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Wood concrete, as a building material, was known back in the days of the USSR, factories worked, houses were built. After the collapse of the country, the technology was forgotten for some time, and a few years ago it was remembered again. The material turns out to be warm, light, durable, conducts sounds poorly, and its cost is also low. Therefore, wood concrete and wood concrete blocks (arboblocks) are increasingly interested in private developers.
Let us immediately determine that wood concrete and sawdust concrete are different materials with different characteristics. The composition of the wood concrete includes waste from the woodworking industry, but only of a strictly regulated size. There is no other placeholder. And everything is spelled out in GOSTs and instructions. And the filler is not sawdust, but wood chips with dimensions not exceeding 40 * 10 * 5 mm recommended by the standard.
Properties, advantages and disadvantages
For a private developer, when choosing a building material, the technical characteristics of the material are important. Let’s look at wood concrete blocks from this side. So, the characteristics and their brief decoding:
- Thermal conductivity – 0,08 – 0,14 W / m ° C (depending on the density, the greater the density, the higher the thermal conductivity). Characteristics comparable to wood. She has this indicator of 0,14 W / m ° C, for ceramic bricks 0,6-0,95 W / m ° C. That is, doi from wood concrete blocks will be warm, and the width of the walls is small. For central Russia in homes of permanent residence, it is recommended to make walls 30-40 cm thick.
- Frost resistance – 25-50 cycles. This parameter means that walls can freeze / unfreeze from 25 to 50 times without compromising their qualities (depending on the manufacturer). If the house is permanent residence, then it will not freeze at all. For unheated dachas, a service life of 25-50 years is quite acceptable.
- Compressive strength – 0,5-5 MPa. This is one of the most attractive features of wood concrete – it is difficult to destroy it. Another point: it restores its shape after the load is removed. That is, by hitting with a sledgehammer, you can make a dent, but after a while it will even out – partly or completely depends on the “severity” of the damage.
Technical characteristics of wood concrete blocks - Bending strength 0,7-1 MPa. This means that when some distortions appear in the structure (the foundation unevenly sat down), the wood concrete blocks will not burst, they compensate for a sufficiently large load.
The properties are very good. Another thing is that they will only be subject to exact observance of proportions and technology. This is what arblelite blocks are dangerous for: you don’t know how well they are made.
Performance specifications
As you can see, the characteristics of the arboblock are not bad. Pluses still need to add light weight, large size and good ability to absorb sounds. A very big plus is that the blocks are easy to cut, it is easy to give them the desired shape. Another positive point is that nails and screws hold well in wood concrete. From this side, too, no problems.
- Shrinkage – 0,5-0,6%. This parameter shows how the geometric dimensions of the wall will change under load. Arbolite has one of the lowest rates.
- Water absorption 40-85%. This figure is very high. If you put the wood concrete block in water, it can absorb a lot of water. For the developer, this means that you need to take care of a good cut-off waterproofing between the foundation and the first row of blocks. Also, the wood concrete house needs an exterior finish that will protect the material from moisture. It’s not all that scary. It is much more important that the hygroscopicity of wood concrete is low (the ability to accumulate vaporous moisture). Even with very humid air, it does not become damp, but passes vapors through itself, regulating the humidity in the room.
- Fire resistance – class G1. Arbolit refers to materials that do not support combustion. This is their definite plus.
If we talk about technical characteristics, then there is essentially one serious minus – high water absorption. There is another drawback, but it is from the field of operation. Arbolite is very fond of mice. The material is natural and warm. You can solve the problem by making a high base – not lower than 50 cm.
Production technology of wood concrete blocks
Arbolit belongs to lightweight concrete, the technology is almost standard, with the exception of some nuances: the need for pressing and using not a conventional gravity concrete mixer, but a forced one when mixing. It mixes wood chips with other components better.
Composition
The composition of the arbolite includes four components:
- high-quality cement (M 400 or M 500);
- wood chips;
- water;
- chemical additives.
The cement must be dry and fresh. Chips – a certain size. The less regrading, the stronger the block will be. Chemical additives are calcium nitrate and chloride (food additive E509), liquid glass, aluminum sulfate and some other substances. Please note that they are first diluted in water and only then added to the chips, mixed. Any drinking water is allowed, but not technical, without pollution. After the chips are evenly wet, cement is added. Any other sequence is not allowed.
