USE OF WOOD WASTE - Building Material Science. T 1


To get a fairly complete idea of ​​the use of wood in construction, consider the construction materials derived from wood waste. Strictly speaking, this group of materials is more related to artificial materials (ICS), because when they are produced, a partial or complete change in the chemical composition of wood under the influence of chemical technology occurs. At the same time, these materials can be considered as an example of the lack of a clear boundary between natural and artificial materials used in construction. Such examples with a not quite clear interface between these types of materials are also encountered when considering stone and other materials.

In our country, an enormous volume (over 400 million m) of timber is annually harvested, which is mainly directed to the needs of construction. However, the more commercial wood is produced, the greater the waste is obtained from logging and processing of stemwood. Now wood waste reaches 140-150 million m per year, most of which is exported to a landfill or burned. Until recently, in the construction industry, up to 25% of the timber received from the cutting area was beneficially used. Currently, the volume of its use is often increased to 75-80%. Technological progress has mainly concerned the mechanized production of carpentry and fibreboard, wood-concrete (arbolite), particle boards, shields, etc. These products are anisotropic in properties, do not warp, do not dry out, and are used as semifinished products for the production of beautiful veneered doors, built-in furniture, , partitions, thermal insulation products and parts, wall blocks and panels (from the arbolite), parquet, roofing, etc.

Glued panels, boards and plates, panel parquet, door frames, roofing and plaster lathing, roofing tiles and shingles are manufactured from lumber scrap of lumber and woodworking; blanks for carpentry production, arbolite and wall blocks and panels made of it, wood-fiber and chipboard, etc. They successfully replace business wood. Very widely used in the construction of wood-fiber plates, 1 m of which replaces 2.5 m planed sawn timber. Plates are used for finishing walls, partitions, doorways, built-in furniture, kitchen furniture and other elements in residential, public and industrial buildings. Plates of chipboard are also in great demand among builders, used as structural and finishing materials. Especially often products made from wood waste are used as heat insulation material. A significant amount of wood lump waste, chips and chips, especially coniferous species, can be used in the production of roofing cardboard.

From sawdust and shavings, materials and products are made either on the basis of binders (sawdust, xylene, thermite, thermoporite, gypsum blocks, etc.), or without the use of special binders (ligno-carbohydrate plastics, vibrolyte, etc.).

In the production of sawdust conglomerates based on astringents, sand, gravel, mineralizers (liquid glass, lime milk, sodium fluoride solution, etc.) are introduced into the mixture. Cement, lime, gypsum, caustic magnesite, etc., are used as binders. Thus, for example, for the preparation of a xylolite mixture in the production of plates (for the device of floors), caustic magnesite is used, which is closed on an aqueous solution of magnesium chloride. In a one and a half volume (by volume) in relation to magnesite, add up to 8% moisture in the sawdust mixture, and if necessary to obtain a hard coating (rather than plastic), a small part of the quartz sand is added. In the so-called solid sawdust plates, resins or a mixture of resin with ammonia are introduced as a binder, and a carbamide resin with an admixture of hardener (Petrov's contact) is used in the production of sheet-shaped tarsolite with a thickness of 1.5 to 8 mm.

In the production of sawdust conglomerates without the introduction of any special binding agents in their composition, the ability of wood to separate its own adhesives during the hydrolytic cleavage of the ligno-carbohydrate complexes of cell walls and polysaccharides is taken into account. Technological regulations are characterized by drying and dosing of wood particles, molding and pressing on a pallet of the required thickness, hot pressing and cooling under pressure of the press. It is according to this scheme that lignocarbohydrate wood plastics are manufactured. The strength of such plastic is influenced by the size of wood particles: with their grinding, the strength of the plastic increases. The most important mode at the stage of hot pressing is carried out at a pressure of 1-5 MPa and a temperature of 160-170 ° C, followed by cooling of the press plates to 20 ° C. The rock of the original wood mixture is of importance. For these plastics, fir, larch, pine, birch and aspen are suitable. Finished products (plastics) are used as a structural and finishing material; In the technological period they are covered with veneer sheet. Similar in production are piezotermoplastics - plate or plate material made at high pressures and temperatures from wood waste, especially sawdust, without the addition of binders. There are two technological schemes for their production: without pre-treatment of wood waste and with the processing of waste (hydrolysis) of sawdust - hot water (or steam), sometimes with chemicals. According to the second method, high-quality plastic is obtained, for example, the tensile strength at static bending is up to 25-40 MPa, at tensile strength up to 20-25 MPa, at compression up to 60-80 MPa, heat conductivity 0.24 W/(mK) etc. Piezotermoplastics are used to cover the floors in place of parquet and door manufacture, as a finishing material, etc. A chip is produced from sawdust and fine shavings after treatment in a hammer mill and vibrating mill, molding and hot pressing. Plates from vibrolyte have sufficiently high quality indices: density 400-800 kg/m, ultimate strength at static bending 3-13 MPa, thermal conductivity 0,08-0,09 W/(m-K), etc. Vibratory is used for flooring of a black floor, the device of partitions, panel doors, the manufacture of built-in furniture, etc.

Materials and articles based on binders or without them are obtained from bark and branches. So, for example, with the use of gypsum binders get coral. To do this, the dried, crushed and sieved bark is loaded into the mixer, filled with solutions of an antiseptic (for example, xyliphenylanatriya) and an inhibitor (for example, casein, borax, mezdra glue). The mixture is combined with a gypsum binder, mixed until uniform and compacted in molds at a pressure of 0.03-0.04 MPa. Instead of gypsum binders, Portland cement and cement-sand mortar can also be used. Korolit is used as a heater for floors and walls.

Among other products made from bark and twigs with or without the addition of binders, it is necessary to take away insulation plates, plates from the whole bark, blockbars, etc. In the manufacture of insulating boards, the press-mass from crushed bark of spruce, hydrophobizer and fire retardant is treated with a binder in the form of a sulphite bard (a waste of cellulose production by a sulfite method), is molded and subjected to hot pressing. In slabs from the whole bark of spruce, fir or larch there is no any additionally introduced binder or adhesive. For their production, the bark is removed in a special way from the trunk, processed and glued into sheets by pressing. These plates have a length of up to 3 m, a width of 0.4-1.2 m and a thickness of up to 25 mm. They are used for covering walls, partitions, roofing (sometimes with a lime mortar coating). In the production of dry blocks, waste from logging is used - freshly chopped branches of pine, spruce, willow, fir, cedar, etc. Pressed block of branches is pulled in two places by wire with a diameter of 3 mm, and unevenness in the form of side knots is removed with a circular saw. The blocks are antiseptic, subjected to atmospheric drying to a humidity of 20-30%, used in frameless one-story construction, as well as for insulation. With an increase in the height of buildings they are used in combination with metal fittings with a diameter of 4-8 mm, laid at the level of the lintel, sills, etc. Dimensions of the blocks: constructive - 500x450x350 mm, insulating - 500x450x250 mm.

In addition to the above materials and products from wood waste, there is a large number of traditional organic heat-insulating and structural-heat-insulating materials that have been mastered by industry and widely used - cane slabs, peat slabs, etc.

Materials and products using wood waste, some of which were listed above, are, as a rule, typical representatives of building conglomerates obtained on artificial or natural (lignin, polysaccharide) binders. Undoubtedly, with optimal structures, they have a complex of the best properties, so their composition should be determined taking into account the previously described general laws (see Chapter 5). At the same time, on their example, some conventionality of the boundary is obvious when the building materials are divided into artificial and natural, especially with a conglomerate type of structure.

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