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Report No.
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Investigation of the interface between cement and geopolymer

Cantarel, V.   ; Yamagishi, Isao 

Cementitious structure repair is one of the potential applications of geopolymer material. The context of decommissioning and decontamination efforts gives rises to several related applications. For instance, geopolymer could be used to manage cement waste, create seals to isolate a section of the decommissioning area, or cover contaminated concrete to protect workers. In that context, the property of geopolymer for immobilization of nuclides such as cesium grants additional benefits. Moreover, in maritime environments, technical studies showed low permeability properties of geopolymer coated concretes. However, the origin of that property was not fully explained and only loosely attributed to the interface between the two materials. The purpose of this study was to investigate the interface between ordinary Portland cement and geopolymer. Other materials, such as activated slags, use the same type of alkaline solution as geopolymer. We wanted to know if the properties achieved at the interface with concrete are related to the aggressive alkaline solution or specific to geopolymer. To this end, cement was either dipped in alkaline silicate solution for various duration or embedded in geopolymer. The immersion in activating solution induced a localized carbonation at the surface of the cement similar to what is observed with waterglass treatment of ordinary Portland cements. Contrary to standard carbonation, the carbonation progresses in a root-like pattern inward, following the CSH gel into the cement. When embedded in geopolymer, a 0.03 mm thick transition zone is formed at the interface with cement. The elemental evolution throughout the transition zone indicates that surface porosity of the cement is plugged by nanoaggregates of alumino-silicate. This phenomenon can explain both that the carbonation does not occur during or after the geopolymerization and the low permeability observed for geopolymer coated cements in other studies.

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