Occurrence of intercalation of PCE superplasticizers in calcium aluminate cement under actual application conditions, as evidenced by SAXS analysis

• Intercalation of polycarboxylates under actual application conditions was studied.
• It was found that PCEs intercalate into hydrates of calcium aluminate cement (CAC).
• Formation of intercalates was confirmed via small-angle X-ray scattering analysis.
• More anionic PCEs exhibit higher tendency to intercalate.
• Because of this effect, low anionic charge PCEs are more effective dispersants.

Intercalation of polycarboxylate (PCE) superplasticizers in calcium aluminate cement (CAC) during early hydration under both idealized and actual application conditions was confirmed by small-angle X-ray scattering (SAXS) analysis. The CaAl-PCE-LDHs were characterized by XRD, TEM, SEM and elemental analysis, and exhibited interlayer distances (d-values) ranging from 5 to 24 nm, owed to the polydispersity of the PCE samples. Intercalating ability of the PCEs was dependent on their grafting density and anionicity, but was independent of their molecular weights. When highly anionic PCEs were utilized, significant amounts of nanocrystalline, colloidal intercalates were recovered, while few intercalates were detected when less anionic PCEs possessing high graft density were employed. Thus, contrary to OPC, less anionic PCEs disperse CAC better as little amount is wasted via intercalation, whereas higher dosages are required for more anionic PCEs, owed to abundant formation of organo-mineral phases. Finally, recommendations for reliable analysis of PCE intercalates in cement are given.