Investigations of Ettringite Morphology with the Use of Different Retarders in CSA/OPC Blends

Normal portland cement (PC) and calcium sulfoaluminate (CSA) cements are two distinct types of cement binders exhibiting different hydration processes and mechanical properties. Blends of these two binders can produce a more suitable material for specific construction purposes. However, the effects of retarders in blended PC-CSA systems are not well understood, despite the well-established properties of retarders in pure PC and CSA cement binders. Therefore, this study aims to investigate the influence of various retarders (citric acid, borax, tartaric acid, and blends of citric acid and borax/tartaric acid) in an 85 wt.% CSA and 15 wt.% PC blend through the use of different techniques, such as calorimetry, ultrasonic testing, thermogravimetry analyses, scanning electron microscopy with electron dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, and mechanical testing. The morphology of ettringite, a mineral formed during the hydration process of CSA cement, is studied and found to vary significantly depending on the retarders used. In addition, these different types of ettringites significantly affect the mechanical properties of the cement. This research provides insight into the impact of retarders on the properties of blended PC-CSA systems and could aid in designing more durable and sustainable concrete structures. The findings of this study could also contribute to the development of new and improved cement-based products by enhancing our fundamental understanding of the setting and hardening of cementitious materials.