Okay, I know that this is really sort of off topic, yet it does have to do with art more or less. What I need to know is the wet weight and dry weight of concrete per cubic yard. This could be something really fun for me to do! So then, any engineers out there? A sculptor is waiting…
Cheers, pix
It depends on the concrete really, there are various types.
Generally dried concrete has 2-2.6 metric tons per cubic meter. Steel reinforced conrete around 2.8 metric tons per cubic meter.
I don´t know the english terms, but there are also (literally translated) light concretes, which are below 2 metric tons per cubic meter, and heavy concretes which are above 2.6 tons per cubic meter (without steel) it really depends on the additives for the various applications.
In 1 cubic meter of concrete are around 25-40 liters of water, so, having an average of 2.4 t/m³, those 25-40 kg of water are neglectable unless you need to cast a ceiling like I already did with ~1600m³ concrete, then the water weighs heavy on the boarding with the weight of a railroadengine, but seldom all at once, as the concrete starts to dry out during casting.
However for sculpting I´d not use regular concrete with gravel, you should use quarry sand to have a fine structure to work on detail. Working on a fine detail and chiseling out a tabletennisball-sized stone is note really desireable 
Depending on the project you´ll most likely also need steel reinforcement, else it will break during chiseling. Especially if it has legs or arms or other “slim” parts. Remember, concrete can only handle pressure good, it´s like glass when it comes to tension or shear.
Also be sure not to use too strong cement, it will get very hot drying out and cause fractures which will repeat on chiseling.
You need to water the concrete during drying to keep it cool and moist. It´s best to wrap it in sheets and keep them wet and prevent it from getting direct sun.
And you also need a concrete vibrator else you´ll have a truckload of airbubbles in the concrete. If you don´t have one, it also works to make the concrete more wet, but then you risk cracks again and uneven concrete strenght because you wash off the fines between the sandgrains.
You can also just use a hammer and hit the boarding so the airbubbles ascend and you get a nice monolithic concrete… whatever… block?
Concrete is a rather expensive construction material, so you better do it right the first time.
Personally I´d not work on concrete itself, I´d sculpt with hardplaster, make a negative again with hardplaster or if it is small with caoutchouc, reinforce it and then cast a concrete final.
I almost exclusiveley did that for miniature models of famous architecture. I worked on many of those:
I thank you for your reply. There is certainly more to it than meets the eye which in itself is a bit strange as the eye is what we wish to capture! I was thinking of using fine sand because as you say, removing large rocks and such does present a problem or two. I certainly would not wish to have a mixer truck (heh! blender truck!) full of unusable goop. Also noted are your references relating to tension and shear, something that I had not considered yet but obviously should be of concern. Let me see here, if I did my maths correctly, a cubic yard should probably weigh somewhere around 4,050 pounds, water not being too significant in the measuring. This at the moment is more of a question about a suitable base to use during the sculpting. Oh goodness me, and I have not even yet considered the logistics! I think that having a basic shape cast in place would be a good idea, yet I need to know what a sufficient base would be required to support it. This is not an overhead thing such as a dome that needs a building to support it, rather it will just sit on its base and hopefully make people that see it ask themselves “what the heck, who did this and why?”.
So, do you see what blender can do to your head? From out of the screen to target zero. 
Cheers, pix