Structural and thermal insulation products based on vegetable raw materials

The author of the article addresses the issues of obtaining insulation products based on flax shives. The article suggests a systematization method for the flax shives based materials, which takes into account the principle of obtaining construction materials based on flax processing waste on various types of binders. It is based on the literature data and the existing research. The possibility of using flax shives as a large structure-forming aggregate of concrete is determined along with the composition and properties of organic aggregate - flax shives. The article presents the optimal ratios selection of flax and binding bonfires in the preparation of granular materials. The characteristics of granulated aggregates on the basis of flax shives are given. The manufacture of cob granules was carried out in two technological ways: on a complex binder and on mineral binders with “dusting” with portland cement. The the method involving the coating of granules with a cement shell was used to produce a granulated material with higher rates of adhesion to the hardened stone of mineral binders in the concrete composition. The technological parameters of the granulation process are determined for two technological methods.


Introduction
Increased requirements for thermal performance of enclosing structures, associated with energy and resource saving, lead to the need to find ways improving the thermal properties of manufactured wall materials. The effective direction of products' quality improving from lightweight concrete is the introduction of structure-forming additives directional: pore-forming, plasticizing, air-entraining, and others [1]. However, this method leads to high material costs. The use of organic raw materials in the form of wood, reeds, flax, straw, bark, peat, etc. shive is rational.

Relevance
The relevance of our study is due to the fact, that thermal insulation materials, based on plant materials, are characterized by high thermal performance, the problem of recycling plant shive is solved from an environmental point of view and at the same time there is an opportunity to obtain environmentally friendly building materials.
A substantial increase in flax fiber production in Russia is planned at the state level. Thus, an increase in the acreage occupied by flax to 221,540 hectares by 2030 is planned according to the department of the agro-industrial complex report. As a rule, shives in the form of spill are practically not used purposefully and are taken to the dump where they are burned or subjected to rotting  [2][3][4]. We consider the use flax shive as organic filler, which is a by-product from flax processing with sufficiently high heat insulating and shaping properties.
Analysis of literary sources showed that the production of some insulation products' types based on flax shive has been developed. Flax shive is used mainly only as a heat-insulating material in the form of plate insulation in the civil engineering. For sure, it is advisable to consider similar types of heatinsulating materials based on vegetable raw materials for a comparative evaluation of properties. The main components of thermal insulation products based on plant shive are a binder, organic filler, and various corrective additives (antiseptics and flame retardants) are used. Various resins, polyvinyl acetate emulsion, synthetic latexes and others are used as organic binders. Liquid glass, cement, gypsum, ash and others are used as mineral binders [5][6]. A variant of materials systematization from flax shive, which is based on the principle of obtaining construction materials according to the flax processing shive on various types of binders on the basis of literature data and developed research directions, is proposed. A significant range of materials based on flax shive is divided into three groups: mineral-based materials (liquid glass, cement, active ashes, etc.), organic (urea resins, polyvinyl acetate emulsion, etc.) and complex binders [7][8][9].
Materials based on mineral binders, depending on a binder type, can be flax-silicate, production technology, which provides for additional mixing, by introducing a foaming agent into the binder solution and then mixing the mixture in high-speed ones. Then the mixture enters the form and, an excess of the binder solution is removed from it by evacuating, after the molded products enter the heat treatment chamber. Plastic clays are used as a binder. The water demand of the molding mixture is 28-40%, depending on the composition, if the ratio of flax to clay shive is 2:1 by weight. The average density of flax silicate products is 320-350 kg/m3, compressive strength at 10% linear deformation is 0.29-0.36 MPa, thermal conductivity is 0.052 W / mK.
Flax magnesia materials are obtained on the basis of foamed magnesia binder and flax bonfires. The raw material mass is mixed at a low speed of a drum rotation for 10-15 minutes, after that, it is placed in special forms for 4-5 hours. Broken into pieces products are subjected to heat treatment for 5-6 hours at 110-1200С. Products based on magnesia binder are characterized by a low density of 345-360 kg/m3, sufficient bending strength of 0.3-0.5 MPa and thermal conductivity of 0.084-0.106 W/mK [10][11][12][13].
Flax-cement materials are made according to the following technology: grinding flax shive in order to obtain an optimal fractional composition of 0.5-3 mm, its processing, component dosage, mixture preparation, laying in forms and compaction, heat treatment of molded products, aging at positive temperatures [14]. At the same time, the moisture content of aggregate should be at least 30-40%, in order to prevent moisture collection by the flax shive and dewatering the contact zone of the material structure. Water in the mixture can be introduced in three ways: in the form of mixing water, with a lock or by introducing it into the mixture in the form of a chemical solution -a "mineralizer". The average density of the samples is 430-510 kg/m3, compressive strength at 10% linear strain of 0.58-0.75 MPa, thermal conductivity 0.125-0.154 W/mK. Phenol-formaldehyde and carbamide resins, polyvinyl acetate emulsion, polymeric binders are used as binders to obtain heat-insulating materials of the second group. Porous and granular products are extruded here [15].

