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

Abstract

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.

A single‐sided 1H NMR study of the self‐drying properties of a ternary self‐levelling underlayment

“…The strength of the measured NMR signal allows a direct correlation to the hydrogen density and thus to the water content of the material [7,8]. After appropriate normalization, a direct inference to the porosity is possible [9][10][11]. The exponential decay of the measurement signal, the socalled relaxation, yields the bond strength of the hydrogen or the pore volume/surface ratio and thus the pore size.…”

Zerstörungsfreie Messung der Carbonatisierungstiefe mittels einseitiger Wasserstoffkernspinresonanz

“…Im Bereich der Baustoffe konnten mithilfe dieser Methode u.a. die strukturellen Veränderungen hinsichtlich der Porosität von zement-basierten Mörteln und Betonen infolge eines auslaugenden Angriffs durch die Lagerung in demineralisiertem Wasser untersucht werden[15].Für die 1 H NMR Messungen an natürlich carbonatisiertem Mörtel wurde eine 1 H NMR MOUSE der Firma Magritek mit einer maximalen Messtiefe von 25 mm verwendet (vgl. Abbildung 1).…”