The performance of an expansion joint in various service conditions depends, in large part, on the material composition of the expansion joint. The service requirements can range from chemical and ultra-violet exposure, continuous or intermittent immersion service to extreme thermal plus wet and dry cycling.
The Expansion Joint Design Process
Expansion joints manufactured for commercial or industrial usage are composed of different raw materials that impart different physical properties and characteristics to the expansion joint. For instance, a basic material can be polyurethane foam. The foam can react with silicone-based polymers that impart a certain set of physical properties and performance characteristics.
There are other expansion joints that are produced from copolymers of ethylene and vinyl acetate. This copolymer is used in the manufacturing process to produce closed-cell foam expansion joints.
The production begins with the polymer granules loaded into a hopper from a storage silo. The polymer granules are then mixed, heated, and extruded into sheets in conjunction with additives that produce specific physical properties and characteristics. The polymer sheets are loaded into an oven and heated again. The high heat starts the crosslinking process.
The next step is to load the sheets or slabs into an autoclave. Nitrogen gas is added to the sheets to purge any residual oxygen. Eventually, the nitrogen gas will diffuse into the sheets. The sheets are cooled under pressure in the autoclave and the nitrogen is locked in the sheets. As a result, the nitrogen bubbles or cells are formed and locked into the sheets. The polymerized sheets are moved through another oven, heated again and the closed-cell foam is formed.
Due to the structure and polymerization of the foam, certain performance characteristics and properties are present. The closed-cell foam expansion joint will have resistance to low temperatures, cracking, and ultraviolet radiation. This material is waterproof and supports heat welding at the job site.
Related Article: Understanding Potable Water Approvals for Tank Coatings and Linings
Expansion Joints in the Wastewater Market
In addition to the foregoing properties, closed-cell foam expansion joints provide resistance to a number of chemicals. This chemical resistance (coupled with the material’s waterproofing properties) makes the closed-cell material fit for use and purpose in the wastewater/water treatment market.
There are many chemicals that are used in the treatment of wastewater. The functions of the chemicals include (but may not be limited to):
- Assisting in the removal of solids and sludge
- Disinfecting water
- pH adjustment
- Odor control
There may be treatment tanks that may require a set of stronger treatment chemicals. In this situation, the use of a duplex system where the tank expansion joint surfaces are, first, properly prepared per the project specification, and then the closed-cell foam system is installed followed by an application of a trowel coat of CIM 1000 Trowel Grade followed by the full coat of CIM 1000 tank lining system.
Note: Please contact Chase Corporation’s technical support for a specific recommendation.
Designing a specification for the rehabilitation of a wastewater/water treatment plant can be a challenge, especially the tank lining section. Working with Chase Corporation’s technical and field support and with the use of Chase Corporation’s Ceva Expansion Joint Systems and CIM Industries Lining Systems, that challenge can be simplified.