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What does the strength of a soil block depend on?

The strength of soil blocks depends on several factors, including the type of soil used, the amount of stabilizing agent used, compaction quality, drying method and strength testing method. The minimum compressive strength of soil blocks in air-dry condition must be at least 25 kg/cm2. Soil blocks are subjected to tests similar to those that bricks and concrete blocks are subjected to. It is necessary to test the first samples of soil blocks at the construction site. These tests will assess the suitability of the block as a wall material.

Normally soil blocks are tested in 28 days, although the same tests can be carried out earlier, e.g. in 7, 14, 21 days, in order to determine the growth of strength with time.

How is strength achieved?

According to the results of testing blocks made of soil (without the use of cement) their strength is estimated from 30 to 100 kg / sq. cm. (depending on the composition of the soil). The blocks have high forming strength, which allows you to lay them immediately out of the machine into the wall.

Compressive strength of soil blocks, that is the pressure they can withstand in the wall without being destroyed, as well as their other properties depends on the type of soil, the type of stabilizer used and, most importantly, on the manufacturing method.

Cement can be used to stabilize all types of soils. However, the greatest strength at the lowest cement consumption is achieved when using coarse clastic and gravelly soils, sandy loam and soil mixtures of the optimal composition. Much more cement is required for heavy loamy and, even more importantly, clay soils.

Test Methods Soil block grade ( with cement)
М50 М75 М100
Compressive strength (kg/cm2) GOST 8462 102 160 187
Heat conductivity (W/m, deg.) GOST 7076 0.6 0.6 0.6
Frost resistance (Cc) GOST 7025 35 35 35
Water absorption (%) GOST 7025 not more than 8% not more than 7% not more than 6%
Block dimensions (mm) 390х190х90
What raw material is used to produce the block?

The main raw material for earthworks are ubiquitous sandy soils Producing durable, high-quality soil products requires a soil mixture that contains, in addition to clay and silt, sand and fine gravel

What are the pros of building from soil?
  • Low price. It is due to the fact that the material is everywhere at hand (and under the feet, too): almost all kinds of soil, except for pure sand, is suitable for work.
  • Fire Safety Buildings constructed out of the soil do not burn, and become even stronger when exposed to the fire.
  • Hygienics The earth structures are dry and quite comfortable to live in.
  • Low heat conductivity. Earth buildings are warmer than brick buildings. They require less fuel to maintain a normal room temperature than in similar conditions in stone and wood buildings.
  • Ecosafety The use of soil for construction contributes to the conservation of forests, reducing energy costs for the manufacture and transportation of building materials. The most famous earth structure in Russia is the Prioratsky Palace in Gatchina.
What does the resistance of the soil to weather and other factors depend on?

Soil itself is not a particularly strong building material. At the same time, there are known methods to improve the natural strength and resistance of soils to physical and mechanical effects. These methods are commonly referred to as soil stabilization, and have been used in worldwide practice for centuries.

The main factor affecting earth products is water. The silt and clay fractions swell in water and shrink as they dry. This compression can cause cracks in the walls.

The purpose of soil stabilization is to increase its resistance to the effects of local weather conditions, including rain, changes in temperature and humidity.

The main ways of increasing the resistance of soils to weather factors include: increasing the density of the soil, introducing a binding agent into the soil that binds the soil particles, adding a hydrophobic substance that acts as a waterproof, water-repellent agent.

The choice and application of the correct stabilization method can increase the strength of the soil by 5-7 times or more and improve its resistance to erosion.

The clay soils available in the area are not always suitable for the manufacture of wall materials, but this does not mean that these soils can not be applied. The quality of soil can be improved either naturally or artificially by increasing or decreasing its plasticity and changing the ratio of clay to sand in the soil.

As inorganic (mineral) additives for soil stabilization in individual production, mainly cement and lime are used, and more rarely gypsum.

What is important when preparing the soil mass?

When preparing the soil mass, it is highly important to mix it. To obtain high-quality, homogeneous blocks, it is necessary to ensure that the mixing of materials is carried out as thoroughly as possible. Dry ingredients shall be mixed first, then water is added and mixing continues until a homogeneous mass is obtained.

Mixing can be done manually on a hard surface (e.g. concrete) with shovels or mechanically by means of mixers.

The required amount of water shall be added to the dry mixture at once or in portions. It is recommended to add a little water by sprinkling it on the mixture from a watering can. Moistened soil shall be stirred several times with a shovel or another convenient tool.

To mechanize the process of mixing the soil mass in the conditions of individual production of soil blocks the most suitable of the existing mixers are electric mixers. Nowadays, small-sized gravity concrete mixers are often used for mixing mortars and concrete mixtures on construction sites in individual construction. Such concrete mixers can not be used to mix soil mass, as low-moisture mixtures are not mixed in them.

