Thermo-mechanical properties and microstructural considerations of MDI isocyanate-based bituminous foams

• Bituminous foams were obtained by reaction of bitumen + MDI-PPG + water.
• The results are explained on the basis of the poly-urethane/urea chemistry.
• Bituminous foams obtained present improved in-service properties.
• Bitumen colloidal structure is altered after this chemical modification.
• An unexpected rheological behaviour is noticed at high temperatures.

Stable bituminous foams have been obtained by using a 35/50 penetration grade bitumen and a reactive prepolymer (MDI-PPG) synthesized by the reaction of polymeric 4,4′-diphenylmethane diisocyanate (MDI) with a low molecular weight polypropylene glycol (PPG). In a first step, MDI-PPG and bitumen were allowed to react for up to 7 days. Foams were then obtained by adding an excess of water. The results obtained point out important changes in the material colloidal structure, as a consequence of the reactions between the –NCO groups and bitumen most polar fractions. Modification led to bituminous foams with low density and improved in-service properties (higher elasticity and resistance to deformation at high in-service temperatures, reduced thermal susceptibility and better flexibility at low temperatures), demonstrating their adequacy to be used in building applications. Properties were enhanced by subjecting the material to longer periods of curing prior to promote foaming.