What is Water Cement Ratio? Comprehensive Guide

If you are working in a small to medium size company then you must see this scenario every day.

Every contract labour working on concrete placement tries to pour extra water to the concrete. Is that what makes them happy? Absolutely.

Because with the optimum water-cement ratio the concrete mixture or cement mortar will look dense and weigh more to transfer (via cement-pond). So they all try to add water to them which makes the concrete less hardened and the cement pond looks full which is easy to transport.

Is this correct? Absolutely not. Adding too much water affects the quality of the concrete or cement mortar.

In this post, we are going to discuss

• What is the water-cement ratio?
• Role of Water in Concrete
• Effect of water-cement ratio on concrete strength
• Workability of concrete
• How to calculate the water-cement ratio
• Minimum water-cement ratio table
• Water cement ratio formula
• Example Calculation of water quantity for concrete

What is Water Cement Ratio?

The ratio between the water weight to the cement weight is known as the water-cement ratio or W/C Ratio.

Role of Water in Concrete or Cement Mortar

As you all know concrete is a macro content which consists of Cement, Sand and coarse aggregates. 

To make a concrete mixture to withstand required compressive strength, Cement needs to react with other micro materials such as sand, coarse aggregate.

Water, when mixed with cement, reacts and forms cement paste (chemical process) which will bind the other micro materials to form a hardened concrete.

Adding water to the concrete beyond this limit will affect the cement paste strength and eventually breaks the concrete strength.

Effect of Water Cement Ratio on Concrete Strength

As stated earlier adding too much water will affect the concrete quality. The coarse aggregate and fine aggregates will freely move in the concrete which will be resulted in 

• Aggregate segregation – The density of aggregates high compared to water. So the extra water will float above the concrete and make the uneven coarse aggregate segregation.
• Concrete Honeycomb formation – The excess water content will be vaporized after placing the concrete and forms honeycomb formation.

Minimum Water Cement Ratio Table – IS code 10262

Water is the critical element that makes or breaks the concrete quality. To obtain perfect concrete, we need the minimum water-cement ratio

Exposure	Plain Cement Concrete			Reinforced Cement Concrete
IS 10262	Minimum Cement Content	Water Cement Ratio	Grade	Minimum Cement Content	Water Cement Ratio	Grade
Mild	220	0.6		300	0.55	M20
Moderate	240	0.6	M15	300	0.5	M25
Severe	250	0.5	M20	320	0.45	M30
Very Severe	260	0.45	M20	340	0.45	M35
Extreme	280	0.4	M25	360	0.4	M40

How to Calculate Water Cement Ratio?

We can’t calculate the water-cement ratio. There is no such thing as a water-cement ratio formula.  We will apply the standards which are provided by the respective government. In our case it is IS Code 10262.

Example Calculation of water quantity for concrete

This calculation applies only for the nominal mix.

From Example, Calculate Water Cement Ratio for M₂₀ RCC 

From the table, we know the water-cement ratio is 0.55 for M₂₀

We take 0.55 as a ratio of W/C. M₂₀ is a volumetric mixing, so we have to take 0.55 of water in volume of cement.

Therefore, the unit weight of cement = 1440 kg/m³.

Quantity of water = 0.55 x 50/1.44  = 19.1 Liters (1 bag cement = 50 Kg)

So the required quantity of water is 19.1 Liters per cement bag.

For Easy calculation Refer Unit weight of materials.