Leaching led deterioration of concrete in service reservoirs: mechanism & service life

Service reservoirs are an integral part of the potable water distribution network and concrete is the preferred material of choice. Deterioration of concrete in service reservoirs is a lesser-known problem. The symptoms are surface deposition of minerals requiring constant cleaning between operations. Debonding and dislodging of aggregates affecting the operation, gradual reduction of the cross-section of the concrete wall and rebar corrosion in reinforced segments. Calcium compounds that dominate the hydrated cement and thus concrete microstructure will be leached away to the potable water which is low in calcium. Data from over 20 reservoir investigations confirm leaching as the dominant mechanism. The damage was evident in the petrographic investigations, from which a depth of leaching was determined. Rate of leaching was defined as depth of leaching/years of service. The rate of leaching and NDT score (a unitless entity) are unique to a structure, as the reservoirs had different concrete, handled water of different quality, at different rate and subjected to variable maintenance programme. For example, half of the structures reported leaching depth >10mm, for a life span of 30-90 years. Equally, structures that have been in service for 60-70 years, recorded a leaching depth below 10mm.