? asked in Science & MathematicsEngineering · 10 years ago

# how to calculate the water cement ratio for concrete mix design?

civil engineering,to avoid excess or deficient water in the concrete mix and to increase the strength of the concrete

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• 10 years ago

Water-cement ratio is the ratio of weight of water to the weight of cement used in a concrete mix. It has an important influence on the quality of concrete produced. A lower water-cement ratio leads to higher strength and durability, but may make the mix more difficult to place. Placement difficulties can be resolved by using plasticizer. The water-cement ratio is independent of the total cement content (and the total water content) of a concrete mix.

Often, the water to cement ratio is characterized as the water to cement plus pozzolan ratio, w/(c+p). The pozzolan is typically a fly ash, or blast furnace slag. It can include a number of other materials, such as silica fume, rice hull ash or natural pozzolans. The addition of pozzolans will influence the strength gain of the concrete.

The concept of water-cement ratio was developed by Duff A. Abrams and first published in 1918.

Concrete hardens as a result of the chemical reaction between cement and water (known as hydration). For every 4 lbs of cement, 1 lb of water is needed to fully complete the reaction. This results in a water-cement ratio of 1:4 or 20% (1/1+4). In reality, a mix formed with 20% water is too dry and does not flow well enough to be placed, and some of the water is taken up by the sand and stone and is not available to participate in the hydration reaction. So more water is used than is technically necessary to react with the cement. More typical Water-Cement ratios of 35% to 40% are used, along with a plasticizer.

Too much water will result in settling and segregation of the sand/stone components (more sand in the top layers because the stone will settle at the bottom). Also, any water that is not consumed by the hydration reaction will eventually leave the concrete as it hardens, resulting in microscopic pores or holes that will reduce the final strength of the concrete (but interestingly - microscopic pores or holes are desired in outdoor concrete that gets wet while experiencing low temperatures resulting in freeze-thaw cycles. For flatwork (driveways, steps, sidewalks, etc) an air-entrainment agent is added to create small bubbles in the concrete. This helps the finished, hardened concrete resist fracturing caused by freeze-thaw temperature cycling. Finished, hardened concrete can be as much as 6% air (by volume) because of this.

And finally, a mix with too much water will experience more shrinkage as the excess water leaves, resulting in internal cracks and visible fractures (particularly around inside corners) which again will reduce the final strength. Anyone who has set wooden fence posts in concrete piers will probably notice cracks radiating from the corners of the post. This can be reduced by keeping the water to an absolute minimum.

Source(s): wiki
• keva
Lv 4
3 years ago

Water Cement Ratio

• Laura
Lv 4
4 years ago

For the best answers, search on this site https://shorturl.im/axrQo

Without a petrographic analysis of existing concrete cylinders you cannot calculate the w/c ratio from existing cylinders. However, you can calculate the intended w/c ratio by looking at the mix design, in which the amount of cement and water is clearly shown. From that data you can calculate the w/c ratio by dividing the weight of the cement by the weight of the water in consistent units. The ratio is dimensionless. It should be in the range of .44 to .48 or so.

• Anonymous
5 years ago

RE:

how to calculate the water cement ratio for concrete mix design?

civil engineering,to avoid excess or deficient water in the concrete mix and to increase the strength of the concrete

Source(s): calculate water cement ratio concrete mix design: https://shortly.im/fOwOe
• 4 years ago

• 5 years ago

water to cement ratio 0.4 how many aggregate for c-25