What is Water-Cement Ratio ?

Water-Cement ratio means the ration between weight of water to the weight of cement used while preparing concrete mix. Water Cement ratio plays important role in developing the strength of concrete.

The water-cement ratio is also responsible for the porosity of the hardened cement paste. Water cement ratio is stated as the amount of water used to the significant amount of cement in the mixture by weight for proper workability.

A minimum water-cement ratio of about 0.3 by weight is necessary to ensure that the water comes in contact with all the cement particles, Which assures complete hydration of the cement paste.

Water-cement theory states that for a given combination of materials and as long as workable consistency is obtained, the strength of concrete at a given age depends on w/c ratio.

In 1918, Duff Abrams made water cement ratio law for strength of concrete.

σc = compressive strength at some fixed age
A = empirical constant (96.5 MPa)
B = constant that depends mostly on the cement properties (about 4) & water cement ratio by weight.

Advantages of Low Water-Cement Ratio

• It provides increased strength.
• Increased resistance to weathering.
• Reduced drying shrinkage and cracking.
• Less volume change from wetting and drying.
• Lower permeability.
• Creates better bond between concrete and reinforcement.

How To Calculate Water Quantity in Concrete Mix.

Normally the water cement ratio varies from 0.4 to 0.6 as per IS 10262 (2009) for nominal mix (M10, M15…) However the maximum strength of concrete is obtained at a water cement ratio of 0.4, besides we know that for a complete hydration of concrete the water requirement is about 38%.

Generally the formula used to calculate the amount of water is given below :

Reqd Amount of Water = W/C Ratio * Cement Volume.

To elaborate lets assume the volume of cement as 50 kg i.e 1 cement bag and W/C ratio as o.4.

Reqd Amt of Water = 50 * 0.4 = 20 liters.