Structural Sealant
Structural Sealant is required to have good adhesion to the substrates and be able to handle a variety of movement. Many architects, engineers, suppliers, contractors and applicators use outdoor weathering tests with movement to determine these factors.
These tests are also used to qualify for sustainability ratings in buildings. These ratings are based on environmental impact and life cycle assessment.
Adhesive
Structural adhesives are used in structural bonding and sealing applications where load-bearing properties are important. They must be able to transmit the external and internal forces to which the bonded materials are subjected, and they must also be resistant to corrosion and aging. There are many different types of structural adhesives, including polyurethanes, cyanoacrylates, and anaerobics. Each has its own set of characteristics, but all of them are capable of handling large loads and resisting fatigue and corrosion.
These adhesives have a high modulus of elasticity, which means they can handle a wide range of temperature changes. This makes them suitable for use in a variety of industrial and commercial applications. They can be applied manually or by using applicator nozzles in automated processes. They can also be used on a range of substrates and can cure at room temperature.
Moreover, they have good un-primed adhesion on most building substrates and exhibit excellent shear strength. They are also low in viscosity, which helps them spread easily across the surface. They also have low shrinkage and are ideal for sealing glass-to-metal joints.
They are a cost-effective alternative to traditional sealants and can be used on many different substrates. They are also easy to work with and clean up well. They are also highly durable and can withstand a range of conditions, including weathering and cyclic loading.
Cohesive
The cohesive properties of a structural sealant must have the capacity to accommodate movement and maintain its Structural Sealant integrity under stresses. This property is achieved by means of internal flow of the sealant or a rubber-like characteristic (variously called stress relaxation, cold flow or plastic flow). During stressing, the sealant deforms internally and then recovers its original shape without loss of adhesion or shear strength. This is also referred to as “stress recovery”.
Structural silicone sealants must have excellent unprimed adhesion to building substrates and tensile strength of over 60 MPa. They must be capable of handling a range of movements within a specified movement class. In addition, the silicone structural sealant must not suffer any adhesive or cohesive failures for an acceptable amount of time during field use and exposure to a variety of environmental conditions.
This test is usually performed by placing the sealant into racks that are exposed to various weathering conditions. The specimens are Structural Sealant then examined for crazing, cracking, dirt pickup and other signs of degradation over an extended period of time. This type of test is not usually found in a specification.
Considering the wide range of polymer chemistry types that can be used in structural bonding, it is critical to determine the capabilities of each product and how they might perform in the anticipated environment. This includes the expected movement, temperature, light, water and chemical exposures.
Durability
Structural sealant is a strong bonding material that can withstand large loads. The material is also resistant to aging, fatigue, and corrosion. The material is designed to withstand movement, so it is important to consider the movements that are expected for the construction project. The sealant should also be compatible with the materials that are used in the construction. The best source of information on this is the sealant manufacturer.
The BAM method allows for a detailed exploration of the mechanical response of the system under extended dynamic loading (extension and shear). This is done by monitoring the course of the swelling dynamically induced force paths over all yearly seasons. In this way, it is possible to detect suitable indicators for the load depending deterioration of the sealing system and thus determine the durability properties of the sealant.
The key requirements for a structural silicone sealant are its tear strength, elongation at break, and tensile strength. It should also be resistant to weathering, and it should have a high modulus of elasticity. The durability of a sealant is influenced by several factors, including the movement in the joint and its environmental exposure. It is important to choose a sealant that has been tested by the manufacturer to ensure that it will perform well in the expected conditions.
Compatibility
Structural Sealant must be compatible with all substrates upon which it is being installed. The manufacturer should provide information about this compatibility including details of test methods and any limits. In addition, a sample of the sealant should be tested at the temperatures that will be experienced on the job site in order to determine whether it can endure those conditions for the duration of the project. This information can only be obtained by contacting the manufacturer of the sealant.
For example, the natural aging test specified in ETAG002-1 requires that sealants pass a destructive tensile and shear strength test on specimens that have undergone weathering and enforced movement. This requires that the test specimens must show no loss of adhesion and exhibit a residual tensile strength of 75% of the initial tensile strength. Today’s structural silicones (2nd generation) have surpassed this requirement with flying colors.
Another important factor is how the sealant will react with other materials of construction and the building components to which it will be applied. For this reason there are several industry test methods that can be used to evaluate compatibility. For example, the AAMA/FGIA 713 Voluntary Test Method to Evaluate Chemical Compatibility of Sealants and Self-Adhered Flexible Flashings tests for discoloration, slumping, degradation and liquefaction. In addition, control assemblies without the sealant are also evaluated for visual inspection of substrates and re-adhesion.