Originally posted by racingtadpole:
"When we move pre-cast concrete at work we allow 2300kg/m3 dry weight."
so since 1m = 39.37 in /(36 in /yd) = 1.09361 yd and 1kg = 2.2 lbs,
then 2300 x 2.2 / (1.09361)3 = 5060 / 1.308 = 3868.5 lbs/ cu yd x (1 cu yd /27 cu ft)
= 143.3 lbs / cu ft dry mix.
Quikrete informs that an 80 lb bag of dry mix yields 0.60 cu ft of concrete.
I use bags of Quikrete that yield 0.75 cu ft (thus 100 lbs /bag) each, for fence posts.
I add about 1.5 gallons of water to each such bag and mix in a wheelbarrow.
The 1.5 gal water adds about (1.5 x 62.4 /7.48) = 12.5 lbs weight to the mix.
Thus, 100 lbs dry mix = 100 /143.3 = 0.7 cu ft and, after adding water,
cures to 0.75 cu ft weighing 112.5 lbs, assuming no evaporation of water (per buening post " you should not lose any water",
ie, 112.5 /0.75 = 150 lbs /cu ft., as widely accepted rule of thumb.
IOW, mixing in the water and curing adds about 7% in volume (0.75 /0.70)
while adding 12.5% in weight, thus the increase in density from 143.3 lbs/ cu ft dry to 150 lbs wet, set, and cured ... an increase of about 4.5% in density.
