The No. 46 document of the Ministry of Public Security and the Ministry of Housing and Urban Affairs and the No. 65 document of the Ministry of Public Security have successively introduced the non-combustible insulation materials to the forefront of the market. Wall insulation plays a dominant role in the insulation of building envelopes, and the external insulation system is the most widely used insulation method in wall insulation. The traditional organic thermal insulation material has the advantages of light weight and relatively mature insulation system, but the fire performance is lacking. If fire prevention measures and management measures are not put in place, it will pose a threat to the people's life safety.
The non-combustible insulation material is basically inorganic material, and its application in the external thermal insulation system is still in its infancy compared with the organic thermal insulation material. Although many pilot work has been carried out on the application of materials, the level of organic insulation materials has not been reached in terms of technical documents (including standards, specifications, atlases, etc.), the scale of pilot projects, and the time required for inspection. The seriousness of the problem lies in the difference between the fuzzy insulation systems, the method applicable to other forms of insulation systems is simply applied to the external insulation system; the difference between the fuzzy organic materials and the inorganic materials will be applied to the organic insulation materials. The thin plastering exterior insulation system is simply transplanted into the inorganic thermal insulation material, resulting in a chaotic situation in the application of inorganic thermal insulation materials in exterior insulation. This paper will analyze the characteristics of external thermal insulation system, the characteristics of non-combustible thermal insulation materials and their adaptability, in order to explain the application focus of non-combustible thermal insulation materials.
1 Classification and characteristics of wall insulation system There are many forms of wall insulation, and various insulation forms have great gaps in performance requirements for insulation materials. Therefore, when discussing the application of thermal insulation materials, it is necessary to combine the differences in their forms and treat them differently.
Form 1: Self-insulating wall. Self-insulating walls are a type of way in which the wall itself has both thermal insulation properties and structural properties. It does not require additional insulation measures to achieve the required heat transfer coefficient requirements. Due to the large thickness of the wall, such materials allow a relatively large thermal conductivity, but at the same time require it to have a certain anti-pressure fund project "Twelfth Five-Year" Science and Technology Support Program (2011BA04B03) Pan Yuyan (1957-), male, The senior engineer is in the construction of the frame structure, and the application of the self-insulating wall form is extensive. The self-insulating wall of single material mainly has a variety of aerated concrete and foam concrete temperature self-insulating walls, including sandwich, cavity filling and other product forms.
Form 2: Insulation inside the wall. The insulation material on the inner wall does not require high waterproof performance and strength performance. Because of the layered construction, the insulation system does not need to withstand the cumulative stress, nor does it need to withstand the wind pressure, and the waterproof performance requirements are also low. Therefore, the gypsum-based material can be used on the inner wall without being used on the outer wall.
Form 3: Center insulation (sand insulation). The insulation is in the middle of the wall. The thermal insulation system integrates the thermal insulation function with the structural requirements of the wall, and the structural requirements of the system are very high, and the thermal insulation material mainly changes with the system design.
: External insulation outside the wall. External wall insulation is the dominant form of wall insulation, which is divided into two types: curtain wall insulation and wall insulation.
Due to the protection of the panel, the curtain wall insulation is lower than the wall insulation, especially the back ventilation closed curtain wall. The requirements for the insulation material are even lower than the internal insulation requirements. It is a typical filling. Insulation.
External wall insulation (thin plaster) is the dominant form of wall insulation. Because insulation materials rely only on the protection layer and the outer layer to protect the material, it requires a certain strength, water resistance, durability, weather resistance, freeze-thaw cycles, etc. Requirements are the most stringent requirements for several types of insulation.
Various insulation materials have the adaptability of their insulation methods, and it is not easy to transplant one suitable method to another insulation method.
2 Technical requirements for external thermal insulation system In general, the technical requirements for external thermal insulation systems can be summarized as follows.
Insulation performance. The external wall thermal insulation system is a special construction structure for the external wall, which requires a low thermal conductivity to achieve a certain thickness for effective insulation. Table 1 shows the thermal conductivity of common non-combustible insulation materials. For cold and cold regions, the heat transfer coefficient is low, and the thermal conductivity of the material should not be too large, so as to avoid excessive thickness of the insulation layer.
Table 1 Thermal conductivity of common non-combustible insulation materials (unit: W/mK) Insulation material Mineral rock wool glass wool aerated concrete foam glass foam cement granular insulation material composite thermal conductivity (2) physical strength properties. The insulation system should ensure the stability and safety of the system under the combined effects of self-weight, negative wind pressure and vibration. The comprehensive test content based on the strength performance of the system includes the strength of each material of the system (for example, the tensile bond strength of the thermal insulation material, the bonding strength of the adhesive to the wall and the thermal insulation material, and the adhesion of the plaster to the thermal insulation material). Connection strength) also includes the requirements of the system's comprehensive performance (eg, wind pressure resistance, seismic performance). These strengths are a combination of tensile strength and shear strength.
The main performance of the material strength is the tensile bond strength perpendicular to the surface. According to the G144-2004 specification, the strength performance should not be less than 0.1 MPa, and the damage is inside the insulation material.
On the other hand, it is required that the insulation material should have a certain compressive strength and ensure that the impact resistance of the system is not less than 3 grades.
Chemical stability. Since the medium in the insulation system is mainly moisture, the material and system chemical stability is mainly reflected in water resistance stability.
