RU2746720C2 - Method for producing wood concrete - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to a method for producing construction composite materials of heat-insulating and structural wood concrete. The method includes low-frequency ultrasonic treatment of a wood filler followed by mixing with a binding Portland concrete M500 solution and mineralizer – aluminum sulfate, shaping, dismantling and hardening in natural conditions. As a wood filler, a fractional mixture of sawdust and woodchip is used, consisting of 4 volume fractions of woodchip and 1 volume fraction of sawdust. At the first stage of producing wood concrete, the mixture of sawdust and woodchip is subject to sounding in water in an ultrasonic contact-type reactor, the walls of which serve as emitters, which provides a temperature increase of up to 70-80ºC with a sounding time of 20-30 minutes due to cavitation with simultaneous acidification of the solution to a pH value of 5.1.

EFFECT: increased efficiency of extracting sugar fractions that prevent the processes of setting and structure formation of wood concrete by 1.5-2 times, which reduces the time of setting the solution mixture by up to 50% and improves the physical and mathematical characteristics of wood concrete.

1 cl, 1 tbl, 4 dwg

Description

The invention relates to a method for the production of building composite materials, heat-insulating and structural wood concrete, consisting of a mineral binder cement, pre-treated wood fillers (different types of medium and fine wood waste) and an aluminum sulfate mineralizer.

A known method of manufacturing wood concrete, which includes the stage of pretreatment of wood filler - soaking in water for 7-8 days at a temperature of 15-20 ° C with a ratio of wood filler and water by weight 1: 9; followed by partial removal of unbound water. Then, with constant stirring, the filler is introduced into a mixture of cement, calcium chloride, gypsum and lignosulfonate, which at the next stage is formed and fed to the curing site. At the same time, the composition of the raw mixture after molding is observed, which includes: wood filler - 52-58%; cement - 23-27%, gypsum 0.5-0.9%, lignosulfonate 0.45-0.75%, calcium chloride 0.75-7.75%, water 16.6% (RU No. 2329999, IPC С04В 40/00, С04В 28/04, С04В 18/26, С04В 111/20, publ. 27.07.2008).

The disadvantage of this method is the long processing time of the wood filler, which requires additional production space and reduces the efficiency of the process. In this case, wood concrete of class B0.75 is obtained - an insulating material.

There is another method of processing wood filler with a solution of iron (III) chloride mineralizer without preliminary soaking in water, which provides for a one-stage processing of the filler with simultaneous preparation of a raw mixture to obtain wood concrete. The wood filler is treated with 2/3 parts of the prepared solution with an iron chloride mineralizer, then cement is added with constant stirring, and then 1/3 of the remaining mineralizer solution is added to the arbolite mixture and mixed until a homogeneous mass is obtained. The raw mixture has the following composition (weight): Portland cement 27.0-33.0%; wood filler 30.0-42.0%; ferric chloride - 2.3-2.9%; water - 28.7-36.7% (RU No. 2153478, IPC С04В 40/00, С04В 18/26, С04В 111/20, publ. 07/27/2000).

The disadvantage of this method is the allocation of water-soluble fractions of sugars in the arbolite mixture, which sharply reduces the rate of setting processes, the structure formation of arbolite is disturbed, its strength decreases and arbolite with an anisotropic structure is obtained.

A known method of manufacturing products from composite materials - wood concrete, which includes electrical processing of wood particles in a plasma-forming gas flow, in a discharge chamber with a high-frequency generator power of 200-600 W and a discharge equal to 100-130 Pa, for 250-380 seconds. Air is used as the plasma-forming gas, the flow rate of which is 0.08-0.12 g / s. After processing, wood particles are introduced into the cement with constant stirring, the arbolite mixture is subjected to molding and heat treatment, which ensures the setting processes (RU No. 2345886, IPC B27N 3/14, publ. 10.02.2009).

