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Introduction
Water-Cement combination
Effect of too much water in concrete
What is workability of concrete?
Water-Cement ratio and compression
The Calculation of the Water-Cement ratio

Introduction

Water Cement Ratio measures how much water to cement is used in a concrete mixture. In simpler words, it's the relationship between the weight of water and cement in a mix. For structural strength, it's recommended to have a low water-cement ratio. According to IS code 10262, the recommended range for a nominal mix is 0.4 to 0.6. This ratio was discovered in 1918 by Abraham, who gave the following statement, “The strength of concrete is dependent on the net quantity of water used per sack of cement.”

Water-Cement combination

Concrete is a combination of microelements like cement, sand and coarse aggregates. And to achieve high tensile concrete that can withstand all the compressive strength, we need a mixture of these micro particles in adequate proportion. This is where the significance of water becomes evident.

When water is combined with cement, it forms a binding material that envelops and coats the mineral aggregate particles, solidifying into a robust composite mass. Since cement and water are the primary active components in a concrete mix, it's essential to monitor the water quantity to guarantee the structure's durability and resistance to water penetration.

Water's significance in concrete can be summarized as follows:

Incorporating an appropriate volume of water renders the concrete mixture workable, facilitating uniform and easy placement between bars and in corners.
It dampens the aggregates, preventing water absorption, and promotes proper hydration. Hydration is the exothermic process that takes place when water combines with cement.
It aids in coating the cementing materials onto the surface of aggregate particles.

Effect of too much water in concrete

The appropriate water amount typically falls within the range of 23-25% of the cement quantity. This triggers the hydration process, constituting 15% of the water-cement paste and serving to fill the gaps in the concrete.

Adding more water than the recommended amount will affect the strength of concrete because an increase in the amount of fluid will cause the aggregates to settle down. Once the water evaporates, voids will remain, impacting the concrete's workability and strength.

What is workability of concrete?

Workability of Concrete refers to its capacity to be handled, transported, and placed while maintaining its uniformity with minimal loss. It is important as it determines the compression of concrete. Factors affecting the workability of concrete are Water-Cement ratio, aggregate shape and size and admixtures. Using plasticisers & super plasticizers will help increase the workability of the mixture without affecting its W/C ratio.

Water-Cement ratio and compression

Water-Cement Ratio	Compressive Strength (kg/cm²)
0.38	450
0.42	400
0.46	340
0.50	320
0.55	300

The above table shows the relation between the Water-Cement ratio and the compressive strength of the concrete. From the table, it is evident that there is a decrease in compressive strength when there is an increase in the Water-Cement ratio.

Theoretical studies and experiments have proved that for 1 part cement, 0.25 part water is required for hydration, setting and setting of the mortar. And an additional 0.15 to 0.45 parts water (by weight) is required for lubrication and workability of the mix, and it has to be done very carefully.

A Concrete Slump is a device that is used to measure the workability and consistency of the concrete mix.

The Calculation of the Water-Cement ratio

Given below is the Water-Cement ratio table as per IS code 10262

Exposure	Plain Cement Concrete			Reinforced Cement Concrete
IS 10262	Minimum Cement Content	W/C ratio	Grade	Minimum Cement Content	W/C 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

The standard set for Water-Cement ratio lies between 0.4 to 0.6

For calculating the required water quantity for the concrete, we first need to calculate the cement content for the volume.

Let us assume that the amount of cement required is 50 kg (1 bag of cement)

We know that,

Required amount of water = W/C ratio X Cement volume

The required amount of water will be= 0.5 X 50 kg= 25 litres of water.

Now that you've learned how to calculate the Water-Cement ratio, you'll be able to precisely determine the right amount of water needed for your concrete mix, ensuring the desired strength and durability of your construction

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