properties of cement / Types of Cement | water cement ratio

Water Cement Ratio | Calculation of Water Cement Ratio | History & Importance

 

Concrete is the blended form of four construction ingredients; aggregate, sand, water, and cement in definite proportion. The amount of water and cement plays a vital role in the strength of concrete. Thus, we will be discussing the water cement ratio in this article.

 

  1.  Introduction  

Water cement ratio (w/c ratio)  is defined as the ratio of the weight of water to the weight of cement used in the concrete mix. 

Mathematically,

Water cement ratio = (Weight of water) / ( Weight of cement)

types of concrete | water cement ratio

Normally, about 38% of water is required for the complete hydration of concrete.

As per IS 10262(2019) for nominal mix ( i.e. M10, M15…, M25);  the w/c ratio varies from 0.4 to 0.6.

 

  2. Brief history of w/c ratio  

Duff A. Abrams was the first to develop the notion of the w/c ratio that had been published in 1918.

Uniform Building Code (1997)  specified a maximum of 0.5 w/c ratio for conditions like the exposure of concrete to freezing, thawing, and humidity. It also specified a maximum of 0.45 w/c ratio for severe or very severe sulfate conditions.

 

  3. Why w/c ratio is important in the concrete mix?   

The chemical reaction between cement and water ( known as hydration ) produces heat during the reaction and results in the hardening of concrete.

Proper hydration reaction is dependent upon water cement ratio and results in strong, sound, and durable concrete if the proper ratio is used.

Therefore, it is crucial to use an accurate (low) w/c ratio to strengthen concrete.

 

  4. Calculation of water cement ratio  

As we know,

w/c ratio =weight of water/ weight of cement

Here, the amount of water required in concrete mix can be also calculated as;

The required amount of water ( in liters) = w/c ratio × weight of cement

Example: 

If M20 concrete is to be prepared to maintain a water cement ratio of 0.5 and 50 kg cement was used. Then, find the water required for mixing concrete.

soln;

The required amount of water ( in liters) = w/c ratio × weight of cement

= 0.5 * 50

= 25 litres

Read Also:    26 Types of concrete

 

  5. What happens when the amount of water is not properly proportioned with cement?   

Higher the amount of water used in concrete; dilution of the cement paste will be greater resulting in more voids after evaporation of water molecules there. Those voids lead to cracking, shrinkage, flexural failure, and distinct color change due to imbalance in compressive strength, tensile and flexural strength, porosity, and so on.

Whereas a very lesser amount of water creates a hindrance in binding the materials together properly. This also affects the strength of the concrete.

 

  6. Does a high or low w/c ratio affect concrete strength?   

Yes, it affects.

A high w/c ratio means greater the amount of water required in a concrete mix that consequences the weakening of concrete strength.

And low w/c ratio ( Generally, 0.38 w/c ratio) means the amount of water is sufficient to complete the hydration of concrete. The low w/c ratio makes the concrete resistant to weathering, shrinkage, cracking and provides better binding.

( w/c ratio less than 0.38 is commonly considered very low because 38% of water is needed for cement to complete hydration. )

 

  7. W/C ratio for different concrete works  

a. For ordinary concrete works; 0.4 to 0.6 w/c ratio is used.

b. For high-quality concrete works; 0.4 w/c ratio is specified.

c. When 2% plasticizers or superplasticizers are used in high-quality concrete; commonly 0.3 to 0.38 w/c is used. 

( Note: Plasticizers or superplasticizers can be used to increase the flowability and workability of higher strength concrete. )

 

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