Bob of I Like to Make Stuff helped make concrete countertops!
 

I swear that we have discussed them here, but all that I found was this thread from 2013: Making a Fiberglass Mold by some guy named Red Pointer?

I don't know.

He (or she! [judgmentally] I don't judge!) wasn't able to make it work.

I have looked into this from time to time, but I doubt that far back.

The only thing that Bob did that I hadn't done before (besides built-in outlets) is using white concrete.

I had never heard of white concrete! :)

They put a fiber mesh in their 11-foot island and it came out great! https://www.youtube.com/watch?v=YqlhEmJ4axc I searched for white concrete and the first result that I saw was this video: https://www.youtube.com/watch?v=uAXdA-DAavE He said that he couldn't buy any white concrete mix locally, so he used white sand, white cement, and pea gravel, which confusingly, wasn't white.

The cross-section reminds me of a Big Hunk candy bar.

He used white aquarium gravel last, but it wasn't as strong. He felt the aquarium gravel was weaker.

Home Depot shows white pea gravel, but it would be vastly cheaper if you could buy it directly.

I've considered concrete countertops before since it's a DIY type of project, but it's about the 4th material I'd choose.

My preference is quartz, then granite, then... maybe granite tile (that's what I've got now).

First step is to have a house to put it in though.

Bob said this was far cheaper than the quartz he had installed and he was able to do it himself.

I heard that you can also pour a thin layer of concrete over your existing countertops. Here is a video about it, although she seems like a lady who would post about a recipe with 5-10 pages of storytelling: https://www.youtube.com/watch?v=4rj-IyJ2pIE

pea gravel makes a weaker concrete, since the aggregate is polished.

You need to use a lot of reducer in concrete counter tops. If not the concrete will shrink and cause cracks. Use fiberglass and 3/8" rebar on 4" or 6" spacing for overhangs and make sure it is at least 1.5" from exposed edges.

My brother in law ran a concrete countertop business for years. Made some cool stuff. He would build in drainboard slots in the concrete forms leading to the sink.

Some of the coolest stuff he used was broken blue glass and some dark bottle glass. Stainless nuts and bolts looks good too when exposed and polished with diamond discs. He poured his countertops at his shop upside down so the finished side was very smooth and consistent before polishing.

For artistic stuff, he would pour a very thick mix, and vibrate it minimally. So it would leave some gaps and voids, then go back and grout those in a different color, so it looked like granite. Using white concrete and powdered dyes you could make about any color you want.

I did my big concrete kitchen island about 3" thick using grey high strength concrete with black powdered dye to darken it. After 15 years it still looks great. I used about 1 part water to 1 part reducer. It was very hard to mix and thick.

Concrete counters are not for everyone. If you are expecting it to be like polished granite, then get granite. Once you start putting tons of sealers on concrete counters trying to get it shiny, the sealers are easy to scratch.

If you are going to mess with high hardness concrete with lots of reenforcement I did a pretty in depth study of ballistic concrete.
What do you want to know?
The best agg is sharp angular gravel or ground up old concrete.

The famous Roman concrete used volcanic ash from one particular outflow at Pozzuol.
The whole PNW is smothered in volcanic ash.

Seeing this makes me want to make a cement picnic table at our backyard. I also saw a video of how to make a cross between an oven, a grill and a stove made from cement.

I found this: https://www.youtube.com/watch?v=dX2nwbrAStI Personally, I would have built it outside--and staggered the bricks.

Oil Pan, what is the best way to grind up concrete? Does it need to be old? Can I make concrete with pea gravel, grind it, and then use that in new gravel? :)

You can use pea gravel but if your goal is ultimately tensile strength something sharp and angular is the way to go.
I have done test pours with busted up ceramic tile, that was one of the best ones. So good I have several old toilets stashed to use as aggregate next time I need some ballistic concrete.
The worst concrete I made used terracotta aggregate. Terracotta rubble is driveway cover, french drain aggregate as far as I'm concerned.
Older concrete is better when you want recycled concrete. It gets harder over time with repeated exposure to water.

Where would the rest of us find old toilets to smash for concrete?

I tried searching, but found claims that some people will pay good money for used toilets.

Meanwhile, someone here said nobody wanted his clean old toilet.

Also, allegedly a bag of toilet paper tubes is worth $50.

I have many questions.