that a water to cementitious materials ratio (w/cm) of 0.25 is needed for the C-S-H and hydration products
to be formed. That, however, is not all of the water that is needed. There is additional water that becomes
physically bound between the cement hydrates. In order to have enough water to possibly enable
complete hydration of the cement, approximately 20 pounds of water to every 100 pounds of cement is
necessary. Combined, this equates to approximately 45 pounds resulting in a w/cm of 0.45. Other studies
have shown that an approximate ratio of 0.4 was necessary for complete hydration of the cement.2, 3 It
should be noted that a concrete rarely gets the benefit of complete cement hydration typically because of
the lack of physical access to the inner unhydrated cement particles and also due to lack the minimum
required curing that would be needed.
Contrary to the above discussion regarding increased w/cm values resulting in the maximum potential for
cement hydration, a concrete designer is faced with the reality that lower w/cm values often enhance
strength and other durability characteristics of their product. The reason is not because the crystals
formed during hydration are weaker, rather, because with the higher amounts of water in the mixture
comes greater dispersion. Therefore, less bridging of the C-S-H crystals can take place. The resulting
concrete is less dense, lower in strength, and higher in permeability.