Blue metal is good stuff, I have it as my driveway...packs down nice & tight

You may have more luck with crushed slate? as the course

If you can source 'sharp' quartz sand, that would be my suggestion for the fine

Sorry I've been too lazy to read up on the rules. Soo what can you have as aggregate? The beads you were going to use is made of what? plastic? I know it said no epoxies but that was for the binding mix. To save a bit of weight how about pouring some epoxy into a thin sheet (3-5mm) then when it sets crush it into the size aggregate you want.

What are the chemical addmixtures you can use? I would be exploring that.

I had a quick look at the addmixtures. Maybe an accelerant would be beneficial. The strength of concrete runs like a parabolic curve, it quickly gets hard then spends a long time getting harder then spends a long time getting softer. If you can make the peak strength happen sooner...

Also you have no reo or metals in the cube so you can use higher rates of accelerant.

http://www.nrmca.org/aboutconcrete/cips/15p.pdf

Any results yet? What was your final mixture?

For the mix we tried 1.25:1:1 Cement:sand:plastic. But that came out to be 120g instead of the required 270g per cube. The molds were also really crappy. We didn't think it'd be so hard to make them.... So a couple days later we did a new batch of 1.25:1:0.5, cutting the plastic way down. I had spent 4 hours the previous night making new molds of cardboard and packing tape. These cubes look amazing. But they are still a little light at 220g but we didn't want to re-pour since time was short....and then he moved the testing date up a week!
We crush tomorrow. Will post up results.

And the results are......
poor, lol

The masses were all 235g with the target of 270g (not too bad I think).

One block took an ultimate load of 12,100lb and one took 14,800lb. To reach the speced 50MPa they should have held 30,000lb. LOL

They averaged 23.18MPa, or, 3362.5psi. About the same strength as standard concrete (3000-4000psi) but a little lighter.

I think the main fault was that the coarse aggregate was too large, and too smooth. There were no fractured plastic pieces. We should have found something a little smaller, more angular, and a rougher surface.

Oh well, the other teams didn't get very strong either. I heard one gal got right up to 30 kips though....

I'll find out more about other mixes in class tomorrow.

Interesting....
 

It would be interesting to hear exactly what mix was used for the best results in regards to strength under the contraints of this test. After reading through some of the suggestions received in here I am sure that everyone would love to know what worked more than other mixes.

Cool! Interesting hearing the result and your perspective on it brainy. I am surprised how light the first batch turned out. I guess the result might seem poor given the target 50mpa but you acheived a light weight concrete with standard 20-25 mpa, using plastic no less! I'm sure there has got to be a market for that in future with today's recycling attitude. I recall seeing bessa blocks (large bricks) made with syrofoam balls (bean bag beans) to make them light and easier to handle. Sounded like a fun project anyway (not everyones cup of tea, I know, but thanks for sharing).

My pleasure in sharing. Sadly we didn't go over each others' mixes and strengths in class...and I don't think we will since this was the last class today. (GRADUATE NEXT SATURDAY! BS in civil engineering)

You can bet I'll be talking with the professor and suggest that next year he reserve an hour of class to discuss the results, so that people can actually learn what worked well and what didn't....

I do know that we did ALOT better than some groups, but much worse than others.