Durable Stability of Silicone Structural Sealant and Quality Control Measures of Glass Curtain Wall

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 which is sealed with adhesive adhesive adhesive. The glass unit is connected with the elastic frame of the metal frame by means of silicone sealant. The structural sealant acts as a structural bond, Transfer and bear the stress of the main structure, so the durability of silicone structural adhesive 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 of the glass curtain wall project, the problem of the quality of the glass curtain wall is becoming more and more prominent. This paper analyzes the typical quality problem of the glass curtain wall from the perspective of silicone structural sealant. Through the elaboration of the new standard of construction industry “The curtain wall with silicone structural sealant products” (hereinafter referred to as “new standard”) set the product quality control project requirements, put forward the corresponding glass curtain wall quality control measures.

1. Quality of glass curtain wall works

1.1 building curtain wall maintenance and service life

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, silicone structural sealant as one of its main constituent materials, and plays a very critical role, life should be At least 25 years. However, the current domestic market sales of silicone sealant in accordance with the national standard GB 16776-2005 “construction of silicone structural sealant” for testing [1], control product quality, the manufacturer according to the standard generally 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. Construction industry has been drawing on the international advanced standards for the preparation of a new standard “curtain wall with silicone structural sealant”, in December 2014 through the audit, the standard curtain wall with silicone structural sealant products clearly proposed a minimum of 25 years of service life To ensure the quality of building curtain wall construction and stability and safety. The minimum 25 years of service life and JGJ 102 “glass curtain wall engineering technical specifications” in the glass curtain wall design life requirements [2], to solve the glass curtain wall after a period of time due to structural adhesive aging caused by maintenance problem.

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, saline soil salt spray environment and Due to environmental pollution caused by acid fog environment and other factors will accelerate the aging of the sealant, so that the application process of discoloration, blistering, cracking or even embrittlement, cracking, debonding and other phenomena, reduced service life, seriously affected the curtain wall works Safety.

1.3 Effects of complex forces on the aging of structural adhesives

Glass curtain wall shape increasingly new and unique, and increasingly high, the new design form of high-rise buildings continue to emerge on the performance of structural sealant made a higher demand. Structural sealants are used in the process of glass curtain walls to withstand a variety of complex external forces: (1) horizontal wind load in the forward and reverse direction; (2) vertical shear force; (3) due to structural adhesive defects tend to cause stress concentration (4) the mechanical fatigue stress caused by the dynamic load such as circulating wind load, vibration and so on; (5) The long-term glass self-weight load causes the structural glue to produce creep stress. 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

Domestic sealant market chaos, the market competition gradually intensified, some sealant enterprises to chase profits, regardless of social responsibility, the use of unfair competition means to sacrifice the quality of products at the expense of manufacturing ultra-low prices of products. Even at high filling, the use of inferior raw materials and other means of harming users, reduce product prices, even worse to fake and shoddy products fake brand, 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].

The pyrolysis of silicone oil is the recovery of the silicone sealant has been cured by high temperature pyrolysis extraction of silicone oil, the volatile high, complex chemical composition, 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 initial performance can meet the national (industry) standards, 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 desperate, 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 a serious risk.

2. Quality control measures

In view of the above problems, the use of scientific and strict product standard requirements is an important measure. Need to set up the corresponding scientific test items, especially on the silicone structural sealant aging test method, to further improve China’s silicone structural adhesive standards, the implementation of mandatory policies to improve the industry access system to improve the stability of silicone structural sealant To ensure that it has a longer life.

Related to the standard silicone adhesive standard is the first foreign ASTM C1184 “silicone sealant”, China’s reference to the ASTM standard developed GB16776-1997 “architectural silicone sealant”, after a partial revision, promulgated the 2005 Version. Europe in 1999 issued the ETAG 002 “European Technical Certification Guide for Structural Sealant Assembly System (SSGS)” and revised in 2012 [4]. In addition, 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 related silicone structure The requirements of the sealant are basically the same, and the corresponding test items are put forward for the influencing factors such as environment, complex force and quality control, and the strict stability of the silicone structural adhesive is put forward, which greatly improves the product quality level. The new standard “silicone sealant for curtain wall construction” draws on the international advanced standard ETAG002-2012, clearly pointed out that the curtain wall with silicone structural sealant products minimum 25 years of service life requirements, and put forward more scientific and strict requirements, For the construction of curtain wall quality control measures.

