Performance comparison between EPS and XPS systems
At present, the external thermal insulation system of insulation board exterior wall mainly includes:
1, polystyrene foam insulation board (also known as foam board and EPS board) is a white object made of expandable polystyrene beads containing volatile liquid foaming agent which are preformed by heating and heated in a mold. With the structural characteristics of fine closed holes, it is mainly used for building wall, roof insulation, composite board insulation, cold storage, air conditioning, vehicle and boat insulation, floor heating, decoration and carving.
2. Extruded polystyrene insulation board (XPS), referred to as extruded board, is a hard board made of polystyrene resin by continuous extrusion and foaming through a special process. Its interior is an independent closed bubble structure, which is an environmentally friendly thermal insulation material with excellent properties such as high compression resistance, water absorption, moisture resistance, air tightness, light weight, corrosion resistance, long service life and low thermal conductivity. Extruded polystyrene (XPS) insulation board is widely used in wall insulation, concrete flat roof and steel roof insulation, moisture-proof insulation of low-temperature storage ground, parking platforms, airport runways, highways and other fields to control ground frost heaving.
Performance comparison of one or two systems
1, thermal insulation performance:
The thermal insulation properties of EPS and XPS with the same thickness are gradually improved. EPS is 0.04 1 and XPS is 0.030. Therefore, in the case of achieving the same thermal insulation effect, XPS board is thinner than EPS board, but the price of pure board is more expensive than EPS board. If technology and building height are considered comprehensively, XPS is more expensive than EPS per square meter.
For thermal insulation, the thermal inertia index D is mainly considered, and the value of D is proportional to the thermal storage coefficient. But as far as the whole system is concerned, the heat storage of 200mm concrete is large enough, and the external insulation layer can completely meet the energy-saving requirements. This is also the reason why the comprehensive thermal conductivity and thermal storage coefficient of the wall meet the requirements at the same time according to the national code. At present, EPS or XPS thin plastering system completely meets the requirements.
2. Strength:
The strength pointed out here should be tensile strength, and the bulk density of polystyrene board is absolutely related to tensile strength. The tensile strength of EPS with bulk density of 18Kg/m3 is110 ~120kpa, and the bulk density of 20Kg/m3 is about 140KPa. XPS usually has a bulk density of 30 kg to 45 kg and a strength of 150 kPa to 700 kPa or higher. (provided that the thermal conductivity is around 0.03).
At present, the strength of XPS board is between 200 kPa and 250 kPa, which cannot be achieved by many XPS boards in China, and EPS board is below 100 kPa. In coastal areas, the facade decoration is more and more abundant and typhoons are frequent, so the strength is very important, especially for some external wall tiles or high-rise buildings, and both boards need to be reinforced or fixed with fasteners. The wire drawing of ceramic tiles exceeds 400KPa, which even XPS can't bear. The solution is to anchor the steel wire mesh on the base with expansion bolts, so that the tensile stress can be dispersed to three-dimensional space. Therefore, as long as the anchorage is proper, the drawing failure must be in the crack-resistant mortar layer of composite steel wire mesh, and the problem is not big.
Compared with EPS, XPS board has higher strength. However, compared with EPS, due to the brittleness of XPS board, the decorative layer of external wall, especially the paint surface layer, is more likely to crack under the condition of large bonding area. Flexibility is a matter of material quality. For plastering, perceptual knowledge is usually to apply plastering to polystyrene board, and then it depends on how much polystyrene board is bent. If it is flexible, it will not crack after several turns. Similar to the ductility index in waterproof materials. But as far as the material itself is concerned, flexible EPS is better than XPS.
3. Weather resistance:
Weather resistance refers to the adaptability of thermal insulation system to external weather changes, and refers to a series of quality-related problems such as whether the overall stability and thermal insulation effect of the system have changed under different climatic conditions. Weather resistance is a very important index of thermal insulation system.
Because the water absorption of EPS board is higher than that of XPS, the weather resistance is not as good as that of XPS system. However, the ductility of EPS board is better than that of XPS board, which can overcome some defects. But as far as the system is concerned, the gypsum on the outer layer of the thin plastering system itself has certain waterproof ability. Except in the construction process, the waterproof performance of the complete two systems can be very good. The contact between rainwater and external walls and walls is vertical. As long as the surface mortar does not crack, there is no problem in waterproofing.
