Inventing Tools: Stephen Steele Invents A New Concrete Mixer ECP 68 [47:58] (links to patents inside)

The interviewee Stephen Steele didn't provide many details, but I eventually found the original patent: Alburn O. Hewitt, 1922. Steele's 2012 patent discusses Hewitt's and claims that testing proves the new one works for (in my words) fluid dynamics reasons which Steele probably correctly claims Hewitt was trying to avoid in focusing on material moving only across the rib.

Anyway, this is not a very information-dense interview, but the product interested me. Here's the guy's site: https://steelemixer.com/ and the mixer looks like this. It strongly resembles a classic clothes washer design by Lehman's, but with the ribs at the bottom, which might work for a manual washer, too.

It looks easy enough to construct yourself out of some steel flashing, maybe with truck bed liner on the inside. It'd be interesting to see whether it would be cheaper and better than existing manual crank mixers. It's still rather expensive at $300 compared to a compost tumbler under $100, which you could adapt or throw tied-off contractor bags of unmixed concrete into, or a cheap plastic barrel with fins glued on, which resembles the "poly drum" mixers (with motors) that cost $150-$500.