How to determine the moisture content of soil?

Without resorting to laboratory tests, you can roughly determine the moisture content of the soil, taking into account the following practical data.

If the lump of soil squeezed in your hand spreads over it, its moisture content is above 18%.

If the soil crumbles into several small pieces when lightly squeezed by hand, it means that it has the right humidity within 11-12%.

Another practical tip. Fill your palm with soil or soil mixture and squeeze it into a lump, then slightly open your palm and, holding the lump formed on the palm, press on it with a thumb of the same hand. If the lump falls apart into small pieces, and the palm remains sufficiently dry and clean, then the moisture content of the soil is acceptable for forming soil blocks.

How to dry an overmoistened soil mixture?

Lime is recommended for drying out an overmoistened soil mixture or soil. It is recommended to mix the stuff for about one hour.

After mixing, if lime is used as a stabilizer, it is recommended to let the mixture rest for a while before forming, so that the soil particles can be better moistened with water. However, if cement is used as a stabilizer, it is recommended to use the mixture as soon as possible, since cement begins to set immediately after moistening, and delaying can lead to weaker blocks.

The amount of mixture shall not exceed the quantity needed for one hour of work. Even if this recommendation is observed, blocks produced at the end of an hour's work may be significantly weaker than those produced immediately after mixing.

What shall be loaded into the mixer first?

Materials shall be loaded into the mixer in the following order: additive, soil, cement. Mixing is done without adding water for 2-3 minutes, until the mixture becomes homogeneous (one color throughout). Water shall be added in small portions to ensure even moistening of the mixture. Water is added until the moisture content of the mixture is close to optimal.

What is meant by earth construction?

Earth construction refers to construction from soil. According to the Great Soviet Encyclopedia, soil (from German Grund – base, soil) is any rocks that lie mainly within the weathering zone (including soils) and that are the object of engineering and construction activities of man.

In earth construction, bricks, blocks, monolithic walls are made of soil, as a rule, taken from under the fertile top layer (humus).

What are the types of earth construction?

Earth construction can be roughly divided into three main types:

  • buildings with walls made in the formwork, where the soil is compacted by ramming, (such buildings are called rammed earth or wattle and daub);
  • buildings made of separately prepared by ramming earth stones or soil blocks;
  • buildings made of earthen bricks made by plastic moulding.

Methods of construction from soil blocks are predominantly used abroad and in Russia, as the use of soil blocks reduces the likelihood of cracks due to the fact that before laying their size and strength become more stable than in the case of padding, when shrinkage occurs during drying of the entire wall. In addition, the quality of soil blocks can always be quite easy to check.

What affects block durability?

Density affects durability. A wall made of blocks with different density will erode unevenly over time due to erosion. Therefore, it is very important to apply such technologies of forming soil blocks, which ensure the production of homogeneous blocks/p>

What is included in the complex for producing building materials?
  • A machine for producing soil blocks;
  • A belt conveyor;
  • A mixer;
  • A shredder;
  • A sieve.
"Drying" the blocks?

To achieve the maximum strength of the formed soil blocks a certain amount of curing (drying) time is required. In this case, the correct implementation of drying minimizes the possibility of defects that appear in the final stage of soil blocks manufacturing.

In case of accelerated drying, when the block is left to dry in the open air, exposed to solar radiation and wind, the surface of the block will quickly lose its moisture as well as give shrinkage. This can cause cracks on the block surface.

Therefore, the drying conditions shall ensure a gradual reduction of moisture in the entire volume of the formed block. At the same time, if cement is used to stabilize the blocks, it is necessary to ensure sufficient amount of moisture remains inside the body of the block for a few days. This is necessary for complete hydration of the cement.

One method of keeping the block hydrated is simply to place it in a plastic bag. Reasonable care is required so as not to break the corners, as they have insufficient strength during the drying period. After filling the bag with blocks, its open end shall be closed to retain free moisture.

The second method consists of laying the freshly formed blocks in a single row on a non-hygroscopic surface and covering them with sheets (plastic, grass mats, burlap, etc.) to prevent moisture evaporation.

In two or three days, depending on the temperature, the blocks (especially cement stabilized) will gain sufficient strength for their relaying. If lime is used as a stabilizer, the blocks shall be left to dry for approximately seven days. After pre-drying, the blocks can be removed from under the protective coating and stacked, also preferably under some kind of cover. The stack of blocks and cover shall be periodically sprinkled with water.

When the blocks are stacked, the top layer shall always be moistened and covered, while the lower layers dry in the air and reach maximum strength.

The drying time for maximum strength varies depending on the type of soil and, most importantly, on the type of the stabilizer used. When stabilized with cement, it is recommended to cure the blocks for at least three weeks. The drying period with lime stabilization shall take a minimum of four Soil blocks shall be completely dried before they are used for the construction.

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