Dispersion, adsorption and retardation effects of phosphonated small molecule superplasticisers in cement hydration

A series of phosphonated small molecule superplasticisers were synthesised by the Mannich reaction of functionalised amines with formaldehyde and phosphonic acid. Their chemical structures and molecular weights were determined by ¹H nuclear magnetic resonance and size exclusion chromatography, respectively. Their dispersion ability, adsorption behaviour and retardation effect in cement hydration were investigated. Results of the cement paste tests indicated that the phosphonated small molecule superplasticisers with longer polyether chain and fewer phosphonate groups exhibited better initial water-reducing ability but weaker retarding ability, and those with shorter polyether chain and more phosphonate groups turned out to be more effective in slump-retaining ability and retarding ability. These findings provide useful information for optimising the performance of phosphonated small molecule chemical admixtures in the future.