Fishwater Flats WWTW Rehabilitation

The Fishwater Flats Wastewater Treatment Works was constructed in 1976. A number of buildings and structures were identified as requiring maintenance and rehabilitation as part of the Maintenance Backlog Study undertaken for the Fishwater Flats Wastewater Treatment Works.

Africoast was appointed for the planning, design, tender documentation and construction monitoring for the maintenance rehabilitation. During the planning and design stage careful consideration was given to the type of repair and protective coatings to be used.

The objective of the rehabilitation method was to fulfil the requirements of minimum acceptable strength and maximum serviceability and ease of construction at least cost. The requirements of minimum strength and maximum serviceability were to ensure adequate safety and performance of the structures subject to loads and environmental conditions. The protection of embedded steel from corrosion was deemed essential for adequate serviceability. The rehabilitation method adopted was in accordance with accepted Codes of Practice for the rehabilitation of concrete structures.

The buildings and structures are situated in a severe marine environment and are exposed to corrosive salt spray from the on-shore prevailing easterly winds. The buildings and structures at theFWFWWTW experienced varying degrees of inadequate maintenance and corrosion related deterioration.

There was visible degradation and concrete spalling of the concrete structures which led to the following primary concerns:

  • Long term durability of the structures being at risk.
  • Visible degradation of the structures.
  • Hidden corrosion to the reinforcing steel that is not externally visible.
  • Increased long-term maintenance costs due to uneconomical maintenance strategies.