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17УДК 691
ТЕХНОЛОГИЯ ИЗГОТОВЛЕНИЯ УТЕПЛЁННЫХ ПОЛИСТИРОЛБЕТОННЫХ СТЯЖЕК СОВМЕЩЁННЫХ КРОВЕЛЬ ЗДАНИЙ МЕТОДОМ ЭЛЕКТРОРАЗОГРЕВА
Васенков Евгений Владимирович.
Новосибирский государственный архитектурно-строительный университет (Сибстрин), магистр, andreevich@gmail.com.
Молодин Владимир Викторович.
Новосибирский государственный архитектурно-строительный университет (Сибстрин), molodin@sibstrin.ru.
Макарихина Инна Михайловна.
Новосибирский государственный архитектурно-строительный университет (Сибстрин), кандидат педагогический наук.
Аннотация. Использование полистирол бетона позволяет совместить два компонента кровли - утеплитель и стяжку в один и сократить один технологический передел. Традиционные технологии полистирол бетона аналогичны стандартным технологиям обычных бетонов. Однако всплывающие в процессе перемешивания и уплотнения гранулы вспененного полистирола ведут к неоднородности материала по прочности и теплопроводности, делают поверхность слоя малопригодной для приклеивания кровельного покрытия. Использование электроразогрева смеси позволяет вспенить равномерно распределённые гранулы суспензионного полистирола в уже уложенной смеси и получить качественную конструкцию, экономя при этом время и деньги.
Ключевые слова: полистиролбетон, технология, однородность, флотация, вспенивание.
TECHNOLOGY OF MANUFACTURING OF POLYSTYRENE CONCRETE CAPS FOR WARMDECKFLAT ROOFS BY ELECTRIC HEATING METHOD
Vasenkov Yevgeniy Vladimirovich.
Novosibirsk State University of Architecture and Civil Engineering, graduate student, ivanov. danil. andreevich@gmail. com.
Molodin VladimirVictorovich.
Novosibirsk State University of Architecture and Civil Engineering, Doctor of tech. sciences, molodin@sibstrin.ru.
Makarihina Inna Mikhailovna.
Novosibirsk State University of Architecture and Civil Engineering, PhD (pedagogic), michmacha@mail.ru
Abstract. Polystyrene concrete allows to combine two components of a roof - a heater and a cap in one and to cut one technological repartition. Traditional technologies of polystyrene concrete are similar to standard technologies of concrete. However, the
flotated polystyrene granules cause the material to be inhomogeneous in strength and thermal conductivity, making the surface of the layer unsuitable for gluing the roofing. Using electrowarming mixture allows foam evenly distributed granules suspension of polystyrene in the already laid mix and get high-quality design, while saving time and money.
Key words: polystyrene concrete, technology, homogeneity, flotation, foaming.
Introduction.
New construction, reconstruction and major overhaul of buildings in the Russian Federation are carried out in accordance with new, increased requirements for thermal protection of enclosing structures. The introduction of new, more stringent, energy saving standards caused the need for a radical revision of the principles of design and construction of buildings. The use of traditional building materials and technical solutions for Russia does not provide the thermal resistance required by modern standards for building enclosures.
The physical and technical properties of the heat-insulating materials have a determining effect on the thermal efficiency and operational reliability of the structures, the laboriousness of the installation, the possibility of repair during operation. They also substantially define the comparative cost-effectiveness of various insulation options for buildings. One of the effective methods for solving the issue of roof insulation is the use of polystyrene concrete. Polystyrene concrete is one of the ways to insulate the warm deck flat roofs. Warming with monolithic polystyrene concrete has several advantages in comparison with other types of insulation [1]:
1. High manufacturability of the material.
2. Good strength characteristics
3. Great durability.
4. High speed of creating.
5. High profitability.
In addition, by making a comparative calculation of the weight of the insulation from the mineral wool board and the monolithic layer of polystyrene concrete, a decrease in the weight of the thermal insulation layer is detected by more than 20%, which is also an advantage over the traditional insulation ways.
There are known methods of manufacturing environmentally friendly lightweight polystyrene concrete products and structures [2], including the preparation of a polystyrene concrete mixture containing pre-foamed granules of thermostated expanded polystyrene, various additives, cement and water.
The actual problem of using polystyrene concrete as a monolithic layer of insulation is the irregularity of distribution of aggregate granules - foamed granular polystyrene. This is due to flotation of previously foamed granules during mixing and during vibration processing. The surface is cemented beads of expanded polystyrene pellets. This makes it difficult to glue the roll materials. In this regard, we have to arrange an additional cement-sand layer, which increases labor costs, cost and duration of work. This is due to the flotation of previously foamed granules during the mixing process and during vibration processing. The surface of the layer of insulation is a cemented polystyrene granules. This makes it difficult to glue the roll materials. In this
regard, we have to arrange an additional cement-sand cap, which increases labor costs, cost and duration of work.
Object of investigation and formulation of the problem.
Polystyrene concrete is a porous structured light concrete with a cement binder and a filler made of expanded granulated polystyrene with the use of additives.The analysis of literature sources shows that the existing experience and inventions that regulate the use of monolithic polystyrene concrete for insulation of structures, including roofs, do not fully take into account the problem of irregularity of distribution of granules. As a result, the question of the strength and frost resistance of the polystyrene concrete laid remains unsolved.
The standard technology of manufacturing polystyrene concrete products and structures [3] suggests the prefabrication of expanded polystyrene aggregate, by single or multi-stage foaming of granules of suspension polystyrene. It is a product of suspension polymerization of styrene with a blowing agent (5-6% of a mixture of pentane and isopentane).There is also in an insignificant amount (for use in construction) - a flame retardant based on bromine mixture (less than 1%).
Preparation of the mixture proceeds by adding a calculated amount of polystyrene aggregate, binding and complex additives, mixing the mixture with water, laying it in a mold, hardening, as a rule, heat treatment and stripping the structure [3]. The disadvantage of this technology is the high heterogeneity of produced material.
Repeated attempts have been made to achieve homogeneityof distribution of granules [4, 5, 6].However, adding of various complex additives and increased stiffness reduced the technological properties of the starting material, causing an increase in labor intensity, cost and duration of the production process. The use of air-entraining additives and plasticizing additives does not provide the production of polystyrene concrete with a stable fine-pored structure. Using of aset-accelerating admixture worsens working conditions in the manufacture of polystyrene concrete products and reduces the protective properties of polystyrene concrete in steel reinforced products.
The purpose of this research is to find effective methods for the insulation of the roof with monolithic heat-insulating structural environmentally friendlypolystyrene concrete.
To achieve this goal, it is necessary to solve the following main tasks:
- to offer a technology for obtaining homogeneous polystyrene concrete structures with qualitative geometric characteristics. Reduce the duration of the technological process by simultaneous and uniform heating of their entire volume.
- to research the possibility of using the proposed technology for the manufacturing monolithic caps of warm deck flat roofs of polystyrene concrete and products for their installation;
- investigate the homogeneity of the received material for structures and products. In this paper, exploratory researches are presented, which were the prerequisite of the proposed technology.
Exploratory researches.
In the course of the research, it was found that for polystyrene concrete, according to [3], the following physico-mechanical characteristics:
- average density;
- compressive strength;
- tensile strength in bending;
- strengthforaxialtension;
- frost resistance;
- thermal conductivity;
- water vapor permeability;
- Shrinkage.
The grade of polystyrene concrete at medium density varies from D150 to D600, the grade (class) of polystyrene concrete for compressive strength varies from M2 to B2.5. The tensile strength at bending for polystyrene concrete is in the range 0.27-0.76 MPa. The normalized values of the strength for axial stretching of polystyrene concrete should not be lower than the tensile strength values for bending multiplied by a factor K = 0.32.The minimum mark for frost resistance of polystyrene concrete is F135, the maximum is F1300. The minimum value of the coefficient of thermal conductivity is 0.052 W / (m x ° C), and the maximum value is 0.145 W / (m x ° C). The hygroscopicity value of polystyrene concrete should not exceed 8% [3]. Polystyrene concrete is subject to shrinkage. The value can reach 1 mm / m2. The vapor permeability is 0.135 mg / (m • h • Pa) and 0.068 mg / (m • h • Pa) for grades D150 and D600, respectively. Based on the requirements for thermal protection of enclosing structures, in particular roofing, as well as requirements due to the need to glue roll roofing materials to the capfrom monolithic polystyrene concrete, polystyrene concrete should have the following characteristics:to be geometrically correct, to be dust-free and dry, to be resistant to thermal effects, including a gas burner. The thermal engineering calculation of the enclosing structures must correspond [7] and [8], the value of the polystyrene concrete layer for each region is determined individually.
Based on the requirements for the device of the heat-insulating layer of the roof [9], the deviation of the plane of the polystyrene concrete cap from the projected should not exceed 0.2%.The moisture of the material should not be more than 5%, and the deviation of the plane of the thermal insulation layer horizontally and vertically should not exceed, respectively, 5 and 10 mm.However the cap from polystyrene concrete corresponds to the flammability group G1 [3], it matches the requirements of [10].
