The replacement of damaged concrete elements requires demolition and removal of existing structural elements and their substitution with new members. The demolition process is carried out after proper jacking is applied to relieve imposed loads on the damaged structural member.
Great care should be practised to avoid damaging existing steel bars if present. This measure is considered to splice the existing bars with the newer ones.
A complete replacement of structural member is considered for structural members that have been damaged severely, and it would be the most cost-effective method or an economic choice for the repair of the member. The replacement method has been widely used to repair structures that suffered from earthquakes.
The newly constructed structural member should possess similar strength to that of the previous element or improve to a certain extent. All damaged concrete structural members such as beam, columns, braces and walls can be replaced.
When is Damaged Concrete Members Replacement Required?
This repair method can be used if none of the other strengthening techniques is adequate. Not only is this technique used to repair deteriorated buildings but also employed to increase life span of structures specifically bridge structure. This method is specifically suitable for strengthen buildings that are hit by earthquakes.
Specification of Repair Materials
Repair materials should be specified based on the specifications and recommendations of applicable codes. For instance, for reinforced masonry walls, open-ended masonry units should be employed, and masonry units, grouts, and mortar used need to meet requirements of ACI530/ASCE 6. For reinforced concrete member, the minimum concrete compressive strength is 21MPa.
Replacement Execution
- If the damaged structural member is load-bearing, shoring needs to be provided adjacent to it to withstand loads while the member is demolished and not present to carry the loads, Fig. 3.
- The structural member must be carefully demolished using proper tools such as saws and chipping tools.
- If present, steel bars should not be damaged in order to splice them with new steel reinforcements which are going to be installed for the new structural member, Fig. 4.
- The surface of the surrounding structure should be prepared to make sure adequate bond is generated between existing and new materials, for example, roughening surfaces.
- New reinforcing bars should be spliced to existing bars, Fig. 5.
- If new reinforcing bars are required to be attached to the existing structure, these bars should be anchored to the existing structure by setting them into holes with epoxy.
- The depth of the holes needs to be adequate in order to make sure that the full potential of the steel bars is utilized. It is advised to consulate epoxy manufacturer for the proper depth of the bar and for the instructions for installing the epoxy.
- The new concrete can be poured using suitable means. For example, using formworks as shown in Fig. 5, or applying shotcrete.
- If formworks are employed, fresh concrete is poured through an access hole near the top of the formwork, and extra holes may be required to provide access for vibrators to consolidate concrete.
- Finally, proper curing regime is used to make sure that concrete achieves the designated strength. For
Practical Consideration
Due to the fact that newly placed concrete would inevitably experience shrinkage and existing concrete would not undergo any movement, the concrete of new constructed member would develop cracks.
These cracks need to be repaired after significant amount of shrinkage has occurred for instance after two to four months. The shrinkage cracks should be repaired using epoxy or any other suitable repair materials.
A percentage of the epoxy-anchored dowels should be load-tested to at least 50 percent of the yield strength of the bar. A special inspector familiar with epoxy installation should observe installation of the epoxy.
Finally, the layout and anchorage of the reinforcing steel should be inspected before forming the concrete.