Reliable specific surface area measurements on anhydrous cements

The specific surface area (SSA) of anhydrous cement has a direct impact on its reactivity and on the properties of fresh and hardened concrete. However, measuring this physical parameter is non-trivial.The choice of the degassing conditions (temperature, pressure and time) is essential for reliable SSA measurements by nitrogen adsorption because of the dehydration of the gypsum it contains. Such dehydration involves a significant increase of the SSABET, whereas Blaine test is poorly sensitive to the hydration state and structural modification of the calcium sulfate carrier. Because of this, SSABET values may be more variable than Blaine fineness. More consistent SSABET results could be obtained by degassing anhydrous cement samples at 40 °C under N2 flow for 16 h, as at these conditions the cement composition is preserved.