Does anyone know how to make the highest strength concrete?

Question

I want to make a sample 100mm cube of concrete to the highest grade i can, does anyone know what mix design i can use?

I am not allowed to use reinforcement and the concrete must cure from hydration. It might be useful if anyone knows where i can get any 3rd generation superplasticercisers from too....

I am not sure that fibres from steel or anything like that will add to the compressive strength of concrete, it is allowed but there is ver little benefits.

Answer 1

The fiberglass and steel reinforcing fibers do NOTHING for the compressive strength of the concrete. Those fibers help with the tensile strength of the concrete as concrete has poor strength in tension The main hope of using the reinforcing fibers is that they hold the concrete together and keep it from cracking as a result of tensile (pulling) loads. ACI has actually said that the fiberglass reinforcing does little if anything to help.

Now the trick to getting high strength concrete is to get the lowest water to cement/cementous materials ratio that you possibly can. Concrete has been taken down to a 0.21 and i tried this once but what i have to tell you is that you will not be able to get the concrete workable with just hand tools at that low of a water to cement ratio. You should probably shoot for a 0.27 to 0.30 water to cement ratio. To even consider this you will need to go with a High Range Water Reducer/Superplasticizer (check out Sika's ViscoCrete 6500). You may actually have to use a mid range as well. If you don't know how to compute the water to cement ratio heres how:

(Weight of Cement + Weight of Cementous Materials)/(WEIGHT of water)

The compressive strength of concrete is directly relatable to the WC ratio.

Next to get the highest strength you'll have to use Portlands cement as well as Fly Ash and Silica Fume. For the portlands i would suggest avoiding Type III because it doesn't get as much late strength as Type I. You'll be testing at 28 or 56 days I assume.

The next consideration is the coarse aggregates (rock). You need to look at the locally available aggregates and find the hardest thing you can get your hands on that is NOT smooth (aka do not use river rock). If you go to college take a few moments to go in and talk to a geology professor to find out what the hardest locally available aggregates are. Also the aggregate needs to be small. The largest you should consider would be in the 3/4" (17mm) nominal size range. The aggregate needs to be well graded and with as little pan material as possible because pan material will soak up water. You have to take into account the water in the aggregate as well. Ideally the aggregate should be at what's called Saturated Surface Dry condition. This means that the aggregate is saturated however will not lose water and will not absorb any more either. Depending on your location one good rock that I can think of is Sioux Quartzite from south dakota and minnesota.

Your fine aggregate should follow similar characteristics to your coarse aggregates.

Things to keep in mind while your mixing...
1.) The Mix will be VERY dry for a long time until it finally hits a certain point then it will become very plastic. Your slump will be around 10"(254mm). DO NOT let it sit still. Keep moving it with your tools because it will seem to set up on you and will be very difficult to get workable again.

2.) Wear gloves because the stuff will be like glue.

For curing (if possible) place the samples in something that they can be submerged in water in. Put water in the container then put the samples in the water (in their molds) and put some wet burlap on top of them with the edge of the burlap in the water. This will pull water to the top of the samples to keep them from drying out. 24 hours after you made the samples go in and remove the mold then submerge them completely in water. Do not let it run out of water. As long as the concrete is in contact with water it will continue to hydrate, however the moment it stops being in contact then it will stop hydrating and won't hydrate again. Make sure the cylinders are completely submerged until right before you test them.

For the supplies I would suggest contacting a local concrete producer and explain what you're doing and ask politely to be given small quantities of the materials you need. You will need to speak to a plant manager or owner so be polite and if they say no ask someone else. Considering that at most you'll need 6 ounces of plasticizer it shouldn't be an issue.

For a mix design to work from look up the Silica Fume Association web site. They have a pamphlet/book that's a free download that shows some example mixes.

Best of luck.

Answer 2

Heheheh... is this an old internet scam or a new internet scam? Haven't heard it, yet, but that only means that I wasn't aware of it, not that it is new. Don't get me wrong. It is, of course, possible to attract Mg and Ca ions from sea water with a suitable electrolytic setup. No questions asked. The problem is that the total concentration of these elements is so small that the energetics of this are absolutely forbidding, especially since both elements can be mined easily and cheaply on land. We have whole mountain ranges that are nothing but Ca deposits. So why would one want to tap into sea water at the expensive of possibly hundreds or thousands of times the energy that it takes to make regular concrete? Just because one can? That is not rational behavior.

Answer 3

I can not understand the practical benefit from trying to find this out. Better by far to use normal materials and site conditions to specify the optimum strength.

Assuming there is no time limit to the cure try this-
3/8" dry ballast mixed two parts to one cement.
Vibrate into mould and leave for three months.
If you have time one year is better.

Answer 4

i have heard that mixing either wood or coal ash into concrete will make it much harder than regular concrete.

Answer 5

I recommend you look at the following site.

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

Answer 6

Can you use fibreglass strands, as we have been told this is now an acceptable standard.

Answer 7

a well graded aggregate