Monitoring the microstructural deterioration of concrete exposed to leaching in purified water

Concrete is considered to be durable in permanent contact with water, making it a preferred material for the construction of drinking water reservoirs. More severe conditions, however, such as contact with purified water lead to the leaching of calcium and the deterioration of concrete surfaces. Due to the diffusive nature, deterioration begins superficially and ingresses with time. Consequently, concrete surfaces are severely damaged and the rebar-protective alkalinity can be lost. In this study, results from long-term laboratory leaching experiments in purified water of differently prepared concrete surfaces relevant for drinking water reservoirs are reported. Samples are monitored by both conventional laboratory techniques and, for the first time, by single-sided ¹H nuclear magnetic resonance to gain knowledge on appearance and performance as well as the microstructural changes with sub-millimeter depth resolution. Results give a deepened insight into the time- and depth-depending material changes. Concrete with a lower w/c ratio, more durable cement, or a densified surface shows a slowed deterioration. The progressing leaching deterioration is described using a combined diffusion-erosion model that allows a more direct comparison of results to other exposures.