Effect of water cement ratio on the strength of concrete

Definition: Water Cement Ratio (w/c)?

The water–cement ratio = the weight of water to the weight of cement utilized in a concrete mix.

Effect of water cement ratio on concrete:-

A lower ratio results in higher strength and durability , but may make the mix difficult to figure with and form. Work-ability are often resolved with the utilization of plasticizers or super-plasticizers.
However, a mix with a ratio of 0.35 might not mix thoroughly, and should not flow tolerably to be placed. More water is thus used is technically necessary to react with cement. Water–cement ratios of about 0.45 to 0.60 are more typically used. For higher-strength concrete, lower ratios are used, along side a plasticizer to extend flowability.

Too much water will end in segregation of the sand and aggregate components from the cement paste. Also, water that's not consumed by the hydration reaction may leave concrete because it hardens, leading to microscopic pores (bleeding) which will reduce final strength of concrete. The mix with an excessive amount of water will experience more shrinkage as excess water leaves, leading to internal cracks and visual fractures (particularly around inside corners), which again will reduce the ultimate strength.