Long-term performance of cement paste during combined calcium leaching–sulfate attack: kinetics and size effect

This paper presents experimental results obtained on cement paste samples (water/cement ratio of 0.4) subjected to a low-concentration (15 mmol/l) external sulfate attack during several weeks. Chemical and microstructural analyses include the continuous monitoring of calcium loss and sulfate consumption within the cement paste, periodic layer by layer X-ray diffraction (XRD)/energy-dispersive spectrometer (EDS) analyses of the solid constituents of the cement matrix (ettringite, portlandite, gypsum) within the calcium-depleted part of the samples. Scanning electron microscopy (SEM) and visual observations are used to follow the crack pattern evolution during the external sulfate attack. The relation between the size of the specimen and crack initiation/development is investigated experimentally by performing tests on samples with different thickness/diameter ratios.