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Joint sealing is the process of applying a sealant to a joint to minimize the infiltration of surface water and incompressibles into the joint system. Sealants do not fully prevent the infiltration of water and incompressibles into the joint as there will always be some infiltration. The infiltration becomes more likely if the sealant is not maintained at the recommended levels and resealed as necessary. Sealing joints and maintaining well-sealed joints may improve performance of the pavement, but currently research is ongoing to determine the effectiveness and benefits of sealing joints.
Joints can either be sealed during initial construction, during maintenance and repair activities, or not at all. If the joint is not being sealed or is going to be filled, the initial saw cut for the joint is all that is required. If a more conventional poured or preformed sealant is to be utilized, after the initial saw cut is made, the joint must be widened and cut again to create the sealant reservoir. The width that the cut will need to be is dependent on the type of sealant and should be based on the manufacturer's recommendations. The width also helps to determine the depth, because the two are related. The proper shape of the saw cut reservoir is required to ensure proper adherence to the sides and proper performance. Most poured sealants require a backer rod to help relieve stresses on the sealant and to reduce the amount of sealant required. Preformed compression seals are designed to be pushed into the joint and remain in compression throughout their service lives. Isolation joints utilize a compressible materials at the bottom of the joint with a bond breaker between the compressible material and the sealant material.
Sealing joint requires a few extra construction steps on top of typical joint construction. Once the initial saw cut for the joint is cut, the sealant reservoir can be created. In some cases the sealant reservoir will only be as wide as the initial saw cut. Once the width and depth of the sealant reservoir are determined, the cut can be applied to the pavement. The width should not be greater than 1 in. The wider the joint is cut, the louder the joint will be under traffic loading. The different seals will require different widths and depths.
Once the reservoir is cut, the joint must be cleaned. The joint should be cleaned immediately behind the saw cutting or joint widening and immediately prior to sealing operations. This removes any saw-cut slurry, soil, sand, or debris. The cleanliness of the joint face is extremely important as it will impact the bond between the concrete and the sealant. A quick way to ensure cleanliness is to run a finger along the face and if dirt or dust is picked up, the joint should be recleaned before being sealed. Cleaning the joint is inexpensive relative to the total cost of sealing the joints but it can have a significant impact on the performance.
Once the joint is cleaned, a backer rod can be installed if it is to be used. The backer rod minimizes excess stress on the sealant material while providing support for the tooling of the surface. The backer rod also prevent the sealant from three-sided adhesion which can cause extra stress in the sealant. It also prevents the sealant from filling the entire joint thus reducing the amount of sealant required.
With the backer rod in place (if it is to be used), the joint can be sealed. The manufacturer's minimum temperature should be observed and followed. The joint faces should be dry to ensure proper adhesion. The joint should be filled from the bottom up to prevent air from getting trapped under the sealant. For best results, the joint should be filled from beginning to end in one smooth operation.
When using hot-pour sealants, field control of heating should should be managed properly with temperatures typically between 175 and 200 °C. A double boiler and insulated hoses should also be utilized while always considering the shape factor of the filler to the sealant. Hot-pour sealants typically last 4-7 years.
Silicone joint sealants come in pre-packaged drums and the manufacturer controls the properties. The shape factor and the cleanliness of the sidewalls are of great importance. Weather and moisture conditions can also impact the application and performance. Moisture in the air can aid curing but moisture in the concrete can deter bonding. Silicone sealants typically last 8-15 years.
Compression seals typically have designs of 5 or 6 cells. For best performance of compression seals, the reservoir width should be uniform. Compression seals do not require a backer rod. Some factors that can impact the installation quality include lubricant, material stretch, twist, and debris. Compression seals typically last anywhere from 15-25 years.
Some local studies have found that sealing joints is not cost-effective and does not provide a long term benefit. The Wisconsin Department of Transportation made the decision to stop sealing joints in 1999 because they found sealing joints to not be cost-effective. Other factors also played a role in this decision such as a the installation and maintenance of proper drainage systems. Maintenance of the drainage system is very important because without maintenance drainage aspects such as edge drains can actually cause deterioration to the pavement. The table below summarizes the main joint sealing practice of a number of states.
|Colorado||Seal||Silicone sealant, one blade width|
|Illinois||Depends ->||Unsealed transverse, Sealed Longitudinal|
|Kansas||Depends ->||Unsealed on bound base, Sealed on aggregate base|
|Minnesota||Depends ->||Unsealed for > 45 mph with drainage, Sealed otherwise|
|Utah||Seal||Seal initially but rehab depends on region|
|Note: Data up to date as of 2014|