You estimate 4.5 cubic yards and concrete weighs 150 lbs per cubic feet. There is 27 cubic feet in a yard.
4.5 X 27 X 150 = 18,225 lbs of cement.
You state eight steps. 18,225 / 8 = 2,278.125 pounds per step.
What does physics have to do with this, other than you unsuccessful attempt to look intelligent? (it's called MATH)
Use YOUR head, those are YOUR numbers!!!!!