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Back callEarth products are local materials and due to the wide variety of soils, most of which are suitable for earth construction and are not regulated by the state standards. Small-piece products: soil: stones, blocks, slabs and bricks in the vast majority, are made from earth. These products are intended mainly for masonry walls of the buildings. For brevity, in the following presentation, such products will be called soil blocks.
Currently produced in Russia and abroad soil blocks differ in various dimensions from 220x105x60 mm to 390x190x90 mm. At the same time, the domestic and foreign literature recommends to produce soil blocks larger than the size of standard bricks. This is due to two main reasons: an increase in the productivity of bricklayers in the construction of walls and a decrease in the amount of mortar used for laying blocks. The selection of the sizes of the soil blocks produced is influenced most of all by the capabilities of the available molding equipment.
The general properties of the soil blocks are shown in the table
| Properties | Indicators |
|---|---|
| Compressive strength, MPa | 2,0-40,0 |
| Density g/cm22 | 1,3-2,0 |
| Coefficient of thermal conductivity, W/m, deg. C | 0,5-0,7 |
| Linear shrinkage | 0,02-0,2 |
The compressive strength of the soil blocks, that is, the pressure they can withstand in the wall without collapsing, as well as their other properties depend on the nature of the soil, the type of stabilizer used, and, most importantly, the method of their manufacture.
The soil blocks manufactured without stabilizers are non-water resistant. Such blocks have significant strength in the dry state and are used mainly for single-story residential buildings, as well as for auxiliary household outbuildings.
The blocks made from soil with the addition of a small number of stabilizers, in addition to a certain strength, acquire the property of indelibility. Such indelible blocks submerged in water at 3/4 of the height and left in it for 24 hours, should not have cracks, swelling, dulling and other visible damages. Anti-washout blocks can be used for load-bearing and frame walls of residential one-and two-story buildings and one-story outbuildings.
The soil blocks produced with the addition of an optimal amount of the stabilizer, in addition to strength, have a certain degree of water resistance (cracks and delaminations should not appear on the samples after several cycles of alternate saturation with water and subsequent drying). At the same time, such water-resistant blocks have a softening coefficient, that is, the ratio of strength in the saturated state to strength in the dry state, not less than 0.6. Water-resistant blocks can be used for the bearing walls of residential one-and two-story buildings, administrative buildings, religious buildings, as well as for buildings for economic purposes.
Basically, ordinary ground blocks are made for masonry walls of various buildings. Special blocks can be made for special purposes:
- blocks that have one or more surfaces or parts with more stabilizer than the rest of the block;
- blocks with embedded facing tiles that have one or more surfaces decorated with special facing tiles;
- blocks with a treated surface that have one or more surfaces specially covered with graphic or decorative elements or treated with chemicals;
- shaped blocks with one or more shaped surfaces.
Numerous studies by the Soviet and foreign scientists have shown that the strength and durability of the soil blocks increase with an increase in its density, and the density and strength of the soil blocks increases with an increase in the compaction load (pressure). However, this increase occurs up to a certain limit, after which the density and strength remain more or less constant. At the same time, the maximum strength and compaction loads for soils of different mineralogical composition are not the same.
Since the quality of the soil blocks at other things being equal, depends on the degree of compaction, the main operation in the manufacture of the blocks is molding. The molding achieves, firstly, by obtaining a block of the extremely high density, on which the strength of the block depends, and, secondly, the given dimensions. Normally, when forming a block, its length and width are fixed by the mold walls, and the thickness is fixed by the processing tool.
Fluctuations in the quantity and quality of the soil mixture can lead to changes in the density and strength of the produced blocks, and the density affects the durability. A wall made up of blocks with different densities will eventually collapse unevenly from erosion. Therefore, it is very important to use such molding technologies of the soil blocks that ensure the production of homogeneous blocks. It is also important that these technologies ensure the production of blocks of the same size, which in turn contributes to the subsequent high-quality laying of the soil blocks into the walls.
It should be noted that the traditionally applied molding technologies using various manual or mechanical presses and rammers do not fully meet these requirements. For centuries, there has been an idea that the more force you squeeze the material in the form, the denser block you will get. Guided by this idea, the powerful devices were created and are being created — rammers that can develop a compression pressure of several tens of MPa, and there are rammers so-called hyperpressing, developing 100 MPa, that is, one centimeter of the surface of the formed block has a force of 1000 kg. To match this gigantic effort, such devices have dimensions, weight, and cost.
In the surrounding world, close examination, you can find examples when materials like soil, and the soil itself, acquire an extremely dense structure without significant effort.
One of the most striking examples is the formation of a dense path along the coastline, called a splash. Over thousands of kilometers of sandy beaches, a dense structure of sand, silt, and shell parts is formed every second without any pressure. This in itself is an amazing phenomenon that has an extremely interesting property of self-organization. A lazy movement of a surf wave that runs in and out of the water leads to the formation of the dense structure, regardless of the characteristics of the soil that forms the shore (rock formations are not taken into account). In addition to the dense structure, a certain familiar geometry of the upper surface of the splash is formed. Moreover, its any damage is "healed" in a matter of moments. Again, this happens by itself.
