CB,

There is a concrete mixing system that will consistently batch good concrete recipes in very remote areas.  It was designed for building in countries like Haiti.

It is called the Concrete MD.  Here is a link to a video.  Watch the unpacking and transporting video to see how it could be pulled with an ATV / Side-by-side. both the mixing unit and the hydralic power unit use wheels to move around and they each weigh less than 750lbs.

I hope that this helps.

Your project in South America sounds interesting... You might want to check out the work of a blog called CementTrust...

Good luck on your project...

BC

The U-cart idea is good... But he may want to use the more modern rotating drum style trailers... They are available at many rental companies around the country.  Here is a link for concrete mixing trailers.

You said you have water on site. Is there a creek/ river? Does it have a gravel bed? Any local source of gravel/ sand could be washed and used for materials. There are ways that it can be done properly with minimal reinforcing steel, but you'll still need some.
Someone makes a small batch plant that hooks up to a hose, has a tiny electric conveyor, and measures materials by weight. The drum is the only burdensome item. I've only seen it in use in Italy, but I expect something similar is available here.

Given the weight constraints, I'd use some structural (not just for shrinkage cracking) plastic fiber in the concrete. For example, PVA.

15 years of experience on 3 continents with IFC. I did a project in Africa with ICF we packed 400pc into a 40ft container. All concrete was mixed on site with a mixer and we fill the forms with several 5 gal bukets. Your job is small but you have plenty of space around.Take 4-5 friends on a vacation and you can do it in no time. You need an extra hand I am available> is an adventure.