Dimensión Plano de la narración y sus componentes.

The bending strengthtests have been carried out for each disc, of every series after the conditioning, up to a weight absolute term of 40% relative humidity and 21°C. That correlates, depending on the treatment type on water content of 1.3 and 1.9 weight %. Some samples could not be tested successfully, because they were already cracked before the measurement, or they burst during the mounting into the measuring fixture. In image, 63 the load curve and strain curve of the successfully tested discs are shown. In the lower area of the curve increase, the material is in the miner elasticity area. The expansion is due to the Hookesches elasticity law, directly

proportional to the inserted strength. In the lower third of this linear range, the increase, for the calculation of the e-module is read off. If the pressure increased, the soil sample starts to yield back irreversibly with plastic flowing. In the vertex of the curve, the sample breaks. Here the power Fmaxis read off for the calculation of the

bending strength σBz . Although the height of the vertex cannot be equated with the

bending strength of the sample, because the different thicknesses of the samples are not considered, it is obvious from this measurement protocol, that the consolidated samples have higher and steeper load curved and strain curves than the non treated series. Therefore, the consolidation leads to a significant rise of the breaking load and the elasticity of the sample.

Neither between the consolidated series nor between the untreated series a significant difference could be seen in the bending strength properties of the single discs.

Therefore, the six series have been summarized in the groups non consolidated (A/E/F) and consolidated (B/C/D) (see image 64).

Image 63 deformation curves from the measurements of the biaxial bending strength at the treated and untreated samples. The affiliation of series is marked in the vertex of the curve. At this point the tensile strength

F

is also read off for the

calculation of the

bending strength. The E module is calculated from the lower linear increase of the curve

Biegezugfestigkeit an ungefestigten (A/E/F) und gefestigten (B/C/D) Scheiben

0,5 1,0 1,5 2,0 2,5 M itt e lw ert (N /m m ²)

Biegezugfestigkeit an ungefestigten (A/E/F) und gefestigten (B/C/D) Scheiben

0,5 1 1,5 2 2,5 N/ mm²

Image 64 above: Statistical evaluation of the biaxial bending strength. (Left: average value with standard deviations; Right: Gauss’s allocation curve in the Box&Whisker diagram) Below: statistical deviations of the statistical E module (Left: average value with standard deviations; Right: Gauss’s allocation curve in the Box&Whisker diagram)

The initial value of the middle biaxial bending strength of the untreated samples is with 0.43 N/mm² very low (image 64) However it is very close to the values, that Micoulitsch (1996) has determined with the uniaxial bending strength test on the stamped soil prisms from Lintong (see image 70). There are not a lot of values for the bending strength of adobe to compare out of the literature; because the dry bending strength has no important specific value for building clays, for these the comprehensive strength is important. The few comparable measurements of silty and clayey adobe mortars have also bending strengths between 0.4 and 0.8 N/mm2

(Böttger, 1999); (Minke, 1995). The dry bending strength of clays depends strongly on the amount of clay minerals. HOFMANN (1967) proved, for the dry bending strength

of clays, a direct correlation between the strength and the cation exchange capacity of the clay minerals. The consolidation with SE leads to an increase of the average dry bending strength up to the factor of 3.8 up to 1.64 N/mm². In consideration of keeping the mechanical compatibility between the unconsolidated and consolidated material, SASSE & SNETHLAGE (1996) and SNETHLAGE (2002) recommend for stone

consolidation, with the increase of the pressure, tensile strength and the bending strength from the non consolidated to the consolidated material in relation to consolidated material does not exceed the factor 1.5. Therefore, in principal the rule applies:

(β(treated) – β(untreated)) / β(untreated) < 0.5

Respectively, the increase of the strength the treatment of the soil with F300E is significant over consolidated. However, in the case of the soil it has to be considered, that the differences in the strength due to moisture, are in the untreated

Statischer E-Modul aus Biegezugversuch an ungefestigten (A/E/F) und gefestigten

(B/C/D) Scheiben 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 A/E/F B/C/D M itt el w er t ( kN /mm² ) ± Standardabw eichung

Statischer E-Modul aus Biegezugversuch an ungefestigten (A/E/F) und gefestigten (B/C/D)

Scheiben 0 0,5 1 1,5 2 2,5 3 3,5 A/E/F B/C/D kN /mm²

material, has the same amount. The increase of the strength in the hygroscopic area (0-6 mass % water content) in image 70 shows an increase for the comprehensive strength of a factor of 0.75 up to 1.2. The bending strength is changing in this area by a factor of 2.3 up to 3.3. In contrary to this, on schilfsandstone the bi axial bending strength changes in the sorption humidity only to a factor of 0.4. (Sattler, 1992). The question arises, if it is possible to transfer these requirements from the stone conservation. The static E module of the untreated sample is at the values of

1.2 kN/mm². Reference values for the static E module on dry clay samples are

between 1 and 6 kN/mm² (Böttger, 1999). The static E module from the bending strength measuring increases by the SE consolidation from 1.2 to 2.2 kN/mm² (image 64). That is a increase of the factor 1.8. The mentioned requirements for the natural stone conservation are E(treated)≤ 1,5 E(un treated).. The increase of the elasticity index is

therefore less than the increase of the breaking strength. According to the day mechanism, the change of the elasticity is the more important factor for the mechanical compatibility to the untreated material.

The relation from changes of the breaking strength and the changes of the elasticity is also postulated as important evaluation criteria for the durability of natural stone consolidations. In SASSE & SNETHLAGE (1996), the following evaluation criteria is

postulated:

E(treated) / E(untreated)≤β(treated) / β(untreated).

For the results, above, there is a relation of 1.8 ≤ 3.8. Therefore, the relation between stability and elasticity is improved.

The specific expansion ε (∆x/x) is calculated, due to the Hooks law, from the proportion of the breaking strength and E Module of the disc samples: ε = ßbz / Ebz.

They represent the upper limit of the elastic, reversible expansion. By exceeding the specific expansion, this leads to a long term to irreversible deformation, that can be seen in general as the start and reason for material detachments and decay (Snethlage, 2002). The correlation between breaking stress and breaking expansion, E- module and the specific expansion is shown in image 65.

spez. Dehnung Bruc hdehnung Bruc hspannung

E

E

⋅

=

=

ε

σ

σ

ε

The correlation between the breaking strength and the elasticity of the disc samples is shown in image 66 and image 67. The average specific expansion is for the treated samples increased from, 0.33% to 9.77%. In average, the consolidated samples can buffer elastically more than the double amount of the expansion. That this correlation is also valuable for the breaking expansion this can be seen in the values in image 67. Thereby, it is to regard, that the breaking expansion is in percentage. It exceeds the elastic specific expansion more than one cubing.

Image 66 Relation between the static

elasticity module and the bending strengthin

the consolidated (B, C, D) and unconsolidated (A, E, F) samples. The

average specific bending strengthexpansion ε

– the upper limit of the elastic expansion- increases from 0,33 ‰ +/- 0,1‰ to 0,77 ‰ +/- 0,1‰.

Image 67 Relation between the bending

strength

(ß and/or expansion at the break

of the

samples. The