At the behest of waves, millions of sand particles occupy the most stable compact position, forming the maximum number of contacts between themselves. And all this happens without applying large pressures to the material being added to. This is confirmed by the experience of everyone.
In zone injection technology, it is possible to achieve the maximum degree of density without high pressures, which radically changes the traditional understanding of compaction processes.
The fluid wedge effect is the formation of a local dense fluid zone of correlated moving particles of a loose medium.
The formation of the mentioned zone occurs as a result of maintaining the flow from the subsequent portions of the same material constantly pressed into the pre-formed layer of bulk material by means of the solid surface of the injection tool.
The main property of this effect is that the density of the material in the zone and its geometric dimensions remain unchanged, despite the incessant pressing of new portions of material into the zone. In this case, the newly pressed portions displace the same amount of material from the zone as they occupy themselves, which leads to a constant renewal or, in other words, the flow of material in it.
When the material portions are no longer pressed in, the effect of the fluid wedge disappears, but due to the special properties of the bulk media, the achieved material density is preserved. (The unique behavior of the bulk media is based on the combination of properties inherent in solid, liquid and gaseous bodies.)
It is easy to see that it is quite simple to reproduce the effect of a flowing wedge. The main thing is to observe the conditions of openness of the process and maintain the flow of the bulk medium. This simplicity opened the way to the creation of a controlled and managed process for the movement of medium particles during the molding of the products, and the molding process itself made it easy to manage and control.
When reproducing the effect of the fluid wedge for technological purposes, the compacted material is injected into a small volume zone determined by the size of the injection tool or working body. Therefore, the process that causes the effect of the fluid wedge occurs only in the limited area adjacent to the contact surface of the working body with the molded material. Hence the name of the technology - zone injection technology.
The zone injection technology is one of the basic technologies used in many industries. First of all - in the construction materials industry, road construction, powder metallurgy, production of refractories, foundry and in a number of other industries where it is necessary to obtain dense structures from bulk media.
The effectiveness of the zone injection technology in these areas is based on its remarkable properties.
Obtaining a high, maximum density for specific materials and molding conditions was covered above. It is very noteworthy that it is achieved with a minimum (one or two orders of magnitude less than when pressing a similar material) force in the zone injection technology. In addition, the molding process does not require pre-dosing of the molded material. Very interesting and important is the ability to control the quality of compaction of the molded material directly during the manufacture of the product.
In zone injection technology, the feeding, distribution, compaction of the formed material and finishing of the upper surface are performed by a single action, called, like the technology itself, zone injection. In view of this feature, the implementation of the technology requires special devices — superchargers of bulk media, the design of which can be very diverse. Each specific design of superchargers is developed taking into account the characteristics of the compacted material, the shape and size of the product, performance and a number of other factors.
The consistently high quality of products in the zone injection technology is ensured by simultaneously achieving the accuracy of the molded products and the maximum density of their structure.
To achieve this, it is necessary to observe the conditions for the formation of the fluid compacted local zone, that is, to maintain the effect of the fluid wedge, throughout the entire process. To do this, one must adhere to certain rules of molding, which allow us to meet the required conditions. These rules are a technological secret or "know-how".
The first case is when the product length is much larger than the width of the supercharger (Fig. 4). In the process of forming such products, the injection of the bulk material into the mold is performed by continuously feeding soil under the moving working surfaces of the supercharger with a layer exceeding the thickness of the molded product, and at the same time the supercharger is moved relative to the mold.
The speed of translational movement of the supercharger relative to the mold is selected and maintained depending on the speed of extrusion of the bulk material from under the injection surface towards the unfilled part of the mold. In this case, the speed of the forward movement of the supercharger should not exceed the speed of the extruded bulk material.
It is extremely important that the extrusion of the bulk material from under the injection surface is over the entire height (thickness) of the molded product.
If the extrusion of the layer is uneven, then when selecting the speed of movement of the mold takes into account that part of the extruded layer that has the lowest speed, which is expressed by the lag of this section from the rest of the bulk material.
This lag may be due to both the design of the supercharger and the uneven supply of material to the molding zone, which may be caused by the mixture hanging either in the transfer hopper or on the supercharger's delivery elements.
When the size of the molded product is comparable to the size of the supercharger, the rules are as follows (Fig. 5).
The injection of the bulk material is as in the first case. And the movement of the supercharger relative to the mold is made after the compression of the injected material is established above (beyond) the open side of the mold. It should be noted here that it is difficult to see this squeezing, which, as a rule, goes to meet the material supplied to the supercharger, without a certain experience. But the skill is acquired quickly in the process.
The combination of these remarkable properties of the zone injection technology has led to the creation of simple and reliable molding devices.
