Mineralogical changes and associated decrease in tritiated water diffusivity after alteration of cement–bentonite interfaces

Abstract

Alteration of cement–bentonite interfaces and accompanying changes in diffusivity of tritiated water (HTO) was investigated experimentally using intact, hardened cement-paste specimens. The alteration by carbonate solution was accompanied by mineralogical changes at the interface and a decrease in the HTO diffusivity to ∼70 ± 7%of the initial value after a 180-day period. Another alteration in contact with compacted bentonite was accompanied by mineralogical changes at the interface and a decrease in the HTO diffusivity to ∼71 ± 10% of the initial value after a 600-day period. The changes in the diffusivity were considerably less than those observed for mixed specimens of ground, granulated hardened cement paste and bentonite where the diffusivity decreased to 20% of the initial value over 180 days. The results were extrapolated to 15 y under simple assumptions and showed good agreement with those observed in the cement–argillite interface at Tournemire URL (France). Such an explanation enhances confidence in the assessment of the alteration of cement-bentonite systems and might be a basis for using the data and models obtained in the long-term assessment of radioactive waste disposal.

Calcite Precipitation at Cement–Bentonite Interface. Part 1: Effect of Carbonate Admixture in Bentonite

“…Early experimental studies on clay-cement contacts utilized batch experiments to investigate the evolution of clay powder or compacted clay samples in alkaline solutions (Gaucher and Blanc 2006). More recently, experimental investigations have focused on examining the interactions between hardened cement/mortar/concrete and compacted clay, including mass transport processes across the cement-clay interface (Dauzeres et al 2010;Fernández et al 2016;Yamaguchi et al 2016;Balmer et al 2017;Luraschi et al 2020).…”

Evolution of HTO and 36Cl− diffusion through a reacting cement-clay interface (OPC paste-Na montmorillonite) over a time of six years

“…Melkior et al (2004) studied the evolution of the HTO and chloride diffusion coefficient of bentonite after contact with alkaline porewater; and observed a decrease of the diffusivity with increasing interaction time. Yamaguchi et al (2016) reported also a decrease of HTO diffusion coefficients to 70% of the initial value after 600 d in samples prepared from hardened cement paste and bentonite.…”

Calcite Precipitation at Cement–Bentonite Interface. Part 2: Acceleration of Transport by an Electrical Gradient

“…Experimental investigations on the cement-clay interfaces often use composite specimens consisting of cement/mortar/concrete and compacted clay (Sugiyama and Tsuji 2008;Dauzeres et al 2010;Shafizadeh et al 2015;Fernández et al 2016;Yamaguchi et al 2016;Balmer et al 2017) same as the first paper. More recently, long-term in-situ experiments in underground research laboratories (URL) on the cement-clay interfaces have also been conducted (Read et al 2001;Gaboreau et al 2012;Mäder et al 2017).…”