Types and sizes of blocks
Depending on the density, arbolite blocks are divided into heat-insulating (up to 500 kg / m3) and structural (from 500 kg/m3 up to 850 kg/m3). For the construction of one-story houses, you can use the lightest of the structural ones with a density of 500 kg / m3. For mansions of 1,5 and 2 floors, the minimum density is 600 kg / m3 and above.
The sizes of wood concrete blocks can be different. The most common – 500 * 200 mm and different thicknesses – from 100 mm to 400-500 mm. But different factories and workshops produce blocks of different sizes. Forms for them can be welded from ordinary sheet iron, so this is not a problem. The photo shows an example of the assortment of one of the workshops.
As you can see, blocks of 600*200 mm and 600*250 mm are also available and the thickness is from 100 to 500 mm. You can choose the appropriate ones for load-bearing walls and for interior partitions. Also, for self-production of wood concrete blocks, it will be possible to make a suitable shape. That is if you decide to make them yourself.
Proportions
Like any building material, wood concrete is divided into strength classes. For the construction of load-bearing walls of houses, the required strength class is B 2.5.
The amount of materials needed per cubic meter of arbolite solution is in the table (photo above).
Pressing technologies
All these components are mixed, blocks are formed from them. There are several technologies:
- just by pressing:
- manual on the floor (requires great effort);
- hand rammer on a vibrating table.
- pressing with vibration on a vibrating machine.
The easiest way to implement manual pressing. But it is difficult to control the density and strength of the resulting blocks in this way.
Normal production conditions
For the normal process of cement hydration, a temperature of at least +12°C is required. There are no other conditions. The peculiarity of the production is that after the block is molded, at least 2-3 weeks must pass before it can be used. During this time, cement will gain about 50-60% strength (depending on temperature) and it is already possible to work with blocks. That is, it is necessary to make blocks long before the start of construction. Given that the wood chips must be aged for at least 4 months before use, then you can start a year before construction.
Another practical point: if you are going to make arbolite blocks with your own hands, in addition to the platform for mixing and storing components, you need a platform for settling the blocks. The place should be covered, protected from rain and sun. There should be no drafts either.
Chips for wood concrete: how to get or where to buy
The best wood chips for wood concrete are obtained from pine and spruce. You can also use larch, but when mixing it is necessary to double the amount of chemical additives. From hardwoods, GOST allows the use of aspen, beech, birch, poplar. The rest of the requirements are:
- Maximum dimensions 40*10*5 mm. The optimal parameters of wood chips were experimentally established – about 25 mm long, 5-10 mm wide, and 3-5 mm thick. From such raw materials, the most durable wood concrete blocks are obtained.
- The amount of bark should not exceed 10%.
- There should be no dust, sand, soil, foreign matter. Chips are removed from small fractions, dust and sand with a sieve, and large foreign inclusions are removed manually (often these are pieces of soil or stones).
- There should be no visible mold or rot.
An example of wood chips for wood concrete
The best wood chips are obtained from lumpy waste wood. It is first passed through chippers, and then crushed in a hammer mill. The following mechanisms can be used for this:
- Disc chippers with adjustable blades. Not all of them can be adjusted to obtain chips of the required size, but the sizes will be close.
- Rotary knife crushers. Narrow and narrow chips come out of them, and the length is adjustable. I mean, it’s a good option. There is only one “but”: there are a lot of knives and with prolonged use they need to be changed or welded on (they do not sharpen). We add to the pluses that crushers of this type can be used for re-crushing technological chips obtained during the first crushing (after reconfiguration).
- Shredders or roller grinders. This is expensive equipment (about 1 million rubles), and mostly imported, but it is excellent, as it is made for certain sizes of wood chips.
If you make arbolite chips yourself – not an option, you can buy it. If it works out, you can negotiate at the factory where wood concrete is produced. Just check the parameters of the chips. If there is none nearby, you can take chips from under the sizing machines. Some of them can be adjusted so that the chips are not thick.
