% of mud or of silt and 15 vol.-% to 25 vol.-% of one or multiple of the mentioned replacement construction materials; and

   e. subsequently compacting the mixture from base material, crushed stone sand, replacement construction materials and mud or silt.
2. The method of claim 1, wherein the crushed stone sand is admixed with 20 vol.-% to 30 vol.-%.
3. The method of claim 1 or 2, wherein the grain size of the replacement construction materials is ≤ 2 mm, preferably ≤ 1 mm.
4. The method according to one of the preceding claims, wherein the base layer is assembled in layers, and wherein a layer preferably has a thickness of 30 cm - 40 cm.
5. The method according to claim 4, wherein the base layer is compacted after the assembly up to a Procter density of 100 % with a vibration smooth drum roller having a weight between 10 t and 15 t.
6. The method according to one of the preceding claims, wherein the water containing mud or silt comprises clearing sludge and /or mud from waters.
7. The method according to any of the preceding claims, wherein the water containing mud has a water content of 40 weight-% - 85 weight-%, preferably 70 weight-% - 80 weight-%.
8. A base layer, in particular for road construction or for a building fabricated with a method according to one of the claims 1-7.