The invention concerns a method for preparing a bitumen base, including the following essential steps: a) introducing a bitumen in a container equipped with mixing means, and bringing the bitumen to a temperature of 120° C. to 300° C.; b) introducing at least one chemical blowing additive into the container, and mixing, said chemical blowing additive being of general formula Ar1-R—Ar2 (I) wherein Ar1 and Ar2 independently of each other represent a benzene ring or a system of condensed aromatic rings of 6 to 20 carbon atoms, substituted by at least one hydroxyl group, and R represents an optionally substituted divalent radical, whereof the main chain comprises 6 to 20 carbon atoms and at least one amide and/or ester group. The invention also concerns a bitumen base obtained by implementing said method, as well as the use of such bitumen bases in road surfacing and industrial applications.