Quantity of Materials for M5, M10, M15, M20 Grade Concrete
The construction process of any RCC structure is quite complicated and requires much calculation. It is especially true in case of preparation of the concrete. And when you need to use different grades of concretes in your work, maintaining proper ratio of cement, sand and aggregate is absolutely of paramount importance. So, today we will talk about calculating the quantity of materials for M5, M10, M15, M20 grade concretes.
These quantities have been, of course, calculated thousands of times over the history of concrete. And therefore, there are ready-made charts available for grade concrete ratios in the building codes and from other sources. But it is always good to know how to calculate the quantity of materials for M5, M10, M15, M20 grade concretes just in case you have some odd type of work in your hand.
What are concrete grades?
Concrete grading is a system where a concrete mix is given an indicative identifier according to its compressive strength.
The identifier has two parts, the letter ‘M’ followed by an integer divisible by 5. The ‘M’ stands for “Mix”, simply enough. And the number stands for the Newton per square millimeter value of the concrete’s compressive strength, which can vary from 5 to 35 (anything above isn’t used in normal work), by multiplications of 5.
Which means, a M15 grade concrete means that this concrete mix, when fully matured, will provide a compressive strength of 15 N/mm2 in the applied section, irrespective of any reinforcements in it. Mostly, only up to 20 N/mm2 strength concrete are used in normal constructions, so we will limit our discussions from M5 to M20.
What is concrete mix ratio?
Concrete is basically a mixture of cement, sand and stone chips (aka aggregates). Sand and stone chips are there to provide structural strength, while the cement is the bonding agent between them. Varying the amounts of these three elements of concrete, you can vary the strength of the concrete. Not only that, these variations will change other properties of the concrete as well, like how fast will it settle, or how long will it last without maintenance, etc.
Since mostly everywhere only specific grades of concrete are used, the mixture needs to be prepared with very particular amounts of materials to achieve the specific grades like M10, M25 etc. These particular amounts are expressed in ratio form. The ratio of cement to sand to aggregate for a given concrete grade is called the mix ratio of that concrete grade. The table below will list the most common grade concrete mix ratios.
|Concrete Grade||Mix Ratio (Cement : Sand : Aggregate)||Compressive Strength|
Why do you need to calculate concrete material quantity?
That chart above is certainly handy. When you need to make concrete of those grades, you can just look it up and use the materials in the volume indicated in the ratio to achieve the intended compressive strength. However, you will have to know that due to many reasons, the above ratios are not followed precisely in some cases. The reason for this can be manyfold.
For example, the quality of sand may differ on availability and that will throw up the compressive strength. Or, the aggregate sizes may differ and again that will change the properties of the concrete. Water quality used to make the mix, or the weather, or even cost-cutting may affect the concrete mix ratios that you are supposed to use in particular cases.
When this happens, the mix ratio needs to be different to accommodate the new conditions. E.g., you may have to use 3.2 parts of sand due to its light quality at the site for an M10 mix, whereas by the book you should have used only 3 parts pf sand. And so, you will need to learn how to calculate the material quantities in concrete mix, by heart.
Below, we will show you how to calculate material requirement for a given type of concrete – say, M20 grade.
Calculating Cement, Sand and Coarse aggregate requirement for M20 Grade concrete
We have the following data:
Given mix ratio of M20 concrete: 1:1.5:3
Given total volume of needed M20 concrete: 1.57 m3
Given density of PPC/OPC cement: 1440kg/m3
Given amount of cement per bag: 50kg/bag
Conversion, 1 m3 = 35.32 ft3
Therefore, volume of materials needed for 1.57m3 of M20 grade cement:
Volume of cement
= Ratio of cement in grade x total volume / total mix ratio in grade
= 1 x 1.57 / (1 + 1.5 + 3)
= 1.57 / 5.5
= 0.285 m3
Volume of Sand
= Ratio of sand in grade x total volume / total mix ratio in grade
= 1.5 x 1.57 / (1 + 1.5 + 3)
= 0.427 m3
Volume of aggregate
= Ratio of aggregate in grade x total volume / total mix ratio in grade
= 3 x 1.57 / (1 + 1.5 + 3)
= 0.854 m3
Therefore, total quantity of materials for 1.57m3 of M20 grade cement:
Weight of cement
= volume of cement x bulk density of cement
= 0.285 x 1440
= 410 kg
Cement bags needed
= total weight of cement needed / weight of cement per bag
= 410 / 50
= 8.2 bags of cement. (You will have to get 9 bags of cement, and use only one-fifth cement from the last bag – discard the rest or reuse it somewhere else.)
Amount of sand needed
= volume of sand in cubic meter converted to cubic feet
= 0.427 x 35.32
= 15.08 cubic feet of sand.
Amount of aggregate needed
= volume of aggregate in cubic meter converted to cubic feet
= 0.854 x 35.32
= 30.16 cubic feet of stone chips.
Water required for different grade concrete
The water used to mix concrete directly affects the quality of the concrete. Depending upon how soupy or how stiff you’ve made the concrete, it will change its whole manners. So, you will have to be careful when mixing concrete properly about how much water to add in there.
Thankfully, the amount of water needed in concreting doesn’t depend upon the quality of sand or aggregates, and remains fixed for the type of concrete. So, you don’t have to calculate it too often – just look it up from the table below.
|Concrete Grade||Water required per 50 kg of cement used|
So, according to this table, we require 410 / 50 x 30 = 246 liters of water to make our example 1.57 m3 of M20 grade concrete, in addition of the other materials.