Expansion joint sealants for bridges increase construction reliability and durability
Expansion joints, or movement joints in bridges are designed to keep parts together as well as safely absorb expansion by temperature changes and contracting of building materials and vibration caused by traffic, ground settlement or seismic activity. The behavior of these joints can be unpredictable if not sealed properly. Therefore, to increase construction reliability, the expansion joint sealants for bridges should be chosen carefully based on factors such as material, environment and possible hazards.
The most common expansion joint sealants for bridges fall under three categories: MS polymers, polysulfide sealants and epoxy polysulfide systems. These three types of sealants all meet the most important requirements for expansion joint sealants for bridges:
- Chemical resistance: most bridges are made for vehicle traffic, which means that the sealant is likely to come in contact with fuels and their fumes.
- Flexibility: as the purpose of expansion joints is to absorb movement caused by various factors, the sealant must be flexible and allow for elastic bonding and sealing.
- Abrasion resistance: the expansion joint sealant is not to be affected by nearly continuous traffic by vehicles of different masses.
Load bearing capacity: the sealant must also endure being under pressure for longer time for example in the case of a traffic jam.
MS polymers as expansion joint sealants for bridges
MS polymers, also known as silyl modified polyethers, are a newer addition to expansion joint sealants. The polymer was first developed in Japan in the 1980 ́s and later introduced to the bigger public. MS polymer joint sealants offer a sustainable alternative to more conventional systems, as they do not contain solvents, isocyanates or silicone. These sealants are also common in bridge foundations. The advantages of MS polymer joint sealants for bridges include:
- No bubbling: when isocyanates come into contact with water, the reaction produces CO2 molecules which may cause bubbling and result in sealant failure. Due to the absence of isocyanate groups, this does not happen with MS polymers.
- No shrinkage: the MS polymer sealants are 100% solid meaning that neither solvent nor water is involved. Other water or solvent based systems cure through evaporation, which leads to shrinkage of the seal as the density increases and volume decreases.
- Easy and fast application: MS polymer based products require minimum surface preparation, are usually applied without a primer and adhere to most surfaces, even when the substrate is damp. Contact us and find out more about MS polymers increasing process efficiency.
Sealing bridge expansion joints with polysulfide sealants
Polysulfide is a synthetic rubber which is commonly used as a sealant for expansion joints due to its versatility and other beneficial properties. A polysulfide sealant is the right choice especially when no plastics are involved and there is a possibility that the joint needs to be disassembled. The solvent used in the sealants may attack plastics resulting in a system failure. When applied to substrates other than plastic, polysulfide joint sealants provide excellent adhesion and flexibility allowing for movement associated with stress, vibration and temperature fluctuation. Further benefits of these movement joint sealants include:
- Low temperature flexibility: as the name implies, polysulfide sealants have a high sulphur content. This grants the systems exceptional low temperature flexibility.
- High impermeability: the high sulphur content also contributes to high impermeability which is a desired property as water and contamination should not seep into the joint.
- Adhesive properties: of all the joint sealant options for bridges, polysulfide sealants have the best adhesive properties.
Epoxy polysulfide bridge sealants
Epoxy sealants are known for their extreme toughness in many industrial applications. The epoxy resins exist in many types and they can be mixed with other ingredients. The type of epoxy sealant most commonly used for expansion joints in bridges contain polysulfide. The epoxy polysulfide sealants are more flexible than regular epoxies and tougher than regular polysulfide sealants.
- Toughness: epoxy polysulfide sealants for expansion joints in bridges are tougher than the alternatives meaning that they are more resistant to abrasion and have better load bearing capacity.
- Increased chemical resistance: epoxy alone is resistant to a wide range of chemicals, however, the addition of sulphur included in polysulfide increases broadens the range and even allow for full immersion of the sealant.
Which sealant is the best for your bridge construction?
Choosing the sealants for expansion joints in bridges is rather simple. The most common options should be considered first, and their suitability should be assessed based on the requirements set by the environment, materials, bridge type and expected traffic. Contact us for free assistance in choosing the perfect product and getting in touch with acknowledged suppliers.