Introduction of Structural Silicone Sealant
In building curtain wall projects, structural silicone sealant plays a vital role in structural bonding and sealing. According to statistics, winter construction accounts for up to 42% of sealant failure cases caused by improper construction environment control worldwide each year (ASTM C1184-20 standard data). This article combines international industry specifications and engineering practices to systematically analyze the core technical points of winter construction to help you avoid construction risks in low temperature environments.
- Temperature control: the technical key to breaking through the curing speed According to Dow Corning laboratory research, when the ambient temperature is below 5°C, the initial curing time of single-component silicone sealant will be extended to 2-3 times that of normal temperature. The American Architectural Glass and Metal Association (GANA) recommends a phased temperature control strategy:
- Material preheating: Store the sealant in an environment of 15-25℃ for 24 hours before construction to ensure that the material reaches the best construction state (refer to ISO 11600 standard)
- Dynamic construction temperature control: Use an infrared heating device to preheat the surface of the substrate to maintain the construction interface temperature above 10℃ (ASTM C1518 specification requirements)
- Post-curing environment management: Build a temporary insulation shed after construction and use an industrial humidifier to increase the relative humidity to more than 40% (Technical Bulletin of the American Sealant Committee SCC-02)
Typical case
During the winter construction of the Shanghai Tower, the curing cycle of the single-component sealant was successfully shortened to 1.5 times that of normal temperature construction through a segmented temperature control system (three-level temperature control of material storage area-construction area-maintenance area).
- Interface treatment: the core link to ensure the reliability of bonding The American Society for Testing and Materials (ASTM) C1401 standard points out that in low-temperature environments, the surface of the substrate is prone to form an invisible condensation layer with a thickness of only 0.1-0.3μm, which is the main cause of bonding failure. It is recommended to adopt a three-level treatment plan:
- Physical cleaning: Use a 50% isopropyl alcohol + 50% water mixed solvent (EPA certified formula) for mechanical wiping to remove microscopic pollutants
- Chemical treatment: In an environment below -5℃, a phosphate primer (such as Dow Corning® 1205 OS Primer) should be used to improve interface wettability
- Real-time monitoring: Use a contact angle meter (in accordance with ISO 27448 standard) to verify that the critical value of the substrate surface energy is greater than 36mN/m
Industry Warning
In 2018, a high-rise project in North America neglected low-temperature interface treatment, resulting in large-scale bonding failure in the spring of the following year, with direct economic losses of US$3.2 million (NBBJ Architectural Firm accident report).
- Material adaptation: scientific selection of winter-specific products The new ISO 11600:2022 regulation emphasizes that low-temperature sealant products designed with special formulas should be used for winter construction. It is recommended to pay attention to the following technical parameters:
- Low-temperature extrusion: select products with a cone penetration value of ≥200 (0.1mm) (ASTM D2202 test standard)
- Elasticity retention rate: The change rate of elastic modulus at -20℃ should be <15% (refer to EN 28339 test method)
- Weathering-resistant reinforced type: products containing nano-silica modified ingredients (such as Sika® 265 HC) are preferred to improve anti-crystallization ability
Innovative Solution
Chemours’ latest Teflon® modified sealant still maintains 92% of the bonding strength in a -15℃ environment (third-party test report number TUV-RT-2023-0456).
【Engineering Practice Suggestions】
- Conduct on-site bonding test 72 hours before construction (refer to ASTM C794 standard process)
- Establish a temperature-humidity linkage monitoring system with a data recording interval of no more than 15 minutes
- Configure emergency heating equipment to ensure that the critical construction temperature can be maintained in the event of sudden cooling
Висновок
Winter silicone structural sealant construction is essentially a system engineering, which requires collaborative innovation in material science, construction technology and environmental control. By strictly implementing international standards such as ASTM and ISO, combined with intelligent monitoring methods, the problem of low-temperature construction can be effectively solved. It is recommended that engineering units regularly refer to the latest winter construction guidelines issued by the American Sealant and Adhesive Committee (ASC) to continuously improve the level of construction quality control.
(Reference sources for technical standards in this article: ASTM International, ISO Standards, Sika Technical Library)