Formatting of the research problem
The flax shive has the following specific properties: low density (110 ... 120 kg/m3), low thermal conductivity (0.037 ... 0.041 W/(m ° С)), low humidity swelling not exceeding 2%, significant lignin content in organic parts up to 46%. The use of flax shive as a large structure-forming aggregate of lightweight concrete is formulated as the purpose of our work, according to the analysis of heatinsulating products obtaining based on flax shive. In order to realize the intended goal, it is necessary to solve a number of tasks: to determine the composition and properties of organic aggregate -flax shive; to select optimal ratios of flax and bonding bonfires in the preparation of granular materials; optimize the technological parameters of the granulation process [16].

Methods and materials
During the research work, the composition and properties of the organic aggregate were determined. Flax shive is a by-product from flax processing and one of the most common agricultural shive. Flax stems break down during fiber extraction in the process of flaking and scutching, and the falling out woody parts form shive particles [17]. The sizes of these particles vary from 1 to 10 mm in length, the thickness is in the range of 0.3 ... 1 mm. The main share of flax production and processing (about 70%) falls in the Central and West Siberian regions. Elevated concentration of lignin in the flax shive was established to 44-46%, using infrared spectroscopy, confirmed by absorption bands in the IR spectrum at 1653 cm-1, as well as bands in the 1540-1510 sm-1 area, characteristic of rings vibrations [18].