2.1 environmental factors on the sealant to accelerate aging

The new standard sets the water – ultraviolet light test, salt spray environmental test, acid mist environmental test, curtain wall cleaner test and other testing items, taking into account the various environmental factors on the impact of structural sealant aging.

Water-UV light test is a combination of ultraviolet radiation and exposure to water, the test of anti-aging properties of sealant, water-UV irradiation test time 1008h, much higher than the national standard (300h), and the water quality and UV Strength put forward higher requirements. Salt spray environmental test and acid fog environmental test were used to simulate the salt spray environment and acid fog environment conditions to assess the aging resistance of sealant.

2.2 mechanics factors on the sealant to accelerate aging

In addition to the national standards for tensile performance requirements, the new standard increases the setting of the shear (entry “cut” provided by the industry encyclopedia), tearing, mechanical fatigue, creep testing items, taking full account of structural sealants The actual use of the process by a variety of complex external forces.

2.3 Sealant product consistency identification aspects

The new standard increases the set of thermogravimetric analysis, infrared spectroscopy, density, hardness and other control items to ensure product stability and uniqueness. Density is related to the amount and proportion of sealant, and product consistency. Hardness too much or too small will also have some adverse effects on the use of sealants, while the hardness of the size can also reflect whether the product is consistent. The thermogravimetric analysis can quantitatively analyze the content of low boiling substances in the sealant. The infrared spectrum can qualitatively determine the molecular structure of the substance and determine the composition of the substance. The use of thermogravimetric analysis and infrared spectroscopy analysis can ensure the consistency of the product, to eliminate the application of fake and shoddy products, and effectively determine whether the silicone sealant mixed with poor plasticizers (such as white oil).

2.4 Determination of mechanical properties of sealant after aging

The new standard uses the method of maintaining the mechanical properties to measure the performance of the sealant. The tensile bondability after the salt spray environment, the tensile bondability after the acid mist environment, the tensile bondability after the ultraviolet light irradiation, the tearing property, the fatigue performance The ratio of the required tensile strength to the tensile strength of the initial condition is the ratio (i.e., the performance retention rate) of ≥ 0.75. The requirements are intended to control the durability of structural adhesive products, which require structural adhesives to withstand various aging factors during long-term use and still maintain good performance and long service life.

In order to meet the requirements of the new standard products and the domestic market sales of ordinary products, long-term atmospheric exposure test and regular sampling tracking test, comparative analysis of its durability. Continuous tracking of 30 months of test results shown in Figure 1.

 

Figure 1, 1 # to meet the new standard products, 2 # ~ 5 # only to meet the national standard products. Through 30 months of continuous atmospheric exposure, to meet the new standard product tensile bond strength remained essentially unchanged, elongation at the beginning of a slight increase in aging, 3 months after the stabilization; and the remaining product tensile bonding Strength showed different degrees of attenuation, decreased elongation at break. The results can be seen to meet the new standard of silicone structural sealant has good mechanical properties to maintain capacity, excellent durability, to better ensure the safety and service life of the curtain wall.

3. Conclusion

Structural adhesive in the glass curtain wall works has an important role, its durability is directly related to the safety of the glass curtain wall, should learn from the international advanced standards, improve China’s silicone structural adhesive standards, the implementation of mandatory policies to improve industry access system to ensure that silicon The ketone sealant has a long life in use. At present, the new standard of construction industry, “the curtain wall with silicone structural sealant” learn from the international advanced standards for the preparation of silicone sealants in the 25-year quality assurance on the basis of the development, and curtain wall structure design life consistent with the test The method is comprehensive, the project is more scientific and reasonable, and it is more suitable for the practical application environment of the silicone sealant. It can strictly control the durability stability of the silicone structural sealant and ensure the quality stability and safety of the curtain wall project The


Post time: Apr-20-2017
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