Microstructural phenomena involved in the expansive performance of cement pastes based on type K expansive agent

Certain aspects related to the microstructural mechanisms involved in the expansion performance of cement pastes with ettringite based expansive agent have been analyzed. The possible microstructural mechanisms associated with the shrinkage observed after the maximum expansion is reached along with the influence of the porosity in the expansion obtained were evaluated in order to define the main microstructural mechanism involved in generating the expansion. Different microstructural techniques were considered, while the pore fluid composition evolution was similarly determined. The results obtained indicate that the shrinkage detected after the maximum expansion value should be related to the transformation of low crystalline ettringite in low crystalline monosulfate but the early formation of monocarboaluminate limits this conversion process. Moreover, the main mechanism involved in this expansion obtained is not the diffusion of constituent components from the expansive agent anhydrous grains and further ettringite precipitation, but rather the in-situ precipitation of these components with the subsequent ettringite formation.