The results of experimental studies
In the process of the granulate filler receiving, a fraction of flax shive no more than 2.5 mm and a bulk density of 125-130 kg/m3 was used. In order to achieve optimum values of bulk density, strength and granulometric composition of granulated materials, compositions were prepared using mineral (Portland cement, liquid glass) and organic (PVA, latex) binders. Granulation of the studied compositions was carried out on a laboratory plate granulator, with a different angle (25-450) of plate inclination and granulation time of 2-12 minutes. The original components were taken in the ratio (%, wt) of flax shive: binder 1: (1-1,15). The granules were prepared using 2 technological methods: 1 -on a complex binder, 2 -on mineral binders with "dusting" with Portland cement. The application of the method, involving the coating of granules with a cement shell is due to granulated material production with higher rates of adhesion to the hardened stone of mineral binders in concrete composition. The results of the experiment are given in 1 table. Crushed flax shive show a good pelletizing ability, the outcome of the 10-15 mm fraction reaches 81%, therefore this fraction is optimal and characterizes the granularity of the tested compounds. The maximum indicators of granularity are shown by flax shive, based on polyvinyl acetate emulsion and liquid glass, the outcome of fractions 10-15 mm in size is 62% and 81% for granules based on liquid glass with a cement shell [19].
The following sequence of technological operations was used in the preparation of granules on the complex binder: moistening flax shive was adding liquid glass and an aqueous polymer solution (latex or PVA) -granulation -hardening -fractionation. Granules using mineral binders were prepared according to the 2nd technological method: moistening flax shive -adding liquid glass -granulationdusting with cement powder -hardening -fractionation. Characteristics of granular materials are given in table. 2. Tests of raw granules were carried out according to the guidelines for testing ashes of TPPs for agloporite gravel production [20].
The bulk density of various fractions aggregate and compositions is 290-345 kg/m3, compressive strength is 0.5-2.6 MPa.
The effect of the mixture moisture on pelletizing was studied. For all compositions, the first signs of pelletization begin with their moisture of 22-25%. The optimum moisture content of mixtures based on flax fires is 28-33% for the 1st mode of production, and 35-40% for the second (figure 1). In order to obtain a filler of a specific particle size distribution, the granulation process is influenced not only by material indicators (mixture composition, moisture content), but also technological parameters, such as granulation time and tilt angle of plate granulator. The optimal time of maximum mixture pelletization according to the 1st technological method is 3-4 minutes; with the 2nd method is about 5-7 minutes. In all cases, the pelletizing time is reduced by 12-15%, using granulated mixture heated at a temperature of 500 ° C. The device of laboratory granulator allows you to change the angle of a plate aggregator inclination from 25 to 50 °.
The optimum tilt angle of the plate was determined, depending on the indicators of bulk density, raw strength and percentage outcome of 10-15 mm granules fraction [21]. The determination results of the raw granules' bulk density, depending on the angle of a plate's inclination, show that compounds 1-3 have the lowest bulk density, if the angle of the plate granulator inclination is 35-40 °. With a smaller and larger angle there is an increased of granulator's small fractions outcome (less than 10 mm). Less sensitive to the process of granulation in a changing process of the plate's angle inclination is a mixture with flax shive and liquid glass. Therefore, the angle of the plate-granulator inclination may be as low as 250 in the process of granules receiving according to the 2nd method.
The technology of preparing granular aggregates involves two main operations: granulation of the initial mixture and the implementation of the hardening process. Between these operations, the process of transportation and reloading (pouring) of molded raw granules takes place. In this regard, a mandatory criterion for the raw granules' properties is their compressive strength. Together with an increase in the angle of the plate granulator inclination to 300, there is a short-term decrease in the compressive strength of raw granules of 10-15 mm in size, the values of strength increase if the angle of inclination increase.
A "passive" formation of granules occurs at smaller angles of the plate inclination and they do not have time to acquire a sufficiently dense and durable structure in the marked range of granulation time. With an increase in the inclination angle of more than 40 °, the fraction outcome increases to less than 10 mm. The strength of raw granules molded from various mixtures during compression varies from 0.09 to 3 MPa.
The hardening of the granules was carried out according to the regime adopted for extruded products.

Results
The technology to produce granulated aggregate for concrete based on flax shive was developed. 2 methods of granulating materials based on crushed flax shives were proposed, depending on the type of binder and preparation technology: single-stage and two-stage. The use of two-stage technology in the preparation of granules is due to the production of granulated material with higher rates of adhesion to hardened stone mineral binders in the composition of concrete. The mixture optimum moisture content after granulation with the maximum fraction outcome of 10-15 mm was established: for granules with a cement shell 35-40%; for granules without shell 28-33%. The technological parameters of costogranule production were determined: for mixtures on a complex binder with the inclination angle of the granulator 35-400, granulation time 3-4 min and for mixtures on mineral binders the angle of inclination was 250, granulation time was 5-7 min Concrete with an average density of 700-800 kg/m3 and compressive strength of 3.5-4.5 MPa was obtained in the process of quartz sand and large granulated aggregates using, based on flax shive as fine aggregate.
It is recommended to use granulated aggregate based on flax shive in concretes with increased noise absorbing and heat insulating ability, as a structural material for erecting internal walls and partitions, and also as a heat insulating backfill.