Leaching Led Deterioration of Concrete Service Reservoirs and Service Life Prediction

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 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) shows no relationship when data from all structures are brought together. The lack of relationship is due to many reasons including differences in initial permeability of concrete, quality of water (pH), rate of flow of water and variable maintenance programmes. For example, half of the structures reported leaching depth > 10 mm, for a life span of 30-90 years. Equally, structures that have been in service for 60-70 years, recorded a leaching depth below 10 mm. The NDT data presented in the form of augmented reality and also the rate of leaching allows asset managers to take informed decisions for managing the assets. Future work should focus on quantifying the water quality among other key parameters.