In addition, the wind pressure resistance is also an important item in weather resistance, because the more cavities in the system, the worse the wind pressure resistance. So the key depends on the size of the bonding area between the whole insulation system and the base. There is nothing wrong with XPS system and EPS system.
4. Permeability:
Breathability and water absorption are two problems! The size of air molecules and water molecules is very different! Of course, there is a saying that it is breathable and airtight. There are experiments to illustrate this point. For example, in Shenzhen. Put a biscuit outside, there is no need to water it. Within a day, cookies will become soft because of water absorption, and the water it absorbs is air water instead of liquid water.
In the current insulation system, no product dares to claim that its products have good air permeability, good thermal conductivity, good waterproof performance and no water absorption, which are all occupied by good people. Because these indicators are contradictory, and infiltration should also pay attention to the infiltration after wet water in the construction process and the infiltration after the system is completed.
As far as the material itself is concerned, EPS is much better than XPS. XPS has almost no air permeability, but in the area with large indoor and outdoor temperature difference, water vapor is easy to condense on both sides of the plate.
5. Bonding strength:
For thin plastering system, this index will directly affect the use of plates. EPS board has low strength and low shear strength. The damage of the plate may not be in the joint surface, but directly in the middle of the plate, so the good strength performance of XPS is more guaranteed. The tensile strength of 0. 1MPa is equivalent to the tensile strength of 0/0 ton per square meter, which is very large.
However, XPS system still has a fatal wound: the interface smoothness is high, and it is difficult to get stuck without high polymer emulsion treatment, but how many manufacturers are willing to greatly increase the cost?
6. Surface smoothness
XPS is difficult to ensure the flatness of the external wall, and it is also difficult to cover the joints, especially the arc sections, with the external anti-crack mortar. If XPS is a coating for wall insulation, domestic boards can't be made! The material determines the roughness of the surface (paint surface). The shadow of the plate and anchor is obvious in the sun. Therefore, it can be said for sure that domestic extruded boards, including Dow and Owens Corning, are not suitable for wall insulation boards with paint as the external decoration! The construction technology of extruded board is that all wrenches must be coated with interfacial agent, then pasted with mucilage, dried and then riveted for reinforcement. So when you roughen the skin of the extruded board, the board has been deformed due to stress, and the deformation is even greater when the interfacial agent is applied. So the plane of the wall can't be controlled and treated. Not as good as EPS polishing. As for the defects such as strength, aging resistance and air permeability.
The EPS system will be much better. Because the nature of the board is soft, it is better than XPS board in ensuring the flatness of the wall.
Second, the advantages and disadvantages of the two systems
EPS insulation system:
EPS board is pre-foamed with expandable polystyrene beads, and then heated and molded in the mold. EPS is composed of a completely closed polyhedral honeycomb. The diameter of the honeycomb is 0.2 ~ 0.5 mm, and the wall thickness of the honeycomb is 0.0065438 0 mm. EPS is composed of about 98% air and 2% polystyrene. The air trapped in the honeycomb is a bad conductor, which plays a decisive role in the excellent thermal insulation performance of foam plastics. Unlike foams containing other gases (for example, the newly made polyurethane foam honeycomb cavity is filled with Freon gas), the air in polystyrene foam can stay in the honeycomb for a long time without changing, so the thermal insulation performance can be stable for a long time.
The relationship between thermal conductivity and density, in the range of density from 30 to 50 kg/m3, the thermal conductivity is the smallest. When the average temperature is 10℃ and the density is 20kg/m3, the thermal conductivity is 0.033 ~ 0.036W/(m? K) When the density is less than 15 kg/m3, the thermal conductivity increases sharply with the decrease of the density.
EPS board is made of countless beads bonded by heating and pressing. The bonding degree between beads is very important, which will directly affect the physical properties of EPS board such as water absorption and mechanical strength. The bonding quality of microbeads is mainly determined by EPS raw materials. In addition, processing technology and product density also have some influence on this. For example, the EPS board with low density (below 10kg/m3) has poor adhesion between beads and the beads are easy to peel off.
