Understanding Mixer Output

One of the most confusing parts of buying (or selling) a concrete mixer is understanding what the output of concrete will be. this not only because different manufactures have different names for the same sized mixers, some metric others imperial. The same mixer will have different output capacities based on the mix design. it is also different whether it is weight or volume  of output that is being analyzed. Generally speaking the weight of the material that you put into the mixer will (almost) always be the same as the weight of concrete that comes. But volume is a different story.

When you have a pile of stone, a good portion of that pile is actually air. There are voids (air space)between the individual stones. Even grains of sand have air voids where they are not touch adjacent grains. in the process of mixing concrete the voids between grains of sand are fill with hydrated cement dust, and the voids in the rock are fill by the combination of sand cement and water. Therefore, if you have cubic foot of stone, and 25% of that volume is air voids, you can expect that you will see that volume of reduction in your finished concrete (as the sand will fill these open spaces). Additionally, there will be further reduction as the cement particles fill the voids left in the sand. Generally, this reduction is around 1/3 to 1/4, though much greater or lesser reductions are not uncommon.

Admixtures can also play a notable role in volume changes to concrete, I think. But a lot of stuff with Admix is beyond me, and I am in know way an expert in that regard.

Really, the important this about mix volume reduction comes down to, how big of a mixer do you need to fill this form, or this Tucker, or this bucket, or machine hopper, etc, etc, etc. with X amount of concrete of X type. the kicker is if you don't get this answer right you will be living with it for years.

Here is my recommendation for getting the right size concrete mixer for your plant... Plan on shrinkage and understand mixer volume capacities. Get the technical information on the mixers you are considering. Compare the volume of the mixers to be sure that you are getting a mixer that can produce the volume of concrete you need. If it is a pan or a planetary mixer make sure that you don't have to go far above the paddles on your mix, as that will not mix as well, and it can be hard to make a mix homogeneous from top to bottom. With Twin shaft and Horizontal shaft mixers the concrete is blended more easily at greater depths, but over filling can lead to a mess.

There is of course much more to evaluating mixers. This is but a small part, but I hope that you find it helpful.