The main characteristics of a building material, primarily of interest to the developer, are: environmental safety, mass ratio of moisture in the material, fire resistance, vapor permeability, frost resistance, thermal performance, strength, and, finally, the cost of this material. Let’s try to figure out the main characteristics of sawdust concrete, clarify its compliance with the requirements for modern building materials.
Sawdust concrete – material based on clean, safe, natural components: cement, sand, sawdust. Due to the high content of organic filler (sawdust), sawdust concrete blocks have excellent sound absorption and vapor permeability. In many respects, sawdust concrete wall blocks correspond to wood. Unique sanitary and hygienic characteristics of the material ensure an excellent microclimate in houses built from sawdust concrete blocks.
Output: Sawdust concrete wall stones are an environmentally friendly, healthy building material that fully meets modern sanitary and hygienic requirements.
The mass ratio of moisture in a material is a very important indicator in construction. Not only the comfort of living depends on the percentage of water, but also the frost resistance of this material directly depends. Naturally, it is desirable to reduce the proportion of water in the material. The water absorption of sawdust concrete is on average 8-12% for operating conditions B (according to SNiP II -3-79 construction heat engineering). This range of indicators is due to the different density of the material (from 600 to 1200 kg / m 3). The mass fraction of water in the material can be significantly reduced. It is possible to process sawdust with preservative, water-repellent compounds, as well as the use of water-repellent concrete additives. For comparison, we present the percentage of water absorption of building materials most often used in construction.
Note that the mass fraction of moisture given above is typical for the listed materials in pure form, and in practice can be reduced by using special hydrophobizing additives, as well as by organizing combined structures. Especially important are the indicators of water absorption of the material during the construction of enclosing structures, when the project does not provide for wall cladding with protective and decorative materials. For example, walls made of ceramic bricks with a fine jointing. A wall made of this material is a completely independent structure that does not require mandatory protection, both for reasons of reducing moisture absorption, and because of insufficient mechanical strength of the material. However, facing clay brick is the most expensive material from our list, the thermal conductivity coefficient of 0.81 W / m o C is too large for a modern wall material, if the requirements of SNiP 23-02-2003 (thermal protection of buildings) are met, a wall with a thickness of at least 150 cm will be required (for Moscow region).
Almost all other wall materials from the list need protection for various reasons. Therefore, water absorption of the material without protective structures is a purely theoretical concept for the builder (in the case of mandatory protection provided for by the project). First of all, the builder is interested in water absorption of the final, combined structure, which includes indicators of both the wall material itself and the material of the protection-facing.
The water absorption of the material, which will be necessarily closed by an additional protective structure, is a value from the field of reasoning about a person’s well-being in socks and a shirt in the cold-15 o C. The situation, say, is not typical, much more practical interest is his state in a sheepskin coat and felt boots, as more close to reality ! So the relatively large water absorption of sawdust concrete can be reduced by using water-repellent additives, or by organizing protective measures (plastering, covering the walls with facing bricks, basement tiles, plastic panels, etc.). Note that the majority of buildings built from wall stones (large-sized blocks) are almost everywhere faced with protective and decorative materials. By the way, the material used for the partitions of bathrooms in multi-storey buildings of Soviet projects is gypsum. The water absorption of this material is from 6 to 15%! However, after protective measures (such as painting with oil paint), the gypsum wall is excellent, moisture resistant construction.
Therefore, taking into account the widespread practice of cladding walls erected from building blocks with protective and decorative coatings, relatively large water absorption of sawdust concrete can be omitted as a purely theoretical value.
Output: The water absorption of sawdust concrete is quite at the level of traditional building materials, and when organizing protective measures, the water absorption of the enclosing structure based on sawdust concrete blocks can be reduced to 2-4%.
The frost resistance of the material is a value that directly depends on the water absorption indicators. A decrease in water absorption indicators invariably leads to an increase in frost resistance indicators. It is possible to obtain sawdust concrete blocks with frost resistance indicators of 75-100 cycles.
Fire resistance (fire resistance)
Sawdust concrete, prepared according to a certain technology, is either slightly combustible or completely non-combustible. The relatively high fire resistance of sawdust concrete is primarily due to the fact that the organic filler is reliably closed with a cement-sand wall. In other words, each wood plate is hermetically packed in a cement shell. When the material is heated, self-extinguishing of organic inclusions is observed. Sawdust concrete block (sawdust content about 50%) has a fire resistance limit of more than 2.5 hours, at a temperature of 1100-1200 o C. The bearing capacity of the blocks does not change even after three hours of exposure to high temperatures.
