MANUFACTURING ARBOLITIC BUILDING PRODUCTS USING SOLAR ENERGY

Natural raw materials can be rationally utilized with industrial and agricultural waste for some materials to be produced depending on the combination of their strength, thermal conductivity and other properties [1-2]. Such materials it is may include arbolite, intended for residence and public walling. Arbolite is known to be an effective heat insulating material. Low-density arbolite-made products are characterized by excellent construction, physical, technical and hygienic properties. They are drillable, cuttable and overcoatable. Arbolite is a durable ecological material that has high heat-saving properties. Its thermal conductivity is 0.08-0.17 W/(mK). This figure 2.5-3.5 times exceeds the LECA thermal conductivity and 4-5 times – the brick thermal conductivity. Twice less utilities are required for heating the space with 30 cm walls of thick arbolite than for heating the space with 75 cm brick walls (three bricks separating the street and the room).


Figure 2: Solar System with Circulating Intermediate Coolant -Pilot Unit
Thus, developing both is the rational option. In all technologically advanced countries (France, Germany, the USA, Sweden, etc.), the share of prefabricated construction is 40%. It is slightly lower (20%) only in the seismic regions, such as Japan [8][9][10][11][12][13][14]. In the Republic of Kazakhstan there is a good industrial base for the prefabricated construction that was developed during the Soviet period and continues to develop.
At the same time, precast concrete industry is a major heat consumer, while the heat treatment is the most energy-consuming technological process (over 70% of heat goes for treatment). In the Republic of Kazakhstan, southern regions are characterized by a dry hot climate. At this point, solar heat treatment is the most rational method to be applied for reducing the energy consumption during the prefabricated reinforced concrete production. The following effective methods have been recently introduced for treating the reinforced concrete products with heat using the solar energy in the open workshops and on the solar grounds. Solar Treatment is combined with the Light Heat-Insulating Covers (including solar chambers with heat-accumulating elements). There has been also introduce the solar heating method implying for the application of special membrane forming compounds. As the mixed methods of solar heat treatment appeared, the solar energy could be used for treating the concrete and reinforced concrete products with heat all year round. At this point, prefabricated reinforced concrete production will be less energy consuming.
Factories begin to learn the solar heat treatment methods for manufacturing not only standard concrete, but also the arbolitic building products. The variety of solar heat treatment methods allows choosing the optimal and cost-efficient method. Solar heating technology, applied for the production of various types of concrete, raises the energy utilization ratio through the internal source (heat evolution) at the stage of concrete hardening acceleration. At the same time, soft heating and cooling modes contribute to the high-quality product manufacture. Methods of treating concrete with heat using solar energy should take a proper cell in the industry. Various research results are being currently commercialized. Conducted studies have shown solar energy is a beneficial method for treating concrete with heat. The purpose of this research is to design and introduce the cost-efficient and environmentally friendly technologies and methods of arbolitic building products manufacture with product hardening intensification, driven by the solar energy utilization.

