Effects of polymer content/structure and bitumen type on viscosity cha
racteristics of styrene-butadiene-styrene (SBS) polymer modified bitum
ens were investigated. The study indicated that SBS polymers were not
inert additives and increases in kinematic and dynamic viscosities of
the modified bitumens were not directly proportional to polymer conten
t; a marked viscosity increase was observed when the polymer content i
ncreased from 3 to 6% by weight of the blend. Modification with a suff
iciently high polymer content also increased the degree of non-Newtoni
an behaviour of the bitumens. The base bitumens and modified bitumens
containing 3% SBS were observed to be essentially shear rate independe
nt, while those containing 6 or 9% SBS displayed shear-thinning behavi
our. Compared to the modified bitumens with linear SBS, the modified b
itumens with branched SBS demonstrated a higher degree of shear-thinni
ng behaviour. These effects were dependent on ranges of shear rate and
temperature. The increased degree of non-Newtonian behaviour was obse
rved to influence the correlations between kinematic and dynamic visco
sities. (C) 1997 Elsevier Science Ltd.