TECHNOLOGICAL PROPERTIES OF CLAYS FROM THE LAGERNY SAD DEPOSIT IN THE CITY OF TOMSK

P. G. USOV

1. The deposit of brick-and-tile clays in the Lagerny Sad district is located in the southern part of the city of Tomsk, on the right bank of the Tom River, between brick plants Nos. 10 and 17 and the Tom River.

The upper horizon of the deposit, to a depth of 3.0–4.0 m, has been worked for several years by the above-mentioned brick plants; as a result, the quarries have moved away from the plants to a distance of up to 900 m.

Detailed exploration in 1945 and 1948, and the study of the rocks in the laboratory and under plant conditions, established that the upper horizon of the deposit, to a depth of 4 m, consists of loams, the sand content of which increases with depth. At a depth of 4.0–4.5 m there occurs sandy loam, unsuitable for brick production. Beneath the sandy loam, to a depth of up to 16 m, clays occur. The layer of sandy loam extends over the area of the entire explored and worked-out tract, with a variable bed thickness from 0.3 to 3.5 m. For the production of building brick, the loams of the upper horizon are a low-quality raw material. The brick produced by the plants from these loams for the most part has low mechanical indices. The quality of the brick produced by plant No. 10 over the last 10 years is presented in Table 1.

Table 1

Note. The table gives the results of testing bricks produced chiefly in the summer months, June–August.

Table 2

Characteristics of the rocks of the deposit by the principal excavations of the explored area

Note. The fraction indicates the boundaries of occurrence of the bed. For example, \(0.40/1.90\) should be read as from 0.40 to 1.90 m.

Table 3

Clays of the lower horizons, as studies have shown, possess higher technological properties and, when mixed with sandy loam and loams, form a body suitable for manufacturing high grades of building brick and roofing tile. Therefore it is absolutely necessary to develop the deposit to the full explored thickness, to a depth of up to 16 m, including the entire worked-out area. Such use of the deposit increases the reserves of raw material by more than 8 times and, most importantly, improves its technological qualities; moreover, as the quarries are brought closer to the plants, the costs of transporting it are also reduced.

During exploration of the site to a depth of up to 16 m, eight main varieties of rock were distinguished; their thicknesses are variable, and in some workings the order of their occurrence also changes.

Brownish-gray and yellowish-gray loams are confined to the upper horizon of occurrence. They extend over the entire area of the explored site, with a total bed thickness from 3.0 to 4.0 m. The underlying layer beneath the loams is quartz-clayey sand, which likewise extends over the entire site. The loams down to the underlying sand layer, as indicated above, are being worked by brick plants Nos. 10 and 17.

Beneath the sand layer, four more rock varieties were distinguished; their thicknesses and extent are shown in Table 2. The layout plan of the workings is shown in Fig. 1.

2. Qualitative characterization of the rocks. Loams of layers II and III are lean and contain a high percentage of sandy fractions. The rocks of the lower horizons, layers V, VI, VII and VIII, are finer. They contain a larger percentage of clayey fractions with grain size less than 0.01 mm.

In granulometric composition, all layers of clays of the lower horizons differ little from one another. The limits of variation in granulometric composition and its average value in the layer are given in Table 3.

In terms of silica content, all the rocks are acidic. In chemical composition, the clays of the lower horizons are more valuable than the loams. They contain a higher percentage of fluxing oxides and, with their high dispersion, sinter at lower temperatures than the loams.

The distinguished varieties of clays of the deep horizons (layers VI, VII and VIII), by macroscopic characteristics and chemical composition, do not differ greatly (Table 4). They may well be assigned to one variety with a somewhat changing composition. In some samples, in small quantities and in a finely dispersed state, carbonates are present, which cannot have a harmful effect on the properties of the ceramic body.

Table 4

Chemical composition of samples by layers

Location of workings.

Legend:

○ — place where boreholes were drilled in 1947 and samples were taken for granulometric analysis.

□ — place where pits were sunk in 1947 and laboratory samples were taken.

▣ — place where a pit was sunk and laboratory and semi-factory samples were taken.

