DE29912010U1 - Mineral sealing building material for a landfill as well as for protecting contaminated sites - Google Patents

Description

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Description

The invention relates to a mineral sealing material, as a component of a sealing system for a landfill construction, as well as for securing contaminated sites, wherein replacement building materials are used as components in the mineral sealing system, preferably using digested water and/or sewage sludge that has been mechanically dewatered and suitable water-absorbent aggregates.

In the publication DE 941 25 55 U1, a special protective layer made of plastic components is described for a known multi-layer structure for landfill construction such as fine waste, drainage layer, protective layer, plastic sealing membrane and mineral sealing to protect the plastic sealing membrane. The plastic components contain threads that have a large surface area. This means that the surfaces become clogged more quickly.

In the publication WO 89 01547 A1, a method is presented according to the invention for sealing soil formations, in particular for the production of landfills, using dried sewage and water sludge with a dry matter content of < 70%, other dried aggregates, powdered water glass and soft gelling agents. The disadvantage of this method is that the water glass-modified sealing systems made from waste and recycled materials require the use of expensive gelling agents to reduce water permeability.

According to the publication DE - OS 44 33 079 A1, the sewage sludge is thermally pre-dried to a dry matter content of > 70%, then ground and mixed with powdered water glass and cohesive soils. The disadvantage of this invention is that the cost of thermally drying the sewage sludge is very high and the additional use of water glass is necessary.
It is known from the state of the art that laboratory and construction studies

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Investigations were carried out using water glass to improve sewage sludge mixtures, which led to the production of mineral seals. The essential prerequisite for water glass to improve the quality of the mixture is a mixture with a graded grain size and sufficient water content that can still be compacted and thus sealed. The publication DE - OS 44 29 346 A1 contains a process for treating sewage sludge using highly active fly ash, clay suspensions and using the end product. It is not clear from the publication that a mixture consisting only of fillers and sealing plasticizing substances is stable in terms of soil mechanics.

The publication DE 195 40 387 C2 contains a process for the production of mineral seals in which the high-quality natural clayey, silty, sandy and gravelly earth building materials are partially replaced by cheap substitute building materials such as bentonite-containing foundry sand and foundry slag. According to the Technical Instructions (TA) for municipal waste, the following is prescribed:

&bull; to produce a combination seal made of a plastic sealing membrane (KDB) and mineral barriers according to the multi-barrier concept for hazardous and municipal waste for above-ground landfills,

&bull; the fine grain content (< 0.002 mm) must be at least 20% according to DIN 18 123,

&bull; the water permeability coefficients [k - values] for base sealings are k < 5 &khgr;10" ¹⁰ m/s and for surface sealings k < 5 &khgr;10' ⁹

The object of the invention is to produce a mineral sealing material as a component of a sealing system for landfill construction and covering of contaminated sites, in which the natural clayey, silty, sandy and gravelly earth building materials are partially replaced by cheap substitute building materials without impairing the properties of the sealing compounds. The required values of k < 5 x 10~ ¹⁰ m/s must be ensured.
According to the invention, the object is achieved according to the features specified in claim 1.

Features. Preferred developments of the invention emerge from the respective subclaims.

The advantages of the invention are that in mineral sealing the natural clayey, silty, sandy and gravelly earth building materials are partially replaced by cheap substitute building materials, such as suitable rotted water and/or sewage sludge, without impairing the properties of the sealing compounds, whereby the properties of the mineral sealing materials with regard to their susceptibility to cracking are significantly improved compared to the standard systems and the k-values are undercut.

The mineral sealing compounds produced using suitable digested water and/or sewage sludge can be used to secure landfills cost-effectively and to make the encapsulation process for contaminated sites more efficient. The waste materials used are recycled in accordance with environmentally safe parameters, and the mineral seals produced in this way have long-term stability when contaminated water flows through them.