Note that sawdust concrete in terms of fire resistance is significantly superior to the popular building material expanded polystyrene concrete. Flammability group G1 (low-combustible material).
And if expanded polystyrene concrete fully complies with the fire resistance requirements for modern building materials, then sawdust concrete is even more so! A filler of polystyrene concrete, these are foam balls, cement-sand walls – reliable protection of the foam from fire.
Output: sawdust concrete blocks (sawdust content about 50%) is practically non-combustible material, suitable for a full range of construction work. Fire resistance of sawdust concrete is higher than that of the popular modern material polystyrene concrete.
In terms of its thermal performance, sawdust concrete fully complies with the requirements of amendments No. 3 and 4 of SNIP 11-3-79 “Construction Heat Engineering” to increase the thermal resistance of building envelopes. So the thermal conductivity of sawdust concrete with a density of 800 kg / m 3 is 0.32 W / (m o -C). Note that the thermal conductivity of gas-foam concrete with a density of 600 kg / m 3 (the most commonly used brand in modern construction) is 0.24 W / (m o -C). In other words, sawdust concrete in terms of the most important indicator (thermal conductivity) is very close to porous concretes, and this despite the fact that porous concretes (gas-foam concrete) are recognized leaders in modern construction!
For comparison, we present the calculated coefficient of thermal conductivity of the most commonly used materials in construction..
In practice, a 40 cm thick sawdust concrete wall surpasses brickwork 100 cm thick in terms of thermal resistance.!
Output: sawdust concrete blocks (sawdust content about 50%) is a wall material that fully meets the thermal engineering requirements for modern building materials. The thermal resistance indicators of sawdust concrete are superior to most traditional building materials and only slightly inferior to porous concrete.
Strength of sawdust concrete wall stones (blocks)
Due to the significant content of fibrous-like inclusions, when testing the bending and tensile strength, sawdust concrete blocks surpass most traditional building materials in these important indicators, including foam-aerated concrete..
Sawdust and shavings in the block play the role of reinforcement, hence the increased bending and tensile strength.
The compressive strength of a sawdust concrete block is an important indicator when calculating loads for choosing the type of floors or the number of storeys of a building.
Sawdust concrete blocks can be made of various densities and compressive strengths..
By changing the ratio of filler (sawdust, shavings), binding components of the mixture (cement, lime), inert components (sand, slag, ash), it is possible to obtain wall material with specified characteristics of density, strength and, which is important, cost. The wide possibilities of obtaining the material of the required properties have a positive effect on the rational use of the components of the mixture and reducing the overall construction costs. So when erecting one-storey buildings for economic purposes, a strength of about 20-25 kg / cm 2 is quite sufficient, which corresponds to the concrete grade for compression M-25. When obtaining this brand of wall stone, there is a significant saving in the binding components of the mixture (cement). For the construction of residential, including multi-storey buildings, it can be recommended to use sawdust concrete blocks (stones) with a strength of at least 50-98 kg / cm 2 concrete grade for compression M-50 M-100. To obtain the maximum strength values of sawdust concrete blocks, it is recommended to use M-500 cement and modifying concrete additives.
Some features of the use of sawdust concrete blocks (stones)
Sawdust concrete blocks (sawdust content about 50%) is a material that lends itself well to mechanical processing. Sawdust concrete is sawn, drilled, and nailed, thus increasing the quality of masonry work and significantly reducing the consumption of wall material. If adjustment is required during the construction of the wall, the blocks do not split off, do not chop, but are cut as accurately as possible with a hacksaw to the required size.
Cement components of sawdust concrete block, an excellent basis for applying all types of protective and decorative coatings. The use of adhesive solutions during the installation of facing materials provides reliable adhesion to the supporting sawdust concrete block.
In terms of ease of processing, sawdust concrete block is similar to foam concrete and gas silicate blocks. Processing methods and features of block laying also do not differ significantly.
Scope of application of sawdust concrete blocks (stones)
Ample opportunities for obtaining sawdust concrete blocks of specified characteristics makes this material suitable for the full scope of general construction work. Building sawdust concrete blocks are a universal material for the construction of independent load-bearing enclosing structures, insulation of walls of finished buildings, foundations, fences and poles.