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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.
The single most important indicator of strength is the ratio of the water used compared to the amount of cement (water/cement ratio).
Basically, the lower this ratio is, the higher the final concrete strength will be.
This concept was developed by Duff Abrams of The Portland Cement Association in the early 1920's and is in worldwide use today.
A minimum w/c ratio (water-to-cement ratio) of about 0.3 by weight is necessary to ensure that the water comes into contact with all cement particles (thus assuring complete hydration).
Typical values are in the 0.4 to 0.6
Advantages of low water/cement ratio ;
* Increased strength.
* Lower permeability.
* Increased resistance to weathering.
* Better bond between concrete and reinforcement.
* Reduced drying shrinkage and cracking.
* Less volume change from wetting and drying.