Features of the manufacture of mortar for wood concrete blocks
Wood waste contains sugars. If fresh raw materials are used, sugars may begin to ferment, which will cause the integrity of the block to be destroyed. When kneading, chemical additives are added to the solution, which neutralize their effects (liquid glass, calcium chloride, alumina sulphate, lime). They can be added in combinations: calcium chloride with liquid glass or alumina sulphate with lime. The total weight of additives should not exceed 8%.
There are other ways to break down sugars. The simplest, but requiring a long period of time, is to withstand the chips for at least 90 days in a pile in the air. If there is no way to wait, the chips are soaked for 3 days in lime milk, stirring occasionally. Then it is filtered, not dried, in this form it is used for kneading. Only in this case, it must be taken into account that much less water will be required. This method works well, but is very troublesome. It is easier to find an opportunity to purchase chemical additives.
The procedure and features of mixing the solution
For mixing the mortar, a forced-type concrete mixer is used. You can also use an ordinary gravity or “pear”, but you have to knead in it for a long time, although you can adapt – tilt the pear as low as possible when kneading (raised, it almost does not mix).
First, sawdust is poured, a certain amount of water is added. While sawdust gets wet, chemical additives are diluted in a small amount of water, then they are unloaded into a concrete mixer. When all the wood is evenly wet, pour cement. It is loaded in portions, waiting for a uniform distribution throughout the volume. Cement should envelop each chip from all sides. This is only possible if the sawdust is well wet, so we monitor this stage carefully.
Block molding
The solution is poured into molds. Most often they are made of metal, they are a box with handles without a bottom. The form is placed on a flat surface (a board, for example). During manual tamping, the molds are filled with arbolite mortar, layer by layer, each of which is pressed with a metal platform with a handle. In order for the air to escape better, the thickness of the material is pierced several times with a metal rod, after which it is pressed again. This procedure can be repeated several times until you reach the desired density of the layer, after which you can fill up the next one. Layers are poured up to the upper edge of the block, after the final tamping, the top is leveled, cutting off the excess with a metal bar.
You can use a lever – mechanical or driven. In this case, the force develops significant and you can load the entire volume at once, if necessary, adding to the edge. To achieve a high density, you can press several times, then increasing, then weakening the pressure. Experience shows that with this principle of manufacturing arbolite blocks, they turn out to be more durable, pressing out (restoring the shape due to the elastic force of the chips) appears much less.
The best blocks in terms of strength and with less effort are obtained if vibration is added to the pressing process. In this case, the efforts that are necessary to obtain the desired strength are reduced significantly. For these purposes, vibrating tables are made. And the process is called vibrating with a load.
The molded block on a stand is transferred to the place of drying. If the solution allows and the block holds its shape, the frame can be removed. But sometimes home-made arbolite blocks sin in that the solution turns out to be too liquid – it’s easier to tamp. In this case, the blocks are left in the form for a day. The use and transportation of blocks is possible no earlier than 2-3 weeks after molding.
Features of the construction of their wood concrete blocks
The laying of blocks is carried out according to the type of brick – with dressing of seams, on a cement-sand mortar. Of the features – the thickness of the seam – about 8-10 mm. Between the foundation and the first row of blocks, it is necessary to make a very high-quality cut-off waterproofing. This eliminates the suction of moisture through the foundation from the ground. We make a combined waterproofing – first we impregnate with bituminous mastic or any other coated waterproofing, we lay a rolled waterproofing on top. Previously, roofing material was always used, but today it is of poor quality and will collapse in a couple of years. And it is important to exclude moisture leakage (due to the high water absorption of wood concrete), so use a hydroisol or something similar. It is possible, in two layers, also smeared with bituminous mastic.
The next nuance is laying over window and door openings. It is best to use special U-shaped blocks, in which to lay a reinforcing frame and 4 bars of reinforcement with a diameter of 10-12 mm. It is better to tie it down so that there is less chance of corrosion. First, blocks with notches are installed above the opening. They can be supported from below with a board and spacers. Then the frame is laid, everything is poured with concrete. Leave the structure for a day, after which the supports can be removed and laying can continue.
There are many nuances of building a house from wood concrete blocks in the video.