GRAPH-ANALYTICAL METHOD FOR DETERMINING THE MINIMUM CAPILLARY MOISTURE CAPACITY OF DISPERSE MATERIALS

V. M. Vitogin, I. N. Lantsman, O. A. Fuks, A. V. Vitogin

A widely used indicator of the water-physical properties of disperse materials, the so-called maximum molecular moisture capacity (MMC), is currently generally determined by the method of “moisture-capacious media” [1]. However, this method has many physically unjustified conventions, leading to significant errors. Thus, for example, the thickness of the annular template may be 1 or 2 mm, the pressing pressure 50–70 kg/cm², and the holding time of the sample under pressure 2 or 10 minutes. The choice of the values of the listed parameters is to a considerable extent subjective.

In the present communication a new method is proposed for determining MMC, based on a graphical interpretation of experimental values of the rate of capillary impregnation of columns of disperse material with different degrees of compaction. As is known, the coefficient of the rate of capillary impregnation \((K_{\text{c.k.p.}})\) of a layer of disperse material can be expressed by the dependence [2]

\[ K_{\text{c.k.p.}}=\frac{V^{2}}{\tau} \tag{1} \]

where \(V\) is the volume of water absorbed by a column of material with a cross section of \(1\ \text{cm}^{2}\), \(\text{cm}^{3}/\text{cm}^{2}\);

\(\tau\) is the impregnation time, sec.

For columns of disperse materials with the same cross section, dependence [1] may be expressed through the column height \((h)\)

\[ K_{\text{c.k.p.}}=\frac{h^{2}}{\tau} \tag{2} \]

For the study, disperse materials of various

nature in an air-dry state. The dependence \(h^2 - \tau\), using as an example clayey soil of different degrees of compaction, is shown in Fig. 1. The tangent of the angle of inclination of the capillary-impregnation straight lines is the coefficient of the rate of capillary impregnation. As can be seen from Fig. 1, the coefficient of the rate of capillary impregnation of a layer of disperse material depends both on the nature and granulometric composition of the material and on the degree of its compaction.

Fig. 1. Kinetics of capillary impregnation of a clayey-soil layer at different compactions:
1 — \(1.294\ \text{g/cm}^3\);
2 — \(1.278\ \text{g/cm}^3\); 3 — \(1.174\ \text{g/cm}^3\); 4 — \(1.020\ \text{g/cm}^3\).

Figure 2 shows the dependences of the moisture capacity of a layer of a number of disperse materials and of the coefficient of the rate of capillary impregnation, which are straight lines cutting off on the ordinate axis segments corresponding in magnitude to the values of the maximum molecular moisture capacity.

Table 1 gives the values of MMC determined by the method of moisture-capacious media and obtained by the proposed procedure (Fig. 2). As can be seen, the MMC values determined by the capillary-impregnation method fall within the interval of MMC values obtained by the method of moisture-capacious media for templates of different thicknesses.

The essence of the proposed procedure, as follows from the preceding, is reduced to constructing a rectilinear dependence of the coefficient of the rate...

growth of capillary impregnation and the moisture capacity of the layer, on the basis of studying the impregnation kinetics of columns of the disperse material under investigation with different degrees of compaction. For determination, four to five degrees of compaction are sufficient. Capillary impregnation is recommended to be carried out in calibrated glass tubes 15–25 mm in diameter, with a layer height of 30–50 mm.

Fig. 2. Dependences of “moisture capacity, % — coefficient of capillary-impregnation rate \(K_{\mathrm{skp}}\)” for various materials.
1 — magnetite concentrate; 2 — dolomite;
3 — chalk; 4 — loam.

Different degrees of compaction of the disperse material in the columns are achieved on a vibration table, or by simple shaking and tamping by hand. Distilled water is used for impregnation. The moisture content of the layer is determined either analytically or by direct measurement of the volume of absorbed moisture. In the proposed method the element of subjectivity is eliminated, and determination of the MMC is significantly simplified.

Table I

References

1. A. M. Vasiliev. Fundamentals of Modern Methods and Techniques for Laboratory Determinations of the Physical Properties of Soils. Gosstroiizdat, 1953.

2. L. E. Chernenko, P. A. Rebinder. Colloid Journal, XII, No. 5, 1950, 386.

3. N. N. Shchurupa. Practicum in Colloid Chemistry. “Vysshaya shkola,” Moscow, 1963.

4. B. V. Deryagin, N. N. Zakhavaeva, M. V. Talaev. Instrument for Determining the Filtration Coefficient and Capillary Impregnation (manual). Moscow, 1953.