Citric, tartaric, and succinic acid effects on C3S dissolution and the nucleation kinetics of CSH and portlandite

Functional additives like hydroxy-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 CSH and portlandite during the early hydration of C₃S. At high undersaturation, we observe that the acids accelerate C₃S dissolution, while their sodium salts exhibit minimal effects. At low undersaturation, citrate reduces the dissolution rate by 50 %, and tartrate can fully suppress dissolution in a model experiment with a water-to-solid ratio of 10 000. The suppression appears to be linked to the precipitation of calcium citrate or calcium tartrate. Potentiometric titration studies indicate that tartrate and citrate inhibit the nucleation and crystal growth of CSH and portlandite. In summary, we find significant inhibiting effects of citrate and tartrate for the dissolution of C₃S and the nucleation of both calcium hydroxide and calcium silicate hydrate.