METHODS
We have designed some methods for mixed solar heat treatment of arbolites in the workshops and on the solar grounds through the solar systems with a circulating intermediate coolant. The method is to manufacture high-quality products year-round by utilizing the solar energy in the autumn-spring and winter periods using solar systems with a circulating intermediate coolant, as well as traditional types of energy in case of zero solar energy accumulated. At this point, products go through the summer heat treatment (HT) at the solar power ground. In the autumnspring-winter periods, when the solar radiation comes down to near zero rates, a year-round solar system with an intermediate coolant is introduced to the process. Solar heat treatment is carried out under the light cover at soft modes with the chamber temperature max fixed as 700. The product rise temperature (rise time: 4-7 hours) increases at the isothermal heating time of 6-7 hours. The product cools down to 35 0 С.
Since the chamber bottom is filled with water, the climate inside the chamber is 100% humid. The 24-hour concrete strength is 50-70% R28. This method of solar heat treatment will provide a year-round heat treatment with the possibility of saving nature and 50-100% of traditional fuels, as well as manufacturing high-quality products. Solar HT method, intended for application through a solar system with an intermediate coolant, was designed for arbolitic building products (Innovation patent No. 28207 Heat Treatment Method for Arbolitic Building Products published by Kazpatent on February 19, 2014). At the moment, heat treatment issue, put forward in relation to almost every type of concrete (including light concrete) and implying for non-traditional energy (solar energy) utilization, is becoming more relevant. The new solar heat treatment charts, designed for arbolitic products and intended for application in the dry hot environment of the Kyzylorda Region (Republic of Kazakhstan) will allow saving nature (no emissions from fuel burning) and 50-100% of traditional fuels, as well as manufacturing high-quality products at low cost. The method is to manufacture the high-quality concrete products year-round, utilizing solar energy at max with the year-round solar systems in the autumnspring and winter seasons (Kazpatent No. 31795 Solar Chamber for Heat Treatment of Concrete Products; Bulletin No. 18 dated December 30, 16). At this point, light solar chamber undergoes heat treatment on the solar grounds next to the solar system in summer. In the autumn-springwinter periods and in cloudy weather, additional energy sources will compensate the lack of solar energy. In the case when the light chamber is on use with the solar system in the autumn-winter-spring periods, the lid is advisable to place at the angle of 35 0 C.
Soft heat treatment is carried out at the max temperature of no more than 70 0 C in a light chamber: temperature rise time is 5-7 hours, conditional isothermal holding time is 5-7 hours, cooling-down temperature is 35-50 0 С. The humid hardening environment is created by wet tarpaulin covering the products. Concrete strength reaches 50-70% R28 at 24-hour age. The mixed type of solar heat treatment in light solar chambers, intended for application under zero solar radiation, allowed manufacturing high-quality products with high physical and technical characteristics. This method of heat treatment will contribute to a yearround treatment and high-quality manufacture and will allow saving nature and almost 100% of traditional fuel.  The arbolite is treated with heat in a solar chamber to get high-quality products year-round using solar energy in combination with additional energy sources. At this point, light solar chamber coated with a film-former undergoes heat treatment in summer and autumnspring periods, namely -7-8 months a year at soft modes with the temperature rising to 40 °C during 4-5 hours (isothermal holding time: 5-7 hours; cooling-down temperature: 20 °C). Film-formers and light cover allow overcoming the loss of concrete moisture and carrying out the cement hydration to reach the maximum possible strength of the 24-hours age concrete -50-70% R28. The conducted research does not allow recommend the intensified modes of heat treatment. The attempt to steam the arbolite as ordinary concrete leads to strength reduction, since steaming sparks the increase in internal stress due to cubic deformations of the filler that break the integrity of the material structure. At the same time, wood filler releases more sugar, poisoning the cement.
The best results were obtained at the soft low-temperature treatment: heat temperature -40-50 °C; relative humidity -80%. At this mode, arbolite acquires the stripping strength after 18-20 hours. However, its strength does not exceed 25.40% of the brand product strength, while the moisture content remains within 30-35%. Products should be also indoor stored at 16-18 ° C for at least 7-14 days for the strength to be improved and the moisture content to be reduced to standard values. After that, products can be sent to storage with any temperature-humidity conditions (natural storage without humidification). Product hardening is an important technological process in the arbolite production, so it is important to study the hardening process and the choice of optimal acceleration methods [3][4][15][16][17][18]. In any case, arbolite should be treated with heat at 40 °C and 50-60% humidity to get the process to be effective. The temperature rise above 40 °C leads to a decrease in the product strength due to stress-strain properties of wood and other cellulosecontaining fillers.
In the case of arbolitic products, heat treatment mode should provide not only the required transport and design strength, but also the handling moisture content in products that would not exceed the target value. The moisture content can be reduced if products are treated with heat in conditions conducive to moisture evaporation from the arbolite. Such heating should be carried out at a temperature of no more than 40 °C in chambers equipped with thermoelectric heaters (TEHs), heating devices, infrared heating elements or gas burners with additional ventilation installed. No heat treatment is allowed in saturated steam or steam-air medium, as well as on thermal trays. Composition of a concrete mixture, based on portland cement binders, is selected with regard to target concrete class and grade in accordance with the current regulatory documents. We have also took into account the experience of previous developments.
There were studied the strength characteristics of arbolite hardened in a solar chamber [19]. The arbolite composition was selected by measurement, based on the manufacturing conditions fixed for a heat insulating material B0.35-B3.5 with an average density of 450-700 kg/m3. At the end of electric heat treatment, each composition was adjusted with regard to temperature and dilution factors affecting the arbolite structure formation. The compressive strength of 15 Grade Arbolite, based on rice husks, reaches 1.61 MPa at hardening in the solar chamber. Hot and dry weather is a serious problem for concrete technology, as it sparks many negative consequences. Therefore, destructive processes that occur during the concrete shrinkage, sparked by intensive dehydration in dry weather, can be frozen by efficient concrete care.

