[en] The adsorption of ⁸⁵Sr²⁺ on bitumen emulsions with well characterized surfaces was studied as function of pH and ionic strength of the equilibrium solution. The bitumen/solution interface is negatively charged due to the deprotonation of weakly acidic carboxyl groups present at the surface. The surface group density is calculated to be 1.37x10¹⁸ groups/m² and the deprotonation behaviour can be fairly well described by the Ionizable Surface Group Model with a pK_H = 6.6. Sr²⁺ adsorbs on the bitumen by an outer sphere complexation reaction in which one surface carboxyl group is involved in the adsorption of one Sr²⁺-ion. The adsorption depends on the ionic strength and pH of the contact solution. The higher the ionic strength, the lower the adsorption. Sorption increases with increasing pH due to the deprotonation of carboxyl groups. In a cementitious environment, Sr²⁺ adsorption on bitumen is negligible due to the strong competition of Na⁺, K⁺ and Ca²⁺ present in the cement pore water. (orig.)