Concrete Mix Design

[tdonov]

Hi guys,
I am trying to design a concrete mix. I will use the concrete for casting counter tops and small things like vases and other alike.
I have attached a screenshot of my design mix.

From what I have been reading a ration 1-1 - cement to sand will produce a very high strength concrete (the cement that I am using is of class 42.5 N/mm2).
Due to the fibers I cant really find out what the tensile strength is, but it should be quite high, because I made a plate (0.5x0.3x0.02m), placed supportes at both ends and jumped on it and I didn't see a crack.

In my opinion the mix design is okay, but if someone knows a way to improve the design I am open to suggestions. Also is there a way to calculate the curing time. I was casting some ashtrays in a silicone mold and some of them I can get out of the mold in a day and a half and others when taking out are cracking.

Best Regards,

Tsvetan Donov

 

[Ron]

As with compressive strength, you cannot calculate the curing time of concrete. It is dependent on many factors, most notably temperature and moisture.

Based on this post and your other similar post, you need to learn a bit more about cement and concrete technology. There are many references available to do so. I suggest two in particular....."Design and Control of Concrete Mixes" and any text by Neville.

 

[epoxybot]

You should be able to buy or rig a small mechanical press to be able to do compression strength tests of either 50mm x 50mm x 50mm cubes or 50mm x 50mm x 100mm blocks. Either round or square. Thin wall plumbing pipe works well. You will need form release. While you won't get the definitive tensile strength, you will have some idea of the movement, gain or lose from average, assuming tensile strength to be 10% of compressive strength. Assuring uniform loading is important to obtaining worthwhile results.