The curtain wall is the enclosure structure of the building's exterior wall, usually composed of glass panels and metal frames, using silicone structural sealant to bond the glass panels and metal frames to form a lightweight wall with decorative effects. Compared with traditional building exterior walls, the curtain wall structure has the characteristics of simple construction, energy saving, and environmental protection. The alloy structure and a large number of glass materials also have obvious advantages in terms of cost of use and are more and more widely used in modern buildings. With the continuous development of curtain wall technology, the types and materials of panels and supporting structures of building curtain walls have been significantly improved. The use of more environmentally friendly materials can reduce building energy consumption and improve building performance. Curtain walls made of different materials put forward more stringent requirements on the bonding performance of structural adhesives. Door and window curtain walls are bonded and sealed with sealants. Once the colloidal structure cracks, it will cause water leakage and air leakage on the curtain wall, which will affect the use, and in severe cases, it will fall off and cause serious safety accidents. Combined with the international industry standard "Silicone Structural Sealants for Buildings", the quality control of high-rise building curtain wall structural sealants is analyzed.
1. Common quality problems of silicone structural sealants
Silicone structural sealant is widely used in building doors, windows, and curtain walls. It can not only play the role of bonding and sealing but also withstand a certain degree of structural stress. In addition to high requirements on adhesive performance, weather resistance, and air tightness should also be considered during the use of sealants. Among them, the aging of silicone structural sealant is an important factor affecting the sealing effect of doors, windows, and curtain walls. The sealant is exposed to the natural environment for a long time, and the impact of light, rain, and temperature will change the internal molecular chain structure and cross-linking effect of the colloid. Silicone structure The phenomenon of adhesive aging is manifested as a decrease in adhesive properties and elongation. High temperature and ultraviolet rays are important causes of the aging of silicone structural adhesives. Since the colloid itself belongs to a polymer structure, the physical and chemical properties of silicone structural adhesives will be changed in high temperatures, ultraviolet rays, humidity, and other links, resulting in a decrease in bonding performance. The following is a detailed analysis of the common quality problems of silicone structural sealants.
1.1 Silicone structural sealant aging
Factors affecting the performance of silicone structural sealants mainly include temperature, environmental factors, mechanical stress, etc. Long-term exposure of the sealant to outdoor temperature will cause cracking of the rubber material, increase the speed of oxygen diffusion and activate the oxidation reaction, and accelerate the speed of the redox reaction. It is thermo-oxidative aging. Ultraviolet rays in sunlight have the greatest impact on the performance of sealants. Ultraviolet light can directly cause rubber molecular chain breakage and crosslinking, and rubber can also generate free radicals by absorbing light energy, triggering oxidation reactions, and light energy can cause reticular cracks in rubber products with high rubber content. Oxygen in the atmosphere can cause free ion radical chain reactions in the sealant molecules, and some molecular weights can be broken and cross-linked, which can change the properties of the sealants. The chemical activity of ozone is higher than that of oxygen, and it is more destructive. The principle is similar to that of oxygen, which is to change the performance of sealants by breaking molecular chains. The water-soluble substances in the sealant are dissolved by water, or the alternating action of water immersion and atmospheric exposure can damage the rubber seal. Under the action of external force, the silicone structural sealant continues to deform and move, resulting in hysteresis, increased internal friction, and internal heat generation, which accelerates the oxidation reaction of the colloidal sealant. If the replacement is not timely, the colloid will be brittle and fractured when it is seriously aged, and when it loses its bonding performance, the door and window structures will fall off, causing very serious safety accidents.
Figure 1 The insulating glass silicone structural sealant 1
1.2 Quality of silicone structural sealant
Silicone structural adhesives will consider many factors during the design process, including adhesiveness, weather resistance, air tightness, easy extrusion, etc. The international industry standard "Silicon Structural Sealants for Construction" specifies the quality is clearly defined, and the appearance is a delicate, uniform paste or viscous liquid. To make huge profits, some businesses add silicone oil or plasticizer to the sealant to improve the appearance characteristics and obtain cheap structural adhesive products, but these inferior additives will affect the physical and chemical properties of silicone structural adhesives cause certain damage to the bonding performance, weather resistance, and air tightness, and reduce the service life of the sealant.
Figure 2 The quality of insulating glass silicone structural sealant
1.3 Colloidal pollution problem
The formulations of silicone structural sealants are different. Some sealants contain mineral oil components, which will continue to volatilize during long-term use and penetrate the interior of the curtain wall panels to cause pollution. Especially for multi-layer door and window curtain wall structures, mineral oil components will enter As for the proportion of central control, it will affect the light transmittance of the glass. If it is not cleaned in time, it will further expand the pollution and affect the decorative effect of doors, windows, and curtain walls.
