How to make 8000 PSI Concrete

If you are not a civil engineer don't bother trying to design 8,000 psi concrete because you'll fail at it miserably. Leave that up to the concrete supplier and their tech support, who are the pros.

If you are a "degreed" Civil Engineer and went through engineering college with the requisite course, then I strongly suggest that you revisit your past materials lab studies and work, plus review the "Strength of Materials" course that you should have taken (and stayed awake in).

Have a great day!

This is a deep, dark secret--revealed only to the strongest shamans, or those who possess the correct licenses. Neither of those two groups will ever tell, so you must fall back on your own research.

First of all: I will tell you how to do get 8000 PSI concrete.
Having said that, I am saddened to see some people in the industry act like jerks, just because an engineer told them how to do YET they make the most money out of it. Greediness truly is the Achilles' heel of this great nation. It's sad seeing people act secretive about 8K psi concrete, when I been studying on making 100K psi concrete (yes 100,000 psi) though my research has already been done, I'm merely bettering the process and attempting to go pass the 106,000 psi barrier.
Anyways, 8K psi concrete is not entirely "tricky" but there are two ways you can make it DEPENDING on why you need it: Personal OR commercial.
If you need it for some personal reason (up to 9K psi but could be a bit less), the ratio is as follows:

NOTE: I did told you I'm working with 100,000 psi concrete right? Although it doesn't apply to my field, try to keep the coarse aggregate as small as possible, between 1-2 inches in diameter. Although it doesn't apply too much in "normal concrete", smaller coarse aggregate will be much better than the crap you get in construction companies. If you're buying, insist in going to their facilities in person.
If you need it for commercial purposes, I may not be able to help you. I think the psi needed to do high rise skyscrapers is around 15K psi to 20K psi... it could be less, but my research started there. We can talk more about this if you're interested, but I find that area boring.

Que Dios te vendiga.