Original Design of Rehabilitation of existing RC drinking water reservoir considered cleaning of the reservoir, removal of old plaster and “ironing” of the walls, plastering of inner roof slab surface.

After the entry to washed reservoir where deposited sludge has been removed, disturbing existing conditions have been revealed. What came immediately to attention is bunch of roof slab reinforcement hanging like spaghetti from the roof slab, deteriorated from corrosion during constant exposure to high humidity where no concrete cover was provided during original reservoir construction. Roof slab reinforcement was ~70% exposed, visible. Previous attempt of exposed reinforcement protection was visible where plastic foil tapes were applied directly over the reinforcement. Holes present in roof slab concrete from where rain, bugs, small animals could easily enter the reservoir. Multiple orange stains on the inner walls indicating serious leaking of the reservoir walls where high level of underground water managed to enter the reservoir. Walls were multiple times coated by all types of hydro-plaster, failing to seal the walls, concrete deteriorated on water entry points. Columns made of oversized aggregate concrete with exposed reinforcement on some sections. Uneven, unlevelled base slab surface with spilled concrete from previous “rehabilitation projects”.

With coordination of Employer and Designer, scope of works has been changed and extended where a New Design consisted of removal of existing roof slab and part of walls – so that new reservoir could be built inside of the existing reservoir shell. Considering doubtful structural stability of vibrating roof slab, no-entry has been declared due to H&S reasons. Demolition of the reservoir’s roof slab exposed that roof slab thickness was 8-10cm with deteriorated & corroded reinforcement (only 1 layer), bars were not even lapped and those which were attempted to over-lap had no contact with each other. Only plain bars were used, no ribbed bars! During walls plaster removal - 5-6 layers of plaster were detected whose removal exposed that during original construction some 20yrs ago – no water stop was used between horizontal 1.0m high layers of concrete installed in walls, next wall-layer of concrete installed directly over the joint from previous layer without any water-stop used. Water has easily found its path through these cold-joints. By revised Design, reservoir has been demolished (roof slab & part of walls), its shell used as a "lost formwork" for construction of new reservoirs inside of existing reservoirs.