1.4 The influence of complex force on the colloid
The curtain wall structure can provide a unique shape to the building, and some complex structures also put forward new requirements for the performance of the sealant. In addition to bearing the stress of the curtain wall structure, the silicone structural sealant also needs to bear the wind load from the horizontal direction and the shear force from the vertical direction. If the stress of the structural adhesive is too concentrated, it will cause mechanical fatigue and cause the silicone structure to seal. The glue is deformed, causing serious safety hazards.
Figure 3 The influence of complex force on the colloid
2. Quality control strategy of structural glue for doors, windows, and curtain walls of high-rise buildings
Sealants are widely used in building curtain walls, especially in the door and window structures of large buildings and super high-rise buildings. The large-scale glass curtain wall becomes the main structure of the building exterior. If there is a quality problem with the structural adhesive, it will not only cause the safety of the curtain wall structure to be Hidden in danger but can even threaten the safety of people's lives and property when serious. The international industry standard "Silicon Structural Sealants for Construction" has clear requirements on the type and quality of structural adhesives for doors, windows, and curtain walls of high-rise buildings. Strict quality control is required in the production and construction of the colloids to improve the use of silicone structural sealants.
Life and safety of doors, windows, and curtain wall structures. The international industry standard "Silicon Structural Sealants for Buildings" requires physical performance standards of silicone structural sealants in Table 1.
The Standards for Physical Properties of Silicone Structural Sealants
|Serial Number||Project||Technical Indicators|
|1||Degree of sagging||Placed vertically||≤3mm|
Surface dry time
|6||Tensile Bonding Properties||Tensile Bond Strength||23℃|
Water - after UV light
|Adhesive failure area||≤5%|
|Elongation at 23°C and maximum tensile strength||≥100%|
|7||Thermal Aging||Thermal weight loss||≤10%|
Table 1 Physical performance standard of silicone structural sealant
2.1 Quality Control in the production process
Sealants are widely used in the door, window, and curtain wall structures of high-rise buildings, and there are very strict requirements for the quality control of sealants. The international industry standard "Silicon Structural Sealant for Construction" stipulates that the silicone structural adhesive is a fine and uniform paste, the colloid is easy to squeeze out, and there are no bubbles, agglomerates, gels, and other impurities. Therefore, in the production process, it is necessary to select raw materials that meet the quality requirements, and the mixing state of structural adhesives also needs to be strictly controlled. The butterfly test and breaking time test are usually used to test the mixing uniformity of silicone structural adhesives.
2.1.1 Butterfly test
Take a piece of white thick paper, fold the paper in half along the long side, and extrude a silicone structural sealant about 200 mm long at the fold line, then fold the paper along the fold line and squeeze the paper surface to spread the silicone structural sealant evenly. Open the paper and observe the state of the sealant. If the color is uniform, and the surface of the colloid is bright and free of impurities, it indicates that the structural adhesive is in a good mixing state and can be used for production.
2.1.2 Pull-off time test
The breaking time test is used to detect whether the curing speed of the silicone structural sealant meets the standard. The main factors of the breaking time of the silicone structural sealant are the temperature and the formula of the sealant. If the curing speed is too fast, the fluidity of the colloid when the glue is applied will become worse, and it easily causes the risk of gun blocking during the construction process (if the sealing robot line for automatic processing of LIJIANG Glass insulating glass or the rotary sealant coating table for semi-automatic insulating glass processing is used, such problems will be eliminated); curing speed If it is too slow, the curtain wall panels cannot be bonded firmly, and it is easy to cause the panel to be unique, which will affect the construction quality of the curtain wall.
Figure 4 Automatic insulating glass rotary sealant sealing table 1
During the test, take a paper cup, squeeze the silicone structural sealant out of about 2/3 of the paper cup, insert a wooden stick into the center of the paper cup, and periodically lift it out of the paper cup to observe the state of the sealant. If the sealant does not break during the lifting process of the wooden stick, it indicates that the breaking time has not been reached, and the test needs to be continued until the sealant is broken when the wooden stick is lifted, and then record the time between when the sealant is poured into the paper cup and when the wooden stick is lifted.
2.2 Quality Control during Construction and Assembly
2.2.1 Hand pull test
The quality control of silicone structural sealants in the construction process usually requires the detection of bonding performance and surface dry time. The adhesive performance is mainly tested utilizing a hand pull test. A certain width of sealant is cut horizontally on one side of the curtain wall panel joint, and the cutting depth must reach the surface of the substrate. Cut a length of about 75mm vertically along both sides of the joint between the structural adhesive and the base material at the horizontal incision, hold the end of the sealant firmly, and press 90. Pull to peel, and record the elongation value of the sealant before breaking or peeling during the pulling process.