The starting point for the investigation was suitable water and/or sewage sludge that has been digested and has a dry residue content of at least 30% [DR]. Mechanical pre-dewatering of the water and/or sewage sludge, e.g. using chamber filter presses, belt dryers or centrifuges, is absolutely necessary. The thickened sewage sludge can be dewatered to 18-30% DR using polymer conditioning using belt filter presses or centrifuges. An increased degree of dewatering can be achieved using chamber filter presses by using metal salt or polymer conditioning. Here, an average dewaterability of 28-38% DR can be achieved. If lime is also used as an additive, dewatering of 35-45% DR is possible. The adhesive and capillary water of the sewage sludge can be largely removed by mechanical dewatering. The absorption and internal water can only be removed by drying (up to around 95% DR). Processing at < 30% TR is

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Not possible due to the mushy consistency. The installation water content is exceeded, thus optimal compaction is impossible.

According to the invention, dry bentonite-containing foundry sand and/or dust with a bentonite content of 3-15% by weight can advantageously be mixed into the sewage treatment plant or other processing plants after mechanical dewatering of the water or sewage sludge for post-treatment. The high water absorption capacity (approx. 60-100%) of these waste materials reduces the water content of the sewage sludge by approx. 10-20% with the preferred addition of 10% by weight of dry bentonite-containing foundry sand and/or dust. The addition of lime can then be dispensed with.

It is known from the state of the art (DE 195 40 387 C2) that used foundry sand and dust containing bentonite have good sealing properties in mineral sealing systems, but are also susceptible to erosion. This deficiency is eliminated by mixing with water and/or sewage sludge, in combination with granular material as a supporting structure.

The use of mineral landfill seals essentially has two main tasks, which are to RETAIN POLLUTANTS AND TO SEALED (convective water storage). A high sealing effect is achieved when there is a maximum or optimal packing density with the smallest pore volume of the sealing material. According to the invention, the above-mentioned requirements are achieved from a soil mechanics point of view when three areas are met:

&bull; Similar to the Fuller curve, a continuous grain gradation of composite granular materials with a grain size of 0-32mm is used as a supporting structure. These are grain-resistant, compactable materials that are also used in earthworks and foundation engineering.

&bull; Another component of mineral seals are fillers.

According to DE 195 40 387 C2, used foundry sand and dust containing bentonite can be used. The grain size distribution of these waste materials is similar to that of loess soil in the medium to coarse silt range. These materials improve the mixtures in the finest grain range.

&bull; Sealing and plasticizing substances such as bentonite, zeolites, water glass, etc. are replaced by the water and/or sewage sludge used according to the invention, which can be classified as fine sandy silt in terms of grain size distribution, in combination with the first two components. The organic components of the water and/or sewage sludge are stored in a finely distributed fibrous form and are responsible for improving the stress cracking behavior.

The fibrous structure of the water and/or sewage sludge, which consists of a sludge-sand mixture with a relatively high water retention capacity, has a significant improvement in terms of susceptibility to cracking compared to conventional standard sealing systems with clay and clay-containing loam.

It is generally known that in mineral soils, especially clays, cracks occur even with small deformations (tensile stress) and even with small changes in water content of Δ w » 1%, thus impairing the sealing effect. To eliminate this deficiency, a mixture of natural, clayey, silty, sandy and gravelly earthwork materials, bentonite-containing foundry sands and dusts and mechanically pre-dewatered water and/or sewage sludge is produced.

The mixtures shown in the following embodiment are applicable for base, preferably for intermediate, and surface covers for landfill classes I: (mono-landfills - excavated earth), landfill class �P: (domestic waste - municipal waste) and landfill class IH: (hazardous waste).
Example:

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To produce a mineral sealing material, as part of a sealing system for a landfill construction, and to secure contaminated sites, the following components are mixed homogeneously:

&bull; 25- 50 wt.% preferably 40 wt.% silty, clayey excavated soil; silty clays; building rubble recycling material; gravel-sand mixtures as supporting structure, grain size 0 -32 mm,

&bull; 25-50 wt.%, preferably 40 wt.%, of dry bentonite-containing foundry sand or dust as a filler with a partial sealing effect due to the bentonite (bentonite content approx. 3-15% wt.%),

&bull; 5- 40 wt.%, preferably 20 wt.%, of digested sewage sludge, post-treated with lime and/or used foundry sand or dust, with TR 35- 60% from a municipal sewage treatment plant, which complies with the sewage sludge ordinance, as a sealing and plasticizing substance.