The development of the design of the zone injection units is the unit for production of RK 250 soil blocks. It combines the most successful technical solutions tested in the above-described designs. In addition to the usual purpose, the RK 250 unit is designed for the production of blocks in heavy and extreme conditions to eliminate the consequences of natural disasters, social disasters and wars. For this purpose, the unit has an excess safety margin, simple operation and increased reliability.
Figure 6. Zone injection unit for RK 250 soil blocks. 1 - base, 2 - mold transfer mechanism, 3 - products release mechanism, 4 - four-cavity mold, 5 - stabilizing device, 6 -injection device, 7 - grid supercharger, 8 -working body electromechanical drive, 9 -support element, 10 - bunker outlet.
The RK 250 unit (Fig. 6) consists of a base 1 with mounted mold transfer mechanisms 2 and products release 3, four-cavity mold 4, stabilizing device 5, discharge device 6 and electrical equipment.
The discharge device includes a working body with a lattice supercharger 7, a compact electromechanical drive of the working body 8, a support element 9, and a bunker outlet 10 for feeding powdery material to the discharge zone.
The form can perform shuttle movement under the supercharger by means of a movement mechanism. Each mold cell is equipped with a lifting bottom with an ejector for immediate release of the molded blocks.
The stabilizing device is installed on the base with the possibility of reciprocating movement across the movement of the mold, and is driven from the supercharger. The stabilizing device has two smoothing soles that cover the supercharger on both sides. On the other two sides, vertical walls protect the feed area of the molded material and prevent it from spilling out. RK 250 unit works as follows.
In the initial state, the form is located on the base in one of the extreme positions. In this case, two cells of the form are located on the outside of the stabilizing device with the bottoms raised to the upper position, two other cells with pubescent bottoms are located inside, with the outermost one being under the blower.
Properly prepared soil mixture or soil is fed to the bunker outlet. At the same time, the drive of the working body is turned on. The soil wakes up through the swinging supercharger and fills the mold cell through its open side. When swinging, the supercharger, periodically moving away and approaching the open side of the mold, pumps into the mold portions of soil that fall under it. After the soil reaches the maximum density in the cell under the supercharger and begins to be forced up through the open side of the mold, the mold movement drive is turned on. At the same time, they continue to feed the soil into the bunker outlet, making sure that there is soil in it all the time. The unit is designed in such a way that under this condition, if there is no material hanging on the grid of the supercharger, the conditions for the formation of the fluid compacted local zone under the supercharger are automatically observed, that is, the conditions for maintaining the effect of a flowing wedge throughout the entire molding process. As the mold passes under the swinging supercharger, its cells are filled with compacted soil and then fall under the smoothing sole of the stabilizing device, through which the molded soil blocks are calibrated. After the exit of the two ground blocks from under the smoothing sole, the bottom of the cells rise up, making the blocks release, and the form stops in the extreme position. The operator removes the released soil blocks from the mold. After that, the mold movement drive is automatically activated, and the mold starts moving to its original position. At the same time, the process of pumping soil into the mold continues. When the initial position is reached, the manufactured blocks are removed from the other two cells of the mold, and the mold stops again. After removing these blocks, the drive for the movement of the mold is switched on again, and it moves to another extreme position, in which the release and removal of the blocks produced in the first two cells takes place again. And so it goes on while the process of forming blocks lasts.
Zone injection units ensure high quality of molds in terms of density and dimensional accuracy without dosing devices for loose mass into the mold, pressure control and size of the molded product. Such types of defects as repressing, air entrapment, elastic aftereffect are completely eliminated.
When working on the zone injection units, no changeover is required when switching from one material to another, for example, from forming blocks from loam to forming blocks from concrete mix or arbolite. Low-skilled workers can operate and maintain these units due to the simplicity and reliability of the installation design. When working with the zone injection units, there is no vibration and excess noise, and the wear of forming elements is minimal compared to traditional pressing.
The considered units enable to form products from a wide range of materials and their compositions with high accuracy of the geometric dimensions of the manufactured products.
The units are small in size and weight, which allows their transportation on any type of cargo transport and use small production areas.
Due to the special design of the units, preparatory works before commissioning is excluded. The drive capacity of the units is small, which makes the molding process less energy intensive.
The most of the presented units can work in automatic mode.
Low power consumption, absence of vibrations and excessive noise, comfortable working conditions for service personnel, as well as easy operation make these units sustainable.
RK 250 zone injection units can be used to produce large-size and high-quality soil blocks that have architectural expressiveness and attractive appearance.
Table 4 demonstrates the ordinary characteristics of the soil blocks made from cement-soil mixtures and soils of Orenburg region.
During the production of the soil blocks, various shaped elements can be inserted into the mold and we can get the blocks with a decorative effect for the buildings finishing. A fragment of a building wall using such blocks is shown in Figure 7.
The practice of using zone injection units for soil-block construction confirms their high efficiency both in the manufacture of stabilized soil blocks and soil blocks without a stabilizing additive.
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