1.0 Introduction
A large portion of ten blocks of 4 storey flats were found to have in-situ concrete compressive strength of between 5mPa to 18mPa. Columns were strengthened by partial demolition and gravity grouting with non-shrink concret of 40mPa. Bean with concrete strength greater than 10mPa but below 18mPa were strengthened by steel plate bonding. 420 beans were plate bonded and 200 columns were gravity grouted.
2.0 Design
The amount of steel plates required for the strengthening were designed to increase the flexural and shear capacity of the affected members. The steel was bonded to the concrete by epoxy resin which is able to effectively transfer the load to the steel plates.
3.0 Method
All cracks found were epoxy injected.Honeycomb and spalled areas were patched up with polymer modified mortar. Steel plates of the required
dimensions and thickness were secured to the affected member by anchor bolts.Holes were drilled into the steel plate for installation of injection ports. Epoxy resin was then injected into the gap between steel plate and concrete and allowed to set. The external surface of the steel plates were cleaned and coated with epoxy sealant.A layer of coarses and is applied onto the epoxy sealant when it is still tacky to provide a rough surface for plastering.
4.0 Results
Three numbers of proof load test were carried out on the beams that were strengthened. The beams were found to perform satisfactorily in accordance to BS8110.