What is the formula used to mix concrete to determine the strenght ( eg.25 MPA.30MPA,40MPA etc)?

Answer 1

Here is good sites on some things:
http://matse1.mse.uiuc.edu/concrete/prin.html
http://www.nrmca.org/aboutconcrete/cips/39p.pdf

One of the factors that determine the strength of concrete is the quality of the mix, as some combinations of various mixes prove to be stronger than others. Another factor is the weather condition while the concrete is being mixed and immediately after pouring because it has been proven that mixing concrete during cool and humid weather produces stronger concrete surfaces. However, one factor that plays a major role in determining the strength of a concrete surface is the finishing techniques used on the surface. This is because it has been proven that some finishing techniques such as using water, increases the chances of chipping and scaling.

Causes of deterioration

Apart from the factors that can determine a concrete surface’s strength, there are also a number of factors that cause concrete surfaces to deteriorate. One of the biggest contributors to concrete surface deterioration is the whether. This is because it has been proven that rain, and snow slowly erode concrete surfaces, which could lead to more damage as water gets to seep into pores on the surface. Other causes of deterioration include spilled chemicals and constant use of the surface. Given these, homeowners need to take necessary measures to prevent the deterioration of concrete surfaces, which includes using concrete sealers.

Answer 2

The strength of concrete is measured by compression and tension. The compressive strength is usually ten times greater than the tensile strength until you add some reinforcement and then the strength will equalize
What is a common type of concrete reinforcer? Rebar and welded wire fabric.

Ready mixed concrete is what you will find in the cement trucks. These trucks mix the concrete by using an agitator mounted on the truck itself.

Now we will determine how much concrete is needed for a 50 by 50 slab 4 inches thick and then how much is needed for a 70 by 70 slab 6 inches thick.
First we start off by multiplying the length and width of the slab to get the area then we take the thickness of our slab and look on the chart to see what # we divide our area by and then we divide our area by that number. This formula will give us the cubic yards of mix that we need for our slab.

We can also take this and convert it into cubic feet needed. Let them know that a 40 lb bag of sac crete costs at least $2 and calculate up what the cost for one of the above slabs would be.

Answer 3

if you talk about the cement sand aggregate ratio, i don't think we'll use other than 1:2:4.

I thought nowadays they use premixed cement correspond to each strength, because they very much depends on the C3S (tricalcium aluminate) and C2S (dicalcium aluminate) content. because the cement sand aggregate ratio not only is important for its ultimate strength, it also affects durability (against frost and whatnot), protection to steel reinforcement and other things. So even if we can increase the strength by altering the ratio, we we might compromise other concrete properties.

By the way, i've read a 1:3:7 ratio somewhere. Maybe you can check on it.

The type of aggregate used also determines the strength.