The physical and mechanical properties of lightweight constructional heat-insulating concrete (sawdust gypsum concrete) with high-strength gypsum binder, modified by food cotton microcrystalline cellulose and organic fillers of plant origin from the waste wood of coniferous and deciduous species in the form of cavitationly processed pine and birch sawdust have been studied. The dependence of the cavitation extraction time of water-soluble reducing substances (sugars) from sawdust on the strength of sawdust gypsum concrete is established. The changes in microstructure of the gypsum matrix, the mean density, bending tension strength and compression strength, the thermal conductivity coefficient of sawdust gypsum concrete on the basis of the cavitationly processed sawdust with the introduction of microcrystalline cellulose are analyzed. It is proven that microcrystalline cellulose compacts the space between the crystalline hydrates of calcium sulfate dihydrate in the gypsum matrix microstructure and improves the physical and mechanical properties of sawdust gypsum concrete.
The article describes the conditions for obtaining new thermal insulation materials from the waste of mechanical processing of soft hardwood wood. The recommendations for the production of new resource-saving technologies of gypsum-wood and chip-and-glue composites are justified, which makes it possible to dispose of waste from the processing of soft hardwood wood. It was found that the birch pulp extract, along with cellulose and lignin, contains d-erythrosis, which is easily washed out of the wood with water or a solution of "mineralizer" and gets into the cement dough, which leads to a slowdown in hardening and a decrease in compressive strength. It is shown that the existing technological processes for eliminating the negative influence of saccharides on the strength of wood aggregate composites are complex, requiring multi-stage treatment of the aggregate with various chemicals or long-term exposure. A method based on the use of binders that do not interact with extractable substances, such as gypsum or urea-formaldehyde glue, is proposed. By scanning electron microscopy, it was found that the structure of the gypsum-wood composite varies depending on the sequence of input components. The nature of the effect of microcrystalline cotton cellulose on the change in the physical and mechanical properties of the gypsum-particle composite using cavitation-treated sawdust was revealed and its optimal dosage was determined. The regression dependences of the influence of the consumption of wood chips and glue on the compressive strength of the chip-and-glue composite were obtained by the experimental planning method.
The properties and microstructure of wood-cement compositions (WCC) with microsilica (MS) additive for the manufacture of small-pieces wall products are studied. The extreme dependences of mean density, thermal conductivity and compressive strength on the content of microsilica additive are established. The mechanism of microsilica effect on wood-cement compositions is offered. Two interrelated factors (chemical and physical) could be distinguished at that. The first factor includes mainly the interaction of silicon dioxide with lime having released during hydration of calcium silicates, i.e. pozzolatic process. The second factor lies in the compaction of wood-cement compositions and the cement stone structure by means of cement hydration products and silica particles. It is established that introducing 20% of microsilica in the composition results in the maximum increase in ultimate compression strength (3 times). It can be explained not only by forming calcium hydrosilicates, uniformly and densely covering the wood aggregate, but by compacting effect of spherical microsilica inclusions, filling the space between the new cement stone formations and wood aggregate.
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