Fig. 1

Sections of the deposit along the principal workings.

Section III–III

Δ No. 11  Δ No. 21  Δ No. 22

Legend.

• topsoil layer
• red loam
• yellow loam
• sandy loam
• gray clay
• brown clay

Fig. 2

Section V–V

Δ No. 4  Δ No. 28  Δ No. 5

Fig. 3

Section VII–VII

Fig. 4

1. The clays of the lower horizons are a more valuable raw material for building ceramics than the loams, also in terms of technological indicators.

Their plasticity falls within the ranges “well-plastic,” “highly plastic,” whereas for the loams it does not exceed the indicator “medium-plastic” (assessment by drying). They have a high bonding capacity in the dry state, which fully ensures the mechanical strength of the dry brick required during its mechanical processing.

The ceramic characteristics of the layered masses are given in Table 5.

Table 5

The dynamics of shrinkage during drying of products made from loams (layers II, +III) and from clays of the lower horizons (layers VI, +VII, +VIII) is shown in Figs. 5 and 6.

Fig. 5. Shrinkage during drying of products made from loams

In terms of refractoriness, all varieties of clays are low-melting. The loams belong to the group of non-sintering materials, while the clays of the lower horizons (layers VI, VII, and VIII) are sintering.

Fig. 6. Shrinkage during drying of products made from clays of the lower horizons

The relation of products made from the bodies to firing is shown in Table 6.

Table 6

The refractoriness of the loams and of layer V is 1240°, and that of the clays of the lower horizons of all layers is 1220°C. Owing to their high plasticity, articles made from the clays of the lower horizons give a large shrinkage during drying. Without the addition of tempering additives, it is difficult to manufacture brick or tile from them with a normal amount of rejects during drying. They sinter at a lower temperature; therefore articles made from these clays more readily develop the required structure during firing and form a shard with higher mechanical strength.

Table 7 gives the results of an investigation of bricks made in the laboratory from layered masses and fired at a temperature of 950°.

Table 7

In terms of plasticity, the loams are a lean rock, with drying shrinkage close to the lower limit for the plastic method of forming. They have a high sintering temperature and a short sintering interval.

Under identical conditions of manufacture and firing, bricks made from them have a more porous structure and a mechanical strength two times lower than those made from the clays of the lower horizons.

The mass that includes all varieties of the rocks of the deposit to a depth of up to 16 m has higher technological indices. The mixture has medium plasticity, intermediate between the loams and the clays of the lower horizons; the sintering interval of the mass is lengthened, and the shard structure required by the standard forms at lower temperatures. Such a change in the properties of the mass considerably facilitates the firing conditions for brick and tile and reduces fuel consumption. Exploitation of the deposit to a depth of up to 16 m, with the direct use of all varieties of the rock for the production of building brick and tile, is advantageous also from an economic standpoint.

The batch for the entire explored thickness of the deposit was processed under factory conditions; building bricks and tiles were made from it there as well. In the units, the mass was processed normally. To create better homogeneity of the mass, processing it on the belt press is insufficient. The plastic clays of the lower horizons mix with loams and sand with difficulty; therefore, before the belt press it is necessary, in addition to the mixer, to pass it also through fine-grinding rolls. The normal forming moisture content of the mass lies within the limits of 21–23%, with brick shrinkage during drying of 7–8%.

In terms of mechanical and other indices, the fired brick had grade 150. By all indices, this same mass is fully suitable for the production of roofing tile. Formed and fired from it...

the tile had high physicoceramic indices and met all the requirements of the standard.

But for tile, the clay should preferably be prepared in advance and used in production only after a certain period of aging, and still better after freezing out. A body treated in this way will fully ensure a normal rejection rate of tile during drying and will give still greater mechanical strength.

Conclusion

The clays of the lower horizons down to a depth of 16 m at the Lagerny Sad deposit are a valuable raw material for building ceramics. Together with loams and sand they form a body suitable for producing high grades of building brick and roofing tile, with an optimum firing temperature of 950–980°.