Passive corrosion of steel reinforcement in blended cement-based material in the context of nuclear waste disposal

Abstract

An experimental campaign was carried out to study the passivity of steel embedded in blended cement paste. Mockup samples made of steel coupons (milled or pre-corroded) embedded in cement paste were tested under controlled relative humidity or in a solution simulating clay underground water and under aerated and de-aerated conditions, during up to 3 years. The results of gravimetric measurements show that the average corrosion rates determined on milled coupons are lower than 1 µm/year and vary from 0.2 to 2.7 µm/year for pre-corroded coupons. An apparent passive corrosion state is reached rapidly whatever the environmental conditions. Moreover, solid characterisations (Raman spectroscopy and SEM-EDS) point to a stable state in terms of the nature of the corrosion products and of the composition of the steel/cement paste interface. These results are similar to the ones previously obtained for steel coupons embedded in Portland cement mortar. ARTICLE HISTORY

Interactions between C-steel and blended cement in concrete under radwaste repository conditions at 80 °C

“…It seems that in the present system magnetite formed more quickly on the steel surface than CFSH formation and was controlled by Ca and Si diffusion from the concrete. Chomat et al 16 have also seen Fe-enriched layers at the concrete interface with steel. Pally et al 18 observed hydroandratite (CFSH like phase) deposits on the iron plate in cementitious solutions at 80 °C, but in their experimental set-up diffusion could have been facilitated by direct contact of the steel with the synthetic solution and not the cement paste.…”

“…The SEM–EDX analyses in Fe and O of corrosion products are also consistent with magnetite. Magnetite is usually the main product formed during the anoxic corrosion of carbon steel 5 , 14 , 16 , 28 . No other corrosion products, such as Fe-silicate or Fe-sulfide, were identified by this technique.…”

“…To our knowledge, the corrosion under elevated temperature and anoxic conditions representative of nuclear waste geological disposal has been much less studied in the literature. Recently, Chomat et al 16 performed experiments with steel coupons embedded in blended (CEM V/A) cement pastes in water-saturated and anoxic conditions at 50 °C for 3 years. A Fe-enriched layer formed directly at the surface of the steel did not increase in thickness with aging time.…”

RTM for Waste Repositories

“…In the highly alkaline interstitial solution of Portland concrete, the corrosion of carbon steel is characterized by a low corrosion rate (passive mode) in the order of 0.1 µm/yr to 1 µm/ yr (Smart et al 2013;Chomat et al 2017;Kursten et al 2017). This corrosion mode is due to the formation of a thin protective layer, with corrosion products similar to those observed at the iron-clay interface: magnetite dominates, accompanied by small amounts of hematite.…”

“…This corrosion mode is due to the formation of a thin protective layer, with corrosion products similar to those observed at the iron-clay interface: magnetite dominates, accompanied by small amounts of hematite. The stability of this layer depends highly on the solution chemistry: pH, buffering effect, carbonate and sulfate content (Chomat et al 2017). Corrosion can therefore resume when the conditions are no longer favorable, i.e.…”