Arbolite
In the course of experimental research, we have manufactured arbolite according to the GOST 19222-84. As raw materials, we have used the portland cement, lime, ash collected at the Kyzylorda Combine Heat and Power Plant, organic plant-based filler (hogged chips) and agricultural waste (shredded rice straw, cotton plants, bulrush and rice husks). The blown sand was used as a mineral additive, while the fluid glass was used as a chemical additive. We have used the collected ash as an active mineral additive, according to the Building codes and regulations.

Materials and Methods of the Experiment
The powdered mixture of cement and rice husk undergone the X-ray diffraction at the room temperature with a diffractometer. An X-ray tube used for the analysis had an accelerating voltage of 30 kV at the current of 10 mA. The phase analysis was carried out in a semiautomatic mode using a PDF database containing 400 candidates. The most closely resembling thereof were selected in manual way.

RESULTS
The X-ray scattering spectra (diffraction pattern) are introduced for both groups of samples (Figures 6 and 8; Tables 4 and 5). The pattern illustrates the phase components as color segments, indicating their shares in percentages. Numbers 1 and 2 indicate the Gaussian approximations made with a special program. The calculated curve is marked with a dark blue line. The phase concrete composition of samples 1 and 2 is the same, only the concrete factor is different. The morphology of samples 1 and 2 is a key to understanding the hardening mechanisms of concrete made with rice husks and hardened with/without a film. In concrete with a film, rice husk surface is smooth without significant defects, and hence, with no crystal formation centers (Figure 7). The microphotographs of concrete, mixed with rice husks and hardened without a film, reveals a multiple defect formation -pores and cracks became filled with crystallizing agents. This is most likely to cause the strengthening of the adhesion bond between the husk surface and the structure-forming substrate that forms the concrete nanostructure, even if the cement moves far from the rice husk surface (Figure 9). Thus, full-scale structural researches on concrete composites allow us to substantiate the application of the film-based hardening method that improves the adhesion relations between the concrete nanocrystals.