The disadvantage of this technical solution is the high energy costs for the processing of wood filler in the discharge chamber and for the heat treatment of the wood concrete mixture, as well as the separation of sugar fractions into cement. In addition, due to heat treatment, an inhomogeneous structure is formed in terms of physical and mechanical properties, which reduces the quality of the composite.

The closest technical solution to the invention is a method of making wood concrete, which includes a preliminary stage of processing wood filler with 4% sodium hydroxide solution. After heating in an ultrasonic bath at a vibration frequency of 30-40 kHz for 20-30 minutes. Further, after draining the sodium hydroxide solution, the wood filler is washed with water by irrigation in the chamber, an arbolite mixture is prepared, consisting of wood filler, cement, sand in a mixer, and is molded. After that, a textured layer is formed by applying fine-grained concrete to the surface of the wood concrete. After compaction on a press and hydrothermal treatment, the stage of holding in stacks in a closed warehouse is envisaged. In this case, the maximum compressive strength of the product samples is 6.69 MPa; tensile strength 7.32 MPa (RU No. 2620696, IPC С04В 40/00, С04В 18/26, publ. 05/29/2017).

The disadvantage of the known solution is the treatment with sodium hydroxide solution, which also provides for intensive washing with water of the wood filler, because in case of insufficient rinsing with water, alkali impurities remain, which impede the setting processes. This method is also energy intensive. In addition, quartz sand is introduced into the mixture, which increases the brittleness, and in order to increase the mechanical strength, a textured layer is applied. This method also includes an additional heat treatment step to increase the setting speed.

The technical result of the proposed invention is to increase the efficiency of extraction of sugary fractions - hemicellulose, which prevent the processes of setting and structure formation of wood concrete, by 1.5-2 times, which reduces the setting time of the mortar mixture to 50% and changes the physical and mechanical characteristics of wood concrete: the density of the obtained samples 700-850 kg / m ³ , prismatic strength 2.62 MPa, which corresponds to the strength class B2.5. Also, the thermal conductivity coefficient decreases by 27%, water absorption decreases to 15-20% instead of 60-65%, frost resistance cycles increase by 1.5-2 times. Due to the introduction of sawdust into the fractional composition of the wood filler, elasticity increases and fragility decreases.

The technical objective of the present invention is to simplify the technological scheme of obtaining arbolite by eliminating the stages of treatment with an alkali solution, heat treatment, excluding quartz sand from the arbolite mixture, introducing an aluminum sulfate mineralizer and adding sawdust to the wood filler. These technological changes provide an increase in physical and mechanical characteristics, which make it possible to use wood concrete as a structural material.

The technical result is achieved by the fact that in the ultrasonic method for the manufacture of wood concrete, hydrolysis and extraction of low molecular weight fractions from wood filler is carried out in water in a low-frequency ultrasonic reactor of the contact type. Cavitation phenomena with a sonication time of 20-30 minutes, a cavitation number of 600-800, at an ultrasound frequency of 20-40 kHz provide an increase in temperature to 70-80 ° C and a simultaneous acidification of the medium to a pH value of 5.1. Establishing the dependence of the temperature change on the sounding time, the pH value of the medium and the extraction efficiency on the sounding time allows us to simulate the technological conditions and the change in the physical and mechanical characteristics of wood concrete. These conditions, with simultaneous mechanical action on the wood filler (a mixture of chips and sawdust) due to cavitation, increase the rate of hydrolysis and the extraction of low molecular weight sugary fractions into the solution, make it possible to achieve the degree of extraction of sugary fractions up to 0.325% of the weight of wood filler. The obtained extract after sonication of wood is recommended to be used as a substrate for growing fodder yeast strains U361 and U967, adapted to lignin impurities.

The invention is illustrated graphically (Fig. 1-4). FIG. 1 shows a diagram of the technological process for producing wood concrete, where 1 is a bunker, 2 is an ultrasonic reactor of a contact type, 3 is a sump, 4 is a mixer for preparing a mixture of Portland cement and a mineralizer, 5 is a mixer for preparing a wood concrete mixture, 6 is a pressing area, 7 is a site. stripping, 8 - finished goods warehouse. Figure 2 shows the dependence of the extraction efficiency of the sugary fractions on the sonication time. Figure 3 shows the dependence of the change in the pH of the medium on the sonication time. Figure 4 shows the dependence of the temperature change on the sounding time.

