Water Cement ratio

What is the Water Cement Ratio in Concrete

The Water Cement ratio is the water and cement ratio (by weight or by volume) in a concrete mix. It is usually expressed in liters of water per bag of cement(50kg). After carrying out many experiments by duff Abrahams, he established a relationship between water and cement, which is known as the water cement ratio law. This law is valid only when the concrete is of workable plasticity.

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 According to this law, the strength of concrete wholly depends upon the amount of water used in the preparation of concrete mix and is quite independent of the proportion of cement and aggregates. The strength of concrete is inversely proportional to the water cement ratio. In other words, the strength of concrete decreases as the water cement ratio increases.

It may be noted that when the water cement ratio becomes less than 0.45, the concrete is not workable and causes a honey-combed structure containing a large number of voids. If the water cement ratio is more, then the capillary voids will be more in the physical structure of hydrated cement. The strength and durability of concrete will also be less.  

water cement ratio table 

S.No	Grade	Concrete mix	Water cement Ratio	User
1	M10	1:3:6	0.6	Mass concrete in piers, abutments, massive reinforced concrete members.
2	M15	1:2:4	0.6	Normal R.C.C works i.c slabs, column, beams, walls, small span arches.
3	M20	1:1.5:3	0.5-0.45	Water retaining structures i.e reservoirs, columns, and piles.
4	M25	1:1:2 1:4:8	0.4-0.5	Long-span arches and highly loaded columns.
5	M30	1:5:10 1:6:12	0.45	Mass concrete foundations.
6	M35	-	0.45	Post-tensioned prestressed concrete.
7	M40	-	0.4	Pre-transition prestressed concrete.

Water is the most important and least expensive ingredient of concrete. A  part of the mixing water is utilized in the hydration of cement to form the binding matrix in which the inert aggregates are held in suspension until the matrix has hardened. The remaining water serves as a lubricant between the fine and coarse aggregates and makes the concrete workable.

Role of  Water Cement ratio  of concrete

23% of water by weight of cement chemically reacts with cement compounds and is called bound water.15% of water is imbibed with getting pores and is called bound water. The total requirement for hydrating is 38% of water by weight of cement. Additional water is needed to lubricant the mix which makes the concrete workable. As a rule, the smaller the percentage of water, the stronger the cement.

Importance of Water Cement ratio  in mixing concrete

1) Effluents from sewerage gas works, waste from the point.

2) An excessive amount of dissolved salts.

3) Large quantities of chlorides.

4) Suspended particles.

5) Salts of zinc,tin,copper,lead,lead nitrate.

6) Carbonates of sodium & potassium in excess quantity.

How to calculate Water in cement Concrete

Let's that one bag of cement weight is = 50 kg.

Required the amount of water is  = Water Cement ratio X Weight of cement.

The required amount of water = 0.4 X 50 = 20 lit.

Water required in M10 Concrete = Water Cement ratio for M10 X Weight of cement = 0.6 X 50 = 30lit.

Water required in M15 Concrete = Water Cement ratio for M15 X Weight of cement = 0.6 X 50 = 30lit.

Water required in M20 Concrete = Water Cement ratio for M20 X Weight of cement = 0.45 X 50 = 22.5lit.

Water required in M25 Concrete = Water Cement ratio for M25 X Weight of cement = 0.4 X 50 = 20lit.

Water required in M30 Concrete = Water Cement ratio for M30 X Weight of cement = 0.45 X 50 = 22.5lit.

Water required in M35 Concrete = Water Cement ratio for M35 X Weight of cement = 0.45 X 50 = 22.5lit.

Water required in M40 Concrete = Water Cement ratio for M40 X Weight of cement = 0.4 X 50 = 20lit.