What is the Best Cement Ratio for Concrete?

Another common question that concrete contractors get asked a lot is – what is the best ratio for making your own concrete.  It’s one of those things that many people may tell you a number of different ratios and a few old experienced workers might just say they play it by ear.  The truth is, while there is certain given ratios that you can start with, a number of factors come in to play, and that ratio may be changed to suit the job as desired.

A general starting ratio will consist of:

1 Part Cement Powder

2 parts Sand

4 parts aggregate (normally rocks or pebbles dependant on the consistency required)

What the above doesn’t mention is the amount of water that is added.  This is because that generally starting off with a predetermined amount of water isn’t always ideal.  Normally, once the above ratio of materials is mixed, water can be slowly added until the consistency required is reached.  Those that are very well known in the science of concrete will go further and tell you that the amount of water required is also dependant on a number of factors including temperature and humidity but also its exposure to the elements, such as direct contact with sunlight (which obviously effects water evaporation form the slab of concrete unit).

While the above is a good starting point, most experts will change it up for different jobs.  For instance, if the end job requires greater strength, the aggregate volume can be reduce, so instead of a 1:2:4 (cement : sand : aggregate) ratio, it may be a 1:2:3.  In construction jobs that have columns or support beams that are heavy duty and holding considerable weight, they may even drop the ratio as far as 1:1:2.  This is because the cement is the strongest adhesive component of concrete, providing the support and durability more so than the other components.

Cement adds a strength known as tensile strength to the end product.  This it’s ability to adhere itself together and prevent it from breaking apart.   The rock aggregate provides compression strength, and gives the material the durability to withstand pure force when pressured from a certain direction.  The sand does not usually provide a specific strength quality but allows it to be more malleable while still in its slurry form.

So why not just have a direct ration of cement and water and not add the additional components?  Well, this is because cement by itself would be extremely expensive.  The cost of a single slab would rise considerably and it is very much unneeded as the existing ratio with additional raw materials provides enough strength and durability for its existing purposes. 

Regardless of the exact ratio you use, or even the specific science and attributes of each articular resource, the mixing of concrete becomes an art to most of its workers.  A good concrete contractor will know when more strength is required because of vehicle may drive over the top, or perhaps the soil moves, and more concrete is required to provide tensile strength to help the slab or pad stick together. 

Logan Concreters can be that company, find us online!

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