Journal Article

FZJ-2020-03248

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Characterization of Cebama low-pH reference concrete and assessment of its alteration with representative waters in radioactive waste repositories

Vehmas, T. (Corresponding author) ; Montoya, V. ; Alonso, M. C. ; Vašíček, R. ; Rastrick, E. ; Gaboreau, S. ; Večerník, P. ; Leivo, M. ; Holt, E. ; Fink, N. ; Ait Mouheb, N.FZJ* ; Svoboda, J. ; Read, D. ; Červinka, R. ; Vasconcelos, R. ; Corkhill, C.

2020
Elsevier Science Amsterdam [u.a.]

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Please use a persistent id in citations: http://hdl.handle.net/2128/25873  doi:10.1016/j.apgeochem.2020.104703

Abstract: Concretes, mortars and grouts are used for structural and isolation purposes in radioactive and nuclear wasterepositories. For example, concrete is used for deposition tunnel end plugs, engineered barriers, mortars for rockbolting and injection grouts for fissure sealing. Despite of the materials anticipated functionality, it is extremelyimportant to understand the long-term material behaviour in repository environments. A reference concrete andmortar for the Cebama project based on a cement, silica and blast furnace slag ternary blend were designed andcharacterized in different laboratories with multiple experimental methods (XRD, XAS at the Fe and Cl K-edges,SEM-EDX, 29Si and 27Al MAS-NMR, TG-DSC, MIP and Kerosene porosimetry) and techniques (punch strengthtests). The reference concrete enabled comparison of results from different institutes and experimental techniques,unifying the individual results to more comprehensive body. The Cebama reference concrete and mortarwere designed to have high durability and compatible formulation with respect to an engineered barrier systemin clay or crystalline host-rocks, having pore solution pH significantly lower than traditional concretes. This workpresents main results regarding their characterization and alteration in contact with representative waterspresent in radioactive waste repositories. Pore solution pH of the matured reference concrete was 11.4–11.6. Themain hydrated phases were C–S–H and C-A-S-H gels with a Ca:Si ratio between 0.5 and 0.7 and an Al:Si ratio of0.05. Minor phases were ettringite and hydrotalcite. Iron(III) could be in the C–S–H phases and no Cl-bearingsolid phases were identified. Connected porosity and pore size distribution was characterized by MIPobserving that, as expected, the size of the pores in the hydrated cement phases varies from the micro-to thenanoscale. Connected porosity of both materials were low. Compressive strength of the concrete was 115 MPa,corresponding to traditional high-performance concrete. Degradation of these materials in contact with differentwaters mainly produce their decalcification and enrichment in Mg for waters containing high amount of thiselement, like the clay waters.

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Contributing Institute(s):

1. Nukleare Entsorgung und Reaktorsicherheit (IEK-6)

Research Program(s):

1. 161 - Nuclear Waste Management (POF3-161) (POF3-161)

Appears in the scientific report 2020

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Database coverage:
; ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; Nationallizenz ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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