Taking into account the revealed physical and mechanical characteristics of the material, it can be concluded that for the production of monolithic caps the most optimal option is the use of polystyrene concrete of grades at an average density of D150 -D250. Using of these marks allows us to perform roof insulation in Novosibirsk with a thickness of the insulation layer within 250mm.Based on the technology of preheating of concrete mix,we propose a one-stage technology of manufacturing expanded polystyrene products and structures.The essence of the method lies in the fact that granular (beaded), non-expanded polystyrene having a density of 1050 kg / m3, when mixed with a solution component having the same order of density of 1800 ^ 1900 kg / m3, is evenly distributed over the volume of the mixture. When the electricity passes between the electrodes immersed in the mixture, the mixture quickly and uniformly heats up. When the temperature reaches 95-1050C, the polystyrene granules expand, increasing in volume (Fig. 1) and form a structure with uniform geometric dimensions that are uniform in density, strength, and heat conductivity.Polystyrene concrete is laid
in one layer with the device of cement-sand leveling cap, which makes it possible to use this technology for buildings of the first category of fire resistance and fire resistance class of CO, i.e. up to 25 floors [11]. The proposed single-stage polystyrene concrete technology assumes the use of beaded polystyrene, which is obtained by suspension polymerization of a styrene monomer in an aqueous medium in the presence of polyvinyl alcohol, and benzoyl or dinitrile peroxide of azodiisobutyric acid.
Fig.1. Polystyrene - the main component of polystyrene concrete. a) beaded, b) foamed.
The polymerization of styrene is carried out in the presence of isopentane, soluble in styrene and insoluble in polystyrene. In the conversion of monomer droplets to polymer, isopentane is isolated as an independent phase. Therefore, in the resulting bead polystyrene, there are inclusions of uniformly distributed droplets of isopentane [12]. The mechanism of foaming is that isopentane boils at a temperature of more than 28 ° C, and polystyrene passes into a viscous-flowing state at a temperature above 80 ° C. Boiling isopentane explodes the granule from the inside, increases it in volume and compacts the cement-sand mixture. In this case, the foaming of each granule of beaded polystyrene occurs directly at the point where it appeared at the end of the mixing of the initial mixture. This ensures the desired properties of the material: uniform density, thermal conductivity and geometric dimensions.
In the laboratory of the Department of Technology and Organization of Construction of NSUACE (Sibstrin) we conducted a series of trial tests of the proposed technology. To this end, we designed and manufactured a unit for the preparation of polystyrene concrete blocks using a one-stage technology (Figure 2). In the grooves of the mold from the current-insulating material are inserted partitions of steel ST-3, equipped with current collectors. The parallel bulkheads functioned as electrodes.The initial mixture was stacked between the electrodes with beaded polystyrene. Immediately after laying the mixture and sealing it, we applied an electricity to the electrodes (industrial frequency). The heating of the mixture lasted 10-15 minutes. During this time, the initial mixture was heated and the bead polystyrene was swollen.
Fig.2. Installation for the production of polystyrene concrete blocks by one-step technology.
After standing for 24 hours at a temperature of + 20 ° C, the samples were taken out of the mold, perpendicularly sawn. Vacuum from the surfaces of the section removed the dust and produced a layer-by-level evaluation of the uniformity of the distribution of polystyrene granules. Vacuum from the surfaces of the section removed the dust and produced a layer-by-level evaluation of the uniformity of the distribution of polystyrene granules. The evaluation was performed visually and with the help of the glossmeter FB-2 in a comparative way.
Homogeneity studies using a glossmeter showed that the degree of blackness of vertical sections of samples manufactured using a one-stage technology amounted to 85-90% of the standard, which fully complies with construction requirements. When comparing the traditional technology and the proposed solution (Fig. 3), it can be noted that the problem of flotation of granules is successfully solved, which is confirmed by experimental data.
Fig.3. Distribution of foamed polystyrene concrete granules. a) traditional technology b) one-step technology.
Conclusion.
In the course of our research we established:
1. The basic parameters of polystyrene concrete, used as insulation for roofs, are identified.
2. The processes occurring during the polymerization of styrene were studied.
3. The positive effect of electric heating on the uniformity of finished polystyrene concrete products was confirmed.
4. The proposed technology will allow under conditions of a construction site, in an accelerated mode, to produce dense, strong, homogeneous and qualitative structural characteristics of polystyrene concrete that fulfill the functions of a heat-insulated cap for warm deck flat roofs.
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