Structural Sealant
Structural sealant is capable of bearing alternating external forces and can withstand higher stress points within the joints. It is important to account for construction tolerances when sizing these types of joints.
DOWSIL 995 Silicone Structural Sealant passes all ETAG 002-1 requirements for ‘Initial Mechanical Strength’ and ‘Residual Strength’ after natural and accelerated aging.
Strength
The ability of a structural sealant to resist primary and secondary loads depends on the sealant joint width (structural bite width or ‘bite’) and thickness. In order to achieve high mechanical strength, a sealant must be capable of transferring both shear and tensile forces without failure or damage.
This characteristic is critical for a four-sided glass curtain wall because shear and tensile stresses are both likely to occur during service. The shear and tensile strengths of a sealant can be increased by using a wider and thicker joint or selecting a stiffer sealant material.
A stiffer sealant can withstand higher shear and tensile forces and will also be more resistant to thermal expansion and contraction of the joint. However, it is important to remember that the shear and tensile strength values of a structural silicone are typically lower than those of weatherproof silicone.
Despite 23+2 years of natural aging, the 1st generation 2-part structural silicone test specimens cut from the hybrid SSG facade tested according to ETAG 002-1 successfully passed the key performance criteria for residual tensile and shear strength. This is very reassuring and may give conservative building code authorities the confidence Structural Sealant they need to allow future four-sided SSG facades to be built without the need for supplementary safety retainers in their corners.
The continuous mechanical characterisation of the tested specimens during combined climatic and shear loading is presented in Figure 6. The dissipated energies in x-direction indicate the structural sealant’s capacity to dampen mechanical energy, with sealants a and b having significantly higher capacities to absorb and disperse dynamic mechanical load cycles.
Durability
Structural Sealant is a durable two-component silicone that is highly resistant to ageing, fatigue and other deteriorating effects. It is an ideal sealant for construction joints with high movement capabilities. The structural silicone also provides excellent adhesion to the most common building substrates such as glass, anodized aluminium and granite.
The natural aging performance of the Structural Sealant installed on the IFT Rosenheim facade has been evaluated by means of an experimental B.Sc. study. After 23+2 years of natural aging the test specimens still met the ETAG002-1 criterion for initial and residual mechanical strength, showing a very good durability of the structural silicone.
In order to simulate the effect of a 50 year service life on a system, the test specimens were subjected to a series of 50 durability cycles. Each cycle simulated one year of weathering and complex multiaxial mechanical loadings. The course of the dynamically induced force paths (extension, compression and shear) was monitored in detail to identify suitable mechanical indicators.
The results show that the stiffer sealant tested in series A dissipates more energy during the combined climatic and mechanical exposure compared to the less stiff sealant tested in series B. This is reflected by the higher moduli of the x-displacement versus the shear displacement. Conventional hardness measurements performed on system specimens cut from exposed and non-exposed series A and B indicate that the weathered sealant material of series B is even harder than the reference, indicating very good durability of the structural sealant.
Adhesiveness
Structural Sealants must be able to bond securely to substrates or to one another to provide a suitable seal. This is critical in structural applications, as failure of the joint will allow external forces to impose stresses on the structure that could impact the safety and integrity of the building components.
One of the most common causes of failure in a structural sealant is cohesive or adhesive (creep rupture) failure. These are caused by the internal flow of the sealant material under stress. A good quality, high modulus Structural Sealant will accommodate movement by a mechanism referred to as “internal flow” or “cold flow”, which allows the sealant to deform under stress and then recover to its original shape.
Another key property of a Structural Sealant is its ability to remain stable and maintain its strength over time. The best way to achieve this is to use a highly cross-linked Polyurethane formulation. This will give the sealant a high modulus and high toughness. The cross-linking also means that the sealant will be able to resist degradation from exposure to sunlight, water, dew, ozone and other chemicals.
Weather Resistance
Structural Sealant can withstand the harsh weather conditions in the construction site. It is commonly used for curtain walls, insulating glass windows, and skylights to ensure long-lasting durability and excellent sealing performance. Structural silicone sealant is also used to provide a watertight barrier for airport runways and other roads and bridges.
It is important to choose the correct structural Structural Sealant sealant for your project. It is recommended to consult an experienced and professional manufacturer for assistance. They can help you find a high-quality, durable product that meets your construction requirements. They can also advise you on the best installation techniques to ensure optimal performance.
In a typical service life, an SSG facade is simultaneously subjected to climatic and mechanical loads. Current durability assessment methods schedule separate testing sequences for accelerated weathering and mechanical ageing. This research suggests a new durability test that combines mechanical and climatic testing simulating a year of real exposure. It enables continuous mechanical characterisation of the bonding strength of a medium-scale system specimen by measuring tensile and shear forces transmitted across the sealant bead, as well as moduli and dissipated energies in the joint.
In addition, it can detect the swelling dynamically induced force paths (extension/ compression, shear) over all yearly seasons and assess the elasticity and visco-elasticity of the sealant. It can also identify the maximum stress states, temperature and humidity sensibility of the sealant.