The technological process for obtaining wood concrete is as follows. Wood waste enters the bunker 1, subject to the volumetric ratio between chips and sawdust 4: 1. An increase in the proportion of sawdust in a mixture of wood chips - wood concrete leads to an increase in the wood concrete coefficient, as well as to an increase in the density of the composite; a decrease in the proportion increases the fragility of wood concrete, reduces the prismatic strength. The resulting mixture enters the ultrasonic reactor 2, where the wood filler is processed by ultrasound and the reducing substances are extracted from the wood, while observing the volumetric ratio between wood filler and water of 1: 8. The processing time is 20-30 minutes, the number of cavitation is 600-800, the temperature of the medium is 70-80 ° C, the pH of the medium is 5.1. The resulting extract is poured into a settling tank 3. At the same time, a solution of Portland cement M500 and a mineralizer of aluminum sulfate is prepared in mixer 4, which is fed into mixer 5 to obtain an arbolite mixture. Also, the processed wood aggregate from the ultrasonic reactor is fed to the mixer 5. After mixing wood filler and Portland cement mortar, the resulting wood concrete mixture, which is fed to the pressing section (molding) 6. The pressing takes place under the action of a vibrating press. After molding, the wood concrete is kept in molds for 2 days, after the time has elapsed, the wood concrete goes to the stripping section 7 of the wood concrete block, then it is sent for further aging for 20 days to the finished product warehouse 8 (Fig. 1).

At the first stage, the treatment of a mixture of chips and sawdust of fractional composition in volume fractions: 1 volume fraction of sawdust and 4 volume fractions of chips in an ultrasonic reactor with water without special water treatment. The ratio of solid aggregate and water is 1: 8, the processing time is 25 minutes, the number of cavitation is 600-800 and the pH value is 5.1. The next stages include mixing wood filler with a mineral component, forming, stripping, hardening in natural conditions.

According to the specified scheme, wood concrete samples were obtained and the optimal technological conditions were experimentally determined - the sounding time was 20-30 minutes. This sounding time provides an increase in the temperature of the treated medium up to 70-80 ° С; acidifying the solution to a pH value of 5.1.

With an increase in the sonication time, the concentration of the extracted reducing sugars increases.

The experimentally established dependence of the change in the temperature of the medium on the sonication time and the dependence of the change in the pH of the solution medium on the sonication time make it possible to simulate the technological process.

The processes of extracting sugary fractions with maximum efficiency occur in the temperature range 70-80 ° C, which provides for a sonication time of 20-30 minutes. With a decrease in the sonication time, the extraction efficiency of the sugary fractions decreases to 2.4%; an increase in the sonication time for more than 30 minutes does not cause an increase in the efficiency of washing out the sugary fractions, since low molecular weight sugary fractions readily soluble in water are washed out during the specified period of time, which are inhibitors of the setting processes of the arbolite mixture. The cellulose remaining after washing does not dissolve in water, does not hydrolyze and loses its inhibitory functions, and is introduced as a filler.

These technological conditions make it possible to obtain wood concrete with improved characteristics: strength - 2.62 MPa, density 700-850 kg / m ³ , thermal conductivity coefficient 0.12 W / mK, frost resistance F50 and water absorption 25%.

At the production site, samples of wood concrete were made and its properties were determined (thermal conductivity was determined using an ITS-1 device, strength - a P-50 hydraulic press, setting speed - a Vic's device, water absorption - by a gravimetric method, toxicity - using a BIOLAT device).

Water is added to this mixture at the optimum volumetric ratio of the mixture of wood filler after sonication and water: 1: 8.

