[en] All experimental works of both Czech partners (ÚJV Řež, a.s. and CEG CTU) within the CEBAMA project focuses on alteration and interaction studies on cementitious materials and bentonite. Laboratory works are based on ageing procedures among Czech bentonite, cement, low pH binder and groundwater from Underground laboratory Josef under high temperature. In-situ experiment deals with long-term behaviour of compacted bentonite, samples from cement paste and underground water. Duration of interaction is planned to be up to 27 months in case of laboratory experiments and 72 months in case of in-situ test. Geotechnical and geochemical analyses provide information for material characterisation and potential changes description (swelling pressure, hydraulic conductivity, liquid limit, mineralogy, bulk chemical analysis, cation exchange capacity and exchangeable cations, specific surface area for bentonite; uniaxial strength, mineralogy, bulk chemical analysis, pH of leachates, diffusion parameters of ${}^3$H and ${}^{36}$Cl for the cement samples). Ageing procedures and results from CEBAMA activities are complementary to and extend those gained already in 2009 - 2013. Laboratory ageing procedures for both types of cementitious materials are ongoing and further sampling is expected in August and September 2017. This paper focuses on preparation of low pH reference cement paste samples (LPC, CEBAMA reference mix design, Vehmas et al., 2016) and evaluation of in-situ experiment in more detail (data set from 2010 - 2016). LPH paste samples, successively prepared by CEG CTU, provide comparable compressive strength results to those reported by VTT. The results gained on bentonite extracted from testing cartridges complete the 6-year long in-situ ageing test in the Underground laboratory Josef. It confirmed slow rate of mineralogical changes. The geotechnical parameters (hydraulic conductivity and swelling pressure) were also influenced in measurable way. Data is available for modelling purposes in WP3.

[en] Characterization of three low pH cement pastes, including the description of their sorption properties for tritiated water (HTO), ${}^{36}$Cl${}^{-<!--\; ???\; -->}$ and ${}^{129}$I${}^{-<!--\; ???\; -->}$ is described in this work. SEM-EDX and NMR analyses show that after 90 days of hydration, the main hydrated phases are C-S-H and C-A-S-H gels with a Ca:Si ratio between 0.8 - 1.0 and a Al:Si ratio of 0.05. TG-DSC and XRD indicate the presence of calcite in the mixtures where limestone filler has been used. Additional techniques were used to identify minor hydrated solid phases like ettringite (i.e., XRD and solid state NMR). Porosity and pore size distribution was characterized by MIP observing that the size of the pores in the hydrated cement phases varies from the micro to the nanoscale. Uptake studies of HTO, ${}^{36}$Cl${}^{-<!--\; ???\; -->}$ and ${}^{129}$I${}^{-<!--\; ???\; -->}$ from batch sorption experiments indicate very weak sorption (K${}_d$ < 0.40 ± 0.13 L/kg) for the 3 selected radionuclides. The uptake process of ${}^{36}$Cl${}^{-<!--\; ???\; -->}$ and ${}^{129}$I${}^{-<!--\; ???\; -->}$ is probably associated with surface processes in the C-S-H and C-A-S-H phases with competition for sorption sites, between them. In the case of HTO, isotopic exchange with the interlayer water of the C-S-H and the C-A-S-H seems to be the main uptake process.

[en] Two-dimensional Hydro-Mechanical-Chemical (H-M-C) coupling analyses with assumptions of several scenarios of long-term alteration of montmorillonite were performed to estimate changes in the mechanical and hydraulic characteristics of clay-based buffer in the barrier system. This paper mainly presents the numerical results of a series of H-M-C coupling analyses focusing on the long-term changes in stress distribution and permeability generated in the bentonite buffer. A newly developed constitutive model to describe the mechanical response of the bentonite buffer considering the effects of volume change of clay minerals induced by the alteration or the dissolution of montmorillonite is also explained briefly.

[en] A reference low-pH concrete and paste mix were manufactured within the Cebama-project. Reference mixtures were casted at VTT in March 2016 and were distributed among some of the Cebama partners. Reference mix designs will be used by different partners as a common material to study their behaviour in contact with waters of different composition and interaction with radionuclides. Additionally, these materials will be used for model calibration. This article provides a summary of the characterization methods used by different partners and gives an overview of the experiments which will be made in the future with the reference materials.