An installation water content of 8-30%, preferably 14.5%, is set.
The following values were determined in the laboratory according to DIN 18 130 at gradient i = 30:

Table 1

Target compaction level
D _Pr [ % ] degree of compaction achieved
D _Pr [ % ] k-value
[m/s] 100%atW _opt 100.7 ^1.8x10-11 97 %, wet side 96.3 5.8 x 10- ¹¹ 97%, dry side 96.0 4.9 x 10 " ¹¹

The k values determined are 1.8 x 10 " ¹¹ to 5.8 x 10 " ¹¹ m/s, which are consistently below the value of k = 5 x 10 " ^1G m/s permitted for mineral landfill base seals according to TA Siedlungsabfall. The mixture produced in this way was tested for shrinkage behavior according to DIN 18 122. The mixture was found to have low shrinkage and swelling behavior and very favorable stress cracking behavior compared to conventional mineral clay seals.

The mineral sealing material, as a component of a sealing system for a landfill construction and for securing contaminated sites, is characterized by the fact that the components:

&bull; silty, clayey excavated soil; silty clays; construction waste recycling material; gravel sand mixtures as supporting structure, with 25-50 wt.% preferably 40 wt.%,

&bull; dry foundry sand or dust containing bentonite as a filler with a partial sealing effect due to the bentonite (bentonite content approx. 3-15% by weight), with 25-50% by weight, preferably 40% by weight,

&bull; digested water and/or sewage sludge treated with lime and/or used foundry sand or dust with TR 35 - 60%, which complies with the Sewage Sludge Ordinance, as a sealing and plasticizing substance, with 5- 40 wt.%, preferably 20 wt.%,

in a stationary mixing plant using a compulsory mixer with the addition of the required amount of water, until the optimum installation water content of 8-30%, preferably 14.5%, is achieved. The different materials are dosed in the mixing plant using a box feeder and weighing belts. The mixed material is then applied to the construction site in layers and compacted to the target density with a smooth-surface roller. Further homogeneous mixing can take place directly on the construction site. Here, dosing is carried out by applying the materials to be mixed precisely, layer by layer (using an all-round laser + 1cm) and by precisely setting the milling depth with a high-speed construction milling machine. The prepared construction site is then milled through with a heavy construction milling machine, if necessary with the addition of water, until the optimum installation water content of 8-30%, preferably 14.5%, is achieved, with the milling depth being set to approx. 26cm. Before another milling step, the pre-mixed material is pre-compacted with a smooth-surface roller to achieve extensive homogenization. The mixed material is then compacted layer by layer to the target density with a smooth-surface roller.

Claims (6)

1. A mineral sealing material, as a component of a sealing system in landfill construction for a base seal, in particular for an intermediate or surface cover of a landfill or for securing contaminated sites, characterized in that the mineral sealing material contains 5-40 wt.% of digested water and/or sewage sludge with TR 35-60%, which has been mechanically dewatered and further water-absorbent additives, which are homogeneously mixed with the addition of water if necessary, until the optimum installation water content of 8-30%, preferably 14.5%, is achieved and mechanically compacted in layers in the construction field. 2. A mineral sealing building material according to claim 1, characterized in that the water-absorbent aggregates are mixed in from 25-50% by weight of silty, clayey excavated earth, silty clays, recycled building rubble material, gravel-sand mixtures with a grain size of 0-32 mm and 25-50% by weight of bentonite-bound old foundry sands and dusts with a bentonite content of 3-15% by weight. 3. A mineral sealing material according to claim 1 and 2, characterized in that the preparation of the mixture takes place in a stationary mixing plant by means of a compulsory mixer, optionally with the addition of water, up to the optimum installation water content of 8-30%, preferably 14.5%. 4. A mineral sealing material according to claims 1-3, characterized in that the mixture is applied in layers and compacted to the desired density with a smooth-surface roller. 5. A mineral sealing building material according to claim 1 and 2, characterized in that in the construction field by exact, layer-by-layer application of the individual materials and then by milling using soil milling machines, if necessary with the addition of water, until the optimum installation water content of 8-30%, preferably 14.5%, is achieved and then compacted to the desired density with a smooth-surface roller. 6. A mineral sealing material according to claim 1, characterized in that after the mechanical dewatering of the water and/or sewage sludge, dry bentonite-containing foundry sand and/or dust with 5-15 wt.% and a bentonite content of 3-15 wt.% is mixed in.