Predicting the Density of Concrete

[smithson1984]

Hello Everyone,

I have a problem which is flummoxing me concerning concrete!

The density of concrete is approx. 2400 kg/m^3 (depending on mix) however the component parts which make up concrete are as follows:

Water (density 998 kg/m^3)
Cement (density 1506 kg/m^3)
Aggregate (density 1602 kg/m^3)
Sand (density 1600 kg/m^3)

My question is how do all of these relatively light materials combine to form a relatively dense material like concrete?

The reason for my question is that I wish to use some steel in the aggregate mix and thus increase the density of the aggregate but I cannot calculate what density of concrete this will produce without understanding the above.

Any help and/or simple estimate formulas would be greatly appreciated!

Thanks a lot in advance,

Ian

 

[phyzguy]

The densities you are quoting (except for the water) contain a significant quantity of air. For example,the density of quartz is about 2650 kg/m^3, and the reason sand is so much less is that it is a mixture of quartz particles and air. The same for the aggregate - typical rock densities are 2000-3000 kg/m^3. When you mix these materials to create concrete, the air is removed, so you get a density closer to the bulk materials without the air. For your problem, why don't you just accept the final concrete density of 2400 kg/m^3, and calculate the density of a mixture of concrete and steel? Presumably you know the volumes of concrete and steel in the final product.

 

[smithson1984]

Hi phyzguy,

Thanks very much for the response! I think you've cracked the problem and it now makes sense. The calculations I'm coming out with are now making much more sense.

It's obvious when you know how!

Cheers,

Ian

 

[phyzguy]

Glad I could help. Good luck with you project.