Chemical stability is the result of a long-term effect that is closely related to the durability of the system. Most materials will undergo hydrolysis under the action of moisture, which will gradually reduce the strength of the material and eventually cause damage to the system. It is the water resistance test result of materials with different acidity coefficients. The material with acidity coefficient of 2.0 is nearly 4 times higher than the acidity coefficient of 1.0.
Freeze-thaw cycle performance. When water condenses into ice, the volume expands. If the external insulation system contains too much water inside, in winter nights, the outdoor temperature is below zero, the water freezes and the volume expands; during the daytime, the temperature is above zero, the ice melts again; the night freezes again; this ice and water change process In the middle, the volume expands and contracts, and the cycle reciprocates, which can cause the system to be loose and form the damage of the external thermal insulation system. Resistance to this damage is called freeze-thaw resistance. The damage of the system by freeze-thaw cycles is characterized by peeling, cracking, chalking, foaming and arching.
Moisture content and water vapor discharge performance. The direct consequences of high water content in the system are: 1 the thermal conductivity of the thermal insulation material decreases sharply with the increase of water content; 2 the water content is too high, creating the medium condition that destroys the chemical stability of the material; 3 the higher the water content, the freezing and thawing The worse the loop performance.
Since the foundation wall concrete itself contains moisture, the bonding mortar and the plastering mortar also contain moisture, and the moisture generated by the system may leak, so the constant moisture content of the entire system is difficult to avoid. This requires systems and materials to have a defined water vapor permeability and emit water vapor to reduce the threat of moisture to the system and materials.
The moisture wicking property is the so-called gas permeable property, and the water repellency of the surface of the fiber product allows moisture to be stored between the fibers, and although it exhibits a large amount of water absorption, its discharge speed is also fast. Therefore, the standards for rock wool products used in exterior insulation systems have made a lot of provisions in this respect, including short-term water absorption, long-term water absorption, mass water absorption and water-repellent rate, which guarantees both water absorption and drainage. Get control. The wet flow density with the plaster layer and the facing layer rock wool system is large, d), which is twice the same as the EPS.
In contrast, foamed cement has a large amount of water absorption. The biggest problem is that the moisture in the capillary structure of the cement is moist, and the rate of moisture removal is much slower.
Weather resistance. The external thermal insulation system will be affected by the natural environment such as sun exposure, wind and rain, cold weather and temperature difference. The system must have the ability to resist these climatic factors, can not damage and maintain the system should have stable performance. This long-term resistance to weather is weathering and durability. Weatherability The damage of the temperature difference caused by the quenching and rapid heat was investigated, and the aging and yellowing properties of the material under ultraviolet light were also investigated.
Fire performance. The continuous fire accidents have made the fireproof performance of thermal insulation materials highly valued by the industry. At present, the Ministry of Public Security and the Ministry of Construction No. 46 document Civil Building External Thermal Insulation System and the Provisional Regulations on Fire Protection of Exterior Wall Decorations are strictly enforced. The civil building exterior insulation materials are made of materials with Class A burning properties.
3 The thermal conductivity of the key issues of the compatibility of non-combustible insulation materials and external thermal insulation systems. The basic principle of insulation materials is to use air with a low thermal conductivity to separate the gas in a material that cannot flow in the solid phase. Therefore, light weight and low bulk density are the basic characteristics of thermal insulation materials.
There is a contradiction between bulk density and strength performance. The weight of EPS thin plaster is about 20kg/m3, while the weight of thin plastering of rock wool board, foam glass, foam enamel is generally 150kg/m3. The increase of bulk density means that the shear stress of the system increases, which is higher for the system. Claim.
Water absorption. The organic insulation material is hydrophobic and has a low water absorption. Inorganic insulation materials are generally hydrophilic, and hydrophobicity can only be obtained after hydrophobic treatment. High water absorption rate will have many adverse consequences. Firstly, moisture provides a reaction medium for material decomposition, which has serious consequences for chemical stability and durability. Secondly, the thermal conductivity of the thermal insulation material after water absorption rises rapidly; again, the water absorbing material may be Many problems are exposed in the freeze-thaw cycle; in the end, excessive moisture causes problems such as condensation, mold, and humidity.
Chemical stability issues. Organic materials degrade slowly in thermal insulation systems, so there is no such indicator in terms of chemical stability issues in standards and specifications. However, the hydrolysis reaction of the inorganic material in the mode of action of water causes the material to be pulverized. The larger the surface area of ​​the material, the faster the hydrolysis. For example, slag wool has a high content of alkaline earth metal oxides, a large surface area of ​​fibers, and its water resistance problem is prominent.
4 Conclusion At present, the energy consumption of buildings in the country accounts for about 30% of the total energy consumption. Building energy conservation will become the primary problem of energy consumption in the whole society. Among the many forms of wall insulation, the external insulation system is the most widely used insulation method at present, and it is also the insulation practice advocated by the state. However, the external thermal insulation system is located on the outer surface of the building and directly faces the natural environment such as the atmosphere, rain, snow, and wind, and has higher requirements on material properties. With the extensive attention to the fire protection of wall insulation materials and systems throughout the country, the research and application of inorganic non-combustible insulation materials is imminent. The key problems in the application of non-combustible insulation materials in external thermal insulation systems are: (1) to resolve the contradiction between bulk density and strength; (2) hydrophobic treatment of inorganic thermal insulation materials; (3) chemical stability of inorganic thermal insulation materials.
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