Glass curtain wall because of its beautiful, energy saving, easy maintenance and many other advantages are widely used. The glass curtain wall is a composite structure of the composite wall of the glass curtain wall with the sealing adhesive and the adhesive structure. The glass unit relies on the silicone structure sealant and the metal frame are elastically connected together. The structural sealant acts as a structural bond, Transfer and bear the main structure of the stress, so the silicone structural adhesive durability is directly related to the curtain wall safety. Once the structural adhesive bonding failure, it will lead to the failure of the entire curtain wall system, and even produce breathable water leakage, glass shedding and other accidents, resulting in extremely bad social impact. With the increasing number of glass curtain wall project, the quality of glass curtain wall caused by the quality of structural plastic products has become more and more prominent. This paper analyzes the typical quality problems of glass curtain wall from the perspective of silicone sealant. Industry new standard JG / T475-2015 "curtain wall with silicone structural sealant" set the product quality control project requirements, comparative analysis of the corresponding glass curtain wall quality control measures.

1. Quality of silicone sealant for building curtain wall
1.1 life problems
JGJ 102 "glass curtain wall engineering technical specifications" clearly pointed out that the glass curtain wall design life is generally not less than 25 years [1]. Silicone structural sealant as one of its main constituent materials, and plays a very critical role, the service life should be at least 25 years. However, the current domestic market sales of silicone sealant in accordance with national standards GB 16776-2005 "construction of silicone structural sealant" for testing [2], control product quality, the manufacturer based on the standard can only provide 10 years Of the quality assurance, obviously can not meet the glass curtain wall design life of the minimum requirements. Therefore, the structural adhesive as a key material to form a glass curtain wall, which became one of the "short board", that is, the life of the structural adhesive determines the service life of the curtain wall. In addition, once the structural glue life of more than 10 years, you need to repair and alteration of the curtain wall, for today's more and more high-rise and high-rise building curtain wall, maintenance will be particularly complex, the cost will be very high, according to the relevant technical staff Statistics, if you want to 100 meters in the high altitude to replace a piece of glass, the cost of up to hundreds of thousands.
1.2 Environmental factors on the aging of structural adhesives
Silicone structural sealant is a high molecular material, in the curtain wall of the actual application process, it is inevitable to be affected by the surrounding environmental factors, such as: rain, ultraviolet light, high temperature, high humidity, cold and coastal, Due to environmental pollution caused by acid fog environment and other factors will accelerate the aging of the sealant, so that in the course of the application of discoloration, blistering, cracking or even embrittlement, cracking, debonding and other phenomena, reduced service life, seriously affected the curtain wall works Safety.
1.3 Effect of complex force on aging of structural adhesive
Glass curtain wall shape increasingly new and unique, and increasingly high, the new design of high-rise buildings continue to emerge on the performance of structural sealant made a higher demand. (1) Horizontal positive and negative wind load, as shown in Figure 1 (a); (2) vertical shear force, as shown in Figure 1 (a); (2) vertical shear force, (4) mechanical fatigue stress caused by dynamic load such as circulating wind load, vibration and so on; (5) long-term glass self-weight load causes the structural glue to produce creep force; (3) due to the structural adhesive defects caused by stress concentration caused by tearing force; Variable stress, as shown in Figure 1 (c). These complex external forces make the structural sealant long in the dynamic deformation of the naked eye can not be observed, to accelerate the aging of structural sealant.

1.4 sealant product quality problems
The domestic sealant market chaos, the market competition gradually intensified, some sealant enterprises to chase profits, regardless of social responsibility, the use of improper means of competition, at the expense of product quality at the expense of manufacturing ultra-low prices of products. Even at high filling, the use of poor quality raw materials and other means of harming users, reduce product prices, and even those fake and shoddy products fake brand names, disrupt the market and seriously endanger the healthy development of the industry. The main performance of the following aspects:
(1) sealant filled with white oil, cracked silicone oil and other poor plasticizer.
White oil is a long-chain alkane, which is a colorless, tasteless white oil, which has a low boiling point and is volatile and can be used to improve the surface gloss of the sealant. Sealant filled with white oil, not only the cost of the sealant greatly reduced, while the appearance of the sealant, extrusion performance has greatly improved, the user can not use the process of temporary quality problems. With the passage of time, the sealant in the white oil gradually volatile, resulting in the sealant itself hardened, brittle, and even cracking phenomenon; while white and butyl sealant polarity is similar, according to similar compatibility principle, butyl Sealant encountered white oil, it will be swollen, dissolved, resulting in hollow glass flow oil, fog, debonding and other phenomena [3].
Pyrolysis of silicone oil is the recovery of the silicone sealant has been cured by high temperature pyrolysis of the silicone oil, the volatile high, chemical composition complex, containing a variety of polar substances, if added to the silicone structure sealant, not only with the main silicon Rubber compatibility is not good, volatile, so that the silicone structure sealant harder and harder, but also with butyl or profile adverse reactions, leading to sealant debonding failure, there are serious security risks.
(2) Sealant itself is poor resistance to aging. Some manufacturers of sealant at the beginning of the performance can meet the national (industry) standard requirements, after a period of wind, rain, sun aging, the performance of the sealant has a significant attenuation, sealant will Hardened, brittle, in the construction after the use of serious cracking, leakage problems.
(3) fake brand name, shoddy. Some manufacturers and contractors in order to pursue high profits in the middle of the production process using low-quality sealant counterfeit brand-name products, shoddy, to the curtain wall project caused serious quality risks. Part of the business by low-cost competition to take risks, the end result is a serious decline in the quality of construction projects, so that the glass curtain wall over the city "from time to time bomb" into reality, to people's personal safety left serious risks.
2. Standard comparative analysis and quality control measures
In view of the above problems, the use of scientific and strict product standard requirements is an important measure. Related to the silicone structure of the standard glue, there are mainly China GB16776-2005 "architectural silicone sealant", the United States ASTM C1184-2005 "silicone structural sealant", the European ETAG 002-2012 "structural sealant assembly ( SSGK) [4], and in Europe there are EN15434: 2006 (2010) "Building glass - structural or anti-UV sealant product standard (for structural seal assembly or exposed sealed hollow glass unit)" [5], which ETAG002 and EN15434 silicone sealant requirements are basically the same, the standard test items in Table 1.

表1.硅酮结构密封胶标准试验项目对比