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The damage process of plain and blended cement mortars subjected to sulfate attack under electrical field was investigated in this paper. The deterioration of mortars was investigated by measuring the loss of compressive strength. To identify the changes of microstructure and mineral phases after the test, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis were performed on the selected samples. The results indicated that compared with sulfate attack alone, the combination of sulfate attack and electrical field accelerated the damage process of mortars, which can be explained through two different mechanisms. On the one hand, Ca 2+ ions directionally moved and then leached out from mortars under the electrical field, leading to the dissolution of portlandite as well as the decomposition of C–S–H gel at the later stage. On the other hand, the electrical field accelerated the migration of sulfate ions and then they reacted with hydration products to form massive ettringite and gypsum, which resulted in the microcracks and strength loss of mortars. Moreover, the deterioration of the mortar blended with fly ash was still visible in spite of its better chemical resistance. The strength loss of limestone powder incorporated mortar increased in comparison with Portland cement mortar as a result of an increase in porosity. [ABSTRACT FROM AUTHOR]

This study investigates the long-term (570 days) performance of alkali-activated slag (AAS) mortar exposed to combined wet-dry cycles and sodium sulphate solutions (i.e. 5 wt% and 10 wt%). Physical and mechanical characteristics of AAS mortars (i.e. visual appearance, compressive/flexural strength, mass change, capillary porosity, water sorptivity) as well as mineralogical and chemical parameters were determined using XRD, FTIR, DSC and BSE. Findings were compared to Portland cement (PC) and high sulphate resistant (HSR) samples. Results indicate that AAS mortars perform better than PC and HSR samples with minimal changes to compressive strength at 570 days (1.7% increasement). The main failure mode for AAS mortar was external spalling, which could be due to the crystallisation/dissolving pressure of sodium sulphate. Moreover, the results indicate key differences in the deterioration mechanism of AAS. Unreacted slag, exposed during sodium sulphate attack under wet-dry cycles, can continue to react in sodium sulphate to form silicon-rich gels. The formation of highly siliceous gel regions has beneficial impacts, such as the increase in flexural strength. While no calcium sulphate phases were detected via XRD and FTIR after 570 days of exposure, it is evident that the molecular changes in the microstructure reveal depolymerisation and enhanced formation of Si–O phases after long-term sodium sulphate exposure. These results are important to understand the long-term degradation mechanisms of AAS materials exposed to sodium sulphate under wet-dry cycles. [ABSTRACT FROM AUTHOR]