What is a expansion joint?
Every material has a tendency to change its dimensions essentially with the change of temperature. Some material in the world are undergoes shrinkage and some materials are goes to elongation in this process. For this reason for any civil or mechanical design it is first and foremost that you put some extra gap or space between the two moving parts,two adjacent parts and two thermally induced material.
In case of civil engineering it is practically implemented by providing gaps between the slabs or box girder of a bridge,by providing a gapbetween the structural elements of any building system etc.
Why expansion joint is necessary?
Most of the material expand when it is subject to temperature and contraction when it is subject to less temperature than it was in before. So if expansion gap is not provided than material will tend to expand and will find no spaces to provide the extra length. Then it will cause the serious damage to the structure by causing expansion cracks. Eventually it may cause surface roughness of any road surface and may disturb the travelers.
If not properly treated it can fully damage the structure and reduce the serviceability.
What are different types of expansion joints used in construction of bridges?
There are many manufacturers and there if of many types. The types and design depends on the traffic mode of any roadway system. Some of the different types of expansion joints the following are the most familiar and is mostly used in construction industry.
a) Finger Type Joint
b) Modular Type Joint
c) WaboCrete Silicone Seal
d) WaboCrete Flex Foam
g)Wabo Evajote UV
How to Change/Replace Expansion Joint of a Existing Bridge?
Step:1: Removing the old expansion joint
To replace the old,fractured or not moving expansion joint with a new,fresh and working one,you first have to remove the existing expansion joint of the bridge. To remove the existing one first you need to remove all the concrete and premix around the joint. You can use different equipment to complete this tremendous job. Different manufacturers like HILTI, BOSCH produce a lot of variety of concrete breaker to break the existing concrete.
You can choose any type of concrete breaker. You can also choose hammer and impact process to break the concrete. Choose any of the method that is easy to implement. Choosing the type of method depends upon the reinforcements types and their bonding with the concrete. You may need to apply both of the methods to do this work quickly and efficiently.
Step:2: Clearing the Loose Material
After removing the joints from the bridge you need to thoroughly clean the surface of concrete. Do not forget to thoroughly clean any dust, sand, broken concrete and other materials so that the joint replacing place is really neat and clean.
Step:3: Place the Shuttering
There should be a gap between the two portion of the bridge. So don’t forget to put a soft rubber like material like Polystyrene foam or any other material that may undertake compression stress. This will help the bridge to take compression stress during its repairing and construction phase. On the other hand, it will prevent the newly placed concrete to flow away to the bottom of the bridge. So carefully place this styrofoam so that there is no leakage underneath the joint.
Step:4: Placing the New Joint and Centering
Now you need to place the new joint over the broken concrete and you also need to align it along the center line. For this purpose you may use crane truck to lift the joint to up and place it. Before placing it weld a piece of U- channel over the joint so that it become on the surface level of the road of the bridge. Then put the joint on the previous joints place. After that you may need to center the joint according to the center line of the joint. You can use a string to center the joint over the expansion gap. Please be sure that you put the joint over the gap on the center line because it is very important to move the joint according to the movement of the bridge. Use try and error process to center the joint. Try several times to be correct.
Step:5: Reinforcement and Welding
At this stage you may need to weld the joints with the existing reinforcements of the bridge. You may also need to provide extra reinforcement depending on the design of the joint. You may need to provide different types of bolt and epoxy depending on the the types and design of the joint.
Step:6: Cleaning and application of Bonding Agent
You need to clean again and again to ensure no loose materials are left on the concrete surface. Because the loose materials will prevent the concreting from being attached to the existing surface. You have to put a bonding agent on the existing concrete surface to ensure proper bonding between the old surface and the newly provided surface. Commonly used bonding agent is Nito Bond. There is a resin and a resin. You have to mix both of them to form a paste. Then you have to apply it on the existing concrete surface with the help of a brush.
Step:7: Concreting and Premix Applying
After you completed applying bonding agent you need to do concreting. For concreting you need to have well graded good quality stone and good quality sand. You also need to have quick concrete hardening and super plasticizer so that concrete gains its strength within a very short time. Generally Glenium Ace 30 JP are used as super plasticizer in bridge expansion joint replacing works. It works fast and gives concrete a suitable strength for traffic movement. It has to apply within the design range to gain maximum result. Good quality cement also have to use to ensure good quality of work.After concreting is applied it is needed to apply premix to ensure good slope of the road surface.
Step:8: Finishing works and Curing
After concreting is done it is needed to maintain the slope of the road surface with the existing concrete surface. After the concrete gain some sort of strength it is needed to use curing agent to ensure good curing. MasterKure is generally used for this purpose. After Masterkure become dry it is needed to continuous curing for 7 days. But the traffic could be opened after two days of concreting.
You are finished with the replacing work now.
- Bridge: Definition,Types and Maintenance (allaboutfreebooks.wordpress.com)
- Engineers Begin Inspections Of I-77 Bridges (wccbcharlotte.com)