The thermal conductivity of EPS board is small, and the elastic porous structure can absorb thermal stress and wet stress. Even if water vapor condenses and freezes in the material under rare climatic conditions, its structure will not be destroyed and it has good service durability. EPS board is light in weight, has certain compressive strength and tensile strength, and can support the plastering protective layer by its own strength without pulling joints, thus avoiding the formation of thermal bridge. EPS board has good chemical stability, acid and alkali resistance and durability.
Due to the above advantages and moderate price, EPS board has become the most widely used thermal insulation material in the world. Let's first introduce several characteristics of EPS board.
(1) aging performance:
Test of aging tester: WEL-6X-HCE aging tester of Japan, xenon lamp power 6kW, rainfall 65438 02 minutes per hour, heating for 48 minutes, temperature 55℃, and relative humidity 95%. The surface of EPS board sample 1 is exposed, and the surface of sample 2 is covered with a layer of kraft paper. After 500 hours' testing, the surface of sample 1 is uneven, the depth of depression is less than 1 mm, and the surface of EPS board of sample 2 remains unchanged.
Outdoor natural exposure test: EPS board is exposed on the roof and balcony. Less than 1 month, the surface of EPS board began to powder. Even if it is placed outside the window facing north, after a winter outdoor exposure, the surface has been obviously powdered.
Usage survey: The exterior wall facing south in Italy is insulated with EPS board, and only a thin layer of paint is sprayed on the surface as a protective layer. After sampling inspection in 10 years, the porous structure, density, thermal properties and mechanical properties of EPS board have not changed. EPS board is used as insulation layer of domestic railway refrigerated trucks. After 8 ~ 10 years of use, the skin becomes rough when it is removed and placed in the open air and exposed to the sun, wind and rain. After cutting with electric heating wire, the cut surface is the same as the new product. The density is 17.8kg/m3 and the thermal conductivity is 0.0335W/(m? K) The density of EPS board at the bottom of the carriage is 103.8kg/m3, and the thermal conductivity is 0.0386W/(m? K) After baking at 70℃ 12, the density decreased to 30.5kg/m3. After crushing, the surface of EPS particles was soaked in salt water and turned yellow. After cutting the granules, the inside is still white.
The above situation shows that EPS board has good durability. However, when the EPS board is directly exposed to outdoor weather conditions, the surface is easy to be damaged. But when the surface of EPS board is well protected, even if there is only one layer of kraft paper, it can have good natural aging resistance.
(2) Heat resistance and dimensional stability:
The size change of EPS board can be divided into thermal effect and post-shrinkage. The deformation caused by temperature change is reversible. EPS board will shrink after heating forming, which belongs to post-shrinkage. The shrinkage rate of post-contraction begins to be faster, and then gradually slows down. After shrinking to a certain limit, it will no longer shrink.
EPS boards produced by different raw materials and different processing conditions have different shrinkage rates in the later period. The shrinkage of EPS board made of BASF raw materials is 0.3% ~ 0.5%.
The dimensional change rate of EPS board at 70℃ is generally between 0.07% and 0.38%. In concrete members, when the curing temperature exceeds 90℃ and the curing time in the kiln is 8h, the thickness of composite wall with EPS board as interlayer is obviously reduced. In high-temperature hot water, the appearance of EPS board changes obviously and the surface is uneven. EPS board will shrink greatly at the ambient temperature above 100℃.
(3) Moisture resistance and its influence on thermal resistance: After the EPS board is soaked in water at 23℃ for 96 hours, the water absorption rate is generally between 0.5 1%-0.74%. In practical use, there are temperature difference and water vapor partial pressure difference between the two sides of EPS board. Generally speaking, when EPS board is used for external wall and roof insulation, it will not cause obvious moisture-proof problems. However, when one side of EPS board is in high temperature and high humidity environment for a long time, and the other side is in low temperature environment, and it is sealed with materials with poor water vapor permeability, EPS board will be seriously affected by moisture.
