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This study investigated the impact of different cuing history on the sulfate resistance of Portland-Limestone cement (PLC). Mortars of Portland cement (PC) and PLC with different dosages of limestone, 10%, 20%, 30% by mass, were cured in water at 20 °C and 60 °C for 28 days before immersed in Na2SO4 solution 50 g/L at 20 °C for sulfate resistance test. In addition to monitoring the length and mass changes of mortars, MIP and XRD were used to investigate microstructure and evolution of phase assemblages. Results show that PLC mortars cured at 20 °C give a poorer sulfate resistance than PC, the higher the limestone dosages in PLC, the worse sulfate resistance of the mortar. However, it is contrary for mortars cured at 60 °C. PLC shows a much better sulfate resistance than PC, and the higher the limestone dosages, the better sulfate resistance of the PLC mortars. The incorporation of limestone in PLC at dosages of 10–30% leads to the increase of carboaluminates content and the deterioration of pore structure, which is the main factor responsible for worsening the sulfate resistance of PLC mortars cured at 20 °C. When cured at 60 °C, the reduction of available aluminate caused by the dilution effect of limestone improves the sulfate resistance of PLC mortars. The formation of gypsum is not the main cause of the expansion. [ABSTRACT FROM AUTHOR]

Calcined clay has become the supplementary cementitious materials with the greatest potential to reduce the clinker/cement. In this research, the mechanical strengths and sulphate resistance of blended cements with a high content of calcined clay as a pozzolanic addition were evaluated to demonstrate that these cements could be designed as CEM (cement) type IV/A-SR and IV/B-SR cements by the current European standard UNE-EN 197-1: 2011. The blended cements were prepared by two Portland cements (P1 and PY6) with different mineralogical compositions and a calcined clay. The level of replacement was greater than 40% by weight. The results obtained confirm the decrease in the mechanical strengths and the increase in the sulfate resistance of the two Portland cements when they are replaced by calcined clay at a level of replacement greater than 40%. These results are a consequence of the chemical effect from the pozzolanic activity of the calcined clay. Therefore, there is an important decrease in portlandite levels of paste liquid phase that causes the increase in sulfate resistance and the decrease of the mechanical strengths. [ABSTRACT FROM AUTHOR]

• Expands previous knowledge on PLC systems evaluating higher limestone contents. • The focus of current standards and is not linked to actual degradation in the field. • Critical evaluation of the role of the experimental parameters in the degradation. • Crucial to develop an accelerated test to predict field performance of concrete. • Potential for damage in gypsiferous environments should not be neglected. The work presented in this paper comprises an extensive testing program on the resistance of portland-limestone cement (PLC) concrete systems to external sulfate attack. Several mixture parameters, namely interground limestone content, C 3 A content, and SCM type and replacement level, were evaluated in a wide range of experimental conditions designed to link, replicate, and predict laboratory and field performances. The presented results have highlighted the role that the experimental parameters play in the degradation process, which were shown to be particularly pronounced in systems of low sulfate resistance with high limestone contents, owing to their high propensity for thaumasite formation. The findings presented will be crucial to evaluate/develop an accelerated testing procedure that provides a better correlation with actual field performance of concrete structures. [ABSTRACT FROM AUTHOR]