Advanced testing and performance specifications for the cementitious materials under external sulfate attacks

A new monitoring approach was developed to enhance the analysis of performance tests and provide new sulfate resistance criteria. Even in the case of low degradation rates or non-swelling materials exposed to external sulfate attacks, the method allows detecting microscopic evolutions via a set of easily accessible monitored parameters. The monitoring has been performed on a set of sulfate-resisting and non sulfate-resisting cement-based mortars. The main phenomena induced by external sulfate attack are leaching, precipitation, aggregates loss and cracking. Based on the monitoring of mass, hydrostatic weighing, elongation and the amount of leached OH− the method provides the samples dimensional variations, the volume and mass changes of minerals and free water, corresponding to the main phenomena of the external sulfate attack. On the one hand, the phenomena decoupling allows a better understanding of the sulfate attack mechanism. The observed equivalence between the volumes of leached and precipitated products highlights the influence of portlandite, the major leached mineral, on the precipitation mechanism. The precipitation-deformation correlation and the samples absolute deformation monitoring showed a common expansion mechanism for the different cement compositions. The cement type was found to influence the magnitude of deformations. On the other hand, the determination of the volume variations corresponding to each phenomenon allows the proposition of new performance indicators from the monitoring approach outputs: the averaged density, the deformation path and the expansion potential. The three indicators were sensitive to the microstructural and macroscopic evolutions. The expansion potential, related to crystallization pressure, was found to depend on cement composition.