Simulation test of common roof humidity in winter: the lower surface of EPS board simulates indoor climate conditions in winter (temperature 2 1℃, relative humidity 42%), and the upper surface simulates outdoor climate conditions in winter (temperature -7℃, relative humidity 100%). The sample density of EPS board is 1.6kg/m3, some peripheral edges are sealed with films with low water vapor permeability, some are sealed with cold surfaces, some are sealed with both edges and cold surfaces, and some samples are not sealed at all. After 120 days test, the weight moisture absorption rate of EPS board is not more than 0.2%, and the thermal conductivity is increased by 2.2% on average.
Humidity simulation test in hot and humid environment: the sample size is 300mm×300mm and the thickness is 25 mm. The periphery and upper surface of the sample are sealed by two layers of gas barriers, so that the lower surface of the sample is in a hot and humid environment (temperature 29℃, relative humidity 100%) and the upper surface is in a low temperature environment (temperature 4℃, relative humidity 75%). This situation represents the harsh boundary conditions that lead to humidity. Water vapor is driven from the wet lower surface to the upper surface, and cannot be dried from the upper surface due to the existence of the sealing layer. Samples are divided into four materials: EPS- 1, EPS-2, URE and XPS. The densities of the four materials are 16, 30, 32 and 38kg/m3, respectively. During the test, the volume water content and thermal resistance of the sample are measured regularly. The thermal resistance ratio is the ratio of the thermal resistance of the sample after wetting to the thermal resistance in the dry state. The experiment shows that the volume moisture content of EPS- 1, EPS-2 and ure has exceeded 30% after 400 days, while the volume moisture content of XPS sample is still less than 10% even after 1800 days.
The actual use survey shows that after some inverted roofs have been used for three years, the volume moisture content of EPS board and ure board both exceeds 40%, and the thermal resistance decreases by 60% ~ 70%. At the same time, it is also found that XPS board has little hygroscopicity.
When EPS board is used for external wall and common roof insulation, the moisture content does not increase much during long-term use, and the insulation performance does not change much. However, when the waterproof layer of the roof fails, the EPS board may still be seriously affected with damp. On the roof of an office building in Beijing, 5cm thick EPS board was laid on the original waterproof layer to strengthen thermal insulation, 8cm thick asphalt perlite was laid on the EPS board, and then the waterproof layer was made on it. Due to the failure and water leakage of waterproof layer, the volume moisture content of EPS board is as high as 25%, and the thermal insulation efficiency is reduced by 60%.
When choosing EPS board, we should pay attention to its aging performance, heat resistance and dimensional stability, moisture resistance and its influence on heat resistance.
The long-term service temperature of EPS board is below 75℃. When used for roof insulation, attention should be paid to prevent EPS board from overheating. Due to the large thermal resistance of EPS board, its upper surface may shrink due to excessive temperature. Light paint or overhead roof can be used to reduce the surface temperature of thermal insulation roof.
In the external thermal insulation system of thin plastering surface of EPS board, in order to avoid cracking of plastering surface caused by later shrinkage, it is required that EPS board be stored at room temperature for at least 40 days after molding. Or curing at 70℃ for at least 65438 0 weeks. At the same time, the dimensional stability is required to be below 0.3%.
When the surface of EPS board is exposed, it is easily damaged by direct sunlight and weathering. Therefore, in the process of external insulation or roof insulation construction, the protective layer should be prepared in time.
Summary:
Advantages of EPS system:
1), has become a systematic and mature technology. This technology has formed a system, and the adhesive layer, insulation layer and facing layer can be used together, and there are many mature technical documents.
2) Good heat preservation effect.
3) Because the thermal insulation material is expanded polystyrene, its price is not very expensive, which makes the whole system moderately expensive. Easy for users to accept.
Disadvantages of EPS system:
1), due to the nature of the board itself, its strength is not high, its bearing capacity is low, and it needs to be strengthened when tiling.
2) The board will go through a mature period when it leaves the factory, and it needs to be placed for a period of time before it can be used. If the curing time is insufficient, the quality of the plate can not be guaranteed, and the plate will shrink after construction, causing the system to crack.
The advantages of XPS system are:
1. Excellent thermal insulation performance:
1, which has good thermal stability and is not affected by temperature and humidity changes. Its attenuation curve is very smooth, and the attenuation with time is very small (80% insulation can be maintained after 10 years), while insulation materials such as polystyrene board decay very quickly (only 40% insulation can be maintained after 10 years).
