Existing studies on bleeding are mostly confined to the study of the n
ormal bleeding of cement paste. Channelled bleeding, which may occur u
nder certain conditions during bleeding, has not been as well research
ed Further in most studies, these processes ave treated as surface phe
nomena, and only surface measurements were made. In this study, the bl
eeding process, including channelling of cement paste and mortar was i
nvestigated. The latter material is a step forward in the study of ble
eding of concrete. Besides surface settlement, pore pressure and densi
ty profiles were also measured during the experiments to;give a better
insight into the mechanism of bleeding and channelling. The effect of
bleeding and channelling on the strength development in a column was
also studied. A difference in strength of about 30% was found between
samples from upper and lower parts of a column. However the effect of
channels on the compressive strength is found to be negligible as the
area of such channels is small compared to the total area. With these
data, a better understanding of the channelling mechanism was achieved
. A simple model was then used to estimate when channelling will occur
.