Influence of citric acid on the hydration of Portland cement

• Published in: Cement and concrete research Vol. 39; no. 4; pp. 275 - 282
• Main Authors: Möschner, Göril, Lothenbach, Barbara, Figi, Renato, Kretzschmar, Ruben
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2009; Elsevier
• Subjects: Admixture; ALUMINATES; Applied sciences; Buildings. Public works; Cement concrete constituents; Cements; CITRATES; CITRIC ACID; COMPLEXES; DISSOLUTION; Exact sciences and technology; HYDRATION; Hydration products; LAYERS; Materials; MATERIALS SCIENCE; Modeling; PORTLAND CEMENT; PRECIPITATION; Properties of anhydrous and hydrated cement, test methods; Retardation; SIMULATION; SLOWING-DOWN; SURFACES; Thermodynamic calculations; Retardation; Thermodynamic calculations; Modeling; Hydration products; Admixture; Composition; Hydration; Thermogravimetry; Concentration; Experimental study; Portland cement; X ray diffraction; Citric acid; Thermodynamics; Computing method
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2009.01.005

Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved K formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution.