Citric, Tartaric, and Succinic Acid Effects on C3S Dissolution and the Nucleation Kinetics of C-S-H and Portlandite

Functional additives like carboxylic acids modify the hydration mechanism of Portland cement and are commonly used as set retarders. These retarders can affect the clinker phase dissolution and the crystallization of hydrate phases. However, their specific effects are not fully understood. This study focuses on understanding the role of citric, tartaric, and succinic acid in the dissolution of tricalcium silicate (C3S) and the crystallization of C-S-H and portlandite. The results reveal that these acids accelerate C3S dissolution, while their sodium salts exhibit minimal effects at high undersaturation. At low undersaturation, citrate reduces the dissolution rate by 50%, and tartrate can fully suppress dissolution in the model experiment. Potentiometric titration studies reveal that the additives inhibit the nucleation and crystal growth of C-S-H and portlandite by stabilizing prenucleation clusters. In summary, the additives’ relative impact on dissolution and crystallization suggests that the retarding effect of citric and tartaric acid is predominantly caused by the inhibition of nucleation and crystal growth.