The discussion centers on the comparison between ettringite and calcium hydroxide in the context of concrete durability and sulfate attack. Ettringite is noted for causing volume expansion during sulfate attacks, which can compromise concrete integrity. In contrast, calcium hydroxide's role is linked to the overall durability of concrete. The hardness of ettringite is identified as 2-2.5 on the Mohs scale, indicating it is relatively soft, while the hardness of calcium hydroxide remains unclear, with a suspicion that it may be softer than ettringite. The conversation also includes a suggestion for a resource that provides foundational knowledge about concrete.