[en] The present work reports the experimental work carried out during the last year within the WP2 in the frame of CEBAMA Project. Namely, this S&T contribution presents the synthesis of pure phases (C-S-H and AFt phases), synthesis and solubility determination of Powellite, and on-going experiments of Mo adsorption kinetics onto C-S-H gels and AFt phases. The characterization techniques used (XRD, SEM-SEI EDX, thermogravimetric measurements…) allowed confirming the good synthesis of both, C-S-H gels and Aft solid phases. Powellite (CaMoO4) was also successfully synthesized and the determination of its solubility product was in very good agreement with the ones reported in the literature.

[en] The incorporation of Se and S in AFm phases was investigated. Se(VI)-, Se(IV)-, S(VI)-, S(IV)- and S(II)-AFm phases were synthesized accounting for a range of redox conditions representative of a cement-based L/ILW repository. The AFm phases were characterized by TGA, FTIR and X-ray diffraction. From bulk chemical analysis of the liquid phase and the pH values, the solubility products were determined. Furthermore, the effect of the equilibration time (3 months vs. 6 months) and pH (higher pH of $\sim <!--\; ???\; -->$ 13 vs. lower pH of $\sim <!--\; ???\; -->$ 12) on the stability of the phases was examined. The X-ray spectra revealed crystalline phases with rhombohedral and monoclinic structure. For the phases with rhombohedral structure different interlayer distances (hkl 003 and 006) were observed, whereas no shift of the reflection referring to the main layer (hkl 110) could be detected. The TGA analyses showed typical water loss patterns for AFm phases giving total water contents of 11 H${}_2$O molecules for the S(IV)- and the Se(IV)-AFm, 12 H${}_2$O molecules for the S(VI)-AFm and 13 H${}_2$O molecules for the S(II)- and Se(VI)-AFm. The variations in the crystal symmetry and the basal spacing seem to be a function of the size of the interlayer atoms and/or the number of water molecules. These observations suggest an intercalation of the Se and S anions in the AFm interlayers.

[en] Reactive transport modelling activities described in this work are focused on the definition of the conceptual model and the selection of the chemical and transport parameters to be applied on laboratory through diffusion experiments performed in KIT-INE (see contribution of Ait Mouheb et al., this proceedings). The model includes different coupled processes which are thought to play a role in a through diffusion experiment of HTO, ${}^{36}$Cl${}^{-<!--\; ???\; -->}$, ${}^{129}$I${}^{-<!--\; ???\; -->}$ and Be across the interface between bentonite porewater and low pH cement. One of these processes is the impact of porosity changes due to dissolution / precipitation reactions.

[en] In cementitious material of the engineered barrier system (EBS) in geological disposal, calcium silicate hydrate (C-S-H) gel may change into crystalline C-S-H by thermal effect. Thereby bentonite alteration behaviour by cementitious material may change. Aged concrete which has been exposed to thermal effect and aged of 40 to 70 years was analysed for condition of C-S-H and its dissolution properties. In the aged concrete, C-S-H gel decreased C/S and changed to crystalline C-S-H (similar to tobermorite) by thermal effect. Due to these phenomena, Ca dissolution and pH value were decreased.

[en] The scope of this work is to understand degradation of concrete exposed to carbonation, chloride attack and external sulfate attack by means of Spin-Echo Small-Angle Neutron Scattering technique (SESANS). CEM I 52.5 N SR3/NA and CEM III 42.5 N LH/SR were exposed to Na${}_2$SO${}_4$ solutions, while CEM III 42.5 N LH/SR and a composite concrete containing ground blast furnace slag (GBFS) were exposed to NH4Cl solutions. CEM I 52.5 N SR3/NA was subjected to carbonation. SEM-EDS and XRD techniques were used additionally to analyse degradation mechanisms of the concrete samples under different exposure conditions. Results showed that, degradation of each specimen varied, depending on the exposure conditions. CEM I 52.5 N SR3/NA subjected to sulfates showed important damages, as was highlighted using SESANS, SEM-EDS and XRD while CEM III 42.5 N LH/SR and GBFS showed similar behaviour to each other with less degradation. Samples immersed in chlorides suffered weakness due to Ca leaching compared to samples subjected to the sulfate attack. Carbonation needs longer time for investigations.

[en] A specific experimental set-up using the osmotic technique has been developed in order to determine diffusion parameters (porosity and diffusion coefficient) in partially saturated conditions. The diffusion of tritiated water (HTO) has been investigated to validate this technique before an investigation of the diffusion properties of inorganic carbon-14 in carbonated and non-carbonated hardened cement paste. Carbonated samples were prepared in an accelerated carbonation device developed at Subatech (Relative humidity 55%, P${}_{CO2}$ 3%). The samples were characterized by different methods (mass monitoring, inorganic carbon measurement, XRD analysis) to ensure a stabilize state of carbonation before the diffusion experiments.