With an increase in the proportion of wood filler, a decrease in the number of cavitation is not observed due to an increase in the viscosity of the solution, a decrease in temperature, and a decrease in the extraction efficiency. With an increase in the volume fraction of water above the specified value, no change in the extraction efficiency of the sugary fractions is observed. Also, the obtained extract, which can be used as a basis for the production of fodder yeast, requires an additional concentration step by evaporation; the extract of the sugary fractions is more diluted and additional concentration is required when it is used as a starting solution for the cultivation of fodder yeast.

The efficiency of extraction of sugary fractions was determined according to the method of GOST 19222-84.

After holding the samples for 20 days, the characteristics of the wood concrete were determined, presented in Table 1.

The method provides a reduction in the costs of consumed energy and water by 36 and 69%, respectively, eliminates the cost of chemical reagents (sodium hydroxide), the process of irrigation with sodium hydroxide, the cost of washing from sodium hydroxide with water, facing and heat treatment. As a result of processing wood filler, an aqueous solution is also formed containing sugar fractions up to 1.37%, which is used as a basis for growing fodder yeast, strains U361 and U967, adapted to this composition.

The main components of wood are cellulose, lignin and hemicellulose. Low molecular weight fractions of hemicellulose and lignin - disaccharides and monosaccharides, which contain free aldehyde groups, prevent the setting of the wood concrete mixture - cement - wood filler - aluminum sulfate, which results in an increase in the setting time, violation of the structure formation of wood concrete, and a change in the physical and chemical properties the quality of wood concrete and its purpose - density, prismatic strength, thermal conductivity. Therefore, any method for the production of wood concrete includes the stage of processing the wood filler to extract the sugary fractions using different technologies.

Thus, in contrast to the known solution, the presented one has a number of advantages: the technological scheme for obtaining wood concrete is simplified, the setting time is reduced by up to 50%. The stages of preparation of an alkaline solution of sodium hydroxide, irrigation of wood filler with a solution of sodium hydroxide and subsequent washing from alkali residues, which also reduces the speed of the setting processes of wood concrete and excludes the stage of facing, heat treatment, and the washing process can be modeled according to the established technological dependencies are excluded.

The claimed method for producing a composite building material - wood concrete has the following advantages:

1. Exclusion from the technological process of the stages of washing from alkali, irrigation, heat treatment and lining, by replacing a 4% solution of alkali with water without special water treatment for washing wood aggregate having the following fractional composition: one volume fraction of sawdust 4 volume fractions of chips and 8 parts by volume of water.

2. By reducing the setting time by 50% and structure formation, there is no need to use large production areas, the energy consumption of wood filler preparation processes, water consumption is reduced, and the stage of liquid waste disposal after washing the wood filler is eliminated.

3. The inclusion of sawdust in the fractional composition increases the elasticity of wood concrete, reduces its fragility, thermal conductivity, increases the prismatic strength, increases the adhesion between the components of the material and changes the designation class from heat-insulating to structural.

4. There is a decrease in the toxicity class of wood concrete, which allows it to be used in civil and industrial construction.

5. The obtained sugary fractions containing residues of disaccharides, monosaccharides, soluble low molecular weight polysaccharides, impurities of lignin and hemicellulose are recommended to be used as a substrate for growing fodder yeast strains adapted to impurities of lignin U361 and U967.

6. The established relationships between the sonication time, the number of cavitation, the temperature change and the pH value of the medium make it possible to regulate the process of washing the sugary fractions from the wood filler.

Claims (1)

A method for producing wood concrete, including low-frequency ultrasonic processing of wood filler, followed by mixing with a binder solution - Portland cement M500 - and a mineralizer - aluminum sulfate, molding, stripping and hardening in natural conditions, characterized in that a fractional mixture of sawdust and chips is used as wood filler, consisting of 4 volume fractions of wood chips and 1 volume fraction of sawdust, which at the first stage of obtaining arbolite is subjected to sonication in water in a contact-type ultrasonic reactor, the walls of which serve as emitters, which provides, with a sonication time of 20-30 minutes, an increase in temperature to 70-80 ° C due to cavitation with simultaneous acidification of the solution to a pH value of 5.1.

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