2.2.2 Determination of the surface dry time
The dry time of silicone structural sealant directly affects the storage and use of the gel. During the test, the sealant is squeezed on a plastic sheet with a clean surface, and the surface of the sealant is touched with a tool every few minutes. The basis for judging the surface drying time of the sealant is that the glue no longer sticks to the tool, and the time from the extrusion of the glue to the surface drying is recorded. If the silicone structural sealant does not dry within the time specified by the manufacturer, it cannot be used normally. During the construction of the building curtain wall, it is necessary to ensure that the bonding parts of the curtain wall panels are clean, clean, evenly applied, and consistent in thickness to ensure waterproof and sealing performance.
3 Quality control of structural glue for doors, windows, and curtain walls of high-rise buildings
In the process of modern urban development, more and more large buildings and super high-rise buildings appear and become new landmarks of the city. Although high-density buildings can meet the functional requirements brought about by urbanization, they also cause huge energy consumption. In building energy consumption, the air conditioning system and daylighting system account for about 2/3 of the energy consumption. To further realize the strategic policy of "energy saving and emission reduction", effectively save resources, protect the ecological environment, and reduce the energy consumption brought by buildings, in the design and promote the use of environmentally friendly materials for exterior wall decoration during the construction process. Especially in the design of building doors and windows, according to relevant statistics, nearly 50% of the energy consumption is lost through doors and windows. Moreover, some countries have a large geographical location span, and the climate difference between the north and the south is obvious, and there are significant regional differences in the thermal insulation function of buildings. sex. At this stage, the glass curtain wall is widely used in large buildings and super high-rise buildings due to its low production cost, sound insulation, heat insulation, lighting, and moisture-proof performance. The use of glass curtain walls can fully collect natural light sources and reduce Energy consumption from lighting systems. At the same time, the glass curtain wall structure also endows the building with aesthetic characteristics, organically integrates the building's function, environmental protection, and architectural structure, and interprets architectural aesthetics from different angles. The main factor that determines the service life of the curtain wall structure is the structural adhesive that plays a bonding role.
Figure 5 The quality control of structural glue for doors, windows, and curtain walls of high-rise buildings
Silicone structural adhesives are commonly used as adhesives for curtain wall panels on the market. With the continuous development of modern technology, the formula of silicone structural sealant has been continuously upgraded. The use of effective additives can not only improve the adhesive performance and tensile properties of the colloid but also effectively delay the aging of the colloid and increase the service life of the curtain wall structure.
Since the sealant is a polymer material and is exposed to the outside for a long time, it is easily affected by environmental factors, and phenomena such as embrittlement and dry cracking affect its use. Therefore, strict quality control of sealants is required before and during construction. The international industry standard "Silicon Structural Sealants for Construction" clearly states that the elastic recovery rate of silicone structural colloids should reach more than 95%, the retention rate of tensile bond strength should be more than 75%, and it can withstand high temperatures and will not be accelerated by environmental factors. Aging, to ensure the airtightness and water tightness of the doors, windows, and curtain walls of high-rise buildings. The use environment of silicone structural sealant is relatively special. Among its many performance-influencing factors, high temperature has the most significant impact on the bonding performance of silicone structural sealant. Especially in summer when there are more and more high-temperature days, the surface of curtain wall structure Long-term exposure to sunlight, the temperature will rise extremely. The molecular structure inside the silicone structural sealant will change, and the aging degree will accelerate with time. When the temperature rises to 90°C, the silicone sealant will fail. Therefore, it is necessary to avoid the construction of curtain wall structures in high-temperature environments, which will affect the quality of the curtain wall structure.
4. The summary
To sum up, glass curtain walls are widely used in modern buildings, especially the doors and windows of super high-rise buildings and large commercial buildings. Glass curtain walls not only play a very important decorative role but also perform well in waterproofing heat preservation and environmental protection. The bonding effect of the sealant directly affects the use quality and service life of the curtain wall. Once aging and cracking of the colloid occurs, the curtain wall structure will become loose, leak air, and even fall off in severe cases, causing safety hazards.
Combined with the construction of the exterior wall of the building, the prevention and control measures of the curtain wall leakage are discussed, and the waterproof and sealing effect is achieved through the silicone structural sealant. To further improve the service life and structural stability of the building curtain wall, it is necessary to conduct a detailed analysis of the factors affecting the bonding performance of the silicone structural sealant. The attenuation value of the adhesive performance under the same conditions, grasp the aging law of the silicone structural sealant and optimize and upgrade it in a targeted manner.