Deflection due to strengthened in Flexural members
Many situations in which flexural members, and especially bridge girders, have been found to have less than their special attention was paid to the paid to the bond between the old concrete and the new anchor blocks. The existing concrete was cut back to the depth of the cover and roughened.
After the new block had been cast in-situ the contact surface was injected with low viscosity epoxy resin under pressure, the injection being monitored ultrasonically. Some of the new tendons were deflected at existing diaphragms, reinforced required.
In view of the importance of the new anchor blocks to the success of the repair, we might have expected that dowel bars would be provided to connect the block to the existing concrete but no mention is made of this possibility and apparently what was done has been found to be successful.
The basis of this success is the roughness imparted to the old concrete. Epoxy jointing between smooth concrete surfaces would be expected to deform over a period over a period of time and relax the stressed tendons.
Strengthening of Beams
The strengthening of a beam, the load acting on it should be reduced by removing the tiles, bed mortar etc. From the slab. In addition props may be erected at mid span of each slab and tightened in such a manner that slabs are not damaged. After chipping off of the existing plaster on the beam, additional reinforcement at the bottom of beam together with new stirrups are provided.
The bars are passed through or inserted in the supporting columns through holes of appropriate diameter drilled in the columns. The spaces between bars and surrounding holes are filled with epoxy grout to ensure a good bond.
Expanded wire mesh is fixed and anchored on three sides of the beam as shown in fig. To ensure a good bond between old concrete and polymer modified mortar, an epoxy bond coat is applied to the concrete surface.
While the bond coat is still fresh, a layer of polymer modified mortar is applied. The required thickness on all the three sides is achieved by application of 2 to 3 layers of mortar. While applying mortar at the bottom of beam, the thickness of mortar layers should be so adjusted that sagging is completely covered and beam looks deflected.
The mortar is cured for appropriate period in water and thereafter it is allowed to cure in air. Epoxy resin should also be injected in the cracks along top of beams. If new stirrups are required for shear strength enhancements should be followed.