Repair, Restoration, and Demolition
Repair, restoration and demolition tests how you assess deteriorated concrete, choose and execute a repair that will last, and remove concrete safely without damaging what stays.
Core rules
- Assess before you repair: visual survey and crack mapping, hammer sounding or chain drag for delamination, cover measurement, half-cell potential for corrosion activity, carbonation depth and chloride testing where relevant.
- Common causes are rebar corrosion from chlorides or carbonation, freeze-thaw scaling, alkali-silica reaction, shrinkage cracking and poor consolidation. A repair that ignores the cause will fail again.
- Patch preparation: saw cut or grind square edges, remove concrete back to sound material, do not feather the edge, roughen the substrate, clean it and bring it to a saturated surface-dry condition. Use a repair mortar compatible with the parent concrete's strength and movement, and cure it.
- Cracks: structural cracks can be injected with epoxy; moving cracks are routed and sealed with an elastomeric sealant; hairline cracks may simply be filled.
- Settled slabs can be lifted by grout or polyurethane injection instead of replacement.
- Demolition: locate services and post-tensioning, obtain engineering approval before cutting structural elements, shore or underpin adjacent work, sequence the removal, control silica dust and noise, protect remaining surfaces, and segregate waste for recycling. Older buildings need a hazardous-materials survey before disturbance.
Worked example
A spalled patch is 1.2 m by 0.8 m and the concrete must come out 75 mm deep. Volume is 1.2 times 0.8 times 0.075, which is 0.072 cubic metres. A repair mortar yields 13.5 L per 20 kg bag, so 0.072 cubic metres is 72 L, divided by 13.5 gives 5.3 bags. With a 10 percent allowance for an uneven, chipped cavity, order 6 to 7 bags. The square-cut edges and saturated surface-dry substrate matter as much as the quantity.
Traps
Feathering a patch to nothing at the edges. Choosing a high-strength, stiff mortar that fails at the bond line. Cutting into a slab without checking for post-tensioning or conduit. Coating or sealing concrete that is still too wet.