Structural Sealant
Structural silicone sealants are designed to be load bearing and are used for bonding components. They can transmit external and internal forces, unlike weatherproof adhesives which can only be used in areas without loads.
Choosing the right structural silicone and ensuring compatibility can have a significant impact on the performance of your glass curtain wall. IQ uses high quality black Dow Corning industrial strength structural silicone.
Strength
Structural Sealant is a strong adhesive which holds surfaces together and protects them from damage. It is used to bond glass, aluminium, copper, steel, stainless steel, and other materials together. It is used in commercial, residential, and industrial buildings, and is a critical part of the glazing industry. Structural Sealant can be applied in a variety of ways, including by injection, spraying, and by using a caulking gun. It can also be used to seal gaps in walls, ceilings, doors, and windows.
During the exposure test, two different structural sealant series were subjected to combined mechanical and climatic loading. Results from continuous mechanical characterisation as well as discontinuous characterisation through tensile and shear tests of cut out small-scale specimens, hardness measurements and visual inspection are presented. In general, the results from the two series show differences in their performance characteristics. The higher moduli and dissipated energies of the stiffer structural sealant in series A indicate increased mechanical resistance and damping capacity. In contrast, the shear strength and rupture behaviour of the less stiff structural sealant in series B are lower, indicating a possible higher susceptibility to artificial ageing and fatigue.
As shown in Figure 6, the dynamic moduli EDyn of both sealant series decrease most strongly during the first climatic cycles. This is mainly due to stress relaxation and the adjustment of the filled silicone elastomer material to the new environmental conditions. The resulting dynamic properties stabilise after the first few climatic cycles.
Durability
Structural Sealant is a highly durable material suitable for the bonding of weight structure, especially in four-sided structural glass facades (SSG). Unlike weatherproof adhesives that fail in the long term due to alternating external forces, silicone structural sealant resists this cyclical stress and provides very high mechanical performance. It is also capable of withstanding aging and UV exposure without loss of initial or residual strength.
Most silicone structural sealants are moisture curing polymers aka Room Temperature Vulcanise (RTV) adhesives that take in the surrounding humidity to begin the chemistry reaction that produces the tough, flexible rubber compound. The cured adhesives exhibit minimal shrinkage and superior bonding to a wide variety of substrates including metals, concrete and glass.
The durability of the adhesive is further enhanced by Structural Sealant the ability to resist a number of environmental and operating conditions such as weathering, ponding water, vibration, low temperatures, harsh chemicals, ultraviolet radiation and oxidation. This capability makes the product ideal for both new construction and retrofit applications.
To demonstrate this ability to withstand the challenges of the real world a newly developed performance-based durability test method was applied on two benchmark sealants representing first and second generation 2-part structural silicones. The system’s reaction to simultaneously exposing test specimens to artificial weathering and complex multi-axial mechanical loadings is used to explore the sealant’s behavior under both these superimposed loads over an annual cycle. This helps to provide insight into the mechanical and chemical changes that occur in the sealant over the anticipated service life of 50 years.
Weather Resistant
Structural Sealant is a high-strength adhesive that is used in structural bonding applications. It is designed to transfer external and internal forces between the bonded materials and maintain its integrity during service. It is also anti-aging, anti-fatigue and anti-corrosion with good toughness. It is also a waterproof sealant and provides UV protection.
The performance of structural Structural Sealant sealant is evaluated by assessing its mechanical response under various climatic conditions. From the stress-strain curves obtained from tensile and shear tests characteristic mechanical parameters such as maximum stresses and the residual strength ratio can be determined.
Additionally, a dissipated energy measurement is made on the accessible sides of the sealant bead during climatic exposure. This parameter reflects the capacity of the sealant to absorb and damp mechanical energy during loading cycles. Test specimens from series A show higher dissipated energies during climatic exposure than those from series B. This could be attributed to the different stress relaxation behaviour of the two sealants.
When selecting a structural sealant, it is important to account for construction tolerances when sizing the joint. In addition, it is important to consider the anticipated movement of the structure during its service life. It is also recommended to discuss the expected conditions of use with the supplier, who can comment on its ability to perform under these conditions.
Aesthetics
Structural Sealant is used in large commercial buildings as the joint sealant around glass curtain walls and other glazed surfaces. This type of sealant must be able to withstand a lot of movement while maintaining its strength and appearance. This type of sealant must also be able to withstand exposure to UV radiation and other weathering conditions that can damage the bond between the sealant and the substrate. This is why it is important for all of the critical sealant properties – adhesion, cohesive strength, recovery after deformation and modulus to be balanced properly with the proper joint design and substrate selection.
Many projects now utilize sustainability rating systems that give credits or points based on the use of environmentally friendly materials. This makes it even more critical for building owners and contractors to select a sealant that can be used in these types of applications and will not negatively impact the performance of the project.
One of the best tests for this is ASTM C920 (Structural Sealants) which is a very rigorous test specification that looks at different types of sealants – single component or multicomponent; grade designations like P = pourable or gunnable and NS = non-sag; and various movement classes. The main test is immersion that exposes the sealant to temperature cycling between -100°F and +300°F and the test method compares both the assembly without the sealant to the assembly with the sealant. The criteria for passing is that 75% of the joints do not have either adhesive or cohesive failure.