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Raster scanning microscopic analyses can be used effectively for the qualitative evaluation of the corn structure in the silt and rough clay area. Further, the use of a Kryo table enables one to visualize the reaction of the structure with moisture. The results of the structural changes due to swellings in wetted samples are explained in chapter 3.4. The examinations have been carried out at the material testing institute in Bremen on a Hitachi S4000 Kryo table. They are focussed on fresh fraction surfaces at undisturbed stamped soil samples at three different moisture levels.

• Dried samples: 48h drying at 60°C, cooling in the exsiccator over a drying agent, Kryo-preparation in melting nitrogen, freeze fracture.

• Normal climate: conditioning of small samples (approx. 2cm³) over 48h at 65% relative humidity.

• Plasticity limit: (images of this step in chapter 3.4). Moistening of a sample with 18 mass % water deionised, 24h storage- rapped in PE plastic film (for the even distribution of the moisture in the sample). Kryo-preparation in melting nitrogen, freeze fracture.

The observations from the thin section microscopy to the composition of the soil are confirmed by the SEM-examination. Larger fine sand gains are floating in a compact matrix out of spherical and platy silt components (see image 20). The matrix consists mostly out of angled and at the edges rounded quartz, feldspar and mica that build up a grain-supported structure with a high porosity between the grains (image 21 and image 22). This inter granulated matrix pores consist of spherical pores with good cross-linking. The pores diameter is up to 15µm.

Singularly, there are also accretion (coagulates) out of clay, fine silt in silt grain size (image 22). The pore sizes inside these accretions are in the scope of 0.1-1µm. Clay and fine silt create, in addition, storage pads between the grain contacts of the silts or garland like connection structures (Image 21). At the grain contacts of the silt matrix dominate “edge to face“ and “edge to edge“-contacts.

The texture and the matrix can be called as non-directional and spherical porous.

Due to the relatively small content of clay, the structure is all together very “clean” and open. However, all the silt components are covered with a fine clay layer (image 23). The clay minerals are lying mostly in “face to face” contact to each other and give, due to the surface of the components, a laminated scaly texture. The thickness of the layer of the coatings varies, it is mostly under one Micrometer (see image 23

and image 24). In this surface layer, that continues also between the contact points (mostly thickened), the main part of the clay minerals of the micro porosity seems to be concentrated. (see chapter 4.3.3).

The coatings of the silt grains are typical for Aeolian sedimentary loesses (Smalley I.J., 1973). At fluviatile coatings, it is often washed off. The accretion out of clay and fine silt are also an indication against a fluviatile sedimentation of the raw material (Derbyshire,1982b).

The Matrix structure of the stamped soil of Lintong matches the description of

DERBYSHIRE (1982B) of the microstructure of Aeolian Malan- and Wucheng loesses

out of the east of von Xi’an positioned Meng Xiang.

An open, non-textured matrix structure with existing accretion (coagulates) and missing clay minerals, (how they deposit themselves in the recent water menisci during the drying out of the pore gussets of the dispersion) indicates a low water content of the raw material during the building of the stamped earth wall (Houben,1994). The water content during the compacting at the building of the stamped soil wall has an strong influence of the building structure of the dry clay. The structure of the stamped soil of Lintong indicate for a low water content during the building, was in the range of the wPL or lower (wPr = optimal

Water content out of the proctor curve ~ 14 mass -% for the stamped soil of Lintong), but in any case beneath the coasting limit (about 18 mass-%)

Image 20:

Kryo-SEM image (secondary electronic image) of a stamped soil sample with “norm climate”. Conditioning: Overview image over the structure of the stamped soil. One fine grain content (yellow) floats in a undirected silt matrix (Blue). Singular larger stratum silicates can be seen in a typical chart house structure and larger Oxalate – tubes (green).

Image 21:

Kryo-SEM image (secondary electronic image) of the matrix of a dried stamped soil sample. The structure building silt grains have a diameter of

5 – 25µm. Spherical quartz and platy shaped stratum silicates are square-edged or slightly rounded at the edges. The texture of the components stands out due to its missing orientation and space creating “edge to face“ and “edge to edge“ contacts. The grains are mostly only over clay bridges adnated. These loose structures creates a lot of space for the inter particle

matrix porosity with a pore diameters of up to 15µm (see.: chapter Fehler! Verweisquelle

konnte nicht gefunden werden.). In the detailed enlargements, you can see that the fine silt-

and clay fraction accumulates its own aggregates (coagulate) (above) or attaches to the surfaces of the larger grains (below).

Image 22:

Kryo-SEM image (reflective electronic image) from the matrix of a dried out stamped soil sample. The structure is denser packed as in image 21. Large pores are often filled with coagulates of spherical fine silt and rough clay particles (e.g. quartz) (small frame). The inter crystalline porosity between these particles are in the area of 0.1 to 1µm pore diameter (see. chapter 4.3.3)

Image 23:

Surface of a quartz grain in the secondary electronic image- Detail out of image 22 (darker edge frame). The surfaces of the silt grains are coated with several stratum clay minerals. Inside these

“coatings” lie intercrystalline porosity

with pore diameters of max. 0.01µm.

Image 24:

Kryo-SEM image at normal climate (secondary electronic image). The oxalate tube in the front and the pearl necklet shaped structure in the background of the picture are selected examples of a lot of evidences from former

and recent microbiological growth

in the pore space of the stamped soil. The tube is lying on “felt” out of clay minerals.