Relation between water cement ratio to the strength of concrete

Water has three functions in concrete

1.Wets aggregate surface
2.Imparts workability
3.Binds aggregate with cement chemically by hydration

For a given degree of compaction with the increase
of percentage of water, percentage of hydration increases.
So sufficient amount of water is necessary for hydration as well
as for increase in strength.Water also imparts workability to
concrete.but excess water cause concrete to be porous.
Hence for a certain limit strength increase with the increase of
water cement ratio.But after that strength decreases with the
increase of water cement ratio.