People who make concrete counter tops use a lot of fibreglass fillers to get them fairly thin but if you wanted it truly light weight you’d probably need to make it out of a dense foam and coat it with something that looks like concrete.
replyMy bathroom is a couple mm of microcement over Schluter Kerdi-Board foam, it's fairly strong. I think it can hold a laptop no problem.
replyConcrete counter top mixes usually use either much smaller, or no aggregate and use more sand. The mixes resemble mortar more than concrete and they are typically a little harder and less forgiving to work with.
replyEven structural items can be made quite thin! There is a college design competition to make concrete canoes which can be 3/8" to 7/16" thick: https://www.concretecanoe.org/2008Triva/Florida2008DesignPap...
replyoh wow that takes me back. I remember touring, i think it was Texas A&M, in HS and they showed off their "concrete canoe" to the group. This would have been in the late 1900s.. 1995 or around there.
replyThere have been ships made of concrete.
replyYou could mix concrete with other materiais too. I worked as a lab assistant in a engineering lab for some time. Putting styrofoam into the mix would result in lighter concrete within acceptable levels of resistance (for low level buildings). You might be onto something
replyI've read that adding a little bit of graphene can make concrete much stronger, lighter and easy to shape, so would allow for thinner objects.
replyThere are a lot of additives to concrete - the industry is large and has put a lot of money into research over the decades. You can read many many books on the pros and cons of different options.
replyTranslucent concrete: https://www.allplan.com/blog/translucent-concrete/
reply> Maybe with clever use of fillers and thin walls you could have a version of this you could actually lift
replyYou could likely also pour something like this out of aircrete, which would make it a lot lighter even at the same thickness