2.XPS board has a dense surface layer and an inner layer with a closed-cell structure. Its thermal conductivity is much lower than that of EPS with the same thickness, so it has better thermal insulation performance than EPS. For the same building exterior wall, its thickness can be less than other types of thermal insulation materials.
3. This is due to the closed-cell structure of the inner layer. Therefore, it has good moisture-proof performance and can still maintain good heat insulation performance in humid environment; It is suitable for buildings with special requirements for thermal insulation, such as cold storage, and can also be used for buildings with brick or stone as exterior wall facing materials.
Two. High-strength compressive performance
1. The unique closed-cell and dense-cell composition of extruded board makes it have excellent compressive performance (150kpa-600kpa), which solves the thermal insulation problem of floor, roof and car body parking lot.
2. The unique closed-cell and dense-hole composition of extruded board makes it have excellent tensile and shear properties, which solves the seed bearing problem of external wall thermal insulation veneer, and the bearing capacity is about twice as high as that of benzene board, and solves the technical problems such as hanging bricks in high-rise buildings.
Third, good sound insulation and noise reduction performance. The unique sound insulation and noise reduction performance of extruded board allows you not to worry about external interference and influence on others whether in hotels, KTV rooms or at home. This feature makes it particularly advantageous in home decoration and engineering decoration.
4. Excellent moisture-proof performance. Extruded board has a dense closed-cell honeycomb structure, and its polystyrene molecules themselves do not absorb water, which makes it have excellent water vapor penetration resistance. The water absorption rate is about 65,438+00 times smaller than that of ordinary foamed polystyrene board. At the beginning, it only absorbs a small amount of water, and then it does not absorb water. Its water vapor permeability is 2-4 times smaller than that of expanded polystyrene. Therefore, the extruded board can not only effectively prevent the invasion of rain and the infiltration of water, but also effectively avoid the accumulation of water caused by condensation and the expansion and cracking caused by thawing and freezing.
5. Excellent environmental protection performance. The extruded board has stable chemical properties and is not easy to decompose and mold. It has good corrosion resistance and efficient heat insulation function, which can reduce the consumption of natural resources; The solid waste produced by it can be recycled, which fully meets the requirements of the world sustainable development strategy and is a new type of environmental protection product.
Disadvantages of XPS system:
1), XPS board itself has high strength, which makes the board brittle and not easy to bend, and the stress on the board is concentrated, which is easy to damage and crack.
2), poor air permeability, almost airtight, if the temperature difference between the two sides of the plate is large, high humidity is easy to condense.
3) The price is higher than that of EPS system.
4) Its structural flexibility is poor, and it is deformed and bulged due to the change of temperature and humidity, resulting in the insulation layer falling off.
5) The adhesive has poor absorbability, and the failure surface after bonding is XPS, so the bonding strength is not enough. Special treatment is needed when bonding.
Three. Comparison of two kinds of system practice
Expanded polystyrene board is similar to extruded polystyrene insulation board. At present, the most widely used method in China is to add thin plastering on thermal insulation materials and reinforce them with glass fiber. Among them, polystyrene board is fixed on the foundation wall in three ways:
1) fixed with adhesive;
2) fix with mechanical clamp;
3) The combination of the above two fixing methods.
This method has the following advantages:
1) Because it has been used in Europe and America for nearly 30 years, the buildings built in the United States are as high as 44 floors. This technology has formed a system, and the bonding layer, insulation layer and facing layer can be used together, and there are many mature technical documents.
3) There is no need for complicated construction technology, and the general construction unit can master the construction essentials after short-term training, which is convenient for technology popularization;
4) it integrates heat preservation, waterproof and decoration, and has universality; 、
5) The whole system has strong weather resistance and good waterproof and moisture permeability;
6) The surface coating has a variety of colors and textures to choose from, which can be used together with the whole system.
At present, this method has been widely used in Beijing, Northeast China and other places, and this method has been adopted in many projects such as Beijing Yujing Garden, Wolong Garden, the reconstruction of the eighth and tenth floors of the Ministry of Construction. Because the ambient temperature required for construction is 4℃, it is not suitable for winter construction.