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Les bétons bas pH - Formulation, caractérisation et étude à long terme

Abstract : Using of Portland cement in association with clay in a deep geological repository could present some difficulties. The clay properties may be altered by the high pH conditions set by the cement pore water. Moreover, a high temperature rise caused by cement hydration in massive concrete elements could induce microcracking of the material. Investigations have thus been carried out to formulate low-alkalinity and low-heat blended cements referred as “low-pH” binders, which would show an improved compatibility with the repository environment and which could be used to elaborate high-strength concrete. A list of specifications to be checked by the concrete materials has been defined including pore solution pH around 11, temperature rise during hydration less than 20°C, moderate shrinkage and high compression strength (superior to 70 MPa).
Several systems comprising Portland cement, a pozzolan (silica fume or fly ash) and blastfurnace slag were compared. All blends were characterized by high amounts of additions, the OPC fractions ranging only from 20 to 60%.
The pore solution pH values of the blended pastes were within the range [11.7 – 12.2] after one year of hydration. The decrease in pH as compared to a reference made with OPC was due to a i) strong reduction of the alkali concentration in the porewater, ii) depletion or decrease of the portlandite content in the blends and iii) enrichment of C-S-H with silica.
These low pH binders were successfully used to prepare high strength concretes (pH porewater values within the range [10.7 – 11.6] according to the binders) with usual tools of civil engineering.
Finally, leaching tests carried out in pure water indicated a very slow decalcification (reduced by a factor 4) of the blended pastes, as compared to a Portland cement paste. The mineralogical evolution and leached fluxes could be modelled by using a coupled reactive transport code (HYTEC).
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https://tel.archives-ouvertes.fr/tel-00199021
Contributor : Maud Codina <>
Submitted on : Tuesday, December 18, 2007 - 11:56:16 AM
Last modification on : Friday, January 10, 2020 - 9:09:32 PM
Long-term archiving on: : Monday, April 12, 2010 - 8:18:45 AM

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  • HAL Id : tel-00199021, version 1

Citation

Maud Codina. Les bétons bas pH - Formulation, caractérisation et étude à long terme. Sciences de l'ingénieur [physics]. INSA de Toulouse, 2007. Français. ⟨tel-00199021⟩

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