Insights into the acting mechanism of ettringite in expansive Portland cement

Abstract

There are different theories about the acting mechanisms of ettringite in the expansive behavior of Portland cement. While it is widely recognized that a reactive source of alumina, sulfate, and calcium hydroxide, along with sufficient water, is required for ettringite formation, there are still varying perspectives on the amount, size, and morphology of ettringite crystals. This work brings insights into the mechanisms underlying the expansion of ettringite. For this purpose, cement pastes containing an expansive mixture were analyzed using an expansion measuring device, in situ X-ray diffraction, isothermal calorimetry and scanning electron microscopy. The results revealed that the content and size of ettringite crystals at the beginning of the acceleration period are critical factors for the development of expansive behavior.