Cement-Based Materials for Nuclear Waste Storage, 2012
The present research belongs to an international project where several of the main nuclear waste ... more The present research belongs to an international project where several of the main nuclear waste management agencies have been involved. The main objective is the development of agreed procedures or protocols for measuring the pH value using low-pH cementitious products (LopHC). Pore Fluid Expression (PFE) identified as Reference method and Ex situ Leaching methods (ELS) with two variants (filtering and without filtering the suspension made) identified as Routine methods have been employed. Both methodologies are based on the extraction of the pore solution of the concrete before pH determination. The protocols employed were based on a broad literature review and in fitting the more critical parameters, such as the sample size, the carbonation affection, the leaching of cement hydrates during the measurement, etc. Moreover, the routine methods were validated with respect to the pore fluid expression results. According with the obtained results, the selected measuring methods were proposed. The proposed methodologies show very promising results having low deviations and high reproducibility when applied to LopHC materials that have given the possibility to develop agreed simple protocols for pH determination considering the chemical requirement in the construction of high nuclear waste repositories.
Hydration of a belite calcium sulphoaluminate cement was investigated over one year as a function... more Hydration of a belite calcium sulphoaluminate cement was investigated over one year as a function of its initial gypsum content (variable from 0 to 35%). Particular attention was paid to the influence of the thermal history of the material at early age on its subsequent evolution. Pastes and mortars (w/c 0.55) were either cured at 20°C or submitted for one
The structural flexibility of the two mains hydrates, ettringite and calcium monosulfoaluminate h... more The structural flexibility of the two mains hydrates, ettringite and calcium monosulfoaluminate hydrate, produced by calcium sulfoaluminate cements (CSA cements) hydration may give rise to chemical entrapment of some heavy metals salts, such as ZnCl2. The properties of mortars made with CSA cement (mechanical strength and length changes) and their hydration process were thus investigated (by calorimetric and XRD measurements) as a function of various parameters: the gypsum content of the CSA cement (from 0 to 35%), the composition of the mixing solution (either pure water, or a ZnCl2 solution with a variable concentration ranging from 0 to 0.5 mol/L) and the thermal evolution at early age, with a view to develop a cementitious material to stabilize Zn-rich waste. Increasing the gypsum content accelerates the hydration process but decreases the total heat of hydration. The precipitation of ettringite is promoted and the porosity increased. The influence of zinc chloride on hydration ...
The Early age hydration of two Calcium SulfoAluminate cements, containing respectively 0% and 10%... more The Early age hydration of two Calcium SulfoAluminate cements, containing respectively 0% and 10% gypsum, by a borate solution was studied using isothermal microcalorimetry. The adjunction of gypsum to the cement results in a longer induction period when the mixing solution contains borate anions. Using XRD analysis, TG analysis and pore solution pH measurements, it has been shown that the presence of gypsum buffers the pore solution pH to a low value that allows the precipitation of amorphous calcium borate C2B3H8. As a result, dissolution of anhydrous phases and precipitation of hydrated phases are inhibited until the increase of the pore solution pH once gypsum is fully depleted. Without any gypsum, the pore solution pH is rapidly raised to a higher value and dissolution/precipitation of the cement phases begins just after mixing. In both cases, borate anions are incorporated in an AFt type phase, similar to ettringite, and containing simultaneously sulfates and borates in its st...
Cement-Based Materials for Nuclear Waste Storage, 2012
The present research belongs to an international project where several of the main nuclear waste ... more The present research belongs to an international project where several of the main nuclear waste management agencies have been involved. The main objective is the development of agreed procedures or protocols for measuring the pH value using low-pH cementitious products (LopHC). Pore Fluid Expression (PFE) identified as Reference method and Ex situ Leaching methods (ELS) with two variants (filtering and without filtering the suspension made) identified as Routine methods have been employed. Both methodologies are based on the extraction of the pore solution of the concrete before pH determination. The protocols employed were based on a broad literature review and in fitting the more critical parameters, such as the sample size, the carbonation affection, the leaching of cement hydrates during the measurement, etc. Moreover, the routine methods were validated with respect to the pore fluid expression results. According with the obtained results, the selected measuring methods were proposed. The proposed methodologies show very promising results having low deviations and high reproducibility when applied to LopHC materials that have given the possibility to develop agreed simple protocols for pH determination considering the chemical requirement in the construction of high nuclear waste repositories.
Hydration of a belite calcium sulphoaluminate cement was investigated over one year as a function... more Hydration of a belite calcium sulphoaluminate cement was investigated over one year as a function of its initial gypsum content (variable from 0 to 35%). Particular attention was paid to the influence of the thermal history of the material at early age on its subsequent evolution. Pastes and mortars (w/c 0.55) were either cured at 20°C or submitted for one
The structural flexibility of the two mains hydrates, ettringite and calcium monosulfoaluminate h... more The structural flexibility of the two mains hydrates, ettringite and calcium monosulfoaluminate hydrate, produced by calcium sulfoaluminate cements (CSA cements) hydration may give rise to chemical entrapment of some heavy metals salts, such as ZnCl2. The properties of mortars made with CSA cement (mechanical strength and length changes) and their hydration process were thus investigated (by calorimetric and XRD measurements) as a function of various parameters: the gypsum content of the CSA cement (from 0 to 35%), the composition of the mixing solution (either pure water, or a ZnCl2 solution with a variable concentration ranging from 0 to 0.5 mol/L) and the thermal evolution at early age, with a view to develop a cementitious material to stabilize Zn-rich waste. Increasing the gypsum content accelerates the hydration process but decreases the total heat of hydration. The precipitation of ettringite is promoted and the porosity increased. The influence of zinc chloride on hydration ...
The Early age hydration of two Calcium SulfoAluminate cements, containing respectively 0% and 10%... more The Early age hydration of two Calcium SulfoAluminate cements, containing respectively 0% and 10% gypsum, by a borate solution was studied using isothermal microcalorimetry. The adjunction of gypsum to the cement results in a longer induction period when the mixing solution contains borate anions. Using XRD analysis, TG analysis and pore solution pH measurements, it has been shown that the presence of gypsum buffers the pore solution pH to a low value that allows the precipitation of amorphous calcium borate C2B3H8. As a result, dissolution of anhydrous phases and precipitation of hydrated phases are inhibited until the increase of the pore solution pH once gypsum is fully depleted. Without any gypsum, the pore solution pH is rapidly raised to a higher value and dissolution/precipitation of the cement phases begins just after mixing. In both cases, borate anions are incorporated in an AFt type phase, similar to ettringite, and containing simultaneously sulfates and borates in its st...
Uploads