Foreign media list of the world's top ten sustainable buildings, nearly half of China on the list

1 Introduction
　　In the modern building structure system, curtain wall is the structure that pays the most attention to the weatherproof sealing of building joints. In order to ensure that the building curtain wall has excellent, long-lasting watertight and airtight performance, in the design and construction, it is often necessary to give special consideration to the sealant on different wall panels, different substrate material bonding, the shape of the weather sealant joints and bonding form of the choice of joints, joints, stress analysis and the calculation of the width and thickness of the joints, and so on, so that for the different structural forms of the building curtain wall, especially high-rise and ultra-high-rise curtain wall, building Therefore, for different structural forms of building curtain wall, especially high-rise and ultra-high-rise curtain wall, building light roof, steel structure main curtain wall in silicone weather sealant selection and use of a greater difference. Take building light roof as an example, compared with ordinary glass curtain wall, building light roof due to the conversion of space angle, its own material (glass, aluminium, stainless steel, PC board, etc.) and structural form of change, external factors such as wind load, ultraviolet rays, rain, snow, temperature changes, etc. on the joint sealing of the impact is very large, in actual use, water leakage and adhesive cracking or even debonding has become the most common quality problems of the building light roof! The industry image is summarised as "nine leaks in ten roofs". Through continuous practical demonstration, research and summary, one of the most critical factors that cause building light roof sealing failure, water leakage is the displacement capacity of silicone weathering sealant and its repeated role in the large displacement of the bonding capacity of the substrate does not meet the requirements.

　　 2 High displacement capacity silicone weathersealant
　　High displacement capacity of silicone weather sealant can better meet the rapid development of China's building light roof and building curtain wall higher and higher, the structure is more and more complex special requirements. For example, Zhengzhou Zhongyuan company produced MF898 silicone weather sealant, the product is a one-component, neutral curing, with high displacement capacity (± 50%) of the weather sealant, its maximum tensile strength elongation up to 400%, with excellent weathering, water, ultraviolet and other aging properties, suitable for high-rise and ultra-high-rise curtain wall, building light roof, etc., the sealing of the joints of the material has a large displacement ability It is suitable for high-rise and ultra-high-rise curtain walls, architectural light roofs and other joint sealing materials with large displacement capacity.
　　 2.1 Displacement capacity
　　Weathering sealant displacement capacity is to ensure that the building curtain wall joints sealing and durability of the vital indicators. At present, the domestic glass curtain wall or building light roof joints with weatherproof sealant general reference standard is JC/T882-2001 "curtain wall glass joints with sealant". But the standard only provides for two displacement capacity of 20 and 25 levels, which obviously can not meet the requirements of actual use.
　　 1. As the building curtain wall is becoming higher and more complex, wind pressure, temperature difference, vibration, deformation of the main structure and other factors also lead to large changes in the displacement of the joints.
　　 2. The base materials used in high-rise and ultra-high-rise curtain walls, architectural light roofs, and steel structure main curtain walls generally have a large coefficient of thermal expansion, which results in a large change in the displacement of the interfaces between the panels, for example, according to the calculations, the change in the joints of architectural light roofs is 3 to 5 times that of ordinary glass curtain walls.
Large joint changes require weathersealant to have a higher displacement capacity to adapt to it. Reference can be made to the standards of the United States ASTMC920 "elastic joint sealant standard" and ASTMC719 "subjected to cyclic movement of the elastic joint sealant adhesion and cohesion of the standard test method". Figure 1 is the standard test block made according to ASTMC719, and Figure 2 is the measured tensile cyclic test diagram of the specimen.

Figure 1 standard test block for tensile cycle test

Figure 2 Tensile cycle test diagram

　　From the above figure, it can be clearly seen that the high displacement capacity silicone weathering sealant was compressed to 50%, while the tension reached 100%, that is, double the stretching, in line with the highest level of ASTMC920 (displacement capacity) -50/+100 requirements.

　　 2.2 Tensile bonding performance
　　In the repeated action of large displacement weathering sealant should ensure that the adhesive substrate has good bonding properties. When the joint displacement changes, the elastic sealant will then produce deformation and lead to the internal stress of the material local concentration, so it is very easy to make the sealant and the substrate debonding, peeling or cracking of the adhesive layer, resulting in the failure of the joint sealing. Therefore, the adhesive properties of weathersealant should be given as much attention as its elastic properties and further refinement in the testing and development of performance indicators.

　　Table 1 is a high displacement capacity silicone weathering sealant in accordance with JC/T882 to do the conventional tensile bonding performance (displacement capacity, 25 levels) measured results.

　　In order to further investigate the final damage resistance and form of high displacement capacity silicone weathering sealant, its mechanical properties under standard conditions were determined in accordance with GB16776 Silicone Structural Sealant for Construction, and the test results are shown in Figure 3 and Table 2.

Fig. 3 Stress-strain curve of sealant tensile test

　　The test results show that the elongation of high displacement capacity silicone weathering sealant at maximum tensile strength is 400%, the maximum tensile strength of 0.93Mpa, and the substrate to be adhered to is completely cohesive destruction, so for the high-rise and ultra-high-rise curtain wall, the building light roof, such as the normal expansion and contraction and shear deformation, the material is able to maintain good elasticity and adhesion to the substrate, to play an effective sealing effect.

　　 2.3 Water aging resistance
　　Lighting roof is located in the top of the building, the catchment area is larger than the vertical facade, and more likely to accumulate water, so when the weathering sealant is used in the construction of the light roof, the material water aging performance requirements are very prominent. In order to thoroughly study the long-term water aging resistance of high displacement capacity silicone weathering sealant, firstly, according to JC/T882 standard determination of its bonding performance after immersion in water, and then further refer to GB16776 standard determination of artificial accelerated aging test of immersion in water for 7 days, the test results are shown in Table 3, the test results show that the material has excellent water aging resistance.
　　

　　It should be stressed that, no matter what kind of material sealant can not withstand prolonged water immersion, so in the building of light roof or curtain wall waterproof construction design and processing, as far as possible to do blocking (weathering adhesive sealing), dredging (drainage) taking into account the maximum avoidance of sealant joints immersed in water for a long time.

　　 2.4 Ultraviolet radiation resistance performance
　　Whether it is a building light roof or high-rise and ultra-high-rise curtain wall, the time and intensity of the sun's ultraviolet irradiation are longer, more intense, the dual role of heat and high-energy radiation is more likely to cause weathering sealant joints of aging and damage. Therefore, UV resistance is also a very important material should have a very important performance [7], especially in areas with strong sunlight, such as Guangdong, Hainan and other regions. Table 4 is the high displacement capacity silicone weathering sealant UV aging performance test results, test results show that the sealant has excellent UV resistance.
　　

　　 3 Conclusion
　　High displacement capacity silicone weathering sealant than ordinary weathering sealant has a higher ability to withstand long-term deformation of the joint performance, displacement capacity of 50 levels (according to ASTMC920), higher than the current standard JC/T882 technical indicators; at the same time, in the repeated action of the large displacement is still maintained on the substrate to be adhered to the excellent adhesion properties; the material also has excellent weathering, water, UV and other aging properties. The material also has excellent weather resistance, water resistance, UV resistance and other aging properties.
　　At present, the building curtain wall and light roof presents a diversified, non-traditional, complex structure development trend, large span, large size plate area, high-rise and ultra-high-rise, hyperbolic and other circling spiral surface and other forms of building facades will continue to emerge, high displacement capacity silicone weathering sealant can well meet the use of these building requirements, play an effective weatherproof waterproof sealing effect.
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