Aggregates and Their Effects on Concrete Properties - Part 1

This course was great and all but i was hoping to see more aggregate types being used in concrete and to know more about their density.
My problem was slightly different from what was said in the segregation part
My aggregates float instead of settling at the bottom of the mixture because their density is much less than water
I measured them like a week ago and it's like nearly 0.5 gr/cm³
I don't know if what i'm gonna do will work but in order for my concrete sample to avoid segregation i will have to decrease the w/c ration to increase it's viscosity so it keeps the aggregates inside... if not vibrated violently