Image analysis of sulfate attack on hardened cement paste

This paper presents an investigation conducted on the sodium sulfate resistance of Portland cements with various C3A contents, and on two blended cements produced by replacing 40% of low C3A cement with fly ashes having different finenesses. Mortar specimens were cast in accordance with ASTM C1012 testing procedure and stored in sodium sulfate solution up to 1 year. Within the content of the investigation, the microstructures of mortars were first studied using scanning electron microscope (SEM). Next, digital analyses were performed on the micro structural images. In this context, different image parameters were obtained to characterize conventional and hemispherical cracks. The results indicated that fly ash fineness has a significant effect on the crack propagation and the amount of expansive sulfate reaction products. Additionally, it is also concluded that the level as well as the connection of cracks, and the amount of expansive reaction products are decreased with increasing fly ash fineness.