Mixture questions for high strength concrete

[Scaplen14]

I'm doing a competition for a construction materials course and need to make the strongest possible cylinder. The only guideline is the cement cannot exceed 450kg/m^3.

So far the assumptions I have made are that I should use the maximum cement allowed and I need the lowest possible water ration to complete the reaction which I think is around 0.25, along with the addition of a super plasticizer. Can anyone tell me if this is correct?

Also, for the aggregates, should I use slag, flyash, metakaolin, silica fume or just a fine aggregate and what ratios should be used.

It's worth noting that I have ~30 days until the competition but I do have access to accelerated curing methods.

Any help or suggestions would be greatly appreciated!

 

[Zambo]

is the 450kg/m3 the maximum cement (OPC) content or the total cementitious material content. I think the latter and in that case any slag, fly ash and silica fume is included in the 450kg/m3.

I would use silica fume and make sure the aggregate is crushed and washed. Better start now with some trials.

http://www.cement.org/basics/concreteproducts_histrength.asp

Fibres not allowed I guess.

 

[macjohnw]

I have heard of guys doing a similar competition that cooled their aggregates in the fridge before mixing, as they did the water. This apparently slowed down the hydration and so increased the long term strength.

Silica fume will increase your density - it might also increase your water demand due to it's increased surface area. The super plasctizer will allow you to use as little water as possible, thus increasing the strength.

I stand to be corrected.

 

[scone38]

good ideas above... definitely use silica fume and instead/in addition of chilling aggregates get some hydration stabilizer like Delvo to delay strength curve a bit

 

[macjohnw]

I once made two batches of test cubes with the same w/c ratio but the 1st batch was the normal stone/sand/cement mix we use on site for water retaining structures, while the 2nd was a sand/cement mix. For the sand/cement mix I just left out the stone and replaced it with more sand.

The sand/cement mix gave higher strengths at 7 and 28 days and also broke in a more "organised" manner - it cracked along the edges of the cubes and did not form the hour glass shape like normal stone/sand/cement cubes normally do.

The damage or cracks on the sand/cement cubes are also less visible than the stone/sand/cement mix cubes. I initially questioned if they were actually crushed, but the lab guy insisted they were. I crushed them again in any case and got some decent figures for a 2nd time. I was amazed at the sand/cement mix's results.