In 2013, I was involved in two balanced cantilever bridges named as Meghna Bridge and Meghna-Gumti Bridge. The bridges are situated near to Dhaka, Bangladesh and are very important as it connects the capital Dhaka with the port city, Chittagong. The rehabilitation work was a comprehensive work of both strengthing of the scoured pier bottom, regulating the river flow and replacing the old, worn out expansion joints. As the project was a big one with a lot of works included, it is not possible to accumulate all of the works done in a single post and therefore, today I am just concerned about how we replaced the expansion joints.
Step-1: Removing the old expansion joint
An expansion joint is a very important structural part of the structure and to remove it the engineer needs to take all kinds of safety precautions. First of all, the bonded concrete with the old expansion joints needs to be broken and in many points, it is also needed to cut the reinforcement. To break the concrete we used HILTI machines. But based on concrete strength you should choose the proper concrete breaking machine. If concrete breaking machines are not available the engineer can also choose hammer and chisel. The selection should be based upon the strength of the concrete and is solely dependent on the engineer’s choice.
Step-2: Cleaning and removing of loose material
After breaking the old concrete, the exposed concrete surface should be cleaned using heavy pressure blower. Any kind of loose concrete or other foreign particles should not be there.
Step-3: Formwork/shuttering and aligning the new expansion joint
After cleaning you are now ready to pour concrete. But to make it steady and settle down you need to have a good shutter. The gap between the two portions of the bridge should be covered with a soft rubber-like material. In our project, we used styrofoam(you can also use that!!) to cover the gap.
After covering the gap, the new joint(pre-prepared) should be placed. Please make sure you have to be precise in placing. Because if it deviates it may not function as an expansion joint at all.
You need to weld the reinforcement of the new joint to the existing reinforcement of the bridge. Please keep in mind that welding length and total welding area are important to ensure proper bonding between the old and new reinforcement. This is also necessary because the concrete and reinforcement need to act simultaneously.
Step-5: Pouring Concrete
Pour the prepared and predesigned concrete of required strength and level the concrete as per the slope of the bridge. For early usage of the bridge, you may use superplasticizers and curing agents.
Replacing the expansion joints is a heavy and troublesome work. It is often a necessity to replace the bridge joints to make it functioning again. Simple mistakes can lead to serious injurious and financial costs. Therefore, everyone should be careful in joining such repairing works and adequate safety measures should be taken into account.