Numerical Simulation of Solar Heat Treatment, Carried Out in Relation to Arbolitic Building Products
The solution of technological problems, related to the solar heat treatment of arbolitic building products, requires the temperature field and the hardening kinetics of a product, shaped in a metal die, to be simulated for the case of mixed convective and radiative heat treatment [16,19]. Let us consider the two-dimensional numerical simulation technique [20]. Nonlinear parabolic equations serve as the basis for many mathematical models. The nonlinear heat conduction (NLHC) equation is often applied in line with the basic conservation laws. The boundary value problems for the nonlinear heat conduction equation are of current interest. The NLHC equation differs from the linear one at the point, when the heat conduction coefficient (HCC) turns to be dependent on temperature.
Thus, many methods for solving the problems of mathematical physics cannot be applied to solve the nonlinear equation. Despite a lot of researching on the processes of nonlinear heat conduction, there are still no analytical solutions.
The mathematical model, where the temperature field is described for the arbolitic block by a two-dimensional NLHC equation with variable constants and heat sources that takes into account the exothermic heat release of cast product, is as follows: (1) ∂t(x, y x C The arbolite structure analysis, conducted after the solar heat treatment, has revealed that the phase chemical composition of the new growth crystals does not differ from the cement stone composition, formed under normal conditions. This proves that their quality is good.
The out-the-chamber heat effect is given by the combined boundary conditions of the second and third kind: ∂t(x, y + = ∂ (5) Die-Product system temperature at the beginning: Equations (1-6) do not have an analytical solution. Therefore, this system was integrated by the finite-difference method [21]. The algorithm for computer-based calculation of the temperature field was built by means of a one-dimensional numerical solution of multidimensional heat conduction equations. The original equations undergone a two-direction (X and Y) approximation according to the two-level conservative schemes on irregular grid.
In the context of one-dimensional method applied to a grid with 0.5λ spacing, original problem of temperature field calculation will be: λ( ) ∂ ) x t(x, y x, y air верт λ( ) Original equations (7)(8)(9)(10)(11)(12)(13) were approximated according to two-level conservative difference schemes, and then solved by sweeping along the rows and columns [22][23]. The hardening product strength and exothermic heat release were calculated according to the procedure, described in [17][18]. The algorithm for solving a problem, based on the difference approximation of original differential equations, was built in the FORTRAN IV program, debugged on an EC-1035 computer [24][25][26]. Calculation results were printed as graphs of temperature changes and strength growth at specified control points.

DISCUSSIONS
The conducted researches on arbolite do not allow recommending traditional intensified modes of heat treatment [19,27]. The attempt to steam the arbolite as ordinary concrete leads to strength reduction, since steaming sparks the increase in internal stress due to cubic deformations of the filler that break the integrity of the material structure. At the same time, wood filler releases more sugar, poisoning the cement. The best results were obtained at the soft lowtemperature treatment: heat temperature -40-50 °C; relative humidity -80%. At this mode, arbolite acquires the stripping strength after 18-20 hours. However, its strength does not exceed 25.40% of the brand product strength, while the moisture content remains within 30-35%. Products should be also indoor stored at 16-18 ° C for at least 7-14 days for the strength to be improved and the moisture content to be reduced to standard values. After that, products can be sent to storage with any temperature-humidity conditions (natural storage without humidification).
We have found that heat treatment of arbolite using solar energy will be way more effective at 40 °C and 50-60% humidity. The temperature rise above 40 °C leads to a decrease in the product strength due to stress-strain properties of wood and other cellulosecontaining fillers. We have analyzed the tensile strength and compressive strength of arbolites treated with solar heat. It turned out that in a dry hot climate, the strength of selected arbolites is directly proportional to the amount of WDFF (water-dispersible film formers) addedd: the lower is that amount the higher is the strength. formation. At the research end, we have determined the relationship between the time of solar energy intake and the arbolite strength growth, the solar energy effect on the temperature fields of products with different sizes and surface areas, treated with solar heat. We have also determined the characteristic features of treated arbolite structure and the most important qualities of arbolites that were alike the concrete treated with solar heat under normal conditions. We have designed some new types of light solar chamber technology, intended for application with film formers and in combination with solar systems with an intermediate coolant.

CONCLUSION
The transition from traditional methods of heat treatment to mixed solar heat treatment with solar energy utilization will save the manufacturer some arbolite production costs, namely -2237.7 tenge/m3 (USD 6.84). Therefore, our mixed solar heat treatment technology, designed for manufacturing the arbolitic building products using film formers, allows stepping back from traditional steam heating for 5-6 warm months in areas with a hot climate. In the cold season, however, mixed technology allows saving up to 70-100 kg of equivalent fuel and 0.6 t of water per one m3 of product, and thus, saving 2237.7 tenge per one m3 of product (USD 6.84). The actual economic effect of manufacturing 1000 m3 of arbolitic building products unig mixed solar heat treatment with filmformers was 2237700 tenge (USD 6843.11). Conducted researches lay ground for a positive assessment of introduced methods and for recommendations, made for a wide-scale application of solar heat treatment in manufacturing arbolitic building products.